Information

Does sunlight kill rotavirus?


Does sunlight Kill Rotavirus? Maybe freezing? Norwalk or similar. Its a practical question for bedding.


According to this study, both a high temperature wash (57C) and full spectrum sunlight will kill rotavirus.

It would appear that a washer with a sanitation cycle (newer models often have a cycle that hits or exceeds 165F) would be your best bet for treating bedding.

See Figure 2.


'One sip can kill': Why a highly toxic herbicide should be banned in Australia

Paraquat is used to spray crops, but can harm humans and wildlife. Credit: Shutterstock

There's a weedkiller used in Australia that's so toxic, one sip could kill you. It's called paraquat and debate is brewing over whether it should be banned.

Paraquat is already outlawed in many places around the world. The Australian Pesticides and Veterinary Medicines Authority has been reviewing paraquat's use here for more than two decades, and its final decision is due later this year.

We are medical and environmental scientists, and have researched the harmful effects of paraquat, even when it's used within the recommended safety range. We strongly believe the highly toxic chemical should be banned in Australia.

The potentially lethal effects on humans are well known. In Australia in 2012, for example, a farmer died after a herbicide containing paraquat accidentally sprayed into his mouth. And our research has found paraquat also causes serious environmental damage.

Paraquat: the story so far

Paraquat, branded as Gramoxone, has been used since the 1950s. It's mostly deployed to control grass and weeds around crops such as rice, cotton and soybeans.

Paraquat is registered as a schedule 7 poison on the national registration scheme, meaning its use is strictly regulated.

Paraquat is now banned in Thailand, among other nations. Credit: Shutterstock

Australia's biggest supplier of paraquat says it should not be banned, insisting herbicides containing it are "safe for people and the environment when used for their intended purpose and according to the registered label instructions."

Farmers have also argued against a ban, saying it would force them to use more expensive, less effective alternatives and reduce crop yield.

Paraquat has been banned in more than 50 countries, including the United Kingdom, China, Thailand and European Union nations. However, it's still widely used by farmers in the developing world, and in Australia and the United States.

Paraquat is a non-selective herbicide, which means it kills plants indiscriminately. It does so by inhibiting photosynthesis, the process by which plants convert sunlight into chemical energy.

Paraquat stays in the environment for a long time. It's well known for causing collateral damage to plants and animals. For example, even at very low concentrations, paraquat has been found to harm the growth of honey bee eggs.

Exposure to living organisms can occur by spray drift or when paraquat is sprayed on crops then reaches surface and underground sources of drinking water.

Research shows paraquat kills common carp at a higher rate than the weed it’s meant to control. Credit: Shutterstock

Paraquat can have unintended consequences for biological organisms and the environment, particular in waterways. Our recent paper summarised the evidence of the harmful effects of paraquat at realistic field concentrations.

We found evidence that paraquat can severely inhibit healthy bacterial growth in aquatic environments, which in turn affects nutrient cycling and the decomposition of organic matter.

The research also shows paraquat can distort tropical freshwater plankton communities by negatively impacting metabolic diversity and reducing phytoplankton growth.

In fish, paraquat has been found to lead to a death rate of common carp three times higher than the weed it is used to control.

In addition to the environmental effects, of course, paraquat is highly toxic to humans. A small accidental sip can be fatal and there is no antidote.

The US Centers for Disease Control and Prevention says paraquat is a leading cause of fatal poisoning in parts of Asia, the Pacific Islands, and South and Central Americas.

A Queensland farmer died in 2012 after paraquat accidentally sprayed in his face when he filled a pressure pump. Credit: Shutterstock

Paraquat enters the body through the skin, digestive system or lungs. If ingested in sufficient amounts, it causes lung damage, leading to pulmonary fibrosis and death through respiratory failure. The liver and kidney can also fail.

Several recent incidents in Australia demonstrate the risks of paraquat poisoning due to human error, even within the current strict regulations.

According to news reports, the Queensland farmer poisoned by paraquat in 2012 was filling a pressure pump to control weeds on his property. The unit cracked and paraquat sprayed over his body and face, entering his mouth.

In 2017, an adult with autism took a sip from a Coke bottle used to store paraquat. The bottle had been left in a disabled toilet at a sports ground in New South Wales. The man was initially given 12 hours to live, but fortunately recovered after two weeks in hospital.

Paraquat: not worth the risk

There's a growing awareness of the threats posed by global chemical use. In fact, a paper released this week suggests the potential risk to humanity is on a scale equivalent to climate change.

Paraquat is no doubt an effective herbicide. However, in our view, the risks it poses to humans and the environment outweigh the agricultural benefits.

Current regulation in Australia has not prevented harm from paraquat. It's time for Australia to join the movement towards a global ban on this toxic chemical.

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Techniques of Sterilization in Bacteria

Ultraviolet rays present in the sun-light are responsible for spontaneous sterilization in natural conditions. In tropical countries the sun light is more effective in killing bacteria due to combination of ultraviolet rays and heat. By killing bacteria in suspended water, sunlight provides natural method of disinfection of water bodies such as tanks and lakes.

Those articles which cannot withstand high temperature can still be sterilised at lower temperature by prolonging the duration of exposure.

(ii) Heat:

It is considered to be the most reliable method of sterilization of articles—that withstand heat. There are two methods of the sterilization: dry heat and moist heat.

It acts by protein denaturation and oxidative damage. Sterilization by dry heat is as follows:

Articles such as bacteriological loops, straight wires, tips of forceps and searing spatulas are sterilised by holding them in a Bunsen flame, till they become hot red.

Articles are passed over a Bunsen flame but not heating it to redness.

Contaminated, materials are destroyed by burning them in incinerator.

Articles are exposed to high temperature (160°C) for duration of one hour in an electrically heated oven (method was introduced by Louis Pasteur).

It acts by coagulation and denaturation of proteins.

(i) At Temperature below 100°C:

This process is developed by Louis Pasteur (1822-95). Articles to be sterilized are heated at 65°C for 30 minutes (holder method) or heated at 72°C for 15 seconds (flash method) followed by quick cooling to below 10°C. This method is suitable to destroy most milk born pathogenic bacteria e.g. Salmonella, Staphylococci and Brucella.

Certain other methods of sterilization at below 60°C temperature are:

Vaccine bath (contaminating bacteria in a vaccine preparation can be inactivated by heating in a water bath at 60°C for one hour), Serum bath (the contaminating bacteria in a serum preparation can be inactivated by heating in a water bath at 56°C for one hour) and inspissation (to disinfect egg and serum containing media by keeping then in the slopes of an inspissator heated at 80-85 °C for 30 minutes on three successive days).

(ii) At Temperature 100°C:

Boiling water (100C°) kills most vegetative bacteria.

Passing the steam at 100°C over articles kills bacteria. Sugars and gelatin in medium may get decomposed by autoclaving. So, these can be sterilised by exposing them to free steaming for 20 minutes for three successive days. This process is known as tyndallisation (after John Tyndall).

(iii) At Temperature above 100°C:

Sterilization can be effectively achieved at a temperature above 100°C using an autoclave.

(b) Structure of Autoclave:

A simple autoclave has vertical or horizontal cylindrical body with a heating element, a per-forted tray to keep the articles, a lid that can be fastened by screw clamps, a pressure gauge, a safety valve and a discharge tap (Fig. 1). The lid is closed but the discharge tap is kept open and the water is heated.

As the water starts boiling the steam drives air out of the discharge tap, when all the air is displaced and steam starts appearing through the discharge tap, the tap is closed. The pressure inside is allowed to rise up to 15 lbs. per square inch. At this pressure the articles are heated for 15 minutes, after which the heating is stopped and the autoclave is allowed to cool.

Once the pressure gauge shows the pressure equal to atmospheric pressure, the discharged tap is opened to let the air in. The lid is opened and articles are removed. Culture media, dressing, certain equipment’s can be sterilised by autoclave.

(iii) Sonic and Ultrasonic Vibrations

Sound waves of frequency 720,000 cycle/second kills bacteria and some viruses exposing for one hour.

(iv) Radiation:

Two types of rays are used for sterilization:

These are low-energy rays with poor penetrative power, e.g., U.V. rays (wavelength 200-280 nms, effective 260 nm).

These are high-energy rays with good penetration power.

These are of two types:

Particulate and electromagnetic. Electron beams are particulate while gamma rays are electromagnetic in nature. High speed electrons are produced by a linear accelerator from a heated cathode. Electromagnetic rays such as gamma rays emanate from nuclear disintegration of certain radioactive isotopes (Co 60 , Cs 137 ).

A degree of 2.5 megabrands of electromagnetic rays kills all bacteria, fungi, virus and spores. In some parts of Europe, fruits and vegetable are irradiated to increase their shelf life up to 500 percent. Since radiation does not generate heat, it is called Cold sterilization.

Chemical Methods of Sterilization:

Chemicals destroy pathogenic bacteria from inanimate surfaces and are all also called disinfectants.

Liquid:

E.g., Ethyl alcohol, Isopropyl alcohol and methyl alcohol. (A 70% solution kills bacteria).

Aldehydeles:

E.g., Fomaldehyele, Gluteraldehydele (40% formaldehyde is used for surface disinfection).

E.g., 50% phenol, 1-5% cresol, 5% lysol, chloroxylenol (Dettol).

E.g., chlorine compounds (chlorine bleach, hydrochloride) and iodine compounds (tincture, iodine, iodophores). Tincture of iodine (2% iodine in 70% alcohol) is antiseptic.

Heavy metals:

E.g., Mercuric chloride, silver nitrate, copper sulfate, organic mercuric salts. Surface active agents: e.g., soaps or detergents.

Acridin dyes e.g., acriflavin and aminacrine are bactericidal (interact with bacterial nucleic acids).

Gaseous:

E.g. Ethylene oxide, formaldehyde gas, highly effective, killing of spores.

Physiochemical Methods of Sterilization:

A physiochemical method adapts both physical and chemical method. Use of steam-formaldehyde is a physiochemical method of sterilization.


Additional Information

There is limited evidence of Ebola virus transmission through the environment or an inanimate object that may be contaminated during patient care with infectious organisms and serve in their transmission (bed rails, doorknobs, laundry). 5 Ebola virus has not been found on surfaces in the absence of visible blood in the patient care environment. 6 Frequently touched surfaces should be cleaned and disinfected on a regular basis to help reduce the risk of contact with contaminated surfaces. In addition, spills of biological fluids should be immediately cleaned and disinfected. Disinfectants should also be added to bagged waste.


1. Elliott LH, McCormick JB, Johnson KM. Inactivation of Lassa, Marburg, and Ebola viruses by gamma irradiation. J Clin Microbiol. 1982 Oct16(4):704-8.

2. Mitchell SW, McCormick JB. Physicochemical inactivation of Lassa, Ebola, and Marburg viruses and effect on clinical laboratory analyses. J Clin Microbiol 1984 20(3):486-9.

4. Chepurnova AA, Bakulina LF, Dadaeva AA, Ustinova EN, Chepurnova TS, Baker JR, Jr,. Inactivation of Ebola virus with a surfactant nanoemulssion. Acta Tropica 2003 87:315-320.

6. Bausch DG, Towner JS, Dowell SF, Kaducu F, Lukwiya M, Sanchez A, et al. Assessment of the risk of Ebola virus transmission from bodily fluids and fomites. J Infect Dis 2007 196:S142&ndash7.

7. Ribner BS. Treating patients with Ebola virus infections in the US: lessons learned. Presented at IDWeek, October 8, 2014. Philadelphia PA.

8. Favero MS, Bond WW. Chemical disinfection of medical and surgical materials. In: Block SS, ed. Disinfection, sterilization, and preservation. Philadelphia (PA): Lippincott Williams & Wilkins, 2001:881-917.

9. Mitchell SW, McCormick JB. Physicochemical inactivation of Lassa, Ebola, and Marburg viruses and effect on clinical laboratory analyses. J Clin Microbiol 1984 20(3):486-9.

10. Russell AD. Bacterial resistance to disinfectants: present knowledge and future problems. J Hosp Infect 199843:S57-68.


Discussion

We observed marked differences in the compositions, abundances, and viabilities of microbial communities associated with household dust when exposure to daylight was experimentally disrupted (Figs. 2 and 3 Table 1). Communities associated with dust were more variable in darkness compared to those in the presence of daylight (Fig. 2a), which may indicate a convergence in community structures under regular disturbances [67, 68], in this case light disturbance [16]. Our results indicate that dust exposed to daylight contains smaller viable bacterial communities (Fig. 2b) that more strongly resemble outdoor air communities (Fig. 3a) and that the bactericidal effects of ordinary window-filtered sunlight may be similar to those achieved by ultraviolet light wavelengths for some taxa (Fig. 3b, e), but not for others (Fig. 3c, d).

Our experimental light exposures were associated with the loss of a related set of numerically dominant, potentially sensitive taxa (Fig. 3e, gray circles) and apparent increases in the abundances of a small number of rare taxa (Fig. 3e, gold and blue circles). However, we were unable to determine whether these apparent increases were due to metabolic activity and bacterial population growth under lighting conditions or the result of sampling artifacts arising from DNA sequencing. Photochemical transformation of organic materials due to exposures to visible or ultraviolet light wavelengths have been shown to increase bacterial growth rates in some ecosystems [69] and are at least one mechanism that could influence bacterial growth under strong daylighting. However, prior research indicates that many if not most built environment-associated bacteria require water activity greater than 95% for growth [64]—conditions that are significantly wetter than what was maintained in our microcosms. Instead, results of our experiment, sampling model, and prior studies point to the explanation that these apparent increases were artefacts resulting from the inactivation and loss of numerically dominant, light-sensitive taxa (Fig. 3e, gray circles). We hypothesize that when highly abundant community members like Saccharopolyspora and Staphyloccocus were lost, the underlying taxonomic abundance distribution was truncated in a way that mitigated our inability to detect very rare RSVs. Sampling theory provides a path to further understand what drives the underlying structure of microbiomes by establishing null expectations for ecological patterns [3, 62, 70] microbiome studies will benefit from a continued consideration of quantitative theories that explicitly account for the technological limitations and biases surrounding the detection of rare microorganisms from environmental DNA [71].

The most diverse and abundant group of organisms associated with dark dust contained members of the genus Saccharopolyspora, which have been previously associated with soils and buildings in rural areas [72], and built environment-mediated respiratory diseases [73, 74]. The observation that these dominant RSVs were largely absent or rare in daylit dust provides some evidence to the hypothesis [21] that sunlight may be used to selectively limit the viabilities of microorganisms in buildings like hospitals, although we are not able to determine the pathogenic potential of any of the bacteria detected in this study. Additional experiments are needed, to determine the microbicidal potential of light exposures under a wider range of conditions, especially in conjunction with the enhanced indoor microbial growth rates reported under elevated water availability [64, 75] and with an explicit focus on known pathogenic microorganisms including viruses, fungi, archaea, and protists. Interactions between sunlight and population sizes have been observed for a small number of viral, [76] fungal [77], and protozoan [78] taxa in other systems, but these relationships have not yet been uncovered for holistic dust communities that comprise multiple microbial kingdoms in real buildings [7]. Experimental studies that include detailed time series measurements are also needed to characterize the transient dynamics and mechanisms underlying sunlight-induced changes in dust microbial communities, which may exhibit phylogenetic signals or depend on functional genes related to photosynthesis, photoreactivation and repair [79], and oxidative stress [80].

We used a model system to study the effects of light exposure on the structure of microbial dust communities, although we expect many of the results observed in this study to apply to real built environments. Our microcosms were designed to approximate conditions in real buildings, including temperatures, reflectances, humidities, and transmittances. While the microcosms used here permit more control compared to typical built environment microbiome studies, these systems are still idealized representations of human-occupied spaces. Our experiment was limited in that it characterized features of the dust microbiome across a relatively narrow range of light dosages. We aimed for dosages relevant to well-daylit buildings, but there are many architectural and geographical instances that produce lower or higher dosages than examined here that may merit additional study. Our microcosms were south-facing and therefore experienced the greatest possible daily exposures. Other latitudes, altitudes, climate zones, building orientations, and obstructions (e.g., trees) would indeed change exposures raising the possibility of linkages between the spatial context of buildings, design decisions that impact the transmittance of light, geographical or seasonal variation in sunlight availability, and the structure of indoor dust microbial communities.


All the Ways to Kill a Coronavirus (So Far)

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The race is on to find a cure for Covid-19. Researchers are testing new vaccines, resurrecting old drugs, and repurposing treatments originally developed for other diseases. Things are moving fast by the time you read this, the situation may have changed (for the better, we hope). So how are scientists thinking they'll fend off this tiny viral adversary? Here are a few lines of attack.

Each particle of the new virus, SARS-CoV-2, is studded with spikes, which allow it to attach itself to a human cell, poke a hole, and burrow inside. Like the germ that caused the SARS epidemic in 2003, it sticks to a protein on human cells called ACE2, which is especially prevalent in the lungs and small intestine. (SARS-CoV-2 is at least 10 times stickier than its cousin, which may account for its rapid spread.) One way to stop the invader is to keep it from attaching in the first place. This is what your immune system tries to do—it sends out antibodies that gum up the spikes so the virus can't stick to ACE2. But there are other ways of achieving the same effect.

1. Make a vaccine. For powerful, long-lasting immunity, a so-called live attenuated vaccine is the gold standard. It contains a defanged version of the virus that your immune system can use for target practice—but it can also cause infection. That's why many researchers are working on vaccines that contain not the whole virus but just the outer spikes. Mixed with immune-boosting molecules called adjuvants, they'll elicit a safe antibody response.

2. Take antibody-rich blood plasma from people who have survived Covid-19 and inject it into newly infected or at-risk patients. Plasma won't teach the body how to fend off the virus, and one injection won't last forever—but it could be a good way to prepare health workers before they head to a hot spot.

3. Flood the zone with decoys—synthetic molecules that look like ACE2 and trick the virus into binding with them instead, protecting lung cells from damage.

4. Invent drugs that hinder ACE2 from binding with the virus. In theory, these compounds would work on both SARS and Covid-19, stopping the viruses from sticking to cells. But ACE2 plays a number of other roles throughout the body it helps regulate blood pressure, kidney function, and even fertility. Messing with it could have dangerous consequences.

All viruses wear heavy-duty protein coats to protect their precious genetic material from the elements. The new coronavirus sports an extra outer layer of fatty molecules. That's great news for humans, because it's easy to tear open with soap or alcohol-based disinfectants. (Soap works best, and you don't need to bother with the antibacterial stuff.) Without its fatty layer, the virus dies. Wipe it away or wash it down the drain.


A nanoscale window to the biological world

Microscopic view of the rotavirus double-layered particle studied in the paper, along with a 3-D reconstruction of the virus.

If the key to winning battles is indeed knowing both your enemy and yourself, then scientists are now well on their way toward becoming the Sun Tzus of medicine by taking a giant step toward a priceless advantage – the ability to see the soldiers in action on the battlefield.

Investigators at the Virginia Tech Carilion Research Institute have invented a way to directly image biological structures at their most fundamental level and in their natural habitats. The technique is a major advancement toward the ultimate goal of imaging biological processes in action at the atomic level.

“It’s sort of like the difference between seeing Han Solo frozen in carbonite and watching him walk around blasting stormtroopers,” said Deborah Kelly, an assistant professor at the Virginia Tech Carilion Research Institute and a lead author on the paper describing the first successful test of the new technique. “Seeing viruses, for example, in action in their natural environment is invaluable.”

The technique involves taking two silicon-nitride microchips with windows etched in their centers and pressing them together until only a 150-nanometer space between them remains. The researchers then fill this pocket with a liquid resembling the natural environment of the biological structure to be imaged, creating a microfluidic chamber. Then, because free-floating structures yield images with poor resolution, the researchers coat the microchip’s interior surface with a layer of natural biological tethers, such as antibodies, which naturally grab onto a virus and hold it in place.

In the study, recently published in Lab on a Chip, Kelly joined Sarah McDonald, also an assistant professor at the research institute, to prove that the technique works. McDonald provided a pure sample of rotavirus double-layered particles for the study.

“What’s missing in the field of structural biology right now is dynamics – how things move in time,” said McDonald. “Debbie is developing technologies to bridge that gap, because that’s clearly the next big breakthrough that structural biology needs.”

Rotavirus is the most common cause of severe diarrhea among infants and children. By the age of five, nearly every child in the world has been infected at least once. And although the disease tends to be easily managed in the developed world, in developing countries rotavirus kills more than 450,000 children a year.

At the second step in the pathogen’s life cycle, rotavirus sheds its outer layer, which allows it to enter a cell, and becomes what is called a double-layered particle. Once its second layer is exposed, the virus is ready to begin using the cell’s own infrastructure to produce more viruses. It was the viral structure at this stage that the researchers imaged in the new study.

Kelly and McDonald coated the interior window of the microchip with antibodies to the virus. The antibodies, in turn, latched onto the rotaviruses that were injected into the microfluidic chamber and held them in place. The researchers then used a transmission electron microscope to image the prepared slide.

The technique worked perfectly.

The experiment gave results that resembled those achieved using traditional freezing methods to prepare rotavirus for electron microscopy, proving that the new technique can deliver accurate results.

“It’s the first time scientists have imaged anything on this scale in liquid,” said Kelly.

The next step is to continue to develop the technique with an eye toward imaging biological structures dynamically in action. Specifically, McDonald is looking to understand how rotavirus assembles, so as to better know and develop tools to combat this particular enemy of children’s health.

The researchers said their ongoing collaboration is an example of the cross-disciplinary work that is becoming a hallmark of the Virginia Tech Carilion Research Institute.

“It’s an ideal collaboration because Sarah provides a phenomenal model system by which we can develop new technologies to move the field of microstructural biology forward,” said Kelly.

“It’s very win-win,” McDonald added. “While the virus is a great tool for Debbie to develop her techniques, her technology is critical for allowing me to understand how this deadly virus assembles and changes dynamically over time.”

The paper “Visualizing viral assemblies in a nanoscale biosphere” was published online this month and will appear in a 2013 edition of Lab on a Chip. The authors are Brian Gilmore, a research associate at the VTC Research Institute Shannon Showalter, a research assistant at the Virginia Tech Carilion Research Institute Madeline Dukes, an applications scientist at Protochips Justin Tanner, a postdoctoral associate at the research institute Andrew Demmert, a student at the Virginia Tech Carilion School of Medicine McDonald, who, in addition to her position at the research institute, is an assistant professor of biomedical sciences and pathobiology in the Virginia–Maryland Regional College of Veterinary Medicine and Kelly, who, in addition to her position at the research institute, is an assistant professor of biological sciences in Virginia Tech’s College of Science.


5 Viruses That Are Scarier Than Ebola

The Ebola virus has now killed more than 1,000 people in West Africa. Although the mortality rate of the most recent outbreak isn't as high as in previous events, it's still the case that most people who become infected with Ebola will not survive. (The mortality rate is about 60 percent for the current outbreak, compared with 90 percent in the past, according to the National Institutes of Health.)

But despite this somber prognosis, health experts in the United States aren't particularly worried about the threat of Ebola in this countryor in other developed countries.

"I see Ebola as a significant threat in the specific regions that it has been identified in, certainly central and west Africa," said Cecilia Rokusek, a public health expert with Nova Southeastern University's Institute for Disaster and Emergency Preparedness in Florida. "But in my opinion, it's not an imminent threat for those in the United States." [7 Devastating Infectious Diseases]

Indeed, other viruses pose a larger threat to U.S. citizens, according to Rokusek.

Although some of these viruses have far lower mortality rates than that of Ebola, they are more prevalent in developed nations, and kill more people annually than Ebola does. Here are five viruses that are just as dangerous (if not more so) than Ebola:

Over the past 100 years, rabies has declined significantly as a public health threat in the United States, according to the Centers for Disease Control and Prevention. Approximately two people now die yearly in the United States from this virus, which is transmitted to people through saliva when they are bitten by infected animals, such as dogs or bats.

People who know they have been bitten by an animal should receive the rabies vaccine, which prevents infection by the virus, according to the CDC. But, especially in the case of bat bites, people may not always realize they have been bitten.

And rabies has one of the highest fatality rates of any virus only three people in the United States are known to have ever survived the disease without receiving the vaccine after exposure to the virus.

Still, the disease remains a greater threat in other areas of the world than in the United States. Approximately 55,000 people die of rabies every year in Africa and Asia, according to the WHO.

Though the number of annual deaths related to human immunodeficiency virus (HIV) has declined in recent years, an estimated 1.6 million people worldwide died of HIV and acquired immune deficiency syndrome (AIDS) related causes in 2012, according to the WHO. The virus attacks a person's immune cells and weakens the immune system over time, making it very difficult for the infected individual to fight off other diseases.

About 15,500 people with an AIDS diagnosis died in 2010 in the United States, according to the CDC. In total, an estimated 650,000 people have died of AIDS in the United States since the disease was discovered in 1981. An estimated 36 million people have died worldwide from the epidemic.

Today, people with HIV do live longer than they used to, a trend that coincides with the increased availability of antiretroviral therapy, as well as the decline in new infections since the peak of the AIDS epidemic in 1997. However, no cure for HIV exists.

The flu may not sound very scary, but it kills far more people every year than Ebola does. The exact number of people who die each year from seasonal flu virus is the subject of much debate, but the CDC puts the average number of annual deaths in the United States somewhere between 3,000 and 49,000.

The large variation in yearly deaths arises because many flu deaths are not reported as such, so the CDC relies on statistical methods to estimate the number. Another reason for this wide range is that annual flu seasons vary in severity and length, depending on what influenza viruses are most prominent. In years when influenza A (H3N2) viruses are prominent, death rates are typically more than double what they are in seasons when influenza A (H1N1) or influenza B viruses predominate, according to the CDC.

A highly contagious virus, influenza sickens far more people than it kills, with an estimated 3 million to 5 million people becoming seriously ill yearly from influenza viruses. Worldwide, the flu causes an estimated 250,000 to 500,000 deaths every year, according to the World Health Organization (WHO).

Despite the relatively low mortality rate of the virus, public health professionals and doctors recommend annual flu shots to keep the risk of complications from influenza at bay.

"Healthy people should get their vaccines every year," Rokusek told Live Science. "Studies have shown that the flu vaccine is an effective preventative measure."

But flu vaccines, which offer immunity from influenza A and B viruses, do not protect against other forms of influenza, which can arise when the virus undergoes genetic changes. New strains of the flu result in higher than average mortality rates globally. The most recent influenza pandemic, the "swine flu" or H1N1 pandemic, killed between 151,700 and 575,400 people globally during 2009 and 2010, according to the CDC.

Mosquito-borne viruses

Spread through the bite of an infected mosquito, viruses such as dengue, West Nile and yellow fever kill more than 50,000 people worldwide every year, according to estimates by the WHO and the CDC. (Malaria &mdash which is also spread by mosquitos, but is caused by a parasite rather than a virus &mdash kills more than 600,00 people yearly.)

At least 40 percent of the world's population, or about 2.5 billion people, are at risk of serious illness and death from mosquito-borne viral diseases, according to the CDC.

Dengue fever, which is endemic to parts of South America, Mexico, Africa and Asia, claims approximately 22,000 lives every year, according to the CDC. Dengue hemorrhagic fever is a deadly infection that causes high fevers and can lead to septic shock.

These diseases occur in regions neighboring the United States, making them a threat in this country.

"Dengue is very active in the Caribbean, and travelers to the Caribbean come back to the United States with dengue," said Dr. Robert Leggiadro, a New York physician and professor of biology at Villanova University in Pennsylvania. [10 Deadly Diseases That Hopped Across Species]

People infected with dengue while traveling abroad can spread the disease at home when mosquitos bite them, and then bite other people, Leggiadro said.

Even more deadly than dengue is yellow fever, which mostly affects people in Latin America and Africa. The disease causes an estimated 30,000 deaths worldwide, according to the WHO.

Less deadly, but still dangerous is West Nile virus, a viral neurological disease that is spread by mosquitos that bite humans after feasting on birds infected with the virus. Although the vast majority of people infected with this virus will not show symptoms of West Nile, the disease has killed an estimated 1,200 people in the United States since it was first seen here in 1999, according to the CDC.

Not everyone is at high risk of contracting rotavirus, but for children around the world, this gastrointestinal virus is a very serious problem. Approximately 111 million cases of gastroenteritis caused by rotavirus are reported every year globally, according to the CDC. The vast majority of those affected by the virus are children under the age of 5, and about 82 percent of deaths associated with the virus occur in children in developing nations.

Globally, an estimated 440,000 children who contract the virus die each year from complications, namely dehydration. In the United States, a vaccine for rotavirus was developed in 1998, but was later recalled due to safety concerns. A newer vaccine, developed in 2006, is now available and is recommended for children ages 2 months and older.

Despite routine vaccinations for rotavirus in the United States, the CDC estimates that between 20 and 60 children under age 5 die every year from untreated dehydration caused by the virus.

While some parents in the United States have expressed concern about the complications that may arise as a result of vaccinating for rotavirus, Leggiadro told Live Science that vaccination for this and other preventable diseases is the best way to safeguard against diseases that, if left untreated, can be deadly.

Editor's Note: This story was updated to reflect the correct definition for the acronym AIDS.


Does sunlight kill rotavirus? - Biology

PART IV. EVOLUTION AND ECOLOGY

16. Community Interactions

16.3. Kinds of Organism Interactions

One of the important components of an organism’s niche is the other living things with which it interacts. Some interactions are harmful to one or both of the organisms, whereas other interactions are beneficial. Ecologists have classified the kinds of interactions between organisms into broad categories.

Competition is an interaction between organisms in which both organisms are harmed to some extent. This is the most common kind of interaction among organisms. Organisms are constantly involved in competition. Competition occurs whenever two organisms need a vital resource that is in short supply (figure 16.5). The vital resource may be such things as soil nutrients, sunlight, or pollinators for plants or food, shelter, nesting sites, water, mates, or space for animals.

Whenever a needed resource is in limited supply, organisms compete for it. Competition between members of the same species is called intraspecific competition. (a) Intraspecific competition for sunlight among these pine trees has resulted in the tall, straight trunks. Those trees that did not grow fast enough died. Competition between different species is called interspecific competition. (b) The lion and vultures are competing for the lion’s zebra kill.

Intraspecific competition takes place between members of the same species. It can involve a snarling tug-of-war between two dogs over a scrap of food or a silent struggle between pine seedlings for access to available light. Interspecific competition occurs between members of different species. The interaction between weeds and tomato plants in a garden is an example of interspecific competition. If the weeds are not removed, they compete with the tomatoes for available sunlight, water, and nutrients, resulting in poor growth of both the tomatoes and weeds. Similarly, there is interspecific competition among species of carnivores (e.g., hawks, owls, coyotes, foxes) for the small mammals and birds they use for food. Competition does not necessarily involve a face-to-face confrontation. For example, if a coyotes kills and eats a rodent, it has had a competitive effect on foxes, hawks, and other carnivores as well as other members of its own species, because there is now one less rodent available to be caught and eaten by others.

Competition and Natural Selection

Competition is a powerful force for natural selection. Although competition results in harm to both organisms, there can still be winners and losers. The two organisms may not be harmed to the same extent, with the result that one gains greater access to the limited resource. Biologists have recognized that, the more similar the requirements of two species of organisms, the more intense the competition between them. This has led to the development of a general rule known as the competitive exclusion principle. According to the competitive exclusion principle, no two species of organisms can occupy the same niche at the same time. If two species of organisms do occupy the same niche, the competition will be so intense that one or more of the following processes will occur: (1) one of the two species will become extinct, (2) one will migrate to a different area where competition is less intense, or (3) the two species will evolve into slightly different niches, so that the intensity of the competition is reduced. For example, a study of the feeding habits of several kinds of warblers shows that, although they live in the same place and feed on similar organisms, their niches are slightly different, because they feed in different places on trees (figure 16.6).

FIGURE 16.6. Niche Specialization

Although all of these warbler species have similar feeding habits, they limit the intensity of competition by feeding on different parts of the tree.

Another example involves the competition of various species of flowering plants for pollinators. Some have bright red tubular flowers that are attractive to hummingbirds. Some have foul odors that attract flies or beetles. Others are open only at night and are pollinated by moths or bats. A few kinds of orchid flowers mimic female wasps and are pollinated when the male wasp tries to mate with the fake female wasp. Many flowers attract several kinds of bees, butterflies, or beetles, but the flowers open only at certain times of the day. All of these differences are niche specializations that reduce competition for pollinators.

Predation is an interaction in which one animal captures, kills, and eats another animal. The organism that is killed is the prey, and the one that does the killing is the predator. Predators benefit from the relationship because they obtain a source of food obviously, prey organisms are harmed. Most predators are relatively large, compared to their prey, and have specific adaptations to aid them in catching prey. There are many different styles of predation. Many predators, such as leopards, lions, cheetahs, hawks, squid, sharks, and salmon, use speed and strength to capture their prey. Dragonflies, bats, and swallows use a technique that involves flying around in an area where they can capture flying insects. Predators such as frogs, many kinds of lizards, and insects (e.g., praying mantis) blend in with their surroundings and strike quickly when a prey organism happens by. Wolf spiders and jumping spiders have large eyes, which help them find prey, which they pounce on and kill. The webs of other kinds of spiders serve as nets to catch flying insects. The prey are quickly paralyzed by the spider’s bite and wrapped in a tangle of silk threads (figure 16.7). Many kinds of birds, insects, and mammals simply search for slow-moving prey, such as caterpillars, grubs, aphids, slugs, snails, and similar organisms. Many kinds of marine snails and starfish are predators of other slow-moving sea creatures.

Often predators are useful to humans because they control populations of organisms that do us harm. For example, snakes eat rats and mice that eat stored grain and other agricultural products. Birds and bats eat insects that are agricultural pests.

FIGURE 16.7. The Predator-Prey Relationship

(a) Many predators, such as lions and cheetahs, use speed and strength to capture prey. (b) Other predators, such as frogs and chameleons, blend in with their surroundings, lie in wait, and ambush their prey. (c) Some spiders use nets to capture prey. Obviously, predators benefit from the food they obtain, to the detriment of the prey.

It is even possible to think of a predator as having a beneficial effect on the prey species. Certainly, the individual organism that is killed is harmed, but the population can benefit. Predators can control the size of a prey population and thus, prevent large populations of prey organisms from destroying their habitat or they can reduce the likelihood of epidemic disease by eating sick or diseased individuals. Furthermore, predators act as selecting agents. The individuals that fall prey to them are likely to be less well-adapted than the ones that escape predation. Predators usually kill slow, unwary, poorly hidden, sick, or injured individuals. Thus, the genes that may have contributed to slowness, inattention, poor camouflage, illness, or the likelihood of being injured are removed from the gene pool.

Symbiosis means “living together.” Unfortunately, this word is used in several ways, none of which is very precise. However, the term symbiosis is usually used for interactions that involve a close physical relationship between two kinds of organisms. The three kinds of relationships discussed in the following sections—parasitism, commensalism, and mutualism—are often referred to as symbiotic relationships because they usually involve organisms that are physically connected to one another.

In parasitism, one organism lives in or on another living organism, from which it derives nourishment. The parasite derives benefit and harms the host, the organism it lives in or on. Parasites are smaller than their hosts. In general, they do not kill their host quickly but, rather, use it as a source of food for a long time. However, the parasite’s activities may weaken the host so that it eventually dies. Parasitism is a very common kind of interrelationship. Nearly every category of living thing has species that are parasites. There are parasitic bacteria, fungi, protozoa, plants, fish, insects, worms, mites, and ticks. In fact, there are more species of parasites in the world than there are nonparasites.

There are many styles of parasitism. Parasites that live on the outside of their hosts are called external parasites. For example, ticks live on the outside of the bodies of animals, such as rats, turtles, and humans, where they suck blood and do harm to their hosts. Internal parasites live on the inside of their hosts. For example, tapeworms live in their hosts’ intestines. Several kinds of plants are parasitic mistletoe invades the tissues of the tree it is living on to derive its nourishment. Some flowering plants, such as beech drops and Indian pipe, lack chlorophyll and are not able to do photosynthesis. They derive their nourishment by obtaining nutrients from the roots of trees or soil fungi and grow aboveground for a short period when they flower. Indian pipe is interesting in that it is parasitic on the fungi that assist tree roots in absorbing water. The root fungi receive nourishment from the tree and the Indian pipe obtains nourishment from the fungi. So, the Indian pipe is an indirect parasite on trees (figure 16.8).

FIGURE 16.8. The Parasite-Host Relationship

Parasites benefit from the relationship because they obtain nourishment from the host. (a) Tapeworms are internal parasites in the guts of their host, where they absorb food from the host’s gut. (b) The tick is an external parasite that sucks body fluids from its host. (c) Indian pipe (Monotropa uniflora) is a flowering plant that lacks chlorophyll and is parasitic on fungi that have a mutualistic relationship with tree roots. The host in any of these three situations may not be killed directly by the relationship, but it is often weakened, becoming more vulnerable to predators and diseases.

Many kinds of fungi are parasites of plants, including commercially valuable plants. Farmers spend millions of dollars each year to control fungus parasites. Many kinds of insects, worms, protozoa, bacteria, and viruses are important human parasites.

Many parasites have extremely complicated life cycles (chapter 23 discusses the life cycle of several kinds of worm parasites). In many of these life cycles, some species carry the parasite from one host to the next. Such a carrier organism is known as a vector. For example, the protozoan that causes malaria is carried from one human to another by certain species of mosquitos, and the bacterium Borrelia burgdorferi, which causes lyme disease, is carried by certain species of ticks (figure 16.9).

FIGURE 16.9. Lyme Disease—Hosts, Parasites, and Vectors

Lyme disease is a bacterial disease originally identified in a small number of people in the Old Lyme, Connecticut, area. Today, it is found throughout the United States and Canada. The parasite Borrelia burgdorferi, is a bacterium that can live in a variety of mammalian hosts (e.g., humans, mice, horses, cattle, domestic cats, and dogs). Certain ticks are vectors that suck blood from an infected animal and carry the disease to another animal when the tick feeds on it.

Special Kinds of Predation and Parasitism

Both predation and parasitism are relationships in which one member of the pair is helped and the other is harmed. But there are many kinds of common interactions in which one is harmed and the other aided that don’t fit neatly into the categories of interactions dreamed up by scientists. For example, when a deer eats the leaves off a tree or a goose eats grass, they are doing harm to the plant they are eating while deriving a benefit. In essence, these herbivores are plant predators or parasites (figure 16.10). In aquatic habitats there are many kinds of organisms (sponges, clams, barnacles, shrimp, etc.) that live as filter-feeders. They are essentially grazers on tiny organisms in the water around them. Most consume a mixture of algae and tiny animals, but they consume the entire organism and can be considered a kind of predator. In addition, there are many animals, such as mosquitoes, biting flies, vampire bats, and ticks, that take blood meals but don’t usually live permanently on the host or kill it. Are they temporary parasites or specialized predators?

FIGURE 16.10. Special Kinds of Predation and Parasitism

Herbivores have a relationship with plants that is very similar to that of carnivores with their prey and parasites with their hosts. The herbivores are aided and the plants they feed on are harmed. Mosquitoes and other kinds of blood-sucking animals can be considered temporary parasites or predators. They do harm to the animal they feed on and benefit from the relationship.

Finally, birds such as cowbirds and some species of European cuckoos do not build nests but, rather, lay their eggs in the nests of other species of bird, which raise these foster young rather than their own. The adult cowbird and cuckoo often remove eggs from the host nest. In addition, cowbird and cuckoo offspring typically push the hosts’ eggs or young out of the nest. For these reasons, typically only the cowbird or cuckoo chick is raised by the foster parents. This kind of relationship has been called nest parasitism. The surrogate parents (hosts) are harmed, and the cowbird or cuckoo is aided by having others expend the energy needed to raise its young (figure 16.11).

FIGURE 16.11. Nest Parasitism

This cowbird chick in the nest is being fed by its host parent, a yellow warbler. The cowbird chick and its cowbird parents both benefit but the host is harmed because it is not raising any of its own young.

Commensalism is a relationship in which one organism benefits and the other is not affected. For example, sharks often have another fish, the remora, attached to them. The remora has a sucker on the top side of its head, which allows it to attach to the shark for a free ride (figure 16.12a). Although the remora benefits from the free ride and by eating leftovers from the shark’s meals, the shark does not appear to be troubled by this uninvited guest, nor does it benefit from its presence.

Another example of commensalism is the relationship between trees and epiphytic plants. Epiphytes are plants that live on the surface of other plants but that do not derive nourishment from them (figure 16.12b ) . Many kinds of plants (e.g., orchids, ferns, and mosses) use the surfaces of trees as places to live. These kinds of organisms are particularly common in tropical rainforests. Many epiphytes derive a benefit from the relationship because they are able to be located in the tops of the trees, where they receive more sunlight and moisture. The trees derive no benefit from the relationship, nor are they harmed they simply serve as support surfaces for the epiphytes.

In commensalism, one organism benefits and the other is not affected. (a) The remora shown here hitchhikes a ride on the shark. It eats scraps of food left over from the shark’s messy eating habits. The shark does not seem to be hindered in any way. (b) The grey Spanish moss hanging on this oak tree is a good example of an epiphyte. The spanish moss does not harm the tree but benefits from using the tree surface as a place to grow.

Mutualism is an interrelationship in which two species live in close association with one another, and both benefit. Many kinds of animals that eat plants have a mutualistic relationship with the bacteria and protozoa that live in their guts. One of the major components of plant material is the cellulose material that makes up the cell wall. Most animals are unable to digest cellulose but rely on a collection of microorganisms in their guts to perform that function. For example, mammals such as cows, goats, camels, giraffes, and sheep have specialized portions of their guts, called a rumen, in which microorganisms live. These microbes produce enzymes, known as cellulases, that break down the cellulose in the food the animal eats. The microorganisms benefit because the gut provides them with a moist, warm, nourishing environment in which to live. The animals benefit because the breakdown of cellulose provides nutrients the animal could not get otherwise. Termites, plant-eating lizards, and many other kinds of herbivores have similar relationships with the bacteria and protozoa living in their digestive tracts which help them digest cellulose.

Lichens and corals exhibit a more intimate kind of mutualism. The bodies of lichens and corals are composed of the intermingled cells of two different kinds of organisms. Lichens consist of fungal cells and algal cells in a partnership corals consist of the cells of the coral organism intermingled with algal cells. In both, the algae carry on photosynthesis and provide nutrients, and the fungus or coral provides a moist, fixed structure for the algae to live in.

Another kind of mutualistic relationship exists between flowering plants and insects. Bees and other insects visit flowers to obtain nectar from the blossoms (figure 16.13). Usually, the flowers are constructed so that the bees pick up pollen (sperm-containing packages) from the plant on their hairy bodies, which they transfer to the female part of the next flower they visit. Because bees normally visit many individual flowers of the same species for several minutes and ignore other species of flowers, they can serve as pollen carriers between two flowers of the same species. Plants pollinated in this manner produce less pollen than do plants that rely on the wind to transfer pollen. This saves the plant energy, because it doesn’t need to produce huge quantities of pollen. It does, however, need to transfer some of its energy savings into the production of showy flowers and nectar to attract the bees. The bees benefit from both the nectar and the pollen they use both for food.

Mutualism is an interaction between two organisms in which both benefit. (a) The British soldier lichen in this photograph consists of a mutualistic association between a fungus and an alga. (b) Ruminant animals have a mutualistic relationship with the microorganisms in their gut that helps them obtain nutrients from the plants they eat. (c) Insects obtain nectar from plants the plants benefit by being pollinated. (Note the yellow pollen on the bee.)

Some plants use birds, bats, mice, beetles, flies, and other kinds of organisms to get their pollen distributed. Each kind of flower is specialized to the kind of pollinating animal. Flowers that are pollinated by bats flower at night and many of those that are pollinated by hummingbirds have long, tubular flowers. Table 16.1 summarizes features of these various kinds of organism interactions.

Another way in which plants and animals participate in a mutually beneficial relationship is in the production and consumption of fruit. The fruit that plants produce contains its seeds. The fruit is attractive to animals that eat it. When the seeds pass through the gut of the animal, they are typically deposited some distance from the plant that produced the fruit. Similarly animals that bury fruits typically carry the fruit away from the plant that produced it.


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