Scientists call for support to study overlap between environmental health and in

[Guest guest]

Thursday 22 April 2010

Pathogens and chemicals: working together

Scientists call for support to study overlap between environmental health and

infectious diseases

http://www.eht-forum.org/news.html?fileId=news100422074459 & from=home & id=0

Hepatitis B virons. Infection with hepatitis B increases the risk of liver

cancer from aflatoxin exposure

Source: CDC/ Dr. Erskine Palmer

Researchers studying the health effects of exposure to toxic chemicals should

also consider how infectious diseases can impact the biological systems

involved, say health scientists this week. Research spanning the boundaries of

the two disciplines can give more realistic results and help to promote

solutions that are more relevant to public health problems, they argue.

" We provide evidence that environmental health research would be strengthened

through finding common ground with the tools and approaches of infectious

disease research, " write Beth Feingold and colleagues.

In an article published online this month in Environmental Health Perspectives,

the group, from the Hopkins Bloomberg School of Public Health in land,

USA, propose a new model of environmental health research that integrates

toxicology and infectious disease. These areas of study are traditionally

investigated and funded separately, they explain. But adopting the framework

could promote research that spans these boundaries by fostering collaboration

and communication between the different research communities.

" Environmental health's focus on the abiotic factors of toxicology has meant

that the field produces relatively little research on how pathogen and toxic

agents interact to increase risks and the severity of diseases, " write Feingold

and colleagues.

Many of the toxic agents studied in toxicological studies could affect the

immune system, they say. This may lower the threshold of how many pathogens are

needed for infection to take hold, or could cause people to shed more pathogens

into the environment, increasing the risk for others. Immune system changes

caused by toxic exposures may also affect the length of time it takes the body

to clear an infection, the severity of disease it can cause, and whether

diseases become chronic.

Bringing microbes into the mix

An example of such an interaction can be seen with aflatoxin, a mould that grows

on crops in tropical climates, and the hepatitis B virus, according to the

authors. Aflatoxin is known to play a part in the development of liver cancer,

and research has shown that people infected with the hepatitis B virus who are

exposed to the toxin are 30 times more likely to develop the disease than

uninfected people, they explain.

In another example, they say that research into cervical cancer caused by the

human papillomavirus suggests that smoking may act as a co-factor in disease

development. Scientists have also seen evidence that people exposed to mercury

cannot develop immunity to malaria.

Nyland, from the University of South Carolina, USA, believes that

taking a wider perspective like that suggested in the research is a " worthwhile "

strategy. Studying toxicology and infectious diseases together can give a better

idea of the potential implications of the research for human health, she says.

Making research more relevant

If scientists want their findings to be relevant to public health, they must

look at what effects both chemical and infectious agents have when the body

comes into contact with them around the same time, according to Nyland, and

researchers are beginning to realise this. But this type of work should not be

promoted at the expense of basic research, she adds, because it is impossible to

look at the health effects of all potential environmental contaminants in tandem

with all potential infections.

Nyland has worked with several of the authors and her research into mercury

exposure and coxsackie B3 virus infection in mice, funded by the US National

Institutes of Health (NIH), is cited in the paper. " Being able to combine the

exposure [to mercury] and the [coxsackie B3 virus] infection in a rational way

allows us to see the synergistic effects. It adds another dimension that can be

informative. "

Nyland adds that combinations of toxic agents and infectious pathogens are not

the only areas to consider. There are health risks when people harbour more than

one infection, or are exposed to mixtures of environmental pollutants.

Jane Selgrade, of the US Environmental Protection Agency (EPA), agrees that

research into environmental exposures should not have a narrow focus. Scientists

are starting to think about the health effects of being exposed to more than one

toxic agent and there is every reason to include infectious pathogens in the set

of environmental exposures that studies take into account, she explains.

" Microbes are part of the environmental mixture, we shouldn't lose sight of

that. "

This idea of integrating infectious diseases into environmental health is not

new, Selgrade points out, adding that for some time scientists at the EPA have

been interested in understanding how immune reactions alter the way cells deal

with toxic exposures, particularly in asthma. But the biological tools to study

this in depth are only just being developed, she says, and regulators have yet

to develop new risk assessment tools so they can make the best possible use of

this information for public health decisions.

Using the knowledge gained from studying the health effects of exposure to

particulate air pollution, which includes a mixture of differently sized

molecules, scientists have a better handle on multiple pollutants, and better

tools to study them.

Pushing forward with a systems approach

For Selgrade, the time is right for the scientific community to start thinking

in this way for toxic agents and infectious pathogens. " If we put things in

[separate] boxes, we lose the interactions between them. "

Biological research is moving towards a more systems-based approach, she

explains, which takes a more holistic look at the body and how different

biological systems, such as genes, proteins and biochemical reactions, interact

with each other.

Nyland believes this is an area of research that will expand in the future, and

argues that there should be an increase in funding directed into the field.

" Funders do try to foster this research, " says Selgrade. The EPA is a regulatory

body so much of the research it supports is directed into studies of substances

that can be regulated. This tends to be chemicals that are dealt with one at a

time, she explains. But the NIH can define the environment more broadly,

suggests Selgrade.

Reference and links

1. Feingold BJ, Vegosen L, M, Leibler J, A, Silbergeld EK.

Environ Health Perspect 2010. doi: 10.1289/ehp.0901866

World Health Organization information about infectious diseases

World Health Organization information about environmental pollution