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Health officials should be watchful of zoonotic diseases
Experts advise proactive public health monitoring for zoonotic diseases.
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TORONTO – Animals are the key origin of more than 25 major infectious diseases in humans — and more than 800 total — thus the jump across species barriers should be of concern to infectious disease researchers.
An expert panel convened to examine the issue of infectious diseases crossing the species barrier at the American Society for Microbiology 107th General Meeting, held here.
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Panelists expressed concern about high profile outbreaks – such as SARS, Nipah virus and avian influenza – and the need to further explore factors that allow species crossover. “The message here is that we cannot rely on drugs and vaccines alone to deal with diseases like SARS, West Nile Virus, Nipah Virus and Ebola because these diseases emerge seemingly sporadically and can often be devastating,” said Peter Daszak, PhD, executive director of the Consortium for Conservation Medicine in New York City. “By the time there’s a huge outbreak, we’ve already missed the boat.”
Daszak and fellow panelists urged prevention before pandemic while still monitoring established zoonotic diseases such as rabies, sleeping sickness and Brucellosis.
“If we are really going to take a good look at handling these diseases as a community, it’s no good to think of the technological fix — the silver bullet vaccine — because it doesn’t work,” Daszak said. “We’ve got HIV now, 30 years on, and no vaccine.”
Bat study may be zoonotic key
A novel approach to examining zoonoses may be through studying bat vectors.
“Bats seem to be the reservoir hosts for so many emerging pathogens that we are concerned about, such as Ebola, SARS, Nipah and hendravirus,” said Andrew P. Dobson, PhD, professor of ecology and evolutionary biology at Princeton University. “Bats are also a reservoir for rabies viruses, including the newly–discovered Australian Lyssavirus.”
Understanding bats as a reservoir could promote prevention at the reservoir stage. However, little is known about bats even though Nipah virus crossed over in Malaysia 10 years ago (from fruit bats, to pigs, to humans) and annually crosses over to Bangladesh.
“We spend millions of dollars a year looking at the immune system of mice to understand human diseases, but bats have a completely different immune system because they have a completely different evolutionary history,” Dobson said.
Zoonotic history
The phenomenon of disease emergence and host switches leading to emergence dates back centuries.
“We talk about this famous species barrier and pathogens being able to jump from one host to another, [but] in fact it’s not clear how much of a barrier there is,” said Sarah Cleaveland, PhD, senior lecturer at the Center for Tropical Veterinary Medicine at the University of Edinburgh.
There is much concern over high profile zoonosis and emerging disease such as SARS and avian influenza H5N1, although other zoonoses – called lingering zoonoses by WHO – are a much greater burden on global health. Lingering zoonosis, including rabies, Brucellosis, sleeping sickness and anthrax, should be considered when analyzing emerging disease, according to Cleaveland.
“They are killing thousands of people each year, but they are not receiving attention or priority because we are thinking about the newly emerging zoonoses,” Cleaveland said.
Preventive measures should be placed at source to best serve the developing countries hardest hit by emerging disease.
“It is critical that we know that this crossover will happen, we cannot predict accurately when and where, but we know that given the opportunities, this will happen,” Cleaveland said. – by Kirsten H. Ellis
For more information:
- Cleaveland S. Zoonotic and human infections.
- Dobson AP. The importance of fruit bats as reservoirs for emerging infections of humans.
- Daszak P. Emerging infections: Threats to human health and biodiversity.
- Colloquium #204. Crossing the species barrier: Relationships between emerging infections in animals and humans. Presented at: The American Society for Microbiology 107th General Meeting; May 21-25, 2007; Toronto.