The notion of connecting fragmented habitats so wildlife have access to critical habitat has been gaining ground. But, disease ecologists say it may also spread disease. Research on wild systems will help us understand whether human beings should interfere in natural ecosystems, and how such interference can affect ecology and evolution, discovers Jim Robbins
![]( "Virus hunter: Raina Plowright, a disease ecologist, with the skull of a bighorn ram. (Photo: Anne Sherwood/NYT)")
High in the Wallowa Mountains of northeastern Oregon, Raina K Plowright and other researchers took blood samples of a herd of bighorn sheep apart from taking swabs of their noses and throats. "There's lots of places for pathogens to hide in the nasal cavity," said Plowright, a wildlife scientist with the Center for Infectious Disease Dynamics at Penn State. This is part of the nascent field of eco-immunology, which seeks both to understand the immune systems of wild animals and to use that knowledge for a better understanding of human immune systems. Until recently, this knowledge was gleaned by studying pampered, genetically similar lab animals, which don't reflect a real-world scenario.
Eco-immunology works to understand how disease spreads in wildlife populations - the bighorn sheep are in trouble because of pneumonia that spread from domestic sheep - and how it can be worsened by human and environmental factors like climate change. Another major goal is to understand the pathways that deadly diseases can follow from wildlife to humans.
Going viral and how!
In the past 30 years, over 300 infectious diseases in humans originated in animals, including AIDS, Ebola, SARS, Lyme, hantavirus, West Nile virus and new strains of flu.
(Humans are also believed to have passed metapneumovirus to mountain gorillas in Africa.) In her native Australia, Plowright was involved in pioneering disease research on the little red flying fox, an intelligent nectar-sipping bat.
After the 1994 emergence of a deadly virus called Hendra in humans and horses in northeastern Australia, biologists found that it came from flying foxes. In 2008, Plowright discovered that stress appears to weaken the bats' immune system, and that is when they are likely to shed the most virus. "Trying to kill or move bats could make things worse by stressing them" and causing them to excrete more of the virus in their waste. This has quieted calls for large-scale bat removal, and Australia has committed millions of dollars to a project to understand viral ecology in bats.
The interconnections between human and animal diseases have led to new efforts to understand these mechanisms. "The wild is a null system, a system without interference," said Peter J Hudson, a biologist at Penn State and founder of the infectious disease centre there. "Research on wild systems," he continued, "will help us answer the question of 'Should we interfere, and how does interference affect the ecology and evolution of these bugs? Will the application of vaccines and antibiotics create more health problems?" "Some researchers believe, for example, that the rise in autoimmune disorders may be caused by a lack of stimulation of human immune systems by certain microbes.
Much about the diseases that originate in wildlife is a mystery. In the case of bat viruses, experts believe they evolved for millions of years in intact bat ecosystems, with the animals passing it to one another over and over, causing low-grade infections and building their immune defenses. Jonathan H Epstein, a veterinarian and a disease ecologist has used experimental infections to understand Nipah virus, closely related to Hendra. The new work on wild immune systems casts disease in a new light: as an environmental issue. One ecological driver of bat virus transmission is development in the flying foxes' natural habitat. Instead of living in a wild forest, the bats swoop into the cities and suburbs that replaced it, feeding on nectar in gardens and trees and then passing viruses along to horses and humans.
Why keep an ecosystem intact?
A common thread, disease ecologists say, is that clearing or altering a forest can be akin to opening a Pandora's box. Keeping nature intact, or developing it in sustainable ways, protects against disease ."If you conserve an ecosystem you have a jolly good chance of conserving human health as well," said Simon Anthony, a molecular virologist with EcoHealth who is studying the ecology of Nipah and other viruses.
Richard S Ostfeld, a disease ecologist at the Cary Institute for Ecosystem Studies in Millbrook, NY, has been studying the causes of Lyme disease. White-footed mice are a reservoir for the bacteria that creates Lyme, and Ostfeld says one reason they are so successful at it is that they reproduce very rapidly when the woods are developed and their predators disappear.
Because they live only six months, they may put their energy into breeding at the expense of immune defense and so magnify the prevalence of Lyme. Diseases might even be spread by things that are otherwise good for the environment. The notion of connecting fragmented habitats so wildlife have access to critical habitat has been gaining ground. But disease ecologists say it may also spread disease. Bighorn sheep, for example, are moved around the West by wildlife agencies to build populations - but with little thought to pneumonia, Plowright said. "When we alter the environment abruptly," Plowright said, "we radically change the balance between diseases and the immune system, which can affect the entire web of life, including humans. We are just beginning to understand this."
High in the Wallowa Mountains of northeastern Oregon, Raina K Plowright and other researchers took blood samples of a herd of bighorn sheep apart from taking swabs of their noses and throats. "There's lots of places for pathogens to hide in the nasal cavity," said Plowright, a wildlife scientist with the Center for Infectious Disease Dynamics at Penn State. This is part of the nascent field of eco-immunology, which seeks both to understand the immune systems of wild animals and to use that knowledge for a better understanding of human immune systems. Until recently, this knowledge was gleaned by studying pampered, genetically similar lab animals, which don't reflect a real-world scenario.Eco-immunology works to understand how disease spreads in wildlife populations - the bighorn sheep are in trouble because of pneumonia that spread from domestic sheep - and how it can be worsened by human and environmental factors like climate change. Another major goal is to understand the pathways that deadly diseases can follow from wildlife to humans.
Going viral and how!
In the past 30 years, over 300 infectious diseases in humans originated in animals, including AIDS, Ebola, SARS, Lyme, hantavirus, West Nile virus and new strains of flu.
(Humans are also believed to have passed metapneumovirus to mountain gorillas in Africa.) In her native Australia, Plowright was involved in pioneering disease research on the little red flying fox, an intelligent nectar-sipping bat.
After the 1994 emergence of a deadly virus called Hendra in humans and horses in northeastern Australia, biologists found that it came from flying foxes. In 2008, Plowright discovered that stress appears to weaken the bats' immune system, and that is when they are likely to shed the most virus. "Trying to kill or move bats could make things worse by stressing them" and causing them to excrete more of the virus in their waste. This has quieted calls for large-scale bat removal, and Australia has committed millions of dollars to a project to understand viral ecology in bats.
The interconnections between human and animal diseases have led to new efforts to understand these mechanisms. "The wild is a null system, a system without interference," said Peter J Hudson, a biologist at Penn State and founder of the infectious disease centre there. "Research on wild systems," he continued, "will help us answer the question of 'Should we interfere, and how does interference affect the ecology and evolution of these bugs? Will the application of vaccines and antibiotics create more health problems?" "Some researchers believe, for example, that the rise in autoimmune disorders may be caused by a lack of stimulation of human immune systems by certain microbes.
Much about the diseases that originate in wildlife is a mystery. In the case of bat viruses, experts believe they evolved for millions of years in intact bat ecosystems, with the animals passing it to one another over and over, causing low-grade infections and building their immune defenses. Jonathan H Epstein, a veterinarian and a disease ecologist has used experimental infections to understand Nipah virus, closely related to Hendra. The new work on wild immune systems casts disease in a new light: as an environmental issue. One ecological driver of bat virus transmission is development in the flying foxes' natural habitat. Instead of living in a wild forest, the bats swoop into the cities and suburbs that replaced it, feeding on nectar in gardens and trees and then passing viruses along to horses and humans.
Why keep an ecosystem intact?
A common thread, disease ecologists say, is that clearing or altering a forest can be akin to opening a Pandora's box. Keeping nature intact, or developing it in sustainable ways, protects against disease ."If you conserve an ecosystem you have a jolly good chance of conserving human health as well," said Simon Anthony, a molecular virologist with EcoHealth who is studying the ecology of Nipah and other viruses.
Richard S Ostfeld, a disease ecologist at the Cary Institute for Ecosystem Studies in Millbrook, NY, has been studying the causes of Lyme disease. White-footed mice are a reservoir for the bacteria that creates Lyme, and Ostfeld says one reason they are so successful at it is that they reproduce very rapidly when the woods are developed and their predators disappear.
Because they live only six months, they may put their energy into breeding at the expense of immune defense and so magnify the prevalence of Lyme. Diseases might even be spread by things that are otherwise good for the environment. The notion of connecting fragmented habitats so wildlife have access to critical habitat has been gaining ground. But disease ecologists say it may also spread disease. Bighorn sheep, for example, are moved around the West by wildlife agencies to build populations - but with little thought to pneumonia, Plowright said. "When we alter the environment abruptly," Plowright said, "we radically change the balance between diseases and the immune system, which can affect the entire web of life, including humans. We are just beginning to understand this."