The Nature Pages

~~~~~~~~~~~~~~~ at Outrider

	Essentials of Disease in Wild Animals by Gary A. Wobeser Blackwell Publishers, 2006.
	Wild birds helped spread the West Nile Virus and deer are unwitting confederates in the dissemination of Lyme Disease. Rodents are harbingers of hantavirus and avian influenza flies in on the wings of wild waterfowl.		The only method that has been developed for mass immunization of wild animals is distribution of vaccine in baits. This technique requires that the vaccine induces immunity by the oral route and raise many safety concerns...
	The emergence, transmission, and control of all these diseases is in some way connected to wildlife, as are rabies, tularemia, plague, brucellosis, SARS and dozens of other human and livestock afflictions.  Today's critter populations may be closely managed and monitored, but the viruses and bacteria within them are still wild and their bite can be lethal.
	Like a stealthy cat that crouches motionless before it strikes, the role of wild animals in epidemics has been largely overlooked by scientists until recently. But in the last two decades physicians and public health officials have had to face up to the fact that most of the emerging infectious diseases of humans are "zoonoses" -- diseases that are shared with animals. Suddenly, a host of scientific disciplines -- epidemiology, ecology, biology, toxicology, medicine, agriculture, veterinary science, animal behavior -- are taking a serious interest in the diseases of wild animals and a new breed of specialist in wildlife medicine has emerged.		Diseases are like weeds in that both thrive in disturbed environments. Just as weeds have great difficulty gaining a foothold in an established forest or grassland, diseases have difficulty being perpetuated in stable systems, but both weeds and some forms of disease quickly invade and proliferate following disturbance. Human history is replete with examples in which pestilence has followed social and environmental disruption... Diseases such as measles have emerged in epidemic form in human populations as a result of the large, dense populations that occur in cities. Refuges on which wild waterfowl are crowded together for months and artificial feeding areas on which some wild species congregate seem very like cities to me, but they are cities without the benefit of sewage disposal, clean water and the immunization programs that protect us from many diseases,
	"Essentials of Disease in Wild Animals" by Gary A. Wobeser is the first academic book on wildlife diseases to take a broad view of the subject rather than focusing on a single disease or species of animal.  Wobeser discusses the nature of diseases and how they emerge, explores how they spread and persist in the environment, and considers the effects they have on both individual animals and their extended species population.
	By approaching disease as an ecological (rather than strictly medical) issue, Wobeser questions the effects that diet, habitat loss, pesticides, and genetics have on the emergence and spread of disease in wild animals. "Disease is one environmental feature among many that affect animals," he points out.  "It is impossible to understand disease without considering the interactions among disease agents and with other factors such as nutrition, predation, climate, and reproduction."		Every organism in the world that has been studied has yielded viruses, and it is safe to assume that every wild species is infected by a number of viruses, many of which have been associated with disease... Some viruses are highly host specific while others have very catholic tastes. For example, West Nile virus and St.Louis encephalitis virus are maintained in mosquitoes and birds but happily infect horses, people, and other mammals. This doesn't seem particularly striking until one considers that these viruses have to be sufficiently adaptable to overcome the defenses of poikilothermic invertebrates as well as those of broadly divergent types of vertebrates.
	There are no simple answers to why animals get sick, nor is there an easy cure. Disease is part of the ecology of the wild and cannot be eradicated with vaccines or quarantines or education the way it is in human populations.
	Wobeser's text makes it clear that  the health of wildlife is important all of us, not just wildlife managers, and that diseases in the wilds pose a threat not only to wild animal populations, but to the livestock and humans they will inevitably contact.