UGA researchers find that hunting can increase the severity of wildlife disease epidemics

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Friday, July 14, 2006

 

Writer: Sam Fahmy, 706/542-5361,

<sfahmysfahmy

Contact: Marc Choisy, 706/542-3580,

<choisychoisy

Pejman Rohani, 706/542-9249, <rohanirohani

 

UGA researchers find that hunting can increase the severity of

wildlife disease epidemics

 

Athens, Ga. - A new study by University of Georgia researchers shows

that the common practice of killing wild animals to control disease

outbreaks can actually make matters worse in some cases.

 

In a study published the August 7 edition of the journal Proceedings

of the Royal Society B: Biological Sciences, post-doctoral researcher

Marc Choisy and Pejman Rohani, associate professor of ecology and UGA

Biomedical and Health Sciences Institute researcher, create a

detailed mathematical model that demonstrates how the combination of

hunting and factors such as birth season and mating season influence

disease outbreaks. Their results suggest that wildlife managers and

health officials use caution when considering hunting or culling as a

means to manage diseases as diverse as rabies, tuberculosis and even

avian influenza.

 

" One consequence of hunting that we show in this paper is that it can

increase the probability of dying from the disease, " Choisy said. " It

can give you results that are contrary to what you expect. "

 

The reasoning behind killing wild animals to control disease

outbreaks is simple: fewer animals should result in reduced

transmission of disease. Hunting has been used to control badger

populations in England, rabies in European foxes and chronic wasting

disease in deer and elk populations in the American West. The

researchers note that in each instance, disease outbreaks have

worsened in response to the hunting.

 

One reason the policies failed, Choisy and Rohani said, is that they

didn't take into account an ecological principle known as

compensation. When a portion of the animal population is reduced,

those that survive are left with more resources such as food and

shelter. As a result of the newly plentiful resources, the death rate

decreases and the birth rate increases, compensating - and sometimes

overcompensating - for the loss.

 

Killing wild animals can also increase the proportion of the

population that's susceptible to disease by removing those

individuals who have contracted a virus but have developed lifelong

immunity as a result of their infection.

 

The researchers found that compensation and lifelong immunity

conferred by a virus interact so that the timing of mating and birth

seasons determine whether hunting increases or decreases disease

prevalence. They found that an outbreak is barely affected when

hunting occurs between mating and birth season while an outbreak

lessens when hunting occurs during the birth season. An outbreak

increases dramatically when hunting occurs between the birth season

and the next mating season.

 

The effect can be so dramatic that in some cases hunting can increase

not only the proportion of infections and deaths, but also the

absolute numbers. For example, their model shows that in the case of

swine fever, a highly infectious disease threatening boars and pigs

in Europe, hunting can increase the number of infected individuals by

twenty five percent.

 

" If we want to preserve the hunted population, we should be careful

about when we schedule the hunting season compared to birth season

because if it's too early or late, it can drive the population to

extinction, " Rohani said. " If we want to control a disease in the

host population, the timing of the hunting season can be chosen to be

optimal for that. "

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Note to Editors: For a pdf of the study, contact Sam Fahmy at

706/542-5361 or <sfahmysfahmy.

 

 

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