PULLMAN, Wash. – In natural ecosystems, a deadly virus can jump between species and thrive, thereby threatening vulnerable animal populations, according to findings of a recently published study.
Canine distemper, a viral disease that's been infecting the famed lions of Tanzania's Serengeti National Park, appears to be spread by multiple animal species, an international team of scientists has concluded. Writing in the journal Proceedings of the National Academy of Sciences, they say domestic dogs are no longer the primary source of the disease's transmission to lions and that wild carnivores may contribute as well. (See http://www.pnas.org/content/early/2015/01/15/1411623112.full.pdf)
"Our study shows that the dynamics of canine distemper virus are extremely complex, and a broadened approach – focusing not only on domestic dogs – is required if we are to control the disease among lions and other wild animal species," said Tanzania-based veterinary researcher Felix Lankester of Washington State University's Paul G. Allen School for Global Animal Health, a co-author of the study.
Dogs and beyond
In 1994, a mysterious neurological ailment wiped out 30 percent of the lion population in the Serengeti, one of the largest wildlife regions in the world. Scientists determined it was canine distemper, a disease previously thought to infect only dogs, coyotes and a small number of other mammals.
Evidence revealed the lions had contracted distemper from dogs living in villages and settlements nearby. A domestic dog vaccination campaign was launched to curb the infection's spread. It worked – among dogs, at least.
After analyzing three decades of blood serum data collected from lions and domestic dogs, the study's researchers discovered that the virus continues to circulate in the lion population while significantly declining among dogs.
The dog's role in spreading the disease appears to be shrinking, conclude the paper's authors, a collaboration of veterinarians, disease ecologists, epidemiologists and mathematical biologists.
Why, then, do the lions continue to get infected?
"Domestic dog populations immediately surrounding the Serengeti National Park are not the sole driver of canine distemper infections in lions, and its persistence is likely to involve a larger multi-host community," the scientists write.
Risk of outbreaks
Other species, including hyenas and jackals, are probably transmitting the disease and keeping it looming in the wild, the authors say. Consequently, outbreaks among lions and other already-threatened animals could occur at any time.
Researchers say more work is necessary to identify which species spread distemper and what triggers the spillovers. For example, previous analyses suggest that an infected hyena or other carnivore feeding on a carcass can disperse the virus through mucus secretions to other predators at the same site.
"A better understanding of canine distemper virus and its dynamics in the wild is necessary to better monitor and control the disease among lions and other threatened animals," said WSU's Lankester.
Felix Lankester, WSU veterinary researcher (Tanzania), [email protected]
Mafalda Viana, University of Glasgow disease biologist (United Kingdom) [email protected]
Linda Weiford, WSU News, 509-335-7209, [email protected]