A paper recently published in Pathogens by an international coalition of researchers, including Cornell faculty Prof. Martin Gilbert, college of veterinary medicine, identified Canine Distemper Virus as an emerging threat to the big cat populations of Nepal. This finding is a conservation concern to these populations and will change the way the ecology of tigers and leopards are studied in Nepal.
CDV is a viral infection that can affect the gastrointestinal, respiratory and neurological systems of dogs, foxes, wolves and other carnivores. It first emerged on a large scale in 1994 in the Serengeti National Park, where it was responsible for the death of a third of the population at the time.
Initial infection typically begins in the respiratory system and moves into the gastrointestinal system. Vomiting, diarrhea and discharge around the eyes, in addition to issues from secondary infections due to a weakened immune system, can all be indicative of CDV. Even animals who endure these stages are not guaranteed to survive, despite signs of healing and recovery.
The virus also has neurological effects following bodily symptoms, which can be observed in a range of behavioral changes and actions. Because the virus is extremely infectious and fatal, researchers usually look for the presence or absence of antibodies from past infection to identify level of exposure for a given population, allowing researchers to understand the extent of the outbreak and determine if it poses a long term threat to the conservation of species.
Although CDV was originally researched in Russia, it has more recently been affecting the wild cat populations of Asia and is responsible for the population decline in tigers and leopards in the area.
During his Ph.D. research, Gilbert found that the virus most likely jumped from other wild carnivorous species to tigers in Russia. One in three tigers were found to have antibodies, making the estimated number of dead enormous.
“When you think that maybe a third or a half of the tigers that are infected will die and you’re seeing a third of the population with antibodies. That equates to a lot of dead tigers.”
Gilbert continued his investigation in Indonesia, Thailand, India and Nepal, where he helped establish research labs to continue to track the spread of CDV outside of Russia. The focus on Gilbert’s last publication was Nepal, where both tigers and leopards were being tested using antibody screening.
Through his work, Gilbert found the first evidence of CDV in the tiger population.
“We found 11 percent of the tigers that we tested were positive,” Gilbert said. This can pose a serious threat to tigers as a species, which have already decreased to a population of roughly 4,500 globally.
“A small population with distemper, maybe 25 tigers, are about 65 percent more likely to decline to extinction in the next 50 years based on our modeling,” Gilbert said.
However, since 2010, the tiger population in Nepal has nearly tripled due to large scale conservation measures. Although this is good news for tigers, it could explain increases in distemper in leopard populations.
Because tigers have large home ranges, more tigers means less space for leopards, causing leopards to edge into more rural and residential areas.
Shashank Poudel grad, who is investigating human-leopard contact, has found that leopards have high levels of contact with human populations through their habit of eating livestock and dogs. This could partly be due to the increasing number of tigers, which has pushed leopards further into residential areas and increased their contact with dog populations. One British veterinarian found 80 percent of dogs in Nepal had antibodies to canine distemper, making it a likely source of CDV that could be spreading to leopards, according to Gilbert.
The source of CDV among tigers is less clear. Since they have much less contact with dog populations and little-to-no contact with leopards, Gilbert suggests there is more investigation to be done.
“It might mean that there’s also circulation in the wildlife population,” Gilbert said. “We really don’t know for sure.”
Gilbert will continue to work with the tiger and leopard populations to help identify the best conservation strategies for Nepal in light of CDV. Going forward, the ecology of both species and their interactions with human populations will provide more context about the effect CDV will have and the best measures of care.
“The real message here is the need for general conservation measures for tigers and for leopards,” Gilbert said.