Canine distemper likely infecting & killing Nepal’s leopards, study shows

KATHMANDU — Canine distemper virus is likely circulating among Nepal’s common leopards (Panthera pardus), causing deaths, according to a recent genetic study that also traced the virus lineage in deceased individuals across the country.

While a previous study established that leopards had been exposed to the virus, evidenced by antibodies to CDV found in the blood of dead leopards, it was unclear whether they had died from the disease. The identification of live viruses now confirms that the animals are indeed dying due to the illness, the lead author of the study said.

“Our study is the first to detect the presence of CDV, and not it antibodies, in common leopards,” said lead author Amir Sadaula, a veterinarian at the National Trust for Nature Conservation (NTNC), a semigovernmental body. “It also establishes a direct link between their deaths and CDV infection,” Sadaula added.

While the presence of antibodies suggests that an individual may have been exposed to the virus during its lifetime, it isn’t a definitive indicator of an active infection. However, the presence of a live virus is a marker of an active infection, Sadaula added.

Leopards are a threatened species categorized as vulnerable on the IUCN Red List. In Nepal, they often come into conflict with humans in rural communities, especially in the middle hills region. In the district of Tanahun, 11 children were killed in encounters with the big cat in the space of four years, leading to fears that people may be killing them in retaliation.

As part of the study, researchers collected tissue samples from leopards that had died with symptoms of canine distemper virus (CDV) such as difficulty and open-mouth breathing and seizures involving muscle stiffness and jerking movements from central (Kathmandu and Dolakha) and western Nepal (Palpa and Parbat). They extracted the virus’ genetic material from the samples and sequenced it. Comparing the sequence with a database of known viruses, they confirmed it was CDV of the Asia-5 lineage.

CDV infection is highly contagious. Researchers have recorded that infected animals, especially mammals excluding humans, develop fever, become unresponsive and give up food and water. Other symptoms include coughing and discharges from the eyes and nose; vomiting and diarrhea; and involuntary muscular twitching, posterior paralysis or convulsions. While some animals survive the infection as their body fends off the virus, others die from it.

Two years later, it is believed to have killed nearly three dozen Asiatic lions (Panthera leo persica) at the Gir National Park in Gujarat. The same virus was also found in the Asian palm civet (Paradoxurus hermaphroditus) and red panda (Ailurus fulgens).

The findings of the study represent a crucial step toward understanding of canine distemper in Nepal’s leopards, Martin Gilbert, Associate Professor of Practice, from the Cornell K. Lisa Yang Center for Wildlife Health in the U.S, who wasn’t involved in the study, told Mongabay in a brief email commenting on the 0study. “Genetic sequence information helps us determine the species that are acting as sources of infection for leopards, which is key to the design of effective control measures,” he added.

To attempt to unlock the mystery behind the sources of infection, the researchers further analyzed the sub-lineage of the viruses found in the samples. “The viruses from the four samples belonged to different sub-lineages, A, B and C, of CDV,” Sadaula said. The sub-lineages represent the distinct branches of evolution of lineage-5 in different areas of Nepal and the region.

“We didn’t find CDV from sub-lineage ‘D’, which was present in the lions of Gujarat,” Sadula said. The researchers found sub-lineage A in Dolakha and Kathmandu, while Palpa and Parbat exhibited sub-lineages B and C, respectively. Sub-lineage A was earlier detected among dogs in Kathmandu and Uttar Pradesh, while sub-lineages B and C were found in both dogs and wild carnivores in India.

This suggests that “the leopards in Nepal may have acquired the virus from multiple sources, potentially facilitated by their generalist dietary habits preying on dogs and even mesocarnivores,” according to the authors of the study. They suggest there may be sylvatic (wild) cycles of the virus and interactions among leopards and other infected wild carnivores could also be a source of infection. Similarly, as leopards as well as other species such as civets and jackals venture into urban areas, especially in search of food in human trash, sylvatic cycles may develop to maintain the circulation of the virus.

In the case of Kathmandu Valley, the study strongly supports the long-held belief that common leopards likely prey on dogs, both feral and domesticated, as CDV of the same sub-lineage was found in both the animals. However, this is not conclusive evidence to support the hypothesis, the authors of the study warn.

Dogs have long been seen as one of the biggest threats to wildlife conservation in Nepal, where there are no laws to govern their ownership and abandonment. People, be it in the plains, hills or the mountains, often simply aband…on their dogs once they tire of keeping them. The dogs have a natural instinct to form packs and even attack and kill wild animals such as spotted deer, a prey species of the leopard and the Bengal tiger (Panthera tigris tigris). This common prey could also be playing a role in the transmission of diseases, researchers say.

Gilbert from Cornell K. Lisa Yang Center for Wildlife Health, said that the cases like the ones documented in the study add to the growing body of evidence suggesting that leopards in Nepal are regularly contracting canine distemper virus infections. “We know that at least some of these cases are fatal, and the priority must now be to understand their significance at a wider population level,” he said.

Sadaula said that while large-scale studies are necessary to assess the real extent of the pervasiveness of the virus and its different lineages and sub-lineages, it shouldn’t stop officials from acting swiftly to control its spread through vaccination.

As vaccinating wild animals against CDV is not possible, the study shows that it is important to inoculate the dogs, said researcher Babu Ram Lamichhane, co-author of the study. He said that although the sample size of the study is small, it provides important insights that have significant implications for conservation. Lamichhane said the Gujarat lion deaths related to CDV serve as a stark reminder that the spread of the disease could also affect Nepal’s achievements in increasing the tiger population.

Feral dogs are also a challenge for wildlife conservation in neighboring India, which shares a border open not just for people, but also for wild animals through connected landscapes. As with its northern neighbor, India also doesn’t have stringent dog ownership laws. The 2018 report “Status of Tigers: Co-predators and Prey in India,” reported that feral dogs were found in most of the tiger reserves in the country.

“We should try to control the spread of CDV here in Nepal first, then we can talk about cross-border collaboration,” Sadaula said.

Banner image: A veterinarian carries a sedated leopard retrieved from a settlement in Nepal. Image courtesy of NTNC

Citation:

Sadaula, A., Manandhar, P., Shrestha, B. K., Thapa, P. J., Nepali, S., Joshi, J. D., … Pandey, G. (2024). Phylogenetic analysis linked fatal neurologic disease in leopards (Panthera pardus) to asia-5 lineage of canine distemper virus in Nepal. Virus Research, 350, 199463. doi:10.1016/j.virusres.2024.199463

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