Leopards in India may be losing their fear of humans due to the Canine Distemper Virus (CDV), a highly infectious virus that causes neurological disorders such as disorientation and lack of fear among carnivores in its advanced stage. In a recent study titled "CDV in Tigers and Leopards in Nepal" published in the international peer-reviewed journal Pathogens, six Indian leopards (P. pardus fusca) were presented to Nepali authorities with a fatal neurological disease consistent with CDV.
The CDV disease is also found to cause impatience in leopards, leading to increasing incidents of the leopard-human conflict. In the recent past, leopard-human conflicts have become more common in India, with increasing reports of leopards entering human habitations for food frequently, and even attacking and injuring people.
The Wildlife Institute of India's (WII) report shows that the disease risk is present across the subcontinent, and not just limited to leopards but also affects other carnivores like tigers, lions, wolves, jackals, and hyenas. Dr Yadvendradev Jhala, the Dean of WII, confirms that CDV-infected animals lose their fear of humans, similar to rabies.
CDV disease follows typical signs in all infected animals and is broadly classified into three stages. The initial phase occurs shortly after exposure and is characterized by intermittent fever and weaker immunity. This is followed by an acute phase where the virus infects epithelial tissue, resulting in various clinical signs, including a crusting discharge from the eyes and nose, respiratory and gastrointestinal symptoms, and hyperkeratosis of the footpads. Some animals succumb at this point, while others make a complete recovery. In the third phase, animals develop the neurological disease, and the signs include disorientation and a lack of fear. Once an animal enters the neurological phase, mortality is almost inevitable, and the phase progresses to seizures and death.
Dog vaccination is the only useful strategy to mitigate CDV disease risk. A 2014 study on India's leopards showed that dogs account for up to 39% of the leopard's diet. Higher levels of predation of dogs could account for greater levels of exposure of leopards to the virus.
The CDV is also known as canine morbillivirus and is a highly infectious single-stranded RNA virus in the Paramyxoviridae family. Feral dogs are a major carrier of CDV, and the predation of domestic dogs by carnivores is the major potential route of getting the infectious virus.
With the increasing incidence of the leopard-human conflict in India, experts stress the need for dog vaccination and better control over feral dog populations. It is important to mitigate the risk of CDV transmission from dogs to wild carnivores and reduce the chances of the virus spreading to more leopards and other carnivores across the subcontinent.