Cats and Dogs: Canine Distemper Virus and the Endangered Amur Tiger

Article: Gilbert, Martin, et al. “Distemper, extinction, and vaccination of the Amur tiger.” Proceedings of the National Academy of Sciences 117.50 (2020): 31954-31962. https://doi.org/10.1073/pnas.2000153117

Above Image: Amur Tiger. Source: Wikipedia.

Introduction

Tigers, like many other animals, are susceptible to infectious diseases – similar to humans. One such disease is canine distemper virus (CDV), named for its initial discovery in dogs.

A recent paper published in the Proceedings of the National Academy of Sciences presents new findings about CDV in Amur tigers, and discusses potential solutions for mitigating the impact of the virus in the tigers.

Paper Overview

The Amur tiger, also called the Siberian tiger, is the largest member of the tiger family – and one of the most endangered. Fewer than 550 of these tigers in far eastern Russia and nearby areas in China, shown below in Figure 2 from the article.

Figure 2 from Gilbert, Martin et al, 2020. Source: PNAS.

Also shown in the figure are documented cases of CDV among the tigers, and the population density of dogs in the area.

CDV is a relatively recent occurrence among Amur tigers; the first documented case (in a tiger blood sample) was in 2003. Since that time CDV has been detected in nearly 40% of the tigers whose blood has been tested (post-mortem samples).

Because CDV was first identified in and is still primarily associated with domesticated dogs, it was largely assumed that the dogs in this area were the primary reservoir for the virus – and that the tigers were contracting the virus solely from the dogs.

However, after counting the total number of dogs in the tiger habitat area, the scientists realized that there are far too few dogs to act as a permanent reservoir for CDV.

This means that while a single or a few dogs may have transmitted CDV to tigers in the past, currently, the virus is circulating among wild animals themselves without continued transmission from dogs.

This was a new finding, and is supported by the fact that the scientists found CDV in blood samples of other wild animals in the area like leopards, lynxes, and bears.

Scientists used current and historical data on CDV and its effects on the wild Amur tiger population, to construct a predictive mathematical model. According to the model, the current tiger populations have more than a 50 percent chance of going extinct within the next 50 years if current rates of CDV infections aren’t counteracted.

Vaccinating Tigers

The good news is that there is an effective vaccine against CDV. The tricky part is that for this vaccine to have any protective effect on the tigers, the tigers themselves have to be vaccinated.

This is not easily done, as the tigers roam over territories that are several hundred square miles in area. Even when spotted, tigers are not easy to approach. They are solitary and shy away from human contact.

These facts, and the idea that only large-scale vaccinations were effective at reducing CDV transmission in the tiger population, often led to a reluctance to undertake any vaccination campaigns. Wildlife officials and scientists assumed that small-scale vaccinations (only a few tigers at a time) would not be effective at combatting CDV in tigers. And the funds, logistics, and resources for a large-scale vaccination campaign simply were not available.

However, the scientists’ model showed that even small-scale vaccination campaigns, conducted annually over several years, could drastically reduce the probability of Amur tigers’ extinction in fifty years.

The funds and logistics for such campaigns are feasible, and these preliminary data show that such campaigns will actually be effective.

That’s great news for one of the world’s most recognized, and also most threatened, big cats.

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Munim Deen

Munim is an epidemiologist and cartographer. His primary interests are infectious disease outbreaks and their intersection with the environment, public policy, and society at large. A geographic information system (GIS) devotee, he incorporates mapping and spatial analysis into his work whenever possible. A former newspaper columnist, he holds a bachelor's degree in microbiology and a master's degree in epidemiology.

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