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In the middle of the global pandemic, vaccines are at the forefront of everyone’s mind. And scientists think a vaccine could help pull another creature back from the brink.
In a new study published Monday on Proceedings of the National Academy of Science, researchers show how vaccinating Amur tigers – one of the rarest big cats in the world – against a common pet problem could help these tigers survive. Without further action, these tigers face the threat of extinction.
Disease transmission – Canine distemper virus occurs primarily in domestic dogs, but also affects other wildlife, including the rare Amur tiger. Scientists detected the first Amur tiger death by CDV in 2003 and has since grown as a threat to the nearly 550 Amur tigers living in Russia’s far east and neighboring China, according to the study.
Dogs from this region were thought to spread the virus to wild animals such as the Amur tiger. If true, then vaccinating dogs against the virus would make sense. But this new research overturns all previous hypotheses.
“Kind of like Covid-19, if dogs had acted as a major reservoir of infection we would have expected to see more viruses in areas where there are more dogs mixing into larger communities,” Martin Gilbert, lead author of the study and Senior Research Associate at Cornell Wildlife Health Center, he says Reverse.
Gilbert and his team compared canine distemper virus outbreaks in dogs from more densely populated areas with outbreaks in dogs from more remote regions.
“In fact, we found that fewer dogs were exposed and outbreaks occurred less frequently at our densely populated study site than in our more remote sparsely populated areas,” Gilbert says.
The findings suggest that although domestic dogs can theoretically infect tigers, they are not the most common source or “reservoir” of transmission of the virus. Rather, other wild carnivores are most likely to be responsible for transmission.
“To deepen the Covid-19 analogy, the equivalent would have been for the virus to take hold in New York state leaving Manhattan relatively unaffected,” Gilbert says.
“The most likely explanation for this pattern of infection would be that more remote communities are experiencing greater transmission from another reservoir, namely wildlife.”
Time to vaccinate – With a better understanding of disease transmission, the scientists used a computer simulation model to test three different strategies for reducing canine distemper virus in the Amur tiger population.
These were:
- Reduce the transmission of the virus to other animals
- Stops the transmission of the virus from other animals to tigers
- Reduce transmission of the virus among tigers
Rather than trying to stop the virus at its source, Gilbert and his team concluded that vaccinating the tigers was the most feasible and cost-effective way to save the species.
“Since we have shown that wildlife is an important reservoir of infection for tigers, and because we have no way to administer the vaccine to wild carnivores at levels that would be sufficient to reduce transmission, and no way to keep tigers apart. from other wildlife, then our only option left is to vaccinate the tigers themselves, ”Gilbert says.
Scientists concluded that vaccinating two tigers a year would reduce the tiger’s chances of extinction by 15.8% to 5.7% over a 50-year period. The average cost of doing this comes in at $ 30,000, cheaper than other strategies, the researchers found.
The big challenge: to catch the tigers and trap them long enough to administer a vaccine.
“Obviously the more tigers we can vaccinate, the better. But tigers are elusive, and catching them for vaccination requires many people to work for long periods of time, which inevitably costs money,” Gilbert says.
According to Gilbert, canine distemper virus is a multi-host pathogen, which functions differently from a pathogen that infects only a single species, such as measles or polio in human populations.
For these single host pathogens, “we have a realistic opportunity to eradicate the virus, but to do so we need to immunize a large percentage of the population – equivalent to 70 or 80 percent of herd immunity – that we hear so much about with COVID. -19 “, says Gilbert.
It’s different with infected tigers, though.
“We have to accept that there will always be a source of infection in other wild carnivores, and so the best we can do is design a tiger vaccination program that immunizes a sufficient percentage of the population to make it very unlikely that [the virus] it will never cause the extinction of the entire population, “Gilbert says.
Light at the end of the tunnel – Tigers around the world face threats to their existence on a daily basis, and the Amur tiger is no exception.
The study results focus on wildlife as a major source of the canine distemper virus pathogen, but also show a way to defeat it.
“It’s still entirely possible that Russian dogs are able to act as a reservoir on their own and we haven’t been able to detect that,” Gilbert says.
“But crucially, the weight of evidence pointing to a wildlife reservoir really determines our options for managing infection in tigers.”
Abstract: Canine distemper virus (CDV) has recently emerged as a threat of extinction for the endangered Amur tiger (Panthera tigris altaica). CDV is vaccine preventable, and control strategies may require vaccination of domestic dogs and / or wild animal populations. However, vaccination of endangered wildlife remains controversial, which has led to a focus on interventions in domestic dogs, often thought to be a source of infection. Effective decision making requires an understanding of true reservoir dynamics, which poses substantial challenges in remote areas with diverse host communities. We have conducted serological, demographic and phylogenetic studies of dog and wild animal populations in the Russian Far East to demonstrate that a number of wildlife species are more important than dogs, both for the maintenance of CDV and as a source of forigers infection. Crucially, then, as CDV circulates between multiple wildlife sources, dog vaccination alone would not be effective in protecting tigers. We show, however, that low-coverage vaccination of the tigers themselves is feasible and would produce substantial reductions in extinction risks. Vaccination of endangered wildlife provides a valuable component of conservation strategies for endangered species.
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