WILDLIFE HEALTH - THE MISSING PIECE OF THE CONSERVATION PUZZLE

Imagine a world without wild tigers.

Statistically, that’s not hard. Tigers are now found in just 7% of their former global territory^[1]. In fact, if wild tigers were in the habit of going to concerts, there wouldn’t be enough of them left to fill the Royal Albert Hall in London for a typical Prom concert. Perhaps most significantly, most tigers now exist in populations of less than 25 individual animals^[2]. While poaching, loss of prey species and habitat destruction remain their primary threat, such small populations of tigers are particularly susceptible to disease.

If you’re a dog owner, you will be familiar with the recommended vaccination schedule, which includes regular boosters to protect them from canine distemper virus (CDV). But CDV, a morbillivirus similar to that which causes human measles, affects a much wider range of species than its name might suggest. It has become an increasing problem for wild carnivores over recent decades, as habitat shrinks and the interfaces between people, domestic animals and wildlife continue to expand. It has been demonstrated that where CDV is present in a small tiger population, it can increase the changes of local extinction by as much as 56%^[3]. Any factor affecting extinction rates needs to be urgently addressed – and CDV is a case in point. Infected tigers can die for a number of reasons. Some will experience respiratory problems, like pneumonia. Others will suffer neurological problems, like seizures. Losing their fear of people means they are also more vulnerable to poaching.

Often spread by free roaming domestic dogs, with mesocarnivores (like foxes, martens and raccoons) also potential reservoir species, CDV is known to have also affected lions, painted dogs, leopards, lynx and even nerpa seals in Lake Baikal in Siberia. The disease is believed to have been largely responsible for the extinction in the wild of the black-footed ferret. In 1994, an outbreak in the Serengeti killed one third of the region’s lions. It’s not unusual for a tiger or leopard to take a village dog as easy prey, and distemper is often endemic in domestic dog populations, providing a clear transmission route for the virus. The first known wild tiger to succumb to the disease died in the Russian Far East in 2003. The virus has now also been identified in tigers in India, Indonesia, Malaysia and Nepal.

WVI has been involved with investigating the prevalence of CDV in wild carnivores for two decades. WVI founder, the late Dr John Lewis, worked closely with Wildlife Conservation Society biologists in the Russian Far East from the 2000s, sharing his expertise in trapping and anaesthetising tigers, and encouraging routine collection of a full range of medical samples, which were later used to confirm the historical presence of CDV. WVI Veterinary Partners were also instrumental in working with Painted Dog Conservation to set up mobile neutering and vaccination clinics for village dogs living on the fringes of Hwange National Park in Zimbabwe, in order to help protect the park’s painted dogs from infection. More recently, WVI Veterinary Partner, Jess Bodgener, working together with Martin Gilbert of Cornell University and others, investigated the prevalence of CDV in archived serum samples from leopards and tigers in Nepal, and found it to be present in 11% of the tiger samples and 30% of the leopard samples^[4].

Developing a Rapid Diagnostic Test that can be used in the field‍

Being able to test samples for CDV is key to understanding how it is spreading and what measures might be taken to tackle its impact. But current testing requires complex laboratory facilities, often not available locally. While Dr Bodgener and Dr Gilbert have helped set up testing facilities in Indonesia,Thailand and Nepal, these have relied on Serum Neutralisation Assays, which are technically complex to carry out. Until now, there has not been any way to quickly test for CDV antibodies in a wild animal in the field. Commercial kits are available for dogs, but they are species specific. However, this lack of ‘point of testing’ tools is set to change. In collaboration with Wildcats ConservationAlliance, WVI has been co-funding a project based at the University of Kent to develop rapid diagnostic tests, including a possible Lateral Flow Test (using the same technology that became so familiar to so many of us during the Covid19 pandemic), that could be used to easily determine the presence of CDV antibodies in tigers and other species in the field, confirming their exposure to the virus.

The process has not been straightforward, but after months of painstaking initial research, the team at Kent have concluded that the best approach is to use a ‘dot blot’ test. This is a common technique in molecular biology and should be as easy to run as a LFT, while at the same time being considerably cheaper. If all goes according to plan, the dot blot assay will be tested on archived serum samples next year, before beginning trials in the field.

Developing a potentially game changing tool like this could mean that it is not long before we have an accessible and affordable test for CDV which can be carried out in the field, giving immediate results. The hope is that it will facilitate the identification of reservoirs of the virus and inform future mitigation and intervention plans, to the benefit of threatened carnivores worldwide.

Why is this kind of disease surveillance so important to conservation?

In the words of the late Dr John Lewis:

“Anybody who has taken their child to the doctors for vaccinations does that because we know there are dangerous infectious diseases out there – which can affect our children. The only way we know that is from disease surveillance in the past. So, we have a way of protecting children and it’s all based on disease surveillance. It’s the same for animals… It’s an Early Warning System – if we have that in place, we know what disasters are about to happen and can mitigate them.”

[1]Gilbert, Martin, D. Miquelle, J.M. Goodrich, R.Reeve, S. Cleaveland, L. Matthews & D.O.

Jolly (2014) Estimating the Potential Impact of Canine DistemperVirus on the Amur

Tiger Population (Panthera tigris altaica) in Russia. PLoS One2014: 9(10): e110811

Published online 2014 Oct 29 http://doi.org/10.1371/journal.pone.0110811

[2] Ibid.

[3] Ibid.

[4]Bodgener J, Sadaula A, Thapa PJ, Shrestha BK, Gairhe KP, Subedi S, Rijal KR, Pandey P, Joshi JD, Kandel P, Lamichane BR, Pokheral CP, Subedi N, Kandel RC, Luitel H, Techakriengkrai N,Gilbert M. Canine Distemper Virus in Tigers (Panthera tigris) andLeopards (P. pardus) in Nepal. Pathogens. 2023 Jan28;12(2):203. doi: 10.3390/pathogens12020203. PMID: 36839475; PMCID:PMC9962338.

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