Gir lions' deaths: Decoding the disturbing Canine Distemper Virus epidemic that killed over 20 big cats
The conservation effort for the Asiatic lion in Gujarat's Gir Forest lies in establishing one or more alternate homes for the endangered species.
“Disease is a fact of life. Of course, the definition of disease depends on the point of view. To human beings, tuberculosis is a disease. But to tubercle bacillus, human beings are a habitat and life source. Similarly, the earth is a habitat and life source of human beings. But to the earth, human habitation is a disease, and human beings are arch parasites. To the pristine earth, the coming of Homo sapiens signaled the onset of a chronic, global illness, the outcome of which is still in doubt." — WW Armistead, former president, The American Veterinary Medical Association
Barring the pristine landmass of Antarctica, nearly every other landmass or ecosystem has been ecologically impacted due to human activities. It is only when the system gets disturbed that the need to manage it to offset the damage arises.
Thus, the need to indulge in various conservation activities like securing corridors, recovering habitats, breeding endangered species, reintroducing animals and even vaccinating animals in extreme cases. In that sense, we as humans are the destroyers as well as saviours.
Not that we do not know of all these conservation prescriptions, but it is only our greed and ego that stop us from putting them into action. The conservation effort for the Asiatic lion lies in establishing one or more alternate homes for the species in safe areas of its former distribution range. Despite the Supreme Court order on this, the Gujarat state government has been sitting over it for years.
We have unfortunately created the states based on linguistic criteria, which has its own advantages and disadvantages. We take great pride in teaching the people of other states our language, but this magnanimity is not extended when it comes to sharing our species. Yes, lions are the pride of Gujarat, but when pride turns into ego, even court rulings are thrown out of the window. Little do they realise that establishing an alternate home is an insurance against any eventuality that may wipe out all the lions from the state. The lions can always be brought back to Gujarat from the newly established home.
The Canine Distemper Virus (CDV) that killed 23 lions in Gir, Gujarat belongs to one of the groups of viruses called the morbillivirus. This virus group has some of the deadliest pathogens. Just like the immunodeficiency viruses for humans (HIV), primates (SIV), cats (FIV) and even cattle (BIV), there are morbilliviruses infecting various taxa. In humans, we have the measles virus, in goats/sheep, the PPR (Peste des Petits Ruminants) virus, in large ruminants the rinderpest virus, in seals the phocine virus, and in whales and dolphins, the Cetacean virus. They are all morbilliviruses.
The viruses are all genetically closely related, as they can adapt and/or mutate and evolve to become a new pathogen for a range of new taxa. For instance, the nuclear protein of human morbillivirus is said to be 65 percent similar to the CDV. Rinderpest, that created havoc along livestock, including wild ruminants like gaur, has been eradicated from the planet by systematic vaccination program. The CDV in lions is a recent phenomenon as evident from large scale deaths in Serengeti, Africa and Gir, India. This means CDV is a recent entrant to felids like lion.
It is when viruses mutate to take advantage of a new host of species that they turn highly pathogenic. Because CD is a contageous disease, the virus can be transmitted airborne. Mere presence of a diseased individual in the vicinity or near proximity is enough. Needless to say that the virus can also be transmitted directly when coming into contact with the body fluids of infected animals, and through contaminated water and food.
How did the CDV get into Gir in the first place? Canine distemper is endemic to the Indian subcontinent, which means dogs regularly suffer from the disease. The chances of survival among pedigree dogs, especially puppies, is negligible. Dogs could have been the source of infection for the lions, but that doesn’t mean they will continue to be the source of infection every time. The virus might also be present in other free ranging wild carnivores, but a confirmation on these possibilities is possible only by conducting routine serological surveys and epidemiological studies.
Lions in Gir might have been getting infected from canine distemper and dying sporadically earlier as well. Dr MK Ranjitsinh, in this Firstpost article, points out that Gujarat lost 184 lions in the two preceding years (2016 and 2017). That is a substantial number because the estimated population is just over 500. It is only when an epidemic like this happens that we wake up and investigate it in great detail.
The CDV has been traced from few stray cases of tiger carcasses also. There is no need to panic in the case of tigers, as of now. The story is different in the case of the lion because of three reasons: First off, it is the only population we have. Secondly, it is not a genetically diverse population and thirdly, being social animals, they live in groups that increases contact rate and thus disease transmission also.
In a genetically diverse population, the spread can come to a halt sooner. In a homogeneous population like the Asiatic lion, that suffered a genetic bottleneck in recent history, the pathogen can succeed in infecting more individuals for a longer period. However, vaccinating dogs alone wouldn’t solve the issue. They have something to learn from the 1994 Serengeti National Park episode of CDV outbreak among African lions. When studies showed that dogs could have been the source of CDV, a massive exercise was launched to vaccinate all the dogs. While this helped the dogs for sure, the sporadic outbreaks due to CD still continued, indicating that other species of wild carnivores would have been the source, or that the virus must have been circulating among the lions itself.
We learn that the Gujarat government has imported 300 doses of a ferret distemper virus vaccine for immunising the lions. These are said to be inactivated or recombinant viral vaccines, unlike the modified-live (live-attenuated) virus CD vaccines we use for dogs. This is a wise decision because the latter can end up causing the disease when administered in species that are very susceptible to CDV infection.
The department would have already vaccinated most of the 30 odd lions brought into captivity. The Gujarat Forest Department has done a good thing by bringing all the surviving animals of the area to captivity. This would have not only curtailed the spread of CDV into other areas, but also given the vets an opportunity to investigate them at close quarters.
The next question is whether the other free ranging lions need immunisation. I would have recommended vaccination had this epidemic happened about 30 or 35 years ago when the number of lions was less. Now that we have over 500, there is a buffer to bear the impact. The back-footed ferrets in the US almost disappeared due to CDV epidemic, before they picked up all the individuals from the wild, and captive-bred them. They regularly vaccinated them against CDV because the population size was meager. In a situation like that, vaccination becomes necessary.
The author is the chief of conservation at the Wildlife Trust of India
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