After we have reported on a study of canine distemper spreading across multiple other animal species in the wild last week, now even more evidence emerges on the potential danger that this viral disease poses for a majority of carnivores in the wild. For many years, canine distemper was known as a disease affecting mostly domesticated dogs, but now the virus is affecting multiple other areas and species of animals, causing death for the most part.
Experts are now expressing their concern over viral virus‘ threat to the conservation of increasingly fragmented populations of threatened carnivores. Moreover, scientists would also like to agree that the disease’s name should not be specific to dogs anymore and shouldn’t be labeled as “canine distemper,” since it infects a very wide variety of other species.
How canine distemper puts wildlife at risk all around the world
The Wildlife Conservation Society (WCS), Cornell University’s College of Veterinary Medicine and its Feline Health Center, and the University of Glasgow’s Institute of Biodiversity, Animal Health and Comparative Medicine have just co-convened the first “Vaccines for Conservation” international meeting at the Wildlife Conservation Society’s Bronx Zoo in New York City, according to press release.
Experts from around the world focused on the threat that canine distemper virus poses to the conservation of increasingly fragmented populations of threatened carnivores. While canine distemper has been known for many years as a problem affecting domestic dogs, the virus has been appearing in new areas and causing disease and mortality in a wide range of wildlife species, including tigers and lions. In fact, many experts agree that the virus should not be called “canine distemper” virus at all, given the diversity of species it infects.
The forum brought together many of the world’s top disease ecologists, wildlife biologists, immunologists, virologists, vaccinologists, epidemiologists, wildlife veterinarians and pathologists, and policy experts to explore whether it would be appropriate and feasible to develop approaches to canine distemper vaccination to protect at-risk wild carnivore populations. The group looked at examples of distemper outbreaks around the world, including the recent case study offered by the Amur tiger population in the Russian Far East.
In 2010 canine distemper virus was diagnosed in tigers that died in widely separated locations across the Amur tiger range. While it is challenging to assess the overall impact on the population of such a wide ranging and elusive big cat, the virus contributed to the decline of one well-studied sub-population, which went from 38 individuals to 9 between the years 2007 and 2012.
“Like many large carnivores, tigers face an array of serious threats throughout their range, including poaching (of tigers themselves and of their prey), habitat loss, and conflict with local people. Addressing these very clear threats remains the top priority for the allocation of scarce tiger conservation resources. Importantly, these threats have led to tiger populations becoming smaller and more fragmented, making them much more susceptible to sudden population declines and even extinction due to disease. I therefore welcome the technical help and resources of the veterinary community to enhance our preparedness for addressing pathogens such as canine distemper virus,” says WCS Russia Program Director Dale Miquelle.
In fact, additional analysis by WCS and international colleagues has shown that smaller populations of Amur tigers are more vulnerable than larger populations to extinction from distemper. Populations consisting of 25 individuals are 1.65 times more likely to disappear in the next 50 years if the virus is present. That finding is profoundly disturbing for wild tigers, given that in most sites where wild tigers persist they are limited to populations of less than 25 breeding adults.
Previous attempts to manage the risk of infectious disease to wild carnivore conservation have mostly focused on vaccination of domestic dogs. While this approach benefits the dogs themselves (and in the case of rabies, can be crucial to protecting local people), it often fails to prevent infections in threatened species that share their environment. This seems to be due to the presence of abundant, small-bodied wild carnivores that act as an alternative reservoir of infection, and a source of canine distemper for endangered species.
“The prospect of controlling an infectious disease in an abundant and wide-ranging wildlife reservoir is remote, particularly when there is no economic or public health justification for doing so. Therefore, the most logical approach for protecting threatened carnivores from canine distemper virus may be to target the vaccine on the endangered species itself,” says Cornell University’s Dr. Edward Dubovi.
The goal would not be to eliminate a disease like distemper from a given ecosystem, but to protect endangered species in places impacted by pathogens that have often been introduced from elsewhere, often by domestic animals.
This point was driven home by the timely release by the University of Glasgow Boyd Orr Centre for Population and Ecosystem Health of a new analysis of decades of data on the impacts of canine distemper virus on the lions of the Serengeti National Park. During an outbreak that began in 1993, more than one thousand lions disappeared in the Serengeti — a 30% decline in the lion population in the park. While the outbreak in 1993-1994 was likely due to transmission of a virus from domestic dogs, it is now clear that the routes of virus spread and maintenance are more complex.
Following the 1993-1994 outbreak, vaccination has successfully reduced the level of infection in the dog population around the Serengeti. However, lion infections have increased over the last 20 years and the timing of infection peaks in lions has not always correlated with dog infection peaks.
“These results suggest that the virus may now be maintained by a broader carnivore community, potentially involving wildlife as well as domestic dogs beyond the immediate vicinity of the Serengeti National Park. Dog vaccination programs are certainly effective at reducing virus infection in dogs and should continue. But our study has shown that, because of the complex and possibly changing pattern of infections, such programs alone might not be sufficient to fully prevent infection in other species,” Glasgow’s Dr. Mafalda Viana, who led the multi-author study with colleague Dr. Tiziana Lembo, has pointed out.
But the threat of canine distemper extends well beyond lions and tigers, and the virus has impacted a number of the world’s other carnivores of conservation concern, including the highly endangered Ethiopian wolf and African wild dog, as well as the black-footed ferret in North America, to name just a few examples.
“The fact that one kind of virus is affecting so many species in so many parts of the world really merits our attention now — while we can potentially do something about it — not after an extinction event has occurred,” noted Dr. Steve Osofsky, WCS’ Executive Director for Wildlife Health & Health Policy. “We brought a group of the world’s top experts together to map out a proactive way forward to protect the world’s most endangered carnivores, and I am very pleased with the consensus that’s been reached.”
The experts attending the Bronx Zoo-hosted Vaccines for Conservation: Exploring the Feasibility of Protecting Wild Tigers and Other Endangered Carnivores Against Distemper recommend the following “Top 5” actions aimed at protecting the world’s wild carnivores of conservation concern from distemper and other infectious diseases:
- Facilitate safe off-label use of existing vaccines — Support collaboration between the zoological community and conservationists in the field to determine the safety as well as efficacy of existing distemper vaccines that could be, at a minimum, administered opportunistically to endangered wild carnivores whenever they are being handled (e.g. during radio-collaring exercises or when being translocated to mitigate human-wildlife conflict).
- Develop field-friendly rapid diagnostic capabilities — Introduce easy-to-use sample collection kits, linked to field-accessible diagnostic technologies, in order to maximize the health information gathered during rare opportunities to handle live or dead wild carnivores.
- Enhance disease surveillance in the field — Facilitate the creation of proactive disease surveillance systems that include both domestic and wild animals, to ensure the early detection of health threats to endangered carnivores, and to develop the epidemiological understanding that is crucial to designing effective control measures.
- Create networks that share health data — Foster sharing of health data among experts within and across wild carnivore range countries, to vastly increase our understanding of disease impacts on endangered populations, and enable proactive and reactive responses when and where they are needed most.
- Explore new vaccine technologies — Longer term, we need to evaluate new ways to vaccinate wild carnivores for distemper, in situations wherein use of an injectable vaccine is not feasible by hand or by dart. The potential for development of both oral and aerosol vaccines, for example, merits attention.