- Researchers say they believe they have identified the potential cause of a foot disease that affected 24 huemul deer in Chile’s Bernardo O’Higgins National Park between 2005 and 2010.
- Preliminary results from tests on tissue samples taken from an infected fawn suggest that a parapoxvirus, a group of viruses that commonly infect and cause lesions in livestock, could have been the main cause of the foot disease.
- If the pox virus is indeed the disease agent, then it’s an additional threat to the endangered species because these viruses are highly contagious, researchers say.
- The study’s authors say they suspect the parapoxvirus may have come from cattle that was illegally introduced in the national park in 1991.
Between 2005 and 2010, 24 huemul deer in Chile’s Bernardo O’Higgins National Park developed a mysterious foot disease. Their hooves swelled, they limped and appeared to be in pain. In some cases, the deer became too incapacitated to move and eventually died. Researchers are now a step closer to finding out what may have caused this outbreak: it could have been a type of pox virus, they report in a new study published in PLOS ONE.
Arriving at this likely disease agent has taken nearly a decade. This is partly because Bernardo O’Higgins National Park (BONP), Chile’s largest protected area, is hard to get to and monitor. It’s located in a remote part of the country, one broken up by a network of fjords and inlets, and includes numerous glaciers and part of the southern Patagonian continental ice cap that runs between Chile and Argentina. Accessible only by a boat ride of several days, the park’s remote location has protective value: Bernardo O’Higgins remains one of the last strongholds for the endangered huemul, or South Andean, deer (Hippocamelus bisulcus) in the world. But the isolation of the park also makes conservation difficult.
Park rangers detected the first case of an infected deer there in 2005. One of the adult females they had been regularly monitoring was showing signs of foot lesions and swelling that caused her to limp painfully. Four days after they first spotted the problem, the rangers found the deer dead in a lagoon, with numerous footprints of culpeo, or Andean foxes (Pseudalopex culpaeus), in the surrounding mud. The deer had probably been chased by the foxes, the rangers thought, and unable to move quickly because of worsening health, she had become easy prey.
“The rangers actually carried her to the field station and carried out the first necropsy,” Marcela Uhart, a wildlife veterinarian with the University of California, Davis, and co-author of the study, told Mongabay. “I was on the roof of my house with a satellite phone, working through the necropsy with them, telling them ‘OK now cut through this, then cut through that.’ It was very emotional and difficult for them. These were animals that they’d grown attached to, but the rangers understood the value of collecting those samples and preserving them the best way possible.”
Over the next five years, the rangers recorded a total of 24 deer with the foot disease. Around 40 percent of these deer died, mostly because the disease destroys the structure of their foot and makes it hard for them to walk or run, Uhart said. “The disease has a high fatality rate but it was mostly related to the animals not being able to move anymore and protect themselves from being attacked by predators or even eat or drink.”
Collecting samples from all the infected deer, however, proved to be a massive challenge in the harsh landscape. In many cases, the rangers followed the animals over several days, Uhart said, only to lose them and not find their bodies or remains again. The rangers did manage to collect samples from a few individuals, but a combination of factors, including issues with preservation of the samples in Chile, meant that samples from only one fawn were good enough to be sent to labs in the United States for further analysis. There, pathologists and molecular biologists associated with the Wildlife Conservation Society ran a wide range of tests on the samples over several years to finally find the potential cause of the foot disease: a parapoxvirus, a group of viruses that commonly infect and cause lesions in livestock.
“The biggest challenge we had was finding disease tests that were sensitive enough to pick DNA of the pathogens without the samples being in ideal condition,” Uhart said. “For virology, for example, the samples we would have to be preserved frozen. That’s not an option in this location. So we have to do what we can with samples fixed in formalin, which actually kills the virus, so then if you want to culture it to know what it is exactly, you can’t. It makes things very complicated.”
Despite the hurdles, the researchers say they think the virus is the mostly likely disease agent. “We call it the potential cause because we identified it in only one animal, so we cannot say that this was the factor in all cases, but all cases were very similar,” Uhart said.
To know for sure, the researchers would have to find the virus in more animals. “In theory you’ll have to infect an animal with this virus and see if this disease develops — that would be the only way to confirm that this is the cause,” Uhart said. “But at least finding it in more animals that are affected would be the first suggestion that there is a role of the virus in all these cases.”
The researchers’ goal now is to follow up to see if there are new cases and get samples as quickly as possible to search for the virus. But while there have been new anecdotal records of this disease in the huemul deer population in the park, these records haven’t been confirmed yet.
“This preliminary study is of high value, but of course it requires more understanding,” Christian Saucedo, a veterinarian and conservation director of the nonprofit Conservacion Patagonica, who was not involved in the study, told Mongabay. “The information that is shared in this study is of a couple years ago. What we need in the near future is a picture of current status of the deer population and the disease in that population.”
As to where the parapoxvirus came from, the study’s authors have a suspicion: their analysis showed that the virus DNA in the sample was closely related to livestock viruses. The researchers say that cattle that were illegally introduced in the Huemules Valley of Bernardo O’Higgins National Park in 1991, which then grew in number, could have played a role in the disease outbreak. Although most cattle were removed by 2004, some escaped into surrounding valleys and may still be around. Of the 24 affected deer, 18 were found in the Huemules Valley, while the remaining deer were found in the more isolated Bernardo and Katraska Valleys, where rangers found six sick deer between 2008 and 2010.
“The cattle were removed from the area before the cases showed up, but not all cattle were removed,” Uhart said. “So while we can’t say that there’s an exact overlap in time, the genetic identity of the virus suggests that it is a virus that is very closely related to livestock viruses.”
This, Saucedo added, is further evidence that shows that the huemul deer population isn’t compatible with livestock in the same areas. “This finding provides additional support to the decision makers to be more strong on the policies to control the livestock in protected areas,” he said.
If the pox virus is indeed the cause of the foot disease in the huemul deer, then it could pose a considerable threat to the species. This is because pox viruses are highly contagious, and close contact between deer, such as mother and fawn, could result in the disease spreading easily, Uhart said. Moreover, the viruses that are shed into the environment, such as from scabs from the infected feet that are in close contact with the soil, water or plants, can also infect other individuals.
“If the environment is infected then you have a huge problem because no matter what you do with the animal, for example if you remove cattle, the environment is already infectious and it’s sustaining the infection on its own, which could be the case here [but] we don’t know,” Uhart said.
Saucedo added that while the study’s results are not conclusive, the virus does seem like one of the most probable causes of the disease for now.
“The remoteness of the area in general makes logistics and access to samples in good condition a real challenge,” he said. “So all the information that is possible to produce is valuable especially since the lack of information is a limitation for conservation.”
Uhart agreed that the disease needs further investigation. But for an endangered species like the huemul deer that’s already suffered severe declines in the past due to habitat loss and poaching, any disease cannot be taken lightly, she said. “And because of that we want to highlight that there is a lot to gain from collaboration, especially with government agencies, academia, NGOs, so that in the future we don’t have so many challenges to identify what’s happening, and we can together contribute to the solutions.”
Citation:
Vila, A. R., Briceño, C., McAloose, D., Seimon, T. A., Armién, A. G., Mauldin, E. A., … & Paredes, J. (2019). Putative parapoxvirus-associated foot disease in the endangered huemul deer (Hippocamelus bisulcus) in Bernardo O’Higgins National Park, Chile. PLOS ONE, 14(4), e0213667.
