By Farnaz Heidari

Canine distemper virus wildlife mortal enemy

May 21, 2017

Diseases are parts of life, but in a well-balanced ecosystem virulent epidemics are rare. Disease can even be beneficial to a population, weeding out old or weak animals. Problems occur when a population of animals is exposed to a new disease to which it has not had a chance to build up natural immunity.

Old and classic story

Introduced diseases can rip through unprotected populations with devastating speed. The classic example is that of the myxomatosis virus. In the 1950s a British farmer decided to use the virus (which originally came from South America) to control the rabbits on his farm. No one could have dreamed it would be so effective. The disease spread so fast that it killed 99 percent of all British rabbits within a year. But farmers barely had the chance to heave a sigh of relief before conservationists realized something was horribly wrong. Over the 2,000 years since rabbits were introduced to Britain, they had helped create and maintain some of the island’s most treasured habitats. They had also become a vital component of the food chain, supporting predators such as foxes and various birds of prey. When rabbit numbers crashed, so did national populations of red kites, buzzards, and many other predators. Fortunately for them, rabbit populations have now recovered, and a large proportion have at least some degree of resistance to the myxomatosis. 

Effects of disease on endangered species

The increased transmission of diseases as a result of human activities and interaction with humans is a major threat to many endangered species and ecosystems. In Iran there is absolutely no data about unknown diseases such as canine distemper in large felines. We know disease-causing organisms such as bacteria, viruses, fungi, and protists can have major impacts on vulnerable species and even the structure of an entire ecosystem. For exmaple Pusa caspica is a relict species, now confined to the Caspian Sea, where its ancestors lived. The Caspian seal was hunted commercially up until the mid-1990s, sometimes with 100s of thousands of animals hunted each year. That was the main reason for the decline of more than 1 million animals at the start of the 20th Century to around 100 thousand today. Today there is still occasional commercial hunting, and at least several thousand seals are caught in (mostly illegal) fishing nets each year. Caspian Seal is also vulnerable to canine distemper virus.

Canine Distemper and related viruses causes disease outbreaks in many seal species and other carnivores, so Caspian seals are not particularly unusual in this respect. What was a little unusual was that this happened as large outbreaks, and so was very visible, rather than as a continual slow process with a lower incidence. Generally outbreaks like this happen when there is a large population with limited prior exposure, and the disease crosses over from a reservoir species. In the case of Caspian seals there are still lots of questions to be answered about the CDV outbreaks, but it may be that the disease jumped into the seals via feral dogs, jackals or wolves.

What is CDV?

A species that is both common and fairly resistant to a disease can act as a reservoir for the disease, which can then infect populations of susceptible species. For example, during the early 1990s in Tanzania’s Serengeti National Park, about 25% of the lions were killed by canine distemper, apparently contracted from the 30,000 domestic dogs living near the park. In January 2015, A study conducted by an international team of researchers has led to evidence that suggests lions in Africa originally got distemper from domesticated dogs, but now it appears there are other unknown carriers.

Distemper, caused by the canine distemper virus (CDV) is a viral disease and has been known to infect dogs, coyotes, foxes, pandas, and a wide variety of other animals, including big cats. It is transmitted through the air, and symptoms generally include a high fever, inflammation of the eyes and nose, and coughing, which is how the disease is spread. Scientists are hoping to learn more about how the disease is transmitted as part of an overall effort to prevent the loss of life wild animals that could lead to extinction in populations already threatened by the encroachment of man.

Unfortunately the situation of this disease for big cats in Iran is unknown. Some evidences exists but there is absolutely no confirmed data because all the cadavers of wildlife in Iran do not undergo scientific autopsy. The effect of this disease on native wildlife can be very serious. For example, domestic dogs in Africa spread canine distemper to wild hunting dogs and lions, causing many to die. Nobody knows how would be the situation for vulnerable cat species in Iran? In cases like these the domestic animals usually suffer only mildly and often receive the benefit of veterinary medicine while their wild counterparts can be devastated.  

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