Friday, October 2, 2009

Canine Distemper in a new species


Once again the Wildlife Disease Listserv and blog has provided an entry into a convoluted story of disease among wildlife, domestic animals and even people.

A recent report published in the journal Microbiology has further broadened the range of species that can contract and die from a nasty virus disease once thought to occur, as its name implies, in dogs. It is canine distemper. The title of the article, written by Zhaozeng Sun, Aixue Li and their colleagues, is Natural Infection with Canine Distemper Virus in Hand-feeding Rhesus Monkeys in China.

It has been known for many years that some other species can contract the virus, or its very close relatives, and it seems obvious that the virus itself is able to undergo slight changes that allow it to infect new hosts. In the last thirty years it has been seen in seals (hence phocine distemper), dolphins, and other species. In Africa it had devastating effects on the African Wild Dog populations and was reported in jackals and hyaenas. It would be no surprise to learn that it also killed other canids like bat-eared foxes, but they tend to fly a bit under the radar and do not have the charismatic appeal of the larger species – they only weigh about 3 kg. Then in 1994 an epidemic occurred in lions in the Serengeti, killing an estimated 30% of the population, something like 1000 animals, in two years!

As I wrote in The Trouble With Lions
“There is a dramatic, but grim, movie clip shown on the Glasgow Veterinary College web site, taken by modeler Professor Ray Holborn, of a lion in the Serengeti in the throes of a grand mal seizure, which is one of the classic signs of distemper”.
I have just spent a fruitless 30 minutes trying to find the video, but it seems to have been taken down.

In dogs some of the classic signs of distemper are fever, loss of appetite, respiratory symptoms and thickening of the footpad. Another name for the condition used to be “Hardpad” and at one time this was even thought to be a different disease. Distemper was once a major killer of inner-city dogs in Glasgow and we students used to go into slum areas and take part in free vaccination clinics. This is much the same as the clinics that now take place around national parks like the Serengeti and Masai Mara in Kenya and Tanzania. You can read more about this on the Wildlife Direct blog here.

Many dogs developed central nervous system signs and seizures were common before they went on to die. There is no mention of CNS signs in any species other than the lions, but deaths certainly occurred. That is exactly what took place in the Chinese Rhesus monkeys where twelve of twenty that were sick went on to die.

So, will distemper jump to humans? Maybe it has done so already, aeons ago, in the form of measles. We may be lucky, because the distemper and measles viruses are closely related. So much so that for many years measles vaccine was used to protect puppies. Another point. When measles vaccines programs fail, or folks take decision not to vaccinate children, the consequences can be terrible. Measles was once a major factor in many areas of the world where European invaders arrived and brought the disease to fully susceptible people.

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