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Growing human settlements and their diseased animals put new and unexpected pressure on wilderness areas.

 

 

The outbrake of CDV on Lions in the Serengeti in 1994:

The Serengeti game reserve in Tanzania, Africa, is one of the largest wildlife areas left in the world and is known in part for its well-documented and studied lion prides. Several years ago, a mysterious virus appeared among the thriving lion population and proceeded to wipe out a third of the population before the eyes of baffled scientists worldwide.  After the virus had run its course for several months the culprit was found: Canine Distemper Virus (CDV). It is a viral disease that causes severe neurological symptoms and usually death. Lions that were severely affected almost inevitably died.  CDV kills by attacking the respiratory, gastrointestinal, immune, and central nervous systems of its victims.  It affected the lions' brains and caused facial twitching, flailing paws, and convulsions. Other symptoms included: lions looking off colour with dull coats to complete paralysis.  The virus struck down lions of all ages throughout a 1,000 squarekilometer area within a few weeks of the initial outbreak.

Tourists, many flying in hot-air balloons over the park to get a better view of the wildlife, were the first to notice that the lions were dying.  One of the first lions suspected of suffering from CDV-like symptoms was observed on February 3, 1994 and was identified because of the uncontrollable twitching and convulsions that wracked its body.

 

Human activity, the underlying cause of the epidemic:

The Serengeti is surrounded by a human and dog population that is growing at four percent a year and the people in the area own roughly 30,000 dogs. People are moving to these areas to look for work and the opportunity to make a living.  Poor soil conditions and job scarcity are often the reasons people leave the surrounding areas to crowd around the national parks. Vaccination of the dogs in these villages against CDV is rare although some dogs in the surrounding villages had been vaccinated against distemper and rabies. It is thought that hyenas were the most likely vectors of the virus because they travel great distances and intermingle with both lions and domestic dogs at separate kill and scavenge sites within and without the park. Nomadic lions (not attached to any pride) could also have contributed to CDV dissemination. The high densities of these susceptible carnivores at kill sites could have provided an ideal environment for CDV amplification and transmission.

For instance – a hyena or jackal scrapping with domestic dogs over a carcass could have picked up the infection and passed it along to the lions in the park in the same way. Lions vulnerability in the park may also be caused by the lions higher population density (3,000 individuals in 1994, an all-time high) or their resistance to disease might have been reduced by other infections or drought. The large lion numbers possibly made it easier for the disease to pass from animal to animal because there was more frequent contact.

 

In 1994 (before the outbreake) there were an estimated 3,000 lions living within the Serengeti, the largest population of big cats in the world. By the time the outbreak was over several months later, approximately 1,000 lions died of CDV and all sixteen prides within the park were affected.  It was hard for scientists to get an exact figure because the park is so large and the lion prides are generally spread out. Combined with the fact that scavengers can reduce a carcass to nothing overnight, it was difficult to calculate how many lions actually died.

 

If the Tanzanian government had the money and the infrastructure in place, it could pass legislation making it mandatory for all dogs in the Serengeti area to be vaccinated for CDV, rabies, and other highly-infectious diseases.  Some sort of dog registration and vaccination could be required, but as long as you have human populations living in close proximity to wild animals, the possibility for outbreaks like the one in 1994 in the Serengeti are inevitable. For now, the threat to the Serengeti lions is past.  No new cases of CDV have been reported within the last years.  Survivors have developed an immunity and the lion population has already recovered a quarter of its losses. Presently, the task of inoculating these village dogs has been taken over by veterinarian groups based outside of Tanzania and funded mostly through private sources.

 

Sources:

http://cheval.vet.gla.ac.uk/vetscape/vet-x/lions/

http://www.fonz.org/animals/sppfactsheets/lion-fact.htm

http://www.american.edu/ted/AFRDOG.HTM