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Monday, 23 April 2012

Rabies in Canada - a rare bird, but one that gets lots of attention and some great Canadian successes

The diagnosis of a human case of rabies in Toronto is the sober reminder of the illness than painfully kills 55,000 people annually, 60% in Asia and 40% in Africa.   Almost all of the human illness caused by dogs.

The disease kills almost all those infected, Herculean efforts are no doubt being expended for the Canadian who was resident in the Dominican when they became symptomatic.  A handful of clinical rabies cases have survived through induced coma and aggressive antiviral therapies.

The mainstay of protection is post exposure prophylaxis which is provided to those unfortunate enought to have been exposed by a potential infected animal.  The number treated each year is something that DrPHealth would like to find, and seems buried in provincial documents at best.  The last Canadian rabies cases were in 2007 (Alberta) 2003 (BC) and 2000 (Quebec).  Canada had gone without a human case for 15 years at that point. The point here, human rabies is fortunately rare. 

A careful analysis of Canadian rabies will show that there are 4 epizoonosis.  To the central provinces raccoons have dominated the rabies scene for many years, but the last Quebec positive was in 2008 and Ontario in 2005.   More centrally Manitoba and Saskatchewan the main culprit being skunks (Alberta’s last skunk case was in 1995 and a testament to an aggressive “depopulation” campaign that eliminated skunk rabies and rats from the province). To the north, foxes still are the main carrier.  Throughout the country bat rabies in endemic.  The Eastern provinces are not rabies free, but isolations are infrequent. 

Both Alberta’s experience with skunks through depopulation and Ontario and Quebec’s experience with the use of rabies vaccine in the wild demonstrate that there is real value in animal control as an effective means of reducing human risk.  Rabies in many animals does follow a pattern for epizoonosis and the history of raccoon rabies is a great example, having spread from Southeastern states in the 1950’s and spreading along the eastern seaboard until its entry into Canada in the 1990s.  Its containment in Canada being bolstered by human intervention.  Wolf related rabies from the north and into Western provinces naturally dissipated in the mid-20th century.

Depending on who you ask, the number of dog bites alone in Canada is in the order of 450,000 per year.  Imagine providing rabies post-exposure prophylaxis to all those people? The most important step in preventing dog rabies is to observe the animal - those dogs (cats and ferrets) capable of transmitting rabies will die within 10 days, and progressively become more ill during the observation period.  Sacrificing a domestic animal for testing is rarely indicated (occassionally for bites to the head or neck)

Less well documented in Canada would be the number of persons bitten by bats or other potentially infected wild animals.   Seems a good surveillance question to be answered.  

A question that seems to circulate is what about small rodent mammals – most will not survive the bite and aggression of a rabid animal – those that do will likely die before the infection becomes manifest due to the short lifespan of the animal, and those that develop symptoms, don’t typically develop the aggressive symptoms or larger animals.  So the natural history, and the collective experience of good documentation for 88 years can reassure that rodents are not transmitters of rabies to humans. 

In the meantime, a few points to remember
1.       Vaccinate domestic animals, dogs in particular
2.       Steer clear of wild animals.
3.       Report wild animal bites, especially bats, skunks, foxes and raccoons to a health professional and through them to local public health offices for assessment of risk.
4.       International travel remains one of the most problematic sources of exposure to rabies.  Consider rabies preexposure vaccination if you are travelling abroad for extended periods in rabies active countries.

Post exposure prophylaxis costs $1000-2000 for a series to provide.  Perhaps one of the reasons that obtaining statistics is so difficult, we would not want to have cost become a barrier to protecting a life. 

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