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The definitive host: Gone, but not forgotten

The definitive host

de·fin·i·tive host (duh-fin'eh-tiv) n. 1) An organism where a parasite undergoes the adult and sexual stages of its reproductive cycle 2) Someone you go to for interesting stories and/or facts, and puts on one hell of a dinner party 3) This blog, devoted to science and other geeky subjects

Monday, September 26, 2011

Gone, but not forgotten

Welcome to my last September Series post, which coincidentally, is also my 150th on this blog! I hope you have all enjoyed this little experiment of mine, and from the feedback I've gotten, it seems like many of you do. 
Therefore, if you'd like me to continue writing about different things every week (or have an idea for a theme month), please  leave a comment below and let me know what you'd like to see.

For this final September Series post, I decided to delve into microbiology, a great passion of mine. I decided to look at it from a prevention, control and bureaucratic angle of a very resilient killer. I hope you like it.

As children, we are taught certain life lessons, such as not taking candy from strangers, looking both ways before crossing the street and not getting too close to wild animals, for fear of being injured and contracting a potentially dangerous disease. The most well known, and one of the most dangerous to humans, is rabies.

A strictly mammalian disease, the rabies virus will usually pass through a bite from an infected animal. The disease attacks the central nervous system, causing paranoia, hallucinations and the trademark agitation up to two years after initial exposure. However, once symptoms begin, it quickly becomes effectively untreatable and over 99 percent fatal.

The rabies virus, if left untreated, is over 99 percent fatal. Therefore, if there is even a risk of getting the virus from an animal bite, get the vaccine.
Since any warm-blooded animal can carry rabies and potentially transmit the disease to humans all over the world, prevention and protection are paramount.

In 2008, the government of Ontario proclaimed in a press release that one of the more dangerous strains, known as raccoon rabies, was “eliminated in Ontario.” This was stated because there were no reported cases in Ontario were seen since 2005, and according to the World Health Organization (WHO), once two years have passed with no reported cases, the virus can be claimed as “eliminated.”

However, according to documents obtained through the Access to Information Act, there were two reported raccoon rabies cases identified in 2005. The number of cases decreased to one in 2006, and to zero in 2007 through to 2010.

While the standing of the government via the WHO guidelines is valid, the time-line is not.
Meanwhile, there are two other rabies variants still prevalent in Ontario, known as “Ontario fox” and “bat,” which still appear north of the Greater Toronto Area.

In 2009, there were a total of 18 cases of fox rabies identified in wide array of affected species, such as cows, sheep, red foxes and striped skunks. But, in 2010, the only cases of the fox strain identified were 10 skunks.

Dr. Rick Rosatte, the senior research biologist for the Ministry of Natural Resources, has been working on rabies since the first case appeared in Canada in the late 1990s.

“Rabies is not eliminated,” he said. “It is a naturally occurring disease. I would never use the term eliminated, that’s for the politicians. I would say it is under control for the time being.”

Rosatte said that the ministry is always on the lookout for rabies, and has many control measures in place if something ever were to occur. And despite the claim that raccoon rabies is ”eliminated” from Ontario, he said that the threat is still ever-present, and closer than you might think.

“There are still cases of raccoon rabies in New York and Quebec, which are a little too close for comfort. We have measures put in place to try to limit the spread from those infected areas.”

Mark Gibson, a rabies and wildlife technician with the government of Ontario said there are three methods used to control rabies once a case is reported and confirmed.

The first is Point Infection Control, where animals are trapped and euthanized within a set distance of five kilometres from the rabies site. In the second stage, the animals are trapped, vaccinated and released within 10 kilometres of the initial case. The final method is aerial baiting, where baits containing vaccines are dropped from a plane within 50 kilometres of the reported site.

The aerial baiting method, according to Gibson, is by far the most effective preventative measure they have. “The baiting is probably the reason why Ontario has been rabies free the past few years.”

The baits are no bigger than a matchbook, but contain a blister pack containing a small dosage of rabies vaccine surrounded by beef fat and flavouring. “Imagine the blister pack is like the jam packets you see at restaurants,” said Gibson. “If you squeeze it a little bit, and then puncture it with a fork, what happens? It squirts! And hopefully, most of the vaccine will be swallowed by the animal.”

Gibson said that the vaccines provide young animals protection for about a year, while in adults, it can last up to three depending on how much vaccine the animal eats.

However, while raccoon rabies is being kept at bay, there are still two other strains of rabies that are keeping the control program very busy. The arctic fox strain is limited to southwestern Ontario, but the real problem is the bat strain.

According to Rosatte, the bats are almost impossible to trace because they migrate and their food, insects, cannot be vaccinated.

“Despite the surge in infected bats, there has not been a death from rabies in Ontario since 1967. However, just because it hasn’t happened yet, doesn’t mean it won’t,” said Rosatte.

“Rabies is not gone, despite what the McGuinty government says. It is still lurking in the background.”

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