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Fall 2009
FOX RABIES – THE FACTS
What is ‘Arctic’ rabies?
• Rabies, the singular most fatal infectious disease of mammals found worldwide can be sub-divided into categories known as ‘variants’ or ‘strains’. Rabies strains are distinguished by the animal or animals that are most frequently infected by a particular strain and region of occurrence. Categorizing rabies to strains was developed in and applied after 1979. ‘Arctic’ variant or strain of rabies originated in northern Canada and was transmitted to Ontario by foxes.
Is Arctic rabies different from other strains of rabies?
• In Ontario, Arctic strain rabies predominantly infects wild Red foxes and Striped skunks, but has also spilled over to domestic cattle, dogs and cats. Also, Arctic strain rabies continues to circulate and re-appear in northern areas. In other parts of Canada, ‘Mid-West skunk’ strain rabies predominates in Manitoba, while solely bat strain rabies occurs in British Columbia. Bat strains of rabies are also evident in other provinces, including Ontario. ‘Mid-Atlantic raccoon’ strain rabies was a presence in Ontario from 1999 to 2005 and in Quebec from 2006 to the present. All strains of rabies have the potential to infect and kill any mammal, including humans.
What is the history of Arctic fox rabies in Ontario?
• This strain of rabies may have been present in southern Ontario sporadically over many centuries. In 1819, the Governor-in-Chief of British North America, the Duke of Richmond, died of rabies in the village of Richmond (near Ottawa) from the bite of a pet fox: the first human death in Canada due to rabies. Although there were incidences of rabid dogs in Ontario prior to the 1950s, there was no rabies in terrestrial wildlife until 1954, when Arctic rabies entered the province from the north. It reached southern Ontario in 1956. From 1958 to 1992, with the exception of 1961-63, southern Ontario annually reported more rabid animals than any other state or province in North America.
• From 1958 to 1992 there were 50923 rabies cases in wild and domestic animals in Ontario, an average of 1455 cases per year. Most of those cases (98%) occurred in southern Ontario – south of the French River. All of those cases, with the exception of 1% rabid bats, were Arctic strain. Foxes accounted for 46% of those cases and skunks 20%.
• Rabies has cost Ontario more than $7 million a year in diagnostics; investigation of animal bites; treatment of humans in contact with rabid animals; compensation to farmers for loss of livestock; cost of quarantine and research. Pet owners spend an additional $50 million a year having their pets vaccinated.
What is the current status of Arctic rabies in Ontario?
• Arctic strain rabies was completely eliminated from southeastern Ontario in 1989-95, by aerial drops of baits containing oral rabies vaccine for foxes. That was the first attempt at rabies control in North America. In 1994, the baiting program was extended right across southern Ontario.
• From 1995 to 2002, when the baiting programs primarily took effect in southern Ontario, there were 1365 rabies cases, an average of 170 cases per year. Foxes accounted for 21% of all cases. Bat strain rabies accounted for 20% of the cases and 9% of the cases were ‘Mid-Atlantic raccoon’ strain rabies, the remainder was Arctic strain.
• From 2003 to 2008 there were only 600 rabies cases, an average of 100 cases per year and an overall decrease in rabies by 93% from the 1958-1992 period. Bat strain comprised 56% of the cases and raccoon strain 1%. Foxes accounted for only 3% of all rabies cases. The baiting programs were very effective in lowering fox rabies cases.
• The disease presently persists, chiefly in skunks, and at low levels, in the area south of Georgian Bay and east of Lake Huron. There have also been renewed invasions from the north. In 2002, there was an outbreak in the Sudbury and Kirkland Lake areas, following on the heels of a rabies outbreak around Cochrane in 2001. Baiting programs continue to the present in order to respond to areas with persistent and re-appearing rabies cases.
Response by the Ministry of Natural Resources (MNR)?
• The MNR is a leader in the development of vaccination techniques for wildlife, such as foxes and raccoons. One of these techniques – the aerial baiting program – has received worldwide acclaim for its success in eliminating fox, raccoon, and coyote rabies from large areas.
• Research and aerial baiting efforts by the MNR have centred on immunizing wild foxes, raccoons and skunks. Scientists now have evidence that if they are able to immunize a large enough percentage of the “species” population that spreads rabies, the disease will die out completely.
• Current baits contain 1.8-millilitres of rabies vaccine sealed in a small plastic blister-pack. This blister-pack is embedded in the bait matrix, a mixture of fat, wax, sugar, oil, and scents. In the recent past the rabies vaccine was a live virus vaccine. More recently a new, genetically engineered vaccine has been developed in Canada – this vaccine will vaccinate foxes, in addition to skunks and raccoons, by the oral route. Oral vaccines must be absorbed in the lining of the mouth to be effective because they would be destroyed by acids if they reached the stomach.
• Research has found a bait attractive for both foxes, raccoons and skunks to eat, but also one easy to mass-produce, store, handle and distribute over large areas. Most importantly, researchers need to ensure the blister-pack of vaccine is chewed along with the bait to ensure that vaccine is deposited in the mouth of any fox, raccoon or skunk eating the bait. The original bait was a khaki green square measuring 35 mm x 35 mm x 10 mm, weighing about 13 grams. A modified version of that original bait was developed in 2006 to reach skunks more effectively. This bait is 40 mm x 22 mm x 10 mm, weighing about 4 grams. All baits distributed by MNR have a label with a contact number.
• Each fall, MNR aircraft now drop baits for wild foxes in rural woods and fields at a density of 20 baits per square kilometer along flight lines spaced two kilometers apart. Bait densities for skunks are higher and might reach 300 baits per square kilometer. Twin Otter aircraft are outfitted with special bait-dispensing machines. Navigation uses the latest satellite and computer technology to spread baits as uniformly as possible and record where they were dropped. In urban areas baits are distributed along river ravines and wooded areas by staff walking in those areas or helicopter.
• Since 1989 to the present approximately 19,250,000 rabies vaccine baits were distributed in southwestern Ontario and parts of northern Ontario to combat ‘Arctic’ strain rabies. Of those, about 1,160,000 baits were deployed in 2009 to reach both foxes and skunks in southwestern Ontario. Annual baiting zones are determined based on up-to-date locations of rabies cases as documented by Canadian Food Inspection Agency which has the responsibility for rabies diagnostics in Canada. .
Contact:
Natalie Gorman
Ministry of Natural Resources
705) 755-1551
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