More raccoons infected with rabies have been found in Hamilton in Ontario's first outbreak of that strain of the virus in a decade.
Officials said on Wednesday that the raccoon strain of the rabies virus was found in a total of four dead animals.
The latest three came from 14 raccoons who were either found dead or were caught after someone reported suspicious behaviour, said Chris Davies, manager of wildlife research for the Ontario Ministry of Natural Resources.
The ministry will expand its vaccination baiting distribution, aiming to drop 32,000 pellets of rabies vaccine in the Hamilton area.
The operation has to unfold in the next few days, before the weather cools and raccoons begin gathering in their dens, Mr. Davies said.
He said it will take months before researchers find out if the outbreak has been contained because more tests will take place in the spring to see if the herd has been immunized. More vaccine must be administered in the fall for raccoons that are now too young to be immunized effectively.
The source of the infection might be an animal that came from the United States aboard a train or a truck, Mr. Davies said.
The problem was detected last week when a raccoon was euthanized and tested after a fight with two dogs in an animal-control van.
"By having four cases, that tells us that rabies is circulating in the raccoon population here," said Jessica Hopkins, associate medical officer of health for Hamilton.
"The overall risk to people remains very low, but there are important steps that everyone should think about," Dr. Hopkins said.
She urged local residents to keep their pets leashed and supervised when outdoors, to make sure pets' vaccinations are up-to-date and to avoid contact with wild animals.
As a result of the increasing number of cases, the Ministry of Natural Resources was expanding the area where it is vaccinating local wildlife from a 36-square-kilometre zone east of the Red Hill Valley to a perimeter six times larger.
Wildlife research staff fanned out to immunize the area's skunks, foxes and raccoons, dropping pellets of oral rabies vaccine in the front yards, farmlands and ravines of east-end Hamilton.
Encased in flavoured bait, the vaccine packets were tossed out by officers either on foot, or from a helicopter.
The raccoon strain is a rabies variant that was detected in Florida and Georgia in the 1950s. Its spread northward was unwittingly helped by hunting clubs that relocated southeastern raccoons to Virginia and North Carolina in the 1970s.
The first Canadian cases of the raccoon-associated variant were reported in 1999 in the Cornwall-Prescott area of eastern Ontario. The province has not had a confirmed case of raccoon rabies in a decade thanks to its control program.
The first new case was confirmed after a municipal worker picked up a sick raccoon in the Stoney Creek area of Hamilton last week.
The raccoon and two runaway bull mastiff dogs were transported together in the back of an animal-services van. The animals got loose and started fighting while the employee was talking with the dogs' owner about paying impound fees.
The raccoon tested positive for rabies.
The situation has now involved three levels of government, with the city's health and animal-services departments working with the Ontario Ministry of Natural Resources and the Canadian Food Inspection Agency, which tested brain samples from dead raccoons.