While coyote attacks on humans are rare, and attacks by rabid ones even rarer, researchers from the Massachusetts Department of Public Health have drawn what they believe is a statistical connection between aggressive behavior in the animals and the deadly disease.
That would certainty set with the popular notion of rabies — a virus that infects the central nervous system — that of rabid animals foaming at the mouth or exhibiting other violent or bizarre behavior. But Dr. Catherine Brown, a state veterinarian, said the reality is often different.
Many animals, in fact, become sleepy or docile when infected by the disease, said Brown, one of the authors of a letter appearing in the February edition of Emerging Infectious Diseases, published by the federal Centers for Disease Control and Prevention. Other species, such as foxes, are far more likely to show aggressive behavior more typically associated with rabies.
Coyotes, which have been surging in population over the last 50 years in Massachusetts, may well fall into the latter category.
"Coyotes don't like humans, they don't like to be near humans, but when you have a situation that a coyote displays aggression ... we need to be much more concerned about the risk for rabies," Brown said.
The researchers said of 107 coyotes tested in the state between 1985 and 2008, 10 were rabid, or 9 percent. All those had Rabies Raccoon Virus, the predominant strain in Massachusetts that first arrived in the state in the early 1990s and quickly decimated the raccoon population while also spreading to animals such as skunks, foxes and woodchucks.
The researchers said coyotes that attacked people or domestic animals without provocation, or clashed with dogs, were far more likely to be rabid than those that did not. Of the 18 coyotes tested that reportedly had bitten either a human or domestic animal, seven had positive rabies tests.
"This association between aggressive behavior and a positive rabies test is of particular concern because of coyotes' relatively large size, their dramatically increased population, and their distribution throughout the state encompassing rural, suburban, and even urban areas," the researchers wrote in the letter.
Fifty years ago, coyotes were found only in a handful of towns in Massachusetts. They're now prevalent throughout the state, with the exception of the islands of Martha's Vineyard and Nantucket.
"Coyotes are an extremely, extremely adaptable species," said Laura Hajduk, a state biologist and coyote expert. While they generally shun people, they migrate to food sources and, with time, grow less fearful of their human neighbors, she said.
Only a handful of human rabies cases are reported in the U.S. each year, virtually all contracted from bats. A person bitten by a rabid animal can prevent the disease by getting treated promptly with a regiment of anti-rabies shots. Left unchecked, however, the disease is nearly always fatal.
State public health officials are not aware of any human rabies cases in Massachusetts in the last half-century, save for one in the 1980s that was believed to have been contracted in another part of the country.
Rabies, however, remains a larger threat to small pets. There were nine cases of rabies in cats in the Bay State last year, said Brown, though none in dogs, likely because dog owners tend to be more vigilant than cat owners in getting mandatory vaccinations for their pets.
Hajduk said the best way for people to keep themselves — and their pets — safe is to keep coyotes out of their yards, and the best way to do that is to show them who's boss. Making loud noises, like banging pots and pans, or even throwing a tennis ball in their direction will give the animals a "negative interaction" and discourage them from returning to the territory in the future, she said.
