Laboratory tests today confirmed Bubonic plague in a Rio Rancho, N.M. dog. State health officials are alerting residents to protect themselves and pets against the zoonotic disease most commonly transmitted by flea bites.
The bacterial disease caused by Yersinia pestis, a gram-negative bacterium, can spread to people through infected flea bites or when people come into contact with infected rodents, rabbits and other animals. The bacterium is endemic to most of the Western U.S.
“The infected dog presented to a local veterinarian in Rio Rancho, N.M. with a history of killing sick rabbits about a week before illness onset,” says Paul Ettestad, DVM, MS, New Mexico public health veterinarian. “It had clinical signs of fever, lethargy and anorexia. The veterinarian drew an acute serology that tested negative in the state health department laboratory for both plague and tularemia. A convalescent serology drawn three weeks later showed a greater than four-fold rise in the plague titer (from <4 to 256) which is confirmatory.”
The Centers for Disease Control map counties where positive plague activity has been reported. Positive fleas, wildlife, cats, dogs and human cases are included.
“You can see that there is the potential for plague activity in most of the western states though it is concentrated more in the Four Corners area of the southwest,” Dr. Ettestad says. “Most of New Mexico’s human plague cases occur around the person’s residence due to a rodent die off from plague. We have had human cases where the exposure was most likely due to hunting dogs bringing plague infected fleas back into the home where the case patient allowed the dog to sleep in bed with them.”
Ettestad wrote 2010 Plague Information for Veterinarians, an educational guide posted on the state’s public health website. The piece discusses how the bacteria is spread, how to test for it and how to treat an infected patient. Ettestad says cats tend to have more severe illness from plague than dogs.
“Every case of cat plague represents a potential risk for human exposure and illness,” Ettestad says. “Acquiring primary pneumonic plague from cats is a particular risk for veterinarians, their assistants and pet owners. In addition, bubonic plague or primary plague septicemia can result from contact with infectious tissues, exudates or fleas.”
Most people acquire plague by the bite of an infectious rodent flea but about one-fifth of all human cases result from direct contact with infected animals.
“Cats are particularly susceptible to plague and can play a role in transmission to humans by a variety of mechanisms including transporting infected fleas or rodent/rabbit carcasses into the residential environment,” Ettestad says. “Direct contact contamination with exudates or respiratory droplets and by bites or scratches can also transmit disease.”
According to Ettestad, dogs are frequently infected with Y. pestis, develop antibodies to the organism and occasionally exhibit clinical signs. Dogs haven’t been shown to be direct sources of human infection.
“Maps of plague cases in animals vary by year,” Ettestad says. “There are some years where we will have over 30 cases in cats and over a dozen cases in dogs in New Mexico. So while plague cases in both dogs and cats are uncommon in most of the Western U.S., we encourage people to keep their dogs and cats from roaming and hunting and to use a flea control product recommended by their veterinarian. There have been human plague cases and human fatalities from people getting plague directly from their sick cats, though none known from sick dogs so far.”