CDC Confirms Human Plague Infection from Dog in Colorado

PetMD Editorial
Published: May 01, 2015
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First Recorded Case of Dog to Human Transmission in the United States

The Centers for Disease Control (CDC) has confirmed that a dog is responsible for infecting humans with the pneumonic plague. This is the first event of its kind in the U.S.

Health officials have reported that a male two-year-old American Pit Bull Terrier became sick on June 24 of last summer. His owner took him to a veterinary clinic with symptoms including a high fever, jaw rigidity, and right forelimb ataxia. The dog was kept overnight at the clinic and was humanely euthanized the next day, after he developed a bloody cough and difficulty breathing.

Four days after the dog’s initial symptoms, the owner began displaying health problems as well, including a bloody cough and fever. Initial tests did not identify the infection, which led to incorrect treatment. The patient's failure to improve led to further lab testing, and on July 8 the bacterium was identified as Yersinia pestis. Upon investigation, the dog’s remains also tested positive for the plague bacterium.

During this period of time, three other people also developed symptoms of pneumonia — two veterinary clinic employees who treated the dog, and a friend of the owner who had contact with both the dog's body and with the owner while he was showing symptoms of bloody cough. After the bacterium was identified on July 8, all of the patients were contacted and received appropriate treatment. All four of the patients recovered.

The CDC believes that the third patient may have been infected by human-to-human transmission from the dog's owner. If this is the case, it would be the first time this type of event has occurred in the U.S. since 1924.

The plague disease is a rare but often fatal bacterial infection caused by the Yersinia pestis bacterium. It is rare in humans and pets in the U.S., but it is a cause for concern in the western U.S., mainly in semi-rural areas of New Mexico, Colorado, California, and Arizona, where Yersinia pestis is commonly found in wild rodent populations.

An average of eight human cases occur each year. Transmission of the bacterium typically occurs after being bitten by a flea from an infected rodent, or from direct contact with the blood or tissue of an infected rodent. Prairie dogs in the American Southwest are known to be one of the primary carriers of infected fleas.

Although possible, it is extremely rare for pets to infect humans with the plague. The only other published case in which a dog transmitted the plague virus to a human was in China in 2009. While still very rare, cats are more likely to display symptoms of the plague disease than dogs because of their frequent contact with rodents.

This particular type of plague, pneumonic plague, is different from the more well known bubonic plague, or black plague. The pneumonic plague, as its name suggests, attacks the lungs, with symptoms that are identical to pneumonia. Bubonic plague is more outwardly visible, with swollen lymph nodes and blackening of the skin due to tissue death.

A third type of plague is also related to Yersinia pestis: septicemic plague. This infection of the blood is even more uncommon than the other two plague types. 

According to the CDC, the pneumonic plague has a fatality rate of more than 93% and can be easily transmitted from person to person through air droplets. Immediate diagnosis and treatment, however, has a high success outcome.

Image: 3d representation of the Yersinia pestis bacteria, by Michael Taylor / Shutterstock


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