Pneumonic plague transmission from dog to man

By Kate Bass, B.Sc.May 1 2015

The case of a man in Colorado who contracted human pneumonic plague in June 2014 was published today by the Centers for Disease Control and Protection (CDC). This case was unusual in that plague only affects around eight people annually in the United State, and that the source of the infection was his dog.

Shutterstock.com / Christin Lola

Pneumonic plague is a rare but life-threatening condition caused by the bacteria Yersinia pestis. Y pestis is usually carried by rodents and can be transmitted to humans through a bite from an infected rodent or rodent flea or inhalation of infectious droplets. However, it usually develops as a complication of untreated bubonic plague. Pneumonic plague is generally fatal if not treated with antibiotics and is the only form of plague with the potential for human-to-human transmission.

The Colorado patient, a previously healthy middle-aged man, was admitted to a local hospital after a fever and cough became rapidly worse. He was diagnosed with pneumonia and P luteola was identified as the causative agent by an automated identification system. Despite treatment, his condition continued to deteriorate so his samples were reanalyzed manually and Y pestis was identified. The man recovered after treatment with broad-spectrum antibiotics.

It transpired that a few days before the man had become ill, his dog had been put down due to respiratory difficulties. Analysis of samples from the dog confirmed that it too was infected with Y pestis. The veterinary clinic confirmed that the man had been in prolonged close contact with his dog during the last hours of its life.

Two veterinary nurses who had cared for the dog and a friend of the Colorado patient also developed fever and respiratory symptoms and tested positive for Y pestis. All three subsequently made a full recovery. It is not known whether the friend contracted the plague from the dog or the Colorado patient.

This is the largest plague outbreak in the United States since 1924, and could also include the first case of human-human plague transmission.

As a result of this outbreak awareness needs to be raised regarding the potential human risk of sick domestic animals. Furthermore, it has drawn into question the use of automated culture identification systems since the initial incorrect diagnosis of the Colorado patient unnecessarily exposed additional medical staff to the plague.