An outbreak of pneumonic plague with likely human-to human transmission, believed to be initially transmitted by a dog, has been identified for the first time in the United States since 1924 in Colorado last year.

Yersinia pestis bacteria, which was grown on a medium of sheep’s blood agar (SBA) Image/CDC

The outbreak  (currently the largest to date) occurred in June 2014 and affected the dog owner and 3 other individuals following their occupational exposure to an American pit bull terrier, which was brought to a veterinary clinic with hemoptysis (coughing up blood), jaw rigidity, drooling, and right forelimb ataxia.

Early diagnostic tests from the canine were negative for the rabies virus, but later  histological analysis confirmed the isolation of the bacterium Yersinia pestis  (the cause of plague) prior to the hospitalization of the owner, as a result of  pneumonia related symptoms and hemoptysis.

Although an automated identification test misidentified the organism in the patient’s clinical specimens as Pseudomonas luteola, the isolate was correctly identified by the Colorado Department of Public Health and Environment (CDPHE) following the patients clinical presentation,  deterioration and reports of errors in the identification of Y.pestis elsewhere.

Contacts of the deceased dog received a differential diagnosis of plague and made a full recovery, following the administration of antibiotics. Further investigations traced a total of 88 contacts who were given antibiotics as a preventative measure. 

Plague, a bacterial disease caused by Yersinia pestis,  is typically spread following contact with rodent fleas infected with the bacterium. Pneumonic plague is acquired via the inhalation of infectious droplets expelled from an infected person. Once deemed a  curse upon humanity in Europe during the Middle Ages and an accessory  the collapse of the Roman Empire, plague may be treated successfully with antibiotics. Infections still occur in parts of the western United States and still remains a predominant threat in developing countries. Both humans and mammals can be infected.

Lavinia Rodney is a qualified microbiologist working in the diagnostics department of a busy UK hospital, alongside studying for the final year of her Masters Degree in Medical Microbiology