DESCRIPTION

Plague is an enzootic disease transmitted by fleas from wild rodents and caused by Yersinia pestis. Humans and their domestic pets occasionally become infected. Human plague has three main forms:

• Bubonic: 80–85% cases
• Septicemic: 10% cases
• Pneumonic: <5% cases
• Other forms include meningeal, pharyngeal, ocular, and gastrointestinal (GI) plague.

EPIDEMIOLOGY

• Worldwide
  • Enzootic in Africa, Asia, and the Americas
  • Between 2010 and 2015, approximately 3,248 people were infected with plague worldwide resulting in 584 deaths.
• In the United States
  • Most cases occur sporadically or in small clusters in Arizona, New Mexico, California, Colorado, Oregon, and Nevada during spring and summer.
  • An average of seven cases (ranges 1 to 17) of plague have been reported each year in the United States between 2000 and 2019.
  • Person-to-person transmission of pneumonic plague is rare with only one possible case reported in the United States since 1924.

ETIOLOGY

Plague is caused by Y. pestis, a pleomorphic, bipolar-staining, gram-negative coccobacillus.

GENERAL PREVENTION

• Reduce rodent shelter and food sources in the immediate vicinity of the home by storing grain and animal food in rodent-proof containers.
• Flea disinfestation of domestic cats and dogs, especially in endemic areas
• Avoid direct contact with ill or dead animals and never feed squirrels, chipmunks, or other wild rodents.
• Apply tick repellents containing N,N-diethyl-meta-toluamide (DEET) when there is a risk of outdoor exposure to rodent fleas.
• Hospital isolation precautions:
  • Patients with suspected or known plague should be placed in standard and droplet precautions until pneumonic plague can be ruled out.
• Postexposure management:
  • All persons with exposure to a known or suspected plague source in the previous 6 days should be offered chemoprophylaxis or be told to report illness or fever >38.3°C.
  • Persons with close (<2 m) contact with a patient with pneumonic plague should receive antimicrobial prophylaxis, but isolation is not necessary.
• Chemoprophylaxis for children aged ≥1 month to ≤17 years:
  • Ciprofloxacin, levofloxacin, or doxycycline (PO) at treatment doses for 7 days from last exposure
• Notify state public health authorities of cases of suspected and proven Y. pestis infection.
• A vaccine to prevent plague is not available.

PATHOPHYSIOLOGY

• Skin portal of entry
  • Y. pestis is transmitted most commonly to humans from fleas via the regurgitation of the organism into the bite during the flea’s blood meal (Y. pestis blocks the flea foregut, causing regurgitation).
  • Ground squirrels, rats, chipmunks, prairie dogs, deer mice, marmots, rabbits, and occasionally domestic dogs and cats harbor infected fleas and may be reservoirs of infection.
  • Direct skin inoculation of organisms from infected animal tissue or blood occurs through breaks in the skin (e.g., during skinning of animals).
  • Lymphatic spread of infection to the regional lymph nodes creates a localized inflammatory response (bubo).
  • Subsequent hematogenous spread of the organism to other organs results in high levels of circulating bacterial endotoxin (septicemic plague).
  • Bubonic and septicemic plague can lead to pneumonic plague through hematogenous spread.
• Respiratory portal of entry
  • Primary pneumonic plague is acquired via inhalation of respiratory tract droplets from a human or animal (e.g., dog or cat) with pneumonic plague.
• Incubation period
  • 2 to 8 days for bubonic or septicemic plague
  • 1 to 6 days for pneumonic plague