Description

Plague is an enzootic disease transmitted by fleas from wild rodents and caused by Yersinia pestis. Humans and their pets can enter this cycle, resulting in human plague. Human plague has 3 main forms: bubonic, septicemic, and pneumonic; rarely presents as meningeal, pharyngeal, ocular, or gastrointestinal (GI) plague

Epidemiology

• Worldwide: enzootic in Africa, Asia, and Americas. Since 2000, 95% of the 22,000 cases reported to the World Health Organization have been from countries in sub-Saharan Africa.
• In the United States, most cases occur in Arizona, New Mexico, California, Colorado, Oregon, and Nevada.
• In the United States, most cases occur in spring/summer.
• 51 cases of plague occurred in the United States from 2004 to 2011.
• 20% of U.S. cases with identified mode of transmission are acquired through direct contact with Y. pestis–infected animals, not via flea bite.
• No cases of person-to-person transmission of pneumonic plague have been reported in the United States since 1924.
• Untreated bubonic plague: >50% fatal
• Untreated pneumonic plague: nearly 100% fatal

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 cats and dogs, especially in endemic areas
• Hospital isolation precautions
  • Patients with bubonic or septicemic plague and no evidence of pneumonia: standard precautions; add droplet precautions for first 24 hours of therapy until chest radiograph persistently clear.
  • Patients with pneumonic plague: standard and droplet precautions. Continue droplet precautions until patient has completed 48 hours of appropriate antimicrobial therapy.
• Postexposure management
  • All persons with exposure to known or suspected plague source in last 6 days
    • Daily surveillance for fever or symptoms of disease for 7–10 days
    • Offer prophylaxis.
    • Initiate treatment if becomes ill
• Persons with close (<2 m) contact with a patient with pneumonic plague should receive antimicrobial prophylaxis, but isolation is not necessary.
• Chemoprophylaxis ≥8 years
  • Doxycycline (PO), OR
  • Ciprofloxacin (PO) at treatment doses for 7 days from last exposure (see “Medications” for dosing)
• Chemoprophylaxis <8 years: ciprofloxacin (PO)
• Notify state public health authorities of cases of suspected and proven Y. pestis infection.
• Vaccination is no longer available and is not considered useful to prevent plague from an enzootic source.

Pathophysiology

• Skin portal of entry
  • Y. pestis is transmitted from fleas to humans via the regurgitation of the organism into the bite during the flea’s blood meal (Y. pestis blocks foregut, causing regurgitation).
  • Rodents, ground squirrels, cats, prairie dogs, marmots, rabbits, and occasionally dogs harbor infected fleas and are reservoirs of infection (enzootic).
  • Direct skin inoculation of organisms from infected animal tissue or blood occurs through breaks in the skin (e.g., cat scratch, skinning quarry).
  • Lymphatic spread of infection to the regional lymph nodes creates a localized inflammatory response (bubo, bubonic).
  • Subsequent hematogenous spread of the organism to other organs results in high levels of circulating bacterial endotoxin (septicemic plague).
  • By hematogenous spread to lungs, both bubonic and septicemic plague can cause secondary pneumonic plague.
• Respiratory portal of entry
  • Primary pneumonic plague: acquired via inhalation of respiratory tract droplets from a human or animal (e.g., cat) with pneumonic plague
• Incubation period
  • 2–8 days for bubonic or septicemic plague
  • 1–6 days for pneumonic plague

Etiology

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