Plague

Description

Plague is a zoonosis involving rodents and their fleas. The causative agent of plague is the bacterium Yersinia pestis. Humans are incidental hosts and are usually infected by the bite of rodent fleas. Plague can also be acquired by direct contact with infectious animals or other materials or inhalation of infective respiratory droplets.

Plague continues to be enzootic in wild rodent populations over large rural areas of the Americas, Africa, and Asia, with occasional outbreaks among commensal rats or other hosts in villages and small towns. Wild rodent plague poses a real, though limited, risk to persons. When infection spreads to rats in urban or populated areas, persons are at markedly increased risk of exposure. In recent decades, however, urban outbreaks have been rare and limited in size.

Occurrence

Wild rodent plague exists in the western third of the United States and the immediately adjoining areas of Canada, widely scattered areas of South America; north-central, northwestern, eastern, and southern Africa; Madagascar; Iran; along the frontier between Yemen and Saudi Arabia; eastern Jordan, central and southeast Asia (Burma, China, India, Indonesia, Kazakhstan, and other former Soviet Republics of central Asia, Mongolia, and Vietnam); and in parts of extreme southern Russia. In recent years, human plague has been identified in Africa from Algeria, Angola, Botswana, Democratic Republic of the Congo, Kenya, Libya, Madagascar, Malawi, Mozambique, Namibia, Tanzania, Uganda, Zambia, and Zimbabwe; in Asia from Myanmar, China, India, Indonesia, Jordan, Kazakhstan, Laos, Mongolia, and Vietnam; and in the Americas from Bolivia, Brazil, Ecuador, and Peru to the United States.

Risk for Travellers

Risk for travellers in any of these areas is small.

Clinical Description

Initial signs and symptoms of plague can be nonspecific, with fever, chills, headache, malaise, myalgia, nausea, and prostration. Bubonic plague, the most common form, usually presents with painful, swollen lymph nodes (buboes) that develop in the afferent lymphatic chain draining the site of the flea bite. Patients with pneumonic plague often have many of the above signs and symptoms, as well as cough, breathing difficulties and, in later stages of the illness, bloody sputum.

Prevention

Vaccine

Plague vaccine is no longer commercially available. Vaccination against plague is not required by any country as a condition for entry. In the past, vaccine was recommended only for persons who were at a particularly high risk of exposure because they worked with plague routinely in the laboratory or because of field exposures to rodents and their fleas in epizootic areas. In most of the countries of Africa, Asia, and the Americas where plague is reported, the risk of infection exists primarily in rural mountainous or upland areas. Persons who travel to plague-infected areas should follow the preventive measures described in the following section.

Other

Travellers considered at high risk for plague because of unavoidable exposures in active epizootic or epidemic areas should be advised to consider antibiotic chemoprophylaxis with tetracycline or doxycycline during periods of exposure. Trimethoprim-sulfamethoxazole is an acceptable substitute for use in infants and children <8 years of age. Personal protective measures should also be recommended, including the use of insect repellents containing DEET on skin and clothing. (See Protection against Mosquitoes and Other Arthropods.) Clothing also can be treated with insecticidal sprays containing permethrin. Travellers should be advised to avoid sick or dead animals or rodent nests and burrows. Whenever possible, travellers should also avoid visiting areas where recent plague epidemics or epizootics have occurred. Travellers are unlikely to be at high risk for plague while staying in modern accommodations.

Treatment

Human plague can be fatal unless cases are promptly treated with appropriate antibiotics. The preferred treatment is streptomycin, although gentamicin, tetracycline, and doxycycline are considered to be effective alternatives. Chloramphenicol has been used to treat human plague and is recommended for conditions that require high tissue penetration of the antibiotic agent, including plague meningitis, pleuritis, endophthalmitis, or myocarditis. Human plague cases also have been treated successfully with trimethoprim-sulfamethoxazole, but this agent is not considered to be a primary choice for therapy. An infectious diseases specialist should be consulted.

Bibliography
  • CDC. Prevention of plague. Recommendations of the Advisory Committee on Immunisation Practices (ACIP). MMWR Morbid Mortal Wkly Rep 1996; 45:RR-14.
  • Dennis DT. Plague. In: Guerrant RL, Krogstad DJ, Maguire JH, et al., eds. Tropical Infectious Diseases: Principles, Pathogens, and Practice, 1999. pp. 506-16.
  • Dennis DT. Plague, Method of. In: Rakel RE, ed., Conn's Current Therapy. W.B. Saunders, Co., Philadelphia, PA., 2001. pp. 115-7.
  • Dennis DT, Gage KL. Plague. In: Infectious Diseases, 2nd ed. Armstrong D, Cohen J. Mosby, Ltd. London. 2003. Vol. 2, Section 6:1641-8.
  • Dennis DT, Meier FA. Plague. In: Horsburgh CR, Nelson AM, eds. Pathology of Emerging Infections. Washington, DC: ASM Press, 1997. pp. 21-47.
  • Gage KL. Plague. In: Collier L, Balows A, Sussman M, general eds.; Hausler WJ, Sussman M, vol. eds. Topley and Wilson's Microbiology and Microbial Infections, 9th Edition. Volume 3, Bacterial Infections. London: Edward Arnold, Ltd. 1998. pp. 885-904.
  • World Health Organization. Human Plague in 2002 and 2003. Wkly Epidemiol Rec. 2004;79:301-8.
  • World Health Organization. Plague Manual. Dennis DT, Gage KL, Gratz N, Poland JD, and Tikhomirov E. (Principal authors). World Health Organization. Geneva, Switzerland. 1999. 172 pp. (Note: This manual is available online at the WHO website.)

- Kenneth Gage

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