Description

Plague, a zoonosis involving rodents and their fleas, is caused by infection with the bacterium Yersinia pestis (1). 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, although 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 (2).

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, including Bolivia, Brazil, Ecuador, and Peru; 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 Burma (Myanmar), China, India, Indonesia, Jordan, Kazakhstan, Laos, Mongolia, and Vietnam (2,3).

Risk for Travelers

Risk for travelers in any of these areas is small. In most of the countries of Africa, Asia, and the Americas where plague is reported, the risk of infection exists primarily in semiarid grassland or rural mountainous areas.

Clinical Description

Plague causes high mortality unless promptly diagnosed and treated. Initial signs and symptoms of plague can be nonspecific, with fever, chills, headache, malaise, myalgia, nausea, and prostration. Bubonic plague, the most common form, is characterized by painful, swollen lymph nodes (buboes) that develop in the afferent lymphatic chain draining the site of the bite from an infected flea. Septicemic plague may be primary when the bacterium invades and multiplies in the bloodstream in the apparent absence of a bubo, or it may also occur secondarily to bubonic plague. 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 (4)

Prevention

Travelers 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 (5). Personal protective measures should also be recommended; including the use of insect repellents containing DEET (see Chapter 2). Clothing also can be treated with insecticidal sprays containing permethrin. Travelers should be advised to avoid sick or dead animals or rodent nests and burrows. Whenever possible, travelers should also avoid visiting areas where recent plague epidemics or epizootics have occurred. Travelers are unlikely to be at high risk for plague while staying in modern accommodations (4,6).

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 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 (4).

Treatment

Human plague can be fatal unless promptly treated with appropriate antibiotics. Historically, streptomycin had been the preferred treatment, but it is no longer available. Gentamicin, tetracycline, and doxycycline are considered to be effective alternatives (6,7). 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. Ciprofloxacin may also be effective, and, along with doxycycline, are recommended for mass treatment or prophylaxis (8). An infectious diseases specialist should be consulted (6).

References

1. Gage KL. Plague. In: Topley and Wilson’s Microbiology and Microbial Infections. 9th ed. Collier L, Mahy BW, Balows A, Sussman M, general eds; Hausler WJ, Sussman M, vol. 3 eds. 1998, Edward Arnold, Ltd.: London. p. 885-904.
2. World Health Organization. Human plague in 2002 and 2003. Wkly Epidemiol Rec. 2004;79:301-8.
3. World Health Organization. Plague manual. 1999, Geneva, Switzerland: World Health Organization.
4. Dennis DT. Plague. In: Tropical Infectious Diseases: Principles, Pathogens, and Practice. Guerrant RL, Krogstad DJ, Maguire JH, et al., eds. 1999. p. 506-16.
5. Dennis DT. Plague, Method of. In: Conn’s Current Therapy. Rakel RE, ed. 2001, W.B. Saunders, Co.: Philadelphia, PA. p. 115-7.
6. Centers for Disease Control and Prevention. Prevention of plague: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morbid Mortal Wkly Rep. 1996;45(RR-14): 1-15.
7. Dennis DT, Chow CC. Plague. Pediatr Infect Dis J. 2004;23:69-71.
8. Inglesby TV, Dennis DT, Henderson DA, Bartlett JG, Ascher MS, Eitzen E, et al. Plague as a biological weapon: medical and public health management. Working Group on Civilian Biodefense. JAMA. 2000;283:2281-90.