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Plague -- United States, 1992

From January 1 through October 15, 1992, 11 human plague cases, including one described recently (1), have been reported in the United States. This report summarizes the epidemiologic information on these cases and provides recommendations for control of plague.

Three of the 11 cases occurred among young children (aged less than or equal to 6 years); eight occurred among adolescents and adults (Table 1). Ten cases occurred among males. Four of the cases occurred among American Indians (three among Navajo and one in a Paiute Indian). Four cases were reported from Arizona, three from New Mexico, and one each from California, Idaho, Nevada, and Utah. Fleas were implicated as the source of infection in seven cases, domestic cats in two, and a wild rodent carcass in one; the source of one case was undetermined. In six cases, the infective exposure probably occurred near the patient's residence. All but one patient recovered with antibiotic treatment.

Reported by: J Doll, PhD, TM Fink, C Levy, MS, L Sands, DO, Acting State Epidemiologist, Arizona Dept of Health Svcs. R Roberto, MD, C Smith, California Dept of Health Svcs. FR Dixon, MD, State Epidemiologist, Div of Health, Idaho Dept of Health and Welfare. J Pierce, MS, D Brus, DVM, State Epidemiologist, Div of Health, Nevada State Dept of Human Resources. C Montman, Albuquerque Environmental Health Dept; T Brown, MS, P Reynolds, M Eidson, DVM, CM Sewell, DrPH, State Epidemiologist, New Mexico Health Dept. S Lanser, MPH, R Tanner, MPA, CR Nichols, MPA, State Epidemiologist, Utah Dept of Health. DR Akin, P Bohan, W Emery, R Fulgham, Office of Environmental Health, Indian Health Svc. Div of Field Epidemiology, Epidemiology Program Office; Bacterial Zoonoses Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: From 1950 through 1991, 336 cases of plague were reported in the United States (Figure 1) (2; CDC, unpublished data, 1991); more than half (194 [58%]) of these have occurred since 1980. Yersinia pestis, the etiologic agent of plague, is maintained in the western United States as an enzootic infection of rodents and their fleas (3,4). Humans become infected through contact with infected animals or fleas, usually during epizootics among rodent species (3). Although human plague cases were reported in 13 western states during 1950-1991, Arizona (14%), California (10%), Colorado (10%), and New Mexico (56%) reported 302 (90%) of the cases, and 97 (29%) were among American Indians. The Navajo composed 77 (23%) of the total cases and 79% of the cases among American Indians (5). The Paiute case-patient is the first reported among this tribe and the first human plague case reported in northeastern Nevada/southwestern Idaho.

American Indians are disproportionately represented among plague cases in the United States, possibly because they frequently reside in rural areas where plague is enzootic among rodents. Because prairie dogs (Cynomys spp.) are abundant and extremely susceptible to plague, they are a major amplifying host throughout the Southwest, including the Navajo Nation (3-5). Epizootics also frequently involve rock squirrels (Spermophilus variegatus), usually in conjunction with prairie dog epizootics. Rock squirrels have a predilection for habitats created by human activity and often live in peridomestic sites (e.g., abandoned cars, rock walls, and mobile-home foundations). Other reasons for the high proportion of plague cases among the Navajo include traditional involvement in pastoral activities such as sheep-herding, which place Navajos in close contact with rodent habitat; killing of prairie dogs for consumption by humans and by domestic animals; and ownership of free-roaming dogs and cats.

The cyclical pattern of plague cases in humans probably reflects the secular trend of plague epizootics in rodents (3). Epizootics among ground squirrels and prairie dogs cause major reductions in the populations of these animals, such as the depopulation following the large southwestern epizootic that occurred during 1983-1985 (CDC, unpublished data, 1991). The recent recovery of these rodent populations (CDC, unpublished data, 1991) suggests that increased risk for human cases will persist into 1993 and beyond.

Plague surveillance and control in enzootic areas should include 1) monitoring die-offs in rodent populations using the public to report sightings of dead animals and reductions in colony size; 2) educating the medical and veterinary communities concerning the manifestations and diagnosis of plague -- including the pneumonic syndrome (1) -- and procedures for reporting suspected cases; 3) systematic monitoring of rodent plague activity in populated areas by public health personnel, and controlling fleas in areas of rodent epizootics near places of human activity; and 4) educating the public about the role of domestic animals, such as cats and dogs, in zoonotic transmission of the disease, including information about control of fleas on pets and confinement of pets.

References

  1. CDC. Pneumonic plague -- Arizona, 1992. MMWR 1992;41:737-9.

  2. CDC. Summary of notifiable diseases, United States, 1990. MMWR 1990;39(no. 53):3.

  3. Barnes AM. Surveillance and control of bubonic plague in the United States. Symp Zool Soc Lond 1982;50:237-70.

  4. Barnes AM. Plague in the U.S.: present and future. In: LR Davis, RE Marsh, eds. Proceedings of the Vertebrate Pest Conference. Davis, California: University of California-Davis, 1990:43-6.

  5. Barnes AM, Quan TJ, Beard ML, Maupin GO. Plague in American Indians, 1956-1987. In: CDC surveillance summaries (July 1988). MMWR 1988;37(no. SS-3):11-6.



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