Human Plague -- United States, 1993-1994
From 1944 through 1993, 362 cases of human plague were reported in the United States; approximately 90% of these occurred in four western states with endemic disease (Arizona, California, Colorado, and New Mexico) (1). During each successive decade of this period, the number of states reporting cases increased from three during 1944-1953 to 13 during 1984-1993 (Figure_1), indicating the spread of human plague infection eastward to areas where cases previously had not been reported. In 1993, health departments in four states reported 10 confirmed cases * of human plague to CDC; one case has been confirmed during 1994 **. This report summarizes information about the 11 cases of human plague reported during 1993-1994 and describes epidemiologic and epizootic trends of plague in the United States.
In 1993, the 10 confirmed cases of human plague were reported from New Mexico (six cases), Colorado (two), Texas (one), and Utah (one) (Table_1). Persons with plague infection were aged 22-96 years (median: 55.5 years); five were aged greater than or equal to 67 years. Six cases occurred among men. Five cases occurred during June-August, three during March-May, and two during September- November. Seven persons were exposed at their homesites, and one (a veterinarian) was exposed at work; exposure sites could not be determined for two cases. Seven cases were bubonic plague; two, primary septicemic; and one, primary pneumonic. Nine of the 10 patients recovered with antibiotic therapy; one patient died (Table_1).
For three patients, the probable mode of transmission was flea bite (based on the presence of an inguinal bubo or a recollection of flea bites). Two patients (including the veterinarian) were infected by domestic cats with visible signs of plague infection (i.e., oral lesions and a swollen tongue). For five cases (including the fatal case), the probable mode of transmission could not be determined; however, evidence of plague infection in local animal populations was detected in association with three of these cases (Table_1).
In 1994, plague infection has been confirmed in a 56-year-old resident of Inyo County, California, who had onset of illness on January 1 (the first report in California of a human plague case during winter since 1928) (Table_1). The patient lived in a county where plague was known to be endemic. In addition, he had recently worked in a subterranean gold mine and slept in a cabin at the minesite; signs of rodent activity were found in the mine shaft and the cabin outbuildings.
Reported by: SB Werner, MD, R Murray, DrPH, K Reilly, DVM, M Madon, MS, M Jay, DVM, C Smith, MS, B Wilson, MS, J Wang, MS, RJ Jackson, MD, California Dept of Health Svcs; R Hurd, J Levesque, MD, Inyo County Health Dept, Independence, California. J Pape, MS, T Davis, MS, RE Hoffman, MD, State Epidemiologist, Colorado Dept of Health. R Stoneberg, Montana Dept of Fish, Wildlife, and Parks; TA Damrow, PhD, State Epidemiologist, Montana State Dept of Health and Environmental Sciences. C Montman, Albuquerque Environmental Health Dept; T Brown, MS, P Reynolds, M Tanuz, New Mexico Environment Dept; M Eidson, DVM, CM Sewell, DrPH, State Epidemiologist, New Mexico Dept of Health. S Lanser, MPH, R Tanner, MPA, CR Nichols, MPA, State Epidemiologist, Utah Dept of Health. W Kramer, Nebraska State Dept of Health. TG Murnane, DVM, BN Hicks, PV Thomas, DVM, J Buck, J Taylor, MPH, GM Moore, MS, Texas Dept of Health; J Wood, City of Dallas, C Vaughn, MS, C Haley, MD, R Farris, MD, Dallas County Health Dept, Dallas. DR Akin, P Bohan, MS, R Enscore, MS, J Sarisky, MPH, L Courtois, Office of Environmental Health, Indian Health Svc. L Handegard, MT Billings, D Virchow, NE Scottsbluff, Animal and Plant Health Inspection Svc, Animal Damage Control, US Dept of Agriculture. RJ Andrascik, Theodore Roosevelt National Park, National Park Svc, North Dakota. Div of Field Epidemiology, Epidemiology Program Office; Bacterial Zoonoses Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.
Editorial Note: The findings in this report emphasize the increasing importance of two related trends in the epidemiology of human plague in the United States: 1) increased peridomestic transmission and 2) the role of domestic cats as sources of human infection. Peridomestic transmission is especially important in the most highly plague-endemic states of Arizona, Colorado, and New Mexico, where rapid suburbanization has resulted in increasing numbers of persons living in or near active plague foci. Domestic cats that are permitted to roam freely in areas where plague occurs in rodents are at increased risk for infection and, therefore, increase the risk for peridomestic transmission to humans. Before 1977, domestic cats were not reported as sources of human plague infection; however, since 1977, cats have been identified as the source of infection for 15 human plague cases. In addition, the proportion of human plague cases with primary pneumonic plague has been substantially higher among cat-associated cases (four of 15 cases) than among cases for which cats were not sources of infection (one of 236 cases). Persons working in veterinary practices should be warned of the risks associated with handling plague-infected cats. Four of the 15 cat-associated cases occurred in veterinarians or their assistants. In addition, CDC recommends that veterinary personnel wear gloves and eye protection and take appropriate respiratory precautions (2) when examining sick cats in or from plague-endemic areas, especially cats with lymphadenopathy, oral lesions, or pneumonia.
Surveillance for plague in rodent and rodent-consuming carnivore populations during the 1990s indicates that plague has spread eastward to counties in areas (e.g., eastern Montana, western Nebraska, western North Dakota, and eastern Texas) believed to be free of this disease since widespread animal surveillance began in the 1930s (3-5). For example, the potential for human plague cases in eastern Texas was demonstrated in 1993 when an infected roof rat (Rattus rattus) and two infected fox squirrels (Sciurus niger) were identified in Dallas. Animal surveillance was initiated in the Dallas metropolitan area to monitor plague in local rodent and carnivore populations as a sentinel of increased risk for plague among humans. The continued expansion of human plague in the United States (Figure_1) underscores the need to enhance plague surveillance and to increase efforts to prevent, detect, and control human plague.
Epizootic plague activity usually peaks during or immediately after years with cooler temperatures and more rain than usual. Such conditions occurred during 1991-1993 in the highly plague-endemic areas of Arizona, Colorado, and New Mexico, as well as in the western Great Plains region, *** and resulted in large populations of many plague-susceptible rodent species -- including deer mice, the principal reservoir of hantavirus in the western United States (6).
Nearly all fatal plague cases in the United States result from delays in seeking treatment and in making the proper diagnosis. The person with fatal plague in 1993 received medical care 6 days after onset of illness and died within 4-6 hours of seeking care at a hospital. Because of similarities in clinical features of plague and the recently discovered hantavirus pulmonary syndrome (HPS) (7), diagnosis of plague may be further complicated. In 1993, HPS was suspected in a person with secondary pneumonic plague; as a result, the patient was transported to a regional medical center in another state for specialized care. At this facility, plague was diagnosed, and the patient recovered with antibiotic treatment. Increasing public and physician awareness about plague can assist in prompt diagnosis and treatment.
Efforts to prevent plague should include public education about risk factors for exposure, methods to prevent plague, and the signs and symptoms of infection; surveillance of rodent populations; and use of insecticides, and occasionally rodenticides, to control populations of fleas and rodents, respectively. Control measures should be undertaken when surveillance indicates epizootic activity among rodent populations.
* A case of human plague is considered to be confirmed when 1) a bacterial culture is identified as Yersinia pestis by biochemical testing and bacteriophage typing or 2) there is a fourfold rise in antibody titers to the F-1 antigen of Y. pestis.
** Provisional data.
*** West North Central, West South Central, and Mountain regions.
TABLE 1. Confirmed human plague cases -- United States, 1993-1994 * ============================================================================================================================================================== Probable Clinical form mode of Epidemiologic/ State/County Date Age (yrs)/ (Bubo location)/ Exposure transmission epizootic of residence of onset Sex Recovery status site or source findings ------------------------------------------------------------------------------------------------------------------------------------------------------------ New Mexico/ Sandoval March 13, 1993 44/M Bubonic (axillary)/ Home Scratch of infected Infected woodrats and woodrat fleas Recovered cat recovered at exposure site; probable rock squirrel die-off a few months before patient became ill. Texas/Kent April 24, 1993 96/F Bubonic (cervical)/ Home Undetermined Infected fleas recovered from rabbit Recovered captured near house; probable woodrat die- off; persons visiting patient's house bitten by fleas; patient had trapped rodents in house. Colorado/ Boulder May 19, 1993 31/F Primary pneumonic/ Work/ Inhaled infectious None. Recovered Veterinary aerosol while Office examining infected cat New Mexico/ Rio Arriba June 28, 1993 71/F Bubonic (axillary)/ Home Undetermined Infected flea pool recovered from deer Recovered mouse trapped near patient's home; patients's cat disappeared a few days before patient became ill. New Mexico/ Bernalillo July 4, 1993 68/M Septicemic/Died Home Undetermined Rock squirrel epizootic near patient's home; patient's dog was seropositive. New Mexico/ San Juan July 24, 1993 22/F Bubonic (axillary)/ Undeter- Undetermined None. Recovered mined New Mexico/ Rio Arriba August 8, 1993 35/M Bubonic (inguinal)/ Home Flea bite None. Recovered Colorado/ La Plata August 17, 1993 40/M Bubonic (inguinal) Home Flea bite Rock squirrel epizootic near home; two family Recovered dogs were seropositive. Utah/Salt Lake October 2, 1993 67/M Bubonic (axillary)/ Undeter- Undetermined None. Recovered mined New Mexico/ Santa Fe October 3, 1993 73/F Septicemic/ Home Flea bite Rock squirrel epizootic near home: plague- Recovered infected rabbit found dead near home; rabbit infected with plague-infected rock squirrel fleas. California/ Inyo January 1, 1994 56/M Septicemic/ Undeter- Undetermined 12 dogs and 3 cats living at or near the Recovered + mined patients's home were seronegative; evidence of rodent activity found at or near patient's home. ------------------------------------------------------------------------------------------------------------------------------------------------------------ * Data for 1994 are provisional. + Four weeks following recovery and discharge from the hospital, the patient died from an acute myocardial infarction; he had a history of heart disease. ==============================================================================================================================================================
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