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Human Plague -- United States, 1988
As of September 1, 14 nonfatal cases of human plague had been reported in the United States during 1988 (Table 1). Ten cases were in males, and patients' ages ranged from 8 to 82 years. One case occurred in February, three in June, six in July, and four in August. Each resulted from exposure to sources of wild rodent plague in the western United States: four cases were acquired in Colorado, six in New Mexico, two in California, and one each in Arizona and Texas. The cases in Pecos County, Texas, and Costilla County, Colorado, are the first human cases reported from these counties, although wild rodent plague has been detected frequently in both areas.
Seven of the cases presented interesting epidemiologic and/or clinical features:
Case 1. A 41-year-old man was exposed while training falcons in rural areas near Fort Stockton, Pecos County, Texas. The patient presumably acquired infection from a falcon, either through a talon scratch or transfer of an infected flea acquired from rodent prey. The patient developed a left axillary bubo, indicating the site of infection. He denied rodent and ectoparasite contact and claimed his falcons were trained to prey on birds. Immediately before and during his onset of illness, a widespread plague epizootic was occurring in west Texas (12 counties) among Cotton rats (Sigmodon hispidus), field mice (Peromyscus species), wood rats (Neotoma albigula), and cottontail rabbits (Sylvilagus auduboni).
Case 2. A 30-year-old male Albuquerque resident acquired his plague infection by skinning a cottontail rabbit in Costilla County, Colorado. He became ill June 3, 2 days after skinning the rabbit. Usually, cases associated with rabbit hunting occur between October and February.
Case 3. Illness in a 12-year-old Zuni Indian boy was diagnosed promptly as plague and treated with oral tetracycline and intravenous gentamicin. He appeared to recover until the sixth day after onset, when he had headaches and recurrence of fever. Physical examination revealed spinal rigidity, and plague meningitis was diagnosed. The boy then was given chloramphenicol and has recovered.
Case 4. An 82-year-old male summer resident of Salida, Chaffee County, Colorado, was hospitalized after he had been found semicomatose approximately 36 hours after collapsing in his home. He was initially treated for cardiac arrythmia (supraventricular tachycardia). Plague was suspected on the third day of hospitalization when an inguinal bubo was noted and the patient revealed he had been shooting prairie dogs and ground squirrels near his summer home.
Case 7. A 19-year-old male Army recruit had received 0.1 mL Plague Vaccine, U.S.P. (Cutter Biological) intramuscularly (IM) in August 1987 and a 0.2 mL booster dose IM in November 1987. On July 14, 1988, he had onset of illness and was hospitalized with fever, malaise, an inguinal bubo, and multiple insect bites on both legs. He was treated with tetracycline and chloramphenicol and recovered. Exposure to infection probably occurred during military training maneuvers at Fort Hunter Liggett in Monterey County, California. This area is a plague focus that principally involves California ground squirrels (Spermophilus beecheyi) and their fleas. During a field investigation in the maneuver area, an intensive localized epizootic was detected and Yersinia pestis isolated from fleas.
Case 8. A 23-year-old man who resides in Houston, Texas, was exposed to infection while vacationing in the Vallecito Reservoir area northeast of Durango, La Plata County, Colorado. Environmental investigations of the reservoir area revealed an epizootic in golden mantled ground squirrels (Spermophilus lateralis).
Case 14. A 37-year-old woman residing in Kingman, Arizona, had onset of illness on June 24 and was hospitalized June 26. Gram-negative rods isolated from blood cultures were not identifiable by the hospital laboratory and were sent to the Arizona State Public Health Laboratory for identification. However, the culture was grossly contaminated and could not be tested. The patient had been treated with various antibiotics, including gentamicin, and had recovered without complications after 18 days of hospitalization. In late August, the hospital laboratory, in evaluating a new bacterial identification system, tested a culture from the patient and identified it as Y. pseudotuberculosis. The state health laboratory identified and CDC confirmed the culture as Y. pestis.
The source of this patient's infection is unknown. She had traveled with her dog to northern Arizona, including the plague-endemic areas of Coconino and Gila counties, and had been back in the Kingman area--not known as a plague focus--for 9-10 days before onset. The interval between her return home and onset of illness supports the hypothesis that her dog acquired plague-infected fleas during the trip and that one or more of these bit the patient sometime after her return.
Other cases. The remaining cases of confirmed plague infections in 1988 were clinically typical of plague. The cases originated in plague-endemic areas of New Mexico, Arizona, or California, and illnesses were diagnosed early and treated appropriately. Reported by: J Doll, PhD, SJ Englender, MD, State Epidemiologist, Arizona Dept of Health Svcs. SB Werner, MD, BC Nelson, PhD, J Wong, MS, KH Acree, MD, State Epidemiologist, California Dept of Health Svcs. R Johnson, CAPT, USA MEDDAC, Fort Ord, California; JH Nelson, COL, US Army Health Svc Command, San Antonio, Texas. D Arnett, MD, Salida Hospital, Salida; J Pape, R Hoffman, MD, State Epidemiologist, Colorado Dept of Health. L Nims, MS, Scientific Laboratory Div, Albuquerque; T Brown, MS, Environmental Improvement Agency, Santa Fe; M Sewall, MD, HF Hull, MD, State Epidemiologist, New Mexico Dept of Health and Environment. W Rosser, DVM, Texas Dept of Health, Lubbock; G Moore, MS, Texas Dept of Health, El Paso; TG Betz, MD, State Epidemiologist, Texas Dept of Health. Plague Br, Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.
Editorial Note: More than 90% of human plague infections occur in the southwestern United States--particularly in New Mexico, Arizona, California, and Colorado (1; CDC, unpublished data). However, plague may occur in residents of or visitors to areas of other western states. In 1988, three of the four Colorado patients (cases 1, 4, and 8) were visitors to the state, and all were hospitalized in areas where human plague is occasionally recognized. Diagnosis would probably have occurred later for two of the patients had they returned to their nonendemic home states before onset of illness. The Arizona patient (case 14) probably was exposed to infected fleas that infested her dog while she and her dog visited plague-endemic areas of the state. She developed an inguinal bubo, consistent with cases of flea-bite origin.
Typically, more than half of human plague cases occur in males (137 (57%) of the 239 cases from 1975 to 1987), and approximately half occur in persons less than 20 years old (1; CDC, unpublished data). Ten (71%) of the 14 cases in 1988 have been in males, and the mean patient age was 30.1 years, although this average is skewed by the two patients greater than 75 years of age.
From 1975 through 1987, 30% of all human plague cases were in Native Americans (2). This trend continues in 1988; four (29%) of the 14 patients were members of the Navajo and Zuni Tribes. Risk factors for Native Americans include residence in plague foci and lifestyle (e.g., sheepherding, hunting of prairie dogs and rabbits, and living in rustic dwellings (e.g., hogans) that may attract rodents).
Plague Vaccine, U.S.P., is commercially available from Cutter Biological in Berkeley, California, and is recommended for persons repeatedly exposed to possible plague infection (laboratory personnel or persons with frequent and regular contact with rodents in plague-infected areas). The manufacturer's recommended adult dosage is one dose of 1.0 mL, followed by a second dose of 0.2 mL given 4-12 weeks after the first injection. A second booster of 0.2 mL is suggested 3-6 months after the first booster. Additional boosters of 0.1-0.2 mL each are advised at 6-month intervals as long as risk of exposure persists. This schedule differs from that recommended by the Immunization Practices Advisory Committee of the Public Health Service, which suggests two doses of 0.5 mL Plague Vaccine greater than or equal to4 weeks apart, followed by a third dose of 0.2 mL 1-3 months after the second injection (3). The two-dose regimen given in case 7 did not prevent infection or serious illness, although the course of illness might have been more severe without prior vaccination. That patient reportedly had evidence of multiple insect bites on the legs, and the severity of illness may have been related to the dose of plague organisms inoculated.
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