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Epidemiologic and clinical characteristics of fatal and nonfatal cases of Rocky Mountain spotted fever (RMSF) were compared to identify risk factors for death caused by this disease. Confirmed and probable RMSF cases reported through US national surveillance for 1981–1998 were analyzed. Among 6388 RMSF patients, 213 died (annual case-fatality rate, 3.3%; range, 4.9% in 1982 to 1.1% in 1996). Use of tetracycline-class antibiotics for treatment of RMSF increased significantly in the 1990s, compared with use in the 1980s. Older patients, patients treated with chloramphenicol only, patients for whom tetracycline antibiotics were not the primary therapy, and patients for whom treatment was delayed ⩾5 days after the onset of symptoms were at higher risk for death. Although the case-fatality rate was lower in the 1990s than in the 1980s, risk factors for fatal RMSF were similar. Despite the availability of effective antibiotics, RMSF-related deaths continue to occur because of delayed diagnosis and failure to use appropriate therapy

A 3-month ecologic investigation was done to identify the reservoir of Ebola virus following the 1995 outbreak in Kikwit, Democratic Republic of the Congo. Efforts focused on the fields where the putative primary case had worked but included other habitats near Kikwit. Samples were collected from 3066 vertebrates and tested for the presence of antibodies to Ebola (subtype Zaire) virus: All tests were negative, and attempts to isolate Ebola virus were unsuccessful. The investigation was hampered by a lack of information beyond the daily activities of the primary case, a lack of information on Ebola virus ecology, which precluded the detailed study of select groups of animals, and sample-size limitations for rare species. The epidemiology of Ebola hemorrhagic fever suggests that humans have only intermittent contact with the virus, which complicates selection of target species. Further study of the epidemiology of human outbreaks to further define the environmental contact of primary cases would be of great value.

By means of a selective DNA amplification technique called polymerase chain reaction, proviral sequences of the human immunodeficiency virus (HIV-1) were identified directly in DNA isolated from peripheral blood mononuclear cells (PBMCs) of persons seropositive but not in DNA isolated from PBMCs of persons seronegative for the virus. Primer pairs from multiple regions of the HIV-1 genome were used to achieve maximum sensitivity of provirus detection. HIV-1 sequences were detected in 100% of DNA specimens from seropositive, homosexual men from whom the virus was isolated by coculture, but in none of the DNA specimens from a control group of seronegative, virus culture-negative persons. However, HIV-1 sequences were detected in 64% of DNA specimens from seropositive, virus culture-negative homosexual men. This method of DNA amplification made it possible to obtain results within 3 days, whereas virus isolation takes up to 3 to 4 weeks. The method may therefore be used to complement or replace virus isolation as a routine means of determining HIV-1 infection.

Mathematical models have been developed to explore the population dynamics of viral diseases among wildlife. However, assessing the predictions stemming from these models with wildlife databases adequate in size and temporal duration is uncommon. An epizootic of raccoon rabies that began in the mid-Atlantic region of the United States in the late 1970s has developed into one of the largest and most extensive in the history of wildlife rabies. We analyzed the dynamics of local epizootics at the county level by examining a database spanning more than 20 years and including 35,387 rabid raccoons. The size, number, and periodicity of rabies epizootics among raccoons were compared with predictions derived from a susceptible, exposed, infectious, and recovered model of raccoon rabies [Coyne, J., Smith, G. & McAllister, F. E. (1989) Am. J. Vet. Res. 50, 2148-2154]. After our methods for defining epizootics were applied to solutions of the model, the time series revealed recurrent epizootics in some counties, with a median first epizootic period of 48 months. Successive epizootics declined in size and the epizootic period progressively decreased. Our reanalysis of the model predicted the initial-epizootic period of 4-5 years, with a progressive dampening of epizootic size and progressive decrease in epizootic period. The best quantitative agreement between data and model assumed low levels of immunity (1-5%) within raccoon populations, suggesting that raccoons develop little or no rabies immune class. These results encourage the use of data obtained through wildlife surveillance in assessing and refining epidemic models for wildlife diseases.

Rocky Mountain spotted fever (RMSF) is the most severe tickborne infection in the United States and is a nationally notifiable disease. Since 1981, the annual case-fatality ratio for RMSF has been determined from laboratory-confirmed cases reported to the Centers for Disease Control and Prevention (CDC). Herein, a description is given of patients with fatal, serologically unconfirmed RMSF for whom a diagnosis of RMSF was established by immunohistochemical (IHC) staining of tissues obtained at autopsy. During 1996–1997, acute-phase serum and tissue samples from patients with fatal disease compatible with RMSF were tested at the CDC. As determined by indirect immunofluorescence assay, no patient serum demonstrated IgG or IgM antibodies reactive with Rickettsia rickettsii at a diagnostic titer (i.e., ⩾64); however, IHC staining confirmed diagnosis of RMSF in all patients. Polymerase chain reaction validated the IHC findings for 2 patients for whom appropriate samples were available for testing. These findings suggest that dependence on serologic assays and limited use of IHC staining for confirmation of fatal RMSF results in underestimates of mortality and of case-fatality ratios for this disease.

The incidence of rabies in humans in the United States is low. However, contacts with potentially rabid animals result in thousands of human rabies postexposure prophylaxis treatments (PEPs) each year. PEP is expensive, not without risk of adverse reactions, and in many instances unnecessary. Increased reports of cases of rabies in animals (4,880 cases in 1990, 9,495 in 1993, and 7,124 in 1996) suggested that PEPs could be increasing. Application of 1981 PEP incidence rates gave an estimate of approximately 16,000 PEPs during 1996, while calculations based on annual sales of a rabies biological during 1996 gave an estimate of approximately 39,000 PEPs. Appropriate usage of PEP requires careful evaluation of human exposure scenarios and adherence to approved guidelines.

An outbreak of hantavirus pulmonary syndrome (HPS) in the southwestern United States was etiologically linked to a newly recognized hantavirus. Knowledge that hantaviruses are maintained in rodent reservoirs stimulated a field and laboratory investigation of 1696 small mammals of 31 species. The most commonly captured rodent, the deer mouse (Peromyscus maniculatus), had the highest antibody prevalence (30%) to four hantavirus antigens. Antibody also was detected in 10 other species of rodent and in 1 species of rabbit. Reverse transcriptase-polymerase chain reaction (RT-PCR) products of hantavirus from rodent tissues were indistinguishable from those from human HPS patients. More than 96% of the seropositive P. maniculatus were positive by RT-PCR, suggesting chronic infection. Antibody prevalences were similar among P. maniculatus trapped from Arizona (33%), New Mexico (29%), and Colorado (29%). The numeric dominance of P. maniculatus, the high prevalence of antibody, and the RT-PCR findings implicate this species as the primary rodent reservoir for a new hantavirus in the southwestern United States.

Rabies is caused by a single-stranded, negative-sense RNA virus, maintained in nature by a variety of animal reservoirs. Rabies virus infects the central nervous system, resulting in progressive encephalopathy and ultimately death in an infected human. Globally, the risk of contracting rabies for humans is greatest in regions of the developing world where dog rabies is enzootic. Where rabies in dogs has been eliminated or otherwise controlled through vaccination programs, the disease can be maintained by wildlife. Wildlife primarily involved in maintenance of transmission cycles are carnivores and bats. Persons having frequent contact with wildlife, such as mammalogists, are at greater risk than the general population for exposure to rabid animals. Rabies prevention can be achieved by elimination of exposure and by vaccination through preexposure prophylaxis and postexposure treatment. Preexposure rabies prophylaxis affords a measure of protection for unrecognized rabies exposures and simplifies postexposure treatment. Postexposure treatment is recommended following exposure to a potentially rabid animal and involves treatment of wound and administration of rabies vaccine as well as rabies immune globulin for individuals not previously vaccinated. Future research on rabies is necessary to define the effects of infection on wildlife populations and to evaluate the potential for intervening in wildlife transmission using oral rabies vaccines.

In studies of Lassa fever in Sierra Leone, the prevalence. of human antibody to Lassa virus ranged from 8% to 52%. Mastomys natalensis, the reservoir of Lassa virus, constituted 50%–60% of the rodents captured in houses but only 10%–20% of those captured in surrounding agriculture and bush areas (χ2 = 90.2, P < 10−6 , dƒ = 1), a finding suggesting that houses are the most-important location for transmission of Lassa virus. Viral infection of Mastomys from houses ranged from 0% to 80%. The incidence of seroconversions in susceptible persons ranged from 5% to 22% per year; the ratio of illness to infection ranged from 9% to 26%, and the proportion of febrile illness associated with seroconversion was 5%–14%. Eightfold rises in titer of antibody occurred in 1%–18% of the antibody-positive population, a result suggesting reinfection. We estimate the ratio of fatalities to infection to be 1%–2%, a rate lower than estimates based on hospitalized cases. The high incidence of Lassa fever makes it a major problem in West Africa.

In May 1993, an outbreak of hantavirus pulmonary syndrome (HPS) occurred in the southwestern United States. A case-control study determined risk factors for HPS. Seventeen case-patients were compared with 3 groups of controls: members of case-patient households (household controls), members of neighboring households (near controls), and members of randomly selected households ⩾24 km away (far controls). Investigators trapped more small rodents at case households than at near (P = .03) or far control households (P = .02). After the number of small rodents was controlled for, case-patients were more likely than household controls to hand plow (odds ratio [OR], 12.3; 95% confidence interval [CI], 1.1-143.0) or to clean feed storage areas (OR, 33.4; 95% CI, 1.7-666.0). Case-patients were more likely than near controls to plant (OR, 6.2; 95% CI, 1.1-34.0) and more likely than far controls to clean animal sheds (OR, 11.9; 95% CI, 1.4-103.0). Peridomestic cleaning, agricultural activities, and an increased number of small rodents at the household were associated with HPS.