Animal-based national surveillance for zoonotic disease: quality, limitations, and implications of a model system for monitoring rabies

Surveillance for zoonotic diseases among wildlife is a research and public health challenge. The inherent limitations posed by the requisite human-animal interactions are often undefined and underappreciated. The national surveillance system for animal rabies in the United States was examined as a model system; reporting of animal rabies is legally mandated, each case of rabies is laboratory confirmed, and data have been consistently collected for more than 50 years. Factors influencing the monthly counts of animal rabies tests reported during 1992-2001 were assessed by univariate and multivariable regression methods. The suitability of passively collected surveillance data for determining the presence or absence of the raccoon-associated variant of rabies within states and within individual counties was assessed by determining critical threshold values from the regression analyses. The size of the human population and total expenditures within a county accounted for 72% and 67%, respectively, of the variance in testing. The annual median number of rabies tests performed was seven for counties without rabies, 22 for counties with non-raccoon rabies, and 34 for counties with raccoon rabies. Active surveillance may be required in locales with sparse human populations when a high degree of confidence in the status of rabies is required.

Assessing the role of long-distance translocation and spatial heterogeneity in the raccoon rabies epidemic in Connecticut

Spatial heterogeneity and long-distance translocation (LDT) play important roles in the spatio-temporal dynamics and management of emerging infectious diseases and invasive species. We assessed the influence of LDT events on the invasive spread of raccoon rabies through Connecticut. We identified several putative LDT events, and developed a network-model to evaluate whether they became new foci for epidemic spread. LDT was fairly common, but many of the LDTs were isolated events that did not spread. Two putative LDT events did appear to become nascent foci that affected the epidemic in surrounding townships. In evaluating the role of LDT, we simultaneously revisited the problem of spatial heterogeneity. The spread of raccoon rabies is associated with forest cover--rabies moves up to three-times slower through the most heavily forested townships compared with those with less forestation. Forestation also modified the effect of rivers. In the best overall model, rabies did not cross the river separating townships that were heavily forested, and the spread slowed substantially between townships that were lightly forested. Our results suggest that spatial heterogeneity can be used to enhance the effects of rabies control by focusing vaccine bait distribution along rivers in lightly forested areas. LDT events are a concern, but this analysis suggests that at a local scale they can be isolated and managed.

Persistence of elevated rabies prevention costs following post-epizootic declines in rates of rabies among raccoons (Procyon lotor)

Determining the benefits to cost relationships among different approaches to rabies control and prevention has been hindered by the inherent temporal variability in the dynamics of disease among wildlife reservoir hosts and a tangible and objective measure of the cost of rabies prevention. A major and unavoidable component of rabies prevention programs involves diagnostic testing of animals and the subsequent initiation of appropriate public health responses. The unit cost per negative and positive diagnostic test outcome can be reasonably estimated. This metric when linked to methodologies subdividing the epizootic process into distinct temporal stages provided the requisite detail to estimate benefits derived from rabies control strategies. Oral rabies vaccine (ORV), for prevention of the raccoon-associated variant of rabies, has been distributed in Ohio and adjoining states in an effort to develop an immune barrier to the westward spread of epizootic raccoon rabies. The costs of ORV delivery have been quantified. Herein, the cost structures required to assess the benefits accrued by prevention were developed. A regression model was developed effectively predicting (r2=0.70) the total number of rabies diagnostic tests performed by 53 counties in five northeastern (NE) states from 1992 to 2001. Five temporal stages sufficed to capture the range of variability in the raccoon rabies epizootic process. Unit costs, dollars per diagnostic test outcome, were calculated for negative and positive results from published reports. Ohio counties were matched to NE counties based on similar socioeconomic characters. A "pseudo-epizootic" of raccoon rabies was introduced into Ohio and the costs savings from ORV were derived as the excess costs imposed by epizootic spread throughout the state. At 46 km/year (range modeled, 30-60 km/year), the pseudo epizootic spread, and reached the enzootic stage, in all Ohio counties by year 13 (range modeled, 11-17 years). Cumulative excess costs for Ohio ranged between $11 and $21 million; counties of low socioeconomic status experienced the greatest relative excess costs. The costs for rabies prevention activities reached apices during the epizootic stage of raccoon rabies (2.7-10.8 times baseline) an unforeseen finding indicated elevated costs persisted (1.7-7.2 times baseline) into the enzootic stage.

Zoonotic viruses of wildlife: hither from yon

The emergence of zoonotic viruses maintained by wildlife reservoir hosts is poorly understood. Recent discoveries of Hendra (HENV) and Nipah (NIPV) viruses in Australasia and the emergence of epidemic West Nile virus (WNV) in the United States have added urgency to the study of cross-species transmission. The processes by which zoonotic viruses are transmitted and infect other species are examined as four transitions. Two of these, inter-species contact and cross-species virus transmission (spillover), are essential and sufficient to cause epidemic emergence. Sustained transmission and virus adaptation within the spillover host are transitions not required for virus emergence, but determine the magnitude and scope of subsequent disease outbreaks. Ecologic, anthropogenic, and evolutionary factors modify the probability that viruses complete or move through transitions. As surveillance for wildlife diseases is rare and often outbreak-driven, targeted studies are required to elucidate the means by which important zoonotic viruses are maintained and spillover occurs.

Temporal dynamics of rabies in a wildlife host and the risk of cross-species transmission

An epidemiological model was developed for rabies, linking the risk of disease in a secondary species (cats) to the temporal dynamics of disease in a wildlife reservoir (raccoons). Data were obtained from cats, raccoons, and skunks tested for rabies in the northeastern United States during 1992-2000. An epizootic algorithm defined a time-series of successive intervals of epizootic and inter-epizootic raccoon rabies. The odds of diagnosing a rabid cat during the first epizootic of raccoon rabies was 12 times greater than for the period prior to epizootic emergence. After the first raccoon epizootic, the risk for cat rabies remained elevated at levels six- to seven-fold above baseline. Increased monthly counts of rabid raccoons and skunks and decreasing human population density increased the probability of cat rabies in most models. Forecasting of the public health and veterinary burden of rabies and assessing the economics of control programmes, requires linking outcomes to dynamic, but predictable, changes in the temporal evolution of rabies epizootics.

Urban zoonoses caused by Bartonella, Coxiella, Ehrlichia, and Rickettsia species

The last half of the 20th Century witnessed an increase in the occurrence and recognition of urban zoonoses caused by members of the genera Bartonella, Coxiella, Ehrlichia, and Rickettsia, all traditionally considered to be members of the family Rickettsiaceae. In recent years, new human pathogens (Bartonella elizabethae, Bartonella henselae, and Rickettsia felis) have been recognized in urban environments. Other newly recognized pathogens (Ehrlichia chaffeensis and Ehrlichia phagocytophila in the United States) have sylvan zoonotic cycles but are present in urban areas because their vertebrate hosts and associated ectoparasitic arthropod vectors are able to survive in cities. Still other agents, which were primarily of historical importance (Bartonella quintana) or have not traditionally been associated with urban environments (Rickettsia rickettsii), have been recognized as causes of human disease in urban areas. Some diseases that have traditionally been associated with urban environments, such as rickettsialpox (caused by Rickettsia akari) and murine typhus (caused by Rickettsia typhi), still occur in large cities at low or undetermined frequencies and often go undetected, despite the availability of effective measures to diagnose and control them. In addition, alternate transmission cycles have been discovered for Coxiella burnetii, Rickettsia prowazekii, and R. typhi that differ substantially from their established, classic cycles, indicating that the epidemiology of these agents is more complex than originally thought and may be changing. Factors leading to an increase in the incidence of illnesses caused by these bacteria in urban areas include societal changes as well as intrinsic components of the natural history of these organisms that favor their survival in cities. Transovarial and transstadial transmission of many of the agents in their arthropod hosts contributes to the highly focal nature of many of the diseases they cause by allowing the pathogens to persist in areas during adverse times when vertebrate amplifying hosts may be scarce or absent. Domesticated animals (primarily cats, dogs, and livestock) or commensal rodents [primarily Norway rats (Rattus norvegicus) and house mice (Mus musculus)] can serve as vertebrate amplifying hosts and bring these agents and their ectoparasitic arthropod vectors into direct association with humans and help maintain transmission cycles in densely populated urban areas. The reasons for the increase in these urban zoonoses are complex. Increasing population density worldwide, shifts in populations from rural areas to cities, increased domestic and international mobility, an increase in homelessness, the decline of inner-city neighborhoods, and an increase in the population of immunosuppressed individuals all contribute to the emergence and recognition of human diseases caused by these groups of agents. Due to the focal nature of infections in urban areas, control or prevention of these diseases is possible. Increased physician awareness and public health surveillance support will be required to detect and treat existing urban infections caused by these agents, to determine the disease burden caused by them, to design and implement control programs to combat and prevent their spread, and to recognize emerging or resurging infections caused by members of these genera as they occur.

Fort Chaffee revisited: the epidemiology of tick-borne rickettsial and ehrlichial diseases at a natural focus

A retrospective cohort study was conducted among troops training at Fort Chaffee, Arkansas, from May through June 1997, to identify infections caused by tick-borne pathogens. Serum samples were tested by IFAs for antibodies to selected Rickettsia and Ehrlichia species and by an investigational EIA for spotted fever group Rickettsia lipopolysaccharide antigens. Of 1,067 guardsmen tested, 162 (15.2%) had antibodies to one or more pathogens. Of 93 guardsmen with paired serum samples, 33 seroconverted to Rickettsia rickettsii or spotted fever group rickettsiae (SFGR) and five to Ehrlichia species. Most (84.8%) of the personnel who seroconverted to SFGR were detected only by EIA, and seropositivity was significantly associated with an illness compatible with a tick-borne disease. In addition, 34 (27%) of 126 subjects with detectable antibody titers reported a compatible illness. The primary risk factor for confirmed or probable disease was finding > 10 ticks on the body. Doxycycline use and rolling up of long sleeves were protective against seropositivity. The risk of transmission of tick-borne pathogens at Fort Chaffee remains high, and use of the broadly reactive EIA suggests that previous investigations may have underestimated the risk for infection by SFGR. Measures to prevent tick bite and associated disease may require reevaluation.

Spatiotemporal analysis of epizootic raccoon rabies propagation in Connecticut, 1991-1995

The quantitative analysis of pathogen transmission within its specific spatial context should improve our ability to predict and control the epizootic spread of that disease. We compared two methods for calibrating the effect of local, spatially distributed environmental heterogeneities on disease spread. Using the time-of-first-appearance of raccoon rabies across the 169 townships in Connecticut, we estimated local spatial variation in township-to-township transmission rate using Trend Surface Analysis (TSA) and then compared these estimates with those based on an earlier probabilistic simulation using the same data. Both the probabilistic simulation and the TSA reveal significant reduction in transmission when local spatial domains are separated by rivers. The probabilistic simulation suggested that township-to-township transmission was reduced sevenfold for townships separated by a river. The global effect of this sevenfold reduction is to increase the time-to-first-appearance in the eastern townships of Connecticut by approximately 29.7% (spread was from west to east). TSA revealed a similar effect of rivers with an overall reduction in rate of local propagation due to rivers of approximately 22%. The 7.7% difference in these two estimates reveals slightly different aspects of the spatial dynamics of this epizootic. Together, these two methods can be used to construct an overall picture of the combined effects of local spatial variation in township-to-township transmission on patterns of local rate of propagation at scales larger than the immediate nearest neighboring townships.

Rabies epizootics among raccoons vary along a North-South gradient in the Eastern United States

The characteristics of rabies epizootics among raccoons were investigated in 11 eastern states along a North-South gradient from New York to North Carolina. Epizootics were defined as discrete intervals of time of at least 5 months in duration, when reported cases of raccoon rabies from an individual county exceeded the median value of raccoon rabies cases reported by that county over the entire period rabies was present among raccoons in the county. Over the approximately 20-year study period, 35,000 cases of raccoon rabies were reported, and epizootics were detected from 251 (64.4%) of 390 counties. The median annual incidence was 0.14 epizootics per year. During the first defined epizootic in a county, the median total number of raccoons reported rabid was 47, with a median monthly incidence of rabies in raccoons of 3.1. The median lag time from the first report of a rabid raccoon in a county to the beginning of the first epizootic was 4 months. Significant differences in the annual incidence of epizootics and monthly incidence of rabid raccoons during epizootics were observed among different states. Although human population density and per capita health spending within counties were positively associated with increasing magnitude of epizootics, a significant difference in the characteristics of rabies epizootics in northern and southern states was apparent. We hypothesize that environmental conditions and perhaps human influence resulted in rabies epizootics in southern states that were smaller, less-frequent, and lacking in well-defined temporal structure compared with those in northern states.

Rabies surveillance in the United States during 2000

During 2000, 49 states, the District of Columbia, and Puerto Rico reported 7,364 cases of rabies in nonhuman animals and 5 cases in human beings to the Centers for Disease Control and Prevention, an increase of 4.3% from 7,067 cases in nonhuman animals reported in 1999. Ninety-three percent (6,855 cases) were in wild animals, whereas 6.9% (509 cases) were in domestic species (compared wth 91.5% in wild animals and 8.5% in domestic species in 1999). Compared with cases reported in 1999, the number of cases reported in 2000 increased among bats, dogs, foxes, skunks, and sheep/goats and decreased among cats, cattle, horses/mules, raccoons, and swine. The relative contributions of the major groups of animals were as follows: raccoons (37.7%; 2,778 cases), skunks (30.2%; 2,223), bats (16.8%; 1,240), foxes (6.2%; 453), cats (3.4%; 249), dogs (1.6%; 114), and cattle (1.1%; 83). Ten of the 19 states where the raccoon-associated variant of the rabies virus has been enzootic reported increases in the numbers of cases of rabies during 2000. Among those states that have engaged in extensive wildlife rabies control programs, no cases of rabies associated with the epizootic of rabies in raccoons (or in any other terrestrial species) were reported in Ohio, compared with 6 cases reported in 1999. No rabies cases associated with the dog/coyote variant (compared with 10 cases in 1999, including 5 in dogs) were reported in Texas, and cases associated with the gray fox variant of the virus decreased (58 cases in 2000, including 38 among foxes). Reports of rabid skunks exceeded those of rabid raccoons in Massachusetts and Rhode Island, states with enzootic raccoon rabies, for the fourth consecutive year. Nationally, the number of rabies cases in skunks increased by 7.1% from that reported in 1999. The greatest numerical increase in rabid skunks (550 cases in 2000, compared with 192 in 1999) was reported in Texas. The number of cases of rabies reported in bats (1,240) during 2000 increased 25.4% over the number reported during 1999 (989) and represented the greatest contribution (16.8% of the total number of rabid animals) ever recorded for this group of mammals. Cases of rabies reported in cattle (83) and cats (249) decreased by 38.5% and 10.4%, respectively, whereas cases in dogs (114) increased by 2.7% over those reported in 1999. Reported cases of rabies among horses and mules declined 20% from 65 cases in 1999 to 52 cases in 2000. Four indigenously acquired cases of rabies reported in human beings were caused by variants of the rabies virus associated with bats. One case of human rabies acquired outside the United States that resulted from a dog bite was caused by the canine variant of the rabies virus.

Analysis of risk factors for fatal Rocky Mountain Spotted Fever: evidence for superiority of tetracyclines for therapy

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 > or =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.

Evidence of rodent-associated Bartonella and Rickettsia infections among intravenous drug users from Central and East Harlem, New York City

We tested serum samples collected in 1997 and 1998 from a cohort of 204 injection drug users (IDUs) recruited from Central and East Harlem, New York City, New York, for antibodies reactive with seven rickettsial or Bartonella spp. antigens. Rodent-associated Bartonella elizabethae and Rickettsia akari were the primary etiologic agents of interest. The testing panel also included Bartonella henselae, Bartonella quintana, Rickettsia prowazekii, Rickettsia rickettsii, and Rickettsia typhi. The highest prevalence of seroreactive serum samples (46%) was found with B. elizabethae antigens; 10% of the samples reacted with B. henselae antigens, while 2% reacted with B. quintana antigens. Reactivity to the latter two antigens was likely due to cross-reactivity with B. elizabethae antigens in most instances. Among the spotted fever group rickettsiae, 18 (9%) samples reacted with R. akari, including 10 samples (5%) that also reacted with R. rickettsii. Cross-adsorption studies demonstrated that most of the spotted fever group rickettsiae antibodies were due to R. akari infections. Among the typhus group rickettsiae, 5 samples reacted weakly to R. prowazekii antigens, and no samples reacted with R. typhi antigens. These findings suggest that Harlem IDUs are commonly exposed to two rodent-associated zoonotic agents. Further study of IDU populations may help elucidate transmission cycles of these agents in inner cities where higher levels of transmission occur.

Infections with Ehrlichia chaffeensis and Ehrlichia ewingii in persons coinfected with human immunodeficiency virus

The clinical course and laboratory evaluation of 21 patients coinfected with human immunodeficiency virus (HIV) and Ehrlichia chaffeensis or Ehrlichia ewingii are reviewed and summarized, including 13 cases of ehrlichiosis caused by E. chaffeensis, 4 caused by E. ewingii, and 4 caused by either E. chaffeensis or E. ewingii. Twenty patients were male, and the median CD4(+) T lymphocyte count was 137 cells/microL. Exposures to infecting ticks were linked to recreational pursuits, occupations, and peridomestic activities. For 8 patients, a diagnosis of ehrlichiosis was not considered until > or =4 days after presentation. Severe manifestations occurred more frequently among patients infected with E. chaffeensis than they did among patients infected with E. ewingii, and all 6 deaths were caused by E. chaffeensis. Ehrlichiosis may be a life-threatening illness in HIV-infected persons, and the influence of multiple factors, including recent changes in the epidemiology and medical management of HIV infection, may increase the frequency with which ehrlichioses occur in this patient cohort.

Persistent infection in Neotoma fuscipes (Muridae: Sigmodontinae) with Ehrlichia phagocytophila sensu lato

Dusky-footed wood rats (Neotoma fuscipes Baird) and two species of Peromyscus mice (P. maniculatus Wagner and P. truei Shufeldt) were collected over a 16-month period from three sites in Sonoma County, California. Blood was collected from 93 wood rats and 177 mice and serum or plasma was tested for seroreactivity with Ehrlichia phagocytophila sensu lato (also known as the human granulocytic ehrlichiosis agent). Thirty-five (37.6%) wood rats and 15 (8.5%) mice were seropositive. Positive Neotoma serology by site ranged from 9.4% to 62.1%. Polymerase chain reaction (PCR) testing for the Ehrlichia groESL heat shock operon was performed on all the seropositive and selected seronegative wood rats; 24 (68.6%) seropositive animals were PCR positive. Two seroconversions and no seroreversions were detected among 18 of the seropositive wood rats that were recaptured and tested multiple times (range = 2-6). Fourteen (77.8%) of the 18 were also PCR positive with six of these positive at every testing point (range = 2-6). One wood rat remained serologically and PCR positive in six specimens collected over a 14-month period. One male of 84 questing adult Ixodes pacificus Cooley & Kohls collected was PCR-positive for E. phagocytophila. Borrelia burgdorferi, the agent of Lyme disease, was cultured from ear punch biopsies from six of seven E. phagocytophila seropositive and one of four seronegative wood rats.

Clinical and serological follow-up of patients with human granulocytic ehrlichiosis in Slovenia

An evaluation of the clinical outcome and the duration of the antibody response of patients with human granulocytic ehrlichiosis (HGE) was undertaken in Slovenia. Adult patients with a febrile illness occurring within 6 weeks of a tick bite were classified as having probable or confirmed HGE based on the outcome of serological or PCR testing. Thirty patients (median age, 44 years) were enrolled, and clinical evaluations and serum collection were undertaken at initial presentation and at 14 days, 6 to 8 weeks, and 3 to 4, 6, 12, 18, and 24 months. An indirect immunofluorescence assay (IFA) was performed, and reciprocal titers of > or =128 were interpreted as positive. Patients presented a median of 4 days after the onset of fever and were febrile for a median of 7.5 days; four (13.3%) received doxycycline. Seroconversion was observed in 3 of 30 (10.0%) patients, and 25 (83.3%) showed >4-fold change in antibody titer. PCR results were positive in 2 of 3 (66.7%) seronegative patients but in none of 27 seropositive patients at the first presentation. IFA antibody titers of > or =128 were found in 14 of 29 (48.3%), 17 of 30 (56.7%), 13 of 30 (43.4%), and 12 of 30 (40.0%) patients 6, 12, 18, and 24 months after presentation, respectively. Patients reporting additional tick bites during the study had significantly higher antibody titers at most time points during follow-up. No long-term clinical consequences were found during follow-up.

Prospective assessment of the etiology of acute febrile illness after a tick bite in Slovenia

A prospective study established the etiology of febrile illnesses in residents of Slovenia that occurred within 6 weeks after a tick bite. A combination of laboratory and clinical criteria identified 64 (49.2%) of 130 patients as having confirmed, probable, or possible cases of tickborne disease during 1995 and 1996. Of the 130 patients, 36 (27.7%) had laboratory evidence of tickborne encephalitis, all of whom had clinically confirmed disease. Evidence of infection with Borrelia burgdorferi sensu lato was identified in 26 patients; 10 (7.7%) had confirmed Lyme borreliosis. Of 22 patients with evidence of Ehrlichia phagocytophila infection, 4 (3.1%) had confirmed ehrlichiosis. Infection by multiple organisms was found in 19 (14.6%) of 130 patients. Patients with meningeal involvement (43 [72.3%] of 59) were more likely to have confirmed tickborne disease than were patients with illness of undefined localization (18 [26.5%] of 68; P<.0001). Tickborne viral and bacterial infections are an important cause of febrile illness in Slovenia.

Rocky Mountain spotted fever in the United States, 1993-1996

During 1993 through 1996, 2,313 cases of Rocky Mountain spotted fever (RMSF) were reported to the Centers for Disease Control and Prevention (CDC) by 42 states and the District of Columbia through the National Electronic Telecommunications System for Surveillance (NETSS). During this same interval, 1,752 case report forms (CRFs) were submitted to CDC and 1,253 (70%) of the cases were categorized as confirmed RMSF by laboratory testing. On the basis of analyses performed with NETSS data, the average annual RMSF incidence during 1993-1996 was 2.2 cases per million persons; the incidence rose from 1.8 in 1993 to 3.3 per million persons in 1996. Incidence for confirmed cases was highest among children 5-9 years of age (3.7 per million) and lowest among individuals older than 70 years of age (1.4 per million). The south Atlantic region accounted for the largest proportion of confirmed cases (52%). The case-fatality rate was highest among persons 70 years of age and older (9.0%) and lowest among adults 40-49 years of age (0.6%).

Serologic evidence of Rickettsia akari infection among dogs in a metropolitan city

OBJECTIVE

To determine whether dogs in New York, NY are naturally infected with Rickettsia akari, the causative agent of rickettsialpox in humans.

DESIGN

Serologic survey.

ANIMALS

311 dogs.

PROCEDURE

Serum samples were obtained from dogs as a part of a study on Rocky Mountain spotted fever and borreliosis or when dogs were examined at area veterinary clinics for routine care. Dog owners were asked to complete a questionnaire inquiring about possible risk factors at the time serum samples were obtained. Samples were tested for reactivity to spotted fever group rickettsiae by use of an enzyme immunoassay (EIA). Twenty-two samples for which results were positive were tested by use of an indirect immunofluorescence antibody (IFA) assay followed by confirmatory cross-absorption testing.

RESULTS

Results of the EIA were positive for 24 (7.7%) dogs. A history of tick infestation and increasing age were significantly associated with whether dogs were seropositive. Distribution of seropositive dogs was focal. Seventeen of the 22 samples submitted for IFA testing had titers to R rickettsii and R akari; for 11 of these, titers to R akari were higher than titers to R rickettsii. Cross-absorption testing indicated that in 6 of 7 samples, infection was caused by R akari.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that dogs can be naturally infected with R akari. Further studies are needed to determine the incidence of R akari infection in dogs, whether infection is associated with clinical illness, and whether dogs can serve as sentinels for human disease.

Mammalian reservoirs and epidemiology of rabies diagnosed in human beings in the United States, 1981-1998

Between 1981 and 1998, 37 cases of rabies were diagnosed in human beings in the United States. Information directly linking the cause of infection to animal bite was available for only eight of these cases. Indirect incrimination of the vector by analysis of cDNA sequences obtained by reverse transcriptase polymerase chain reaction of samples indicated that for all cases (12/12) believed to have been acquired in foreign countries, variants of the rabies virus (VRVs) associated with dogs (7/12 involved known bite histories) were the cause of the rabies infections. In contrast, VRVs associated with bats (bat-associated VRVs or BAVs) were implicated as the cause of 88% (22/25) of infections believed to have been acquired within the United States (1/22 involved known bite histories). Sequence analyses revealed that a single BAV (Ln/Ps), associated with rabid silver-haired (Lasionycteris noctivagans) and Eastern pipistrelle (Pipistrellus subflavus) bats, was implicated in 73% (16/22) of bat-associated infections. Silver-haired bats are predominantly solitary and migratory. Eastern pipistrelle bats may occur individually or in small clusters. Both species are only infrequently submitted for rabies testing. Unrecognized bites and unique properties of the Ln/Ps BAV may explain its association with the majority of rabies infections in human beings in the United States.

Rabies surveillance in the United States during 1999

During 1999, 49 states, the District of Columbia, and Puerto Rico reported 7,067 cases of rabies in nonhuman animals to the Centers for Disease Control and Prevention, a decrease of 11.2% from 7,961 cases in nonhuman animals and 1 case in a human being reported in 1998. More than 91% (6,466 cases) were in wild animals, whereas 8.5% (601 cases) were in domestic species (compared with 92.4% in wild animals and 7.6% in domestic species in 1998). No cases of rabies were reported in human beings in 1999. Decreases were evident in all major species groups, with the exception of cattle, sheep/goats, and swine. The relative contributions of the major groups to the total reported were as follows: raccoons (41.0%; 2,872 cases), skunks (29.4%; 2,076), bats (14.0%; 989), foxes (5.4%; 384), cats (3.9%; 278), cattle (1.9%; 135), and dogs (1.6%; 111). Reported cases (6) associated with the epizootic of rabies in raccoons in Ohio declined from the 26 cases reported in 1998. Fifteen of the 19 states where the raccoon variant of the rabies virus is enzootic reported fewer cases of rabies during 1999. Massachusetts and Rhode Island, states with enzootic rabies in raccoons, each reported more rabid skunks than rabid raccoons for the third consecutive year. In Texas, cases associated with the enzootic canine variants of the rabies virus remained low (10 cases), whereas cases associated with the gray fox variant of the virus increased (66). Cases of rabies in skunks decreased by 8.6%, compared with those reported in 1998. Michigan reported the largest percentage increase in rabid skunks (950.0%; 2 cases in 1998 to 21 in 1999). Cases of rabies in horses and mules declined 21%, from 82 cases in 1998 to 65 in 1999. Cases of rabies reported in bats (989) were similar in number to those reported in 1998 (992) and represented almost 14.0% of the total number of rabid animals reported during 1999. Reported cases of rabies in cats (278) and dogs (111) decreased by 1.4% and 1.8%, respectively, whereas cases in cattle (135) increased by 16.4%, compared with those reported in 1998.

Predicting the local dynamics of epizootic rabies among raccoons in the United States

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.

Detection of antibodies reactive with Ehrlichia chaffeensis in the raccoon

Antibodies reactive with Ehrlichia chaffeensis were detected in raccoon (Procyon lotor) serum samples by using an indirect immunofluorescence assay. Samples from 411 raccoons trapped in the southeastern United States from 1977 to 1999 were tested. Serologically reactive samples with reciprocal titers of > or =16 were detected from 83 raccoons (20%) from 13 of 16 counties in eight states, indicating that raccoons are commonly exposed to E. chaffeensis. Samples collected as early as 1977 were positive. A polymerase chain reaction assay specific for E. chaffeensis failed to detect the presence of ehrlichial DNA in serum samples from 20 representative seroreactive raccoons. Because of serologic cross-reactivity among antigens derived from different Ehrlichia spp., additional immunologic, molecular, or culture-based studies will be required to confirm E. chaffeensis infections of raccoons in the southeastern United States.

Experimental evidence of host specificity of Bartonella infection in rodents

A large number of Bartonella species and genetic variants were compared for their ability to cause bacteremia in different rodent species: the cotton rat (Sigmodon hispidus), white-footed mouse (Peromyscus leucopus), BALB/c mouse and Wistar rat. Experimental data supported field observations that host specificity can occur among certain Bartonella species and rodent species. Bacteremia could only be readily produced in cotton rats or white-footed mice if the strains used for inoculation were originally obtained from the same species or from a phylogenetically close species. A few Bartonella colonies could be observed in the blood of some BALB/c mice by 7 days after inoculation, but no evidence of the persistence of the infection was found. Host specificity suggests the possibility of a long co-speciation of Bartonella species with their rodent hosts. Host-parasite relationships measured by the duration and level of bacteremia and the minimal infectious dose may serve as additional criteria for classification of Bartonella isolates obtained from natural environments.

Survival of Ehrlichia chaffeensis in refrigerated, ADSOL-treated RBCs

BACKGROUND

The purpose of this study was to investigate the persistence of viable Ehrlichia chaffeensis in ADSOL-treated RBCs stored at 4 to 6 degrees C.

STUDY DESIGN AND METHODS

The continuous monocytic cell lines THP-1 and DH82 were infected with E. chaffeensis (St. Vincent isolate). Packed RBC units were inoculated in separate experiments with E. chaffeensis-infected cells as final concentrations of 8.02 x 10(4) (DH82) and 1.43 x 10(4) (THP-1) infected cells per mL. Aliquots were stored at 4 to 6 degrees C for 1 to 42 days. At selected intervals, nucleated cells from the RBC aliquots were obtained by using a ficoll-isopaque separation procedure. Uninfected DH82 cell cultures were inoculated with the harvested nucleated cells or supernatant. The cell cultures were evaluated for infection by weekly examination of Wright's (Diff-Quik) stained cytocentrifuged slides. PCR amplification was also used to test the harvested nucleated cells or supernatant for the presence of E. chaffeensis DNA.

RESULTS

In both types of infected cell lines, E. chaffeensis was reisolated in DH82 cells for as long as 11 days from the cellular fraction and for up to 5 days from the supernatant fraction. PCR results were positive throughout the 42-day testing period.

CONCLUSION

Cell-associated E. chaffeensis remains viable in ADSOL-treated RBCs stored at 4 to 6 degrees C for at least 11 days. These data suggest that transfusion-acquired infection is possible. Successful reisolation was achieved from the supernatant fraction, which suggests that RBC products treated with a WBC-reduction procedure may still present a risk for transfusion transmission. No correlation between PCR positivity and viability of bacteria was noted.

Appropriateness of rabies postexposure prophylaxis treatment for animal exposures. Emergency ID Net Study Group

CONTEXT

Rabies postexposure prophylaxis (RPEP) treatments and associated costs have increased in the United States. The extent to which RPEP use is consistent with guidelines is not well understood.

OBJECTIVE

To characterize animal contacts and determine the frequency and factors associated with inappropriate RPEP use.

DESIGN, SETTING, AND PATIENTS

Prospective case series study of patients presenting with an animal exposure-related complaint from July 1996 to September 1998 at 11 university-affiliated, urban emergency departments (the Emergency ID Net).

MAIN OUTCOME MEASURES

Exposure type, circumstances, and RPEP use (appropriateness defined by local public health departments).

RESULTS

Of 2030 exposures, 1635 (81%) were to dogs; 268 (13%) to cats; 88 (4%) to rodents/rabbits; 10 (0. 5%) to raccoons; 5 (0.2%) to bats; and 24 (1.2%) to other animals. Among those exposed, 136 (6.7%) received RPEP after dog (95), cat (21), raccoon (8), bat (4), or other animal (8) exposures. Use of RPEP varied by site (range, 0%-27.7% of exposures), with most frequent use reported at sites in the eastern United States. Management was considered appropriate in 1857 exposures (91.5%). Use of RPEP was considered inappropriate in 54 cases (40% of those in which it was given), owing to factors including animal availability for observation and exposure in a low-endemicity area. Rabies postexposure prophylaxis was considered inappropriately withheld from 119 cases (6.3% of those not receiving RPEP), often because a domestic animal was unavailable for observation or testing.

CONCLUSION

These results suggest that use of RPEP is often inappropriate. Greater compliance with current guidelines would increase RPEP use. Physician education, improved coordination with public health officials, and clarification of RPEP guidelines could optimize use of this expensive resource. JAMA. 2000;284:1001-1007

Isolation of lactate dehydrogenase-elevating viruses from wild house mice and their biological and molecular characterization

Lactate dehydrogenase-elevating virus (LDV) was first identified as a contaminant of transplantable mouse tumors that were passaged in laboratory mice. It has been assumed that these LDVs originated from LDVs endemic in wild house mouse populations. In order to test this hypothesis and to explore the relationships between LDVs from wild house mice among each other and to those isolated from laboratory mice, we have isolated LDVs from wild house mice and determined their biological and molecular properties. We have screened for LDV tissues of 243 wild house mice that had been caught in various regions of North, Central and South America between 1985 and 1994. We were able to isolate LDVs from the tissues of four mice, three had been caught in Baltimore, MD and one in Montana. We demonstrate that the phenotypic properties (ability to establish a long-term viremic infection, low immunogenicity of the neutralization epitope, high resistance to antibody neutralization and lack of neuropathogenicity) of the four wild house mouse LDVs are identical to those of the primary LDVs isolated from transplantable tumors (LDV-P and LDV-vx), which are distinct from those of the neuropathogenic LDV-C. Furthermore, ORF 5 and ORF 2 and their protein products (the primary envelope glycoprotein VP-3P, and the minor envelope glycoprotein, respectively) of the wild house mouse LDVs were found to be closely related to those of LDV-P and LDV-vx. The LDVs caught in Baltimore, MD were especially closely related to each other, whereas the LDV isolated in Montana was more distantly related, indicating that it had evolved independently. The ectodomain of VP-3P of all four wild house mouse LDVs, like those of LDV-P and LDV-vx, possess the same three polylactosaminoglycan chains, two of which are lacking in the VP-3P ectodomain of LDV-C. These results further strengthen the conclusion that the three polylactosaminoglycan chains are the primary determinants of the phenotypic properties of LDV-P/vx.

Primary isolation of Ehrlichia chaffeensis from patients with febrile illnesses: clinical and molecular characteristics

Ehrlichia chaffeensis was sought among patients with a history of tick exposure and fever, and the accuracy of other diagnostic tests was compared with that of primary isolation. Among the 38 patients enrolled, E. chaffeensis was isolated from the blood of 7 (18%) and from cerebrospinal fluid specimens of 2 of these 7. All 7 patients also were positive by polymerase chain reaction (PCR) of blood, and 6 patients developed diagnostic titers of antibody to E. chaffeensis. The isolates were characterized by molecular analysis of the 16S rRNA gene, the 120-kDa protein gene, and the variable-length PCR target (VLPT) of E. chaffeensis. On the basis of the 120-kDa and VLPT genotypes, the cerebrospinal fluid and blood isolates from the same patients were identical. This study demonstrates that both PCR and culture of blood for E. chaffeensis have high diagnostic yields. More frequent isolation of E. chaffeensis from patients with infection should further our understanding of the pathogenesis of this infection.

Prevalence of antibody to hepatitis E virus among rodents in the United States

The recent identification of antibody to hepatitis E virus (HEV) in pigs, sheep, and cattle and characterization of an HEV isolated from domestic pigs suggest animal reservoirs for this virus. To investigate whether rodents might be a natural reservoir of HEV, the prevalence of anti-HEV was determined among a variety of species throughout the United States. Serum samples were obtained from 806 rodents of 26 species in 15 genera. Anti-HEV prevalence was assessed by 2 EIAs (mosaic protein- and 55-kDa protein-based), which gave concordant results. The highest prevalence of antibody was found in the genus Rattus (59.7%; 166/278). Overall, rodents from urban habitats had a significantly higher prevalence of anti-HEV than did animals captured from rural areas. A high prevalence of anti-HEV was found in animals captured on mainland versus barrier islands. The results from this study provide convincing evidence of widespread HEV or HEV-like infection in rodents of the United States.

Incidence of Rocky Mountain spotted fever among American Indians in Oklahoma

OBJECTIVE

Although the state of Oklahoma has traditionally reported very high incidence rates of Rocky Mountain spotted fever (RMSF) cases, the incidence of RMSF among the American Indian population of the state has not been studied. The authors used data from several sources to estimate the incidence of RMSF among American Indians in Oklahoma.

METHODS

The authors retrospectively reviewed an Indian Health Service (IHS) hospital discharge database for 1980-1996 and available medical charts from four IHS hospitals. The authors also reviewed RMSF case report forms submitted to the Centers for Disease Control and Prevention (CDC) for 1981-1996.

RESULTS

The study data show that American Indians in the IHS Oklahoma City Area were hospitalized with RMSF at an annual rate of 48.2 per million population, compared with an estimated hospitalization rate of 16.9 per million Oklahoma residents. The majority of cases in the IHS database (69%) were diagnosed based on clinical suspicion rather than laboratory confirmation. The incidence of RMSF for Oklahoma American Indians as reported to the CDC was 37.4 cases per million, compared with 21.6 per million for all Oklahoma residents (RR 1.7, 95% confidence interval [CI] 1.5, 2.1).

CONCLUSIONS

Rates derived from the IHS database may not be comparable to state and national rates because of differences in case inclusion criteria. However, an analysis of case report forms indicates that American Indians n Oklahoma have a significantly higher incidence of RMSF than that of the overall Oklahoma population. Oklahoma American Indians may benefit from educationa campaigns emphasizing prevention of tick bites and exposure to tick habitats.

Dual captures of Colorado rodents: implications for transmission of hantaviruses

We analyzed dual-capture data collected during longitudinal studies monitoring transmission and persistence of Sin Nombre virus in rodents in Colorado. Our data indicate that multiple captures (two or more rodents captured in a single trap) may not be random, as indicated by previous studies, but rather the result of underlying, species-specific social behavior or cohesiveness. In the pairs we captured, most often, rodents were of the same species, were male, and could be recaptured as pairs. Therefore, dual captures of rodents, which are unusual but not rare, tend to occur among certain species, and appear to be nonrandom, group-foraging encounters. These demographic and ecologic characteristics may have implications for the study of the transmission of hantaviruses.

Survey of rabies preexposure and postexposure prophylaxis among missionary personnel stationed outside the United States

BACKGROUND

Of the 36 cases of human rabies that have occurred in the United States since 1980, 12 (33%) were presumed to have been acquired abroad. In the United States, it is recommended that international travelers likely to come in contact with animals in canine rabies-enzootic areas that lack immediate access to appropriate medical care, including vaccine and rabies immune globulin, should be considered for preexposure prophylaxis. In 1992, the death of an American missionary who had contracted rabies while stationed in Bangladesh highlighted this high-risk group.

METHODS

To assess their knowledge of rabies risk, rabies exposures, and compliance with preventive recommendations, we asked 695 missionaries and their family members to complete questionnaires about their time stationed abroad.

RESULTS

Of the 293 respondents stationed in countries where rabies is endemic, 37% reported prior knowledge of the presence of rabies in their country of service. Only 28% of the personnel stationed in rabies-endemic countries received preexposure prophylaxis. Having preexposure prophylaxis specifically recommended increased the likelihood of actually receiving it (O.R. 15.6, 95%CI 7.4 - 34.9). There were 38 reported exposures (dogs = 66%, another human = 20%), proven or presumed to be rabid. Three of the people exposed received rabies immune globulin and vaccine; 11 received vaccine alone; 8 received only basic first aid, and 16 received no treatment.

CONCLUSIONS

Although American missionaries stationed abroad are at an increased risk for exposure to rabies, compliance with established preventive measures was low. Prior to being stationed abroad, an educational rabies-prevention briefing, including encouragement to receive preexposure prophylaxis, could be an effective intervention for missionaries to decrease their risk of rabies.

Rabies surveillance in the United States during 1998

During 1998, 49 states, the District of Columbia, and Puerto Rico reported 7,961 cases of rabies in nonhuman animals and 1 case in a human being to the Centers for Disease Control and Prevention, a decrease of 6.5% from 8,509 cases in nonhuman animals and 4 cases in human beings reported in 1997. More than 92% (7,358 cases) were in wild animals, whereas > 7.5% (603 cases) were in domestic species (compared with 93% in wild animals and 7% in domestic species in 1997). Decreases were evident in all of the major contributing species groups, with the exception of skunks and bats. The relative contributions of the major groups to the total reported for 1998 were reccoons (44.0%; 3,502 cases), skunks (28.5%; 2,272), bats (12.5%; 992), foxes (5.5%; 435), cats (3.5%; 282), cattle (1.5%; 116), and dogs (11.5%; 113). No further discernable westward extension of the epizootic of rabies in raccoons in Ohio was reported. Twelve of the 19 states enzootic for the raccoon variant of the rabies virus and the District of Columbia reported decreased numbers of cases of rabies during 1998, compared with 13 states and the District of Columbia that reported increases during 1997. Three states, Rhode Island (143.2%), Massachusetts (77.2%), and New Hampshire (69.4%), reported increases of > 50% during 1998, compared with totals reported for 1997. In Texas, the number of cases of rabies associated with enzootic canine variants of the rabies virus remained greatly diminished; however, overall totals of reported cases of rabies increased in Texas and 12 other states where skunks are the major terrestrial reservoir of rabies. At the national level, the total of 82 reported cases of rabies among horses and mules was greater than that reported for any year since 1981 (88 cases) and represented a 74.5% increase, compared with the total for 1997. The 992 cases of rabies reported in bats during 1998 were the greatest proportionate contribution by bats since 1990. Reported cases of rabies in cats (282), dogs (113), and cattle (116) decreased 6.0%, 10.3%, and 4.9%, respectively. One indigenously acquired case of rabies reported in a human being during 1998 was the result of infection with a rabies virus variant associated with silver-haired and eastern pipistrelle bats.

Population dynamics of a naturally occurring heterogeneous mixture of Borrelia burgdorferi clones

Two unique isolates of Borrelia burgdorferi, differing in plasmid content and outer surface protein C expression, were cultured on sequential captures of a single free-living Peromyscus leucopus mouse and were examined for differences in transmissibility. Both isolates were transmissible from inoculated C.B-17 mice to larval Ixodes scapularis ticks and, subsequently, from infected nymphal ticks to C3H/HeJ mice. Plasmid and protein analyses suggested that the original isolates were a mixed population of B. burgdorferi, and cloning by limiting dilution resulted in the identification of two clonal groups. In addition to being heterogeneous in plasmid and genomic macrorestriction analyses, the clones varied with respect to the electrophoretic mobilities and antigenicity of their OspC proteins, as shown by their reactivity to a panel of monoclonal antibodies. Plasmid analysis of sequential isolates from C3H mice experimentally infected with the primary isolate or various mixtures of its subclones showed an apparently random fluctuation in clonal dominance in the majority of mice. Surprisingly, mice infected with each subclone were permissive to superinfection with the heterologous subclone, despite the presence of anti-B. burgdorferi antibodies at the time of the secondary challenge. These results show conclusively that mice captured at Lyme disease enzootic sites may be infected by mixed populations of genetically and antigenically distinct B. burgdorferi clones and that these infections can be acquired by coinfection or by sequential infection. The lack of cross-immunization between clones existing within a naturally occurring population may play a role in the maintenance of the genetic heterogeneity of B. burgdorferi in nature.

Dusky-footed wood rats (Neotoma fuscipes) as reservoirs of granulocytic Ehrlichiae (Rickettsiales: Ehrlichieae) in northern California

Dusky-footed wood rats (Neotoma fuscipes) and Peromyscus sp. mice (P. maniculatus and P. truei) were collected from one site in Placer County, one site in Santa Cruz County, and two sites in Sonoma County in northern California. Serum or plasma samples from 260 rodents were tested for antibodies to the agent of human granulocytic ehrlichiosis. Of these, samples from 25 wood rats (34% of those tested) and 10 (8%) Peromyscus sp. mice were found to be seropositive, but only those from one site. PCR assays targeting the groESL heat shock operon were conducted on all seropositive specimens and a subset of seronegative blood specimens. Ehrlichial DNA was identified in 17 (68%) of the 25 seropositive wood rat blood samples and in 1 of the 10 (10%) Peromyscus sp. specimens. None of 40 seronegative blood samples was PCR positive. Both seropositive and PCR-positive animals were collected during each trapping period. One male tick out of 84 Ixodes pacificus adults collected was PCR positive; samples of Dermacentor occidentalis nymphs and adults were negative. Nucleotide sequences of amplicons from three wood rat blood specimens and from the single PCR-positive tick differed by one and two bases, respectively, from a sequence previously obtained from Ehrlichia equi. At one site in Sonoma County, wood rats had a concurrent high prevalence of seropositivity and PCR positivity, while other sigmodontine rodents collected at the site were only occasionally infected. We suggest that dusky-footed wood rats serve as reservoirs of granulocytic ehrlichial agents in certain areas of northern California. The tick species involved in the transmission of granulocytic ehrlichiae among wood rats remains unknown.

Outcome of diagnostic tests using samples from patients with culture-proven human monocytic ehrlichiosis: implications for surveillance

We describe the concordance among results from various laboratory tests using samples derived from nine culture-proven cases of human monocytic ehrlichiosis (HME) caused by Ehrlichia chaffeensis. A class-specific indirect immunofluorescence assay for immunoglobulin M (IgM) and IgG, using E. chaffeensis antigen, identified 44 and 33% of the isolation-confirmed HME patients on the basis of samples obtained at initial clinical presentation, respectively; detection of morulae in blood smears was similarly insensitive (22% positive). PCR amplifications of ehrlichial DNA targeting the 16S rRNA gene, the variable-length PCR target gene, and the groESL operon were positive for whole blood specimens obtained from all patients at initial presentation. As most case definitions of HME require a serologic response with compatible illness for a categorization of even probable disease, PCR would have been required to confirm the diagnosis of HME in all nine of these patients without the submission of a convalescent-phase serum sample. These data suggest that many, if not most, cases of HME in patients who present early in the course of the disease may be missed and underscore the limitations of serologically based surveillance systems.

Shared vector-borne zoonoses of the Old World and New World: home grown or translocated?

Humans inhabiting the Old World and New World share a wide variety of pathogens. Processes that result in the disjunct biogeographic distribution of pathogens with common vertebrate reservoirs or vectors are more difficult to unravel than those influencing the distribution of infections spread only through human-to-human transmission. The origins of species and complexes of tick-borne bacteria are unclear. The agent of Lyme borreliosis may have speciated in the New World following geographical isolation of ticks harboring ancestral spirochetes; the subsequent spread to Europe of B. burgdorferi sensu stricto may have occurred within historical times. Other tick-borne agents, such as the ehrlichiae causing human granulocytic ehrlichiosis, are genetically very similar in the Old World and New World. As the taxonomic distinctions among these related agents of human and veterinary importance appear increasingly blurred, the processes leading to the current discontinuous geographic distributions will also become the source of continuing speculation. Accumulating data suggest an Old World origin for a group of bacteria that include B. elizabethae, a human pathogen first identified from the New World. The potential public health significance of these newly described organisms is undefined, but of international interest as their vertebrate reservoir has been introduced throughout the world.

An outbreak of acute bartonellosis (Oroya fever) in the Urubamba region of Peru, 1998

During May 1998, we conducted a case-control study of 357 participants from 60 households during an outbreak of acute bartonellosis in the Urubamba Valley, Peru, a region not previously considered endemic for this disease. Blood and insect specimens were collected and environmental assessments were done. Case-patients (n = 22) were defined by fever, anemia, and intra-erythrocytic coccobacilli seen in thin smears. Most case-patients were children (median age = 6.5 years). Case-patients more frequently reported sand fly bites than individuals of neighboring households (odds ratio [OR] = 5.8, 95% confidence interval [CI] = 1.2-39.2), or members from randomly selected households > or = 5 km away (OR = 8.5, 95% CI = 1.7-57.9). Bartonella bacilliformis isolated from blood was confirmed by nucleotide sequencing (citrate synthase [g/tA], 338 basepairs). Using bacterial isolation (n = 141) as the standard, sensitivity, specificity, and positive predictive value of thin smears were 36%, 96%, and 44%, respectively. Patients with clinical syndromes compatible with bartonellosis should be treated with appropriate antibiotics regardless of thin-smear results.

An investigation into the possibility of transmission of tick-borne pathogens via blood transfusion. Transfusion-Associated Tick-Borne Illness Task Force

BACKGROUND

Tick-borne illnesses were diagnosed in a group of National Guard members, including some who had donated blood a few days before the onset of symptoms. A voluntary recall of those blood components was issued and a multistate investigation was conducted to determine if transfusion-transmitted illness had occurred.

STUDY DESIGN AND METHODS

Donors and recipients were asked to complete questionnaires regarding symptoms and risk factors for infection and to provide blood samples for laboratory analysis.

RESULTS

Among National Guard personnel who donated blood, 12 individuals were found to have a confirmed or probable case of Rocky Mountain spotted fever or ehrlichiosis. A total of 320 units (platelets or packed red cells) from 377 donors were transfused into 129 recipients. Although 10 recipients received units from National Guard personnel with confirmed or probable infection, none became ill.

CONCLUSION

Transfusion-transmitted illness did not occur. Despite the awareness of the risk for tick-borne diseases and the use of tick-preventive measures, many National Guard personnel reported exposure to ticks. In addition to augmenting current tick-preventive measures, scheduling blood drives before rather than after field exercises could further reduce the potential for transmission of tick-borne pathogens.

Rats of the genus Rattus are reservoir hosts for pathogenic Bartonella species: an Old World origin for a New World disease?

Bartonella species were isolated from the blood of 63 of 325 Rattus norvegicus and 11 of 92 Rattus rattus from 13 sites in the United States and Portugal. Infection in both Rattus species ranged from 0% (e.g., 0/87) to approximately 60% (e.g., 35/62). A 337-bp fragment of the citrate synthase (gltA) gene amplified by polymerase chain reaction was sequenced from all 74 isolates. Isolates from R. norvegicus were most similar to Bartonella elizabethae, isolated previously from a patient with endocarditis (93%-100% sequence similarity), followed by Bartonella grahamii and other Bartonella species isolated from Old World rodents (Clethrionomys species, Mus musculus, and Rattus species). These data suggest that Rattus species are a reservoir host for pathogenic Bartonella species and are consistent with a hypothesized Old World origin for Bartonella species recovered from Rattus species introduced into the Americas.

Comparison of methods for introducing and producing artificial infection of ixodid ticks (Acari: Ixodidae) with Ehrlichia chaffeensis

Only 29.5 +/- 8.91% of engorged Amblyomma americanum (L.) nymphs that we inoculated with Ehrlichia chaffeensis molted successfully to adults compared with 75.8 +/- 7.46% of engorged nymphs that were not inoculated. However, 65.4 +/- 6.02% of unfed nymphs of this species were exposed for 2 h to E. chaffeensis suspension introduced to them through glass capillaries gained weight. These nymphs were placed on rabbits, and approximately 50% of them completed their feeding and molted successfully to adults. Weight gained was higher (71.8 +/- 17.33% and 69.8 +/- 23.26%) for unfed A. americanum females that fed from capillaries for 2 and 24, h respectively, than for nymphs. Similar values were recorded for Dermacentor variabilis (Say) (61.0 +/- 16.23%) and Rhipicephalus sanguineus (Latreille) (59.0 +/- 18.62%) females after 24 h of capillary feeding. The amount of E. chaffeensis suspension taken in by females of A. americanum, D. variabilis, and R. sanguineus during 24 h of feeding was 11.2 +/- 3.56, 10.9 +/- 4.29 and 6.3 +/- 2.35 microliters, respectively. This volume is equivalent to approximately 12,969, 12,622, and 7,295 infected cells ingested by the species mentioned above. Positive correlation between the volume taken in by the ticks and the weight gained by the females was found, but the initial weight of the unfed females did not effect the weight they gained. The pathogen was found in the females of all 3 species by polymerase chain reaction procedures for at least 7 d, indicating that the capillary feeding method can be successfully used for infecting unfed ticks. The potential use of this method is discussed.

Serologic evidence of rickettsialpox (Rickettsia akari) infection among intravenous drug users in inner-city Baltimore, Maryland

We tested single serum samples from 631 intravenous (i.v.) drug users from inner-city Baltimore, Maryland for serologic evidence of exposure to spotted fever group rickettsiae. A total of 102 (16%) individuals had titers > or = 64 to Rickettsia rickettsii by an indirect immunofluorescence assay. Confirmation that infection was caused by R. akari was obtained by cross-adsorption studies on a subset of serum samples that consistently resulted in higher titers to R. akari than to R. rickettsii. Current i.v. drug use, increased frequency of injection, and shooting gallery use were significant risk factors for presence of group-specific antibodies reactive with R. rickettsii. There was a significant inverse association with the presence of antibodies reactive to R. rickettsii and antibodies reactive to the human immunodeficiency virus. This study suggests that i.v. drug users are at an increased risk for R. akari infections. Clinicians should be aware of rickettsialpox, as well as other zoonotic diseases of the urban environment, when treating i.v. drug users for any acute febrile illness of undetermined etiology.

Hidden mortality attributable to Rocky Mountain spotted fever: immunohistochemical detection of fatal, serologically unconfirmed disease

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.

Molecular cloning and characterization of the Ehrlichia chaffeensis variable-length PCR target: an antigen-expressing gene that exhibits interstrain variation

A clone expressing an immunoreactive protein with an apparent molecular mass of 44 kDa was selected from an Ehrlichia chaffeensis Arkansas genomic library by probing with anti-E. chaffeensis hyperimmune mouse ascitic fluid. Nucleotide sequencing revealed an open reading frame (ORF) capable of encoding a 198-amino-acid polypeptide. The ORF contained four imperfect, direct, tandem 90-bp repeats. The nucleotide and deduced amino acid sequences did not show close homologies to entries in the molecular databases. PCR with primers whose sequences matched the sequences flanking the ORF was performed with DNA samples extracted from cell cultures infected with nine different isolates of E. chaffeensis, blood samples from seven patients with monocytic ehrlichiosis, and Amblyomma americanum ticks collected in four different states. The resulting amplicons varied in length, containing three to six repeat units. This gene, designated the variable-length PCR target, is useful for PCR detection of E. chaffeensis and differentiation of isolates.

Experimental infection of cotton rats with three naturally occurring Bartonella species

The kinetics of infection and humoral immune response of laboratory-bred cotton rats (Sigmodon hispidus) challenged with three Bartonella spp. recovered from the blood of naturally infected cotton rats captured in Georgia (USA) are described. Bartonella spp. infection, as determined by bacteremia, occurred in all 18 cotton rats inoculated with live Bartonella of each species at either a low dose, 10(3) colony-forming units (CFU's), or high dose, 10(7) CFU. Cotton rats inoculated with lower doses of Bartonella spp. developed higher bacteremia that persisted for longer periods than in those inoculated with high doses. Peak bacteremia varied among Bartonella spp, ranging from 10(4) to 10(6) CFUs per 1.0 ml of blood. Antibody measured by immunofluorescence assays using species-specific antigens indicated more rapidly rising and higher antibody titers in cotton rats challenged with high doses vs. low doses and with inactivated bacteria vs. live bacteria. Each group of rats produced high IgG titers to the homologous challenge antigen; low or unmeasurable cross-reactivity was detected to heterologous Bartonella antigens. Exposure of cotton rats to a specific Bartonella sp. resulted in protection, as measured by detectable bacteremia, in eight of nine animals challenged with the same Bartonella sp. used initially; no evidence of resistance to secondary challenge with different Bartonella spp. was obtained. Cross-protection between Bartonella spp., isolated from the same rodent species, may not occur.

Family cluster of Rocky Mountain spotted fever

Soon after a patient from Tennessee died of Rocky Mountain spotted fever (RMSF), several family members developed symptoms suggestive of the disease and were treated presumptively for RMSF. Fifty-four persons visiting the index patient's home were interviewed; serum samples were collected from 35. Three additional cases of RMSF were confirmed, all of which occurred in first-degree relatives. Time spent at the family home and going into the surrounding woods were significantly associated with developing antibodies to Rickettsia rickettsii. Ticks were collected and examined for rickettsiae by polymerase chain reaction analysis. Because hyperendemic foci and family clusters of RMSF can occur, when a case is suspected clinicians should be vigilant for signs and symptoms consistent with R. rickettsii infection in other persons who may have been similarly exposed.

Longitudinal study of infection with Borrelia burgdorferi in a population of Peromyscus leucopus at a Lyme disease-enzootic site in Maryland

The maintenance of Borrelia burgdorferi in a population of Peromyscus leucopus was investigated from 202 mark and recapture mice and 61 mice that were removed from a site in Baltimore County, Maryland. Borrelia burgdorferi infection was detected by culture and polymerase chain reaction (PCR) of ear tissue, and exposure to the spirochete was quantified by serology. Overall prevalence of B. burgdorferi, as determined by culture and PCR of ear tissue at first capture, was 25% in the longitudinal sample and 42% in the cross-sectional sample. Significantly more juvenile mice were captured in the longitudinal sample (18%) than in the cross-sectional sample (0%). Among 36 captured juvenile mice, only one was infected with B. burgdorferi; this contributed to a significant trend for infection with B. burgdorferi with age. Recovery from infection with B. burgdorferi was not detected among 77 mice followed for an average of 160 days. The incidence rate of infection with B. burgdorferi was 10 times greater in mice captured during two periods of high risk of exposure to nymphal Ixodes scapularis ticks compared with a period of low risk. Maintenance of B. burgdorferi in this population was dependent on indirect transmission of the organism from infected ticks to susceptible mice and development of chronic infection with the spirochete, which had no measurable effect on the survival of infected mice.

Serologic testing for human granulocytic ehrlichiosis at a national referral center

An indirect immunofluorescence assay (IFA) was used to identify patients with antibodies reactive to the human granulocytic ehrlichiosis (HGE) agent. Serum samples collected from clinically ill individuals were submitted to the Centers for Disease Control and Prevention by physicians via state health departments from throughout the United States and tested against a panel of ehrlichial and rickettsial pathogens. Antibodies reactive to the HGE agent were detected in 142 (8.9%) of 1,602 individuals tested. There were 19 confirmed and 59 probable (n = 78) cases of HGE as defined by seroconversion or a fourfold or higher titer to the HGE agent than to the Ehrlichia chaffeensis antigens. The average age of patients with HGE was 57 years, and males accounted for 53 (68%) of the patients. Cases of HGE occurred in 21 states; 47 (60%) of the cases occurred in Connecticut (n = 14), New York (n = 18), and Wisconsin (n = 15). Onset of HGE was identified from April through December, with cases peaking in June and July. The earliest confirmed cases of HGE occurred in 1987 in Wisconsin and 1988 in Florida. No fatalities were reported among the 78 patients with confirmed or probable HGE. Reactivity to the HGE agent and to either Coxiella burnetii, Rickettsia rickettsii, or Rickettsia typhi was infrequent; however, 74 (52%) of the 142 individuals who were positive for HGE had at least one serum sample that also reacted to the E. chaffeensis antigen. Thirty-four persons with confirmed or probable human monocytic ehrlichiosis due to E. chaffeensis also had antibodies to the HGE agent in at least one serum sample. The specific etiologic agent for 30 patients was not ascribed because of similarity of titers to both ehrlichial antigens. The use of both antigens may be required to correctly diagnose most cases of human ehrlichiosis, especially in geographic regions where both the HGE agent and E. chaffeensis occur.