Duration of tick attachment necessary for transmission of Anaplasma phagocytophilum by Ixodes scapularis (Acari: Ixodidae) nymphs.

This study assessed the duration of tick attachment necessary for a successful transmission of Anaplasma phagocytophilum by an infected I. scapularis nymph. Individual nymphs were placed upon BALB/c mice and allowed to feed for predetermined time intervals of 4 to 72 h. Ticks removed from mice at predetermined intervals were tested by PCR for verification of infection and evaluation of the bacterial load. The success of pathogen transmission to mice was assessed by blood-PCR at 7, 14 and 21 days postinfestation, and IFA at 21 days postinfestation. Anaplasma phagocytophilum infection was documented in 10-30 % of mice, from which ticks were removed within the first 20 h of feeding. However, transmission success was ≥70% if ticks remained attached for 36 h or longer. Notably, none of the PCR-positive mice that were exposed to infected ticks for 4 to 8 h and only half of PCR-positive mice exposed for 24 h developed antibodies within 3 weeks postinfestation. On the other hand, all mice with detectable bacteremia after being infested for 36 h seroconverted. This suggests that although some of the ticks removed prior to 24 h of attachment succeed in injecting a small amount of A. phagocytophilum, this amount is insufficient for stimulating humoral immunity and perhaps for establishing disseminated infection in BALB/c mice. Although A. phagocytophilum may be present in salivary glands of unfed I. scapularis nymphs, the amount of A. phagocytophilum initially contained in saliva appears insufficient to cause sustainable infection in a host. Replication and, maybe, reactivation of the agent for 12-24 h in a feeding tick is required before a mouse can be consistently infected.

Detection of West Nile Virus and other common equine viruses in three locations from the Leeward Islands, West Indies.

Equines in the West Indies are used for recreational purposes, tourism industry, racing and agriculture or can be found in feral populations. Little is known in the Caribbean basin about the prevalence of some major equine infectious diseases, some with zoonotic potential, listed as reportable by the OIE. Our objective was to study the prevalence of antibodies for West Nile Virus (WNV), Equine Herpes Virus-1 and 4 (EHV-1 and EHV-4), Equine Influenza (EI), Equine Viral Arteritis (EVA) and Equine Infectious Anemia Virus (EIAV) using a retrospective serological convenience study. We used 180 equine serum samples, 140 from horses and 40 from donkeys in St. Kitts, Nevis, and Sint Eustatius, collected between 2006 and 2015 that were tested with ELISA kits and virus neutralization (for WNV and EVA). Combining ELISA with virus neutralization testing, 25 (13.8%) equine sera were WNV positive (a mixture of indigenous and imported equines) and 3 sera (1.6%) showed doubtful results. For EHV-1, 41 equines (23.7%), mean age 6.7 years, were seropositive. For EHV-4, 138 equines were found seropositive (82.8%), mean age 6.3 years. For EI, 49 equines (27.2%), mean age 7.5 years, were seropositive on ELISA, some previously vaccinated horses. No antibodies against EAV were found on virus neutralization testing, although one animal (0.6%), was EAV positive on ELISA. All samples were EIAV negative. The seroprevalence for EHV-1 and EHV-4 is similar to other parts of the world. For the first time in the study location serologic evidence of antibodies against WNV and EI is reported. This was found in both indigenous and imported animals, highlighting the need for developing proper surveillance plans based on complementary methods of virus detection. Further studies will be needed to define the prevalence, rates of transmission, characterize local virus strains, and study their impact on these populations.

Ecology of Bats, Their Ectoparasites, and Associated Pathogens on Saint Kitts Island.

Ectoparasites of bats and bat-associated pathogens are poorly studied in the Lesser Antilles Islands. We report on an 11-mo field study on Saint Kitts Island of bat populations, their associated ectoparasites, and pathogens. We report on five ectoparasite species, including four Streblidae (Diptera) and a Spinturnicidae (Acari). Several genotypes of unnamed Bartonella were isolated from bats and ectoparasites. Microfilaria of an undetermined Litomosoides spp. were detected in blood from Artibeus jamaicensis Leach (Chiroptera: Phyllostomidae) (and associated ectoparasites: Trichobius intermedius Peterson and Hurka (Diptera: Streblidae) and Periglischrus iheringi Oudemans (Acari: Spinturnicidae)). In addition, an Ehrlichia sp. and Rickettsia africae were detected in the blood of several bat species. Our study is one of the first surveys of ectoparasite-borne pathogens in wild mammals from St. Kitts.

Rickettsia parkeri Rickettsiosis, Arizona, USA.

In the United States, all previously reported cases of Rickettsia parkeri rickettsiosis have been linked to transmission by the Gulf Coast tick (Amblyomma maculatum). Here we describe 1 confirmed and 1 probable case of R. parkeri rickettsiosis acquired in a mountainous region of southern Arizona, well beyond the recognized geographic range of A. maculatum ticks. The likely vector for these 2 infections was identified as the Amblyomma triste tick, a Neotropical species only recently recognized in the United States. Identification of R. parkeri rickettsiosis in southern Arizona demonstrates a need for local ecologic and epidemiologic assessments to better understand geographic distribution and define public health risk. Education and outreach aimed at persons recreating or working in this region of southern Arizona would improve awareness and promote prevention of tickborne rickettsioses.

Prevalence of Tick-Borne Pathogens in Host-Seeking Amblyomma americanum (Acari: Ixodidae) and Odocoileus virginianus (Artiodactyla: Cervidae) in Florida.

Amblyomma americanum (L.), the lone star tick, is an aggressive tick that is expanding its geographic range within the United States. This tick is the vector for the human and veterinary pathogens Ehrlichia chaffeensis and Ehrlichia ewingii and is associated with other microbes of unspecified pathogenicity including Rickettsia amblyommii, Panola Mountain Ehrlichia, and Borrelia lonestari In Florida, there has been sparse contemporary data on the prevalence of these organisms in host-seeking lone star ticks. To determine the prevalence of this tick and associated microbes in North Central Florida state parks, ∼1,500 lone star tick specimens were collected between 2010 and 2012 analyzed by polymerase chain reaction (PCR) sequencing. Additionally, 393 white-tailed deer, Odocoileus virginianus (Zimmerman), samples were analyzed for pathogen prevalence using molecular methods and serology. In lone star ticks, 14.6, 15.6, and 57.1% were positive for E. chaffeensis, E. ewingii, and Rickettsia spp. DNA, respectively. Panola Mountain Ehrlichia or B. lonestari DNA were each detected in nearly 2% of tick specimens. In white-tailed deer, 7.3% were PCR positive for E. chaffeensis, 6.0% for E. ewingii, and 3.2% for rickettsial species. Approximately 45% of white-tailed deer specimens had antibodies to Ehrlichia spp., and <1% had antibodies to Borrelia burgdorferi In summary, E. chaffeensis, E. ewingii, and spotted fever group rickettsia are highly prevalent in host-seeking lone star ticks and in white-tailed deer in Florida. The molecular and serological evidence of these microbes underscore their zoonotic potential in this region.

Panola Mountain Ehrlichia in Amblyomma maculatum From the United States and Amblyomma variegatum (Acari: Ixodidae) From the Caribbean and Africa.

Panola Mountain Ehrlichia (PME) has been suggested as an emerging pathogen of humans and dogs. Domestic goats and white-tailed deer (Odocoileus virginianus) are also susceptible and likely serve as reservoirs. Experimentally, both the lone star tick (Amblyomma americanum (L.)) and the Gulf Coast tick (Amblyomma maculatum Koch) can transmit PME among deer and goats. In the current study, we detected PME in adult wild-caught A. maculatum from the United States and Amblyomma variegatum (F.) from the Caribbean and Africa. This significantly expands the range, potential tick vectors, and risk for exposure to PME.

Multispecies Epidemiologic Surveillance Study after an Outbreak of Yersiniosis at an African Green Monkey Research Facility.

After an outbreak of Yersinia enterocolitica at a NHP research facility, we performed a multispecies investigation of the prevalence of Yersinia spp. in various mammals that resided or foraged on the grounds of the facility, to better understand the epizootiology of yersiniosis. Blood samples and fecal and rectal swabs were obtained from 105 captive African green monkeys (AGM), 12 feral cats, 2 dogs, 20 mice, 12 rats, and 3 mongooses. Total DNA extracted from swab suspensions served as template for the detection of Y. enterocolitica DNA by real-time PCR. Neither Y. enterocolitica organisms nor their DNA were detected from any of these samples. However, Western blotting revealed the presence of Yersinia antibodies in plasma. The AGM samples revealed a seroprevalence of 91% for Yersinia spp. and of 61% for Y. enterocolitica specifically. The AGM that were housed in cages where at least one fatality occurred during the outbreak (clinical group) had similar seroprevalence to that of AGM housed in unaffected cages (nonclinical group). However, the nonclinical group was older than the clinical group. In addition, 25%, 100%, 33%, 10%, and 10% of the sampled local cats, dogs, mongooses, rats, and mice, respectively, were seropositive. The high seroprevalence after this outbreak suggests that Y. enterocolitica was transmitted effectively through the captive AGM population and that age was an important risk factor for disease. Knowledge regarding local environmental sources of Y. enterocolitica and the possible role of wildlife in the maintenance of yersiniosis is necessary to prevent and manage this disease.

Development of a generic Ehrlichia FRET-qPCR and investigation of ehrlichioses in domestic ruminants on five Caribbean islands.

BACKGROUND: The Ehrlichia are obligate intracellular Gram-negative tick-borne bacteria that are important human and animal pathogens. There is a need for assays to rapidly and reliably detect and differentiate the five generally recognized species into groups in a single reaction: E. canis, E. chaffeensis, E. ewingii, E. muris and E. ruminantium. METHODS: We developed primers and probes against the 16S rRNA gene to enable us to reliably detect the five major Ehrlichia spp. in a single FRET-qPCR. We tested the Ehrlichia FRET-qPCR on reference strains and on DNA from the blood of domestic ruminants from five Caribbean islands. The Ehrlichia present were determined using melting point analysis and by sequencing the Ehrlichia FRET-qPCR products as well as those of a nested PCR against the citrate synthase gene (gltA). RESULTS: Our Ehrlichia FRET-qPCR was negative for the closely related Anaplasma marginale and A. phagocytophilum but gave positive reactions with reference strains of the most generally recognized species and with other less characterized Ehrlichia of domestic ruminants, mainly E. ovina, the Panola Mountain Ehrlichia, and Ehrlichia sp. BOV2010. Melting point analysis revealed 4 distinct groups: E. ruminantium (T m ~55.8 °C); E. chaffeensis and E. ewingii (T m ~57.7 °C); E. canis, E. muris, E. ovina and Ehrlichia sp. BOV 2010 (T m ~62.0 °C); and the Panola Mountain Ehrlichia (T m ~65.5 °C). The detection limit of the FRET-qPCR was ~ 5 gene copies in a reaction and the sequences of the FRET-qPCR products were as expected. With DNA from domestic ruminants from the Caribbean we found 12.2 % (134/1,101) positive: cattle (76/385; 19.7 %), sheep (45/340; 13.2 %) and goats (13/376; 3.5 %). Melting point analysis and sequencing of the FRET-qPCR and nested PCR gltA products showed the Ehrlichia we detected were E. canis or very closely related organisms. CONCLUSIONS: In a single reaction, our Ehrlichia FRET-qPCR can detect the Ehrlichia spp. we studied and differentiate them into four groups. Domestic ruminants in the Caribbean are not uncommonly exposed to Ehrlichia, possibly E. canis or very closely related organisms.

Molecular detection of tick-borne pathogens in captive wild felids, Zimbabwe.

BACKGROUND: The populations of wild felids in Africa, of especially lions (Panthera leo) and cheetahs (Acinonyx jubatus), are declining and the species are classified as vulnerable to extinction by the International Union for Conservation of Nature. As infections with tick-borne pathogens (TBP) can become more of a problem in wild felids, there are relatively few studies on TBP in wild felids in Africa and on how these infections might influence population numbers. METHODS: To gain further knowledge on TBP in captive wild felids in Southern Africa, we collected whole blood from captive lions, Southern African wildcats, cheetahs and servals in Zimbabwe for PCRs against the 18S rRNA gene of the piroplasmids (Babesia, Theileria, Cytauxzoon) and Hepatozoon spp., and the 16S rRNA gene of Ehrlichia and Anaplasma spp. RESULTS: Overall, 78% of the lions (67/86) and all the Southern African wildcats (6/6), cheetahs (4/4) and servals (2/2) had evidence of infection with at least one organism. The organisms most commonly detected in the lions were B. leo (59%; 51/86), B. vogeli (12%; 10/86) and H. felis (11%; 9/86) while all the Southern African wildcats and servals were positive for B. vogeli and all the cheetahs were positive for B. leo. Mixed infections were found in 22% (15/67) of the PCR positive lions, most commonly B. leo and H. felis (27%; 4/15), and in 1 (50%) of the servals (B. vogeli and A. phagocytophilum). Two lions were infected with three TBP, mainly B. leo, H. canis and T. parva, and B. leo, A. phagocytophilum and T. sinensis. Mixed infections with B. vogeli and A. phagocytophilum were seen in a serval and a Southern African wildcat. Other TBP were detected at a low prevalence (≤2%) in lions, mainly H. canis, T. sinensis, T. parva, C. manul, E. canis, and E. canis-like and B. odocoilei-like organisms. CONCLUSIONS: Infections with tick-borne agents are common in captive wild felids in Zimbabwe.

Molecular detection of leptospiral DNA in environmental water on St. Kitts.

Leptospirosis is an important waterborne zoonotic disease caused by pathogenic Leptospira. The pathogen is maintained in a population due to chronic colonization and shedding from renal tubules of domestic and wild animals. Humans and other animals become infected when they come in contact with urine from infected animals, either directly or through urine-contaminated surface water. In this study, we screened environmental water on the island of St. Kitts by using a TaqMan based real time quantitative polymerase chain reaction (qPCR) targeting a pathogen specific leptospiral gene, lipl32. Our results indicate that around one-fifth of tested water sources have detectable leptospiral DNA.

Seroprevalence of seven zoonotic pathogens in pregnant women from the Caribbean.

Studies examining the prevalence of zoonotic agents in the Caribbean are very limited. The objective of this study was to examine the seroprevalence of seven zoonotic agents among individuals residing on 10 English-speaking Caribbean countries. Sera from healthy, pregnant women were collected from Antigua-Barbuda, Belize, Bermuda, Dominica, Grenada, Jamaica, Montserrat, St. Kitts-Nevis, St. Lucia, and St. Vincent-Grenadines and tested for the presence of IgG antibodies to dengue virus, hepatitis E virus, hantaviruses, leptospiral agents, spotted fever group rickettsiae (SFGR), typhus group rickettsiae (TGR), and Coxiella burnetii (Q fever). The highest seroprevalence values were observed for dengue virus, SFGR, and leptospirosis, although the lowest seroprevalence values were observed for hepatitis E virus, C. burnetii, and TGR. Antibodies to hantaviruses were not detected in any individuals.

Diagnosis of canine leptospirosis by a highly sensitive FRET-PCR targeting the lig genes.

Canine leptospirosis is underdiagnosed due to its wide spectrum of clinical presentations and the lack of a rapid and sensitive test for the accurate diagnosis of acute and chronic infections. In this study, we developed a highly sensitive and specific fluorescence resonance energy transfer (FRET)-PCR to detect common pathogenic leptospires in dogs, including Leptospira interrogans serovars Autumnalis, Canicola, Copenhageni (Icterohaemorrhagiae serogroup) and Pomona, and Leptospira kirschneri serovar Grippotyphosa. This PCR targets the lig genes, exclusively found in the pathogenic Leptospira species but not in saprophytic species (L. biflexa). A robust, high-stringency step-down real-time platform was coupled to the highly specific detection of leptospiral DNA by fluorescently labeled FRET probes. This enabled the detection of a single copy of the lig gene in a PCR containing DNA from up to 50 µL canine blood or 400 µL urine. Sensitivity determination by use of limiting serial dilutions of extracted leptospiral DNA indicated that the lig FRET-PCR we established was almost 100-fold more sensitive than the widely accepted lipL32 SYBR assay and 10-fold more sensitive than a 16S rRNA TaqMan assay. Application of this method to 207 dogs with potential leptospiral infection enabled us to diagnose three cases of canine leptospirosis characterized by low amounts of leptospiral DNA in body fluids. Detection of canine leptospirosis with the lig FRET-PCR was more sensitive with the lig FRET-PCR than with the 16S rRNA TaqMan PCR, which detected only 2 of the 3 cases, and the lipL32 SYBR PCR, which detected none of the 3 dogs with leptospirosis.

Tick-borne pathogens and disease in dogs on St. Kitts, West Indies.

Between 2009 and 2011, we conducted a case-control study of ticks and tick-associated pathogens affecting dogs on the island of St. Kitts, eastern Caribbean, including 55 cases of clinically suspected tick-borne disease (TBD) and 110 presumably healthy animals presented for elective surgeries. Rhipicephalus sanguineus caused year-round infestations of dogs, and 36% of the dogs in the study were infested at the time of examination. Overall, 62% of suspected TBD cases and 24% of presumably healthy dogs tested positive by PCR for infections with: Anaplasma platys (0% and 4%), Babesia canis vogeli (20% and 6%), Babesia gibsoni (18% and 5%), Ehrlichia canis (35% and 7%), and Hepatozoon canis (5% and 2%). Co-infections were documented in 15% of these PCR-positive dogs. Antibodies against A. platys or E. canis were noted in 36% of the dogs. Thrombocytopenia was the most common sign of infection, followed by anemia. This is the first detection of A. platys, B. canis vogeli, or H. canis on St. Kitts and the first detection of B. gibsoni in the Caribbean. We conclude that tick-borne pathogens of dogs are highly prevalent in this region and may present in dogs that appear healthy, in spite of hematologic abnormalities that may increase surgical risk.

Ehrlichiosis, babesiosis, anaplasmosis and hepatozoonosis in dogs from St. Kitts, West Indies.

BACKGROUND: Although tick-borne diseases are important causes of morbidity and mortality in dogs in tropical areas, there is little information on the agents causing these infections in the Caribbean. METHODOLOGY: We used PCRs to test blood from a cross-section of dogs on St Kitts for Ehrlichia (E.) canis, Babesia (B.) spp., Anaplasma (A.) spp. and Hepatozoon (H.) spp. Antibodies against E. canis and A. phagocytophilum/platys were detected using commercial immunochromatography tests. Records of the dogs were examined retrospectively to obtain clinical and laboratory data. PRINCIPAL FINDINGS: There was serological and/or PCR evidence of infections of dogs with E. canis (27%; 46/170), Babesia spp. (24%; 90/372) including B. canis vogeli (12%; 43/372) and B. gibsoni (10%; 36/372), A. platys (11%; 17/157) and H. canis (6%; 15/266). We could not identify the Babesia sp. detected in nine dogs. There was evidence of multiple infections with dual infections with E. canis and B. canis vogeli (8%; 14/179) or B. gibsoni (7%; 11/170) being the most common. There was agreement between immunochromatography and PCR test results for E. canis for 87% of dogs. Only 13% of exposed dogs had signs of a tick-borne disease and 38% had laboratory abnormalities. All 10 dogs presenting for a recheck after treatment of E. canis with doxycycline were apparently healthy although all remained seropositive and six still had laboratory abnormalities despite an average of two treatments with the most recent being around 12 months previously. Infections with Babesia spp. were also mainly subclinical with only 6% (4/67) showing clinical signs and 13% (9/67) having laboratory abnormalities. Similarly, animals with evidence of infections with A. platys and H. canis were largely apparently healthy with only occasional laboratory abnormalities. CONCLUSIONS: Dogs are commonly infected with tick-borne pathogens in the Caribbean with most having no clinical signs or laboratory abnormalities.

Coxiella burnetii, the agent of Q fever, in domestic sheep flocks from Wyoming, United States.

Coxiella burnetii, the agent of Q fever, is an intracellular bacterial pathogen. It has a nearly cosmopolitan distribution. We conducted a serological survey of domestic sheep herds for infections with C. burnetii in Wyoming following reports of abortion and open ewes. Based on the serologic evidence, there was no link between reproductive problems and exposure to C. burnetii. However, the overall prevalence of C. burnetii in WY sheep was 7%, which indicates that the agent is present in the environment and could pose a threat to public health.

Detection of Coxiella burnetii in commercially available raw milk from the United States.

Unpasteurized (raw) milk can be purchased in 39 U.S. states, with direct consumer purchase for human consumption permitted in 29 of those 39 states. Raw milk (n=21; cow, 14; goat, 7) was purchased in 12 states, and Coxiella burnetii, the agent of Q fever, was detected in 9 of 21 (42.9%) samples tested by polymerase chain reaction. Viability of the pathogen was demonstrated by isolation of the agent in tissue culture. The demonstration of viable C. burnetii in commercially available raw milk poses a potential public health risk.

Presence of Coxiella burnetii DNA in the environment of the United States, 2006 to 2008.

Coxiella burnetii is an obligate intracellular bacterium that causes the zoonotic disease Q fever. Because C. burnetii is highly infectious, can survive under a variety of environmental conditions, and has been weaponized in the past, it is classified as a select agent and is considered a potential bioweapon. The agent is known to be present in domestic livestock and in wild animal populations, but the background levels of C. burnetii in the environment have not been reported. To better understand the amount of C. burnetii present in the environment of the United States, more than 1,600 environmental samples were collected from six geographically diverse parts of the United States in the years 2006 to 2008. DNA was purified from these samples, and the presence of C. burnetii DNA was evaluated by quantitative PCR of the IS1111 repetitive element. Overall, 23.8% of the samples were positive for C. burnetii DNA. The prevalence in the different states ranged from 6 to 44%. C. burnetii DNA was detected in locations with livestock and also in locations with primarily human activity (post offices, stores, schools, etc.). This study demonstrates that C. burnetii is fairly common in the environment in the United States, and any analysis of C. burnetii after a suspected intentional release should be interpreted in light of these background levels. It also suggests that human exposure to C. burnetii may be more common than what is suggested by the number of reported cases of Q fever.

Isolation of Rickettsia parkeri and identification of a novel spotted fever group Rickettsia sp. from Gulf Coast ticks (Amblyomma maculatum) in the United States.

Until recently, Amblyomma maculatum (the Gulf Coast tick) had garnered little attention compared to other species of human-biting ticks in the United States. A. maculatum is now recognized as the principal vector of Rickettsia parkeri, a pathogenic spotted fever group rickettsia (SFGR) that causes an eschar-associated illness in humans that resembles Rocky Mountain spotted fever. A novel SFGR, distinct from other recognized Rickettsia spp., has also been detected recently in A. maculatum specimens collected in several regions of the southeastern United States. In this study, 198 questing adult Gulf Coast ticks were collected at 4 locations in Florida and Mississippi; 28% of these ticks were infected with R. parkeri, and 2% of these were infected with a novel SFGR. Seventeen isolates of R. parkeri from individual specimens of A. maculatum were cultivated in Vero E6 cells; however, all attempts to isolate the novel SFGR were unsuccessful. Partial genetic characterization of the novel SFGR revealed identity with several recently described, incompletely characterized, and noncultivated SFGR, including "Candidatus Rickettsia andeanae" and Rickettsia sp. Argentina detected in several species of Neotropical ticks from Argentina and Peru. These findings suggest that each of these "novel" rickettsiae represent the same species. This study considerably expanded the number of low-passage, A. maculatum-derived isolates of R. parkeri and characterized a second, sympatric Rickettsia sp. found in Gulf Coast ticks.

Seroprevalence of Q fever in the United States, 2003-2004.

We performed serum testing for IgG antibodies against Coxiella burnetii (phase I and phase II) and analyzed questionnaire data from 4,437 adults > or = 20 years of age who participated in the National Health and Nutrition Examination Survey 2003-2004 survey cycle. National Q fever seroprevalence was determined by enzyme-linked immunosorbent assay and confirmed by using immunofluorescent antibody testing. Overall seroprevalence for Coxiella burnetii was 3.1% (95% confidence interval [CI] = 2.1-4.3%) among 4,437 adults > or = 20 years of age. Coxiella burnetii age-adjusted antibody prevalence was higher for men than for women (3.8%, 95% CI = 2.7-5.2% versus 2.5%, 95% CI = 1.5-3.7%, respectively, P < 0.05). Mexican Americans had a significantly higher antibody prevalence (7.4%, 95% CI = 6.6-8.3%) than either non-Hispanic whites (2.8%, 95% CI = 1.7-4.3%) or non-Hispanic blacks (1.3%, 95% CI = 0.6-2.5%) (P < 0.001). Multivariate analysis showed that the risk for Q fever antibody positivity increased with age and was higher among persons who were foreign-born, male, and living in poverty. These findings indicate that the national seroprevalence of Q fever in the United States is higher than expected on the basis of case numbers reported to the Centers for Disease Control and Prevention from state health departments. Potential differences in risk for exposure by race/ethnicity warrant further study.

Serological evidence of typhus group rickettsia in a homeless population in Houston, Texas.

We tested sera from 176 homeless people in Houston for antibodies against typhus group rickettsiae (TGR). Sera from 19 homeless people were reactive to TGR antigens by ELISA and IFA. Two people had antibodies against Rickettsia prowazekii (epidemic typhus) and the remaining 17 had antibodies against Rickettsia typhi (murine typhus).