Rickettsia species identified in adult, host-seeking Dermacentor occidentalis (Acari: Ixodidae) from Baja California, Mexico, and Oregon and Washington, United States

The Pacific Coast tick (Dermacentor occidentalis Marx, 1892) is a frequently encountered and commonly reported human-biting tick species that has been recorded from most of California and parts of southwestern Oregon, southcentral Washington, and northwestern Mexico. Although previous investigators have surveyed populations of D. occidentalis for the presence of Rickettsia species across several regions of California, populations of this tick have not been surveyed heretofore for rickettsiae from Baja California, Oregon, or Washington. We evaluated 1,367 host-seeking, D. occidentalis adults collected from 2015 to 2022 by flagging vegetation at multiple sites in Baja California, Mexico, and Oregon and Washington, United States, using genus- and species-specific assays for spotted fever group rickettsiae. DNA of Rickettsia 364D, R. bellii, and R. tillamookensis was not detected in specimens from these regions. DNA of R. rhipicephali was detected in D. occidentalis specimens obtained from Ensenada Municipality in Baja California and southwestern Oregon, but not from Washington. All ompA sequences of R. rhipichephali that were amplified from individual ticks in southwestern Oregon were represented by a single genotype. DNA of the Ixodes pacificus rickettsial endosymbiont was amplified from specimens collected in southwestern Oregon and Klickitat County, Washington; to the best of our knowledge, this Rickettsia species has never been identified in D. occidentalis. Collectively, these data are consistent with a relatively recent introduction of Pacific Coast ticks in the northernmost extension of its recognized range.

Transfusion-transmitted Babesia spp.: a changing landscape of epidemiology, regulation, and risk mitigation

Babesia spp. are tick-borne parasites with a global distribution and diversity of vertebrate hosts. Over the next several decades, climate change is expected to impact humans, vectors, and vertebrate hosts and change the epidemiology of Babesia. Although humans are dead-end hosts for tick-transmitted Babesia, human-to-human transmission of Babesia spp. from transfusion of red blood cells and whole blood-derived platelet concentrates has been reported. In most patients, transfusion-transmitted Babesia (TTB) results in a moderate-to-severe illness. Currently, in North America, most cases of TTB have been described in the United States. TTB cases outside North America are rare, but case numbers may change over time with increased recognition of babesiosis and as the epidemiology of Babesia is impacted by climate change. Therefore, TTB is a concern of microbiologists working in blood operator settings, as well as in clinical settings where transfusion occurs. Microbiologists play an important role in deploying blood donor screening assays in Babesia endemic regions, identifying changing risks for Babesia in non-endemic areas, investigating recipients of blood products for TTB, and drafting TTB policies and guidelines. In this review, we provide an overview of the clinical presentation and epidemiology of TTB. We identify approaches and technologies to reduce the risk of collecting blood products from Babesia-infected donors and describe how investigations of TTB are undertaken. We also describe how microbiologists in Babesia non-endemic regions can assess for changing risks of TTB and decide when to focus on laboratory-test-based approaches or pathogen reduction to reduce TTB risk.

Borrelia miyamotoi Infection in Immunocompromised Man, California, USA, 2021

Infection with Borrelia miyamotoi in California, USA, has been suggested by serologic studies. We diagnosed B. miyamotoi infection in an immunocompromised man in California. Diagnosis was aided by plasma microbial cell-free DNA sequencing. We conclude that the infection was acquired in California.

Correction: A forty-year review of Rocky Mountain spotted fever cases in California shows clinical and epidemiologic changes

[This corrects the article DOI: 10.1371/journal.pntd.0010738.].

Assessment of Physician Knowledge, Attitudes, and Practice for Lyme Disease in a Low-Incidence State

Lyme disease (LD), caused by the bacterium Borrelia burgdorferi, is transmitted to humans in California through the bite of infected blacklegged ticks (Ixodes pacificus). Overall, the incidence of LD in California is low: approximately 0.2 confirmed cases per 100,000 population. However, California's unique ecological diversity results in wide variation in local risk, including regions with local foci at elevated risk of human disease. The diagnosis of LD can be challenging in California because the prior probability of infection for individual patients is generally low. Combined with nonspecific symptoms and complicated laboratory testing, California physicians need a high level of awareness of LD in California to recognize and diagnose LD efficiently. This research addresses an under-studied area of physicians' knowledge and practice of the testing and treatment of LD in a low-incidence state. We assessed knowledge and practices related to LD diagnosis using an electronic survey distributed to physicians practicing in California through mixed sampling methods. Overall, responding physicians in California had a general awareness of Lyme disease and were knowledgeable regarding diagnosis and treatment. However, we found that physicians in California could benefit from further education to improve test-ordering practices, test interpretation, and awareness of California's disease ecology with elevated levels of focal endemicity, to improve recognition, diagnosis, and treatment of LD in California patients.

A forty-year review of Rocky Mountain spotted fever cases in California shows clinical and epidemiologic changes

Rocky Mountain spotted fever (RMSF) is a life-threatening tick-borne disease documented in North, Central, and South America. In California, RMSF is rare; nonetheless, recent fatal cases highlight ecological cycles of the two genera of ticks, Dermacentor and Rhipicephalus, known to transmit the disease. These ticks occur in completely different habitats (sylvatic and peridomestic, respectively) resulting in different exposure risks for humans. This study summarizes the demographic, exposure, and clinical aspects associated with the last 40 years of reported RMSF cases to the California Department of Public Health (CDPH). Seventy-eight RMSF cases with onsets from 1980 to 2019 were reviewed. The incidence of RMSF has risen in the last 20 years from 0.04 cases per million to 0.07 cases per million (a two-fold increase in reports), though the percentage of cases that were confirmed dropped significantly from 72% to 25% of all reported cases. Notably, Hispanic/Latino populations saw the greatest rise in incidence. Cases of RMSF in California result from autochthonous and out-of-state exposures. During the last 20 years, more cases reported exposure in Southern California or Mexico than in the previous 20 years. The driver of these epidemiologic changes is likely the establishment and expansion of Rhipicephalus sanguineus sensu lato ticks in Southern California and on-going outbreaks of RMSF in northern Mexico. Analysis of available electronically reported clinical data from 2011 to 2019 showed that 57% of reported cases presented with serious illness requiring hospitalization with a 7% mortality. The difficulty in recognizing RMSF is due to a non-specific clinical presentation; however, querying patients on the potential of tick exposure in both sylvatic and peridomestic environments may facilitate appropriate testing and treatment.

Borrelia burgdorferi and Borrelia miyamotoi seroprevalence in California blood donors

The western blacklegged tick, Ixodes pacificus, an important vector in the western United States of two zoonotic spirochetes: Borrelia burgdorferi (also called Borreliella burgdorferi), causing Lyme disease, and Borrelia miyamotoi, causing a relapsing fever-type illness. Human cases of Lyme disease are well-documented in California, with increased risk in the north coastal areas and western slopes of the Sierra Nevada range. Despite the established presence of B. miyamotoi in the human-biting I. pacificus tick in California, clinical cases with this spirochete have not been well studied. To assess exposure to B. burgdorferi and B. miyamotoi in California, and to address the hypothesis that B. miyamotoi exposure in humans is similar in geographic range to B. burgdorferi, 1,700 blood donor sera from California were tested for antibodies to both pathogens. Sampling was from high endemic and low endemic counties for Lyme disease in California. All sera were screened using the C6 ELISA. All C6 positive and equivocal samples and nine randomly chosen C6 negative samples were further analyzed for B. burgdorferi antibody using IgG western blot and a modified two ELISA test system and for B. miyamotoi antibody using the GlpQ ELISA and B. miyamotoi whole cell sonicate western blot. Of the 1,700 samples tested in series, eight tested positive for antibodies to B. burgdorferi (0.47%, Exact 95% CI: 0.20, 0.93) and two tested positive for antibodies to B. miyamotoi (0.12%, Exact 95% CI: 0.01, 0.42). There was no statistically significant difference in seroprevalence for either pathogen between high and low Lyme disease endemic counties. Our results confirm a low frequency of Lyme disease and an even lower frequency of B. miyamotoi exposure among adult blood donors in California; however, our findings reinforce public health messaging that there is risk of infection by these emerging diseases in the state.

New Exposure Location for Hantavirus Pulmonary Syndrome Case, California, USA, 2018

We describe a case of hantavirus pulmonary syndrome in a patient exposed to Sin Nombre virus in a coastal county in California, USA, that had no previous record of human cases. Environmental evaluation coupled with genotypic analysis of virus isolates from the case-patient and locally trapped rodents identified the likely exposure location.

Detection of Rickettsia Species in Fleas Collected from Cats in Regions Endemic and Nonendemic for Flea-Borne Rickettsioses in California

Rickettsia typhi, transmitted by rat fleas, causes most human flea-borne rickettsioses worldwide. Another rickettsia, Rickettsia felis, found in cat fleas, Ctenocephalides felis, has also been implicated as a potential human pathogen. In the continental United States, human cases of flea-borne rickettsioses are reported primarily from the southern regions of Texas and California where the cat flea is considered the principal vector. In California, more than 90% of locally acquired human cases are reported from suburban communities within Los Angeles and Orange counties despite the almost ubiquitous presence of cat fleas and their hosts throughout the state. The objective of this study is to assess the presence and infection rate of Rickettsia species in cat fleas from selected endemic and nonendemic regions of California. Cat fleas were collected from cats in Los Angeles County (endemic region) and Sacramento and Contra Costa counties (nonendemic region). Sequencing of 17 amplicons confirmed the presence of R. felis in both the endemic and non-endemic regions with a calculated maximum likelihood estimation of 131 and 234 per 1000 fleas, respectively. R. typhi was not detected in any flea pools. Two R. felis-like genotypes were also detected in fleas from Los Angeles County; Genotype 1 was detected in 1 flea pool and Genotype 2 was found in 10 flea pools. Genotype 1 was also detected in a single flea pool from Sacramento County. Results from this study show that R. felis is widespread in cat flea populations in both flea-borne rickettsioses endemic and nonendemic regions of California, suggesting that a high prevalence of this bacterium in cat fleas does not predispose to increased risk of human infection. Further studies are needed to elucidate the role of R. felis and the two R. felis-like organisms as etiologic agents of human flea-borne rickettsioses in California.

Tickborne relapsing fever - United States, 1990-2011

Tickborne relapsing fever (TBRF) is a zoonosis caused by spirochetes of the genus Borrelia and transmitted to humans by ticks of the genus Ornithodoros. TBRF is endemic in the western United States, predominately in mountainous regions. Clinical illness is characterized by recurrent bouts of fever, headache, and malaise. Although TBRF is usually a mild illness, severe sequelae and death can occur. This report summarizes the epidemiology of 504 TBRF cases reported from 12 western states during 1990-2011. Cases occurred most commonly among males and among persons aged 10‒14 and 40‒44 years. Most reported infections occurred among nonresident visitors to areas where TBRF is endemic. Clinicians and public health practitioners need to be familiar with current epidemiology and features of TBRF to adequately diagnose and treat patients and recognize that any TBRF case might indicate an ongoing source of potential exposure that needs to be investigated and eliminated.

Description of Babesia duncani n.sp. (Apicomplexa: Babesiidae) from humans and its differentiation from other piroplasms

The morphologic, ultrastructural and genotypic characteristics of Babesia duncani n.sp. are described based on the characterization of two isolates (WA1, CA5) obtained from infected human patients in Washington and California. The intraerythrocytic stages of the parasite are morphologically indistinguishable from Babesia microti, which is the most commonly identified cause of human babesiosis in the USA. Intraerythrocytic trophozoites of B. duncani n.sp. are round to oval, with some piriform, ring and ameboid forms. Division occurs by intraerythrocytic schizogony, which results in the formation of merozoites in tetrads (syn. Maltese cross or quadruplet forms). The ultrastructural features of trophozoites and merozoites are similar to those described for B. microti and Theileria spp. However, intralymphocytic schizont stages characteristic of Theileria spp. have not been observed in infected humans. In phylogenetic analyses based on sequence data for the complete18S ribosomal RNA gene, B. duncani n.sp. lies in a distinct clade that includes isolates from humans, dogs and wildlife in the western United States but separate from Babesia sensu stricto, Theileria spp. and B. microti. ITS2 sequence analysis of the B. duncani n.sp. isolates (WA1, CA5) show that they are phylogenetically indistinguishable from each other and from two other human B. duncani-type parasites (CA6, WA2 clone1) but distinct from other Babesia and Theileria species sequenced. This analysis provides robust molecular support that the B. duncani n.sp. isolates are monophyletic and the same species. The morphologic characteristics together with the phylogenetic analysis of two genetic loci support the assertion that B. duncani n.sp. is a distinct species from other known Babesia spp. for which morphologic and sequence information are available.

A review of the small canine piroplasms from California: Babesia conradae in the literature

Small piroplasms as a cause of canine babesiosis in southern California were first documented in 1990. Initially these piroplasms were considered to be Babesia gibsoni, the only small Babesia parasite known to infect dogs at that time. In the following decade, the use of molecular analysis made it clear that small canine Babesia in fact are comprised of at least three distinct species, and the isolates from dogs in southern California were not B. gibsoni. Molecular, antigenic, and morphological characteristics of the southern California species of canine piroplasm supported naming it as a distinct species, Babesia conradae. The renaming of this species prompted this literature review of small canine piroplasms in California in order to clarify clinical, diagnostic, epidemiological, and molecular characteristics of B. conradae in comparison to other small canine piroplasms. Clinical symptoms of B. conradae are similar to those of B. gibsoni; however, B. conradae infections may be more pathogenic, resulting in higher parasitaemia and more pronounced anaemia when compared with B. gibsoni-infected dogs. The immunofluorescent antibody test is the most commonly used test to diagnose B. conradae. It is important to specify which small Babesia species to test for since there is little serological cross reactivity between the small canine Babesia antigens or cross-detection in the newer molecular tests. Molecular characterization of B. conradae, based principally on the 18S small subunit rRNA gene, and recently the second internal transcribed spacer region, demonstrate that B. conradae is most closely related to piroplasms recovered from humans and animals in the western United States.

Babesia conradae, sp. Nov., a small canine Babesia identified in California

Small piroplasms as a cause of canine babesiosis have usually been identified as Babesia gibsoni. Recent genetic studies suggested that small piroplasms are more likely comprised of at least three genotypically distinct species. In southern California, canine babesiosis caused by a small piroplasm has been documented since 1990. Morphological characteristics of this parasite include a small (0.3-3.0 microm) intraerythrocytic merozoite stage with predominantly ring, piriform, tetrad, amoeboid, or anaplasmoid forms. Transmission electron microscopic images of merozoites demonstrate the presence of an apical complex consisting of an inner subplasmalemmal membrane and rhoptries. Based on phylogenetic analyses of the 18S rRNA and the ITS-2 genes, the Californian small piroplasm isolate is more closely related to piroplasm isolates from wildlife and humans in the western United States than it is to B. gibsoni. Molecular and morphologic evidence supports naming the small piroplasm from southern California as a distinct species, Babesia conradae.

Lyme borreliosis

Despite more than 25 years' experience with Lyme borreliosis, much remains to be learned about this complex zoonosis. Practicing veterinarians, particularly those in the northeastern and upper midwestern states, where Lyme borreliosis is highly endemic, should be familiar with the ecologic features and typical clinical signs of Lyme borreliosis. Interpretation of signs and serologic test results should be made with consideration of the regional prevalence of Lyme borreliosis and the animal's opportunity for exposure to infected Ixodes spp. The availability of recently marketed topical acaracides is a valuable adjunctive measure in prevention of Lyme borreliosis. A maximally effective prevention strategy should include consideration of environmental modification, activity restrictions, routine examinations for ticks, prompt removal of attached ticks, and vaccination. Technologic advances, such as the C6 EIA and the Osp A recombinant vaccine, offer the promise of additional tools for the clinical management and prevention of this tick-borne zoonosis.

Investigation of transfusion transmission of a WA1-type babesial parasite to a premature infant in California

BACKGROUND

A premature infant in California developed respiratory distress associated with infection with a protozoal parasite, Babesia. The infant had received two blood transfusions, one from the father and one from an anonymous donor (Donor A). This study describes the follow-up required to identify the source and species of Babesia that infected the infant.

STUDY DESIGN AND METHODS

At the time of the infant's illness, whole blood from the infant, father, and mother was evaluated for Babesia infection. Similar evaluation of whole blood from Donor A was performed 2 months after the suspected donation to the infant. Samples were tested using blood smear examination, serology, PCR, and hamster inoculation. Identity of the recovered Babesia parasites was confirmed by DNA amplification by PCR, genetic sequencing of the 18S gene, and phylogenetic analysis.

RESULTS

WA1-type Babesia was recovered from the infant. Neither parent was the source of infection. Serology and hamster inoculation confirmed WA1-type Babesia infection in Donor A. DNA sequences of the 18S gene from the infant and donor isolates were 100% identical.

CONCLUSION

WA1-type Babesia infections may be difficult to detect among blood donors because such infections can be subclinical. This is the second WA1-type Babesia transmission via blood transfusion and the first in an infant. Physicians in the western United States should consider Babesia as a possible cause of nonspecific febrile illness after a blood transfusion.

Babesia leo n. sp. from lions in the Kruger National Park, South Africa, and its relation to other small piroplasms

Babesia leo, a small piroplasm isolated from lions in South Africa is described as a distinct species based on a phylogenetic analysis of the 18S rRNA gene. Intraerythrocytic trophozoite and merozoite stages of B. leo are morphologically indistinguishable from other small piroplasms of felids. Previous studies showed that B. leo was biologically and antigenically distinct from B. felis, which is known to infect wild and domestic felids in South Africa. Molecular characterization showed strong support for the phylogenetic seperation of B. leo as a distinct species from B. felis and other felid piroplasms. Phylogenetic analysis also showed that Babesia microti and all of the felid piroplasms from Africa with known 18S rRNA gene sequences available, including B. leo, formed a single, separate clade, sister to the other babesial and theilerial piroplasm parasites.

Description and epidemiology of Theileria youngi n. sp. from a northern Californian dusky-footed woodrat (Neotoma Fuscipes) population

An epidemiologic study designed to identify the small mammal reservoir for the zoonotic WA1-type babesial parasite resulted in the discovery of a small, intraerythrocytic piroplasm in smeared blood from dusky-footed woodrats (Neotoma fuscipes) in northern California. The woodrat parasites were isolated and compared to other piroplasm parasites based on their morphology, antigenicity, and genetic characteristics. These studies indicated that the woodrat parasites were not the WA1-type babesial agent but were of the genus Theileria. We accordingly named it Theileria youngi. The prevalence in the woodrat population was high (61%). Infection was unrelated to gender or age of the woodrats. Potential vectors for this tick-transmitted parasite included 3 species of ticks recovered from the woodrats. Dermacentor occidentalis, Ixodes woodi, and Ixodes pacificus. Mostly larval or nymphal stages were recovered, suggesting transstadial transmission is possible. This is the first piroplasm fully characterized from a dusky-footed woodrat.

There are at least three genetically distinct small piroplasms from dogs

The 18S nuclear subunit ribosomal RNA (18S rRNA) gene of small piroplasms isolated from dogs from Okinawa (Japan), Oklahoma, North Carolina, Indiana, Missouri, and Alabama, was isolated and sequenced. Phylogenetic analysis of these sequences and comparisons with sequences from other Babesia, Cytauxzoon, and Theileria species revealed that all canine small babesial isolates, with the exception of isolates from California and Spain, were placed in a group containing the Babesia spp. sensu stricto. Within the Babesia spp. sensu stricto, there was support for separating the small canine piroplasms from the large canine piroplasm, Babesia canis. The isolate from California was in a distinct phylogenetic clade, closely related to babesial isolates from wildlife and humans from the Western US. The canine isolate from Spain was closely related to Babesia microti. These results suggest that there are multiple small piroplasm species in dogs. The isolates from the Midwestern and Eastern US and the one from Japan probably represent a single species with wide geographic distribution.

Human babesiosis: an emerging tick-borne disease

Human babesiosis is an important emerging tick-borne disease. Babesia divergens, a parasite of cattle, has been implicated as the most common agent of human babesiosis in Europe, causing severe disease in splenectomized individuals. In the US, Babesia microti, a babesial parasite of small mammals, has been the cause of over 300 cases of human babesiosis since 1969, resulting in mild to severe disease, even in non-splenectomised patients. Changing ecology has contributed greatly to the increase and expansion of human babesiosis in the US. A relatively recently described babesial parasite, the WA1-type, has been shown to be the causative agent in seven human cases in the western US. This parasite is closely related to babesial parasites isolated from large wild ungulates in California. Like B. microti, WA1-type parasites cause mild to severe disease and the immunopathogenesis of these parasites is distinctly different from each other in experimental infections of hamsters and mice. A B. divergens-like parasite was also identified as the cause of a fatal human babesiosis case in Missouri. Isolated cases of human babesisosis have been described in Africa and Mexico, but the causative parasites were not well characterized. Standard diagnostic techniques for human infection, such as examination of Giemsa-stained thin blood smears and serology, have been complemented with molecular techniques, such as PCR. Current treatment for babesiosis is focused on a regimen of clindamycin and quinine, although new drugs have shown promise. Prevention of infection relies on self-monitoring for the presence of ticks and, in some locations, targeted application of pesticides to decrease tick abundance. Identification of human infection with Babesia spp. will probably increase as physicians and the public become more aware of the disease, as people live and recreate in rural tick-infested areas, and as the numbers of immunocompromised individuals increase.

Phylogenetic relationships of human and wildlife piroplasm isolates in the western United States inferred from the 18S nuclear small subunit RNA gene

The 18S nuclear small subunit ribosomal RNA gene of piroplasms from wildlife and human cases of babesiosis in the western USA were isolated by PCR and sequenced. Phylogenetic analyses of these sequences and comparisons with sequences from other Babesia and Theileria species revealed that piroplasm isolates from the human cases were indistinguishable from some of the isolates from the western wildlife species, most notably the isolates from mule deer (Odocoileus hemionus). These results suggest that large ungulates may serve as reservoirs for human piroplasm infection. The western piroplasm isolates from humans and wildlife formed a distinct clade, separate from other piroplasms found worldwide.

Theileriosis in a Missouri beef herd caused by Theileria buffeli: case report, herd investigation, ultrastructure, phylogenetic analysis, and experimental transmission

A 6-year-old Simmental cow infected with Theileria buffeli had a clinical disease characterized by theilerial parasitemia, macrocytic normochromic anemia with acanthocytosis and spherocytosis, lymphoid hyperplasia (lymphocytosis, edematous lymphadenomegaly), dysproteinemia, evidence of liver disease, and a low serum antibody titer against T. buffeli. The cow was in a herd in which all cattle originated in Missouri; 22/75 (29%) of cattle had a theilerial parasitemia and 26/75 (35%) had titers to T. buffeli of > or =1:160. Classification of the Missouri bovine organism as T. buffeli was based on DNA sequencing and comparison to sequences for T. buffeli and Theileria sp. type A obtained from GenBank. Intraerythrocytic veils and piroplasms were seen during transmission electron microscopy. The organism was successfully transmitted to two splenectomized calves, which developed mild anemias while parasitemic. Blood from the second calf was used as the source of T. buffeli antigen for an indirect immunofluorescence antibody test. Theilerial isolates from a Missouri white-tailed deer were also sequenced and resembled Theileria sp. types F and G and were not consistent with the bovine organism.

Seroepidemiology of emerging tickborne infectious diseases in a Northern California community

A seroprevalence and risk factor study of emerging tickborne infectious diseases (Lyme disease, ehrlichiosis, and babesiosis) was conducted among 230 residents of a semirural community in Sonoma County, California. Over 50% of residents reported finding a tick on themselves in the preceding 12 months. Samples from 51(23%) residents were seroreactive to antigens from one or more tickborne disease agents: 1.4% to Borrelia burgdorferi, 0.4% to Ehrlichia equi, 4.6% to Ehrlichia chaffeensis, and 17.8% to the Babesia-like piroplasm WA1. Only 14 (27%) of these seroreactive residents reported one or more symptoms compatible with these diseases. Seroreactivity was significantly associated with younger age (<16 years), longer residence in the community (11-20 years), and having had a physician's diagnosis of Lyme disease. In northern California, the risk of infection with these emerging tickborne diseases, particularly in children, may be greater than previously recognized.

Transfusion-transmitted babesiosis in Washington State: first reported case caused by a WA1-type parasite

Most cases of babesiosis reported in the United States have been tickborne and caused by Babesia microti, the etiologic agent of all previously described transfusion-transmitted cases. A 76-year-old man with the first recognized case of transfusion-transmitted infection with the recently identified WA1-type Babesia parasite is described. The subject received multiple blood transfusions in 1994. Indirect immunofluorescent antibody testing of serum from 57 blood donors implicated a 34-year-old man (WA1 titer, 1:65,536) whose donation had been used for packed red cells. Isolates of the organisms that infected the recipient and the donor, both of whom were spleen-intact residents of Washington State, were obtained by hamster inoculation. The DNA sequence of a 536-bp region of the nuclear small subunit-rRNA gene of both isolates was identical to that of WA1 (isolated in 1991 from the index WA1 case-patient). Effective measures for preventing transmission of babesiosis by blood transfusion are needed.

Seroprevalence of two Babesia spp. isolates in selected bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus) populations in California

Sera from 111 bighorn sheep (Ovis canadensis) and 95 mule deer (Odocoileus hemionus) were tested using an indirect immunofluorescence assay for antibodies to two isolates of Babesia spp. recently obtained from these hosts in California (USA). The study populations were from six locations: three areas of real or potential sympatry of bighorn sheep and deer, one area with deer only, and two areas with bighorn sheep only. Antibody titers from seroreactive individuals were similar with both babesial isolate antigens (P < 0.05), and seroprevalence was highest in the areas of host sympatry. A moderate to high seroprevalence (> or = 30%) in some of the study populations was evidence that babesial parasites may be common in bighorn sheep and mule deer in some areas of California.