Borrelia burgdorferi promotes the establishment of Babesia microti in the northeastern United States.

Babesia microti and Borrelia burgdorferi, the respective causative agents of human babesiosis and Lyme disease, are maintained in their enzootic cycles by the blacklegged tick (Ixodes scapularis) and use the white-footed mouse (Peromyscus leucopus) as primary reservoir host. The geographic range of both pathogens has expanded in the United States, but the spread of babesiosis has lagged behind that of Lyme disease. Several studies have estimated the basic reproduction number (R0) for B. microti to be below the threshold for persistence (<1), a finding that is inconsistent with the persistence and geographic expansion of this pathogen. We tested the hypothesis that host coinfection with B. burgdorferi increases the likelihood of B. microti transmission and establishment in new areas. We fed I. scapularis larva on P. leucopus mice that had been infected in the laboratory with B. microti and/or B. burgdorferi. We observed that coinfection in mice increases the frequency of B. microti infected ticks. To identify the ecological variables that would increase the probability of B. microti establishment in the field, we integrated our laboratory data with field data on tick burden and feeding activity in an R0 model. Our model predicts that high prevalence of B. burgdorferi infected mice lowers the ecological threshold for B. microti establishment, especially at sites where larval burden on P. leucopus is lower and where larvae feed simultaneously or soon after nymphs infect mice, when most of the transmission enhancement due to coinfection occurs. Our studies suggest that B. burgdorferi contributes to the emergence and expansion of B. microti and provides a model to predict the ecological factors that are sufficient for emergence of B. microti in the wild.

Borrelia miyamotoi sensu lato seroreactivity and seroprevalence in the northeastern United States.

Borrelia miyamotoi sensu lato, a relapsing fever Borrelia sp., is transmitted by the same ticks that transmit B. burgdorferi (the Lyme disease pathogen) and occurs in all Lyme disease-endemic areas of the United States. To determine the seroprevalence of IgG against B. miyamotoi sensu lato in the northeastern United States and assess whether serum from B. miyamotoi sensu lato-infected persons is reactive to B. burgdorferi antigens, we tested archived serum samples from area residents during 1991-2012. Of 639 samples from healthy persons, 25 were positive for B. miyamotoi sensu lato and 60 for B. burgdorferi. Samples from ≈10% of B. miyamotoi sensu lato-seropositive persons without a recent history of Lyme disease were seropositive for B. burgdorferi. Our results suggest that human B. miyamotoi sensu lato infection may be common in southern New England and that B. burgdorferi antibody testing is not an effective surrogate for detecting B. miyamotoi sensu lato infection.

Quantitative PCR for detection of Babesia microti in Ixodes scapularis ticks and in human blood.

Babesia microti, the primary cause of human babesiosis in the United States, is transmitted by Ixodes scapularis ticks; transmission may also occur through blood transfusion and transplacentally. Most infected people experience a viral-like illness that resolves without complication, but those who are immunocompromised may develop a serious and prolonged illness that is sometimes fatal. The geographic expansion and increasing incidence of human babesiosis in the northeastern and midwestern United States highlight the need for high-throughput sensitive and specific assays to detect parasites in both ticks and humans with the goals of improving epidemiological surveillance, diagnosis of acute infections, and screening of the blood supply. Accordingly, we developed a B. microti-specific quantitative PCR (qPCR) assay (named BabMq18) designed to detect B. microti DNA in tick and human blood samples using a primer and probe combination that targets the 18S rRNA gene of B. microti. This qPCR assay was compared with two nonquantitative B. microti PCR assays by testing tick samples and was found to exhibit higher sensitivity for detection of B. microti DNA. The BabMq18 assay has a detection threshold of 10 copies per reaction and does not amplify DNA in I. scapularis ticks infected with Babesia odocoilei, Borrelia burgdorferi, Borrelia miyamotoi, or Anaplasma phagocytophilum. This highly sensitive and specific qPCR assay can be used for detection of B. microti DNA in both tick and human samples. Finally, we report the prevalence of B. microti infection in field-collected I. scapularis nymphs from three locations in southern New England that present disparate incidences of human babesiosis.

Transovarial transmission of Borrelia spirochetes by Ixodes scapularis: a summary of the literature and recent observations.

Transovarial transmission (TOT) of Borrelia burgdorferi (sensu lato), the agent of Lyme disease, by the Ixodes persulcatus group of hard ticks (Ixodidae) has frequently been reported in the literature since the discovery of Lyme disease 1982. Evidence for and against TOT by B. burgdorferi has led to uncertainty and confusion in the literature, causing misconceptions that may have public health consequences. In this report, we review the published information implicating B. burgdorferi as a bacterium transovarially transmitted among ticks of the Ixodes persulcatus group and present new data indicating the transovarially transmitted agent is actually Borrelia miyamotoi. B. miyamotoi, first described in 1995, is antigenically and phylogenetically related to B. burgdorferi, although more closely related to the relapsing fever-group Borrelia typically transmitted by soft ticks (Argasidae). Borrelia infections of unfed larvae derived from egg clutches of wild-caught Ixodes scapularis are demonstrated to result from transovarial transmission of B. miyamotoi, not B. burgdorferi. The presence of this second Borrelia species, apparently sympatric with B. burgdorferi worldwide also may explain other confusing observations reported on Borrelia/Ixodes relationships.

Colpodella spp.-like parasite infection in woman, China.

The phylum Apicomplexa comprises intracellular protozoa that include many human pathogens. Their nearest relatives are chromerids and colpodellids. We report a case of a Babesia spp.-like relapsing infection caused by a newly described microorganism related to the Apicomplexa. This case is highly suggestive of a previously undescribed type of colpodellid that infects vertebrates.

Effects of tick control by acaricide self-treatment of white-tailed deer on host-seeking tick infection prevalence and entomologic risk for Ixodes scapularis-borne pathogens.

We evaluated the effects of tick control by acaricide self-treatment of white-tailed deer on the infection prevalence and entomologic risk for three Ixodes scapularis-borne bacteria in host-seeking ticks. Ticks were collected from vegetation in areas treated with the "4-Poster" device and from control areas over a 6-year period in five geographically diverse study locations in the Northeastern United States and tested for infection with two known agents of human disease, Borrelia burgdorferi and Anaplasma phagocytophilum, and for a novel relapsing fever-group spirochete related to Borrelia miyamotoi. Overall, 38.2% of adults and 12.5% of nymphs were infected with B. burgdorferi; 8.5% of adults and 4.2% of nymphs were infected with A. phagocytophilum; and 1.9% of adults and 0.8% of nymphs were infected with B. miyamotoi. In most cases, treatment with the 4-Poster device was not associated with changes in the prevalence of infection with any of these three microorganisms among nymphal or adult ticks. However, the density of nymphs infected with B. burgdorferi, and consequently the entomologic risk for Lyme disease, was reduced overall by 68% in treated areas compared to control areas among the five study sites at the end of the study. The frequency of bacterial coinfections in ticks was generally equal to the product of the proportion of ticks infected with a single bacterium, indicating that enzootic maintenance of these pathogens is independent. We conclude that controlling ticks on deer by self-application of acaricide results in an overall decrease in the human risk for exposure to these three bacterial agents, which is due solely to a reduction in tick density.