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The Lyme borreliosis agent Borrelia burgdorferi and the relapsing fever group species Borrelia miyamotoi co-occur in the United States. We used species-specific, quantitative polymerase chain reaction to study both species in the blood and skin of Peromyscus leucopus mice and host-seeking Ixodes scapularis nymphs at a Connecticut site. Bacteremias with B. burgdorferi or B. miyamotoi were most prevalent during periods of greatest activity for nymphs or larvae, respectively. Whereas B. burgdorferi was 30-fold more frequent than B. miyamotoi in skin biopsies and mice had higher densities of B. burgdorferi densities in the skin than in the blood, B. miyamotoi densities were higher in blood than skin. In a survey of host-seeking nymphs in 11 northern states, infection prevalences for B. burgdorferi and B. miyamotoi averaged approximately 0.20 and approximately 0.02, respectively. Co-infections of P. leucopus or I. scapularis with both B. burgdorferi and B. miyamotoi were neither more nor less common than random expectations.

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.

The number of Lyme disease cases in Oregon has increased in recent years despite the fact that the pathogen, Borrelia burgdorferi, has never been isolated in the state. Rodent and tick surveys were undertaken in 1997 to isolate and characterize strains of B. burgdorferi from Oregon and to identify potential reservoirs and vectors of Lyme disease. Borrelia burgdorferi was isolated from Neotoma fuscipes, Peromyscus maniculatus, P. boylii, and Ixodes pacificus. Both N. fuscipes and P. maniculatus were infested with I. pacificus and I. spinipalpis. Although I. pacificus infested P. boylii, I. spinipalpis was not found on this rodent, and only 4% of the P. boylii were infected with B. burgdorferi compared with the 19% and 18% infection rates found in N. fuscipes and P. maniculatus, respectively. Variation in the molecular weights of the outer surface proteins A and B were found in these first confirmed isolates of B. burgdorferi from Oregon, as well as truncated forms of outer surface protein B.

The purposes of this study were to determine if hantaviruses were present in the Great Lakes port areas of Wisconsin and Minnesota and if so, to identify which virus and which rodent host species were involved. Rodents were trapped in Duluth, Minnesota, Superior, Green Bay, and Milwaukee, Wisconsin, all ports of call for international maritime shipping. A total of 675 wild rodents were captured and tested, including 310 meadow voles (Microtus pennsylvanicus), 173 Norway rats (Rattus norvegicus), 179 Peromyscus spp., (including white footed mice [P. leucopus] and deer mice [P. maniculatus gracilis and P. maniculatus bairdii]), and 13 house mice (Mus musculus). Twenty percent of the rats, 17% of the meadow voles, 8% of the house mice, and 3% of the Peromyscus spp. had antibody to a hantavirus by immunofluorescent antibody assay (IFA). By the plaque-reduction neutralization test (PRNT), nine of 36 meadow voles, one of 4 P. leucopus, and one of 34 rats had hantavirus antibody, with the highest titers to Prospect Hill (PH) virus. All of the PRNT-seropositive individuals were from the twin cities of Superior and Duluth. Hantavirus antigen was detected in lung tissue by IFA in M. pennsylvanicus and Peromyscus spp., but not in rats. Two hantaviruses, designated SD-1 and SD-2, were isolated from M. pennsylvanicus captured in Duluth and found to be very similar to prototype PH virus by cross-IFA and cross-PRNT. Virus isolation attempts were unsuccessful from tissues of the Peromyscus spp. and the rats.

We determined if deer mice (Peromyscus maniculatus) could be infected by Borrelia burgdorferi and develop sufficient spirochetemia to infect larval Ixodes dammini. Ten P. maniculatus were infected orally with 0.05 ml phosphate buffered saline containing approximately 400 B. burgdorferi. On days 21 or 28 after infection (AI) larval I. dammini were fed on the deer mice. Each of the P. maniculatus developed antibodies (up to 7 log2) to B. burgdorferi and B. burgdorferi was isolated from the blood of 1 deer mouse on day 51 AI. Nymphs resulting from these larvae were then allowed to feed on 10 uninfected P. maniculatus. All 10 of these tick-infected P. maniculatus developed antibodies (up to 7 log2) to B. burgdorferi, and B. burgdorferi was isolated from the blood of 1 of the 10 P. maniculatus 15 days after tick feeding and from the pooled organs of another of the tick-infected P. maniculatus. Six of the orally infected P. maniculatus developed clinical signs including ruffled hair coat, inappetence, reluctance to move, and lameness in the rear legs. All P. maniculatus tissues were grossly and histologically normal on necropsy. These findings show that P. maniculatus are susceptible to oral infection and develop sufficient spirochetemias to infect I. dammini larvae.

Using the vector tick, Ixodes dammini, we described the reservoir competence of the white-footed mouse, Peromyscus leucopus, for the Lyme disease spirochete, Borrelia burgdorferi. Nymphal I. dammini were used to infect mammals, and larval ticks were used to diagnose infection (a form of xenodiagnosis). One tick was nearly as efficient as more than 1 in transmitting the spirochete to mice. The duration of the prepatent period was about 1 week. Prevalence of infection approached 100% in ticks that fed as larvae on mice infected 2 or 3 weeks previously. Thereafter, infectivity gradually decreased, but duration exceeded 200 days. Hamsters, too, became infectious for larval I. dammini. This report formally demonstrates the life cycle of B. burgdorferi as it seems to occur in nature. We conclude that the white-footed mouse is a competent reservoir for the Lyme disease spirochete.

In evaluating the white-footed mouse as a reservoir host for the Lyme disease spirochete, we compared spirochete infection in vector ticks (Ixodes dammini) having different histories of attachment to these mice, estimated their relative importance as hosts for immature I. dammini and compared the seasonality of tick activity and spirochetemia in mice. Infection in trapped white-footed mice appears to be universal. Prevalence of spirochetal infection in I. dammini correlates with frequency of attachment to mice, and in mice, with the season of vector activity. The relative abundance of this mouse makes it numerically the most important host for I. dammini. Most immature I. dammini appear to attach to white-footed mice. Taken together, these considerations demonstrate that the white-footed mouse serves as reservoir for the Lyme disease spirochete in coastal Massachusetts.

In order to determine if Peromyscus spp. could become infected with the Lyme disease spirochete (Borrelia burgdorferi) by direct inoculation and to determine the duration of spirochetemia, 4 P. leucopus and 5 P. maniculatus were inoculated by the intramuscular, intraperitoneal, and subcutaneous routes with an isolate of B. burgdorferi obtained from the blood of a trapped wild P. leucopus from Camp McCoy, Wisconsin. All of the mice developed antibodies to B. burgdorferi which reached a peak indirect immunofluorescent (IFA) geometric mean antibody titer of 10 log2 21 days post-inoculation. B burgdorferi was recovered from the blood of 1 P. maniculatus 21 days post-inoculation. One uninfected Peromyscus of each species was housed in the same cage with the infected Peromyscus as a contact control. Both of the contact controls developed IFA B. burgdorferi antibodies by day 14, indicating contact infection. To determine if B. burgdorferi was being transmitted by direct contact, 5 uninfected P. leucopus and 5 uninfected P. maniculatus were caged with 3 B. burgdorferi infected P. leucopus and 3 infected P. maniculatus, respectively. Each of these contact-exposed P. leucopus and P. maniculatus developed antibodies to B. burgdorferi, and B. burgdorferi was isolated from the blood of 1 contact-exposed P. maniculatus 42 days post-initial contact. These findings show that B. burgdorferi can be transmitted by direct contact without an arthropod vector.

Identification of foci of vector-borne diseases does not require knowledge of exact abundances of vectors and pathogens; rather, a focus is defined by the presence, or some minimal level of abundance, of a vector and pathogen. Stepwise discriminant analysis (DA) was applied to data on free-ranging adult wood ticks (the vector) and to data on isolations of Colorado tick fever virus from small mammals. Trap stations were grouped on the basis of relative abundance of wood ticks for one set of analyses and on the presence or absence of virus for another set of analyses. Additional data consisted of easily measured environmental variables. It is concluded that DA provides a useful tool for analysis of ecosystem structure and an effective means of identifying foci of infection.