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PubMed1987

Oral infection of Peromyscus maniculatus with Borrelia burgdorferi and subsequent transmission by Ixodes dammini.

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.

Animals↗
PubMed1990

Systemic disease in Peromyscus leucopus associated with Borrelia burgdorferi infection.

Sixteen wild Peromyscus leucopus, trapped for the establishment of a breeding colony, developed signs of neurological damage (trembling, incoordination, circling, head tilt, and lameness of the rear legs) 2-47 days after capture in southern Wisconsin. Spirochetes were cultured from the brain of 5/11 mice, and Borrelia burgdorferi was cultured from 1 brain. A spirochete was isolated from the bladder of 1 mouse. The spirochete was identified by fluorescent antibody staining with the monoclonal antibody specific for B. burgdorferi, H5332. Serum antibodies to the spirochete were found in 14/15 mice. Negative results were obtained in all tests for viruses and bacteria, including Listeria (2/2), Mycoplasma (2/2), mouse hepatitis virus (10/10), Theilers's encephalomyelitis virus (GD VII) (8/8), REO 3 virus (2/2), and lymphocytic choriomeningitis virus (4/4). There was no bacterial growth from brains cultured on eosin methylene blue or blood agar (3/3). Histologic lesions included nonsuppurative cellular infiltrates in the brain, kidney, liver, and lung. Three outbred Swiss-Webster mice were inoculated orally with a suspension of the brain in BSKII medium, and 3 were inoculated with unpassed B. burgdorferi cultured from the brain of a P. leucopus with motor dysfunction. Five of the inoculated mice developed antibody titers of 1:128; one mouse was positive at 1:256. Motor signs of neurologic damage developed in 3/6 mice 2-24 weeks post-inoculation, and B. burgdorferi was detected in the brains of 2 mice by isolation and by fluorescent antibody.

Animals↗
PubMed1999

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.

Animals↗
PubMed1978

Effects of bot fly (Cuterebra) parasitism on activity patterns of Peromyscus maniculatus in the laboratory.

Peromyscus maniculatus subjected to bot fly (Cuterebra) parasitism in the laboratory showed significant changes in amount and temporal distribution of several activity patterns. Strenuous activities, such as running in an exercise wheel or stereotypic somersaulting, declined while less strenuous activities associated with maintenance behaviors increased. Diurnal response to handling and disturbance declined significantly in infected mice. The temporal distribution of nocturnal activity was altered, and may affect vulnerability of infected mice to small predators. Most changes persisted for at least a week postinfection.

Animals↗
PubMed1978

Vulnerability of bot fly (Cuterebra) infected Peromyscus maniculatus to shorttail weasel predation in the laboratory.

In the laboratory, Peromyscus bearing a single Cuterebra larva are no more vulnerable to weasel predation than are uninfected control mice, and may be taken less often under certain conditions. Mice bearing two or more larvae appear to be more vulnerable than either controls or singly infected mice. Their increased vulnerability probably results from their failure to use arboreal pathways. Decreased activity may be responsible for the relative advantage of singly infected mice. Previous reports of higher survivorship among mice with a single bot parasite than among uninfected mice, and of lower survivorship among multiply infected mice, may result in part from differential predation rates.

Animals↗
PubMed1980

Modes of ectoparasite reinfestations of deer mice (peromyscus maniculatus).

Modes of ectoparasite reinfestations were studied on ectoparasite-free deer mice (Peromyscus maniculatus) returned to their natural habitat on the Tule Lake National Wildlife Refuge, Siskiyou County, California, during the summer of 1977. The age of the host made no significant difference in the mode of reinfestation of lice, fleas, or mites. Flea reinfestation rates were related to the sex of the host, requiring 4 and 2 days, respectively, to reach control levels on male and female hosts. Mite populations reached the control level within 1 day, regardless of the sex of the host. No statistically significant louse reinfestations were noted within 8 days after the hosts were released. The percent of the host population reinfested with each ectoparsite followed the same patterns of reinfestation as the numbers of each parasite per host. It is suggested that the mode of ectoparasite reinfestations is a function of the behavior of the host relative to the lifestyles of the ectoparasite species.

Age Factors↗
PubMed1987

Experimental infection and horizontal transmission of Modoc virus in deer mice (Peromyscus maniculatus).

Deer mice (Peromyscus maniculatus) were inoculated with a sublethal dose of a field strain of Modoc virus to determine patterns of viral persistence, shedding, and transmission. Blood, serum, urine, fecal, and oral swab samples were collected at selected intervals until 63 days postinoculation (PI) after which lung, liver, spleen, kidney, and salivary glands were explanted. Viral assays were conducted by intracranial inoculations of suckling mice and antibody titers were determined by the micro-complement-fixation test. Viremias lasted for up to 4 days PI. Antibody titers were present by day 8 PI, peaked at day 13-20 PI, and persisted until day 63 PI. There was no evidence of viral shedding in urine, fecal, or oral swab samples. Virus was detected in explanted lungs only. In a separate experiment, deer mice were inoculated with virus and lungs were removed from five mice per wk for 10 wk. Indirect fluorescent antibody (IFA) techniques were used to determine the location of virus in lung tissue and to examine fixed tissue for lesions. IFA showed virus in lung parenchymal cells beginning 42 days PI and persisting at least 70 days PI. No histopathologic changes were seen. Horizontal transmission of the virus was studied by placing uninoculated mice with inoculated mice for 42 days and determining if the test animals developed antibodies or had virus in their lungs. Fifty-percent of the uninoculated mice developed antibody. One of these animals had virus in its lungs. Therefore, Modoc virus may be transmitted by direct contact.

Animals↗
PubMed1989

Annual cyclicity of gall stone prevalence in deer mice (Peromyscus maniculatus gambelii).

The prevalence of gall stones (100% cholesterol) in a deer mouse (Peromyscus maniculatus) population located in Siskiyou County, California (USA) was studied on a monthly basis from February 1985 through January 1988. During each year we documented a pronounced annual cyclicity with peak prevalence (31 to 53%) during the winter and low prevalence (2 to 3%) during late summer. Gall stone prevalence was not related to sex or age of the animal. The earliest onset of gall stone production and the maximum prevalence achieved were associated with the greatest abundance of deer mice; lower levels of population abundance were associated with later onset of gall stone production and lower peak prevalences. This association of gall stone prevalence with both season and population abundance levels suggests that the causative factor(s) is/are related to the quality and availability of the diet.

Age Factors↗
PubMed1992

Seasonal prevalence of Taenia taeniaeformis: relationship to age, sex, reproduction and abundance of an intermediate host (Peromyscus maniculatus).

Livers from 4,501 deer mice (Peromyscus maniculatus) collected from a weedy habitat in northeastern California during 48 consecutive monthly samplings were examined microscopically for Taenia taeniaeformis larva. Although there were pronounced seasonal fluctuations in host density, there were no significant annual or season-related differences in cestode intensities in adult deer mice. There were no significant differences in prevalences associated with sex of the host, nor were there significant changes in level of reproduction noted between infected and non-infected hosts. There were, however, significant differences in prevalences between young (1.2%) and adult (4.2%) hosts. Plausible mechanisms for this age-related difference in prevalence rates include (1) differential susceptibility due to the activity pattern of adult mice and/or (2) passive immunity in neonates as a result of colostrum- and/or transplacentally-transferred immunoglobulins and (3) capture of subadult animals before they had completed the period of highest susceptibility to T. taeniaeformis. Density of larvae per mouse liver was determined during a 21 mo consecutive period. The intensity of T. taeniaeformis larvae was not significantly different between the sexes of the adult mice. The larval stage showed an overdispersion pattern within the adult population. These results suggest that determinations of T. taeniaeformis abundances can be accurately made, at least in this P. maniculatus population, at any time of the year provided adjustment is made for the relative age structure of the host population.

Age Factors↗
PubMed1992

Isolation of Borrelia burgdorferi from Peromyscus leucopus in Oklahoma.

Borrelia burgdorferi was isolated from a field-caught Peromyscus leucopus from central Oklahoma (USA). The strain was identified as B. burgdorferi by reaction with monoclonal antibody H5332 specific for the outer surface protein OspA of B. burgdorferi. This represents the first isolation of B. burgdorferi from a wild mouse outside of the normal range of the known vectors Ixodes dammini and I. pacificus.

Animals↗
PubMed1992

Borrelia burgdorferi infection in white-footed mice (Peromyscus leucopus) in hemlock (Tsuga canadensis) habitat in western Pennsylvania.

White-footed mice (Peromyscus leucopus) were captured and their tissues sampled from 27 sites in seven counties of western Pennsylvania in 1990 for isolation and identification of Borrelia burgdorferi. Two hundred sixty mice were captured from which there were 27 isolations. Significantly more mice were captured and significantly more isolations made from hemlock (Tsuga canadensis) habitat than from deciduous species forest. Hemlock habitat is sparse and focal but evidently increases winter survival of mice, and thus possibly results in increased infection rates in mice.

Animals↗
PubMed1995

Ear biopsy location influences detection of Borrelia burgdorferi by PCR, but not by culture in naturally infected Peromyscus leucopus.

We determined if the ear biopsy location affected detection of Borrelia burgdorferi when either culture or the polymerase chain reaction (PCR) was used among 50 white-footed mice (Peromyscus leucopus), live-captured in a Lyme disease enzootic area in Maryland (USA) between March and October of 1991 and 1992. The infection status of individual mice was determined by organ culture; ear biopsy samples were obtained from the peripheral and central part of the ear for detection of B. burgdorferi by culture and by PCR. Overall, B. burgdorferi was cultured from one or more tissue samples in 33 (66%) of 50 captured mice. Among infected mice, B. burgdorferi was detected by culture in 29 (88%) of 33 peripheral and 28 (85%) of 33 central ear biopsy samples. By PCR it was detected in 24 (73%) of 33 peripheral and all 33 central samples (P = 0.002). Detection of B. burgdorferi by culture was independent of the ear biopsy location; however, the organism was detected by PCR with greater frequency in central ear biopsy samples as compared to peripheral samples. Agreement between culture and PCR was moderate (Kappa = 0.64) on peripheral ear samples and excellent (Kappa = 0.79) on central samples. We propose that when ear biopsy samples are used to detect B. burgdorferi by PCR in wild-caught P. leucopus, removal of biopsy samples from the central part of the ear will achieve maximum sensitivity and will achieve the highest concordance between assays when both culture and PCR of ear biopsy samples are conducted in parallel.

Animals↗
PubMed2003

Analyses of gene flow among populations of deer mice (Peromyscus maniculatus) at sites near hantavirus pulmonary syndrome case-patient residences.

Gene flow and potential for Sin Nombre virus (SNV) trafficking of the deer mouse (Peromyscus maniculatus) was studied in Delta and Mesa counties of western Colorado (USA). The study areas included Grand Mesa and surrounding grazing and agricultural areas. This area has several natural potential barriers to rodent gene flow, including rivers, cliffs, and mountains. Ten study sites were utilized in a spatially nested design ranging from 0.65-81 km apart; four of these sites were at or near human hantavirus pulmonary syndrome (HPS) case-patient residences. One HPS case occurred on the north side of Grand Mesa in 1993; the other three (two confirmed, one presumptive) occurred on the south side of Grand Mesa between 1999-2000. Blood and tissue samples were collected from each of 221 deer mice captured from 1999-2000. Blood samples were tested for IgG antibody to SNV. At least one deer mouse had antibody to SNV at nine of 10 sites. Genomic DNA was isolated from tissue samples and alleles at six microsatellite loci were amplified by polymerase chain reaction (PCR). Polymorphisms were resolved on denaturing polyacrylamide gels and visualized by silver staining. Traditional population genetic analyses of this study indicated moderate population subdivision among the populations surveyed, slight evidence of isolation by distance, and that the Gunnison River system may hinder gene flow in this area. Application of assignment tests indicated that approximately 73-85% of mice were assigned to their population of capture. Many of the misclassifications occurred among sites less than 1 km apart; however, some long-distance misclassifications were noted. Additionally, some misclassifications were noted among study sites on different sides of the Gunnison River system, indicating that the riparian corridor of this system may facilitate some gene flow. Overall, these data indicate that SNV trafficking is more likely at the local level, but some long-distance trafficking may be possible, especially where select habitat variables favor long-distance movements.

Animals↗
PubMed2004

Effects of heavy metals on immunocompetence of white-footed mice (Peromyscus leucopus).

Continued human population growth and industrialization result in increased contamination of wildlife habitats. Effects of such habitat deterioration on the well-being of natural populations are unclear. Exposure to contaminants may impair immunocompetence, thereby increasing disease susceptibility. The mammalian immune system is important in maintaining health and in its sensitivity to toxins. In our study conducted from May 1999 through May 2001, we examined assays of immnnoompetence in the white-footed mouse (Peromyscus leucopus) that inhabited reference sites and sites significantly contaminated with mixtures of heavy metals. We estimated potential exposure and uptake of heavy metals by measuring the level of each contaminant in representative soil and tissue samples. Intraindividual variation across mice, but not sex, explained a large portion of the overall variance in immune response, and spleen weight was significanltly afflicted by mouse age. We found no evidence that residence on contaminated sites had any effect on immunopathology and humoral immunity as measured in our study. We suggest that field and laboratory studies in ecotoxicology provide estimates of exposure to contaminants (i.e., tissue analyses) to establish a database suitable to clarify the dose-response relationship between contaminants and target systems.

Age Distribution↗
PubMed1999

Hematology values from clinically healthy Peromyscus leucopus.

Reported herein are hematocrit and total and differential WBCs obtained from 132 clinically healthy male and female white-footed mice (Peromyscus leucopus) of four different age groups: 4, 5-8, 9-20, and >32 wk old. Minimal differences were identified between the age groups. The number and percentage of neutrophils in the 4-wk-old mice were significantly higher than those in the other groups; the relative percentage of lymphocytes in the 4-wk-old mice was significantly lower than in the 9-20-wk-old mice. The only significant gender effects identified were higher numbers of WBCs and lymphocytes in females of the 4-wk-old group and higher hematocrits in males of the 5-8- and >32-wk-old groups.

Aging↗
PubMed2000

Type 2 diabetes mellitus, hyperlipidemia, and extremity lesions in California mice (Peromyscus californicus) fed commercial mouse diets.

BACKGROUND AND PURPOSE: We characterized abnormalities of carbohydrate and lipid metabolism and determined whether those metabolic abnormalities are associated with extremity lesions in California mice (Peromyscus californicus). METHODS: Blood samples were evaluated for glucose, cholesterol, triglyceride, and insulin concentrations. Necropsy and histologic evaluation were done on selected mice, including staining pancreatic sections for insulin. Physical examinations also were performed. RESULTS: California mice were found to have Type 2 diabetes mellitus (T2DM). Sections of pancreas from diabetic and prediabetic mice had pathologic changes consistent with T2DM. After six months of feeding a low-fat diet, mice were normoglycemic, normotriglyceridemic, and normocholesterolemic. Some mice remained hyperinsulinemic. Traumatic lesions were not associated with T2DM. CONCLUSIONS: California mice develop diet-related T2DM when fed a diet containing 25.8% kcal from fat. California mice may be a useful animal model of human T2DM, and traumatic lesions result from housing California mice in multiple male groups.

Animal Feed↗
PubMed2001

Establishment of a deer mouse (Peromyscus maniculatus rufinus) breeding colony from wild-caught founders: comparison of reproductive performance of wild-caught and laboratory-reared pairs.

The deer mouse (Peromyscus maniculatus) is a natural reservoir for several human pathogens, but little is known about the mechanisms by which such pathogens are maintained in nature. As a first step toward developing a colony of deer mice that were permissive for infection with Sin Nombre (SN) hantavirus, we collected 68 wild P. maniculatus rufinus from central New Mexico. Mice from this cohort were used to establish 26 breeding pairs, of which 85% were fertile. In subsequent generations, fertility decreased slightly to 73% (N = 59) in laboratory-reared F1 and F2 pairs. Wild-caught females delivered 7.2 litters on average (range, 1 to 18), whereas laboratory-reared pairs delivered 5.5 (range, 1 to 13). The average time between pairing and first litter was 106 days for wild-caught animals, whereas that for laboratory-reared pairs was 71 days. None of the pairs displayed a seasonal breeding preference. Cannibalistic behavior increased from 5% in founders to 26% in laboratory-reared pairs. Mean litter size for wild-caught females was 4.3, whereas that for laboratory-reared dams was 4. Founding animals have been maintained in captivity for longer than 2 years, with only 2 deaths (4.8%). Our colony is competent for infection with SN virus. Thus, it should be useful for testing of models for maintenance of SN virus in wild rodents, and other aspects of the virus-host relationship.

Animal Husbandry↗
PubMed1992

Survival and reproduction in Peromyscus leucopus in the laboratory: viable model for aging studies.

White-footed mice Peromyscus leucopus reared in our laboratory from wild-caught parents lived at least to 5.5 years. Once past weaning, over 80% of the mice lived at least until two years. Females maintained a constant weight whereas the weight of males increased until four years and decreased thereafter. At four-years of age both sexes bred successfully with mates of the same age, but had lower success with younger mice. Some males and females reproduced at five years of age.

Aging↗