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PubMed1995

Transmission of Borrelia burgdorferi by Ixodes pacificus nymphs and reservoir competence of deer mice (Peromyscus maniculatus) infected by tick-bite.

The transmission of Borrelia burgdorferi to deer mice (Peromyscus maniculatus) by Ixodes pacificus nymphs was investigated experimentally. Deer mice were exposed to infected nymphs for 24, 48, or 72 hr, or until ticks had fed to repletion (> or = 96 hr). Infection status of hosts was assessed 4 wk later by culture of ear-punch biopsies in BSK II medium and by indirect immunofluorescence. Eight mice exposed to ticks for 24 hr did not become Infected. In contrast, infection was acquired by 1 of 9 (11%), 2 of 8 (25%), and 8 of 10 (80%) mice exposed for 48, 72, and > or = 96 hr, respectively. Eight weeks after exposure to infected nymphs, the infectivity of 5 deer mice for I. pacificus larvae was assessed. Overall, 33% of I. pacificus larvae fed on these mice acquired and transstadially passed spirochetes. We conclude that most I. pacificus nymphs require 4 days or longer to transmit spirochetes to deer mice, and that larvae efficiently acquire and maintain spirochetes from mice that have been infected by tick-bite.

Animals↗
PubMed1995

Oocyst output, periodicity, and immunity of two deer mouse (Peromyscus maniculatus) eimerians (Eimeria arizonensis and Eimeria delicata).

We compared the life histories of 2 eimerians (Eimeria arizonensis and Eimeria delicata), which co-occur in the deer mouse (Peromyscus maniculatus). Laboratory-reared deer mice were given 10(3), 10(4) (E. delicata), or 10(3), 10(4), or 10(5) (E. arizonensis) oocysts by stomach intubation. Eimeria arizonensis infections lasted longer (11-13 days) than E. delicata infections (9-10 days). Eimeria arizonensis infections also produced more oocysts for each oocyst ingested at both levels compared. Both parasites exhibited periodicity in oocyst output at all levels compared. However, peaks in E. arizonensis output occurred at approximately 20-24-hr intervals, whereas peaks in E. delicata output occurred at 12-16-hr intervals. Finally, deer mice developed immunity to both eimerians after only 1 inoculation at all levels tested. Based on these parameters, we expect E. arizonensis to have a greater reproductive potential than E. delicata in free-living deer mice.

Analysis of Variance↗
PubMed1993

Detection of Borrelia burgdorferi in tissues of experimentally infected Peromyscus leucopus by the polymerase chain reaction.

A polymerase chain reaction (PCR) assay was used to amplify a 158 base pair (bp) DNA fragment from the ospA locus of Borrelia burgdorferi. This assay could identify all of four distinct B. burgdorferi isolates from Oklahoma and could detect as little as 50 x 10(-15) g of purified DNA from B. burgdorferi (JD-1) after agarose gel electrophoresis and ethidium bromide staining. The assay was used to detect the Lyme spirochete in the heart, liver, spleen, kidney and urinary bladder of four experimentally infected Peromyscus leucopus and results were compared with detection by in vitro cultivation in BSK-II media. Fifteen of twenty organs examined showed 158 bp amplification products. Except for one kidney sample all organs that were culture-positive were also positive by PCR. Two culture-negative heart samples and one culture-negative liver sample were PCR positive. The results indicate that this PCR assay may be useful for detection of B. burgdorferi from field-caught wildlife hosts in epidemiological investigations.

Animals↗
PubMed1993

Enteral and parenteral phases of Trichinella nativa and Trichinella pseudospiralis in the deer mouse, Peromyscus maniculatus.

Trichinella nativa and Trichinella pseudospiralis infections in a wild rodent host, the deer mouse (Peromyscus maniculatus), were characterized. Forty-six percent of 400 inoculated T. nativa were recovered on day 4 postinoculation (PI); 77% and 23% were found in the small and large intestines, respectively. Thirty-one percent of the worms recovered on day 4 remained in the large intestine beyond day 20 PI. Worms were embedded in the mucosa of the small intestine, cecum, and colon. Females recovered from the small and large intestines had statistically indistinguishable in vitro larval releases. Distension of the cecum and passage of loose stools were associated with the presence of worms in the large intestine. The ability of T. nativa to establish and thrive in the large intestine of deer mice was confirmed following intracecal implantation of first-stage larvae. On day 4 PI, 35% of 400 inoculated T. pseudospiralis were recovered, with 91% and 9% found in the small and large intestines, respectively. Although T. pseudospiralis established in the large intestine of deer mice, few worms remained beyond day 20. Females recovered from the small and large intestines had statistically indistinguishable in vitro larval releases. Although higher establishments of T. nativa (56% vs. 46%) and T. pseudospiralis (52% vs. 35%) were observed in CD-1 mice than in deer mice on day 4 PI, neither was able to colonize the large intestine of the former. The large intestine may be a more important habitat for adult trichinae than previously recognized.

Animals↗
PubMed1993

Age- and gender-related variations in the activities of drug-metabolizing and antioxidant enzymes in the white-footed mouse (Peromyscus leucopus).

The effects of aging on the activities of drug-metabolizing enzymes and antioxidant enzymes were studied in male and female White-Footed mice (Peromyscus leucopus) at ages of 6, 8, 12, 18, 24, 30, 36, and 48 months. Male mice had significantly higher liver microsomal cytochrome P450 (P450) content and NADPH:cytochrome P450 oxidoreductase (P450 reductase) activities than females at all age groups. Many of the P450-dependent enzyme activities were also generally higher in males. Female mice showed age-dependent decreases in P450 content and the activities of P450 reductase, pentoxyresorufin O-dealkylase (PROD) and N-nitrosodimethylamine demethylase (NDMAd) in the liver from 6 to 24 months; while, the males showed an age-dependent decrease only for the liver PROD activity from 6 to 24 months. The old males (30-month old) appeared to have significantly higher activities for 6 beta-, 2 beta-, 16 alpha- and 16 beta-testosterone and androstenedione formation than the middle-aged (6- to 18-month old) and very old (48-month old) males. Females showed age-dependent decreases for the formation of 6 beta-, 2 beta-, 16 alpha- and 16 beta-testosterone in liver microsomes from 6 to 24 months. Lung microsomes from 6- and 8-month old males had much higher activities of ethoxyresorufin O-deethylase (EROD) and PROD than older males. The total NNK alpha-hydroxylation activities changed in the same pattern as lung microsomal EROD and PROD activities in both male and female mice. The activities of several phase II drug-metabolizing enzymes: glutathione S-transferase (GST), DT-diaphorase, sulfotransferase and UDP-glucuronosyl-transferase (UDPGT) did not show any significant age-dependent changes, with the possible exception that the GST activity in males decreased from 18 to 36 months. Males had about 3-fold higher UDPGT activities than females among all age groups. Glutathione peroxidase activities were drastically lower in old and very old males, and 6 to 24 months old males had significantly higher activities than the corresponding females. In females, superoxide dismutase activities decreased linearly to extremely low levels as mice aged. Catalase activities showed a tendency for increase with age in males. In conclusion, some P450-dependent activities and antioxidant enzymes, but not phase II drug-metabolizing enzymes, showed age-dependent changes; and most of these changes occur from 6 to 24 months. The demographic attributes of the White-Footed mouse are well-suited for physiological and biochemical studies of aging and can complement the more standard laboratory mouse model with its typical two year life span.

Age Factors↗
PubMed1996

Population dynamics of two species of Eimeria (Apicomplexa: Eimeriidae) in deer mice (Peromyscus maniculatus): biotic and abiotic factors.

I investigated whether biotic factors (competitive exclusion between parasites and host immunity), abiotic factors (high temperature, low temperature, and rainfall), or a combination of the 2 affected the population dynamics of Eimeria arizonensis and Eimeria delicata in naturally infected deer mice (Peromyscus maniculatus). There was no evidence of competitive exclusion between E. arizonensis and E. delicata, nor were E. arizonensis population dynamics affected by host immunity (young deer mice were not infected significantly more frequently than adults). However, high temperatures were negatively associated with the prevalence of observed infections (r = -0.725, P < 0.001), suggesting sporulation of oocysts might be affected. In contrast, juvenile deer mice were infected with E. delicata more frequently than adults (z = 2.05, P < 0.02), suggesting that host immunity plays a role in the population dynamics of E. delicata. Temperature and rainfall during oocyst sporulation were not significantly associated with the prevalence of observed E. delicata infections. Finally, there was no evidence that a combination of biotic and abiotic factors was important in the population dynamics of either eimerian. Thus, the population dynamics of E. arizonensis seem to be controlled by abiotic factors, whereas those of E. delicata seem to be affected by biotic factors.

Age Factors↗
PubMed1997

Spatial distribution of larval Ixodes scapularis (Acari:Ixodidae) on Peromyscus leucopus and Microtus pennsylvanicus at two island sites.

Larval blacklegged ticks, Ixodes scapularis, were collected from white-footed mice. Peromyscus leucopus, on Prudence Island (where Microtus pennsylvanicus were not captured) and from meadow voles. M. pennsylvanicus, on Patience Island (where P. leucopus was absent) in Narragansett Bay, Rhode Island from June to October 1992. Ixodes scapularis larvae were also collected by flagging in the vicinity of host captures. On both islands, the relative density of larvae changed from July to September in samples from hosts, but not in flagging samples. Consequently, different sampling techniques can give different assessments of tick populations. Larvae were highly aggregated on both of the host species throughout the sampling period. As the mean relative density of larvae increased in the environment (based on flagging samples), larvae on the hosts became more dense and more crowded. Increased densities of larvae in the environment were not correlated with increased patchiness in the distribution of larvae among host animals on either island. Changes in the spatial distribution of larval I. scapularis on each host species had similar trends as larval densities and distributions within the environment. These results suggest that M. pennsylvanicus can serve as an alternative host for immature I. scapularis in a P. leucopus-free environment and have similar distributional characteristics.

Analysis of Variance↗
PubMed1997

Susceptibility of Peromyscus leucopus and Mus musculus to infection with Baylisascaris procyonis.

In this study, we compared the susceptibility of Peromyscus leucopus (white-footed mouse), a common natural intermediate host, and Mus musculus, a commonly used experimental model, to infection with larvae of the raccoon ascarid, Baylisascaris procyonis. Three groups of 10 mice of each species were given 50, 250, or 500 infective B. procyonis eggs by gavage. The mice were observed daily for clinical signs of central nervous system (CNS) disease and at necropsy the distribution of larvae in 10 body regions and organs was determined and compared. Clinical CNS disease developed in 57% of P. leucopus and 93% of M. musculus. The average clinical incubation period was significantly longer in P. leucopus (20.6 days postinfection [PI]) than in M. musculus (10.7 days PI), and clinical disease progressed slower in P. leucopus. Significantly fewer larvae were recovered from P. leucopus than from M. musculus. Most larvae were recovered from the anterior carcass and viscera of P. leucopus and from the carcass, head, and brain of M. musculus. CNS invasion was dose dependent in M. musculus but not in P. leucopus. Few or no grossly visible larval granulomas were present in P. leucopus but were abundant in M. musculus. We concluded that P. leucopus was less susceptible than M. musculus to B. procyonis infection, based on a decreased intensity of infection, longer clinical incubation period or lack of clinical disease, slower progression of disease, different larval distribution, and lower tissue reactivity to larvae.

Animals↗
PubMed1998

Physiological responses of deer mice (Peromyscus maniculatus) to infection with Capillaria hepatica (Nematoda).

Negative effects due to infection have not been documented for most natural host-parasite associations. I performed an infection experiment to measure the physiological consequences of infection by Capillaria hepatica in deer mice (Peromyscus maniculatus gracilis). Compared to their uninfected siblings, infected mice displayed increased serum concentrations of alkaline phosphatase and total proteins and reduced concentrations of albumin. Infected mice also had higher hematocrits and enlarged livers and spleens. There was no difference in swimming endurance between infected and control animals, possibly because mice did not perform at maximum aerobic capacity. Sex differences in alkaline phosphatase and albumin levels suggest that females are more sensitive to similar burdens of C. hepatica. Different hematocrit responses between mice from 2 localities suggest that historical associations can lead to evolutionary change in pathophysiology caused by this nematode. Further experiments would reveal whether these disturbances lead to reductions in host fitness.

Alkaline Phosphatase↗
PubMed1997

Paternal investment and reproductive success in the California mouse, Peromyscus californicus

In species with biparental care, the degree of parental investment of each parent may be related to the size of the litter, the parental effort of the partner and the probability of future reproductive success with the same partner. These factors were examined in single females and mated pairs of Peromyscus californicus who were required to 'forage' for food by running in a wheel. Offspring survival and growth, parental behaviour, amount of food obtained by running in the wheel and inter-birth intervals between litters were recorded. Females alone were able to raise litters of two pups, but not four pups. Mated pairs were able to raise a litter of four pups. Litters of one or two pups reared with the mother alone grew as fast as pups reared with both parents. Single females that kept their pups alive had a mean inter-birth interval of 53 days; paired females had a mean inter-birth interval of 37 days. These results show the effect of male parental investment on reproductive success when parents must forage for food: the presence of the male resulted in four times as many pups reared over a 74-day period as a female could rear on her own.

Journal Article↗
PubMed1996

Copper, Zinc, and Cadmium Concentrations in Peromyscus maniculatus Sampled Near an Abandoned Copper Mine

Concentrations of zinc, copper, and cadmium were determined in soil and liver, kidney, bone and stomach contents of deer mice (Peromyscus maniculatus) from two sites near an abandoned mine and one control site, on Vancouver Island, British Columbia, Canada. Soil concentrations of copper were significantly elevated at the mine and off site vs the reference site. In contrast, there was no difference in soil cadmium and zinc concentrations between the mine and reference site. Concentrations of copper, cadmium and zinc in livers of mice from the mine site were significantly elevated relative to the reference and off site locations. Cadmium kidney concentrations tended to be greater in mice from the mine versus the off site and reference site. No differences in bone cadmium, copper and zinc and, kidney copper and zinc concentrations were noted among mice from the three locations. Diet of mice from mine and off sites contained significantly greater copper concentrations than the reference population; no differences in cadmium or zinc diet concentrations in mice from the three sites were noted. Comparison of ratios of metal concentrations in diet:soil and concentrations in liver:soil suggest that for zinc and copper, soil and diet are of equal importance as a source of metal contamination to these mice. In contrast, cadmium diet:soil and cadmium liver:soil ratios were much greater than one indicative of bioconcentration of cadmium from soil to diet and from soil to liver. For assessing routes of metal exposure, in this case for deer mice inhabiting an abandoned mine site, for copper and zinc, soil will most likely be indicative of exposure conditions. In contrast, concentrations of cadmium in diet will be more representative of amounts that the animal is potentially ingesting. Of further importance is that relative to reference sites, mice inhabiting an abandoned copper mine site have significantly elevated tissue levels of copper. This is turn will provide a route of metal exposure to carnivorous birds such as owls and hawks. The toxicological significance of this exposure to birds of prey has yet to be assessed adequately.

Journal Article↗
PubMed1976

Genetic and developmental variation of hemoglobin in the deermouse, Peromyscus maniculatus.

A genetic investigation of electrophoretic hemoglobin variants of the deermouse, Peromyscus maniculatus, shows three alleles, Hblf, Hblr, and Hblo, at a duplicated site controlling the six adult phenotypes. The Hblf allele has not been described previously. The hemoglobin locus is not closely linked to the albino locus. Fetal hemoglobin is distinct from any of the adult components and has a slower electrophoretic mobility. The fetal phenotype changes to the adult type between the days 15 and 18 of prenatal life.

Alleles↗
PubMed1976

Hemoglobin polymorphism in the encinal mouse, Peromyscus pectoralis.

Horizontal starch gel electrophoresis revealed five hemoglobin phenotypes in natural populations of the encinal mouse, Peromyscus pectoralis, from northeastern Mexico. Populations of the encinal mouse from Texas, Oklahoma, and northwestern and north central Mexico were monomorphic for multiple-band phenotypes. Analysis of the hemoglobin polymorphism indicates that two loci control this variation.

Animals↗
PubMed1975

Hereditary cataracts in deer mice (Peromyscus maniculatus).

A new type of hereditary cataract was predicted in the deer mouse (Peromyscus maniculatus) by the presence of syndactyly of the hind feet. Early morphologic changes were found in the equatorial cells that differentiated into new lens fibers. Later swelling at the anterior and posterior poles of these cells produced lens opacities. Anterior and posterior subcapsular cataracts progressed to a hypermature shrunken lens.

Animals↗
PubMed1977

Space utilization of Peromyscus: social and spatial factors.

Space utilization of Peromyscus maniculatus bairdi and P. leucopus noveboracensis was studied in laboratory enclosures. After 1 week, individuals were given access to twice as much space for an additional week. The new rea was either vacant or was occupied by a similarly experienced conspecific of the same or opposite sex. Patterns of space utilization and reaction to the doubling of space were species specific. Each species displayed specific patterns of social behaviour and only P. maniculatus reproduced. Both species exhibited similar patterns of space utilization in the presence of another individual. Social regulation of space utilization did not result from territorial defence of mutually exclusive areas, but from the initial mutual avoidance of two individuals.

Aggression↗
PubMed1985

Two daily melatonin injections differentially induce nonshivering thermogenesis and gonadal regression in the mouse (Peromyscus leucopus).

Female white-footed mice (Peromyscus leucopus) were injected twice daily with 5, 10, 50, 100 micrograms melatonin (MEL) or saline. Injections were given for 7 weeks at 2 and 12 hours after lights-on under a long day (LD 16:8) photoperiod. Afternoon administration of MEL induced gonadal regression, although a dose of 50 micrograms or more was necessary to obtain a maximal response. A 5 micrograms MEL injection in the afternoon resulted in intermediate reproductive tract weights. In white-footed mice a morning MEL injection did not abolish the reproductive regression induced by an afternoon injection. Mice receiving 10, 50 or 100 micrograms MEL daily exhibited increased nonshivering thermogenesis (NST), irrespective of the timing of the injection. Daily injections of 5 micrograms MEL had little effect on NST. These observations suggest that "up and down regulation" of MEL receptors may not be important in P. leucopus. Further, the mechanism by which MEL controls reproduction is different from that for NST.

Animals↗
PubMed1988

Effect of smelter emissions on the hemogram of the deer mouse (Peromyscus maniculatus).

Blood samples were obtained from 284 deer mice (Peromyscus maniculatus) live-trapped near two base metal smelters in northern Manitoba, Canada. Hemoglobin and hematocrit values were significantly higher in mice trapped within 40-70 km of the smelters compared to those in control areas 185 to 190 km from the smelter. These increases appear to be normal physiological responses to a mild respiratory stress, as in a true secondary polycythemia of anoxic tupe. The mice are sensitive bioindicators of sulphur dioxide emissions that apparently induce the higher blood values.

Journal Article↗
PubMed2000

Phylogeography of Peromyscus furvus (Rodentia; muridae) based on cytochrome b sequence data.

We conducted phylogenetic analyses of cytochrome b sequence data to assess genetic variation within and among the three allopatric segments of the distribution of Peromyscus furvus from the Sierra Madre Oriental in eastern Mexico. We identified 24 unique haplotypes among the 54 individuals examined and genetic distances ranged up to 0.078 substitutions per site. Populations from the central portion of the range formed a monophyletic unit, whereas samples from the southern distributional unit were polyphyletic. Furthermore, the southernmost population sampled may represent a distinct species. This high degree of genetic differentiation among populations, currently recognized as conspecific, mirrors the result of other genetic studies of highland rodents in Mesoamerica. Together these studies indicate that the region, already considered hyperdiverse on the basis of species diversity and endemism, may contain considerably greater diversity than is currently appreciated.

Animals↗