Bartonella species were isolated from the blood of 63 of 325 Rattus norvegicus and 11 of 92 Rattus rattus from 13 sites in the United States and Portugal. Infection in both Rattus species ranged from 0% (e.g., 0/87) to approximately 60% (e.g., 35/62). A 337-bp fragment of the citrate synthase (gltA) gene amplified by polymerase chain reaction was sequenced from all 74 isolates. Isolates from R. norvegicus were most similar to Bartonella elizabethae, isolated previously from a patient with endocarditis (93%-100% sequence similarity), followed by Bartonella grahamii and other Bartonella species isolated from Old World rodents (Clethrionomys species, Mus musculus, and Rattus species). These data suggest that Rattus species are a reservoir host for pathogenic Bartonella species and are consistent with a hypothesized Old World origin for Bartonella species recovered from Rattus species introduced into the Americas.

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Small mammals were livetrapped during 12 months in crop fields and weedy borders at 18 sites in central Argentina. A total of 1,652 mammals of 14 species was captured during 33,060 trap-nights. Six species of rodents comprised >95% of captures. Periodically disturbed fields of crops were dominated by Calomys musculinus and C. laucha, and to a lesser extent Mus musculus. A second group composed of Akodon azarae, Bolomys obscurus, and Oligoryzomys flavescens primarily inhabited the more stable, weedy borders of cultivated fields. Peaks in relative densities of C. musculinus, C. laucha, and M. musculus were observed in summer and early autumn, and populations declined to low numbers in winter, following harvest. In contrast, maxima for A. azarae, B. obscurus, and 0. flavescens were in late autumn and early winter, and numbers never declined to low values seen for the other species. These characteristic differences in habitat associations and relative densities of pampas rodents may reflect colonizing potential, as both Calomys and Mus potentially are highly opportunistic genera. The common rodent species of the central Argentine pampas show distinct habitat associations, interspecific interactions, and reproductive rates. Akodon azarae and Bolomys obscurus, for example, are found predominantly in more stable linear habitats (fencerows, roadsides, and railroad rights-of-way), and may be behaviorally dominant over the two species of Calomys (de Villafanie et al., 1977; Kravetz, 1977). Species of Calomys frequently are numerically dominant in cultivated fields and have been described as better colonizers than Akodon and Bolomys by virtue of larger litter size, reproduction at younger age, and high frequency of postpartum estrus (de Villafanie et al., 1977). Interspecific interactions and seasonal changes in suitability of habitats may result in different patterns in population processes among rodent species that inhabit the pampas. Four of >10 species of rodents present (C. musculinus, C. laucha, A. azarae, and Mus musculus) were implicated as hosts of Junin virus, etiologic agent of Argentine hemorrhagic fever (Sabattini and Contigiani, 1982; Sabattini et al., 1977), a serious viral disease infecting humans in a small area in southern Santa Fe and C6rdoba, and northern Buenos Aires and La Pampa provinces. As a consequence, many ecological studies during the past 30 years were directed toward understanding and controlling the rodent reservoir of this disease. In crop fields, lower densities of rodents were found in soybeans than in corn (Busch et al., 1984; Maiztegui et al., 1986), suggesting that reducing cultivation of corn in favor of soybean production would decrease populations of rodents. Further, as a correlation was observed between high densities of rodents in corn fields and high incidence of Argentine hemorrhagic fever (Instituto de Virologia de C6rdoba, 1966; Sabattini and Maiztegui, 1970), this change of cultivation practices also may lead to lower incidence of the disease (Busch et al., 1984). A model of ...

Abstract. 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.Since Lyme disease was first described in 1977, 1 it has become the most commonly reported vector-borne disease in the United States. 2 The disease, which is caused by the spirochete Borrelia burgdorferi, 3,4 is transmitted to humans by the bite of an Ixodid tick: Ixodes scapularis in the eastern and northcentral parts of the United States (I. dammini 5 as synonymized by Oliver and others 6 ) and I. pacificus 7,8 in the western United States. An enzootic cycle involving vertebrate hosts and ticks is critical for the maintenance of the spirochete in Lyme disease enzootic areas in the eastern and mid-central parts of the United States because the rate of transovarial transmission of the spirochete in I. scapularis is extremely low. 9 Transovarial transmission of B. burgdorferi in I. pacificus has been demonstrated; 10 however, on the west coast of the United States the relative importance of ticks and vertebrate animals in the maintenance of B. burgdorferi remains unclear.Although B. burgdorferi has been isolated from a wide variety of mammalian and avian hosts in the eastern and northcentral parts of the United States, 11,12 only white-footed mice (Peromyscus leucopus), 13,14 chipmunks (Tamias striatus) and meadow voles (Microtus pennsylvanicus), 15 skunks (Mephitis mephitis) and raccoons (Procyon lotor), 16 and Norway rats (Rattus norvegicus) 17 have been shown to be competent reservoir hosts of B. burgdorferi in enzootic cycles of the organism in those areas. White-footed mice, in comparison with meadow voles and chipmunks 15 and skunks and raccoons, 16 are generally recognized in these areas as the most important reserv...

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