Transmission of Toxoplasma gondii in Panama City, Panama: a five-year prospective cohort study of children, cats, rodents, birds, and soil

A cohort of more than 500 children from Panama City, Panama was studied prospectively over five years for acquisition of antibody to Toxoplasma gondii. The direct agglutination test showed that 72 of 571 children seroconverted between one and six years of age, for a cumulative incidence of 12.6%. Children were examined by pediatricians quarterly, and illnesses that had occurred in the interval and their activities were noted on questionnaires. Thirty-eight variables were examined for their role as risk factors for seroconversion. There was a higher correlation between children's seroconversion and contact with dogs than with cats. Combinations of significant predictors without dogs explained only 67% of the seroconversions, but the same factors with dogs explained 90%. On the other hand, ingestion of raw or rare meat or eggs appeared to play no role in transmission. Cats were examined and 110 (45.6%) of 241 had Toxoplasma antibody on the first bleeding. Only two (0.5%) of 383 cat fecal specimens, when tested in mice, resulted in seroconversion. Ten (1.1%) of 924 soil samples resulted in seroconversion in mice that had been injected. Antibody to Toxoplasma was found in 52 (23.3%) of 226 rats (Rattus norvegicus) and two (0.035%) of 571 mice (Mus musculus). Two hundred sixteen birds of 16 different species were bled. Antibody to Toxoplasma was found in 13.4% of these birds, mostly in grackles, blue-gray tanagers, and doves. The rate of isolation of Toxoplasma was low: one of 23 in rats and three of 201 in birds. High relative risks (RRs) of transmission to children were predicted by contact histories with nursing dogs (RR = 5.8), weaned dogs (RR = 4.7), many flies (RR = 3.6), 6-12-month-old dogs (RR = 3.4), weaned cats (RR = 3.0), 6-12-month-old cats (RR = 2.7), nursing cats (RR = 2.5), much garbage (RR = 2.4), and many roaches (RR = 2.2). The high statistical correlation of dog contact with seroconversion in children suggests the possibility that dogs, by eating and rolling in cat feces, are instrumental in mechanically transmitting Toxoplasma infection. In addition, flies, and to a lesser extent, cockroaches, may have practically important roles in transmission.

Coexistence of several novel hantaviruses in rodents indigenous to North America

Three genetically distinct members of the Hantavirus genus have been detected in Nevada rodents by RT-PCR and nucleotide sequence analysis. These include Sin Nombre (SN), El Moro Canyon (ELMC), and Prospect Hill (PH)-like viruses which are primarily associated with Peromyscus maniculatus (deer mouse), Reithrodontomys megalotis (western harvest mouse), and Microtus spp. (voles), respectively. Although this region of the United States is ecologically diverse, rodents infected with different hantaviruses appear to coexist in several different geographical and ecological zones. In two widely separated states, Nevada and North Dakota, PH-like viruses are present in three different species of vole. In addition, ELMC-like virus has been detected in both R. megalotis and M. montanus (mountain vole). SN virus is a cause of hantavirus pulmonary syndrome throughout much of the United States. SN virus RNA is found in 12.5% of P. maniculatus in Nevada and eastern California. Two lineages of SN virus coexist in this region and differ from SN viruses originally found in infected rodents in New Mexico, Arizona, and Colorado. These data show the complexity of hantavirus maintenance in rodents. Distinct hantaviruses or virus lineages can coexist either in different or the same rodent species and in either different or the same geographic or ecological zones.

An investigation into the health and welfare of red squirrels, Sciurus vulgaris, involved in reintroduction studies

The threats posed by parapoxvirus infection, metabolic bone disease and coccidiosis to the reintroduction of red squirrels into Thetford Chase were investigated by making blood biochemical, radiological and parasitological examinations on the squirrels before they were released and on resident squirrels. Red squirrels found dead in Thetford Chase were examined post mortem by parasitological, electron microscopical and radiological techniques. Parapoxvirus infection was the probable cause of death of two red squirrels. Parapoxvirus infection may be a significant threat to remnant populations of red squirrels in England, and to the success of conservation measures.

Hemangiomas and hemangiosarcomas in inbred laboratory mice

Hemangiomas and hemangiosarcomas are rare, naturally developing tumors of blood vessels. In a retrospective study covering a period of 57 contiguous months between 1986 and 1991, four cavernous hemangiomas, eight capillary hemangiomas, and three hemangiosarcomas developed spontaneously in A/J, BALB/cJ, BALB/cByJ, C57BL/6J, NU/J, and 129/SvJ inbred mouse strains. When data were correlated to actual numbers of each sex in the colony, no sexual dimorphism was determined. At the time of submission, mice ranged in age from 100 to 434 days, with a mean of 217 days. Tumors principally affected the skin but were also diagnosed in the seminal vesicles, liver, muscle tissue, and cerebellum. Immunohistochemistry, with antisera directed against human von Willebrand factor (factor VIII-related antigen) as an endothelial cell marker, labeled mouse endothelial cells inconsistently. A monoclonal antibody directed against the smooth muscle actin isoform, but not the sarcomeric muscle actin isoform, outlined vascular structures in tumors and normal vascular smooth muscle in adjacent normal tissues.

Is the small mammal (Clethrionomys glareolus) or the tick vector (Ixodes ricinus) the primary overwintering reservoir for the Lyme borreliosis spirochete in Sweden?

We determined the capacity of bank voles (Clethrionomys glareolus) to infect feeding Ixodes ricinus ticks with Borrelia burgdorferi sensu lato (infectivity), during June to October 1991 and June to September 1992 in south-central Sweden. In both years, the infectivity of older voles to ticks was higher in August to September (48% to 59%) than in June to July (20% to 32%). We propose that the infectivity of bank vole populations in Sweden decreases during winter and spring due to death of highly infective voles and recruitment of uninfective young ones, and that the tick vector, rather than the mammalian host, is the primary overwintering reservoir of B. burgdorferi.

Bot fly (Cuterebra fontinella fontinella) parasitism of cotton mice (Peromyscus gossypinus) on St. Catherines Island, Georgia

From February 1993 through October 1994, 382 cotton mice (Peromyscus gossypinus) were live-trapped and examined for bot fly (Cuterebra fontinella fontinella) larvae. Thirty-nine (10%) of the mice were parasitized by a total of 44 bot fly larvae. All bots were situated in the inguinal or lower abdominal region of the mice. Monthly data strongly suggested that this bot is bivoltine at this latitude with distinct summer and winter population peaks. Prevalence of parasitism was highest in June 1994 when 56% of 16 mice examined were infested with a mean intensity of 1.3 bots. Adult flies were successfully reared from 10 bots that exited from mice; the time period (58-98 days, mean = 79.5) that these specimens spent in the soil as pupae further supports the contention that C. f. fontinella is bivoltine on St. Catherines Island.

Mice as carriers of Salmonella enteritidis on persistently infected poultry units

Evidence of the possible role of wild mice in the epidemiology of Salmonella enteritidis infection on broiler breeder and layer breeder units was obtained by a bacteriological examination of local mice. Persistent S enteritidis infection in birds on these units had been a problem and a high proportion of the mice were found to carry salmonella. S enteritidis was isolated from the liver and the intestine of most of the mice, indicating a systemic infection. Three-week-old chicks were infected by contact with droppings from mice which had been infected experimentally with S enteritidis two and five months previously. Wild mice infected artificially or naturally excreted S enteritidis intermittently, with up to 10(4) organisms in some individual droppings. A naturally infected mouse which died after intermittently excreting small numbers of S enteritidis in its droppings for 19 weeks had 10(4) organisms/g of liver and 10(3)/g of macerated intestine and contents. S enteritidis was also found in fetal tissue in a naturally infected mouse suggesting the possibility that the organism might be transmitted vertically.

Evidence for the existence of Puumula-related virus among Clethrionomys rufocanus in Hokkaido, Japan

We conducted field surveys of indigenous rodent species in Hokkaido, Japan from 1980 to 1993. Serum samples were collected from 663 rodents, including Clethrionomys rufocanus, Apodemus speciosus, A. argenteus, and C. rutilus. Antibody to hantavirus was determined by the protein G antibody assay. Positive C. rufocanus were detected in seven of eight collection sites, but no antibody was detected in the remaining rodent species. To reveal the serotype of the circulating virus in C. rufocanus, antibody titers to Hantaan, Seoul, Puumala, and Prospect Hill viruses were compared by means of the focus reduction neutralization test. The titers in positive sera were extremely high to the Sotkamo strain of Puumala virus. Results were confirmed by the reverse transcriptase-polymerase chain reaction, and suggested that Puumala-related viruses are in circulation among C. rufocanus populations in Hokkaido.

Gastrointestinal helminths from the endangered Hualapai vole, Microtus mogollonensis hualpaiensis (Rodentia: Cricetidae)

The Hualapai vole (Microtus mogollonensis haulpaiensis) is an endangered rodent occurring in northwestern Arizona. Helmiths were examined from 47 voles collected from 9 localities in northwestern Arizona. A toal of 375 helminths was collected, including 2 species of cestodes Anoplocephaloides troeschi and Paranoplocephala macrocephala, and 1 cecal nematode Syphacia obvelata. Pinworms were the most common helminth, but prevalence and abundance varied among localities. Comparison of the pinworms we found with the types of S. obvelata and Syphacia nigeriana indicate that those in M. m. hualpaiensis were S. obvelata.

Borrelia burgdorferi in eastern Virginia: comparison between a coastal and inland locality

In Virginia, Borrelia burgdorferi was more prevalent in a site along the Atlantic Ocean, near Maryland, than in an inland site near Williamsburg and Yorktown. At the coastal site on Assateague Island, B. burgdorferi was isolated from 4.2% of 475 animals sampled, including four species of small mammals. Serologic tests indicated that 25-37% of the small rodents assayed had been exposed to B. burgdorferi. Immunofluorescence antibody assays specific for B. burgdorferi showed spirochete infection in Ixodes scapularis and Dermacentor variabilis but not in other species of ticks also examined from this site. At another coastal site (Parramore Island), no evidence of Peromyscus leucopus was found, no immature specimens of I. scapularis were collected, and no isolations were made from numerous raccoons or small mammals sampled. Borrelia burgdorferi infection was found in one I. cookei nymph, but not in numerous specimens of I. scapularis or other tick species from this locality. At the inland site between Williamsburg and Yorktown, B. burgdorferi was isolated from two small mammal species and antibodies to B. burgdorferi were found in only 7-10% of the small mammals sampled. Ixodes scapularis were less abundant at this locality than at the Assateague Island site. Borrelia burgdorferi spirochetes were found in I. scapularis and a single nymph of Amblyomma americanum, but not in any of numerous specimens of four other species. Infection with B. burgdorferi was found in 20% of unfed adult I. scapularis from vegetation, but in only 0.2% of numerous adults from hunter-killed deer. Infection in immature ticks was much lower than at Assateague Island. Borrelia burgdorferi may be more prevalent along the Atlantic coast than in inland areas. Isolations, seroprevalence, immature I. scapularis densities, and spirochete infection rates in ticks were higher at the Assateague Island site than the Williamsburg/Yorktown site. Consequently, the risk of human exposure to Lyme disease may be higher in some parts of the coastal area than elsewhere in Virginia. Overall, B. burgdorferi is less intense in Virginia than in the northeastern United States.

Isolation of Leishmania (L.) mexicana from wild rodents and their possible role in the transmission of localized cutaneous leishmaniasis in the state of Campeche, Mexico

Leishmania parasites were isolated from four of seven small rodent species captured in the State of Campeche, Mexico. Signs and/or symptoms of leishmanial infection were restricted to the tail of the mice. Peromyscus yucatanicus endemic to the peninsula of Yucatan and Oryzomys melanotis were added to the list of carriers of Leishmania. Leishmania (L.) mexicana, characterized by an indirect immunofluorescence antibody method using monoclonal antibodies, was identified in one Sigmodon hispidus and one Or. melanotis. The possible role of the different species as primary reservoirs of Leishmania in the peninsula of Yucatan is discussed.

Temporal dynamics of Puumala virus antibody prevalence in voles and of nephropathia epidemica incidence in humans

Puumala (PUU) virus is the etiologic agent of nephropathia epidemica (NE) in humans. This disease is highly endemic in Vasterbotten county, Sweden, with an annual incidence of 19.2 (range 3.7-37.4) per 100,000 inhabitants. Voles are considered to be both the main reservoir and the vector of PUU virus. A total of 3,591 rodents (mainly Clethrionomys glareolus, C. rufocanus, and Microtus agrestis) trapped in Vasterbotten between 1979 and 1987 were tested for the presence of PUU virus antibodies by enzyme-linked immunosorbent assay. The predominant species, C. glareolus (71% [2,544 of 3,591]), also had the highest antibody prevalence (19% [483 of 2,544]). In C. glareolus, the antibody prevalence rate increased with weight (age), reaching more than 50% in the heaviest weight group, and suggesting that horizontal infection may be important. The highest frequency (25%) of antibody-positive C. rufocanus was also found in the highest weight groups. Microtus agrestis showed low absolute numbers and a low antibody prevalence rate (5%). In C. glareolus, both antibody prevalence and weight were recurrently higher in the spring than in the previous fall. The antibody prevalence rate in spring was positively correlated with the vole density in the previous fall and spring. The fall antibody prevalence rate was directly dependent on C. glareolus density. The incidence of human NE in the fall was dependent on the concurrent density of C. glareolus, whereas the incidence of NE in the spring was dependent on vole density the previous fall.

Spontaneous renal tubular carcinoma in Fischer-344 rat littermates

Two of 632 Fischer-344 rats in a food restriction study had spontaneous, bilateral, multicentric renal tubular cell carcinomas. Although there were 104 litters represented in this study, both rats that developed this rare neoplasm were from the same litter. The littermates, one male and one female, were in the food-restricted treatment groups (60% of ad libitum intake) and were 550 and 447 days old, respectively, at death. The probability that the two rare bilateral renal neoplasms occurred by a chance event in littermates is approximately 0.8%. The apparent familial predisposition for development of specific types of neoplasms emphasizes the importance of randomization of individuals into treatment groups and consideration of lineage for rare tumors.

[Comparison of 4 microscopy techniques for the diagnosis of leptospirosis in wild rodents in a rural area of Valdivia, Chile]

Kidneys of six different species of 93 wild rodents captured in the rural area of Valdivia (Chile) were simultaneously examined for leptospira infection by means of Levaditi silver stain, dark ground microscopy in wet smears, and immunofluorescence and immunoperoxidase techniques using pooled antiserum against hardjo and pomona serovars. Leptospira was shown to be present in 40 (43.0%) rodents. They were detected in five of the six species: Akodon olivaceus, Akodon longipilis, Rattus rattus, Oryzomis longicaudatus and Mus musculus. Levaditi's technique detected the highest number of positive samples (67.5%) and the dark field microscopy the lowest (32.5%). The detection of leptospira in the kidneys of these wild rodents suggests that their urine may play an important role in the dissemination of leptospirosis in this area of Valdivia.

Occurrence of Penicillium marneffei infections among wild bamboo rats in Thailand

Penicilliosis marneffei has emerged as an endemic systemic mycosis in Southeast Asia among humans and wild bamboo rats. To gain an insight into the epidemiology of this life-threatening disease, a survey of bamboo rats for natural infections by Penicillium marneffei was carried out in the central plains of Thailand during June-September, 1987. Thirty-one lesser bamboo rats (Cannomys badius) and eight hoary bamboo rats (Rhizomys pruinosus) were trapped. Portions of their internal organs were cultured to determine if they had been infected by P. marneffei. Six each of C. badius (19.4%) and R. pruinosus (75%) yielded cultures of this unique, dimorphic Penicillium species. All of the isolates were readily converted to their unicellular form that multiplies by the process of schizogony by incubating them at 37 degrees C on plates of brain heart infusion agar. Their identity was further confirmed by a specific immunological test. Among the internal organs of the positive rats, the lungs had the highest positivity (83.3%), next in decreased order of frequency were the liver (33.3%) and the pancreas (33.3%). The use and value of domestic and wild animals in locating and demarcating endemic areas of geophilic fungal pathogens are discussed. Penicilliosis marneffei is considered to be a zooanthroponosis--a disease that occurs in lower animals, as well as, humans.

[Prevalence of protozoa infections in synanthropic rodents in Valdivia City, Chile]

In order to determine the prevalence of infection by blood and intestinal protozoa in 57 synanthropic rodents from Valdivia city, a study was carried out in the period march-september 1986. The group of rodents studied was constituted by 31 Mus musculus, 19 Rattus rattus and 7 Oryzomys longicaudattus, being 42 males and 15 females. Diagnostic forms of protozoa were found in 70.2% of the investigated animals. The presence of five species of enteroprotozoa and one species of hemoflagelate was detected. The number and the corresponding percentages of infected animals were the following: Giardia muris, 21 (36.8%), Hexamita muris, 22 (38.6%), Trichomonas muris, 27 (47.4%), Entamoeba muris 9 (15.8%), Eimeria sp. 15 (26.3%) and Trypanosoma lewisi 9 (15.8%). Not significant differences were observed when considering host or sex of the species found infected. Furthermore, the yielding of fecal examination considering direct examination, sugar solution flotation and SAFS were compared. The sugar solution flotation technique showed the highest percentage diagnosis of coccidia, whereas SAFS was more efficient for detecting G. muris and E. muris.

Female-predominant occurrence of spontaneous gastric adenocarcinoma in cotton rats

In a colony of cotton rats (Sigmodon hispidus) consisting of 258 female and 283 male animals, 61 females and 2 males had a gastric mucosal lesion. This lesion developed in rats over 2 months of age, with a gradual increase in incidence thereafter. The lesion was grossly characterized by diffuse, often irregular thickening of the fundic mucosa, but the antrum was not affected. In 46% of the rats with this lesion, the serosal surface of the stomach was also involved. There was no evidence of disseminating or blood-borne metastasis. Histologically the mucosal thickening indicated a monotonous, diffuse proliferation of gastric glands with slight nuclear atypia, interpreted to be adenomatous hyperplasia. Invasion into submucosal, muscular, and subserosal layers by neoplastic cells with more atypia than the adenomatous hyperplasia was also noted and interpreted to be a tubular adenocarcinoma. In the adenocarcinoma lesions the infiltrating glands were surrounded by a desmoplastic reaction. In several of the adenocarcinoma lesions there were poorly differentiated adenocarcinoma cells with distorted gland formation. Lesions were diagnosed by soft X-ray examination with barium, without the need for laparotomy. Because these combined data demonstrate the spontaneous occurrence of gastric adenocarcinoma in the background of adenomatous hyperplasia, this cotton rat model can be used to examine, in minute detail, multistep carcinogenesis in the digestive tract.

Prevalence of antibodies to Borrelia spirochetes among wild small rodents in central and western Japan

Field rodents serve as a reservoir for Lyme disease spirochetes. To evaluate the antibody responses of rodents against different Borrelia species in relation to fauna of vector ticks feeding on them, we examined 272 sera of wild rodents, Apodemus speciosus, A. argenteus, and Eothenomys smithii, obtained in 27 locations in central and western Japan from 1981 to 1994. As to prevalences by rodent species using immunoperoxidase test, A. speciosus, A. argenteus and E. smithii showed 29.4%, 11.6% and 30.8% reactivity to Borrelia japonica, 10.7%, 7.2% and 3.8% to B. afzelii, 0.6%, 1.4% and 0% to B. garinii, and 14.7%, 7.2% and 11.5% to an unknown Borrelia species designated as It type, respectively. Each antibody to B. japonica, B. afzelii and B. sp. It type was detected widely both in central and western Japan, but the antibody to B. garinii was scarcely detectable in any area and rodent species examined. Apodemus mice in high mountain altitudes tend to have antibody to B. afzelii or B. japonica, and those in lower altitudes tend to have B. japonica or B. sp. It type. All 13 Apodemus mice from which B. japonica or B. sp. It type were isolated showed higher titers of antibodies to each homologous Borrelia species. The present results indicate that these antibody prevalences among rodents may be associated with dominant Ixodes ovatus and sporadic I. persulcatus on the mainland of Japan, and that Apodemus mice may not be an efficient reservoir for B. garinii. Such a serosurvey is a useful measure to evaluate the natural distribution of the pathogen.

A household-based, case-control study of environmental factors associated with hantavirus pulmonary syndrome in the southwestern United States

During an outbreak of hantavirus pulmonary syndrome (HPS) in the southwestern United States, trained environmental assessment teams conducted surveys at 17 case-patient homes and matched controls from June through August 1993. Variables related to rodent abundance were quantified and standardized rodent trapping was conducted around and within households. The majority of households were located in pinon-juniper vegetation zones, and there were no significant differences in the type of house in which cases and controls lived. The only environmental factor that distinguished case households from controls was significantly higher small rodent densities (median trap success for case sites = 17.3%, 12.7% for near controls, and 8.3% for far controls). Frequency of hantaviral infection in deer mice (Peromyscus maniculatus) did not vary significantly among households of cases and controls, with a range of 27.5-32.5% antibody-positive. Indices of rodent fecal contamination were slightly higher in case houses. The data indicate that higher rodent densities were associated with households in which HPS cases occurred. Strategies that control rodent numbers and decrease rodent access to dwellings may reduce risk of human infection.

Zoonotic hantaviruses; new concerns for the United States

Hantaviruses have emerged as agents of significant morbidity and mortality in human beings. These pathogens are maintained in nature as not clinically apparent, persistent infections in roden reservoirs, varying with each virus, and are shed via rodent feces, urine, and salivary excretions. Human exposure to hantaviruses principally occurs through the respiratory tract route and is focal and discontinuous, paralleling the distribution of virus in reservoir species and the likelihood of human-rodent interactions. Prior to 1993, hantaviruses were established etiologic agents of human febrile nephropathies and hematologic abnormalities on several continents, exclusive of North America. An episode of severe respiratory tract illness developed in association with a group of novel hantaviruses in the United States during 1993-1994, resulting in at least 98 confirmed cases of disease from 21 states and 51 deaths. Current evidence suggests that hantaviruses of zoonotic potential have long existed across widespread areas of the United States but have gone unrecognized.

New isolates of pneumonia virus of mice (PVM) from Japanese rat colonies and their characterization

Two virus strains were isolated from the lungs of athymic rats and mice used as sentinel animals in 2 colonies of laboratory rats in Japan in which antibodies to the pneumonia virus of mice (PVM) had been detected. The new isolates were identified as PVM by the following characteristics: RNA virus, susceptibility to ether treatment, long filamentous viral structure in the cytoplasm of infected cells, and hemagglutinating activity in various erythrocytes, including those of mice and rats. In addition, cross neutralization with the prototype of PVM (No. 15 strain) was observed. This is the first report of the isolation of PVM from laboratory animals in Japan.

Parasites of the Abert's squirrel (Sciurus aberti) and red squirrel (Tamiasciurus hudsonicus) of New Mexico

Between 1989 and 1991, 29 Abert squirrels (Sciurus aberti) and 45 red squirrels (Tamiasciurus hudsonicus) were collected in New Mexico and examined for parasites. Of 29 S. aberti examined, 86.2% (25/29) were infected with at least 1 parasite species. Helminths were found in 62.1% (18/29) of S. aberti; 37.9% (11/29) were infected with fleas and 37.9% (11/29) with the coccidian Eimeria tamiasciuri. Among T. hudsonicus, 82.5% of the squirrels examined were infected with at least 1 parasite. Helminths were found in 57.8% (26/45) of T. hudsonicus; 22.2% (10/45) were infected with fleas and 26.7% (12/45) with Eimeria tamiasciuri. Citellinema quadrivittati was found in squirrels of both species; 55.2% (16/29) of S. aberti were infected, with 57.8% (26/45) of T. hudsonicus carrying the parasite. Enterobius sciuri was only found in S. aberti with 17.2% (5/29) carrying the infection. One cestode, Hymenolepis sp., was found only in T. hudsonicus with 6.7% (3/45) carrying the infection. Four species of flea were found on squirrels of both species. Ceratophyllus vison was found on 6.9% (2/29) of S. aberti and 6.7% (3/45) of T. hudsonicus examined. Opisodasys robustus was found on 6.9% (2/29) of S. aberti and 8.8% (4/45) of T. hudsonicus examined. Orchopeas caedens caedens was found on 3.4% (1/29) of S. aberti and 6.7% (3/45) of T. hudsonicus examined. Orchopeas neotomae was found on 10.3% (3/29) of S. aberti and 6.7% (3/45) of T. hudsonicus examined. Two species of flea were only found on T. hudsonicus; Orchopeas leucopus was found on 2.2% (1/45) and Oropsylla idahoensis was found on 2.2% (1/45) of the T. hudsonicus examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of antibodies to Borrelia burgdorferi in Danish rodents

Six rodent species from six Danish localities were examined for antibodies to Borrelia burgdorferi by immunofluorescence assay (IFA). A total of 1097 specimens were tested using a serum titre of 1:8. The wild mice Apodemus sylvaticus and A. flavicollis had high prevalences of B. burgdorferi antibodies of 42.1% and 27.9% respectively, but the vole Microtus agrestis also showed an exceptionally high prevalence of 32.7%. Clethrionomys glareolus had a low average prevalence of 17.4%. The lowest and highest prevalences of rodents seropositive for B. burgdorferi of 6.5% and 100% were found for Micromys minutus and Mus musculus respectively. Twice as many of the Microtidae voles (M. agrestis and C. glareolus) as of the family Muridae were caught, and in Denmark the actual number of seropositive Microtidae was 1.6 times higher than for Muridae. The results indicate that in Denmark the family Microtidae species plays an important role as an animal reservoir host for B. burgdorferi. The prevalence of antibodies against B. burgdorferi varied from locality to locality, but seropositive rodents were found at all localities examined, indicating that the spirochete was widely present in Denmark.