Seasonal and age distributions of Babesia, Hepatozoon, Trypanosoma and Grahamella species in Clethrionomys glareolus and Apodemus sylvaticus populations

Potential drivers of vector-borne pathogens in urban environments: European hedgehogs (Erinaceus europaeus) in the spotlight

Vector-borne diseases (VBDs) are considered as (re-)emerging, but information on the transmission cycles and wildlife reservoirs is often incomplete, particularly with regard to urban areas. The present study investigated blood samples from European hedgehogs (Erinaceus europaeus) presented at wildlife rehabilitation centres in the region of Hanover. Past exposure to B. burgdorferi sensu lato (s.l.) and tick-borne encephalitis virus (TBEV) was assessed by serological detection of antibodies, while current infections with Borrelia spp., Anaplasma phagocytophilum, Rickettsia spp., Neoehrlichia mikurensis, Bartonella spp., Babesia spp. and Spiroplasma ixodetis were investigated by (q)PCR. Of 539 hedgehogs tested for anti-Borrelia antibodies, 84.8% (457/539) were seropositive, with a higher seropositivity rate in adult than subadult animals, while anti-TBEV antibodies were detected in one animal only (0.2%; 1/526). By qPCR, 31.2% (168/539) of hedgehog blood samples were positive for Borrelia spp., 49.7% (261/525) for A. phagocytophilum, 13.0% (68/525) for Bartonella spp., 8.2% for S. ixodetis (43/525), 8.0% (42/525) for Rickettsia spp. and 1.3% (7/525) for Babesia spp., while N. mikurensis was not detected. While further differentiation of Borrelia spp. infections was not successful, 63.2% of the A. phagocytophilum infections were assigned to the zoonotic ecotype I and among Rickettsia spp. infections, 50.0% to R. helvetica by ecotype- or species-specific qPCR, respectively. Sequencing revealed the presence of a Rickettsia sp. closely related to Rickettsia felis in addition to a Bartonella sp. previously described from hedgehogs, as well as Babesia microti and Babesia venatorum. These findings show that hedgehogs from rehabilitation centres are valuable sources to identify One Health pathogens in urban areas. The hedgehogs are not only exposed to pathogens from fleas and ticks in urban areas, but they also act as potent amplifiers for these vectors and their pathogens, relevant for citizens and their pets.

Candidatus Neoehrlichia mikurensis and Hepatozoon sp. in voles (Microtus spp.): occurrence and evidence for vertical transmission

Candidatus Neoehrlichia mikurensis (CNM) and Hepatozoon spp. are important vector-borne parasites of humans and animals. CNM is a relatively recently discovered pathogen of humans. Hepatozoon are parasites of reptiles, amphibians and mammals, commonly found in rodents and carnivores worldwide. The present study aimed to determine the prevalence of CNM and Hepatozoon spp. in three species of Microtus and to assess the occurrence of vertical transmission in naturally-infected voles. Molecular techniques were used to detect pathogen DNA in blood and tissue samples of captured voles and their offspring. The prevalence of CNM in the vole community ranged 24-47% depending on Microtus species. The DNA of CNM was detected in 21% of pups from three litters of six infected Microtus dams (two Microtus arvalis and one M. oeconomus) and in 3/45 embryos (6.6%) from two litters of eight CNM-infected pregnant females. We detected Hepatozoon infection in 14% of M. arvalis and 9% of M. oeconomus voles. Hepatozoon sp. DNA was detected in 48.7% of pups from seven litters (6 M. arvalis and 1 M. oeconomus) and in two embryos (14.3%) obtained from one M. arvalis litter. The high prevalence of CNM infections in the Microtus spp. community may be a result of a relatively high rate of vertical transmission among naturally infected voles. Vertical transmission was also demonstrated for Hepatozoon sp. in M. arvalis and M. oeconomus. Our study underlines the significance of alternative routes of transmission of important vector-borne pathogens.

Diversity of Hepatozoon species in wild mammals and ticks in Europe

BACKGROUND

Hepatozoon spp. are tick-borne parasites causing subclinical to clinical disease in wild and domestic animals. Aim of this study was to determine Hepatozoon prevalence and species distribution among wild mammals and ticks in Europe.

METHODS

Samples of wild mammals and ticks, originating from Austria, Bosnia and Herzegovina, Croatia, Belgium and the Netherlands, were tested with PCR to amplify a ~ 670-bp fragment of the small subunit ribosomal RNA gene.

RESULTS

Of the 2801 mammal samples that were used for this study, 370 (13.2%) tested positive. Hepatozoon canis was detected in samples of 178 animals (3 Artiodactyla, 173 Carnivora, 1 Eulipotyphia, 1 Lagomorpha), H. martis in 125 (3 Artiodactyla, 122 Carnivora), H. sciuri in 13 (all Rodentia), Hepatozoon sp. in 47 (among which Hepatozoon sp. Vole isolate, all Rodentia) and H. ayorgbor in 4 (all Rodentia). Regarding origin, 2.9% (6/208) tested positive from Austria, 2.8% (1/36) from Bosnia and Herzegovina, 14.6% (173/1186) from Croatia and 13.9% (190/1371) from Belgium/the Netherlands. Of the 754 ticks collected, 0.0% (0/35) Hyalomma sp., 16.0% (4/25) Dermacentor spp., 0.0% (0/23) Haemaphysalis spp., 5.3% (24/50) Ixodes and 1.4% (3/221) Rhipicephalus spp. tested positive for Hepatozoon (4.2%; 32/754), most often H. canis (n = 22).

CONCLUSIONS

Hepatozoon canis is most present in mammals (especially in Carnivora such as gray wolves and golden jackals) and ticks, followed by H. martis, which was found merely in stone martens and pine martens. None of the rodent-associated Hepatozoon spp. were detected in the ticks, suggesting the possible implication of other arthropod species or non-vectorial routes in the transmission cycle of the hemoprotozoans in rodents. Our findings of H. canis in ticks other than R. sanguineus add to the observation that other ticks are also involved in the life cycle of Hepatozoon. Now that presence of Hepatozoon has been demonstrated in red foxes, gray wolves, mustelids and rodents from the Netherlands and/or Belgium, veterinary clinicians should be aware of the possibility of spill-over to domestic animals, such as dogs.

Circulation of Babesia Species and Their Exposure to Humans through Ixodes Ricinus

Human babesiosis in Europe has been attributed to infection with Babesia divergens and, to a lesser extent, with Babesia venatorum and Babesia microti, which are all transmitted to humans through a bite of Ixodes ricinus. These Babesia species circulate in the Netherlands, but autochthonous human babesiosis cases have not been reported so far. To gain more insight into the natural sources of these Babesia species, their presence in reservoir hosts and in I. ricinus was examined. Moreover, part of the ticks were tested for co-infections with other tick borne pathogens. In a cross-sectional study, qPCR-detection was used to determine the presence of Babesia species in 4611 tissue samples from 27 mammalian species and 13 bird species. Reverse line blotting (RLB) and qPCR detection of Babesia species were used to test 25,849 questing I. ricinus. Fragments of the 18S rDNA and cytochrome c oxidase subunit I (COI) gene from PCR-positive isolates were sequenced for confirmation and species identification and species-specific PCR reactions were performed on samples with suspected mixed infections. Babesia microti was found in two widespread rodent species: Myodes glareolus and Apodemus sylvaticus, whereas B. divergens was detected in the geographically restricted Cervus elaphus and Bison bonasus, and occasionally in free-ranging Ovis aries. B. venatorum was detected in the ubiquitous Capreolus capreolus, and occasionally in free-ranging O. aries. Species-specific PCR revealed co-infections in C. capreolus and C. elaphus, resulting in higher prevalence of B. venatorum and B. divergens than disclosed by qPCR detection, followed by 18S rDNA and COI sequencing. The non-zoonotic Babesia species found were Babesia capreoli, Babesia vulpes, Babesia sp. deer clade, and badger-associated Babesia species. The infection rate of zoonotic Babesia species in questing I. ricinus ticks was higher for Babesia clade I (2.6%) than Babesia clade X (1.9%). Co-infection of B. microti with Borrelia burgdorferi sensu lato and Neoehrlichia mikurensis in questing nymphs occurred more than expected, which reflects their mutual reservoir hosts, and suggests the possibility of co-transmission of these three pathogens to humans during a tick bite. The ubiquitous spread and abundance of B. microti and B. venatorum in their reservoir hosts and questing ticks imply some level of human exposure through tick bites. The restricted distribution of the wild reservoir hosts for B. divergens and its low infection rate in ticks might contribute to the absence of reported autochthonous cases of human babesiosis in the Netherlands.

Trypanosoma (Herpetosoma) diversity in rodents and lagomorphs of New Mexico with a focus on epizootological aspects of infection in Southern Plains woodrats (Neotoma micropus)

Protozoan parasites of the genus Trypanosoma infect a broad diversity of vertebrates and several species cause significant illness in humans. However, understanding of the phylogenetic diversity, host associations, and infection dynamics of Trypanosoma species in naturally infected animals is incomplete. This study investigated the presence of Trypanosoma spp. in wild rodents and lagomorphs in northern New Mexico, United States, as well as phylogenetic relationships among these parasites. A total of 458 samples from 13 rodent and one lagomorph species collected between November 2002 and July 2004 were tested by nested PCR targeting the 18S ribosomal RNA gene (18S rRNA). Trypanosoma DNA was detected in 25.1% of all samples, with the highest rates of 50% in Sylvilagus audubonii, 33.1% in Neotoma micropus, and 32% in Peromyscus leucopus. Phylogenetic analysis of Trypanosoma sequences revealed five haplotypes within the subgenus Herpetosoma (T. lewisi clade). Focused analysis on the large number of samples from N. micropus showed that Trypanosoma infection varied by age class and that the same Trypanosoma haplotype could be detected in recaptured individuals over multiple months. This is the first report of Trypanosoma infections in Dipodomys ordii and Otospermophilus variegatus, and the first detection of a haplotype phylogenetically related to T. nabiasi in North America in S. audubonii. This study lends important new insight into the diversity of Trypanosoma species, their geographic ranges and host associations, and the dynamics of infection in natural populations.

Blood parasites (Babesia, Hepatozoon and Trypanosoma) of rodents, Lithuania: part I. Molecular and traditional microscopy approach

Wild rodents, as natural reservoir hosts carrying various species of pathogens, play an important role in the evolution and emergence of zoonotic diseases. In this study, protist parasites, namely Babesia sp., Trypanosoma sp. and Hepatozoon sp. were studied in rodent populations in Lithuania. Two hundred forty rodent specimens of seven species were analysed by a combined approach using polymerase chain reaction (PCR)-based techniques and traditional microscopic examination. The total prevalence of blood parasites reached 35% in rodent communities. The prevalence of Hepatozoon sp. reached the highest value (32%), followed by Trypanosoma sp. (5%) and Babesia sp. (3%). Myodes glareolus and Microtus agrestis were the most heavily infected rodent species. Comparison of microscopy and PCR-based methods showed that the two approaches might give different results and thus can lead to an underestimation of the actual prevalence and abundance of parasites. In our study, PCR-based assays were more sensitive and robust than traditional microscopy. However, precise molecular results for the estimation of the prevalence of Babesia sp. and Hepatozoon sp. were achieved only by using several sets of primers. To avoid inaccurate results, the improvement and detailed description of molecular and microscopy protocols are required.

Translational Rodent Models for Research on Parasitic Protozoa-A Review of Confounders and Possibilities

Rodents, in particular Mus musculus, have a long and invaluable history as models for human diseases in biomedical research, although their translational value has been challenged in a number of cases. We provide some examples in which rodents have been suboptimal as models for human biology and discuss confounders which influence experiments and may explain some of the misleading results. Infections of rodents with protozoan parasites are no exception in requiring close consideration upon model choice. We focus on the significant differences between inbred, outbred and wild animals, and the importance of factors such as microbiota, which are gaining attention as crucial variables in infection experiments. Frequently, mouse or rat models are chosen for convenience, e.g., availability in the institution rather than on an unbiased evaluation of whether they provide the answer to a given question. Apart from a general discussion on translational success or failure, we provide examples where infections with single-celled parasites in a chosen lab rodent gave contradictory or misleading results, and when possible discuss the reason for this. We present emerging alternatives to traditional rodent models, such as humanized mice and organoid primary cell cultures. So-called recombinant inbred strains such as the Collaborative Cross collection are also a potential solution for certain challenges. In addition, we emphasize the advantages of using wild rodents for certain immunological, ecological, and/or behavioral questions. The experimental challenges (e.g., availability of species-specific reagents) that come with the use of such non-model systems are also discussed. Our intention is to foster critical judgment of both traditional and newly available translational rodent models for research on parasitic protozoa that can complement the existing mouse and rat models.

Long-term spatiotemporal stability and dynamic changes in the haemoparasite community of spiny mice (Acomys dimidiatus) in four montane wadis in the St. Katherine Protectorate, Sinai, Egypt

BACKGROUND

Long-term field studies of parasite communities are rare but provide a powerful insight into the ecological processes shaping host-parasite interactions. The aim of our study was to monitor long-term trends in the haemoparasite communities of spiny mice (Acomys dimidiatus) and to identify the principal factors responsible for changes over a 12 year period.

METHODS

To this end we sampled four semi-isolated populations of mice (n = 835) in 2000, 2004, 2008 and 2012 in four dry montane valleys (wadis) located in the Sinai Massif, Egypt.

RESULTS

Overall 76.2 % of spiny mice carried at least one of the five haemoparasite genera (Babesia, Bartonella, Haemobartonella, Hepatozoon, Trypanosoma) recorded in the study. Prevalence of haemoparasites varied significantly between the sites with the highest overall prevalence in Wadi Tlah and the lowest in W. El Arbaein, and this changed significantly with time. In the first two surveys there was little change in prevalence, but by 2008, when the first signs of a deepening drought in the region had become apparent, prevalence began to drift downwards, and by 2012 prevalence had fallen to the lowest values recorded from all four sites over the entire 12-year period. The overall mean species richness was 1.2 ± 0.03, which peaked in 2004 and then dropped by more than 50 % by 2012. Species richness was highest among mice from Wadi Tlah and peaked in age class 2 mice (young adults). Site was the most significant factor affecting the prevalence of individual parasite species, with Trypanosoma acomys and Hepatozoon sp. occurring mainly in two wadis (W. Tlah & W. Gharaba). In four of the five genera recorded in the study we observed a significant drop in prevalence or/and abundance since 2004, the exception being Hepatozoon sp.

CONCLUSIONS

During the 12-year-long period of study in the Sinai, we observed dynamic changes and possibly even cycles of prevalence and abundance of infections which differed depending on parasite species. Although the exact reasons cannot be identified at this time, we hypothesize that the effects of a 15-year-long scarcity of rainfall in the local environment and a fall in host densities over the period of study may have been responsible for a drop in transmission rates, possibly by a negative impact on vector survival.

Babesia behnkei sp. nov., a novel Babesia species infecting isolated populations of Wagner's gerbil, Dipodillus dasyurus, from the Sinai Mountains, Egypt

Background

Although a number of new species of Babesia/Theileria have been described recently, there are still relatively few reports of species from Africa. In this study based on the evaluation of morphology and phylogenetic relationships, we describe a novel species from Wagner’s gerbil, Babesia behnkei n. sp.

Methods

Rodents (n = 1021) were sampled in four montane valleys (wadies) in 2000, 2004, 2008 and 2012 in the Sinai Mountains, Egypt. The overall prevalence of Babesia spp. was highest in the Wagner’s gerbil (Dipodillus dasyurus; 38.7%) in comparison to the prevalence in the spiny mice species, Acomys dimidiatus and A. russatus. Morphological investigations were conducted for the comparison of trophozoites of the novel species of Babesia with the B. microti King’s 67 reference strain. Thirty-two isolates derived from D. dasyurus over a 9 year period (2004-2012) from two wadies (29 isolates from Wadi Gebel and 3 from Wadi El-Arbaein) were investigated by microscopic, molecular and phylogenetic analysis. A near-full-length sequence of the 18S rRNA gene and the second internal transcribed spacer (ITS2) region were amplified, sequenced and used for the construction of phylogenetic trees.

Results

A novel species of Babesia was identified in two isolated populations of D. dasyurus. Phylogenetic analysis of 18S rDNA and ITS2 sequences revealed that B. behnkei n. sp. is most closely related to B. lengau from cheetahs from South Africa and to Nearctic species found only in North America (the pathogenic B. duncani and B. conradae) and that it is more distant to the cosmopolitan rodent parasite B. microti. Trophozoites of B. behnkei were smaller and less polymorphic than trophozoites of B. microti.

Conclusion

Babesia behnkei n. sp. is a novel species of the ‘Duncani group’ maintained in isolated populations of Dipodillus dasyurus occurring in the Sinai Mountains of Egypt.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0572-9) contains supplementary material, which is available to authorized users.

Long-term spatiotemporal stability and dynamic changes in the haemoparasite community of bank voles (Myodes glareolus) in NE Poland

Long-term field studies on parasite communities are rare but provide a powerful insight into the ecological and evolutionary processes shaping host-parasite interactions. The aim of our study was to identify the principal factors regulating long-term trends in the haemoparasite communities of bank voles, and to this end, we sampled three semi-isolated populations of bank voles (n = 880) in 1999, 2002, 2006 and 2010 in the Mazury lake district region of NE Poland. Overall, 90.8 % of the bank voles harboured at least one of the species of haemoparasites studied. Whilst overall prevalence (all species combined) did not vary significantly between the surveys, different temporal changes were detected among voles in each of the three sites. In voles from Urwitałt, prevalence increased consistently with successive surveys, whereas in Tałty, the peak years were 2002 and 2006, and in Pilchy, prevalence oscillated without a clear pattern. Across the study, bank voles harboured a mean of 1.75 ± 0.034 haemoparasite species, and species richness remained stable with no significant between-year fluctuations or trends. However, each of the five constituent species/genera showed a different pattern of spatio-temporal changes. The overall prevalence of Babesia microti was 4.9 %, but this varied significantly between years peaking in 2006 and declining again by 2010. For Bartonella spp., overall prevalence was 38.7 %, and this varied with year of study, but the temporal pattern of changes differed among the three sites. The overall prevalence of Haemobartonella (Mycoplasma) was 68.3 % with an increase in prevalence with year of study in all three sites. Hepatozoon erhardovae had an overall prevalence of 46.8 % but showed a marked reduction with each successive year of the study, and this was consistent in all three sites. The overall prevalence of Trypanosoma evotomys was 15.4 % varying significantly between sites, but showing temporal stability. While overall prevalence of all haemoparasites combined and species richness remained stable over the period of study, among the five haemoparasites, the pattern of spatiotemporal changes in prevalence and abundance of infections differed depending on parasite species. For some genera, host age was shown to play an important role, but a significant effect of host sex was found only for Haemobartonella spp.

Natural history of Zoonotic Babesia: Role of wildlife reservoirs

Babesiosis is an emerging zoonotic disease on all inhabited continents and various wildlife species are the principal reservoir hosts for zoonotic Babesia species. The primary vectors of Babesia are Ixodid ticks, with the majority of zoonotic species being transmitted by species in the genus Ixodes. Species of Babesia vary in their infectivity, virulence and pathogenicity for people. Various factors (e.g., increased interactions between people and the environment, increased immunosuppression, changes in landscape and climate, and shifts in host and vector species abundance and community structures) have led to an increase in tick-borne diseases in people, including babesiosis. Furthermore, because babesiosis is now a reportable disease in several states in the United States, and it is the most common blood transfusion-associated parasite, recognized infections are expected to increase. Because of the zoonotic nature of these parasites, it is essential that we understand the natural history (especially reservoirs and vectors) so that appropriate control and prevention measures can be implemented. Considerable work has been conducted on the ecology of Babesia microti and Babesia divergens, the two most common causes of babesiosis in the United States and Europe, respectively. However, unfortunately, for many of the zoonotic Babesia species, the reservoir(s) and/or tick vector(s) are unknown. We review the current knowledge regarding the ecology of Babesia among their reservoir and tick hosts with an emphasis of the role on wildlife as reservoirs. We hope to encourage the molecular characterization of Babesia from potential reservoirs and vectors as well from people. These data are necessary so that informed decisions can be made regarding potential vectors and the potential role of wildlife in the ecology of a novel Babesia when it is detected in a human patient.

The ecology of Bartonella spp. infections in two rodent communities in the Mazury Lake District region of Poland

Prevalence and abundance of Bartonella spp. infections were studied over a 3-year period in woodland and grassland rodents in North-Eastern Poland. Prevalence of bacterial infections was similar in the two rodent communities, with one leading host species in each habitat (46.3% in Apodemus flavicollis versus 29.1% in Myodes glareolus in forest, or 36.9% in Microtus arvalis versus 13.7% in Mi. oeconomus in grassland). Prevalence/abundance of infections varied markedly across the 3 years with 2006 being the year of highest prevalence and abundance. Infections were more common during autumn months in My. glareolus and A. flavicollis, and in juvenile and young adult (age classes 1 and 2) My. glareolus and Mi. oeconomus than in adults (age class 3). Higher prevalence and abundance of Bartonella infections were found in male A. flavicollis in comparison to females. These data are discussed in relation to the parasite genotypes identified in this region and with respect to the role of various ecological factors influencing Bartonella spp. infections in naturally infected host populations.

Trypanosomes, fleas and field voles: ecological dynamics of a host-vector--parasite interaction

To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.

Is the prevalence of Taenia taeniaeformis in Microtus arvalis dependent on population density?

Populations of common voles Microtus arvalis were studied as hosts of the tapeworm Taenia taeniaeformis during a 14-yr survey. They were monitored in spring, summer, and autumn in a pastoral ecosystem in eastern France. A total of 7,574 voles were sampled during 2 multiannual population fluctuations. A third fluctuation was sampled during the increase phase only. Overall prevalence was lowest in summer (0.6%), increased by 3 times in autumn (1.5%) and a further 5 times in spring (7.8%). Analysis of prevalence, based on 7,384 voles, by multiple logistic regression revealed that extrinsic factors such as season and intrinsic factors such as host age and host density have a combined effect. In the longer term, host age and host density were positively associated with prevalence in summer. Host density was strongly associated with autumn prevalence. There was no association between the fluctuation phase and prevalence. The study shows that a long timescale (here a multiannual survey) is necessary to demonstrate the positive effect of host density on the prevalence of this indirectly transmitted parasite. The demonstration of this relationship depends on the rodents being intermediate rather than definitive hosts.

Haemogregarines of the genus Hepatozoon (Apicomplexa: Adeleina) in rodents from northern Europe

We studied the prevalence and distribution of Hepatozoon infections in small rodents from Finland and other areas in northern Europe. Hepatozoon infections were more common in voles (Arvicolinae) than mice (Murinae) and more prevalent in voles of the genus Clethrionomys than in voles of the genus Microtus. Transmission electron microscopical examination of Hepatozoon erhardovae Krampitz, 1964 from bank voles Clethrionomys glareolus (Schreber) showed that intracellular lung meronts were located in alveolar septa. Meronts consisted of varying numbers of merozoites packed with amylopectin vacuoles inside electron-lucent parasitophorous vacuole. The size of the meronts was approximately 19 x 14 microm. Monozoic or dizoic cysts were frequent findings in the lung alveoles; the size of cysts was approximately 10 x 6 microm. Gametocytes were found inside eosinophilic granulocytes in the capillaries of lung tissue. Ultrastructurally, micronemes, microtubules, mitochondria, nuclei and lipid droplets were visible.

Disease patterns in field and bank vole populations during a cyclic decline in central Finland

Declining field vole (Microtus agrestis) and bank vole (Clethrionomys glareolus) populations were sampled (117 field voles and 34 bank voles) in south-central Finland during the winter of 1988-89. The last surviving field voles were caught in April and bank voles in February. A subsample (16) of the April field voles were taken live to the laboratory for immunosuppression. The histopathology of the main internal organs and the presence of aerobic bacteria and certain parasites were studied. In the lungs, an increase in lymphoid tissue, probably caused by infections, was the most common finding (52% of all individuals). The prevalences in the voles, in the whole material, of Chrysosporium sp. and Pneumocystis carinii in lungs were 13 and 10% in field voles, and 9 and 0% in bank voles, respectively. Cysts of Taenia mustelae (9 and 27%) were the most common pathological changes in the liver. Enteritis was also rather common (14 and 34%). In field voles the prevalences of Frenkelia sp. in the brain and Sarcocystis sp. in leg muscles were low (both 6%). Bordetella bronchiseptica was commonly (31%) isolated from field vole lungs and Listeria monocytogenes from the intestines (34%). Salmonella spp. could not be found. The dynamics and abundance of inflammations in the lungs and intestines, as well as B. bronchiseptica isolations from the lungs, indicate that obvious epidemics took place in declining vole populations. Of the Luhanka subsample of 16 field voles brought to the laboratory in April, one died of listeriosis, two of Bordetella, and five died for unknown reasons. Even if small mustelids are the driving force in microtine cycles, it is possible that diseases also contribute to the decline.

Primary infections with Babesia microti are not prolonged by concurrent Heligmosomoides polygyrus

Seven experiments were carried out to test the hypothesis that concurrent infection with the chronic and immunomodulatory intestinal nematode parasites, Heligmosomoides polygyrus, and the piroplasm, Babesia microti, would result in more intense and long-lasting infections with the hemoprotozoan. However, despite variations in the experimental protocols (different mouse strains, varying levels of infection and different intervals between infection with the two species) a significantly higher B. microti parasitaemia was detected on only one occasion, and a significantly lower parasitaemia on two occasions, relative to control mice. In none of our experiments was the duration of infection prolonged. We conclude that the presence of H. polygyrus does not interfere markedly with the host's ability to mount a protective response against B. microti and hence season-dependent peaks of abundance of H. polygyrus in wild rodents are unlikely to present a particular threat to human communities by providing a greater reservoir of infection with B. microti in wild rodents than at other times of the year.

Current knowledge of Bartonella species

Bartonella species are now considered emerging pathogens. Of the 11 currently recognized species, four have been implicated in human disease, although only two have been encountered in Europe. Bartonella quintana infections are now being diagnosed among the urban homeless and deprived, manifesting as trench fever, and Bartonella henselae has been shown to be the causative agent of cat scratch disease. Both species also cause a variety of HIV-associated infections, including bacillary anglomatosis. However, perhaps the most significant presentation of bartonellae infection is culture-negative endocarditis. The epidemiologies of Bartonella infections are poorly understood; most Bartonella henselae infections are probably acquired from infected cats, either directly by contact with a cat or indirectly via fleas. No animal reservoir has been implicated for Bartonella quintana; however, infection can be transmitted via the human body louse. Diagnosis of Bartonella infections can be made using histological or microbiological methods. The demonstration of specific antibodies may be useful in some instances, although certainly not in all. Cultivation of Bartonella is difficult, as the bacteria are extremely fastidious. Polymerase chain reaction-based or immunological methods for the detection of bartonella in infected tissues have proven useful. Clinical relapse is often associated with Bartonella infections despite a wide range of prescribed regimens. Only aminoglycosides display in vitro bactericidal activity against intracellular Bartonella species; therefore, they are recommended for treatment of Bartonella infections.

Quantifying parameters in the transmission of Babesia microti by the tick Ixodes trianguliceps amongst voles (Clethrionomys glareolus)

The estimation of two parameters in the transmission of Babesia microti by the tick Ixodes trianguliceps amongst small mammals, (1) the duration of infectivity in natural hosts and (2) the probability of transmission from an infected to a susceptible vole, is described. When B. microti was maintained by direct tick transmission, the probability of a complete cycle of transmission via the larval-nymphal and nymphal-adult transstadial routes was 1.0 and 0.71 respectively, but only if the larvae or nymphs had engorged, as distinct from feeding slowly, while the source parasitaemia exceeded 2 or 0.2% respectively, but had not yet passed the peak level. The duration of this condition for infectivity in voles infected by nymphal bites was only 1-4 days, whilst infections delivered by adult ticks barely reached the threshold level necessary for successful transmission. When syringe passage was introduced into the parasite maintenance schedule (a) the probability of transmission declined markedly and (b) the time-course of the parasitaemia was altered. If these parameter values are put into a simple model, together with field data on tick and host survival rates, it becomes apparent that additional factors, such as the highly aggregated distribution of ticks on their hosts, must account for the maintenance of B. microti at the levels seen in wild small mammal populations.

Density-dependent acquired resistance to ticks in natural hosts, independent of concurrent infection with Babesia microti

The question of whether the known immunosuppressive effects of Babesia microti may disrupt the development of acquired resistance to its tick vector, Ixodes trianguliceps, in natural rodent hosts (Clethrionomys glareolus), and thus enhance the disease transmission potential, is addressed experimentally. The results show for the first time that natural hosts can acquire resistance to ticks; that this acquired resistance is manifested chiefly by a strongly density-dependent reduction in the percentage of attached larvae that engorge; that the density dependence is quantitatively similar whether the host receives occasional large tick challenges or frequent low infestations; but that infection with B. microti does not disrupt this pattern of acquired resistance. Of two important natural host species, Apodemus sylvaticus can support repeated infestations of I. trianguliceps, but is a poor host to B. microti, while C. glareolus develops acquired resistance to the tick vector, but supports much higher-level, longer-lasting B. microti infections.

Nearly right or precisely wrong? Natural versus laboratory studies of vector-borne diseases

Recent studies that compare experimental vector-borne disease systems incorporating elements of natural pathogen-vector-host interactions with model systems using unnatural associations have highlighted quantitative, and even qualitative, differences in the results. Here, Sarah Randolph and Pat Nuttall argue that the use of mathematical models to explore epidemiological processes and patterns depends on accurate parameter values obtained from natural systems.

Anemia at the onset of winter in the meadow vole (Microtus pennsylvanicus)

1. From 1981 to 1986, 6120 meadow voles (Microtus pennsylvanicus) were sampled for hematological indices in southeastern Manitoba, Canada. This survey revealed the sporadic occurrence of anemia in early winter at mean temperatures below about -5 degrees C. 2. Anemia was associated with leukocytosis and circulating normoblasts, suggesting a sudden, large blood loss. Individuals became anemic quickly, with no obvious predisposing factors. 3. Attempts were made to induce anemia by exposing voles in traps to various temperatures. Temperatures characteristic of most trapping sessions failed to induce anemia in both wild and laboratory-born voles. 4. Short-term exposure to more extreme temperatures (-20 to -30 degrees C) induced anemia. Voles lost blood through erosions of the epithelium of the glandular stomach, and developed other pathological lesions characteristic of hypothermia. 5. Although there was a strong association between cold weather and anemia, we could find no clear relationship between winter survival and winter weather. However, in 1984, extraordinarily cold temperatures were associated with anemia and a subsequent population decline. These events suggest a threshold mean daily temperature of about -15 degrees C, below which vole survival is grossly affected. 6. Deteriorating protein levels and energy reserves of small mammals in winter may make them particularly susceptible to cold stress. Hence, sporadic bouts of sustained cold may be responsible for some of the enigmatic winter declines seen in northern small mammals.

Studies on cross-immunity in Herpetosoma trypanosomes of Microtus, Clethrionomys and Apodemus

Laboratory-bred rodents of three species were inoculated with heterologous Herpetosoma trypanosome species as follows: Microtus agrestis with Trypanosoma evotomys or T. grosi, Apodemus sylvaticus with T. evotomys or T. microti and Clethrionomys glareolus with T. grosi or T. microti. The three rodent species were subsequently challenged with their natural trypanosome parasite, i.e. T. microti for M. agrestis, T. grosi for A. sylvaticus and T. evotomys for C. glareolus. The parasitaemias and courses of infection that developed were followed. All challenged animals showed some degree of cross-immunity; not all became infected, and those that did had lower levels of parasitaemia and shorter patent periods than control animals. No C. glareolus previously inoculated with T. microti developed T. evotomys infections on challenge, and an infection was observed in just one of ten M. agrestis inoculated first with T. evotomys and later with T. microti.