Towards integrated surveillance of zoonoses: spatiotemporal joint modeling of rodent population data and human tularemia cases in Finland

Background

There are an increasing number of geo-coded information streams available which could improve public health surveillance accuracy and efficiency when properly integrated. Specifically, for zoonotic diseases, knowledge of spatial and temporal patterns of animal host distribution can be used to raise awareness of human risk and enhance early prediction accuracy of human incidence.

Methods

To this end, we develop a spatiotemporal joint modeling framework to integrate human case data and animal host data to offer a modeling alternative for combining multiple surveillance data streams in a novel way. A case study is provided of spatiotemporal modeling of human tularemia incidence and rodent population data from Finnish health care districts during years 1995–2012.

Results

Spatial and temporal information of rodent abundance was shown to be useful in predicting human cases and in improving tularemia risk estimates in 40 and 75% of health care districts, respectively. The human relative risk estimates’ standard deviation with rodent’s information incorporated are smaller than those from the model that has only human incidence.

Conclusions

These results support the integration of rodent population variables to reduce the uncertainty of tularemia risk estimates. However, more information on several covariates such as environmental, behavioral, and socio-economic factors can be investigated further to deeper understand the zoonotic relationship.

Human noroviruses in the faeces of wild birds and rodents-new potential transmission routes

Human noroviruses (HuNoVs) are one of the leading global causes of diarrhoeal diseases and are transmitted mainly from person to person but also through contaminated food, water and fomites. The possible zoonotic nature of NoVs has occasionally been discussed, although the viruses are generally considered to be host-species-specific. We investigated whether wild birds and rodents could serve as carriers of HuNoVs, thereby transmitting the virus to humans directly or indirectly by contaminating foods. All samples, 115 avian and 100 rat faeces collected in springs 2009-2013 from dump sites, and 85 faeces from yellow-necked mice trapped in late autumn 2008 and 2009 after the rodents entered human settlements due to the first night frosts, were screened for HuNoV using real-time reverse transcription PCR. HuNoVs were detected in 31 (27%) faecal samples of wild birds, in two (2%) faecal samples of rats and in no samples of mice. Most (25) of the positive bird samples and both rat samples contained genogroup II, and six positive bird samples contained genogroup I HuNoV. The avian species shedding faeces containing HuNoVs were identified as gulls and crows using DNA barcoding. Our results show that wildlife, birds and rats in particular, is capable of spreading HuNoVs in the environment.

Incidence and seroprevalence of tularaemia in Finland, 1995 to 2013: regional epidemics with cyclic pattern

We studied the incidence of reported tularaemia by year and region and the prevalence of antibodies against Francisella tularensis in the adult general population in Finland. Moreover, we assessed the correlation between vole population cycles and human tularaemia outbreaks. The seroprevalence study made use of serum samples from a nationwide population-based health survey (Health 2000). The samples of 1,045 randomly selected persons, representative for the Finnish population in each region, were screened with an enzyme-linked immunosorbent assay (ELISA) for the presence of IgG antibodies against F. tularensis, and positive results were further confirmed by immunoblotting. A serological response to F. tularensis was found in 2% (95% confidence interval: 1.1–3.5) of the population. Incidence and seroprevalence were highest in the same areas, and vole population peaks clearly preceded tularaemia outbreaks one year later.

Landscape features and helminth co-infection shape bank vole immunoheterogeneity, with consequences for Puumala virus epidemiology

Heterogeneity in environmental conditions helps to maintain genetic and phenotypic diversity in ecosystems. As such, it may explain why the capacity of animals to mount immune responses is highly variable. The quality of habitat patches, in terms of resources, parasitism, predation and habitat fragmentation may, for example, trigger trade-offs ultimately affecting the investment of individuals in various immunological pathways. We described spatial immunoheterogeneity in bank vole populations with respect to landscape features and co-infection. We focused on the consequences of this heterogeneity for the risk of Puumala hantavirus (PUUV) infection. We assessed the expression of the Tnf-α and Mx2 genes and demonstrated a negative correlation between PUUV load and the expression of these immune genes in bank voles. Habitat heterogeneity was partly associated with differences in the expression of these genes. Levels of Mx2 were lower in large forests than in fragmented forests, possibly due to differences in parasite communities. We previously highlighted the positive association between infection with Heligmosomum mixtum and infection with PUUV. We found that Tnf-α was more strongly expressed in voles infected with PUUV than in uninfected voles or in voles co-infected with the nematode H. mixtum and PUUV. H. mixtum may limit the capacity of the vole to develop proinflammatory responses. This effect may increase the risk of PUUV infection and replication in host cells. Overall, our results suggest that close interactions between landscape features, co-infection and immune gene expression may shape PUUV epidemiology.

Landscape genetics highlights the role of bank vole metapopulation dynamics in the epidemiology of Puumala hantavirus

Rodent host dynamics and dispersal are thought to be critical for hantavirus epidemiology as they determine pathogen persistence and transmission within and between host populations. We used landscape genetics to investigate how the population dynamics of the bank vole Myodes glareolus, the host of Puumala hantavirus (PUUV), vary with forest fragmentation and influence PUUV epidemiology. We sampled vole populations within the Ardennes, a French PUUV endemic area. We inferred demographic features such as population size, isolation and migration with regard to landscape configuration. We next analysed the influence of M. glareolus population dynamics on PUUV spatial distribution. Our results revealed that the global metapopulation dynamics of bank voles were strongly shaped by landscape features, including suitable patch size and connectivity. Large effective size in forest might therefore contribute to the higher observed levels of PUUV prevalence. By contrast, populations from hedge networks highly suffered from genetic drift and appeared strongly isolated from all other populations. This might result in high probabilities of local extinction for both M. glareolus and PUUV. Besides, we detected signatures of asymmetric bank vole migration from forests to hedges. These movements were likely to sustain PUUV in fragmented landscapes. In conclusion, our study provided arguments in favour of source-sink dynamics shaping PUUV persistence and spread in heterogeneous, Western European temperate landscapes. It illustrated the potential contribution of landscape genetics to the understanding of the epidemiological processes occurring at this local scale.

Multiple parasites mediate balancing selection at two MHC class II genes in the fossorial water vole: insights from multivariate analyses and population genetics

We investigated the factors mediating selection acting on two MHC class II genes (DQA and DRB) in water vole (Arvicola scherman) natural populations in the French Jura Mountains. Population genetics showed significant homogeneity in allelic frequencies at the DQA1 locus as opposed to neutral markers (nine microsatellites), indicating balancing selection acting on this gene. Moreover, almost exhaustive screening for parasites, including gastrointestinal helminths, brain coccidia and antibodies against viruses responsible for zoonoses, was carried out. We applied a co-inertia approach to the genetic and parasitological data sets to avoid statistical problems related to multiple testing. Two alleles, Arte-DRB-11 and Arte-DRB-15, displayed antagonistic associations with the nematode Trichuris arvicolae, revealing the potential parasite-mediated selection acting on DRB locus. Selection mechanisms acting on the two MHC class II genes thus appeared different. Moreover, overdominance as balancing selection mechanism was showed highly unlikely in this system.

Serological survey for viral pathogens in Turkish rodents

Wild rodents (n = 330) were trapped around the villages of Altindere and Coşandere (Maçka, Trabzon Province), Ayder, Ortan, and Yolkiyi (Camlihemşin, Rize Province), and Bozdag (Odemiş, Izmir Province) in northeastern and western Turkey during April 2004. Samples were tested for arenavirus, hantavirus, and cowpox virus (family Poxviridae, genus Orthopoxvirus, CPXV) antibodies by using immunofluorescence assays (IFAs). Antibodies against arenaviruses were found in eight of 330 (2.4%) rodents. Arenavirus sero-positive animals were found from all study sites. Antibodies to Puumala virus (family Bunyaviridae, genus Hantavirus, PUUV) were detected in four of 65 Microtus voles tested. Of the PUUV-IFA-positive voles, one Microtus guentheri lydius was caught from Izmir, and one Microtus roberti and two Microtus rossiaemeridionalis were captured near Trabzon. All 264 Apodemus spp. mice tested negative for antibodies to Saaremaa virus (family Bunyaviridae, genus Hantavirus, SAAV); the single Dryomys nitedula tested negative for both PUUV and SAAV antibodies. Only one (0.3%) of the rodents, an Apodemus sylvaticus from Trabzon area, tested seropositive to CPXV. This is the first serologic survey for rodent-borne viruses in their natural hosts in Turkey. Although these preliminary results support presence of several virus groups with zoonotic potential, additional studies are needed to identify the specific viruses that are present in these populations.

Population structure in a critically endangered arctic fox population: does genetics matter?

The arctic fox (Alopex lagopus) in Scandinavia is classified as critically endangered after having gone through a severe decline in population size in the beginning of the 20th century, from which it has failed to recover despite more than 65 years of protection. Arctic foxes have a high dispersal rate and often disperse over long distances, suggesting that there was probably little population differentiation within Scandinavia prior to the bottleneck. It is, however, possible that the recent decline in population size has led to a decrease in dispersal and an increase in population fragmentation. To examine this, we used 10 microsatellite loci to analyse genetic variation in 150 arctic foxes from Scandinavia and Russia. The results showed that the arctic fox in Scandinavia presently is subdivided into four populations, and that the Kola Peninsula and northwest Russia together form a large fifth population. Current dispersal between the populations seemed to be very low, but genetic variation within them was relatively high. This and the relative F(ST) values among the populations are consistent with a model of recent fragmentation within Scandinavia. Since the amount of genetic variation is high within the populations, but the populations are small and isolated, demographic stochasticity seems to pose a higher threat to the populations' persistence than inbreeding depression and low genetic variation.

Hantavirus and arenavirus antibody prevalence in rodents and humans in Trentino, Northern Italy

The spatial and temporal distribution of hantavirus and arenavirus antibody-positive wild rodents in Trentino, Italy, was studied using immunofluorescence assays (IFA) in two long-term sites trapped in 2000-2003, and six other sites trapped in 2002. The overall hantavirus seroprevalence in the bank voles, Clethrionomys glareolus (n=229) screened for Puumala virus (PUUV) antibodies was 0.4%, and that for Apodemus flavicollis mice (n=1416) screened for Dobrava virus (DOBV) antibodies was 0.2%. Antibodies against lymphocytic choriomeningitis virus (LCMV) were found in 82 (5.6%) of the 1472 tested rodents; the seroprevalence being 6.1% in A. flavicollis (n=1181), 3.3% in C. glareolus (n=276), and 14.3% in Microtus arvalis (n=7). Of the serum samples of 488 forestry workers studied by IFA, 12 were LCMV-IgG positive (2.5%) and one DOBV-IgG positive (0.2%), however, the latter could not be confirmed DOBV-specific with a neutralization assay. Our results show a widespread distribution but low prevalence of DOBV in Trentino, and demonstrate that the arenavirus antibodies are a common finding in several other rodent species besides the house mouse.

Is there an association ofPneumocystisinfection with the presence of arena-, hanta-, and poxvirus antibodies in wild mice and shrews in Finland?

As part of studies on the nature of the endemic virus infections in natural rodent hosts, the possible association of cyst forms ofPneumocystisspp. with the presence of hanta-, cowpox-, and arenavirus antibodies in wild mice (Apodemus flavicollis,N=105;Apodemus agrarius,N=63;Micromys minutus,N=50) and the common shrew (Sorex araneus,N=101) was studied in south-central Finland. One hantavirus (Saaremaa virus, SAAV) seropositiveA. agrarius, and 2 cowpoxvirus (CPXV) seropositiveS. araneuswere detected, and antibodies against an arenavirus (Lymphocytic choriomeningitis virus, LCMV) were found in all 3 mouse species but not in shrews. Cyst forms ofPneumocystisspp. were detected in all species exceptA. agrarius. There was no significant association between virus antibodies (LCMV in mice, and CPXV in shrews) and cyst forms ofPneumocystisin any of the species. Concurrent presence of virus antibodies (LCMV) and cyst forms ofPneumocystiswere detected only in 1M. minutus. In conclusion, we found no evidence of any association betweenPneumocystisand antibodies to any of the viruses tested.

Description ofParanoplocephala yoccozin. sp. (Cestoda: Anoplocephalidae) from the snow voleChionomys nivalisin France, with a review of anoplocephalid cestodes of snow voles in Europe

We describe Paranoplocephala yoccozi n. sp. (Cestoda: Anoplocephalidae) from the snow vole Chionomys nivalis in Bourg-Saint-Maurice, French Alps, compare it with several related species from rodents, and review the anoplocephalid cestodes of snow voles in Europe. Paranoplocephala yoccozi n. sp. is primarily distinguished from the related species by its large scolex of characteristic shape, robust neck region, and the structure of the cirrus sac, vitellarium and vagina. We show that the anoplocephalid cestodes of snow voles in Europe, representing the genera Anoplocephaloides and Paranoplocephala, include at least seven species. This fauna consists primarily of species that snow voles share with other voles inhabiting the high-mountain areas. Some of the species, including P. yoccozi n. sp., appear to have a very localized distribution, which is assumed to be a consequence of the historical fragmentation of snow vole populations.

Rapid field test for detection of hantavirus antibodies in rodents

Puumala virus (PUUV) is the causative agent of nephropathia epidemica, a mild form of haemorrhagic fever with renal syndrome. PUUV is transmitted to humans via aerosolized excreta of the infected bank vole (Clethrionomys glareolus). Current methods for screening of the PUUV prevalence among bank vole populations are laborious, combining sampling in the field and subsequent analyses in the laboratory. In order to facilitate animal testing, a new serological immunochromatographic rapid test was developed. The test uses PUUV nucleocapsid protein as antigen, and it detects anti-PUUV IgG antibodies in rodents. With fresh and undiluted bank-vole blood samples (n = 105) the efficacy of the test was 100%, and with frozen and diluted samples (n = 78) the efficacy was 91%. The test was also shown to detect related hantavirus infections in Norway lemmings and sibling voles (n = 31) with 99% efficacy. The test provides an applicable tool for studying PUUV and related hantavirus infections in arvicoline rodents.

Phylogeography of the circumpolarParanoplocephala arcticaspecies complex (Cestoda: Anoplocephalidae) parasitizing collared lemmings (Dicrostonyxspp.)

The Paranoplocephla arctica complex (Cyclophyllidea, Anoplocephalidae), host-specific cestodes of collared lemmings Dicrostonyx, include two morphospecies P. arctica and P. alternata, whose taxonomical status now must be considered ambiguous. The genetic population structure and phylogeography of the P. arctica complex was studied from 83 individuals sampled throughout the Holarctic distribution range using 600 bp of the mitochondrial cytochrome c oxidase subunit I gene (COI). The mitochondrial DNA (mtDNA) phylogeny divides the species complex into one main Nearctic and one main Palaearctic phylogroup, corresponding to the main phylogenetic division of the hosts. In the Palearctic phylogroup, the parasite clades correspond to the host clades although the parasites from Wrangel Island form an exception as the host on this island, D. groenlandicus, belongs to the Nearctic phylogroup. In the Nearctic, northern refugia beyond the ice limit of the Pleistocene glaciations are proposed for the hosts. All reconstructions of parasite phylogeny show a genetically differentiated population structure that in the Canadian Arctic lacks strict congruence between phylogeny and geography. The parasite phylogeny does not show complete congruence with host relationships, suggesting a history of colonization and secondary patterns of dispersal from Beringia into the Canadian Arctic, an event not proposed by the host phylogenies alone.

Description of Paranoplocephala etholeni n. sp. (Cestoda: Anoplocephalidae) in the meadow vole Microtus pennsylvanicus, with a synopsis of Paranoplocephala s. l. in holarctic rodents

Paranoplocephala etholeni n. sp., parasitizing the meadow vole Microtus pennsylvanicus in Alaska and Wisconsin, USA, is described. Paranoplocephala etholeni is morphologically most closely related to the Nearctic Paranoplocephala ondatrae (Rausch, 1948). Available data suggest that P. etholeni is a host-specific, locally rare species that may have a wide but sporadic geographical distribution in North America. The finding of P. ondatrae-like cestodes in Microtus spp. suggests that this poorly known species may actually be a parasite of voles rather than muskrat (type host). A tabular synopsis of all the known species of Paranoplocephala s. l. in the Holarctic region with their main morphological features is presented.

Rodent host specificity of European hantaviruses: evidence of Puumala virus interspecific spillover

In order to investigate rodent host specificity of European hantaviruses, experimental infection of colonized and wild-trapped rodents was performed. In addition to the natural rodent reservoir, Clethrionomys glareolus, Puumala hantavirus (PUUV) could infect colonized Microtus agrestis and Lemmus sibiricus, but not Syrian hamsters or Balb/C mice. Neither C. glareolus, nor M. agrestis, could be readily infected by Tula hantavirus (TULV). Wild-trapped Apodemus flavicollis and A. agrarius, the natural reservoirs of Dobrava (DOBV) and Saaremaa (SAAV) hantaviruses, respectively, could both be infected by SAAV. NMRI mice could also be infected by SAAV, but with lower efficiency as compared to Apodemus mice. Balb/C and NMRI laboratory mice, but not C. glareolus, could be infected by DOBV. To our knowledge, this is the first time DOBV and SAAV have been shown to infect adult laboratory mice. Moreover, potential hantavirus spillover infections were investigated in wild-trapped rodents. In addition to the natural host C. glareolus, we also found M. arvalis and A. sylvaticus with a history of PUUV infection. We did not find any C. glareolus or A. sylvaticus infected with TULV, a hantavirus which is known to circulate in the same geographical regions of Belgium.

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.

Echinococcus multilocularis on Svalbard: introduction of an intermediate host has enabled the local life-cycle

The taeniid tapeworm Echinococcus multilocularis is here reported for the first time at the Svalbard Archipelago in the Norwegian Arctic. This new finding is interesting because the establishment of E. multilocularis is due to a recent anthropogenic introduction of its intermediate host--the sibling vole Microtus rossiaemeridionalis at Svalbard. The parasite itself has probably become naturally transferred to Svalbard due to migratory movements of its final host--the arctic fox Alopex lagopus between source areas for E. multilocularis in Siberia and Svalbard. We report macroscopically determined prevalence of E. multilocularis from a sample of 224 voles trapped in August in 1999 and 2000. The prevalence was among the highest ever recorded in intermediate hosts and was dependent on age and sex of the hosts approaching 100% in overwintered males. The high prevalence and the simplicity of the vole-arctic fox-E. multilocularis system at Svalbard makes it an eminent model system for further epidemiological studies.

Isolation of Dobrava virus from Apodemus flavicollis in Greece

Dobrava virus (DOBV) carried by Apodemus flavicollis is the causative agent of severe hemorrhagic fever with renal syndrome (HFRS). DOBV was isolated from an A. flavicollis mouse trapped in northeastern Greece. This is the third DOBV cell culture isolate in the world, clustering together with other Greek DOBV sequences from HFRS patients and rodents.

Biogeography of helminth parasitism in Lemmus Link (Arvicolinae), with the description of Paranoplocephala fellmani n. sp. (Cestoda: Anoplocephalidae) from the Norwegian lemming L. lemmus (Linnaeus)

We describe the gastrointestinal helminth fauna of true lemmings (Lemmus spp., Arvicolinae) based on published and original material throughout the Holarctic range of these hosts. According to the existing data, the helminth fauna of true lemmings consists of three widespread and/or locally common taxa: Hymenolepis horrida (sensu lato) (Hymenolepididae), Anoplocephaloides lemmi (Anoplocephalidae) and Heligmosomoides spp. (Heligmosomidae). Despite the taxonomic boundaries and ancient phylogenetic splits in the hosts, there are no major faunistic differences for parasites within western (Siberian) L. sibiricus and L. bungei, and eastern (North American) L. trimucronatus throughout their distribution range. In contrast, the Norwegian lemming L. lemmus, which is a Fennoscandian endemic and closely related to the western populations of L. sibiricus, has only a single host-specific helminth, the cestode Paranoplocephala fellmani n. sp. (Anoplocephalidae). We describe the new species and show that it differs consistently from related species by its long and slender cirrus-sac. However, there are also a number of other significant differences, e.g., P. fellmani n. sp. and Andrya primordialis in Tamiasciurus hudsonicus (Sciuridae) evidently have a unique (sub)type of uterine development among Andrya/Paranoplocephala spp. Because P. fellmani n. sp. was also found to occur in Alaska (host L. trimucronatus), this species seems to follow the same biogeographical pattern as the other specialist helminths of Lemmus. We suggest alternative explanations for the absence of three major helminth taxa in the Norwegian lemming in Fennoscandia.

Molecular evolution of puumala hantavirus in Fennoscandia: phylogenetic analysis of strains from two recolonization routes, Karelia and Denmark

Like other members of the genus HANTAVIRUS: in the family BUNYAVIRIDAE:, Puumala virus (PUUV) is thought to be co-evolving with its natural host, the bank vole Clethrionomys glareolus. To gain insight into the evolutionary history of PUUV in northern Europe during the last post-glacial period, we have studied wild-type PUUV strains originating from areas along two postulated immigration routes of bank voles to Fennoscandia. Full-length sequences of the S RNA segment and partial sequences (nt 2168-2569) of the M segment were recovered by RT-PCR directly from bank vole tissues collected at three locations in Russian Karelia and one location in Denmark. Phylogenetic analysis showed that strains from Karelia and Finland belong to the same genetic lineage, supporting the hypothesis that PUUV spread to present Finland via a Karelian land-bridge. The Danish PUUV strains showed no particularly close relatedness to any of the known PUUV strains and formed a distinct phylogenetic lineage on trees calculated for both S and M segment sequences. Although no direct link between the Danish PUUV strains and those of the southern Scandinavian lineage was found, within the S segment of Danish PUUV strains, two regions with higher similarity to either northern Scandinavian or - to a less extent - southern Scandinavian genetic lineages were revealed, suggesting evolutionary connections of their precursors.

Are lemmings prey or predators?

Large oscillations in the populations of Norwegian lemmings have mystified both professional ecologists and lay public. Ecologists suspect that these oscillations are driven by a trophic mechanism: either an interaction between lemmings and their food supply, or an interaction between lemmings and their predators. If lemming cycles are indeed driven by a trophic interaction, can we tell whether lemmings act as the resource ('prey') or the consumer ('predator')? In trophic interaction models, peaks of resource density generally have a blunt, rounded shape, whereas peaks of consumer density are sharp and angular. Here we have applied several statistical tests to three lemming datasets and contrasted them with comparable data for cyclic voles. We find that vole peaks are blunt, consistent with their cycles being driven by the interaction with predators. In contrast, the shape of lemming peaks is consistent with the hypothesis that lemmings are functional predators, that is, their cycles are driven by their interaction with food plants. Our findings suggest that a single mechanism, such as interaction between rodents and predators, is unlikely to provide the 'universal' explanation of all cyclic rodent dynamics.

Ultrastructure of Frenkelia sp. from a Norwegian lemming in Finland

An apparently healthy Norwegian lemming (Lemmus lemmus) caught in northern Finland was observed to have a whitish body 0.5 to 1.0 mm in diameter in the external layer of the cerebral cortex. By light microscopy a highly lobulated cyst of Frenkelia sp. was observed. By transmission electron microscopy lemmus) collected in the cyst wall was seen consisting of a parasitophorous vacuolar membrane, an underlying electron-dense layer and a granular layer. The membrane was only slightly convoluted. The protrusions of the cyst wall appeared round but were often not distinctive. A very thin septum divided the interior of the cyst into compartments packed with bradyzoites and maturing zoites. The bradyzoites were elongate measuring 5-8 x 1.5-2 microm. This is the first electron microscopical study of Frenkelia sp. from L. lemmus.

Description and morphometric variability of Paranoplocephala serrata n. sp. (Cestoda: Anoplocephalidae) in collared lemmings (Dicrostonyx spp., Arvicolinae) from Arctic Siberia and North America

We describe Paranoplocephala serrata n. sp. (Cestoda, Anoplocephalidae) from collared lemmings Dicrostonyx torquatus and D. groenlandicus (Arvicolinae, Rodentia) in Arctic Siberia and North America. The new species was recorded from the Yamal Peninsula (type-locality), Yana Delta, Kolyma Delta, Wrangel Island, Alaska and Victoria Island/Kent Peninsula (Northwest Territories). P. serrata n. sp. is characterised by a long, ribbon-like strobila, distinctly serrated segments, a small scolex, unilateral or infrequently alternating genital pores and testes confined to the antiporal part of the segment. It differs from the related species (Andrya bairdi, Parandrya feodorovi and Paranoplocephala manseri) by several morphological features, including the distribution of testes (several testes antiporal to ventral longitudinal osmoregulatory canal), structure of the cirrus-sac and vagina, and large eggs (0.053-0.068 mm in the type-material). The material of P. serrata n. sp. from North America differs from the Siberian material by the shorter cirrus-sac, smaller dimensions of the female reproductive organs, larger seminal receptacle and larger eggs. However, the statistical differences in the dimensions of reproductive organs mainly reflect the larger size of mature segments in Siberian specimens compared with North American specimens. The main diagnostic features, i.e. the size and form of scolex and suckers, number and distribution of testes, position of female glands, vagina/cirrus-sac ratio and morphology of reproductive organs, do not differ markedly between the Palaearctic and Nearctic specimens. According to the structure of the early-stage uterus, A. bairdi Schad, 1954 belongs to the genus Paranoplocephala. Parandrya Gulyaev & Chechulin, 1996 is probably a synonym of Paranoplocephala. A redescription is provided for Paranoplocephala bairdi n. comb.

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.

Epidemiological study of nephropathia epidemica in Finland 1989-96

This study presents data on 33,000 serum samples studied from July 1989 to June 1996 in Finland, with 6,701 serologically confirmed Puumala virus (PUU) infections. In addition, a PUU serosurvey of 8,000 sera from Finland is presented. On average, 957 PUU infections were detected annually, resulting in an incidence of 19/100,000; mortality was less than 0.1%. The infection was most common in the district of Ita-Savo with an incidence of 90/100,000. The seasonal peak was in November-December; however, the urban population had its incidence peak in August. Local epidemics mirrored bank vole densities, with 3-4-y cycles. Males contracted the disease at a mean age of 40 y, females at 44 y (male:female ratio 2:1). The disease was relatively rare in children and elderly people. The nationwide PUU antibody prevalence for women entering Finnish maternity clinics was 3%, suggesting 5% for the total population. The highest prevalences (7% for young women) were encountered in eastern Finland. In the district with the highest clinical alert, approximately 30% of all PUU infections were estimated to lead to clinical disease with serological confirmation.

Analysis of puumala hantavirus genome in patients with nephropathia epidemica and rodent carriers from the sites of infection

Reverse transcription-polymerase chain reaction (RT-PCR) followed by sequence and phylogenetic analyses were used to study specimens from nine Finnish nephropathia epidemica (NE) patients admitted to hospital during the epidemic in winter 1996-1997. Blood samples from six patients were found to be positive for the partial M- and/or S-segment sequences of Puumala hantavirus (PUUV). Analyses of these sequences (nt 2168-2610 for the M segment, and nt 819-1082 for the S segment) revealed six distinct PUUV strains showing highest similarity to previously described PUUV strains from Finland: 90-95% for the S segment, and 90-99% for the M segment. Accordingly, on the phylogenetic trees calculated for both viral segments, all six human strains were placed within the Finnish genetic lineage of PUUV. Attempts were made to trace five RT-PCR-positive patients to local bank voles (Clethrionomys glareolus) infected with wild-type PUUV, and for two patients a comparative analysis of human- and rodent-originated viral sequences was undertaken. Whereas in the first case the differences between the sequences were substantial (5. 7% for the S segment, and 10.8%, for the M segment), in the other case the M segment sequence recovered from the clinical specimen was 100% identical to three sequences recovered from rodent lungs, and the S sequences differed by one silent substitution only. This is the first finding of virtually identical PUUV sequences in an NE patient and a natural rodent host from the site of infection.

Isolation and characterization of a hantavirus from Lemmus sibiricus: evidence for host switch during hantavirus evolution

A novel hantavirus, first detected in Siberian lemmings (Lemmus sibiricus) collected near the Topografov River in the Taymyr Peninsula, Siberia (A. Plyusnin et al., Lancet 347:1835-1836, 1996), was isolated in Vero E6 cells and in laboratory-bred Norwegian lemmings (Lemmus lemmus). The virus, named Topografov virus (TOP), was most closely related to Khabarovsk virus (KBR) and Puumala viruses (PUU). In a cross focus reduction neutralization test, anti-TOP Lemmus antisera showed titers at least fourfold higher with TOP than with other hantaviruses; however, a rabbit anti-KBR antiserum neutralized TOP and KBR at the same titer. The TOP M segment showed 77% nucleotide and 88% amino acid identity with KBR and 76% nucleotide and 82% amino acid identity with PUU. However, the homology between TOP and the KBR S segment was disproportionately higher: 88% at the nucleotide level and 96% at the amino acid level. The 3' noncoding regions of KBR and the TOP S and M segments were alignable except for 113- and 58-nucleotide deletions in KBR. The phylogenetic relationships of TOP, KBR, and PUU and their respective rodent carriers suggest that an exceptional host switch took place during the evolution of these viruses; while TOP and KBR are monophyletic, the respective rodent host species are only distantly related.

Interspecific and intraspecific competition as causes of direct and delayed density dependence in a fluctuating vole population

A 3- to 5-year cycle of vole abundances is a characteristic phenomenon in the ecology of northern regions, and their explanation stands as a central theoretical challenge in population ecology. Although many species of voles usually coexist and are in severe competition for food and breeding space, the role of interspecific competition in vole cycles has never been evaluated statistically. After studying community effects on the population dynamics of the gray-sided vole (Clethrionomys rufocanus) in the subarctic birch forest at Kilpisjärvi, Finland, we report statistical results showing that both interspecific and intraspecific effects are important in the direct year-to-year density dependence. However, interspecific effects are not detectable in the 2-year delayed density dependence that is crucial for generating the characteristic cycles. Furthermore, we show that most of the competition takes place during the winter. The results are evaluated against two models of community dynamics. One assumes that the delayed effects are caused by an interaction with a specialist predator, and the other assumes that they are caused by overgrazing food plants. These statistical results show that vole cycles may be generated by a species-specific trophic interaction. The results also suggest that the gray-sided vole may be the focal species in the birch-forest community, as field voles may be in the taiga and as lemmings may be on the tundra.

Isolation and characterization of Dobrava hantavirus carried by the striped field mouse (Apodemus agrarius) in Estonia

Dobrava hantavirus (DOB) was isolated from the striped field mouse (Apodemus agrarius) trapped on Saaremaa Island, Estonia, and its genetic and antigenic characteristics were subsequently analysed. Phylogenetic analysis showed that the Estonian DOB strain, together with several wild strains carried by Apodemus agrarius, forms a well-supported lineage within the DOB clade. The topography of the trees calculated for the S, M and L nucleotide sequences of the Estonian DOB suggests a similar evolutionary history for all three genes of this virus and, therefore, the absence of heterologous reassortment in its evolution. A cross-neutralization comparison of the Estonian virus with the prototype DOB, isolated from a yellow-necked mouse (A. flavicollis) in Slovenia, revealed 2- to 4-fold differences in the end-point titres of rabbit and human antisera. When studied with a panel of 25 monoclonal antibodies (MAbs), the Estonian and Slovenian DOB isolates showed similar antigenic patterns that could be distinguished by two MAbs. Genetic comparison showed sequence differences in all three genome segments of the two DOB isolates, including an additional N-glycosylation site in the deduced sequence of the G2 protein from the Estonian virus. Whether any of these mutations relates to the different rodent hosts rather than to the distant geographical origin of the two isolates remains to be resolved. Taken together, our observations suggest that A. agrarius, which is known to harbour Hantaan virus in Asia, carries another hantavirus, DOB, in north-east Europe.

Seasonal dynamics of Pneumocystis carinii in the field vole, Microtus agrestis, and in the common shrew, Sorex araneus, in Finland

Seasonal dynamics of Pneumocystis carinii in the field vole, Microtus agrestis, and in the common shrew, Sorex araneus, were investigated in southern and central Finland by microscopical examination of methenamine silver-stained tissue sections. In both host species at both localities the number of P. carinii cyst forms was highest in late autumn (November). In S. araneus, prevalence was higher than in M. agrestis during all seasons. None of the animals was heavily infected or apparently ill, and neither species showed any extrapulmonary dissemination. In this study covering an increase phase and 4 peak host-density phases of the vole cycle, the occurrence of P. carinii seemed to be related to the population density of M. agrestis.

Puumala hantavirus genome in patients with nephropathia epidemica: correlation of PCR positivity with HLA haplotype and link to viral sequences in local rodents

Reverse transcription-PCR was used to analyze specimens from 20 Finnish nephropathia epidemica (NE) patients hospitalized during the period from October 1994 to January 1995. Blood and/or urine sediment specimens from seven patients were found to be positive for the genome sequences of Puumala hantavirus (PUU). PCR positivity of the specimens from the patients correlated well with the HLA-DRB1*0301 and HLA B8 alleles, which previously were shown to associate with severe courses of NE. Genetic analysis of the partial M-and/or S-segment sequences obtained from three severely ill NE patients revealed three PUU strains related to but distinct from previously reported strains from Finland. The M-segment sequence of PUU from bank voles trapped near the probable site of infection for one of the patients showed 98.2% identity to that of the PUU strain obtained from the patient, suggesting a link between wild-type PUU from the natural focus and the NE case. The S-segment sequences from the patient and the bank voles, however, showed substantially lower identity (95.8%). As this difference in diversity for M and S genes (1.8 and 4.2%) is atypical for PUU genetic drift, one possibility is that the strain acquired at the putative place of infection is a reassortant one.

Isolation and characterization of Tula virus, a distinct serotype in the genus Hantavirus, family Bunyaviridae

A Vero E6 cell culture isolate of Tula virus (TUL), a hantavirus first detected in European common voles (Microtus arvalis and M. rossiaemeridionalis) by RT-PCR was obtained after initial passaging of TUL-infected vole lung samples in laboratory-colonized M. arvalis. TUL was defined as a classical serotype by a cross-focus-reduction neutralization test (FRNT) and was also shown to be distinct from other hantaviruses by haemagglutination inhibition assay. The sequences of S, M and partial L genome segments of the isolate were determined: the S segment was 99.9% identical to the original rodent-derived sequence. Serological evidence for a previous TUL infection was obtained from the serum of a blood donor living near a TUL focus in Moravia, Czech Republic, showing at least a 16-fold higher FRNT titre to TUL as compared to Puumala or other hantaviruses.

Variability of sex ratio, mating probability and egg production in an intestinal nematode in its fluctuating host population

In dioecious parasites, the chances of co-occurring with the opposite sex depend on the sex ratio, abundance and distribution pattern of parasites within the host population. Theory suggests that if the abundance and degree of aggregation are very low, mating probability may decrease so much that the parasite population is vulnerable to extinction. Our aim is to determine the factors affecting the mating probability and egg production in Heligmosomum mixtum (Heligmosomidae), an intestinal nematode of the bank vole, Clethrionomys glareolus, at Pallasjärvi, Finnish Lapland. We also search for factors responsible for the persistence of H. mixtum in its fluctuating host population. The results showed that during high parasite abundance practically all nematode females co-occurred with males, but during a phase of very low abundance only 15% of females had a chance to mate. Comparison of observed mating probabilities and those predicted by a theoretical model (May & Woolhouse, 1993) showed that deviation from the assumption of complete aggregation between males and females results in underestimation of the mating probability. Sex ratio and the degree of aggregation showed a minor effect on mating probability. The sex ratio (proportion of females) of H. mixtum, which was female-biased (0.58), showed a negative correlation with the mean intensity of infection in the monthly samples (decreasing female-bias at high mean intensity), but no significant relation to the intensity of infection (number of worms in a host individual). The long-term persistence of H. mixtum in its strongly varying host population seems to be due to the high transmission efficiency and long life-span of the parasite.

Hantavirus infections in Finland

Hantaviruses cause haemorrhagic fever with renal syndrome (HFRS) and hantaviruspulmonary syndrome (HPS), and occur throughout the world. The viruses aretransmitted to humans in aerosols of rodent secretions. About 200 000 people,mainly in Eurasia, develop

Genetic variation of wild Puumala viruses within the serotype, local rodent populations and individual animal

Reverse transcriptase polymerase chain reaction cloning and sequencing were used to determine the range of S gene/N protein variability in wild Puumala virus (PUU) strains and to study phylogenetic relationships between two groups of strains which originated from Finland and from European Russia. Analyses of the nucleotide and predicted amino acid sequences showed: (1) all PUU strains shared a common ancient ancestor; and (2) the more recent ancestors were different for the Finnish branch and the Russian branch of PUU strains. A cluster of amino acid substitutions in the N protein of Finnish strains was found; this cluster was located within a highly variable region of the molecule carrying B-cell epitopes (Vapalahti et al., J. Med. Virol., 1995, in press). Different levels of S gene/N protein diversity of PUU were revealed supporting the view of geographical clustering of genetic variants. Puumala virus from individual voles was found to be a complex mixture of closely related variants-quasispecies. The ratio of non-silent to silent nucleotide mutations registered in the S genes/N proteins of PUU quasispecies was 4- to 16-fold higher than that in Puumala virus strains, resulting in a more wide range of quasispecies N protein sequence diversity.

Hantavirus infections in Finland

Hantaviruses cause haemorrhagic fever with renal syndrome (HFRS) and hantaviruspulmonary syndrome (HPS), and occur throughout the world. The viruses aretransmitted to humans in aerosols of rodent secretions. About 200 000 people,mainly in Eurasia, develop

Pneumocystis cariniiin arvicoline rodents: seasonal, interspecific, and geographic differences

We studied the seasonal prevalence of Pneumocystis carinii in Microtus agrestis (n = 289, two locations), Clethrionomys glareolus (n = 37), and Myopus schisticolor (n = 31) in southern and central Finland, in C. glareolus (n = 406) and Microtus oeconomus (n = 167) in Finnish Lapland, and in Lemmus lemmus (n = 35) in a fall sample in northern Norway. All material came from populations at peak and declining densities. The highest prevalence of P. carinii in M. agrestis in both locations in southern and central Finland was observed in November (30 and 10%). Two M. oeconomus were infected with P. carinii. No individual of the other species examined was positive for P. carinii. The prevalence and intensity of P. carinii infection in M. agrestis fed experimental low-protein diets were similar to those found in the field material.

Tula virus: a newly detected hantavirus carried by European common voles

A novel hantavirus has been discovered in European common voles, Microtus arvalis and Microtus rossiaemeridionalis. According to sequencing data for the genomic RNA S segment and nucleocapsid protein and data obtained by immunoblotting with a panel of monoclonal antibodies, the virus, designated Tula virus, is a distinct novel member of the genus Hantavirus. Phylogenetic analyses of Tula virus indicate that it is most closely related to Prospect Hill, Puumala, and Muerto Canyon viruses. The results support the view that the evolution of hantaviruses follows that of their primary carriers. Comparison of strains circulating within a local rodent population revealed a genetic drift via accumulation of base substitutions and deletions or insertions. The Tula virus population from individual animals is represented by quasispecies, indicating the potential for rapid evolution of the agent.