Range expansion of muskox lungworms track rapid arctic warming: implications for geographic colonization under climate forcing.

Rapid climate warming in the Arctic results in multifaceted disruption of biodiversity, faunal structure, and ecosystem health. Hypotheses have linked range expansion and emergence of parasites and diseases to accelerating warming globally but empirical studies demonstrating causality are rare. Using historical data and recent surveys as baselines, we explored climatological drivers for Arctic warming as determinants of range expansion for two temperature-dependent lungworms, Umingmakstrongylus pallikuukensis and Varestrongylus eleguneniensis, of muskoxen (Ovibos moschatus) and caribou (Rangifer tarandus), in the Canadian Arctic Archipelago from 1980 through 2017. Our field data shows a substantial northward shift of the northern edge of the range for both parasites and increased abundance across the expanded ranges during the last decade. Mechanistic models parameterized with parasites' thermal requirements demonstrated that geographical colonization tracked spatial expansion of permissive environments, with a temporal lag. Subtle differences in life histories, thermal requirements of closely related parasites, climate oscillations and shifting thermal balances across environments influence faunal assembly and biodiversity. Our findings support that persistence of host-parasite assemblages reflects capacities of parasites to utilize host and environmental resources in an ecological arena of fluctuating opportunity (alternating trends in exploration and exploitation) driving shifting boundaries for distribution across spatial and temporal scales.

Papaya latex supernatant has a potent effect on the free-living stages of equid cyathostomins in vitro.

The control of equid gastrointestinal nematodes in developed countries, in particular the cyathostomins, is threatened by high levels of anthelmintic resistance. In recent years, there has been increasing interest in the evaluation of traditional 'ethnoveterinary' medicines as alternatives to chemical anthelmintics. The cysteine proteinases (CPs), a group of enzymes derived from fruits such as papaya (Carica papaya), pineapple (Ananas comosus) and figs (Ficus spp.), have shown good efficacy against adult stages of a range of parasitic nematodes, in vitro and in vivo. The efficacy of CPs against cyathostomins remains to be explored. In this study, the efficacy of a crude preparation of CPs, papaya latex supernatant (PLS), against the free-living stages of cyathostomins was evaluated using two in vitro tests, the egg hatch test (EHT) and the larval migration inhibition test (LMIT). It was demonstrated that PLS had a potent effect in the EHT, with EC-50 values in the range of 0.12-0.22µM. At concentrations above 6.25µM the eggs did not develop, below this concentration the L1 developed but they lost integrity of the cuticle upon hatching. These effects were inhibited by pre-incubation of PLS with the CP inhibitor L-trans-epoxysuccinyl-l-leucylamido-(4-guanidino butane) (E64), indicating that CPs were responsible for the anti-parasitic activity. A dose-dependent inhibition of migration of third stage larvae (L3) in the LMIT was demonstrated at higher concentrations of PLS, with EC-50 values in the range of 67.35-106.31µM. Incubation of PLS with E64 prior to use in the LMIT did not reverse the anti-migratory effect, suggesting that CPs were not responsible for the reduced migration of cyathostomin L3 and that PLS also contains an additional active compound. This is the first report of PLS and/or CPs showing activity against the free-living stages of a parasitic helminth. In addition, it suggests that cyathostomins are highly sensitive to the effects of CPs and further evaluation of their efficacy against parasitic stages and in vivo are strongly indicated.

Biased sex ratio among worms of the family Heligmosomidae--searching for a mechanism.

According to Fisher's principle, an equal sex ratio is an evolutionary stable strategy. However, biased sex ratios have been reported in many metazoan parasite species, although the causes and mechanisms of the observed bias are still poorly understood. In the present study, we analysed sex ratios in long-term datasets from three populations of bank voles (Clethrionomys (=Myodes) glareolus) infected with Heligmosomum mixtum and Heligmosomoides glareoli. The overall sex ratios of both species were female-biased but in contrast to previous studies we did not find a relationship between the proportion of females and infection intensity. A higher female bias was observed in older hosts, suggesting that the sex ratio changes over time; the lifespan of nematodes in the family Heligmosomidae is known to be comparable with that of their hosts. We also compared the distributions of sexes in voles infected with two, three, four or five worms and we found significant differences from the expected values in both parasite species. In infections with four and five H. glareoli we observed more single-sex infections than expected, both female- and male-dominated, whereas in the case of H. mixtum female-dominated infections were more frequent.

A highly conserved, inhibitable astacin metalloprotease from Teladorsagia circumcincta is required for cuticle formation and nematode development.

Parasitic nematodes cause chronic, debilitating infections in both livestock and humans worldwide, and many have developed multiple resistance to the currently available anthelmintics. The protective collagenous cuticle of these parasites is required for nematode survival and its synthesis has been studied extensively in the free-living nematode, Caenorhabditis elegans. The collagen synthesis pathway is a complex, multi-step process involving numerous key enzymes, including the astacin metalloproteases. Nematode astacinsare crucial for C. elegans development, having specific roles in hatching, moulting and cuticle synthesis. NAS-35 (also called DPY-31) is a homologue of a vertebrate procollagen C-proteinase and performs a central role in cuticle formation of C. elegans as its mutation causes temperature-sensitive lethality and cuticle defects. The characterisation of DPY-31 from the ovine gastrointestinal nematode Teladorsagia circumcincta and its ability to rescue the C. elegans mutant is described. Compounds with a hydroxamate functional group have previously been shown to be potent inhibitors of procollagen C-proteinases and were therefore examined for inhibitory activity against the T. circumcincta enzyme. Phenotypic screening against T. circumcincta, Haemonchus contortus and C. elegans larval stages identified compounds that caused body morphology phenotypes consistent with the inhibition of proteases involved in cuticle collagen synthesis. These compounds correspondingly inhibited the activity of recombinant T. circumcincta DPY-31, supporting the hypothesis that this enzyme may represent a potentially novel anthelmintic drug target.

Retrospective study on the occurrence of the feline lungworms Aelurostrongylus abstrusus and Troglostrongylus spp. in endemic areas of Italy.

Aelurostrongylus abstrusus is a metastrongyloid nematode infesting the respiratory system of domestic cats worldwide. Troglostrongylus brevior and Troglostrongylus subcrenatus, two lungworms thought to infest wild felids, have been found recently in domestic cats from Spain and Italy. These unexpected findings have raised doubts about the assumed past and present occurrence of Troglostrongylus spp., especially T. brevior, in domestic hosts and suggest that there may have been missed detection or misdiagnosis. The present retrospective study evaluated the presence of lungworms in cats from Italy with a diagnosis of respiratory parasitism or with compatible lung lesions from 2002 to 2013. Sixty-eight samples of DNA and larvae from cats with a diagnosis of aelurostrongylosis, and 53 formalin-fixed paraffin-embedded lung samples from cats confirmed as lungworm infested or with compatible lesions, were investigated using two DNA-based assays specific for A. abstrusus or T. brevior. All DNA and larval samples were positive for A. abstrusus and one was additionally positive for T. brevior. Most paraffin-embedded lung tissues were positive only for A. abstrusus, but two samples tested positive for both lungworms and one for T. brevior only. This study supports the major role of A. abstrusus in causing feline respiratory parasitism in endemic areas of Italy.

Developmental stage of strongyle eggs affects the outcome variations of real-time PCR analysis.

Strongyle and trichostrongyle parasites are ubiquitous nematodes of grazing livestock. Several molecular diagnostic tests are based upon measuring and quantifying DNA obtained from parasite eggs. It is well known that such eggs undergo development during storage, but it remains unknown to which extent developmental stages can affect the variation of diagnostic test results. This study investigated the influence of developmental stages of strongyle eggs on the variation real-time polymerase chain reaction (PCR) results. Mixed species strongyle eggs were obtained from the faeces of a naturally infected horse. Eggs were isolated and placed in microtiter plates with demineralized water. A total of 25 wells containing 100 eggs each were set up and kept refrigerated for up to five days. Once daily, five wells were examined on an inverted microscope at 100× magnification, where the developmental stages of the eggs were noted, and then eggs harvested for DNA extraction. The protocol was repeated three times. Genomic DNA was extracted using a commercial kit previously validated for strongyle type eggs. PCR reactions were performed with a primer set specific for the ribosomal DNA region for all strongyle type parasites (NC1, NC2). SYBR Green Real-Time PCRs were performed in triplicates. Results revealed a statistically significant increase in PCR yield after three days, which was statistically associated with beginning embryonation of the eggs. In conclusion, storage time and developmental stage of strongyle eggs are significant sources of error in studies based on quantitative real-time PCR analysis. This study suggests that for refrigerated storage of more than three days, eggs should be inactivated and preserved for further analysis.

Synergistic effects of seasonal rainfall, parasites and demography on fluctuations in springbok body condition.

1. Seasonality of rainfall can exert a strong influence on animal condition and on host-parasite interactions. The body condition of ruminants fluctuates seasonally in response to changes in energy requirements, foraging patterns and resource availability, and seasonal variation in parasite infections may further alter ruminant body condition. 2. This study disentangles the effects of rainfall and gastrointestinal parasite infections on springbok (Antidorcas marsupialis) body condition and determines how these factors vary among demographic groups. 3. Using data from four years and three study areas, we investigated (i) the influence of rainfall variation, demographic factors and parasite interactions on parasite prevalence or infection intensity, (ii) whether parasitism or rainfall is a more important predictor of springbok body condition and (iii) how parasitism and condition vary among study areas along a rainfall gradient. 4. We found that increased parasite intensity is associated with reduced body condition only for adult females. For all other demographic groups, body condition was significantly related to prior rainfall and not to parasitism. Rainfall lagged by two months had a positive effect on body condition. 5. Adult females showed evidence of a 'periparturient rise' in parasite intensity and had higher parasite intensity and lower body condition than adult males after parturition and during early lactation. After juveniles were weaned, adult females had lower parasite intensity than adult males. Sex differences in parasitism and condition may be due to differences between adult females and males in the seasonal timing of reproductive effort and its effects on host immunity, as well as documented sex differences in vulnerability to predation. 6. Our results highlight that parasites and the environment can synergistically affect host populations, but that these interactions might be masked by their interwoven relationships, their differential impacts on demographic groups, and the different time-scales at which they operate.

Comparison of molecular and McMaster microscopy techniques to confirm the presence of naturally acquired strongylid nematode infections in sheep.

Patent strongylid nematode infections were identified using McMaster worm egg counts (WEC) and PCR assays (ITS-2 nuclear ribosomal DNA) to screen genomic DNA extracted directly from lamb faecal samples. Lambs from four different farms in southern Western Australia were sampled rectally on two separate occasions, with McMaster WECs and PCRs conducted on a total of 858 samples. Negative controls (n=96) (WEC <50 eggs per gram [epg]) and positive controls (n=96) (faecal samples spiked with a 100 µL suspension of third-stage larvae (L(3)) containing approximately equal proportions of Teladorsagia circumcincta, Trichostrongylus colubriformis, Haemonchus contortus, Oesophagostomum spp. and Chabertia ovina) were generated. All control samples amplified in accordance with positive controls. High levels of agreement (Kappa values ≥ 0.93) were identified between the two diagnostic tests. PCRs detected an additional 2.0% of samples as strongylid-positive but there was no significant difference in the number of strongylid-positive samples identified using PCR or McMaster WEC.

Observations on development of natural infection and species composition of small strongyles in young equids in Kentucky.

Early development and maturation of species of small strongyles have not been studied extensively. Most information is on the first appearance of strongyle eggs in feces of foals. However, species cannot be determined in this manner because of similarity of the morphological features of the eggs. To determine more definitive knowledge on development and species composition of natural infections of small strongyles, eight equid foals were necropsied and examined at various ages (31 to 92 days of age). The entire contents of the large intestine were examined, and all worms (6,671) recovered were identified. This was done to recover small strongyle specimens in an effort to find the stage of development of the worms for different time periods. The primary interest was to obtain data on the potential prepatent period. A total of 17 species of small strongyles were recovered. The earliest gravid female was Cylicostephanus longibursatus in a 57-day-old foal; then Cylicostephanus goldi was positive at 64 days, Cyathostomum catinatum at 68 days, Coronocyclus coronatus and Cylicostephanus calicatus at 70 days, Coronocyclus labiatus, Cylicocyclus leptostomus, Cylicocyclus nassatus, Cylicostephanus hybridus, and Cylicostephanus minutus at 74 days, and Cylicostephanus bidentatus at 92 days. While it is not known exactly when the foals began eating pasture vegetation (typically they begin to graze a short time after birth) and first ate infective free-living third-stage larvae, the results give an indication of the natural prepatent period of several species of small strongyles. Additional data are presented on the number of worms per foal, distribution of the worms in the parts (cecum, ventral colon, and dorsal colon) of the large intestine, and proportion of species found.

Anthelminthic efficacy of aqueous extract of Acanthus montanus leaf against strongylid nematodes of small ruminants.

The anthelminthic efficacy of the crude aqueous extract of Acanthus montanus (Nees) T. Anders (Acanthaceae) against strongylid nematodes of small ruminants was investigated using the in-vitro egg hatch and larval growth inhibition assays. Faecal samples collected per rectum from sheep and goats were subjected to parasitological examination using the McMaster counting technique with a yield of 700 eggs per gram (E.P.G.) of faeces. Crude aqueous leaf extract of Acanthus montanus was extracted using cold water extraction with a yield of 13.01% w/w. Egg hatch assay revealed a 91.75% reduction in egg hatch at concentration of 25 mg/ml of the extract. The extract had a 100% inhibition, at 200mg/ml concentration which was equivalent to the activity of 3.125 mg/ml albendazole. The distilled water control however, showed a 0% inhibition. Larval growth inhibition assay results showed the extract on Day 1 at 25 mg/ml and 200mg/ml concentrations yielded 67.02% and 85.26% larval inhibition. On Day 2, 100% inhibition was obtained on all concentrations of the extract except for 25 mg/ml that yielded 88.30%. Albendazole however, had a 100% larval inhibition for all concentrations on Day 2. A 100% larval inhibition was recorded on Day 3 from the 25 mg/ml concentrations. The mean percentage larval inhibition of the extract at 200mg/ml (92.63%) was comparable to the standard anthelminthic (albendazole) at 12.50mg/ml (92.28%). These findings showed that there is a pharmacological basis for the folkloric claim of the anthelminthic effect of Acanthus montanus.

Variation in the hatching behaviour of Nematodirus battus: polymorphic bet hedging?

Previous work on the transmission dynamics of Nematodirus battus, an important nematode parasite of farmed ruminants in temperate regions, suggests that it operates a bet-hedging strategy. Hatching of cold-sensitised eggs is concentrated in spring, while alternative hatching of non-cold-sensitised eggs in autumn mitigates the risk of poor conditions for hatching in spring or host absence during peak larval availability. Isolates from Scotland showed much less propensity to hatch without chilling than the previously characterised isolate from southern England. Nematodirus battus eggs from a hill farm in Scotland showed intermediate proportions of non-chilled hatching, perhaps related to unpredictability of climate at higher altitudes. Geographic polymorphism in larval behaviour appears to be present in the form of differing chilling requirements for egg hatching. Since bet-hedging through trait diversification is a plausible and demonstrated strategy for coping with environmental unpredictability, it is a likely target for adaptation to climate change. Predictions of disease epidemiology in a changing climate should incorporate parasite adaptation, but further theoretical and empirical characterisations of likely evolutionary responses are needed before this is possible for the most economically important systems.

Effects of fecal collection and storage factors on strongylid egg counts in horses.

Fecal analyses are becoming increasingly important for equine establishments as a means of parasite surveillance and detection of anthelmintic resistance. Although several studies have evaluated various egg counting techniques, little is known about the quantitative effects of pre-analytic factors such as collection and storage of fecal samples. This study evaluated the effects of storage temperature, storage time and airtight versus open-air storage on fecal egg counts. The experimental protocols were replicated in two study locations: Copenhagen, Denmark and Athens, Georgia, USA. In both locations, the experiment was repeated three times, and five repeated egg counts were performed at each time point of analysis. In experiment A, feces were collected rectally and stored airtight at freezer (-10 to -18 degrees C), refrigerator (4 degrees C), room (18-24 degrees C), or incubator (37-38 degrees C) temperatures. Egg counts were performed after 0, 6, 12, 24, 48, and 120h of storage. In experiment B, feces were collected rectally and stored airtight or in the open air in the horse barn for up to 24h. Egg counts were performed after 0, 3, 6, 12, and 24h of storage. In experiment A at both locations, samples kept in the refrigerator showed no decline in egg counts, whereas storage in the freezer and incubator led to significantly declining egg numbers during the study. In contrast, storage at room temperature yielded marked differences between the two study locations: egg counts remained stable in the U.S. study, whereas the Danish study revealed a significant decline after 24h. In experiment B, the Danish study showed no differences between airtight and open-air storage and no changes over time, while the U.S. study found a significant decline for open-air storage after 12h. This difference was attributed to the different barn temperatures in the two studies. To our knowledge, this is the first study to evaluate the pre-analytic factors affecting egg counts in horses using an experimental protocol replicated in two contrasting geographic and climatic locations. Our results demonstrate that refrigeration is the best method for storage of fecal samples intended for egg count analysis, but that accurate results can be derived from fecal samples collected from the ground within 12h of passage.

Hatching behaviour of Nematodirus filicollis in a flock co-infected with Nematodirus battus.

The development and survival of larvae of Nematodirus filicollis, an important nematode parasite of ruminants, were extensively investigated in the laboratory for the first time, using eggs harvested from sheep grazing in the UK in winter. Third-stage larvae (L3s) developed within the eggs between 12 and 25 degrees C, with the proportion of eggs developing successfully being highest at the upper end of this range. Eggs required chilling below 10 degrees C before being able to hatch at all, and maximum hatch was observed only following chilling to 4 degrees C. Hatching occurred above 6 degrees C, and peaked at 13 degrees C, with the proportion of eggs hatching decreasing to 17-20 degrees C, which appears to form an upper threshold temperature for hatching. When fully developed eggs were placed at 11-13 degrees C, L3 emerged very rapidly with hatching being completed within 6 days. Mortality of emerged L3s increased with temperature, particularly above 20 degrees C. For this parasite, given the low minimum hatching thresholds and the rapid emergence of L3, the existence of an upper hatching threshold is likely to have limited impact on patterns of larval availability on pasture. The strict requirement for chilling is surprising, being at odds with both previous observations and the wide geographical distribution of this species. It is possible that the proportion of eggs requiring chilling is an adaptable trait, enabling early infection of naïve hosts in the face of competition from N. battus, yet also persistence in regions that do not provide good conditions for the chilling of eggs. Further study of selectable variation in this trait could help us to understand the contrasting geographical ranges and disease patterns within the genus, and how different species might respond to climate change.

The contribution to the epidemiology of gastrointestinal nematodes of sheep with special focus on the survival of infective larvae in winter conditions.

Tracer tests conducted over a 3-year period were aimed at measuring the level and species nematode composition of survival on pastures with a special focus on winter months. The survival of infective larvae in chilly conditions is not significantly affected by Trichostrongylus axei, Trichostrongylus colubriformis, Trichostrongylus vitrinus and Chabertia ovina. On the contrary, the number of Teladorsagia circumcincta and Nematodirus filicollis significantly increased in milder winter conditions. The results confirmed an epidemiological strategy of overwintering in the arrested stage for Teladorsagia circumcincta and Nematodirus filicollis; the epidemiological strategy of genus Trichostrongylus used both strategies-in particular the tolerance of free-living stages to cold conditions. Part of the population overwintered in the arrested stage as well.

Host-parasite ecology of the helminths in mountain gorillas.

To understand patterns of intestinal parasitism in healthy, undisturbed endangered mountain gorillas (Gorilla beringei), we regularly collected fecal samples from a group of 14 wild gorillas residing in Bwindi Impenetrable National Park (BINP), Uganda, for about 1 yr. The objectives of the study were to collect baseline data in order to document the helminth parasites infecting this group of gorillas and to examine the effects of season and host age-sex class on patterns of parasite infection. In addition to weekly surveys of feces from all group members, fecal samples from 4 identified individuals were examined almost daily. We identified the diagnostic stages of the following parasites: strongylids (Strongylida), Anoplocephala gorillae, Probstmayria sp., Strongyloides fuelleborni, and a trematode. Monthly and daily fluctuations in strongylid egg counts were observed. Infants had lower strongylid egg counts compared with other group members. Both of the silverbacks had higher mean egg counts in the wet season than in the dry season. Examination of fecal samples from identifiable gorillas revealed high day-to-day variation in strongylid egg counts. No evidence of anthropozoonotic transmission of intestinal helminths was found.

Arrested development of sheep strongyles: onset and resumption under field conditions of Central Europe.

Two tracer tests were conducted between August 2004 and March 2007 at an ecological farm in western Bohemia. The first tracer test was performed for the summer-autumn grazing period (onset of arrested development), the second for spring (resumption of arrested development). In the first tracer test, the percentage of nematodes arresting development over the winter months reached 87.7% for Teladorsagia circumcincta, 66.7% for Haemonchus contortus, 89.9% for Nematodirus filicollis, 21.6% for Trichostrongylus axei, and 23.9% for both Trichostrongylus vitrinus and Trichostrongylus colubriformis. None of the arrested larvae were observed with species Cooperia curticei, Nematodirus battus, and Oesophagostomum venulosum. In the second tracer test, a significant increase of adult worms was discovered in March of species T. circumcincta and N. filicollis and Trichostrongylus spp. in February. Redundancy analysis and generalized linear models analyses have confirmed that environmental conditions play a crucial role in hypobiosis of sheep strongyles in the Czech Republic. The analysis of influences of various environmental factors revealed that the number of arrested larvae was negatively influenced by light-day length, sunshine, or daylight decrease (p < 0.01).

The influence of temperature on the development, hatching and survival of Nematodirus battus larvae.

Although Nematodirus battus (Nematoda: Trichostrongyloidea) is an economically important and highly pathogenic parasite of sheep in the temperate regions, very little is known about the population dynamics of its free-living stages and their relationship with ambient temperature. Here we describe the temperature-related vital rates and thresholds of egg development, hatching and larval survival for the first time. N. battus eggs were able to develop between 11.5 and 27 degrees C, but development at the lower end of this range was more successful. Embryonated eggs did not hatch below 11 degrees C or above 17 degrees C. This is the first description of an upper threshold for hatching in trichostrongyloids. In contrast with most previous studies, although some eggs hatched only after being chilled, substantial proportions of eggs were also found to hatch without the need for chilling. These proportions were lower with increasing, within-hatching range, temperatures. Larval death rates significantly increased at temperatures towards and above the upper hatching threshold. The peculiar hatching behaviour of N. battus may therefore be explained in terms of optimization of larval survival. We argue that our findings confirm the likelihood of an arctic origin of the parasite. Probable changes and adaptations of parasite behaviour in the temperate regions, and the driving forces behind them, are discussed, as well as factors affecting persistence and geographical spread against a background of climate change.

Prevalence of Toxocara spp., Toxascaris leonina and ancylostomidae in public parks and beaches in different climate zones of Costa Rica.

This epidemiological study was conducted in different regions of Costa Rica to determine the prevalence of the developmental stages of potential zoonotic intestinal helminths of dogs and cats in public places. Samples were collected within three main climate zones including rural and urban areas during both the rainy and the dry season. Faecal and environmental samples were taken from 69 parks and beaches. Of the faecal samples 3% contained Toxascaris spp. eggs, 7% Toxocara spp. eggs and 55% contained ancylostomidae eggs. Of the soil samples, 2% contained ancylostomidae eggs and 0.8% contained ascarid eggs. Significant differences in the presence of parasites were found in faecal samples of dry, moist and wet climate zones and between the dry and rainy seasons. Significant differences in the presence of eggs and larvae were also found in the grass samples in the dry, the moist and the wet climate zones and between the different seasons. No significant differences were found between rural and urban areas.

Population dynamics of nematode parasites of reindeer in the sub-arctic.

Nematode parasite infections of semi-domestic reindeer grazing in their natural habitat in northern Finland were monitored for approximately 2 years. This was achieved by monthly faecal egg counts of male and female calves and adult females from an experimental reindeer herd, in addition to estimating the acquisition of nematode infection from pasture using tracer reindeer calves. The most abundant parasite was Ostertagia gruehneri in the worm counts of tracer animals and in faecal egg counts of adult female reindeer. Capillaria sp. eggs were detected in calves and adults, but Nematodirinae eggs were only recovered from calves. Faecal egg counts showed variations between months for each nematode species, with male and female calves shedding similar numbers of eggs. During each year, calves shed more Capillaria sp. eggs than adult female reindeer, but similar numbers of O. gruehneri eggs. Egg counts of O. gruehneri were more abundant in late summer-autumn (July-September), whereas Capillaria sp. and the Nematodirinae dominated the winter months (November-February). The seasonal trends of adult worm burdens of O. gruehneri in the tracers paralleled the egg count patterns. Capillaria sp. was not detected in tracer worm counts. Tracer worm burdens showed that the proportion of inhibited larvae of O. gruehneri and Nematodirinae steadily increased from spring to early winter, followed by a decline and a commensurate increase in the number of adult parasites in the second summer. This investigation showed that parasite transmission occurs continuously throughout the year for nematode parasites of reindeer in northern Finland.

Field study on the survival, migration and overwintering of infective larvae of horse strongyles on pasture in central Ukraine.

Experimental studies on the survival of infective stage larvae of horse strongyles and their ability to overwinter on pasture were carried out in central Ukraine (Poltavska oblast). Faecal pats (1.5 kg each) of naturally infected horses were placed on pasture, and samples of faeces and surrounding vegetation (10 g each) were collected each month, excluding the winter months, from November 2002 until April 2004. The number of infective third stage larvae was calculated in each sample and compared with that from the control faecal samples cultivated in the laboratory. In the control samples, the ratio of infective third stage larvae to the initial number of eggs was from 54.7% in June up to 84.2% in November. This ratio depended on the presence of nematophagous fungi growing in the faeces. On pasture, the development of larvae to the infective third stage took approximately 4 weeks in the warm season, from April until September. In October, a percentage of the eggs (25% to EPG value) did not hatch. No larval development was observed in faeces in November. A minute quantity of larvae, about 0.03% of their initial number, was observed to survive on pasture for the 12 months. Migration of infective larvae from the faeces to vegetation was not intensive, between 71% and 89% of larvae remained in the faeces 4 weeks after deposition of the faecal pats, the percentage related to soil humidity in each month. The proportion of larvae successfully surviving during winter appeared to be maximal in faecal pats deposited on pasture in September of the previous year (up to 42.0% of the initial number of larvae). Some larvae were observed surviving winter in soil beneath the faecal pats. The results of the study demonstrated that horse pastures in the central part of Ukraine are never free from the infective third stage larvae of strongyles.