Allopatric combination of Fasciola hepatica and Lymnaea truncatula is more efficient than sympatric ones.

Parasites are capable of rapid evolutionary changes relative to their hosts, due to short life cycle, short generation time, and high fecundity. The direction of the evolution of parasite virulence can be studied in cross-transfer experiments, combining hosts and parasites from different localities, and comparing the outcome of established (sympatric and potentially locally adapted) and novel (allopatric) combinations of hosts and parasites. We aimed to compare the compatibility with snails hosts, the infectivity of metacercariae in rabbits and rats, and the fitness among different combinations (French-FF and Spanish-SS sympatries and allopatry-FS). The first isolate of Fasciola hepatica and its corresponding intermediate host, Lymnaea truncatula originated from Lugo's northwestern Spain. The second isolate of parasite and snail was collected in the Limoges area in central France. The Spanish snails were more susceptible to their sympatric trematode than the French snails. The Spanish flukes were more infective to intermediate hosts (snails) than the French flukes, but subsequent definitive hosts (rats or rabbits) infections remained similar. The estimated fitness was low in sympatric infections and highly similar (from 4.7 to 5.3). The fitness similarity corresponds, however, to different variations in life-history traits that could represent different strategies among the host-parasite local combinations. The infection rate in snails, metacercarial productivity, metacercarial infectivity, and the estimated fitness were better for allopatric combination (FS). The susceptibility data showed a higher efficiency of flukes in the allopatric snail population than in their local snail population. However, our results were obtained after one generation and from a single isolate and it remains to be determined if all allopatric fluke-snail isolates may present a better fitness. Nevertheless our results indicate that introduction of liver fluke-infected cattle should be monitored carefully, as it could result in the introduction of more efficient parasites.

Morphological variability in Fasciola hepatica eggs in ruminants, rodents and lagomorphs.

The length and width of 1297 Fasciola hepatica eggs shed in cattle hosts, 337 in sheep and 199 in nutria, were measured from several parts of France. The data were compared with those obtained from other studies in Spain, France (where rats were also investigated), Germany and the Netherlands. One way analysis of variance and discriminant analysis were used to assess differences between host origins. The distribution of length and width of eggs were analysed using skewness and kurtosis Fisher coefficients. The eggs recovered from sheep, cattle, rodents and lagomorphs were different in size: the eggs found in rodents (length L x width W in microm: 8592) and lagomorphs (L x W in microm: 9100) were smaller than those found in sheep and cattle (L x W in microm: 10,000). These morphological differences in F. hepatica eggs were host-induced in rats (L x W in microM: 9709 in cattle to 8949 in rats) and rabbits (L x W in microm: 9709 in cattle to 8432 in rabbits). These differences in size of eggs might correspond to their being less able to develop into miracidia in less frequent hosts such as rodents and rabbits.

Faecal egg counts are representative of digestive-tract strongyle worm burdens in sheep and goats.

The relationship between faecal egg counts and worm burdens in sheep and goats was studied in a large array of environments, from temperate (ewes, lambs or dairy-goats in France) or steppic (ewes in Middle-Atlas of Morocco) to Sahelian (young sheep and goats of Mauritania in West Africa) climates. The studied temperate worm communities were dominated by Teladorsagia and Trichostrongylus sp., and those from steppic areas by Teladorsagia, Marshallagia and Trichostrongylus sp.; Haemonchus contortus was highly predominant in the Sahelian regions. The fertility of worms depended on density (10 to 50% of variance) and presence of H. contortus to a lesser extent. For sheep and goats from several temperate and steppic areas, a good relationship between egg counts and worm burdens was established (r = 0.62). It was ameliorated when the percentage of H. contortus, the most prolific species was incorporated in the model. The predictive value of faecal egg count for assessing worm burden was only of interest for groups of hosts.

Stable and unstable environments influence the genetic diversity of the nematode Teladorsagia circumcincta, a parasite of small ruminants.

Acclimation of animal parasitic nematodes in the laboratory is the result of environmental disturbance; moderate numbers of infective larvae are introduced into and develop in a few naive hosts (versus many hosts with a resistance status to parasite infection under natural conditions), and stable conditions such as convenient moisture and temperature (versus the unstable climatic environment in the field) are offered to the free-living stages. The acclimation of sheep and goat lines of the nematode Teladorsagia circumcincta in lambs was arranged in the following putative order of increasing disturbance: sheep line and high success of experimental infection, sheep line and poor success of infection, goat line and high success of infection, sheep line with very poor success of infection, goat line and poor success of infection, and sheep isofemale line with founder and inbreeding effects. The genetic variability was assessed using the enzymes glucose-phosphate isomerase, lactate dehydrogenase, malate dehydrogenase, mannose-phosphate isomerase, and phosphoglucomutase, in starch-gel electrophoresis. The ranking on increasing Fst values (increasing genetic differentiation) observed between initially introduced and twice-passaged generations ranged from 0.003 (sheep line in sheep with high infective success) to 0.19 (sheep isofemale line) and matched to a certain extent with disturbance. The introduction of a goat line in sheep was a major disturbance, whereas in sheep lines the major factor of variation was due to the founder effect, i.e., the effective number of nematodes introduced to seed the acclimated lines. The deficiency in heterozygotes, which remains largely unexplained, was not modified during acclimation. In most cases the introduction of worms from nature resulted in lower overall genetic variability in the subsequent laboratory-reared populations.

Sheep and goat lines of Teladorsagia circumcincta (Nematoda): from allozyme to morphological identification.

Previous allozyme analyses demonstrated the existence of Teladorsagia circumcincta sheep and goat lines, based on the presence (goat line) or absence (sheep line) of an allele at the cathodic loci of malate dehydrogenase (MDH), with rapid migration (coded sR or super rapid) when starch gel electrophoresis was used. Simultaneous allozyme and morphometric characterization of individual worms from 3 natural populations harbored by goats were assessed. The nematodes with sR allele could be identified by a combination of measures of the dorsal ray of the bursa. Simple and fast morphological differentiation of worms with sR allele constitute an attractive tool for thorough studies on the frequency of these 2 types of worms and finally to assess the prevalence of goat and sheep lines.

Species diversity in gastrointestinal nematode communities of dairy goats: species-area and species-climate relationships.

Gastrointestinal nematode communities (12 species) of dairy goats were studied in four regions located in the centre of the western part of France. These regions had very similar annual mean temperatures (11 to 12.5 degrees C) but had rainfall accumulations ranging from 600 to 1330 mm per year. Breeding management (area of pastures, number of goats in the flock, the age of the farm, and the size of the initial goat population) was investigated only in the driest region. The number of helminth species and Shannon diversity index were positively correlated to the permanent pasture area and negatively to the age of the farm. Evenness was negatively correlated to the age of the farm and increased with the increasing levels of rainfall. The results are interpreted in the following terms: i) large areas of permanent pasture include a large array of environments favourable to the development of the free-living stages of various species of nematodes; ii) age of the farm is unfavourable to the maintenance of all introduced species as the farms are helminth-isolated and infestation can only occur during the grazing season thus imposing the necessity of successive annual recolonization of the pastures; and iii) free-living stages are very susceptible to dryness and survive better in areas with heavy rainfall.

Relationship between genetic diversity in the nematode Trichostrongylus colubriformis and breeding management in ten dairy-goat farms.

Ten dairy-goat farms were investigated in center-west of France for genetic variability of Trichostrongylus colubriformis in relation to breeding management. Farm management data were obtained from a questionnaire. Genetic variability was based on two polymorphic enzymes, malate dehydrogenase (MDH) and glucose-phosphate isomerase (GPI). After their establishment, the farms were subsequently isolated from introduction of strongyle worms as shown in the questionnaire; this was also suggested by the absence of a relationship between genetic variability and distance between farm locations. The genetic variability which was recorded could then be ascribed in part to the influence of management. The breeding management estimates combined the fact that animal breeding was the main economic resource; that goats were or were not the only animal bred; and that there was or was not free access to exercise yards in winter. The farms that were similar on the basis of breeding management, were also similar in the frequency of allozymes, indicating that the chosen allozymes were not neutral in respect to environment. Genetic variability was not related to the frequency of T. colubriformis in the strongyle community, this being possibly due to the fact that our farm samples predominantly harboured T. colubriformis. Between-farm genetic variability was positively correlated to the size of herd (P < 0.01), probably due to the fact that larger herds were originally constituted from several different herds.

Host, season and year do not play an important role on genetic variability in a trichostrongyle nematode as assessed from allozymes.

The isolates of the trichostrongyle nematode Teladorsagia circumcincta in sheep may vary from one site to another as assessed from allozyme studies. This genetic variability could be host (on the parasitic stages) or/and environmentally (on the free-living stages) induced. In the present study the role of host (susceptible to the establishment of the parasite and partly resistant ones) and environmental changes expressed by season (Autumn versus Spring) or year of sampling (1990 or 1992) were investigated. Five polymorphic enzymes were studied: glucose-phosphate-isomerase (GPI), lactate dehydrogenase (LDH), malate dehydrogenase (MHD), mannose-phosphate isomerase (MPI), and phosphoglucomutase (PGM). No significant difference in allelic frequencies was recorded between 4 susceptible lambs from a flock grazed in 1990 as well as in 3 lambs selected on their susceptibility or resistance to natural infection in a flock grazed in 1992. The mode of infection (natural--frequently repeated small infections, versus experimental--3 repeated large infections) did not modify the allelic frequencies of the nematodes. The allelic frequencies remained stable along the seasons and during the 2 years investigated. The largest distance of Rogers (0.07) and Fst (0.012) were recorded between worms originating from susceptible and resistant lambs or in Autumn versus Spring populations of worms (0.08 and Fst 0.010). A deficiency in heterozygotes of the same magnitude was recorded in the worm populations obtained from the different infections. The stability of allelic frequencies and genetic structure are surprising when one considers the evolution of the same parasite in several generations of laboratory conditions. This stability could be related to the fact that levels of disturbance on parasitic and free-living stages are neither too low (as in laboratory conditions) nor too high (as in farms when anthelmintic treatment are used regularly and destroy the adult stages).

Evidence for the existence of a sheep and a goat line of Teladorsagia circumcincta (Nematoda).

Populations of Teladorsagia circumcincta harbored by sheep and goats were investigated by means of isoenzyme electrophoresis. Genetic characterization of 16 natural goat populations was based on 5 polymorphic enzymes. Malate dehydrogenase (MDH-1) was the most informative; it had three alleles, the electrophoretically fast migrating one being named sR. We distinguished three groups with presence to over 20%, low frequency, and absence of sR, respectively. In four sheep flocks, only the third group was found. Neither of two laboratory-reared lamb populations originating from two geographic origins presented this third allele. When populations of worms with high sR frequency were passaged into lambs, a steep decrease in the sR-allele frequency was recorded, which was no longer demonstrated in lambs after the third passage. We suggest that the worms lacking the third allele belong to the sheep line and that those with the sR allele belong to the goat line. Thus, goats would be infected with worms of both goat and sheep lines, whereas sheep would harbor only the sheep line.

Farm history and breeding management influences on the intensity and specific diversity of nematode infection of dairy goats.

Sixteen dairy-goat farms were investigated in the centre-west of France for nematode infection. The intensity of infection was assessed by means of faecal egg counts and nematode counts at necropsy for digestive-tract nematodes and faecal larval counts for Muellerius capillaris. The specific diversity and prevalence were estimated by worm counts of 28 necropsied culled goats. The history and breeding management were recorded by means of a questionnaire. Specific diversity was estimated on two culled goats. Specific diversity and prevalence were related to the area of permanent pasture, age of farm, and to the number of goats introduced at the establishment of the farm. The most common species were Teladorsagia circumcincta and Trichostrongylus colubriformis. Teladorsagia trifurcata was absent from zero-grazing farms. Trichostrongylus vitrinus and Oesophagostomum venulosum were present in significant numbers on only one farm out of 16. The importance of Haemonchus contortus varied from farm to farm. The historical and breeding management factors that influenced the proportions of the most common species were the age of farm, size of flock, percentage of Alpine breed, duration of kidding period, age of goats and number of farms of origin. Age of farm and size of flock exerted opposing effects on the proportions of Teladorsagia circumcincta and Trichostrongylus colubriformis, respectively. The historical and breeding management factors were confounded and their respective effects on infection and the proportions of species was difficult to assess.

Allozyme variations between sheep or rabbit laboratory reared and goat wild populations of Trichostrongylus colubriformis.

Allozyme variation at 3 polymorphic enzyme loci (GPI, PGM, MDH) was studied in Trichostrongylus colubriformis. By means of a multivariate analysis it was shown that populations of worms harboured by naturally infected goats were genetically different from populations laboratory reared in lambs or rabbits. A deficiency of heterozygotes was recorded in each population studied.

Species and morphs in the Ostertagiinae: an allozyme study of seven species.

Five enzymes, malate dehydrogenase, lactate dehydrogenase, mannose-phosphate isomerase, glucose-phosphate isomerase and phosphoglucomutase from seven putative species of Ostertagiinae were compared using starch-gel electrophoresis. The Nei distances were not much affected by origin of specimens or host species. Six of the putative species could form polymorphic pairs: Ostertagia ostertagi and Ostertagia lyrata, Ostertagia leptospicularis and Ostertagia kolchida, Teladorsagia circumcincta and Teladorsagia trifurcata. The Nei distance was of the same magnitude (> 0.6) between species pairs, O. ostertagi, O. leptospicularis, T. circumcincta and Spiculopteragia spp.

Allozyme variation between laboratory reared and wild populations of Teladorsagia circumcincta.

The technique of allozyme electrophoresis was applied to two laboratory strains (isolated from the center or south-east of France) and wild populations of Teladorsagia circumcincta from the center of France. Five systems out of 13 (GPI, MPI, MDH, LDH, PGM) could be interpreted. By means of a multivariate analysis, it was shown that the laboratory strains were very similar with each other and genetically different from the wild populations. A deficiency of heterozygotes was recorded for each enzyme locus (except for MDH) in all populations studied.

A method for studying interbreeding of nematodes of the subfamily Ostertagiinae in sheep with abomasal fistulae.

Interbreeding in two nematode species, Teladorsagia circumcincta and Ostertagia leptospicularis, was studied in lambs using small populations. Offspring from a single mated female were investigated for T. circumcincta. The following protocol was found to be satisfactory for small populations: virgin females and adult males were obtained from donor lambs infected artificially and transferred into the abomasa of fistulated sheep or lambs being treated with a long-acting corticosteroid. Infective larvae obtained from cultures of faeces of fistulated sheep were given to a recipient lamb and when this animal was slaughtered it was possible to examine the adult nematodes resulting from the interbreeding. Interbreeding between one male and one female was not successful while there was limited recovery of infective larvae from the implantation of a single mated female.