Description of Haemonchus placei (Place, 1893) (Nematoda, Trichostrongylidae, Haemonchinae), identification and intra-specific morphologic variability

Haemonchus placei in cattle has never been completely described, possibly due to great morphological similarity with small ruminants Haemonchus contortus. It is newly described on one isolate from Argentina. It has clear distinct morphological features from sheep and goats Haemonchus contortus and presents only two female morphotypes (linguiform and knobbed) instead of three recorded in H. contortus. A key is proposed to identify females. Female as well as male Haemonchus placei from New World (Argentina, Mexico, USA) are morphologically different from those of Old World (Africa: Burkina-Faso, Mauritania and Ivory Coast) or Australia, possibly due to local evolution since their introduction several centuries ago from Africa or India. We propose to differentiate three sub-species, H. placei placei in Australia, H. placei africanus in western Africa and H. placei argentinensis in the New World.     

Genetic diversity patterns of Haemonchus placei and Haemonchus contortus populations isolated from domestic ruminants in Brazil

Parasitic nematodes of the genus Haemonchus infect a range of ruminant hosts and are of major veterinary and economic importance. In this study, the genetic variability of seven isolates of Haemonchus placei and Haemonchus contortus was evaluated using the mitochondrial gene cytochrome oxidase subunit I and the nuclear gene b-tubulin isotype 1. A total of 156 specimens were obtained from cattle, sheep, goat and buffalo herds raised on commercial properties from the southern and southeastern regions of Brazil and identified to the species level by sequencing of the nuclear internal transcribed spacer 2. Thirty-four percent of the specimens were identified as H. placei and 66% as H. contortus. Cattle were the preferred hosts for H. placei, whereas H. contortus was most frequent in the other three ruminant species. Analysis of genetic differentiation between isolates revealed that high rates of gene flow are operating among populations of both nematode species, including among those from different ruminant host species. Populations of H. placei were less polymorphic and presented a lower frequency of single nucleotide polymorphisms associated with benzimidazole resistance compared with H. contortus. In line with the low amount of genetic structure observed among isolates, alleles of b-tubulin 1 associated with benzimidazole resistance were present at relatively high frequencies of 5–20% in isolates of H. contortus from farms that never used this class of anthelmintic. The results presented here are consistent with the hypothesis of multiple origins of alleles associated with benzimidazole resistance, with the trade of animals among properties acting as the main factor promoting the spread of anthelmintic resistance.     

Ashworthius Patriciapilittae n. sp. (Trichostrongyloidea: Haemonchinae), an abomasal nematode in Odocoileus virginianus from Costa Rica,and a new record for species of the genus in the Western Hemisphere

A species of Ashworthius is reported for the first time in the Western Hemisphere, and A. patriciapilittae n. sp. is described on the basis of specimens in white-tailed deer Odocoileus virginianus from Costa Rica. Among 8 known species, A. patriciapilittae is morphologically similar to A. tuyenquangi in red muntjac Muntjacas muntjak from northern Vietnam. The synlophe in A. patriciapilittae is composed of 26 ridges in the cervical zone and is continuous to the caudal extremity in males and females. Males are characterized by a complex dorsal ray and narrow trifurcate spicules (351-356 microm long) lacking an "eyelet." with dissimilar ventral and dorsal processes; the gubernaculum is 45-48% of the spicule length. Females have a prominent linguiform flap at the vulva and large eggs (108-142 microm long). The presence of A. patriciapilittae in Costa Rica is examined in the context of competing hypotheses for cospeciation or contemporary host-switching in cervids: either A. patriciapilittae is a component of an endemic Central and South American fauna that has diversified through coevolution of Ashworthius and cervid hosts or it has been introduced. Among haemonchines in the Western Hemisphere, specimens of A. patriciapilittae may be confused with 3 species of Haemonchus, including H. contortus, H. placei, and H. similis, that occur in both domestic and wild ruminants. Discovery of A. patriciapilittae emphasizes the continued need for survey and inventory to define the structure and distribution of parasite faunas in wild and domestic ruminants from the Nearctic and Neotropical regions.     

A preliminary study of the effect of microclimate on third-stage larvae of Haemonchus contortus and Haemonchus placei on irrigated pasture.

Assessments were made on the influence of several microclimatic variables on the availability of third-stage larvae of Haemonchus contortus and Haemonchus placei on four strata of irrigated Kikuyu pasture. Three replicates of these pasture samples were collected on 18 sample days over 12 months and the log10 mean counts of the larvae recovered were analysed by a step-wise regression model. Predictors for the log counts of the four strata for the two nematode species included relative humidity, illumination, air temperature and windspeed. The effect of air temperature on larvae of both Haemonchus species was similar; as air temperature increased, the number of larvae on pasture increased. The inverse was true for windspeed; as windspeed increased larval counts decreased. For H. contortus, relative humidity increased as the number of larvae increased on all strata except upper herbage. The R2 values ranged from 0.11 to 0.21 for H. contortus and from 0.04 to 0.12 for H. placei. Under the conditions of this study, only 21% of the effect on H. contortus and 12% on H. placei third-stage larvae on pasture can be explained by microclimatic conditions.     

Host Movement and the Genetic Structure of Populations of Parasitic Nematodes

Mitochondrial DNA (mtDNA) sequence data were used to compare the population genetic structures of five species of parasitic nematodes from three different hosts: Ostertagia ostertagi and Haemonchus placei from cattle, H. contortus and Teladorsagia circumcincta from sheep, and Mazamastrongylus odocoilei from white-tailed deer. The parasites of sheep and cattle showed a pattern consistent with high gene flow among populations. The parasite of deer showed a pattern of substantial population subdivision and isolation by distance. It appears that host movement is an important determinant of population genetic structure in these nematodes. High gene flow in the parasites of livestock also indicates great opportunity for the spread of rare alleles that confer resistance to anthelmintic drugs. All species, including the parasite of deer, had unusually high within-population diversities (averages of 0.019-0.027 substitutions per site between pairs of individuals from the same population). Large effective population sizes (Ne), perhaps in combination with rapid mtDNA evolution, appear to be the most likely explanation for these high within-population diversities.     

Generalist nematodes dominate the nemabiome of roe deer in sympatry with sheep at a regional level

The growth of livestock farming and the recent expansion of wild ungulate populations in Europe favor opportunities for direct and/or indirect cross-transmission of pathogens. Comparatively few studies have investigated the epidemiology of gastro-intestinal nematode parasites, an ubiquitous and important community of parasites of ungulates, at the wildlife/livestock interface. In this study, we aimed to assess the influence of livestock proximity on the gastrointestinal nematode community of roe deer in a rural landscape located in southern France. Using ITS-2 rDNA nemabiome metabarcoding on fecal larvae, we analysed the gastrointestinal nematode communities of roe deer and sheep. In addition, we investigated Haemonchus contortus nad4 mtDNA diversity to specifically test parasite circulation among domestic and wild host populations. The dominant gastrointestinal nematode species found in both the roe deer and sheep were generalist species commonly found in small ruminant livestock (e.g. H. contortus), whereas the more specialised wild cervid nematode species (e.g. Ostertagia leptospicularis) were only present at low frequencies. This is in marked contrast with previous studies that found the nemabiomes of wild cervid populations to be dominated by cervid specialist nematode species. In addition, the lack of genetic structure of the nad4 mtDNA of H. contortus populations between host species suggests circulation of gastrointestinal nematodes between roe deer and sheep. The risk of contact with livestock only has a small influence on the nemabiome of roe deer, suggesting the parasite population of roe deer has been displaced by generalist livestock parasites due to many decades of sheep farming, not only for deer grazing close to pastures, but also at a larger regional scale. We also observed some seasonal variation in the nemabiome composition of roe deer. Overall, our results demonstrate significant exchange of gastrointestinal nematodes between domestic and wild ungulates, with generalist species spilling over from domestic ungulates dominating wild cervid parasite communities.     

Helminth parasites of intermingling axis deer, wild swine and domestic cattle from the island of Molokai, Hawaii

Helminth infections of axis deer (Cervus axis), wild swine (Sus scrofa) and domestic cattle (Bos taurus) were studied among intermingling herds on the Puu-O-Hoku Ranch, Molokai, Hawaii. Twenty-four species of helminths were collected from the 10 deer, 10 swine and 10 cattle. Capillaria bovis, Cooperia punctata, Haemonchus contortus and Trichostrongylus axei infected both axis deer and cattle, whereas Gongylonema pulchrum infected both axis deer and wild swine. None of the species of helminths occurred in both wild swine and cattle nor was any species found in all three hosts. Wild swine and domestic cattle supported separate and distinct helminth communities. In contrast, the helminth community of axis deer appeared to be derived from the helminth communities of cattle and wild swine and consisted only of those species capable of parasitizing either a broad range of ruminants or many mammalian taxa.     

Haemonchus horaki n. sp. (Nematoda: Trichostrongyloidea) from the grey rhebuck Pelea capreolus in South Africa.

In the course of a revision of species of Haemonchus Cobb, 1898 (Nematoda), commonly referred to as large stomach worms and significant pathogens of ruminants, a new species was discovered in the grey rhebuck Pelea capreolus, and the bontebok Damaliscus pygarthus, in South Africa. The new species, Haemonchus horaki, was previously reported as a long-spicule form of H. contortus (Rudolphi, 1803) Ransom, 1911. The new species, compared with H. contortus, can be distinguished by significantly longer spicules (555-615 microm vs. 383-475 microm); a synlophe with fewer ridges (26 vs. 30 in the region of the posterior part of the esophagus) that extend more posteriorly (within 1 mm of the copulatory bursa in males and postvulvar in females, vs. 2/3 to 3/4 of prebursal and prevulvar lengths); and an asymmetrical dorsal lobe with a long dorsal ray divided for more than half of its length, forming 2 branches of unequal length (vs. a dorsal ray divided for less than half of its length and forming 2 equal branches in H. contortus).     

Discovery of (Z)-2-phenyl-3-(1H-pyrrol-2-yl)acrylonitrile derivatives active against Haemonchus contortus and Ctenocephalides felis (cat flea)

A series of 2-phenyl-3-(1H-pyrrol-2-yl)acrylonitrile derivatives were synthesized and evaluated for in vitro activity against the endoparasite Haemonchus contortus and the ectoparasite Ctenocephalides felis. Some compounds had significant in vitro activity against these parasites.     

Distribution of nematode parasites of the digestive system in sheep (Ovis aries) and goats (Capra hircus) of the Piedmontese and Valdostano Alpine arc

A survey, carried out on gastro-intestinal nematodes of sheep and goats of Piemonte and of Valle d'Aosta (87 sheep and 12 goats) has shown the presence of the following species in sheep, Bunostomum trigonocephalum, Chabertia ovina, Cooperia curticei, Haemonchus contortus, Marshallagia marshalli, Nematodirus abnormalis, Nematodirus filicollis, Nematodirus helvetianus, Nematodirus spathiger, Oesophagostomum venulosum, Ostertagia circumcincta, Ostertagia lyrata, Ostertagia trifurcata, Skrjabinema ovis, Trichostrongylus axei, Trichostronglus colubriformis, Trichostronglus vitrinus, Trichuris ovis and Trichuris skrjabini; in goats, Bunostomum trigonocephalum, Chabertia ovina, Haemonchus contortus, Nematodirus filicollis, Nematodirus helvetianus, Oesophagostomum venulosum, Ostertagia circumcincta, Ostertagia ostertagi, Ostertagia trifurcata, Trichostrongylus axei, Trichostrongylus colubriformis and Trichostrongylus vitrinus. The percentage of each species in the two host is given in the text table.     

Bloodmeal analysis reveals avian Plasmodium infections and broad host preferences of Culicoides (Diptera: Ceratopogonidae) vectors

Changing environmental conditions and human encroachment on natural habitats bring human populations closer to novel sources of parasites, which might then develop into new emerging diseases. Diseases transmitted by host generalist vectors are of special interest due to their capacity to move pathogens into novel hosts. We hypothesize that humans using forests for recreation are exposed to a broad range of parasites from wild animals and their vectors. A corollary of this is that new vector-host, parasite-host, and vector-parasite associations could eventually develop. Thus, we expect to observe atypical vector-host associations. Using molecular bloodmeal analysis via amplification of the mtDNA COI gene we identified the vertebrate hosts of Culicoides (Diptera: Ceratopogonidae) species in a sub-urban forest of Southwestern Germany. Bloodmeals were also checked for haemosporidian infections by amplifying a fragment of the mtDNA cyt b gene. We identified a total of 20 Culicoides species, thirteen of which fed on humans. From 105 screened bloodmeals we obtained high quality sequences for 77 samples, 73 (94.8%) originated from humans, two from livestock (Bos taurus and Equus caballus), and two from wild birds (Sylvia atricapilla and Turdus merula). We found that four Culicoides species previously assumed to feed exclusively on either birds (C. kibunensis) or domestic mammals (C. chiopterus, C. deltus, C. scoticus) fed also on humans. A total of six Culicoides abdomens were infected with avian haemosporidian parasites (Plasmodium or Haemoproteus), four of those abdomens contained blood derived from humans. Our results suggest that parasites of wild animals may be transferred to humans through infectious bites of Culicoides vectors. Further, we show that Culicoides vectors believed to be a specialist on specific vertebrate groups can have plastic feeding preferences, and that Culicoides are susceptible to infection by Plasmodium parasites, though vector viability must still be experimentally demonstrated.     

Genetic and phenotypic differences between isolates of Haemonchus contortus in Australia

We believe this study is the first to consider the genetic and phenotypic divergence between isolates of Haemonchus contortus in Australia. Microsatellite markers have been used to investigate genetic divergence, whilst phenotypic divergence has been considered through individual worm morphology, isolate life history traits and the effect of isolates upon the host. The results are discussed in the context of the likely introduction of H. contortus to Australia, its recent isolation, and the characteristics of sheep and goat farming which might act to either isolate or distribute parasites. We conclude that there is significant observable genetic divergence between isolates of H. contortus in Australia. The divergence may have been under-estimated in this study due to a variety of factors. Phenotypic divergence is also observed, and potentially has significant implications for both economic losses due to haemonchosis on individual properties and for decisions regarding the regulation of stock movements in Australia.     

A preliminary evaluation of factors affecting an experimental system for vaccination-and-challenge with Haemonchus contortus in sheep

A preliminary evaluation of factors affecting an experimental system for vaccination-and-challenge with Haemonchus contortus in sheep. International Journal for Parasitology 19: 169-175. Studies were made with Haemonchus contortus in sheep to ascertain the influence of a range of factors in the domain of the host, the parasite or the vaccine on the formulation of protocols for vaccination-and-challenge to be used in identifying protective immunogens. The results corroborate earlier findings that protective immunity can follow vaccination with homogenates of parasites and show that initial processing of parasites for a vaccine leaves protective immunogen in a functional state. Sonicates of adult worms produced protective immunity and were identified as raw stock in which to prospect for candidate immunogens. By contrast, sonicates of infective larvae and exsheathing fluid invoked no significant protection and were not accredited for the same purpose. In an experiment unaccompanied by protective immunity, ewes contained lower worm burdens than castrate males indicating that vaccination experiments should be made with hosts of one sex only. Again in an experiment unaccompanied by protective immunity, Freund's complete adjuvant increased susceptibility to infection compared with Freund's incomplete adjuvant or no adjuvant implying a profound and persistent interference from killed mycobacteria on resistance against H. contortus.     

Synlophe patterns of the Haemonchinae of ruminants (Nematoda: Trichostrongyloidea)

The pattern of longitudinal ridges (synlophe) on the external cuticular surface of trichostrongylid nematodes has been shown to be of value for distinguishing species and determining relationships among higher taxa. In the process of studying Mecistocirrus digitatus, the large stomach worm of bovids of Asia that has been imported and established in the Americas, we observed remarkably similar synlophe patterns to those described for 3 species of Haemonchus and to those we examined in a species of Ashworthius. In all 3 genera, the synlophe is absent from the posterior part of the body. Only in Haemonchus does the synlophe extend beyond midbody. In both M. digitatus and Ashworthius sidemi, the synlophe extends posteriorly only about 1/4 of body length. In all 3 genera, the synlophe consists of about 30 ridges in the region of the esophagus with variation among species in specific areas, including additional pairs of subventral and subdorsal ridges and different lengths of sublateral ridges. This information is useful for identifying species and determining relationships among these large stomach worm parasites of cattle, sheep, goats, and farmed and wild cervids.     

Haemonchus contortus: characterization of a glutamate binding site in unselected and ivermectin-selected larvae and adults.

A specific ivermectin-sensitive, glutamate binding site has been identified in the parasitic nematode Haemonchus contortus. Glutamate binding in H. contortus was saturable and occurred in a single class of high-affinity binding sites which appeared to have pharmacological properties different from those of mammalian glutamate receptors. Adult and larval forms of H. contortus had dramatically different glutamate binding kinetics, the larvae showing nearly up to 200-fold higher Bmax values and up to 9-fold increases in Kd values compared to adults. Treatment of adult H. contortus with the anthelmintic, ivermectin, decreased the Bmax value for glutamate binding in the susceptible strain but not in the resistant parasites. Furthermore, selection for ivermectin resistance was associated with a significant increase in Bmax for glutamate binding in adults and a similarly significant increase in glutamate binding affinity in larvae. These results suggest that the H. contortus glutamate binding site identified in this study may be involved in the phenomenon of ivermectin resistance.     

Structure, biodiversity, and historical biogeography of nematode faunas in holarctic ruminants: morphological and molecular diagnoses for Teladorsagia boreoarcticus n. sp. (Nematoda: Ostertagiinae), a dimorphic cryptic species in muskoxen (Ovibos moschatus)

Discovery of the ostertagiine nematode Teladorsagia boreoarcticus n. sp. in muskoxen, Ovibos moschatus, from the central Canadian Arctic highlights the paucity of knowledge about the genealogical and numerical diversity of nematode faunas characteristic of artiodactyls at high latitudes across the Holarctic. Teladorsagia boreoarcticus is a dimorphic cryptic species distinguished from Teladorsagia circumcincta/Teladorsagia trifurcata in domestic sheep by a 13% divergence in the ND4 region of mitochondrial DNA, constant differences in the synlophe, and significantly longer esophageal valve, spicules, gubernaculum, and bursa. Teladorsagia boreoarcticus represents an archaic component of the North American fauna and may have a Holarctic distribution in muskoxen and caribou. Recognition of T. boreoarcticus in muskoxen, in part, corroborates hypotheses for the existence of a cryptic species complex of Teladorsagia spp. among Caprinae and Cervidae at high latitudes and indicates the importance of climatological determinants during the late Tertiary and Pleistocene on diversification of the fauna. Also reinforced is the concept of the North American fauna as a mosaic of endemic and introduced species. Discovery of a previously unrecognized species of Teladorsagia has additional implications and clearly indicates that (1) our knowledge is incomplete relative to potentially pathogenic nematodes that could be exchanged among domestic and wild caprines; (2) we do not have sufficient knowledge of the fauna to understand the ecological control mechanisms (limitations) on dissemination and host range; and (3) an understanding of historical and geographical influences on the genealogical diversity and distribution of nematode faunas in domestic and wild ruminants is requisite to define the interface between agricultural and natural ecosystems across the Holarctic.     

Some factors affecting the location of Arthritica crassiformis (Bivalvia: Leptonacea) commensal upon Anchomasa similis (Bivalvia: Pholadidae).

Arthritica crassiformis Powell is found in New Zealand waters commensally associated with the pholad Anchomasa similis (Gray). Its location on the host is highly specific and is occasioned by the complex needs of the commensal and the facilities and limitations imposed by the tunnelling activity of the host. Other species of pholad because of different morphological adaptations do not serve as hosts. With increasing size of the host, the number of commensals/host increases which is due to (a) retention of young individuals within the parental burrow and (b) by colonization from the external environment.
A. crassiformis typically, however, occurs in pairs and is probably a protandric consecutive hermaphrodite. The young are incubated in the interlamellar spaces of the ctenidia of the parental female. This anatomical adaptation together with others including strong rejectory tracts suit the commensal for a life with an active tunnelling host.
The ciliary currents of the mantle cavity of A. similis are described.     

The metabolism of flubendazole and the activities of selected biotransformation enzymes in Haemonchus contortus strains susceptible and resistant to anthelmintics

SUMMARY Haemonchus contortus is one of the most pathogenic parasites of small ruminants (e.g. sheep and goat). The treatment of haemonchosis is complicated because of recurrent resistance of H. contortus to common anthelmintics. The aim of this study was to compare the metabolism of the anthelmintic drug flubendazole (FLU) and the activities of selected biotransformation enzymes towards model xenobiotics in 4 different strains of H. contortus: the ISE strain (susceptible to common anthelmintics), ISE-S (resistant to ivermectin), the BR strain (resistant to benzimidazole anthelmintics) and the WR strain (resistant to all common anthelmintics). H. contortus adults were collected from the abomasums from experimentally infected lambs. The in vitro as well as ex vivo experiments were performed and analysed using HPLC with spectrofluorimetric and mass-spectrometric detection. In all H. contortus strains, 4 different FLU metabolites were detected: FLU with a reduced carbonyl group (FLU-R), glucose conjugate of FLU-R and 2 glucose conjugates of FLU. In the resistant strains, the ex vivo formation of all FLU metabolites was significantly higher than in the susceptible ISE strain. The multi-resistant WR strain formed approximately 5 times more conjugates of FLU than the susceptible ISE strain. The in vitro data also showed significant differences in FLU metabolism, in the activities of UDP-glucosyltransferase and several carbonyl-reducing enzymes between the susceptible and resistant H. contortus strains. The altered activities of certain detoxifying enzymes might protect the parasites against the toxic effect of the drugs as well as contribute to drug-resistance in these parasites.     

In vitro variation of glycogen content in three sheep nematodes.

In vitro variation of glycogen content under aerobic conditions was measured on fresh weight basis in 3 sheep nematodes inhabiting different niches; Haemonchus contortus, Oesophagostomum columbianum and Trichuris ovis. The parasites were saparated into species and then sexes and starved for varying periods of time up to 24 h in glucose-free physiological saline. The differences between females and males and among the species with respect to glycogen content and its rate of change with time are discussed.