Gastrointestinal Nematode Parasites Research Articles

Variability in the fecal egg count and the parasitic burden of hair sheep after grazing in nematode infected paddocks

Gonzalez-Garduno R., Mendoza-de Gives P. & Torres-Hernandez G. 2013. Va- riability in the fecal egg count and the parasitic burden of hair sheep after grazing in nematode infected paddocks. Pesquisa Veterinaria Brasileira 33(4):469-475. Universidad Autonoma Chapingo, Unidad Regional Universitaria Sursureste, P.O. Box 29 Teapa, 86800 Tabasco, Mexico. E-mail address: robgardu@hotmail.com This study aimed to evaluate the variability in the fecal egg count (FEC) and the parasi- tic burden of naive hair sheep after grazing in nematode infected paddocks. The research was carried out in Tabasco, Mexico, during two periods (August and December). In each period 32 lambs were grazed for one month on African star grass (Cynodon plectostachyus) contaminated with gastrointestinal parasitic nematodes. FEC, packed cell volume (PCV) and body weight (BW) were recorded. Gastrointestinal worms were recovered at necropsy. Data were analyzed with the MIXED procedure of SAS using a model of repeated measure- ments over time. A higher number of Haemonchus contortus worms was found in Decem- ber (2814±838) than in August (1166±305). The opposite occurred with Cooperia curticei (2167±393 and 3638±441, respectively). The FEC and correlation coefficient in respect to the worm burden were higher in December (6516 ± 1599, r=0.83, respectively) than in August (4364±771, r=0.44, respectively). A high variability in resistance-susceptibility to gastrointestinal nematodes (GIN) occurred in Katahdin × Pelibuey lambs after grazing.

First report of interaction of nematophagous fungi onLibyostrongylus douglassii (Nematoda: Trichostrongylidae)

Libyostrongylus douglassii is a gastrointestinal nematode parasite of ostriches that can cause up to 50% mortality in young birds. The objective of this study was to compare the predatory capacity of two isolates of the predatory fungi Duddingtonia flagrans (AC001 and CG722 isolates) and one of Arthrobotrys cladodes (CG719) on infective larvae (L3) of L. douglassii under laboratory conditions, in 2% water-agar medium. The results showed that the fungi tested were effective in preying upon the L3 of L. douglassii (P < 0.05), compared with the control group. However, there was no difference in predatory capacity between the fungi tested (P > 0.05) during the seven days of experimental testing. In comparison with the control, without fungus, there were significant decreases (P < 0.05) of 85.2% (AC001), 81.2% (CG722) and 89.2% (CG719) in the average numbers of L3 of L. douglassii recovered from treatments with the isolates tested. In the present study, the three isolates of the predatory fungi D. flagrans (AC001 and CG722) and A. cladodes (CG719) were efficient at in vitro destruction of the L3 of L. douglassii.

The immunology and genetics of resistance of sheep to Teladorsagia circumcincta

Teladorsagia circumcincta is one of the most economically important gastrointestinal nematode parasites of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. This is a very common parasite and viable sheep production requires the extensive use of anthelmintic drugs. However, the emergence of drug-resistant parasites has stimulated the search for alternative control strategies to curb production losses. Lambs become infected soon after weaning and begin to control parasite burden within 8-10 weeks of continual infection. This control is an acquired characteristic mediated by the development of parasite-specific antibodies. This paper describes the immunology associated with resistance and susceptibility, focussing on differential T cell activation that regulates the production of specific effector mechanisms. It continues by summarizing the methods used to identify genes that could be exploited as molecular markers of selection for resistance. In particular it focusses on the link between understanding the molecular immunology of infection and the identification of candidate genes for selection.

Potential contribution of P-glycoproteins to macrocyclic lactone resistance in the cattle parasitic nematode Cooperia oncophora

Resistance against macrocyclic lactones such as ivermectin is widespread among parasitic gastrointestinal nematodes of small ruminants and is rapidly increasing in cattle parasites. ABC transporters of the subfamily B, the so-called P-glycoproteins (Pgps) have been frequently implicated in ivermectin resistance and are a major cause of multi-drug resistance in protozoa and helminths. The Pgp inhibitor verapamil (VPL) dramatically enhanced susceptibility of the cattle parasitic nematode Cooperia oncophora to ivermectin in vitro as measured in a larval developmental assay and a larval migration inhibition assay using third stage larvae. Moreover, VPL completely restored susceptibility to ivermectin in a resistant isolate resulting in virtually identical dose–response curves of susceptible and resistant isolates in the presence of VPL. Further characterisation of the molecular mechanisms resulting in Pgp-mediated ivermectin resistance is still hampered by the lack of molecular and biochemical information for Pgps of parasitic nematodes. Using PCR with degenerate primers, fragments of four different C. oncophora Pgps could be amplified and the Conpgp-2, previously implicated in macrocyclic lactone resistance in Haemonchus contortus, and Conpgp-3 full-length cDNAs were obtained by RACE PCR. The pgp sequences presented here contribute important data required to systematically screen resistant C. oncophora isolates for up- or down-regulation of Pgps and for the detection of single nucleotide polymorphisms in Pgps to detect selection of specific Pgp alleles by anthelmintics as early as possible.

Hair-type sheep generate an accelerated and longer-lived humoral immune response to Haemonchus contortus infection

Antibody levels produced in response to gastro-intestinal nematode (GIN) parasite infection are typically higher in GIN-resistant breeds than susceptible breeds. Consequently, GIN-resistant ewes should generate greater parasite-specific antibody in colostrum and milk, potentially providing greater passive immunity to young lambs. To test this hypothesis, we monitored immunoglobulin levels in wool and hair-type sheep infected with Haemonchus contortus for 35 days following the end of a 45-day autumn breeding season and subsequently for 6 weeks around the time of parturition. Ten, first-parity ewes of each type were infected with 12,000 H. contortus L3 larvae following the end of breeding. In response to infection, hair ewes generated greater serum IgA (P<0.05), although the pattern of IgA production was similar between the types. Following experimental infection, wool ewes were incapable of clearing the parasite infection well in advance of parturition. Prior to parturition, hair ewes had lower FEC and greater circulating H. contortus-specific IgA. However, no difference was seen in total or antigen-specific IgA production in the colostrum and milk of either breed. These data further demonstrate that hair-type sheep can rapidly reduce fecal egg output and generate greater humoral immunity as evidenced by higher levels of circulating antigen-specific antibody, but there is no evidence to suggest GIN-resistant sheep preferentially mobilize antigen-specific IgA to colostrum or milk. Thus, no clear difference exists between types of sheep in ability to deliver parasite-specific IgA to their offspring.

Grazing systems and worm control in sheep: a long-term case study involving three management systems with analysis of factors influencing faecal worm egg count

Managing infections of sheep with gastrointestinal nematode parasites (worms) and problems of resistance to anthelmintic treatments continue to be major challenges for graziers on the Northern Tablelands of New South Wales, Australia. The whole-farmlet study of grazing enterprises undertaken by the Cicerone Project tested the broad hypotheses that compared with typical management (farmlet B), internal parasites can be more effectively managed with improved nutrition (farmlet A) or by intensive rotational grazing (farmlet C). Further aims were to identify the major sources of variation in faecal worm egg count (WEC) over the 6-year period and to examine the efficacy of the various anthelmintic treatments used during the experiment. This paper describes the management of sheep worms at the whole-farmlet level during the experiment, and analyses data from the routine WEC monitoring (5644 records) and larval differentiation tests (322 records) carried out on behalf of the Cicerone Management Board and by a doctoral candidate. It complements more detailed investigations published elsewhere. Over the period from July 2000 to December 2006, worm infections in ewes, lambs, hoggets and wethers were, with some exceptions, successfully controlled on the farmlets through a combination of regular monitoring of WEC, treatment with a wide array of anthelmintics and grazing management. Farmlet C had lower mean WEC (444 epg) and annual anthelmintic treatment frequency (3.1 treatments/year) over the whole experimental period than farmlets B (1122 epg, 4.3 treatments/year) or A (1374 epg, 4.7 treatments/year). The main factors influencing WEC were the time since the last anthelmintic treatment, and the anthelmintic used at that treatment. The magnitude of these effects dwarfed those of climatic and management factors that might be expected to influence the epidemiology of gastrointestinal nematode infections via environmental or host-mediated mechanisms. Nevertheless management factors associated with stocking rate and grazed proportion (proportion of each farmlet grazed at any one time), and climatic indicators of both temperature and moisture availability had significant effects on WEC. The results show that, in a region with Haemonchus contortus as the major sheep nematode, improved host nutrition in a higher input system (farmlet A) did not provide more effective control of gastrointestinal nematodes than typical management (farmlet B); however, it was observed that gastrointestinal nematode control was no worse on farmlet A than on farmlet B in spite of farmlet A supporting a 48% higher stocking rate by later in the trial period (2005). The study provided strong support for the proposition that intensive rotational grazing (farmlet C) provides more effective control of gastrointestinal nematodes than typical management (farmlet B) as evidenced by significantly lower WEC counts and anthelmintic treatment frequency. Tactical worm control based on routine monitoring of WEC provided adequate control of worms on all three farmlets for much of the experimental period but failed to prevent significant spikes in WEC to values associated with significant production loss on multiple occasions, and significant ewe mortality on farmlets A and B on one occasion.

Prevalence and intensity of infection with gastrointestinal nematodes in sheep in eastern Serbia

A coprological examination of 680 grazing sheep was performed in Eastern Serbia from March 2011 to November 2012 in order to determine the presence of gastrointestinal (GI) nematode parasites. Fecal samples were randomly collected and examined by using qualitative and quantitative coprological techniques. It was found that 74.56% sheep were infected. Samples that contained nematode eggs were processed for larval development and eleven nematode genera were identified: Haemonchus (46.91%), Ostertagia (25.88%), Marshallagia (21.91%), Cooperia (14.12%), Trichostrongylus (39.85%), Nematodirus (35.88%), Bunostomum (23.97%), Strongyloides (17.06%) Oesophagostomum (40.73%), Chabertia (32.79%) and Trichuris (10.88%). Higher prevalence of infection was observed in females (p<0.01), as well as in adults (p<0.001). Regarding the intensity of infection, in 40.63% sheep it was low, in 51.87% moderate and in 7.50% high. There was no difference in intensity of infection considering sex and age of animals. Moreover, simultaneous infection with different number of nematode genera was dependent on sheep’s age (p<0.001). These results suggest that GI nematodes are a conspicuous problem of grazing sheep in the study area.

Galectin-like molecule in parasite inhibits remission of experimental autoimmune encephalomyelitis by enhancing auto-reactive B cells

Event Abstract Back to Event Galectin-like molecule in parasite inhibits remission of experimental autoimmune encephalomyelitis by enhancing auto-reactive B cells So Jin Bing1, Seung-Hong Lee1, Danbee Ha1, Jinhee Cho1, Sang Kyun Park2, Hak Sun Yu2 and Youngheun Jee1* 1 jeju national university, Veterinary medicine, South Korea 2 Pusan National University, Department of Parasitology, South Korea Galectins are widely expressed in host cells and play important roles during different steps of infection. Although the expression and function of host galectins have been extensively appreciated, there is still scarce information on the repertoire of ‘galectin-like molecules’ expressed by pathogens and associated to their virulence. In a recent study, researchers reported that rTl-gal isolated from an adult worm of the gastrointestinal nematode parasite Toxascaris leonina attenuated clinical symptoms of inflammatory bowel disease in mice treated with dextran sulfate sodium (DSS). Noting that the role of rTl-gal in the inflammation disease, we tried to elucidate the effect of parasite via its galectin-like molecules (rTl-gal) on experimental autoimmune encephalomyelitis (EAE), a mouse inflammatory and demyelinating autoimmune disease model of human multiple sclerosis (MS). When we administered rTl-gal to EAE mice, no significant difference in clinical disease severity was observed between rTl-gal-treated and control group at peak stage. At remission stage, interestingly, rTl-gal-treated mice not only failed to recover after the peak of disease but also showed increased EAE severity, leading to autoreactive inflammation cell activation and persistent CNS damages such as neuroinflammation, demyelination, gliosis and axonal damages. We further verified the cell population whose infiltration was altered by rTl-gal treatment and observed that rTl-gal-treated EAE mice markedly increased the infiltration of CD45R/B220+ B cells. Consistent with these, cell population of CD45R/B220+ B cell and autoantibody production in periphery were significantly up-regulated. Our results suggest that galectin-like molecule isolated from a gastrointestinal parasite can deliver a harmful effect to EAE via strengthening autoreactive B cell function contrary to its beneficial effect on inflammatory bowel disease. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2012011645) Keywords: galectin like molecule, Toxascaris leonina, Experimental autoimmune encephalomyelitis, parasite, autoreactive B cell Conference: 15th International Congress of Immunology (ICI), Milan, Italy, 22 Aug - 27 Aug, 2013. Presentation Type: Abstract Topic: Host-pathogen interactions Citation: Bing S, Lee S, Ha D, Cho J, Park S, Yu H and Jee Y (2013). Galectin-like molecule in parasite inhibits remission of experimental autoimmune encephalomyelitis by enhancing auto-reactive B cells. Front. Immunol. Conference Abstract: 15th International Congress of Immunology (ICI). doi: 10.3389/conf.fimmu.2013.02.00067 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 09 Mar 2013; Published Online: 22 Aug 2013. * Correspondence: Prof. Youngheun Jee, jeju national university, Veterinary medicine, jeju, South Korea, yhjee@jejunu.ac.kr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers So Jin Bing Seung-Hong Lee Danbee Ha Jinhee Cho Sang Kyun Park Hak Sun Yu Youngheun Jee Google So Jin Bing Seung-Hong Lee Danbee Ha Jinhee Cho Sang Kyun Park Hak Sun Yu Youngheun Jee Google Scholar So Jin Bing Seung-Hong Lee Danbee Ha Jinhee Cho Sang Kyun Park Hak Sun Yu Youngheun Jee PubMed So Jin Bing Seung-Hong Lee Danbee Ha Jinhee Cho Sang Kyun Park Hak Sun Yu Youngheun Jee Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Efficacy of oral, injectable and pour-on formulations of moxidectin against gastrointestinal nematodes in cattle in New Zealand

The efficacy of moxidectin administered by different routes, against naturally acquired infections of gastrointestinal nematode parasites of cattle, was compared using faecal egg count reduction tests on 14 commercial farms throughout New Zealand. On each farm, groups of 15 calves were sampled for faecal nematode egg count and then treated with ivermectin administered orally, or with moxidectin administered either by the oral, subcutaneous injection or topical (pour-on) route. Samples were again collected 14 days after treatment and efficacy was calculated as the percentage reduction in-group mean egg count between the pre- and post-treatment samples. In addition, efficacy was calculated for individual animals, in order to compare the variability of the different treatments. On four farms untreated control groups were run and five animals from each of the control and all of the moxidectin-treated groups were bled over time to estimate plasma–moxidectin concentrations.Averaged across all tests, the reduction in faecal egg count was significantly greater after treatment with moxidectin oral (91.1%) than following treatment with moxidectin injection (55.5%) or with moxidectin pour-on (51.3%). Low efficacies were invariably against Cooperia oncophora. The oral treatments were significantly less variable in efficacy than the injection and pour-on treatments. Moxidectin concentrations in plasma were highest following subcutaneous injection and lowest following pour-on administration. Plasma levels following oral administration were intermediate, being significantly lower than post-injection and significantly higher than post-pour-on. There was no evidence of transfer of moxidectin to untreated animals through licking. Based on these results, along with those of other studies, it is proposed that oral administration of macrocyclic lactone anthelmintics results in higher concentrations of active reaching the target worms in the gastrointestinal tract than following either administration by injection or by pour-on.

&lt;i&gt;In vitro &lt;/i&gt;anthelmintic effects of &lt;i&gt;Artemisia afra&lt;/i&gt; and &lt;i&gt;Mentha longifolia&lt;/i&gt; against parasitic gastro-intestinal nematodes of livestock

Gastrointestinal nematodes are the most widespread and economically important class of the helminths. The major threat posed by nematode infections is the productivity loss due to their ability to disrupt nutrient utilization of the livestock resulting in hunger and malnutrition. Acetone and aqueous extracts were prepared from Mentha longifolia and Artemisia afra and tested on egg hatch, larval development and larval mortality assays at three concentrations 2.5, 5.0 and 7.5 mg/mL. Certain percentages of egg hatch and larval mortality were inhibited by both plants; however, larval development was totally inhibited at all concentrations as compared to the negative control. Generally the acetone extracts from the two plants were most effective against parasitic gastrointestinal nematodes of livestock. This report therefore validates the folkloric use of these species in the management of internal parasites by the Basotho of the eastern Free State Province of South Africa.

Trichinella spiralis Secreted Enzymes Regulate Nucleotide-Induced Mast Cell Activation and Release of Mouse Mast Cell Protease 1

Extracellular nucleotides are important triggers of innate immunity, acting on a wide variety of cells via signaling through purinergic receptors. Mucosal mast cells contribute to expulsion of a number of gastrointestinal nematode parasites, and mouse mast cell protease 1 has been shown to have a critical role in clearance of Trichinella spiralis from the intestinal tract. We show here that adenosine, ADP, ATP, UDP, and UTP all stimulate calcium mobilization in bone marrow-derived mast cells with a mucosal phenotype. Secreted proteins from T. spiralis infective larvae inhibit nucleotide-induced mast cell activation, and that induced by ADP and UDP is specifically blocked by parasite secretory 5'-nucleotidase. Release of mouse mast cell protease 1 is stimulated by ADP and ATP. Both parasite secreted products and the 5'-nucleotidase inhibit ADP-induced release of mast cell protease, whereas that stimulated by ATP is partially inhibited by secreted products alone. This indicates that the 5'-nucleotidase contributes to but is not solely responsible for inhibition of nucleotide-mediated effects on mast cell function. Secretion of nucleotide-metabolizing enzymes by parasitic nematodes most likely evolved as a strategy for suppression of innate immune responses and is discussed in this context.

Development and characterization of multiplex panels of microsatellite markers for Syphacia obvelata, a parasite of the house mouse (Mus musculus), using a high throughput DNA sequencing approach

Syphacia obvelata is a common gastro-intestinal parasitic nematode of the house mouse (Mus musculus), a prime model rodent species. Investigations of the genetic structure, variability of parasite populations and other biological aspects of this host–parasite system are limited due to the lack of genetic resources for S. obvelata. To fill this gap, we developed a set of microsatellite markers for S. obvelata, using a 454 pyrosequencing approach. We designed three multiplex panels allowing genotyping of 10 polymorphic loci and scrutinized them on 42 samples from two different regions inhabited by two different house mouse subspecies (Mus musculus musculus and M. m. domesticus). The numbers of alleles ranged from 2 to 6 with mean observed heterozygosities 0.1476 and 0.2095 for domesticus and musculus worms, respectively. The described markers will facilitate further studies on population biology and co-evolution of this host–parasite system.

The response of monocyte derived dendritic cells following exposure to a nematode larval carbohydrate antigen

The glycolipid CarLA (carbohydrate larval antigen) is present on the epicuticle of the infective-stage larvae of gastrointestinal nematode parasites infecting livestock. The molecule is lost from the surface of the larvae in the few days post-ingestion by a host animal, and the resulting anti-CarLA antibody response has been demonstrated to be protective in vivo. Both the anti-CarLA response, and anti-parasite immunity in general, are slow to develop, and several months of natural exposure to ingested larvae is required. The current study was designed to provide information on how the anti-CarLA response develops, and focuses on the initial recognition of the molecule by human monocyte derived dendritic cells (mdDC) in vitro.Immunofluorescence and flow cytometry demonstrated that mdDC recognise and internalise both the purified and the native form of CarLA, in the case of the latter once it is shed from the larval surface. However, the recognition of CarLA did not result in classical maturation of DC, while there was only transient or minor up-regulation of CD86, CD83, HLA-DR and CD40.Exposure of mdDC to purified CarLA resulted in the increased production of the pro-inflammatory cytokines IL-6 and to a lesser extent of IL-8 and TNF-α, and a reduced production of the anti-inflammatory cytokine IL-1RA. CarLA therefore has little ability to mature and functionally alter monocyte derived dendritic cell function.

GENETIC IDENTIFICATION OF FIVE STRONGYLE NEMATODE PARASITES IN WILD AFRICAN ELEPHANTS (LOXODONTA AFRICANA)

African savannah elephants (Loxodonta africana) are an ecologically and economically important species in many African habitats. However, despite the importance of elephants, research on their parasites is limited, especially in wild populations. Currently, we lack genetic tools to identify elephant parasites. We present genetic markers from ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) to identify five elephant-specific nematode parasites in the family Strongylidae: Murshidia linstowi, Murshidia longicaudata, Murshidia africana, Quilonia africana, and Khalilia sameera. We collected adult nematodes from feces deposited by wild elephants living in Amboseli National Park, Kenya. Using both morphologic and genetic techniques, we found that the internal transcribed spacer (ITS) region in rDNA provides a reliable marker to distinguish these species of strongyles. We found no evidence for cryptic genetic species within these morphologic species according to the cox-1 region of mtDNA. Levels of genetic diversity in strongyles from elephants were consistent with the genetic diversity seen within other strongyle species. We anticipate that these results will be a useful tool for identifying gastrointestinal nematode parasites in elephants.

Disease transmission in an extreme environment: Nematode parasites infect reindeer during the Arctic winter

Parasitic nematodes are found in almost all wild vertebrate populations but few studies have investigated these host–parasite relationships in the wild. For parasites with free-living stages, the external environment has a major influence on life-history traits, and development and survival is generally low at sub-zero temperatures. For reindeer that inhabit the high Arctic archipelago of Svalbard, parasite transmission is expected to occur in the summer, due to the extreme environmental conditions and the reduced food intake by the host in winter. Here we show experimentally that, contrary to most parasitic nematodes, Marshallagia marshalli of Svalbard reindeer is transmitted during the Arctic winter. Winter transmission was demonstrated by removing parasites in the autumn, using a novel delayed-release anthelmintic bolus, and estimating re-infection rates in reindeer sampled in October, February and April. Larval stages of nematodes were identified using molecular tools, whereas adult stages were identified using microscopy. The abundance of M. marshalli adult worms and L4s increased significantly from October to April, indicating that reindeer were being infected with L3s from the pasture throughout the winter. To our knowledge, this study is the first to experimentally demonstrate over-winter transmission of a gastro-intestinal nematode parasite in a wild animal. Potential mechanisms associated with this unusual transmission strategy are discussed in light of our knowledge of the life-history traits of this parasite.

First identification of benzimidazole resistant Haemonchus contortus in sheep in Greece

The present study investigated for the first time benzimidazole (BZ) resistance in Haemonchus contortus originating from sheep in the area of Thessaloniki, Northern Greece, using an allele-specific PCR. This method detects a polymorphism (Phe/Tyr) that affects the amino acid at position 200 of the β-tubulin protein, and is known to be linked to BZ resistance. Forty adult worms were collected from local abattoir from 8 flocks. From each flock a total of 5 sheep were sampled and from each sheep one worm was collected. It was found that all 40 worms were homozygous benzimidazole resistant, which demonstrates for the first time that resistant strains of H. contortus do exist in sheep farms in Northern Greece. These results have practical implications in sheep farmer consulting in Greece, because sensitive screening of important worms using molecular methods may offer in the future a valid estimation on the correct use of anthelmintics towards a more effective control of gastrointestinal nematode parasites of small ruminants.

Selective effect of the anthelmintic bephenium on Haemonchus contortus levamisole-sensitive acetylcholine receptors

Acetylcholine receptors (AChRs) are pentameric ligand-gated ion channels involved in the neurotransmission of both vertebrates and invertebrates. A number of anthelmintic compounds like levamisole and pyrantel target the AChRs of nematodes producing spastic paralysis of the worms. The muscle AChRs of nematode parasites fall into three pharmacological classes that are preferentially activated by the cholinergic agonists levamisole (L-type), nicotine (N-type) and bephenium (B-type), respectively. Despite a number of studies of the B-type AChR in parasitic species, this receptor remains to be characterized at the molecular level. Recently, we have reconstituted and functionally characterized two distinct L-AChR subtypes of the gastro-intestinal parasitic nematode Haemonchus contortus in the Xenopus laevis oocyte expression system by providing the cRNAs encoding the receptor subunits and three ancillary proteins (Boulin et al. in Br J Pharmacol 164(5):1421-1432, 2011). In the present study, the effect of the bephenium drug on Hco-L-AChR1 and Hco-L-AChR2 subtypes was examined using the two-microelectrode voltage-clamp technique. We demonstrate that bephenium selectively activates the Hco-L-AChR1 subtype made of Hco-UNC-29.1, Hco-UNC-38, Hco-UNC-63, Hco-ACR-8 subunits that is more sensitive to levamisole than acetylcholine. Removing the Hco-ACR-8 subunit produced the Hco-L-AChR2 subtype that is more sensitive to pyrantel than acetylcholine and partially activated by levamisole, but which was bephenium-insensitive indicating that the bephenium-binding site involves Hco-ACR-8. Attempts were made to modify the subunit stoichiometry of the Hco-L-AChR1 subtype by injecting five fold more cRNA of individual subunits. Increased Hco-unc-29.1 cRNA produced no functional receptor. Increasing Hco-unc-63, Hco-unc-38 or Hco-acr-8 cRNAs did not affect the pharmacological characteristics of Hco-L-AChR1 but reduced the currents elicited by acetylcholine and the other agonists. Here, we provide the first description of the molecular composition and functional characteristics of any invertebrate bephenium-sensitive receptor.

The efficacy of a combined oral formulation of derquantel–abamectin against anthelmintic resistant gastro-intestinal nematodes of sheep in the UK

The objective of the present studies was to evaluate the efficacy of a combined formulation (Startect® Dual Active Oral Solution for Sheep, Pfizer Animal Health) of derquantel (DQL) and abamectin (ABA) for the treatment of: (1) sheep experimentally infected with a moxidectin (MOX)-resistant isolate of Teladorsagia circumcincta, and (2) multi-drug resistant gastrointestinal nematode parasites under UK field conditions. In the first study, a total of 40 animals were allocated into 4 treatment groups, and were either left untreated or treated with DQL+ABA, MOX or ABA. Faecal samples were collected on days 1–5 and on day 7 after treatment to examine the reduction in faecal egg excretion and to evaluate the egg viability. On day 14 post treatment all animals were euthanised for abomasal worm counts. There was a 100% reduction in geometric mean worm counts for the DQL+ABA treated animals compared to the untreated control animals (P<0.0001), whereas the percentage reduction in worm counts for the MOX- (P>0.05) and ABA-treated (P=0.0004) animals was 12.4% and 71.8%, respectively. The data from the egg hatch assay (EHA) indicated that in the MOX-treated and the ABA-treated animals, the majority of the eggs hatched after treatment. In the field study, performed on four farms, animals were allocated into 6 groups of 11–15 animals each in order to conduct a faecal egg count reduction test (FECRT), based on arithmetic mean egg counts. One group of animals remained untreated, whereas the other animals were treated with DQL+ABA, MOX, fenbendazole (FBZ), levamisole (LV) or ivermectin (IVM). On each of the farms the reduction in egg excretion after treatment with FBZ, LV or IVM was below 95.0%, indicating anthelmintic resistance. The efficacy of DQL+ABA ranged from 99.1 to 100%, yielding significantly lower egg counts compared to the untreated control group (P≤0.003). For MOX the egg counts were significantly (P≤0.003) lower compared to the untreated group at each farm, with reductions varying from 98.2 to 100%. The post-treatment copro-cultures for larva identification indicated that T. circumcincta was the most abundant worm species after treatment (52–99% of the larvae). The results of these studies confirm the high efficacy of the DQL+ABA combination formulation against anthelmintic resistant nematodes in the UK.

Macrocyclic Lactones in the Treatment and Control of Parasitism in Small Companion Animals

Macrocyclic lactones (MLs) have many anti-parasitic applications in small companion animal medicine. They were first developed as chemoprophylactics against heartworm (Dirofilaria immitis) infection to be applied monthly for retroactive killing of third- and fourth-stage larvae. ML-containing products formulated for oral (ivermectin, milbemycin oxime), topical (selamectin, moxidectin) or injectable sustained release (moxidectin, ivermectin) are approved for heartworm prevention in dogs or cats. Clearance of microfilariae and gradual or "soft" killing of adult heartworms constitute increasingly prevalent extra-label uses of MLs against D. immitis. Some commercial ML formulations contain sufficient levels of active ingredient (milbemycin oxime, selamectin, moxidectin) to support additional label claims against gastrointestinal nematode parasites such as hookworms (Ancylostoma spp.) and ascarid round worms (Toxocara spp. and Toxascaris leonina). Beyond these approved applications, safe, extra-label uses of MLs against nematodes parasitizing the urinary tract, such as Capillaria spp., and parasites of the tissues, such as Dipetalonema reconditum, Dirofilaria repens, Thelazia spp. and Spirocerca lupi, in dogs and cats as well as exotic pets have been reported. MLs as a group have intrinsic insecticidal and acaricidal activity, and topical or otic formulations of certain compounds (selamectin, moxidectin, milbemycin oxime or ivermectin) are approved for treatment and control of fleas, certain ixodid ticks, sarcoptiform and demodectic mange mites and psoroptiform ear mites. Extra-label applications of MLs against ectoparasites include notoedric mange mites, dermanyssids such as Ornythonussus bacoti, numerous species of fur mite (e.g. Cheyletiella spp. and Lynxacarus) and trombiculids ("chiggers") in cats, dogs and nontraditional or exotic pets.

Climate and the epidemiology of gastrointestinal nematode infections of sheep in Europe

The free-living stages of gastrointestinal nematode parasites of sheep are strongly affected by climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperatures generally accelerate development but increase mortality. Moisture is needed for development and translation of larvae from faeces to pasture, and so rainfall is a limiting factor for transmission. Together, these factors underpin seasonal patterns of infection in sheep, as well as geographic variation in the epidemiology and relative importance of different species within Europe. Local knowledge and experience enable treatment to be targeted appropriately to prevent dangerous levels of infection. This traditional know-how can be supplemented by predictive epidemiological models, built on thorough understanding of the influence of climate on larval availability. However, management also has a dominant role in determining patterns of infection, and is itself influenced by climate. Current geographic variation in nematode epidemiology across Europe, and knowledge of systems from outside Europe, can provide only limited perspectives on the likely effects of climate change on disease in future. This is because disease arises from complex interaction between host and parasite factors, and the implementation of optimal control strategies to meet new challenges will be slowed by the inertia of current systems. Approaches to nematode control must therefore take account not only of parasite biology, but also the forces that shape sheep farming systems and management decisions.