Infective Nematode Larvae Research Articles

A Review of the Epidemiology of Gastrointestinal Nematode Infections in Sheep and Goats in Ghana

In this paper, the gastrointestinal nematode parasites infecting small ruminants (sheep and goats) in Ghana and the epidemiological factors influencing their prevalence are reviewed and discussed. Twelve nematode species belonging to six families have been reported to infect these livestock in the country with Haemonchus contortus being the most prevalent helminth parasite in both animals. Parasitic gastroenteritis is caused by mixed infection of several nematode species. Management /husbandry practices, climate and host influence are found to be the main factors that affect gastrointestinal nematode infections in sheep and goats. Seasonal changes in the level of infective strongylate nematode larvae on pasture in the different agro-ecological zones of Ghana are reviewed. The number of infective larvae on pasture is reported to be directly related to the pattern of rainfall. Consequently, rainfall could be relied on to predict the rate of transmission of infection in grazing animals. Finally, the relevance of epidemiological knowledge in the development of efficient measures for controlling gastrointestinal nematode infections in sheep and goats in Ghana is discussed.

Gastrointestinal Parasites of Savanna Chimpanzees (Pan troglodytes schweinfurthii) in Ugalla, Tanzania

Understanding variability in patterns of parasite infections requires studies of multiple populations inhabiting a variety of habitats. Gastrointestinal parasites of chimpanzees (Pan troglodytes) have been studied extensively at several forested sites, but the parasite fauna of chimpanzees living in dry, open habitats is less well known. We studied the parasites of savanna chimpanzees (Pan troglodytes schweinfurthii) living in the Issa Valley, Ugalla (Tanzania). We examined 119 fresh fecal samples using standard coproscopical methods. We detected protozoans including Blastocystis sp., Entamoeba coli, E. histolytica/dispar, Iodamoeba buetschlii, Troglodytella abrassarti, and Troglocorys cava, but only two types of spirurid nematodes among the helminths. The parasites of the Ugalla chimpanzees differ from those of forest chimpanzees in the absence of Strongyloides sp. and strongylid nematodes and a high prevalence of spirurids. Strongylids and Strongyloides sp. have thin-shelled eggs and larvae, which develop in the external environment; thus they may not be able to survive for prolonged periods in the extreme environment of Ugalla. The Ugalla chimpanzees also live at a lower population density and exhibit a larger home range than forest chimpanzees, factors that may lead to lower exposure to infective nematode larvae. Spirurid eggs, however, have thick shells and a life cycle dependent on intermediary hosts, making their survival and transmission in such extreme conditions more feasible. These differences between parasite fauna of closed and open forest chimpanzees contribute to our understanding of the ecology of infectious disease, and have the potential to contribute to conservation policies and practices.

Evaluation of the effectiveness of Duddingtonia flagrans and Monacrosporium thaumasium in the biological control of gastrointestinal nematodes in female bovines bred in the semiarid region

Brazil has a herd of 212 million cattle and 171 million hectares of pastures that produce approximately 96% of Brazilian beef. The Brazilian production system enables animal infection by endoparasites, which are considered one of the main obstacles for the development of this industry and are responsible for considerable economic losses. The control of parasitic diseases is performed via the administration of antiparasitic drugs, but they leave residues of the products in the treated animal, affect non-target organisms and select resistant strains of the parasites. The species D. flagrans and M. thaumasium are promising and sustainable alternatives for controlling gastrointestinal helminths of ruminants and other herbivores. In this study, we evaluated the efficacy of isolates of these species, formulated in a sodium alginate matrix and administered twice a week, to reduce the number of environmental infective larvae of gastrointestinal nematodes that affect prepubescent zebu females. The treated animals presented fewer eggs and a lower number of infective larvae per gram of faeces (p < 0.05). The pastures occupied by treated animals showed a statistically significant reduction (p < 0.05) of the number of L3 and, furthermore, the genera Cooperia sp., Haemonchus sp., and Oesophagostomum sp. were the most prevalent. The average weight of the animals did not differ statistically (p > 0.05) among the treated and control groups. The use of sodium alginate pellets as vehicle for delivery of the fungus mycelia D. flagrans (isolate AC001) and M. thaumasium (isolate NF34A) proved effective in controlling trichostrongylids in prepubescent cows bred in the semi-arid region, with an effective reduction in the number of infective larvae in the pastures.

Influence of Plant Age, Tomato Variety and NematodeInoculum Density on Pathogenicity of Meloidogyneincognitaon Tomato in AbakalikiAgro-Ecology

Pathogenicity of Meloidogyne incognita on tomato which is influenced by plant age, tomato variety and nematode inoculum density was studied. The experiment was a 2 x 3 x 4 factorial in completely randomized design with 4 replications. Two tomato varieties: Roma VF and Pimpinellifolium at 4, 6 and 8 weeks old were variously treated with O, 500, 1000 and 1500 nematode infective larvae. Results showed that root gall damage on both tomato varieties increased with increased inoculum density. The same was true for number of days to 50% flowering. An inverse relationship however occurred between mean root length, weight, percentage dry matter and nematode inoculum density. The same was true for mean shoot dry matter, fresh weight, length and number of branches/plant. Plants inoculated at 6 weeks after sowing into the container had highest galling response which was significantly different from others.

Conserved miRNAs Are Candidate Post-Transcriptional Regulators of Developmental Arrest in Free-Living and Parasitic Nematodes

Animal development is complex yet surprisingly robust. Animals may develop alternative phenotypes conditional on environmental changes. Under unfavorable conditions, Caenorhabditis elegans larvae enter the dauer stage, a developmentally arrested, long-lived, and stress-resistant state. Dauer larvae of free-living nematodes and infective larvae of parasitic nematodes share many traits including a conserved endocrine signaling module (DA/DAF-12), which is essential for the formation of dauer and infective larvae. We speculated that conserved post-transcriptional regulatory mechanism might also be involved in executing the dauer and infective larvae fate. We used an unbiased sequencing strategy to characterize the microRNA (miRNA) gene complement in C. elegans, Pristionchus pacificus, and Strongyloides ratti. Our study raised the number of described miRNA genes to 257 for C. elegans, tripled the known gene set for P. pacificus to 362 miRNAs, and is the first to describe miRNAs in a Strongyloides parasite. Moreover, we found a limited core set of 24 conserved miRNA families in all three species. Interestingly, our estimated expression fold changes between dauer versus nondauer stages and infective larvae versus free-living stages reveal that despite the speed of miRNA gene set evolution in nematodes, homologous gene families with conserved “dauer-infective” expression signatures are present. These findings suggest that common post-transcriptional regulatory mechanisms are at work and that the same miRNA families play important roles in developmental arrest and long-term survival in free-living and parasitic nematodes.

Morphological identification of parasitic nematode infective larvae of small ruminants and cattle: A practical lab guide

In 2004, a new concept was introduced for simplifying identification of larvae of the common nematodes of cattle, sheep and goats that comprises estimates of the lengths of the sheath tail extensions of infective third-stage larvae (L3) of each genus and/or species to that of Trichostrongylus spp., instead of having to be dependent only on measurements in micrometre. For example, if the mean length of the sheath tail extension (the extension of the sheath caudad, beyond the caudal tip of the larva) of Trichostrongylus colubriformis and Trichostrongylus axei is assumed to be 'X', then that of Haemonchus contortus is 2.0-2.7 'X' - a difference that is not difficult to estimate. An additional new approach suggested now, particularly for L3 of species and/or genera difficult to differentiate (such as Chabertia ovina and Oesophagostomum columbianum), is to estimate the proportion of the larval sheath tail extension comprising a terminal thin, whip-like filament. For the experienced person, it is seldom necessary to measure more than one or two sheath tail extensions of L3 in a mixed culture, because the identity of most of the remaining L3 can thereafter be estimated in relation to those measured, without having to take further measurements. The aim of this article was to present the novel approach in the form of a working guide for routine use in the laboratory. To facilitate identification, figures and a separate organogram for each of small ruminants and cattle have been added to illustrate the distinguishing features of the common L3.

Control of infective larvae of gastrointestinal nematodes in heifers using different isolates of nematophagous fungi

The effect of different nematophagous fungi [Duddingtonia flagrans (AC001 and CG722) and Monacrosporium thaumasium (NF34)] with regard to controlling infective larvae (L3) of nematodes after gastrointestinal transit in female cattle (3/4 Holstein × Zebu) was evaluated. A total of 24 pubescent female cattle were used, weighing approximately 320 kg each one. There were three treatment groups, each contained six animals that received 150 g of pellets (0.2 g of mycelium), orally in a single dose, in a sodium alginate matrix containing mycelial mass of the fungus D. flagrans (AC001 or CG722) or M. thaumasium (NF34); and one control group (without fungi). Fecal samples were collected from the animals at intervals of 12, 15, 18, 21, 24, 48, and 72 hours. At the end of 17 days, the L3 not subjected to predation were recovered by means of the Baermann method. The fungal isolates tested were capable of destroying the L3 after gastrointestinal transit. It was observed that within 72 hours, the isolates AC001, CG722, and NF34 showed a higher predatory activity (81.2%, 97.3%, and 98.3%, respectively). The results justify the need for studies in the field, and over longer intervals, in order to observe the efficiency of the fungus D. flagrans, or even M. thaumasium, for environmental control over nematodes in naturally infected cattle.

Variability in the intensity of nematode larvae from gastrointestinal tissues of a natural herbivore

The migration of infective nematode larvae into the tissues of their hosts has been proposed as a mechanism of reducing larval mortality and increase parasite lifetime reproductive success. Given that individual hosts differ in the level of exposure, strength of immune response and physiological conditions we may expect the number of larvae in tissue to vary both between and within hosts. We used 2 gastrointestinal nematode species common in the European rabbit (Oryctolagus cuniculus) and examined how the number of larvae in the tissue changed with the immune response, parasite intensity-dependent constraints in the lumen and seasonal weather factors, in rabbits of different age, sex and breeding status. For both nematode species, larvae from the gastrointestinal tissue exhibited strong seasonal and host age-related patterns with fewer larvae recovered in summer compared to winter and more in adults than in juveniles. The number of larvae of the 2 nematodes was positively associated with intensity of parasite infection in the lumen and antibody responses while it was negatively related with air temperature and rainfall. Host sex, reproductive status and co-infection with the second parasite species contributed to increase variability between hosts. We concluded that heterogeneities in host conditions are a significant cause of variability of larval abundance in the gastrointestinal tissues. These findings can have important consequences for the dynamics of nematode infections and how parasite's life-history strategies adjust to host changes.

EFEITO DE TRÊS ESPÉCIES DE GRAMÍNEAS FORRAGEIRAS SOBRE A ESTRUTURA DA PASTAGEM E DISTRIBUIÇÃO VERTICAL DE LARVAS INFECTANTES DE NEMATÓDEOS GASTRINTESTINAIS DE OVINOS

The knowledge of interaction between infective larvae setting and the type of grass is important to epidemiological studies and the control of gastrointestinal nematodes in sheep. The objective of this work was to evaluate the effects of three species of forage grasses on pasture characteristics and the vertical distribution of infective larvae (L3) of gastrointestinal nematodes of woolless sheep on the grasses during the rainy season. We used 60 non-periparturients ewes, naturally infected, equally distributed on 2 ha paddocks sowed with Tanzania, star, and gamba grasses, managed under continuous grazing system, from October 2003, to march 2004, at Santa Bárbara farm, Barreiras–Bahia-Brazil. Data of three samples between December 2003 and March 2004 were analyzed by SAS, using split-plot design, with 10 replications. Infective larvae of Haemonchus spp. and Trichostrongylus spp. were observed on forage in all stratus of vertical layer of the grasses without a defined pattern. Pastures with different characteristics under continuous grazing system had good conditions for developing of infective larvae of sheep.

Ultrastructural changes in the third-stage, infective larvae of ruminant nematodes treated with sainfoin ( Onobrychis viciifolia) extract

Plants rich in condensed tannins are an alternative to chemical anthelmintics to control gastrointestinal nematodes (GINs) in ruminants. Previous functional studies have shown that sainfoin extracts affect the two forms of infective larvae (L3), ensheathed and exsheathed. However, the mechanisms of action remain unknown. The aim of this study was thus to compare ultrastructural changes in ensheathed and exsheathed L3 of two GIN species after in vitro contact with sainfoin extracts using transmission electron microscopy. The main changes identified were an alteration of the hypodermis, the presence of numerous vesicles in the cytoplasm and degeneration and/or death of muscular and intestinal cells. The changes suggested similar and nonspecies-specific lesions in the two nematode species. Comparison of the modifications found in the ensheathed vs. exsheathed L3s revealed different locations of the main cellular changes depending on the larval form. It is hypothesized that these spatial differences in lesions are mainly influenced by the presence of the sheath which favors contact between the active compounds and either the cuticle or the digestive tract. Overall, our observations suggest that the functional changes observed in the biology of GIN L3s after contact with sainfoin extracts are mediated through a direct mode of action, i.e. different interactions between the bioactive plant metabolites and the nematode structure depending on the route of contact.

Involvement of tannins and flavonoids in the in vitro effects of Newbouldia laevis and Zanthoxylum zanthoxyloïdes extracts on the exsheathment of third-stage infective larvae of gastrointestinal nematodes

The present study aimed at examining the possible role of tannins and flavonoids on the in vitro anthelmintic properties of the extracts of two plants from the southern area of Western Africa, i.e. Newbouldia laevis and Zanthoxylum zanthoxyloïdes. Extracts of the two plants were prepared by use of acetone/water (70/30) and their anthelmintic activity was measured by use of the larval exsheathment inhibition assay (LEIA) applied on the abomasal species, Haemonchus contortus and the intestinal species Trichostrongylus colubriformis. Three concentrations of extracts were evaluated to examine the possible dose effect. In addition, the possible involvement of tannins and flavonoids was examined by comparing the levels of inhibition of larval exsheathment obtained with the same extracts, after of not addition of PVPP which forms complexes with these compounds. The results indicate significant effects with both plants and both nematode species. In the range of concentrations examined, the results were dose-dependent for N. laevis extracts but not for Z. zanthoxyloïdes because the three doses applied provoked a similar highly significant inhibition whatever the tested dose. The use of PVPP indicated for both plant and nematode species, that tannins and flavonoids are involved partly in the effect but that some other biochemical compounds were also involved in both plants.

VERMINOSE EM CAPRINOS E OVINOS MANTIDOS EM PASTAGENS DE Panicum maximum Jacq. NO PERÍODO CHUVOSO DO ANO

The objective of this work was to evaluate the worm disease on goats and sheep kept on Panicum maximum Jacq. pastures, in the rainy season of the year. The dry matter density (DM) of different layers (0-15, 15-30 and above 30 cm) of Panicum maximum Jacq. pastures, and the forage contamination by gastrintestinal nematode infective larvae (L3) were quantified. Forty animals were submitted monthly to coproparasitological examinations (ECG and coproculture) during the rainy season. The experiment was carried out in Barreiras-Bahia-Brazil, in a split-plot design, with 10 replications on pastures and 20 replications on animals, from October of 2003 to March of 2004, and samples were taken from December to February. The number of infective larvae per kg/DM did not change with the grass layer, with average of 22.2 L3/kg DM. On the forage, Haemonchus sp. and Trichostrongylus sp. L3 larvae were indentified, reflecting the coproculture results. Goats showed higher ECG counting (2602) than Sheep (865), demanding more sanitary care.KEYWORDS: Coproculture, dry matter, ECG, nematodes.

Transcripts analysis of infective larvae of an intestinal nematode, Strongyloides venezuelensis

Free-living infective larvae of Strongyloides nematodes fulfill a number of requirements for the successful infection. They need to endure a long wait in harsh environmental conditions, like temperature, salinity, and pH, which might change drastically from time to time. Infective larvae also have to deal with pathogens and potentially hazardous free-living microbes in the environment. In addition, infective larvae must recognize the adequate host properly, and start skin penetration as quickly as possible. All these tasks are essentially important for the survival of Strongyloides nematodes, however, our knowledge is extremely limited in any one of these aspects. In order to understand how Strongyloides infective larvae meet these requirements, we examined transcripts of infective larvae by randomly sequencing cDNA clones constructed from S. venezuelensis infective larvae. After assembling successfully sequenced clones, we obtained 162 unique singletons and contigs, of which 84 had been significantly annotated. Annotated genes included those for respiratory enzymes, heat-shock proteins, neuromuscular proteins, proteases, and immunodominant antigens. Genes for lipase, small heat-shock protein, globin-like protein and cytochrome c oxidase were most abundantly transcribed, though genes of unknown functions were also abundantly transcribed. There were no hits found against NCBI or NEMABASE4 for 37 (22.3%) EST out of the total 162 EST. Although most of the transcripts were not infective larva-specific, the expression of respiration related proteins was most actively transcribed in the infective larva stage. The expression of astacin-like metalloprotease, small heat-shock protein, S. stercoralis L3Nie antigen homologue, and one unannotated and 2 novel genes was highly specific for the infective larva stage.

Activation of Nippostrongylus brasiliensis infective larvae is regulated by a pathway distinct from the hookworm Ancylostoma caninum

Developmentally arrested infective larvae of strongylid nematodes are activated to resume growth by host-derived cues encountered during invasion of the mammalian host. Exposure of Nippostrongylus brasiliensis infective larvae to elevated temperature (37°C) is sufficient to activate signalling pathways which result in resumption of feeding and protein secretion. This occurs independently of exposure to serum or glutathione, in contrast to the hookworm Ancylostoma caninum, and is not initiated by chemical exsheathment. No qualitative differences in protein secretion were induced by host serum as visualised by two-dimensional SDS–PAGE, although exposure of larvae to an aqueous extract of rat skin did stimulate secretion of a small pre-synthesised bolus of proteins. Infective larvae began feeding after a lag period of 3–4h at 37°C, reaching a maximum of 90% of the population feeding by 48h. Neither a membrane permeant analogue of cyclic GMP nor muscarinic acetylcholine receptor agonists stimulated feeding at 20°C, and high concentrations of both compounds inhibited temperature-induced activation. LY294002, an inhibitor of phosphatidylinositol 3-kinase, Akt inhibitor IV, an inhibitor of Akt protein kinase, and ketoconazole, an inhibitor of cytochrome P450, all blocked resumption of feeding and protein secretion at 37°C. Serotonin increased the rate of feeding assessed by uptake of radiolabelled BSA, but could not initiate feeding independently of elevated temperature. Collectively, the data suggest that the early signalling events for larval activation in N. brasiliensis differ substantially from A. caninum, but that they may converge at pathways downstream of phosphatidylinositol 3-kinase involving steroid hormone synthesis.

A modified baermann apparatus for the recovery of infective nematode larvae from herbage and manure.

Summary A technique for the assessment of a larval population on herbage and manure is presented. A modified Baermann apparatus with screens was used. Tests of the technique showed that 58–83% of added larvae of a mixture of Ostertagia ostertagi and Cooperia oncophora were recovered from 200 and 100 g. of herbage. From 1,000, 500, and 100 g. of solid and liquid manure 8–51% were recovered. From 10 and 5 g. of solid manure 70–95% were recovered, as against 9–48% by the common Baermann technique. The present method gives a high recovery rate when an adequate amount of sample is tested. The proper amounts are considered to be 200 g. of herbage and 500–1,000 g. of manure. The operation time for the present method should be 24 hours, especially for manure samples. Zusammenfassung Ein modifizierter Baermann-Apparat für die Gewinnung von infektionsfähigen Nematodenlarven aus Gras und Dung Es wird ein Verfahren zur Schätzung der Nematodenlarvenpopulation in Gras und Dung beschrieben. Ein modifizierter, mit Sieben ausgestatteter Baermann-Apparat kam zur Verwendung. Bei der Erprobung des Verfahrens ließen sich aus 200 und 100 g Gras 58–83% der vorher beigemengten Larven einer Mischkultur der Spezies Ostertagia ostertagi und Cooperia oncophora wiedergewinnen. Aus 1000, 500 und 100 g festem und flüssigem Dung wurden 8–51% wiedergefunden. Aus 10 und 5 g festem Dung wurden 70–95% wiedergewonnen, gegenüber 9–48% bei der herkömmlichen Baermann-Technik. Die beschriebene Methode führt zu einer hohen Ausbeuterate, wenn eine adäquate Probenmenge untersucht wird. Bei Gras werden 200 g und bei Mist 500–1000 g als günstige Mengen angesehen. Die Laufzeit des Verfahrens sollte bei der dargestellten Methode 24 Stunden betragen, insbesondere bei Dungproben. Résumé Un appareil modifié de Baermann pour l'obtention des larves infectieuses de nématodes à partir de l'herbe et du fumier On décrit un prodédé d'évaluation d'une population de larves de nématodes dans l'herbe et le fumier. On a employé un appareil de Baermann modifié. Lors des essais, on a résolé 58–83% des larves d'une culture mixte d'Ostertagia ostertagi et Cooperia oncophora mélangée à 200 et 100 g d'herbe. Le réisolement fut de 8–51% a partir de 1000, 500 et 100 g de fumier et de lisier. On a atteint le 70–95% dans 10 et 5 g de fumier alors que la technique originale de Baermann n'a permis de trouver que le 9–48%. La méthode décrite donne un haut pourcentage si la quantité de l'échantillon examiné est adéquate. On compte 200 g pour l'herbe et 500–1000 g pour le fumier. La durée de la recherche devrait être de 24 heures, en particulier pour le fumier. Resumen Un aparato modificado de Baermann para la recuperación de larvas infestantes de nematodos de la hierba y el estiércol Se describe un procedimiento para calcular la población de larvas de nematodos en la hierba y el estiércol. Se empleó un aparato modificado de Baermann, provisto de tamices. Al probarse el método se pudieron recuperar de 200 y 100 g. de hierba el 58–83% de las larvas mezcladas antes de un cultivo mixto de las especies Ostertagia ostertagi y Cooperia oncophora. De 1000, 500 y 100 g. de abono sólido y líquido se volvieron a hallar del 8–51%. De 10 y 5 g. de abono sólido se recuperaron del 70–95%, frente al 9–48% siguiendo la técnica convencional de Baermann. La técnica descrita conduce a una tasa elevada de rendimiento cuando se analiza una cantidad adecuada de la muestra. Como cantidades convenientes se consideran 200 g. de hierba y 500–1000 g. de estiércol. El tiempo de desarrollo del procedimiento debería alcanzar las 24 horas en el método expuesto, sobre todo cuando se trata de muestras de estiércol.

Merino ewes bred for parasite resistance reduce larval contamination onto pasture during the peri-parturient period

The peri-parturient period is crucial for controlling worms as the acquired immunity of ewes is disrupted, resulting in an increase in faecal worm egg counts. Two hypotheses were tested in this experiment – that ewes bred for worm resistance would have lower faecal worm egg counts than unselected control ewes, during late pregnancy and lactation, under similar but separate grazing areas; and also that numbers of infective nematode larvae would be lower on pastures grazed by resistant ewes than pastures grazed by unselected control ewes. Faecal samples were collected from resistant and unselected ewes in late pregnancy and early lactation, during the winter rainfall season, and analysed for numbers of Trichostrongylus colubriformis and Teladorsagia circumcincta. Pasture samples were taken 1 week before and 7 weeks after lambing started and analysed for infective larvae. In all sheep, worm egg counts rose 2 weeks prior to lambing and continued into lactation. Worm egg counts were significantly lower in the resistant ewes from 1 week before lambing to 2 weeks after lambing. There were no differences in egg counts between single- and twin-bearing ewes in the resistant line. However, twin-bearing control ewes had significantly higher egg counts than single-bearing control ewes. Following lactation, plots grazed by resistant ewes had substantially less contamination with T. colubriformis larvae, but there were no differences in numbers of T. circumcincta larvae. Our results demonstrate that sheep bred for worm resistance has lower worm burdens during the peri-parturient phase and that lambs born to resistant ewes face a lower larval challenge during their introduction to grazing. In our environment, selection for low worm egg counts has produced sheep highly resistant to T. colubriformis, but has had less impact on resistance towards T. circumcincta.

Intraspecific Epitopic Variation in a Carbohydrate Antigen Exposed on the Surface of Trichostrongylus colubriformis Infective L3 Larvae

The carbohydrate larval antigen, CarLA, is present on the exposed surface of all strongylid nematode infective L3 larvae tested, and antibodies against CarLA can promote rapid immune rejection of incoming Trichostrongylus colubriformis larvae in sheep. A library of ovine recombinant single chain Fv (scFv) antibody fragments, displayed on phage, was prepared from B cell mRNA of field-immune sheep. Phage displaying scFvs that bind to the surface of living exsheathed T. colubriformis L3 larvae were identified, and the majority of worm-binding scFvs recognized CarLA. Characterization of greater than 500 worm surface binding phage resulted in the identification of nine different anti-CarLA scFvs that recognized three distinct T. colubriformis CarLA epitopes based on blocking and additive ELISA. All anti-CarLA scFvs were specific to the T. colubriformis species of nematode. Each of the three scFv epitope classes displayed identical Western blot recognition patterns and recognized the exposed surface of living T. colubriformis exsheathed L3 larvae. Surprisingly, each of the anti-CarLA scFvs was able to bind to only a subset of worms. Double-labelling indirect immunofluorescence revealed that the three classes of anti-CarLA scFvs recognize distinct, non-overlapping, T. colubriformis sub-populations. These results demonstrate that individual T. colubriformis L3 larvae display only one of at least three distinct antigenic forms of CarLA on their surface at any given time, and suggest that antigenic variation within CarLA is likely a mechanism of immune evasion in strongylid nematodes.

Resistance of Santa Ines and crossbred ewes to naturally acquired gastrointestinal nematode infections

This trial was carried out in Piracicaba, São Paulo State, Brazil, to comparatively evaluate the degree of resistance to naturally acquired gastrointestinal nematode infections in sheep of the following genetic groups: purebred Santa Ines (SI), SI crossbred with Dorper (DO × SI), Ile de France (IF × SI), Suffolk (SU × SI), and Texel (TE × SI). Fifteen ewes from each group were raised indoors until 12 months of age. At this age, they were moved to pasture that was naturally contaminated by nematode infective larvae and were evaluated from December to May, 2007. Rainfall ranged from 267 mm in January to 37 mm in April. Maximum and minimum mean temperatures ranged from 32.5 °C to 19.0 °C in March and from 25.9 °C to 12.8 °C in May. There was an increase in the mean number of eggs per gram of feces (EPG) after animals were placed on pasture with significant difference between the SI (80 EPG) and IF × SI (347 EPG) groups in January; and the DO × SI (386 EPG) and TE × SI (258 EPG) groups in May. The highest mean fecal egg count (FEC), 2073 EPG, was recorded for the TE × SI group in February. All groups showed a progressive reduction in body weight throughout the experiment of 12.0% (TE × SI) to 15.9% (SU × SI). In general, the animals with the highest FEC presented the lowest packed cell volumes (PCV); the highest correlation coefficient between FEC × PCV occurred in the SU × SI sheep in January ( r = −0.70; P < 0.01). Similarly, there was an inverse relationship between FEC and blood eosinophil values, with the highest correlation coefficient in the TE × SI sheep in February ( r = −0.64; P < 0.05). Immunoglobulin G (IgG) levels against Haemonchus contortus antigens increased in all groups as a result of the exposure to parasites and remained relatively constant until the end of the study, with the exceptions of SU × SI and TE × SI, which showed a rise in IgG levels during the last sampling that coincided with a reduction in mean FEC. In conclusion, crossbreeding Santa Ines sheep with any of the breeds evaluated can result in a production increase and the maintenance of a satisfactory degree of infection resistance, especially against H. contortus and Trichostrongylus colubriformis, the major nematodes detected in this flock.

Morphogenesis of Strongyloides stercoralis infective larvae requires the DAF-16 ortholog FKTF-1.

Based on metabolic and morphological similarities between infective third-stage larvae of parasitic nematodes and dauer larvae of Caenorhabditis elegans, it is hypothesized that similar genetic mechanisms control the development of these forms. In the parasite Strongyloides stercoralis, FKTF-1 is an ortholog of DAF-16, a forkhead transcription factor that regulates dauer larval development in C. elegans. Using transgenesis, we investigated the role of FKTF-1 in S. stercoralis' infective larval development. In first-stage larvae, GFP-tagged recombinant FKTF-1b localizes to the pharynx and hypodermis, tissues remodeled in infective larvae. Activating and inactivating mutations at predicted AKT phosphorylation sites on FKTF-1b give constitutive cytoplasmic and nuclear localization of the protein, respectively, indicating that its post-translational regulation is similar to other FOXO-class transcription factors. Mutant constructs designed to interfere with endogenous FKTF-1b function altered the intestinal and pharyngeal development of the larvae and resulted in some transgenic larvae failing to arrest in the infective stage. Our findings indicate that FKTF-1b is required for proper morphogenesis of S. stercoralis infective larvae and support the overall hypothesis of similar regulation of dauer development in C. elegans and the formation of infective larvae in parasitic nematodes.

Migration of gastrointestinal nematode larvae from cattle faecal pats onto grazable herbage

This study investigated the effect of successive harvests of grazable herbage around cattle faecal pats on the population dynamics of infective gastrointestinal nematode larvae (L 3). Faecal material, collected from naturally infected calves, was deposited as pats during summer, autumn and winter on three different topographical aspects within a moist, temperate region of New Zealand. Herbage was harvested four times (22–248 days) from around the faecal pats to a height of 2 cm in three radial zones (0–20 cm, 20–35 cm and 35–45 cm from the centre of the faecal pat) and L 3 extracted. Harvest date was determined by herbage mass to simulate grazing events. L 3 extracted from herbage were predominantly Cooperia spp. More L 3 were recovered from faeces deposited in summer and autumn, than those deposited during winter. L 3 concentration on herbage was highest ( P < 0.001) in the zone nearest the pat for all except the fourth harvest. Mean concentrations of L 3 on herbage were 11,447, 3154, 337 and 102 L 3/kg dry matter herbage, for the four successive harvests, respectively. Microclimate differences as affected by aspect had a marked effect on herbage growth, but did not significantly affect L 3 concentration on herbage. In this study, L 3 remained aggregated close to the faecal pats they emerged from even after two successive harvests and significant rainfall. Successive harvests simulated the effect of repeated grazing events by a non-infective stock class. Two such grazings and the associated time, reduced L 3 presence on grazable herbage to <3% of the original population. Grazing strategies to generate clean pasture for vulnerable cattle are discussed in relation to these results.