Arrested development of nematodes and some related phenomena

Acyl-CoA oxidase ACOX-1 interacts with a peroxin PEX-5 to play roles in larval development of Haemonchus contortus

Hypobiosis (facultative developmental arrest) is the most important life-cycle adaptation ensuring survival of parasitic nematodes under adverse conditions. Little is known about such survival mechanisms, although ascarosides (ascarylose with fatty acid-derived side chains) have been reported to mediate the formation of dauer larvae in the free-living nematode Caenorhabditis elegans. Here, we investigated the role of a key gene acox-1, in the larval development of Haemonchus contortus, one of the most important parasitic nematodes that employ hypobiosis as a routine survival mechanism. In this parasite, acox-1 encodes three proteins (ACOXs) that all show a fatty acid oxidation activity in vitro and in vivo, and interact with a peroxin PEX-5 in peroxisomes. In particular, a peroxisomal targeting signal type1 (PTS1) sequence is required for ACOX-1 to be recognised by PEX-5. Analyses on developmental transcription and tissue expression show that acox-1 is predominantly expressed in the intestine and hypodermis of H. contortus, particularly in the early larval stages in the environment and the arrested fourth larval stage within host animals. Knockdown of acox-1 and pex-5 in parasitic H. contortus shows that these genes play essential roles in the post-embryonic larval development and likely in the facultative arrest of this species. A comprehensive understanding of these genes and the associated β-oxidation cycle of fatty acids should provide novel insights into the developmental regulation of parasitic nematodes, and into the discovery of novel interventions for species of socioeconomic importance.

Parasites of domestic and wild pigeons in the south of Ukraine

Pigeons are closely related to human life and are both a source of food and object for hobbies and sports. Parasitic diseases of birds are the main reason for their growth retardation, reduced productivity and viability. The article presents the results of studying the prevalence of trichomonosis, cestodes and nematodes among the population of wild and domestic pigeons in the south of Ukraine. According to the results of the conducted researches it is established that in the south of Ukraine endoparasitoses of domestic and wild pigeons are quite widespread, and all species of this bird are carriers of Trichomonas gallinae. At the same time, the highest rate of Trichomonas infection was recorded in Columba palambus and C. livia domestica, and the overall infestation of males is higher by 4.4% compared to females. It was determined that domestic pigeons C. livia domestica were infested with trichomonosis (27.5%) and nematodes (Ascaridia columbae, 57.1%), C. palambus – trichomonosis (32.1%) and cestodes (Raillietina spp., 82.4%), Streptopelia turtur – cestodes (Raillietina spp., 12.5%) and S. decaocto – cestodes (Raillietina spp., 71.4%) and nematodes (Heterakis gallinarum, A. columbae – 33.3% and 44.4% respectively). The overall rate of infestation of pigeons with cestodes was 28.4% and the incidence in males was higher by 3.9% compared to females. It was found that the most common species among pigeon cestodes is Raillietina spp. In addition, 22.9% of pigeons are carriers of nematodes (H. gallinarum, A. columbae and Capillaria spp.). Continuous monitoring of pigeon parasites is necessary because they, in most cases, come into contact with other species of poultry and are a source of general invasion. In terms of further research, it would be promising to study the prevalence of helminthic infestation among wild migratory birds.

Advances in the Development of Anti-Haemonchus contortus Vaccines: Challenges, Opportunities, and Perspectives

The gastrointestinal nematode parasite Haemonchus contortus (H. contortus) is a resident of tropical and subtropical regions worldwide that imposes significant production losses, economic losses, and animal health issues in the small ruminant industry, particularly sheep and goats. Considerable efforts have been made to understand how immunity is elicited against H. contortus infection. Various potential vaccine antigens have been tested by different methods and strategies applied in animal models, and significant progress has been made in the development of vaccines against H. contortus. This review highlighted and shared the knowledge about the current understanding of host immune responses to H. contortus and ongoing challenges in the development of a protective, effective, and long-lasting vaccine against H. contortus infection. We have also pinpointed some achievements and failures in the development and testing of vaccines, which will establish a road map for future research directions to explore new effective vaccine candidates for controlling and preventing H. contortus infection.

De novo identification of toxicants that cause irreparable damage to parasitic nematode intestinal cells

Efforts to identify new drugs for therapeutic and preventive treatments against parasitic nematodes have gained increasing interest with expanding pathogen omics databases and drug databases from which new anthelmintic compounds might be identified. Here, a novel approach focused on integrating a pan-Nematoda multi-omics data targeted to a specific nematode organ system (the intestinal tract) with evidence-based filtering and chemogenomic screening was undertaken. Based on de novo computational target prioritization of the 3,564 conserved intestine genes in A. suum, exocytosis was identified as a high priority pathway, and predicted inhibitors of exocytosis were tested using the large roundworm (Ascaris suum larval stages), a filarial worm (Brugia pahangi adult and L3), a whipworm (Trichuris muris adult), and the non-parasitic nematode Caenorhabditis elegans. 10 of 13 inhibitors were found to cause rapid immotility in A. suum L3 larvae, and five inhibitors were effective against the three phylogenetically diverse parasitic nematode species, indicating potential for a broad spectrum anthelmintics. Several distinct pathologic phenotypes were resolved related to molting, motility, or intestinal cell and tissue damage using conventional and novel histologic methods. Pathologic profiles characteristic for each inhibitor will guide future research to uncover mechanisms of the anthelmintic effects and improve on drug designs. This progress firmly validates the focus on intestinal cell biology as a useful resource to develop novel anthelmintic strategies.

Elucidating the molecular and developmental biology of parasitic nematodes: Moving to a multiomics paradigm

In the past two decades, significant progress has been made in the sequencing, assembly, annotation and analyses of genomes and transcriptomes of parasitic worms of socioeconomic importance. This progress has somewhat improved our knowledge and understanding of these pathogens at the molecular level. However, compared with the free-living nematode Caenorhabditis elegans, the areas of functional genomics, transcriptomics, proteomics and metabolomics of parasitic nematodes are still in their infancy, and there are major gaps in our knowledge and understanding of the molecular biology of parasitic nematodes. The information on signalling molecules, molecular pathways and microRNAs (miRNAs) that are known to be involved in developmental processes in C. elegans and the availability of some molecular resources (draft genomes, transcriptomes and some proteomes) for selected parasitic nematodes provide a basis to start exploring the developmental biology of parasitic nematodes. Indeed, some studies have identified molecules and pathways that might associate with developmental processes in related, parasitic nematodes, such as Haemonchus contortus (barber's pole worm). However, detailed information is often scant and 'omics resources are limited, preventing a proper integration of 'omic data sets and comprehensive analyses. Moreover, little is known about the functional roles of pheromones, hormones, signalling pathways and post-transcriptional/post-translational regulations in the development of key parasitic nematodes throughout their entire life cycles. Although C. elegans is an excellent model to assist molecular studies of parasitic nematodes, its use is limited when it comes to explorations of processes that are specific to parasitism within host animals. A deep understanding of parasitic nematodes, such as H. contortus, requires substantially enhanced resources and the use of integrative 'omics approaches for analyses. The improved genome and well-established in vitro larval culture system for H. contortus provide unprecedented opportunities for comprehensive studies of the transcriptomes (mRNA and miRNA), proteomes (somatic, excretory/secretory and phosphorylated proteins) and lipidomes (e.g., polar and neutral lipids) of this nematode. Such resources should enable in-depth explorations of its developmental biology at a level, not previously possible. The main aims of this review are (i) to provide a background on the development of nematodes, with a particular emphasis on the molecular aspects involved in the dauer formation and exit in C. elegans; (ii) to critically appraise the current state of knowledge of the developmental biology of parasitic nematodes and identify key knowledge gaps; (iii) to cover salient aspects of H. contortus, with a focus on the recent advances in genomics, transcriptomics, proteomics and lipidomics as well as in vitro culturing systems; (iv) to review recent advances in our knowledge and understanding of the molecular and developmental biology of H. contortus using an integrative multiomics approach, and discuss the implications of this approach for detailed explorations of signalling molecules, molecular processes and pathways likely associated with nematode development, adaptation and parasitism, and for the identification of novel intervention targets against these pathogens. Clearly, the multiomics approach established recently is readily applicable to exploring a wide range of interesting and socioeconomically significant parasitic worms (including also trematodes and cestodes) at the molecular level, and to elucidate host-parasite interactions and disease processes.

Dafachronic acid promotes larval development in Haemonchus contortus by modulating dauer signalling and lipid metabolism

Here, we discovered an endogenous dafachronic acid (DA) in the socioeconomically important parasitic nematode Haemonchus contortus. We demonstrate that DA promotes larval exsheathment and development in this nematode via a relatively conserved nuclear hormone receptor (DAF-12). This stimulatory effect is dose- and time-dependent, and relates to a modulation of dauer-like signalling, and glycerolipid and glycerophospholipid metabolism, likely via a negative feedback loop. Specific chemical inhibition of DAF-9 (cytochrome P450) was shown to significantly reduce the amount of endogenous DA in H. contortus; compromise both larval exsheathment and development in vitro; and modulate lipid metabolism. Taken together, this evidence shows that DA plays a key functional role in the developmental transition from the free-living to the parasitic stage of H. contortus by modulating the dauer-like signalling pathway and lipid metabolism. Understanding the intricacies of the DA-DAF-12 system and associated networks in H. contortus and related parasitic nematodes could pave the way to new, nematode-specific treatments.

In the present study, using an integrative multi-omics approach, we show that dafachronic acid (DA) plays a critical functional role in the developmental transition in larvae of the parasitic nematode Haemonchus contortus (barber’s pole worm) by modulating the dauer-like signalling pathway and lipid metabolism. The DA-DAF-12 signalling module in H. contortus provides a paradigm to explore its developmental and reproductive biology at the molecular level, to study physiochemical cross-talk between the parasite and its hosts, and to discover novel anthelmintic targets.

Are sleeping site ecology and season linked to intestinal helminth prevalence and diversity in two sympatric, nocturnal and arboreal primate hosts (Lepilemur edwardsi and Avahi occidentalis)?

BACKGROUND

Various factors, such as climate, body size and sociality are often linked to parasitism. This constrains the identification of other determinants driving parasite infections. Here, we investigate for the first time intestinal parasites in two sympatric arboreal primate species, which share similar activity patterns, feeding ecology, body size and sociality, and cope with the same climate conditions, but differ in sleeping site ecology: the Milne-Edward's sportive lemur (Lepilemur edwardsi) and the Western woolly lemur (Avahi occidentalis). Comparison of these two species aimed to test whether differences in sleeping sites are related to differences in parasite infection patterns. Additionally, gender and seasonal factors were taken into account. Animals were radio-collared to record their sleeping site dynamics and to collect fecal samples to assess intestinal parasitism during both the dry and the rainy season.

RESULTS

Only low parasite diversity was detected, which is attributable to the strict arboreal lifestyle of these lemurs, limiting their contact with infective parasite stages. L. edwardsi, which sleeps in tree holes and repeatedly uses the same sleeping site, excreted eggs of strongyle and oxyurid nematodes, whereby strongyles always occurred in coinfection with oxyurids. In contrast, A. occidentalis, which sleeps on open branches and frequently changes sleeping sites, only excreted eggs of strongyle nematodes. This difference can be attributed to a potential favorable environment presented by tree holes for infective stages, facilitating parasitic transmission. Additionally, Strongylida in A. occidentalis were only observed in the rainy season, suggesting an arrested development during the dry season in the nematodes' life cycle. Males and females of both lemur species showed the same frequency of parasitism. No differences in body mass of infected and non-infected individuals were observed, indicating that the animals' body condition remains unaffected by the detected gastrointestinal parasites.

CONCLUSIONS

The comparison of two primate hosts with a very similar lifestyle suggests an influence of the sleeping site ecology on intestinal parasites. In A. occidentalis there was a clear seasonal difference in strongyle egg excretion. These results improve our understanding of the parasite ecology in these endangered primate species, which may be critical in the light of species conservation.

Assessment of the behaviour and survival of nematodes under low oxygen concentrations

Oxygen is required for the completion of almost all known metazoan lifecycles, but many metazoans harbour abilities to withstand varying degrees and periods of hypoxia. Caenorhabditis elegans, one of the most popular model organism is extensively used as a model for the study of hypoxia and anoxia biology and it has been found that this nematode is capable of tolerance to varying degrees of hypoxia. Considering the extremely high diversity of nematodes, the effects of low oxygen concentration and mechanisms of adaptation to oxygen depletion differ among species. In this study, we used a simple assay to examine anoxia tolerance in four nematode species, including three free-living and one plant parasitic nematode. We found that the plant parasitic nematode Bursaphelenchus xylophilus can survive more than 14 days under anoxic conditions. Comparisons of behaviour during anoxia induction and the repertoire of oxygen sensation genes among the tested species suggested the existence of different oxygen sensation systems between B. xylophilus and C. elegans, which quickly introduce suspended animation in response to oxygen depletion to survive long-term anoxia.

Autonomy and integration in complex parasite life cycles

Complex life cycles are common in free-living and parasitic organisms alike. The adaptive decoupling hypothesis postulates that separate life cycle stages have a degree of developmental and genetic autonomy, allowing them to be independently optimized for dissimilar, competing tasks. That is, complex life cycles evolved to facilitate functional specialization. Here, I review the connections between the different stages in parasite life cycles. I first examine evolutionary connections between life stages, such as the genetic coupling of parasite performance in consecutive hosts, the interspecific correlations between traits expressed in different hosts, and the developmental and functional obstacles to stage loss. Then, I evaluate how environmental factors link life stages through carryover effects, where stressful larval conditions impact parasites even after transmission to a new host. There is evidence for both autonomy and integration across stages, so the relevant question becomes how integrated are parasite life cycles and through what mechanisms? By highlighting how genetics, development, selection and the environment can lead to interdependencies among successive life stages, I wish to promote a holistic approach to studying complex life cycle parasites and emphasize that what happens in one stage is potentially highly relevant for later stages.

Arrested development of abomasal trichostrongylid nematodes in lambs in a steppe environment (North-Eastern Algeria)

Arrested development of abomasal trichostrongylid nematodes was studied in 30 permanent grazing lambs on a large farm in the North-East of Algeria. The steppe climate has cold winters and hot and dry summers. The lambs were monitored monthly for gastrointestinal nematodes using nematode faecal egg counts, from February 2008 to February 2009. Every 2 months, two of the original 30 permanent lambs were necropsied after being held in pens for three weeks so that recently ingested infective larvae could develop into adults. The highest percentage of fourth stage larvae (L4), reaching 48% of the total worm burden, was recorded in abomasal contents in June. Teladorsagia and other Ostertagiinae constituted the highest percentage of L4 larvae (71%), whereas the percentage of Trichostrongylus (17.4%) or Haemonchus (11.6%) remained low. The dynamics of infection observed here (highest faecal egg count in August) and the stage composition of worm burden (highest percentage of L4 in June) provide strong evidence that arrested development had occurred.

The effect of dietary fish-meal supplementation on parasite burdens of periparturient sheep

Pregnant ewes were offered 0·80, 1·0 or 1·25 of estimated protein requirement, groups P80, P100 and P125, respectively and trickle infected with Teladorsagia circumcincta (average of 10000 larvae per day) and Trichostrongylus colubriformis (average of 7000 larvae per day) for 42 days prior to parturition. Eleven days after lambing half (group TC) received a single challenge infection of 25000 T. circumcincta and 17500 T. colubriformis larvae and the remainder (TO) no further larval challenge. Worm burdens were determined 21 days post partum.

Worm burdens were inversely related to dietary protein concentration. Mature worms (L5) of T. circumcincta recovered were (log10 (count + 1)) 4·002, 3·806 and 3·444 in TO sheep and 3·812, 3·633 and 3·113 in TC sheep from P80, P100 and P125 groups, respectively. The corresponding burdens of T. colubriformis were 2·665, 2·893 and 2·029 for TO and 3·985, 2·363 and 1·188 for TC sheep. The numbers of L4 larvae recovered from TC sheep were (log10 (count + 1)) 3·532, 3·288 and 3·127 for T. circumcincta and 3·080, 2·180 and 0·949 for T. colubriformis on P80, P100 and P125 diets, respectively. There was no evidence of inhibition of larval development or egg laying with either worm species suggesting that the major effect of protein supply in enhancing resistance was operating at the larval establishment stage. There was evidence that the post-partum challenge infection affected the fecundity and survival of the established adult worm population of T. circumcincta but not of T. colubriformis.

The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants

The parasitic nematode Haemonchus contortus occurs commonly in small ruminants, and it is an especially significant threat to the health and production of sheep and goats in tropical and warm temperate zones. The main signs of disease (haemonchosis) relate to its blood-feeding activity, leading to anaemia, weakness and frequently to deaths, unless treatment is provided. Due to the high biotic potential, large burdens of H. contortus may develop rapidly when environmental conditions favour the free-living stages, and deaths may occur with little prior warning. More chronic forms of haemonchosis, resulting in reduced animal production and eventually deaths, occur with smaller persistent infections, especially in situations of prolonged, poor nutrition. The global distribution of the main haemonchosis-endemic zones is consistent with the critical requirements of the egg and larval stages of H. contortus for moisture and moderate to relatively warm temperatures, but the seasonal propensity for hypobiosis (inhibition of the fourth-stage larvae within the host) largely explains the common, though sporadic, outbreaks of haemonchosis in arid and colder environments. The wide climatic distribution may also reflect the adaptation of local isolates to less favourable ecological conditions, while an apparent increase in the prevalence of outbreaks in environments not previously considered endemic for haemonchosis - especially cold, temperate zones - may be attributable to climatic changes. Although the risk of haemonchosis varies considerably on a local level, even where H. contortus is endemic, the extensive range of ecological investigations provides a sound basis for predictions of the relative geographical and seasonal risk in relation to climatic conditions.

The Identification of Haemonchus Species and Diagnosis of Haemonchosis

Diagnosis is often equated with identification or detection when discussing parasitic diseases. Unfortunately, these are not necessarily mutually exclusive activities; diseases and infections are generally diagnosed and organisms are identified. Diagnosis is commonly predicated upon some clinical signs; in an effort to determine the causative agent, identification of genera and species is subsequently performed. Both identification and diagnosis play critical roles in managing an infection, and involve the interplay of direct and indirect methods of detection, particularly in light of the complex and expanding problem of drug-resistance in parasites. Accurate and authoritative identification that is cost- and time-effective, based on structural and molecular attributes of specimens, provides a foundation for defining parasite diversity and changing patterns of geographical distribution, host association and emergence of disease. Most techniques developed thus far have been grounded in assumptions based on strict host associations between Haemonchus contortus and small ruminants, that is, sheep and goats, and between Haemonchus placei and bovids. Current research and increasing empirical evidence of natural infections in the field demonstrates that this assumption misrepresents the host associations for these species of Haemonchus. Furthermore, the capacity of H. contortus to utilize a considerably broad spectrum of ungulate hosts is reflected in our understanding of the role of anthropogenic forcing, the 'breakdown' of ecological isolation, global introduction and host switching as determinants of distribution. Nuanced insights about distribution, host association and epidemiology have emerged over the past 30years, coincidently with the development of increasingly robust means for parasite identification. In this review and for the sake of argument, we would like to delineate the diagnosis of haemonchosis from the identification of the specific pathogen. As a foundation for exploring host and parasite biology, we will examine the evolution of methods for distinguishing H. contortus from other common gastrointestinal nematodes of agriculturally significant and free-ranging wild ruminants using morphological, molecular and/or immunological methods for studies at the species and genus levels.

Acquisition of resistance after continuous infection with Ascaridia galli in chickens

SUMMARY Acquired resistance against Ascaridia galli infection was studied in seventy-two 18-week-old white Leghorn chickens allocated to six groups (G1-G6). In order to understand the population dynamics following trickle-infection (100 eggs per chicken twice weekly), chickens of subgroups of G1 were necropsied 3 days after 1, 6 or 12 inoculations (G1A, G1B and G1C respectively), while G2-G4 were inoculated for 6 weeks. G2 was necropsied 4 weeks after the last inoculation. The number of established larvae increased initially (between G1A and G1B) but decreased after repeated inoculations (G1C, G2). G3, G4 and G5 were used to measure the efficacy of anthelminthic treatment and to monitor the acquisition of resistance following a challenge infection. At week 7 G3, G4 and G5 were treated with flubendazole for 7 days in the feed. Two weeks after treatment the chickens in G4 and G5 were challenged with 500 eggs. G6 was left as uninfected control. Necropsy at week 10 after first inoculation revealed a lower establishment rate, an impaired development and a more posterior localization of the larvae in G4 (trickle-infected-treated-challenged) compared with G5 (treated-challenged). IgY level in serum reached noticeable level at 14 dpi in G2 and G4 chickens, and in G4 chickens IgY level further increased after challenge infection. The study provides evidence that acquired resistance against A. galli in chickens leads to a significant yet incomplete protection against re-infection.

Exploiting parallels between livestock and wildlife: Predicting the impact of climate change on gastrointestinal nematodes in ruminants

Global change, including climate, policy, land use and other associated environmental changes, is likely to have a major impact on parasitic disease in wildlife, altering the spatio-temporal patterns of transmission, with wide-ranging implications for wildlife, domestic animals, humans and ecosystem health. Predicting the potential impact of climate change on parasites infecting wildlife will become increasingly important in the management of species of conservation concern and control of disease at the wildlife-livestock and wildlife-human interface, but is confounded by incomplete knowledge of host-parasite interactions, logistical difficulties, small sample sizes and limited opportunities to manipulate the system. By exploiting parallels between livestock and wildlife, existing theoretical frameworks and research on livestock and their gastrointestinal nematodes can be adapted to wildlife systems. Similarities in the gastrointestinal nematodes and the life-histories of wild and domestic ruminants, coupled with a detailed knowledge of the ecology and life-cycle of the parasites, render the ruminant-GIN host-parasite system particularly amenable to a cross-disciplinary approach.

Population dynamics of Ascaridia galli following single infection in young chickens

The population dynamics of Ascaridia galli was studied in 70 ISA Brown layer pullets, 42 of them were each experimentally infected with 500 embryonated A. galli eggs and 28 chickens were kept as uninfected controls. Six chickens from the infected group and 4 from the control group were necropsied at 3, 7, 10, 14, 21, 28 and 42 days post-infection (d.p.i.). The mean worm recovery varied from 11-20% of the infection dose with the highest recovery at 3 d.p.i. and the lowest at 21 and 42 d.p.i. (P < 0·05). More larvae were recovered from the intestinal wall than from the content (P < 0·0001) and intestinal content larvae were longer than those from the wall (mean length 1·6 and 1 mm, respectively, P < 0·0001). Although larvae were growing over time, a population of small-sized larvae (length < 1 mm) was recovered at all d.p.i. During the first week of infection most of the larvae were located in the anterior half of the jejunoileum but they moved posteriorly with the age of infection. Thus, a subpopulation of larvae mainly in the lumen grew with time while another subpopulation remained small and associated with the mucosa. During the infection both subpopulations moved to a more posterior localization in the gastrointestinal (GI) tract.

Climate changes influence free-living stages of soil-transmitted parasites of European rabbits

Climate warming has been suggested to augment the risk of infectious disease outbreaks by extending the seasonal window for parasite growth and by increasing the rate of transmission. Understanding how this occurs in parasite-host systems is important for appreciating long-term and seasonal changes in host exposure to infection and to reduce species extinction caused by diseases. We investigated how free-living stages of two soil-transmitted helminths of the European rabbit (Oryctolagus cuniculus) responded to experimental changes in temperature by performing laboratory experiments with environmental chambers and field manipulations using open-top-chambers. This study was motivated by our previous observations that air temperature has increased over the last 30 years in our field site and that during this period intensity of infection of Graphidium strigosum but not Trichostrongylus retortaeformis was positively associated with this temperature increase. Laboratory and field experiments showed that both parasites accelerated egg development and increased hatching rate and larval survival in response to accumulating thermal energy. Both parasites behaved similarly when exposed to diverse temperature regimes, decadal trends, and monthly fluctuations, however, T. retortaeformis was more successful than G. strigosum by showing higher rates of egg hatching and larval survival. Across the months, the first day of hatching occurred earlier in warmer conditions suggesting that climate warming can lengthen the period of parasite growth and host exposure to infective stages. Also, T. retortaeformis hatched earlier than G. strigosum. These findings showed that seasonal changes in intensity, frequency, and duration of daily temperature are important causes of variability in egg hatching and larva survival. Overall, this study emphasizes the important role of climate warming and seasonality on the dynamics of free-living stages in soil-transmitted helminths and their contribution to enhance host exposure to parasitic infections. Yet, the ability to infect might ultimately depend on how hosts interact with parasites.

A longitudinal study on the effect of lambing season on the periparturient egg rise in Ontario sheep flocks

The epidemiology of the periparturient egg rise (PPER) of gastrointestinal nematodes (GINs) in sheep remains unclear, and may be influenced by the lambing season. This longitudinal study was performed to determine the effect of out-of-season lambing on the PPER in ewes in Ontario, and whether total plasma protein (TPP) and packed cell volume (PCV) were associated with the PPER. Six farms that practiced out-of-season lambing were enrolled, and sampled for three consecutive lambing seasons (winter, spring and autumn). For each lambing season, all farms were visited five times. On the first visit for each lambing season, 15-20 pregnant ewes and 15-20 non-pregnant/early gestation ewes were randomly selected. At each visit, fecal samples were collected from all selected animals and processed individually to measure GIN fecal egg counts (FECs). Blood samples were collected on three visits in each lambing period and processed to measure TPP and PCV. The ewes were classified into one of five production stages (maintenance [i.e. not pregnant], early or late gestation [<120 d and ≥ 120 d, respectively], and early or late lactation [<40 d and ≥ 40 d, respectively]) based on information collected during farm visits. Linear mixed models were developed for the TPP, PCV and logarithmic-transformed FEC (lnFEC). During the winter and spring lambing season, the FECs increased gradually over the gestation period and peaked during lactation, with these increases being larger in ewes with a low PCV (three-way interaction in the final model). In the autumn lambing season, the FECs started off higher in early gestation, and increased rapidly to peak in late gestation, particularly for animals with low PCV levels. In the TPP model, PCV and lnFEC were positively associated with TPP. During both autumn and winter lambing seasons, the TPP decreased from maintenance throughout gestation and early lactation, followed by an increase in late lactation, except for when there were high FECs. During the spring lambing season, TPP peaked at early gestation, and then decreased in late gestation, to increase more gradually over lactation. In the PCV model, PCV increased with TPP and decreased exponentially with increases in lnFEC. The PPER occurred during all three lambing seasons, and its magnitude and distribution varied with the lambing season, suggesting that the PPER in ewes depends on both environmental and animal physiological factors, an important consideration when implementing preventive parasite control strategies on sheep farms that practice out-of-season lambing.

Development of Graphidium strigosum (Nematoda, Haemonchidae) in its natural host, the rabbit (Oryctolagus cuniculus) and comparison with several Haemonchidae parasites of ruminants

The morphogenesis (studied for the first time) and the chronology of the life cycle of Graphidium strigosum (Dujardin, 1845) were studied in detail in its natural host, Oryctolagus cuniculus. Naive rabbits were each infected per os with G. strigosum infective larvae (L3). Animals were euthanized each day for the first 10 days after infection (DAI), then every 2 days from 12 to 40 DAI. The free living period lasted 5-8 days at 24°C. By 1 DAI, all the larvae were exsheathed in the stomach. The third molt occurred between 9 and 17 DAI. The last molt occurred between 24 and 32 DAI. The prepatent period lasted 42-44 DAI, while the patent period lasted at least 13 months. For each experiment, the morphology of the different stages of the life cycle was described. The chronology of the G. strigosum life cycle and its morphogenesis were compared to those of different Haemonchidae parasites of ruminants (Ostertagia ostertagi, Teladorsagia circumcincta, Haemonchus contortus, and Haemonchus placei) in their natural hosts.

In vitro development of cyathostomin larvae from the third stage larvae to the fourth stage: morphologic characterization, effects of refrigeration, and species-specific patterns

A mixed population of equine cyathostomin (Nematoda, Strongyloidea) infective third stage larvae (L3) was cultured in vitro using a cell-free medium. Some L3 were cultured immediately after Baermann collection from fecal cultures, while others were kept in water at 4 degrees C for 7 days before initiating the in vitro cultures. Cultures were examined daily for viability. At days 2, 7, 14 and 21 larvae were collected for identification of developmental stage and morphological changes, using both light and scanning electron microscopy. Larvae were classified as early L3 (EL3), developing L3 (DL3), late L3 (LL3) and fourth stage larvae (L4) on the basis of morphological features. Viability remained high throughout the entire study period in cultures of both non-refrigerated (84.7%) and refrigerated (77.4%) larvae. However, viability of the non-refrigerated was significantly greater from 7 through 21 days of culture. Significant differences were also observed in the percentage of DL3 between the non-refrigerated and refrigerated larval cultures by day 7. The highest percentage of DL3 larvae (22.5%) was reached at the end of study in those larvae that were not previously refrigerated. The data suggests that prior refrigeration decreases viability and slows L3 development. At day 21 LL3 larvae were only a small percentage of the DL3: 6.9 and 5% in non-refrigerated and refrigerated cultures, respectively. Few of these larvae freed themselves from the L3 cuticle and moulted to L4 stage. Characteristics of individual species in vitro developmental patterns were determined by the molecular identification of individual larvae in pools of larvae randomly collected at days 0 and 21. Seven species (Coronocyclus coronatus, Cylicostephanus goldi, Cylicostephanus longibursatus, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicocyclus ashworthi, Petrovinema poculatum) were identified in the day 0 pool. The greatest tendency to develop in vitro was shown by the genus Cylicostephanus with the species C. goldi and C. longibursatus that developed to the LL3-L4 stages. C. nassatus, C. ashworthi and C. coronatus did not progress in their development beyond the EL3 stage, while no apparent signs of development were registered for C. catinatum.

To delay once or twice: the effect of hypobiosis and free-living stages on the stability of host-parasite interactions

The life cycle of many endoparasites can be delayed by free-living infective stages and a developmental arrestment in the host referred to as hypobiosis. We investigated the effects of hypobiosis and its interaction with delay in the free-living stages on host-parasite population dynamics by expanding a previous attempt by Dobson & Hudson. When the parasite life cycle does not include free-living stages, hypobiosis destabilizes the host-parasite interactions, irrespective of the assumptions about the regulation of the host population dynamics. Interestingly, the destabilizing effect varies in a nonlinear way with the duration of hypobiosis, the maximal effect being expected for three to five months delay. When the parasite life cycle involves free-living stages, hypobiosis of short or intermediate duration increases the destabilizing effect of the first time delay. However, hypobiosis of a duration of five months or more can stabilize interactions, irrespective of the regulation of the host population dynamics. Overall, we confirmed that hypobiosis is an unusual time delay as it can stabilize a two-way interaction. Contrary to the previous conclusions, such an atypical effect does not require self-regulation of the host population, but instead depends on the existence of free-living stages.

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

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

Climate disruption and parasite-host dynamics: patterns and processes associated with warming and the frequency of extreme climatic events

Levels of parasitism and the dynamics of helminth systems is subject to the impact of environmental conditions such that we may expect long term increases in temperature will increase the force of infection and the parasite's basic reproduction number, R0. We postulate that an increase in the force of infection will only lead to an increase in mean intensity of adults when adult parasite mortality is not determined by acquired immunity. Preliminary examination of long term trends of parasites of rabbits and grouse confirm these predictions. Parasite development rate increases with temperature and while laboratory studies indicate this is linear some recent studies indicate that this may be non-linear and would have an important impact on R0. Warming would also reduce the selective pressure for the development of arrestment and this would increase R0 so that in systems like the grouse and Trichostrongylus tenuis this would increase the instability and lead to larger disease outbreaks. Extreme climatic events that act across populations appear important in synchronizing transmission and disease outbreaks, so it is speculated that climate disruption will lead to increased frequency and intensity of disease outbreaks in parasite populations not regulated by acquired immunity.

Consequences of the unusually warm and dry summer of 2003 in The Netherlands: poor development of free living stages, normal survival of infective larvae and long survival of adult gastrointestinal nematodes of sheep

During 2003 a grazing study was performed at Utrecht University to evaluate evasive grazing and application of Duddingtonia flagrans for the control of parasitic gastroenteritis in sheep. However, the summer of 2003 (June-August) was unusually warm and dry. As a result the patterns of gastrointestinal nematode infections deviated from those observed in more average years. The proportion of eggs that developed to infective larvae was far lower than normal in July-August. On the other hand, survival of larvae that had developed before the middle of July was not affected compared to other years. In fact, severe haemonchosis was observed in (tracer) lambs grazed at the end of July on pastures that had been contaminated from 26-05 to 16-06 and from 16-06 to 07-07. Moreover, tracer lambs grazing in September on some of these plots still acquired large Haemonchus contortus burdens. Over 60% of H. contortus that had established before the middle of July appeared to be able to survive until October in the virtual absence of re-infection. That may have consequences for the application of evasive grazing as a control option in that suppression of adult burdens might still be necessary, through a limited use of anthelmintics or through alternative deworming strategies.

Arrested development of Ostertagia ostertagi: effect of the exposure of infective larvae to natural spring conditions of the Humid Pampa (Argentina)

The aim of this study was to determine the effect of environmental conditions and the time of exposure to the conditions required for Ostertagia ostertagi to become inhibited in development at the early fourth larval stage in the host. Two comparable experiments were conducted from September to January, experiment I in 1997-1998 and experiment II in 1999-2000. Twenty-thousand third-stage larvae (L3), freshly obtained from coprocultures, were spread in different parasite-free grass plots at the beginning of September, October and November in each experiment and exposed to environmental conditions throughout spring and early summer. Duplicate plots for each exposure period were grazed for 3 days by two dewormed tracer calves after 1, 2, 3, 4 weeks of exposure during the corresponding month, and the remaining plots were grazed for 3 days at monthly intervals until the end of the experimental period. For each month in both experiments, control animals were inoculated orally with 20,000 L3 newly recovered from coprocultures (week 0 animals; infection controls). The control and tracer calves were sacrificed and their parasite burdens analysed. The time required to obtain greater than 50% inhibited larvae (IeL4) in the tracer animals during September and October was 3 weeks, whereas during November around 60% of the parasites were inhibited after one week of exposure. During the period tested, greater than 50% inhibition was found in concurrence with a photoperiod ranging between 13 and 14 h. The highest proportion of IeL4 (75% average) in the animals was found concomitant with a 14 h 43 min photoperiod. A high correlation between the percentage of inhibition and day length was established (0.870 p < 0.001 and 0.815 p < 0.001 for experiment I and II, respectively). In both years, the capacity for developmental arrest was lost by the end of December, when the photoperiod begins to decrease, suggesting either a disappearance of the induction stimulus, or that an excess of the stimulus could block the mechanism of inhibition. The induction time was extended 2 weeks in all months tested when the coprocultures were maintained in the dark (experiment II), suggesting that accumulation of the light stimulus contributes to shortening of the induction time. The data presented here would suggest that photoperiod is a key environmental factor for the induction of hypobiosis.

Schistosoma mansoni: sex-specific modulation of parasite growth by host immune signals

Development of female schistosomes from infectious cercariae to mature egg-producing adults requires both male schistosomes and an intact adaptive immune system. By examining single sex infections in immunodeficient mice, we provide evidence that female schistosome development is not directly influenced by the adaptive immune system, whereas male development is. Our data are consistent with a sequential model of schistosome development, where the adaptive immune system signals development of mature males, which subsequently stimulate development of mature females. The male schistosome therefore appears to play a central role both in transducing signals from the adaptive immune system and in facilitating female development.

Periparturient increase in faecal egg counts in a captive population of mohor gazelle (Gazella dama mhorr)

The objective of this study was to assess whether there was a periparturient rise in the faecal egg output of a population of North African gazelles (Gazella dama mhorr) kept in captivity in Almeria, southern Spain. In one experiment faeces were collected from 47 female gazelles on three days in winter, in November and December 1995 and January 1996; in a second experiment faecal samples were collected from nine pregnant gazelles at weekly intervals from July 1996 to June 1997. The mean trichostrongylid faecal egg counts were significantly higher (P < 0.05) in the periparturient gazelles than in the pregnant and non-pregnant animals only when the births took place in winter. Other factors, including the gazelle's age, its level of inbreeding, the number of previous births, and its trichostrongylid egg output at the beginning of the study did not affect whether it showed a periparturient rise. The parasites responsible for the rise were different in the two experiments.

Developmental plasticity in schistosomes and other helminths

Developmental plasticity in helminth life cycles serves, in most cases, to increase the probability of transmission between hosts, suggesting that the necessity to achieve transmission is a prominent selective pressure in the evolution of this phenomenon. Some evidence suggests that digenean trematodes from the genus Schistosoma are also capable of limited developmental responses to host factors. Here we review the currently available data on this phenomenon and attempt to draw comparisons with similar processes in the life cycles of other helminths. At present the biological significance of developmental responses by schistosomes under laboratory conditions remains unclear. Further work is needed to determine whether developmental plasticity plays any role in increasing the probability of schistosome transmission and life cycle propagation under adverse conditions, as it does in other helminth life cycles.

Response to carbon dioxide by the infective larvae of three species of parasitic nematodes

The response of infective third-stage larvae (L3) of three species of parasitic nematodes, Ancylostoma caninum, Strongyloides stercoralis, and Haemonchus contortus to carbon dioxide (CO(2)) at physiological concentrations was investigated. L3 of the skin-penetrating species, A. caninum and S. stercoralis, were stimulated by CO(2) at the concentration found in human breath (3.3-4%); these larvae responded by crawling actively, but not directionally. Crawling was not stimulated by breath passed through a CO(2)-removing "scrubber" or by "bench air". Both A. caninum and S. stercoralis L3 stopped crawling when exposed to 5% CO(2) for 1 min. L3 of A. caninum became active 9-14 min after exposure to 5% CO(2) ended, but activity resumed more rapidly (10-15 s) if larvae were subsequently exposed to breath or breath through the scrubber. L3 of S. stercoralis resumed crawling 30-35 s after exposure to 5% CO(2), but resumed crawling within a very few seconds when exposed to breath or breath through the scrubber. Thus, while 5% CO(2) was inhibitory, lower concentrations of this gas stimulated L3 of both species. Apparently, exposing immobilized larvae to breath or breath through the scrubber causes the environmental CO(2) concentration to drop to a level that is stimulatory. The L3 of H. contortus ceased crawling and coiled when exposed to human breath or to 1% CO(2), but continued to move within the coil in both cases. The crawling response of the L3 of the two skin-penetrating species, A. caninum and S. stercoralis, to stimulation by CO(2) probably relates to their active host-finding behavior, while the cessation response elicited by CO(2) in H. contortus larvae may relate to the fact that they rely on passive ingestion by a ruminant host.

Incidence of Haemonchus spp. and effect on haematocrit and eye colour in goats farmed under resource-poor conditions in South Africa

The diversity and predominance of nematode genera in goats of resource-poor farmers at Rust de Winter, Gauteng Province, Impendle, KwaZulu-Natal Province, and Kraaipan, North-West Province, South Africa, was determined by means of a longitudinal study of the nematode faecal egg counts (FECs) and differential third-stage nematode larvae. The animals were bled for haematocrit determination and scored for pallor of ocular mucous membranes using the FAMACHA( Copyright) method, an assay for clinical evaluation of anaemia caused by Haemonchus spp. Animals considered to be in danger of dying from anaemia caused by haemonchosis were selectively treated with an anthelmintic. Lower haematocrit values were registered during periods of heavier Haemonchus infection, which occurred from December/January to March for Rust de Winter; from December to March/April for Impendle; and from November/December to February or April for Kraaipan. There was agreement too between the lower haematocrits and paler mucous membranes scored according to the FAMACHA( Copyright) method. The use of this system may be recommended as part of an integrated approach to worm control in goats kept in the resource-poor areas studied.

Contrasting regulation of fecundity in two abomasal nematodes of Svalbard reindeer (Rangifer tarandus platyrhynchus)

Stability of trichostrogylid populations indicates that some form of density-dependent regulation occurs which could act through fecundity. We present evidence for intraspecific density-dependent effects in 1 of 2, dominant, abomasal nematodes species (Ostertagia gruehneri) of Svalbard reindeer (Rangifer tarandus platyrhynchus). We found evidence in O. gruehneri, for density-dependent regulation of female worm length in April, July and October 1999. However, it is only in July that female worm length explains the variation in the number of eggs in utero which is also related to egg production per female worm only in this month and not at other times of the year. The seasonal pattern in faecal egg output in this species focuses egg production in the summer months when conditions are favourable to transmission. In contrast, we found no evidence in the other common species (Marshallagia marshalli) for density-dependent regulation of female worm length during or the number of eggs in utero. Faecal egg output in M. marshalli was positively related to worm burden but not to the mean number of eggs in utero. Neither inter-specific interactions nor host body condition appeared to influence worm fecundity. The contrasting patterns of density-dependent regulation of fecundity provides further evidence for divergent life-histories in this nematode community.

Chemo- and thermosensory neurons: structure and function in animal parasitic nematodes

Nematode parasites of warm-blooded hosts use chemical and thermal signals in host-finding and in the subsequent resumption of development. The free-living nematode Caenorhabditis elegans is a useful model for investigating the chemo- and thermosensory neurons of such parasites, because the functions of its amphidial neurons are well known from laser microbeam ablation studies. The neurons found in the amphidial channel detect aqueous chemoattractants and repellants; the wing cells-flattened amphidial neurons-detect volatile odorants. The finger cells-digitiform amphidial neurons-are the primary thermoreceptors. Two neuron classes, named ADF and ASI, control entry into the environmentally resistant resting and dispersal dauer larval stage, while the paired ASJ neurons control exit from this stage. Skin-penetrating nematode parasites, i.e. the dog hookworm Ancylostoma caninum, and the threadworm, Strongyloides stercoralis, use thermal and chemical signals for host-finding, while the passively ingested sheep stomach worm, Haemonchus contortus, uses environmental signals to position itself for ingestion. Amphidial neurons presumably recognize these signals. In all species, resumption of development, on entering a host, is probably triggered by host signals also perceived by amphidial neurons. In the amphids of the A. caninum infective larva, there are wing- and finger-cell neurons, as well as neurons ending in cilia-like dendritic processes, some of which presumably recognize a sequence of signals that stimulate these larvae to attach to suitable hosts. The functions of these neurons can be postulated, based on the known functions of their homologs in C. elegans. The threadworm, S. stercoralis, has a complex life cycle. After leaving the host, soil-dwelling larvae may develop either to infective larvae (the life-stage equivalent of dauer larvae) or to free-living adults. As with the dauer larva of C. elegans, two neuron classes control this developmental switch. Amphidial neurons control chemotaxis to a skin extract, and a highly modified amphidial neuron, the lamellar cell, appears to be the primary thermoreceptor, in addition to having chemosensory function. The stomach worm, Haemonchus contortus, depends on ingestion by a grazing host. Once ingested, the infective larva is exposed to profound environmental changes in the rumen. These changes stimulate resumption of development in this species. We hypothesize that resumption of development is under the control of the ASJ neuronal pair. Identification of the neurons that control the infective process could provide the basis for entirely new approaches to parasite control involving interference with development at the time and place of initial host-contact.

Breed and season effects on the peri-parturient rise in nematode egg output in indigenous ewes in a cool tropical environment

A study was carried out at the International Livestock Research Institute (ILRI) Debre Berhan Research Station in Ethiopia from 1992 to 1995 to compare the peri-parturient rise (PPR) in faecal nematode egg counts (FEC) in ewes of two indigenous sheep breeds. A total of 1439 Menz and 1347 Horro ewes were single sire mated following oestrus synchronization to lamb in the wet and dry season. Three ewe treatment groups were constituted as mated/lactating/undrenched; mated/lactating/drenched; unmated/undrenched for three wet and three dry lambing seasons. All ewes grazed naturally contaminated pasture. Levels of faecal egg output were monitored at mating, 3 months after mating, 2 weeks before lambing, 4, 8 and 12 weeks post-lambing. A significant PPR in FEC occurred 2 weeks before lambing and peaked at 4 weeks post-parturition in ewes lambing just before the beginning of the dry season (October/November). There was no significant increase in FEC when lambing occurred before the onset of the long rainy season (May/June). The PPR in this study was associated with both lactation and seasonal availability of third-stage infective larvae on pasture. There was no consistent breed difference in FEC during the six sampling periods from mating to weaning. Faecal cultures and worm counts from both breeds confirmed the presence of Longistrongylus (Pseudomarshallagia) elongata, Trichostrongylus spp.and Haemonchus contortus. The role of the peri-parturient rise of FEC in ewes in gastrointestinal nematode transmission is discussed.

Some aspects of inhibited development of trichostrongylids in ruminants

Inhibited development is an important aspect of the biology of some gastrointestinal nematodes of ruminants, particularly species of the subfamily Ostertagiinae and Haemonchus spp. There is a seasonality in the occurrence of the phenomenon. It tends to occur predominantly during the unfavourable season for the free-living stages. Thus 'winter' and 'summer-dry season' patterns of inhibition can be observed. Furthermore, the phenomenon is influenced by immunity of the host and by management factors. Different studies show conflicting results on the phenomenon of inhibition. This is examplified by studies related to H. contortus in small ruminants. Other studies indicate that large differences in propensity for inhibition can indeed occur in a single region. However, it has to be stressed that inadequate necropsy techniques can easily result in underestimation of the proportion of inhibited larvae, particularly in Haemonchus spp. in cattle. The macrocyclic lactones are highly effective against inhibited larvae of gastrointestinal nematodes. Treatment may even prevent establishment of inhibited larvae of Ostertagia and Trichostrongylus axei up to 1 month after treatment. The efficacy of benzimidazoles seems to be lower in the middle of the 'inhibition' period than at the beginning or the end. Some studies indicated that the presence of inhibited stages may be important for the build up of immunity. However, removal of high inhibited O. ostertagi burdens at housing does not impair development of immunity. Very little progress has been made on the molecular mechanisms of inhibited development.

Comparison of the post-parturient rise in faecal egg counts of indigenous and cross-bred ewes

The breed differences in post-parturient rise (PPR) in faecal egg counts in lambing ewes of different breeds naturally infected with Haemonchus contortus were compared. The ewes of Nali, 50% Nali x 50% Russian Merino/Corriedale and 37.5% Nali x 62.5% Russian Merino/Corriedale were treated with fenbendazole while ewes of the above three breeds as well as 25% Nali x 75% Russian Merino/Corriedale, were kept untreated. Observations from 3 weeks before lambing to 12 weeks post-lambing at weekly intervals revealed that in treated ewes, egg counts of Nali did not differ significantly with 50% Nali whereas 37.5% Nali had significantly higher egg counts than those of Nali and 50% Nali. In untreated ewes egg counts of 50% Nali were significantly higher than that of Nali on some occasions, while 25% Nali had significantly higher egg counts than the other three breeds. None of the ewes from the Nali breed showed signs of haemonchosis, whereas few lambing ewes of the three Nali crosses (50%, 37.5% and 25% Nali) showed signs of haemonchosis and one ewe of the latter breed died.

Epidemiological observations on gastrointestinal nematode infections in grazing cow-calf pairs in Belgium

The epidemiology of gastrointestinal helminth infections in beef cows and calves on pasture was studied in Belgium during the 1990 and 1992 grazing seasons. Weight gain, faecal egg counts, generic differentiation of infective larvae, serum pepsinogen levels, herbage larval counts and worm burdens of tracer calves were used as parameters. In Study 1 two groups of ten cows with their spring-born calves grazing on separate pastures (A and B) were monitored during the 1990 grazing season. Ostertagia ostertagi was the predominant species shed by cows and calves. Cows on Pasture A had significantly higher egg counts at turn-out than the B cows, creating a high pasture contamination in the autumn, evidenced by high Ostertagia worm burdens in the Pasture A tracer calves. Calves of both groups showed low egg counts (mean < 60 eggs g-1 faeces, EPG) throughout the grazing season. In Study 2 nine cow-calf pairs were monitored during the 1992 grazing season. The calves were born in winter or spring. Faecal egg counts of the cows remained low throughout the trial period. During the grazing season high egg counts were observed in the calves (mean up to 778 EPG). Cooperia oncophora was the predominant species in the calves. In the cows O. ostertagi, Oesophagostomum, C. oncophora and Trichostrongylus axei were present. It is suggested that, in the first study, the cows were the major source of pasture contamination, while in the second study the winter-born calves, being older and having a higher herbage intake resulting in a higher infection level, were largely responsible for the high Cooperia pasture infection level at housing.

Prevalence and epidemiology of trichostrongylids in Wyoming cattle with consideration of the inhibited development of Ostertagia ostertagi

During 1988, monthly collections of abomasa and the cranial portion of the small intestine of 208 native Wyoming cattle were examined for adult and larval helminth parasites. Egg counts were performed on colonic faecal specimens. The animals ranged from 7 months to 8 years of age and were sampled at slaughter houses or diagnostic laboratories from five different counties in the State. Most of the cattle had ranged for a long time on non-irrigated, high altitude grass plains from about 1250 to 2500 m above sea level. All animals examined were found infected. Nematode genera (and number of species) found included Ostertagia (4), Trichostrongylus (2), Haemonchus (1), Cooperia (4) and Nematodirus (2). One trematode, Fasciola hepatica, and a cestode, Moniezia benedeni, also were found. Trichostrongylus axei, Trichostrongylus longispicularis and Cooperia lyrata were found for the first time in Wyoming, Ostertagia circumcincta was found for the first time in cattle in Wyoming, and Haemonchus placei, tentatively identified in a previous survey, was definitively confirmed. Predominant species (and prevalence) were Ostertagia ostertagi (98%), Cooperia oncophora (60.6%), Ostertagia bisonis (41.8%), Cooperia bisonis (33.6%) and T. Axei (27.9%). One or more of the four species of Ostertagia were found in all animals. Inhibited O. ostertagi and O. bisonis larvae predominated from November to April and reached a peak in January to comprise 88% of the total nematode burden for that month. The adult population of abomasal nematodes peaked in April and predominated thereafter until October. Haemonchus placei also spent the autumn-winter period in an inhibited state of development. Faecal egg counts were lowest during winter months, when the highest number of worms were present as L4 larvae, as determined by luminal and mucosal counts. Nematode populations in the small intestine peaked in June and persisted until November. The results of this study showed the magnitude and species composition of nematode parasitism in cattle raised on high altitude grass plains, underscored the inaccuracy of faecal egg counts as an indicator of worm burden during fall and winter seasons, and provided information on which anthelmintic treatment timing would be most efficacious.

Analysis of proteins related to conditioning for arrested development and differentiation in Haemonchus contortus by two-dimensional gel electrophoresis

The abundance of the majority of proteins of infectious third-stage larvae (L3) of Haemonchus contortus, conditioned for arrested development, remained unaltered. Only seven proteins showed quantitative differences as observed by two-dimensional gel electrophoresis. These differences were also observed in a laboratory strain which has lost the ability for arrested development. The abundance of two of these proteins increased dramatically during conditioning of larvae for 5-10 weeks. This coincided with the highest percentage of inhibited larvae in experimental infections. Moreover, the abundance of these proteins decreased again after prolonged conditioning (22 weeks). The abundance of the other 5 proteins was not correlated to the percentage of inhibition. We therefore conclude that these proteins are involved in the aging process of larvae. The changes in protein between free-living (L3) and parasitic stages (L4) were large and seem to reflect the large environmental changes experienced by the larvae when entering a mammalian host. Early fourth- (EL4) and late fourth- (LL4) stage larvae differed in 9 proteins. One protein was stage-specific for EL4. These results imply that only minor alterations do occur in these stages notwithstanding the large morphological differences between these larvae.

A comparison of early and mid grazing season suppressive anthelmintic treatments for first year grazing calves and their effects on natural and experimental infection during the second year

A comparison was made of the efficacy and parasitological sequelae over 2 years, of continuous and intermittent periods of anthelmintic suppression applied both early and in the middle of the first grazing season of calves. Five groups of 15 calves grazing separate paddocks within the same field were allotted to one of the following treatment regimes during their first year at grass: Group 1, untreated controls; Group 2, treated with ivermectin injections at 3, 8 and 13 weeks after turnout; Group 3, treated with ivermectin injections at 10, 15 and 20 weeks after turnout; Group 4, treated with a morantel slow release intraruminal bolus at turnout; Group 5, treated with a morantel slow release bolus at 10 weeks after turnout. Five animals from each group were slaughtered at the end of both grazing seasons. Two months after the end of the second season the remaining five calves were challenged with an experimental infection of 250,000 third-stage larvae (L3) of both Ostertagia ostertagi and Cooperia oncophora. All treatment regimes protected the respective calves from parasitic gastroenteritis. Over the 2 year observation period Groups 2 and 4 showed significantly better weight gain than other groups, and at the end of the first season, they were found to harbour significantly fewer O. ostertagi in the early fourth stage of development. During Year 1, Groups 2 and 3 excreted much lower percentages of Ostertagia spp. eggs than other groups. In Year 2, Group 2 excreted a higher percentage of Ostertagia spp. eggs although the total egg output was approximately half that of Group 1 during the same period. The results showed that the effects of anthelmintic suppression on egg output of different nematode species was affected by the activity of the anthelmintic used.

Chemosensory regulation of development in C. elegans

The dauer larva is a specialized third-larval stage of Caenorhabditis elegans that is long-lived and resistant to environmental insult. The dauer larva is formed in response to a high external concentration of a constitutively secreted pheromone. Response to the dauer-inducing pheromone of C. elegans is a promising genetic model for metazoan chemosensory transduction. More than 20 genes have been identified that are required for normal pheromone response. The functions of these genes include production of the pheromone, exposure of sensory neuron endings to the environment, structural and functional integrity of those sensory endings, and the capacity of sensory neurons to make appropriate output. Genetic evidence suggests that two partially redundant sensory pathways act in concert to control dauer formation. At least two classes of chemosensory neurons, ADF and ASI, are implicated in the pheromone response. On the basis of on these findings, a speculative model for the pheromone response is proposed. In this model, the neurons ADF and ASI are pheromone sensors that repress dauer formation in the absence of pheromone and derepress dauer formation in response to pheromone. It is currently unclear whether or not the two genetically defined sensory pathways both act in ADF and ASI.

Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism

Bulls and rams are notorious among stockmen and stud breeders for their apparently greater susceptibility than cows, ewes, steers or wethers to diseases caused by excessive infection with parasitic nematodes. Extension advice given to farmers generally includes a recommendation to treat entire male animals as though they were weaners. In contrast, the scientific literature contains little documentation of this fact, although the phenomenon has been well-described in laboratory animals. Scientific interest in the susceptibility of lactating cows and especially ewes to nematode parasitism has been more extensive, but unproductive in terms of elucidating responsible mechanisms. Where ewes have acquired immunity to nematode infection, they tend to lose it around the time of parturition and during lactation, with important epidemiological and productivity consequences. In strains of sheep selected for resistance to nematode infection, principally through a more rapidly acquired immune response, resistant ewes still undergo a periparturient loss of immunity but retain their relative superiority over unselected or susceptible ewes. The mechanisms involve effects of hormones associated with lactation on the immune system, but an unequivocal role for prolactin or any other hormone has not yet been identified. Collaboration between immunologists, endocrinologists and parasitologists is required.

Interactions of Ostertagia species with their bovine and ovine hosts

Ostertagia spp. affect their hosts in several complex interactions involving structural, biochemical, hormonal, nutritional and immunological mechanisms. Following infection with Ostertagia spp. the specialised secretory function and junctional integrity of gastric epithelial cells is lost. The pH of the abomasal contents is elevated and pepsinogen concentration in the plasma increases. There is a concurrent elevation in the concentration of blood gastrin. The effects may be a response to the physical interaction of parasite with epithelial cells, may be mediated through parasite excretory/secretory products, or by neural mechanisms. There may also be interactions between the responses since elevated abomasal pH stimulates secretion of gastrin. Hormonal changes may also have a role in the increased susceptibility of host to parasite during the periparturient period. Prolactin was considered the most likely hormone candidate although there is now a body of evidence to suggest that elevated prolactin concentrations are not solely responsible. Infection with Ostertagia spp. causes a marked inappetance, negative nitrogen balance and reduction in apparent gross energy digestion. The level of nutrition may also affect the response of the host to the parasites and establishment of O. circumcincta is lower in animals on a low plane of nutrition than those on a high plane. Immunity of Ostertagia spp. develops slowly and once established is manifest following challenge by an initial hypersensitivity response, followed by a cell mediated response and then an antibody response. Parasites may fail to establish or may be expelled from immune animals and if they do establish may be stunted with small vulval flaps and lower biotic potential and may become inhibited at the early fourth stage of development.

The presence of an early L4 larvae population in relation to the immune response of calves against Ostertagia ostertagi

The influence of different levels of infection with Ostertagia ostertagi on the development of a protective immune response in calves was investigated. Four groups of calves were infected with either 5000 (Group A), 10,000 (Group B), 20,000 (Group C) or 40,000 (Group D) infective larvae (O. ostertagi L3) weekly until treatment began. Group E functioned as controls. All animals were treated with oxfendazole (9 mg ml-1) at Week 17 (Groups A, B and E) or Week 18 (Groups C and D). Sixteen days post-treatment all calves received a challenge infection of 150,000 O. ostertagi L3 spread over 10 consecutive days. Faeces and blood were collected weekly for egg counts and to assess levels of pepsinogen, gastrin and IgG1 and IgG2 Ostertagia antibodies. All calves were necropsied 31 days post-challenge for worm counts. Egg counts and pepsinogen levels were proportional to the infection level during the first few weeks of the experiment. Only in the high-dosed Group D was a gastrin response evoked. Ostertagia IgG1 antibodies increased between Day 25 and Day 95, and in the non-infected control group an antibody rise was observed from Day 67 onwards. All measured parameters except Ostertagia antibodies showed a gradual decrease from Day 70 until the day of treatment. At necropsy there was no significant difference between the groups in the total worm populations. Only the composition of the worm populations differed, with 35% early L4 (EL4) larvae in the previously infected Groups A, B, C and D and only 5% in the control Group E. The results indicate a slow immune response against O. ostertagi in cattle and question the possible role of the EL4 stage in developing immunity.

An outbreak of haemonchosis associated with anthelmintic resistance in sheep

An outbreak of haemonchosis associated with anthelmintic resistance was recorded in a flock of 150 crossbred lambs. Closantel and ivermectin were 100% effective against Haemonchus contortus while fenbendazole and morantel reduced faecal egg counts by 87 and 29%, respectively. Levamisole showed an efficacy of 95%. At double the recommended dose (10 mg kg-1), fenbendazole had an efficacy of 99% against H. contortus infection. This appears to be the first report of an outbreak of haemonchosis associated with fenbendazole and morantel resistance in a strain of H. contortus in sheep.

Genetic structure of populations of Ostertagia ostertagi

Most genetic work to distinguish strains of parasitic helminths focuses on searching for genetic markers to correlate with phenotypes of interest, but in this study genetic diversity among individual Ostertagia ostertagi adults is partitioned into components within and between populations. Restriction fragment polymorphism data on mitochondrial DNA from ten individual worms from each of five different parasite populations are analyzed. Three of these populations are characterized by arrested larval development (hypobiosis) over the summer months, and the other two by hypobiosis over the winter months. Sequence divergence is scored by the presence or absence of 37 different restriction sites. Although the populations are genetically differentiated with respect to the timing of hypobiosis, greater than 98% of the total mitochondrial DNA sequence diversity is partitioned within a single population, and the geographic distribution of individual mitochondrial DNA haplotypes suggests high gene flow among populations. Further, estimates of within-population mitochondrial DNA diversity are five to ten times greater in O. ostertagi than typical estimates reported for species in other taxa.