Anthelmintic effects of forage chicory (Cichorium intybus) against gastrointestinal nematode parasites in experimentally infected cattle

Two experiments studied the effects of dietary chicory against gastrointestinal nematodes in cattle. In Experiment (Exp.) 1, stabled calves were fed chicory silage (CHI1; n = 9) or ryegrass/clover hay (CTL1; n = 6) with balanced protein/energy intakes between groups. After 16 days, all calves received 10 000 Ostertagia ostertagi and 66 000 Cooperia oncophora third-stage larvae (L3) [day (D) 0 post-infection (p.i.)]. In Exp. 2, calves were assigned to pure chicory (CHI2; n=10) or ryegrass/clover (CTL2; n = 10) pastures. After 7 days, animals received 20 000 O. ostertagi L3/calf (D0 p.i.) and were moved regularly preventing pasture-borne infections. Due to poor regrowth of the chicory pasture, CHI2 was supplemented with chicory silage. At D40 p.i. (Exp. 1) and D35 p.i. (Exp. 2) calves were slaughtered for worm recovery. In Exp.1, fecal egg counts (FEC) were similar between groups. However, O. ostertagi counts were significantly reduced in CHI1 by 60% (geometric mean; P < 0·01), whereas C. oncophora burdens were unaffected (P = 0·12). In Exp. 2, FEC were markedly lowered in CHI2 from D22 p.i onwards (P < 0·01). Ostertagia ostertagi adult burdens were significantly reduced in CHI2 by 66% (P < 0·001). Sesquiterpene lactones were identified only in chicory (fresh/silage). Chicory shows promise as an anti-Ostertagia feed for cattle and further studies should investigate its on-farm use.

Variations in T Cell Transcription Factor Sequence and Expression Associated with Resistance to the Sheep Nematode Teladorsagia circumcincta

This study used selected lambs that varied in their resistance to the gastrointestinal parasite Teladorsagia circumcincta. Infection over 12 weeks identified susceptible (high adult worm count, AWC; high fecal egg count, FEC; low body weight, BW; low IgA) and resistant sheep (no/low AWC and FEC, high BW and high IgA). Resistance is mediated largely by a Th2 response and IgA and IgE antibodies, and is a heritable characteristic. The polarization of T cells and the development of appropriate immune responses is controlled by the master regulators, T-bet (TBX21), GATA-3 (GATA3), RORγt (RORC2) and RORα (RORA); and several inflammatory diseases of humans and mice are associated with allelic or transcript variants of these transcription factors. This study tested the hypothesis that resistance of sheep to T. circumcincta is associated with variations in the structure, sequence or expression levels of individual master regulator transcripts. We have identified and sequenced one variant of sheep TBX21, two variants of GATA3 and RORC2 and five variants of RORA from lymph node mRNA. Relative RT-qPCR analysis showed that TBX21, GATA3 and RORC2 were not significantly differentially-expressed between the nine most resistant (AWC, 0; FEC, 0) and the nine most susceptible sheep (AWC, mean 6078; FEC, mean 350). Absolute RT-qPCR on all 45 animals identified RORVv5 as being significantly differentially-expressed (p = 0.038) between resistant, intermediate and susceptible groups; RORCv2 was not differentially-expressed (p = 0.77). Spearman’s rank analysis showed that RORAv5 transcript copy number was significantly negatively correlated with parameters of susceptibility, AWC and FEC; and was positively correlated with BW. RORCv2 was not correlated with AWC, FEC or BW but was significantly negatively correlated with IgA antibody levels. This study identifies the full length RORA variant (RORAv5) as important in controlling the protective immune response to T. circumcincta infection in sheep.

Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season

Gastrointestinal nematodes (GIN) infection can impair milk production (MP) in dairy cows. To investigate whether MP would be optimized by spring targeted-selective anthelmintic treatment in grazing cows, we assessed (1) the effect on MP of an anthelmintic treatment applied 1.5 to 2 months after turn-out, and (2) herd and individual indicators associated with the post-treatment MP response. A randomized controlled clinical trial was conducted in 13 dairy farms (578 cows) in western France in spring 2012. In each herd, lactating cows of the treatment group received fenbendazole orally, control cows remained untreated. Daily cow MP was recorded from 2 weeks before until 15 weeks after treatment. Individual serum pepsinogen and anti-Ostertagia antibody levels (expressed as ODR), faecal egg count and bulk tank milk (BTM) Ostertagia ODR were measured at treatment time. Anthelmintic treatment applied during the previous housing period was recorded for each cow. In each herd, information regarding heifers’ grazing and anthelmintic treatment history was collected to assess the Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving. The effect of treatment on weekly MP averages and its relationships with herd and individual indicators were studied using linear mixed models with two nested random effects (cow within herd). Unexpectedly, spring treatment had a significant detrimental effect on MP (-0.92 kg/cow/day on average). This negative MP response was particularly marked in high producing cows, in cows not treated during the previous housing period or with high pepsinogen levels, and in cows from herds with a high TEC or a high BTM ODR. This post-treatment decrease in MP may be associated with immuno-inflammatory mechanisms. Until further studies can assess whether this unexpected result can be generalized, non-persistent treatment of immunized adult dairy cows against GIN should not be recommended in early grazing season.

Infection with the gastrointestinal nematode Ostertagia ostertagi in cattle affects mucus biosynthesis in the abomasum

The mucus layer in the gastrointestinal (GI) tract is considered to be the first line of defense to the external environment. Alteration in mucus components has been reported to occur during intestinal nematode infection in ruminants, but the role of mucus in response to abomasal parasites remains largely unclear. The aim of the current study was to analyze the effects of an Ostertagia ostertagi infection on the abomasal mucus biosynthesis in cattle. Increased gene expression of MUC1, MUC6 and MUC20 was observed, while MUC5AC did not change during infection. Qualitative changes of mucins, related to sugar composition, were also observed. AB-PAS and HID-AB stainings highlighted a decrease in neutral and an increase in acidic mucins, throughout the infection. Several genes involved in mucin core structure synthesis, branching and oligomerization, such as GCNT3, GCNT4, A4GNT and protein disulphide isomerases were found to be upregulated. Increase in mucin fucosylation was observed using the lectin UEA-I and through the evaluation of fucosyltransferases gene expression levels. Finally, transcription levels of 2 trefoil factors, TFF1 and TFF3, which are co-expressed with mucins in the GI tract, were also found to be significantly upregulated in infected animals. Although the alterations in mucus biosynthesis started early during infection, the biggest effects were found when adult worms were present on the surface of the abomasal mucosa and are likely caused by the alterations in mucosal cell populations, characterized by hyperplasia of mucus secreting cells.

Identification and characterization of a novel specific secreted protein family for selected members of the subfamily Ostertagiinae (Nematoda)

It has been shown that the bovine abomasal parasite, Ostertagia ostertagi, drastically modulates its microenvironment, causing epithelial cell damage, accumulation of inflammatory cells and pH changes in the stomach. The mechanisms used by the parasite to change the abomasal environment are largely unknown, but an important role has been attributed to excretory-secretory (ES) products from the parasite. In this study we have identified proteins representing a novel ES protein family, characterized by the SCP/Tpx-1/Ag5/PR-1/Sc7 protein motif. These proteins were named Oo-AL1 and Oo-AL2 (O. ostertagi ASP-like protein). Both proteins contain a signal peptide and 1 predicted N-glycosylation site. The transcript for Oo-AL1 was present from the L4 stage onwards in both male and female adult worms, whereas the Oo-AL2 transcript was hardly detectable. Western blots of somatic extracts and ES products from different developmental stages of O. ostertagi, probed with anti-Oo-AL1 antibodies, revealed Oo-AL proteins in the ES products of adult worms. An analysis of the nematode genome and EST databases indicated that these novel ES proteins are unique to O. ostertagi and its relative, Teladorsagia circumcincta, suggesting a key function in these abomasal parasites.

Thermotolerance of L3 Ostertagia (Teladorsagia) circumcincta and some of its enzymes

Parasitic nematodes of ruminants can be expected to experience temperatures in excess of 40 degrees C in faeces on pasture and, perhaps, in the host. L3 Ostertagia (Teladorsagia) circumcincta survived for at least 90 min at 45 degrees C in vitro in water, but the larvae were inactivated rapidly by only slightly higher temperatures. The glycolytic enzymes hexokinase and pyruvate kinase were inactivated in a similar temperature range, whereas malate dehydrogenase maintained its activity at temperatures in excess of 50 degrees C. These data imply that the loss of glycolytic activity might explain the loss of larval motility at temperatures between 45 degrees C and 50 degrees C.

Mathematical models to assess strategies for the control of gastrointestinal roundworms in cattle

Mathematical models were constructed to simulate the effect of Ostertagia ostertagi infections on the growth of young cattle. The equations are based on System Dynamics using the DYSMAP 2 software package in their construction. A pasture and animal growth model simulates the growth of pasture and the influences of management and climate on it; cattle feed intake and conversion into energy for maintenance and liveweight gain; the effect of the parasite burden on feed intake and utilization of energy. This model was then combined with one of the life cycle of O. ostertagi in order to determine the effect of worm burdens on animal growth rate in a range of farm conditions, such as stocking rate, grazing history of the pasture, and rainfall. By converting the resultant liveweight gain into a monetary value, an economic assessment of alternative worm control strategies can be made. In this paper the construction of the models with equations and assumptions is given in detail.

Toxicity of Bacillus thuringiensis to parasitic and free-living life-stages of nematode parasites of livestock

A collection of Bacillus thuringiensis (Bt) strains (Bts) were screened for activity against the free-living larval stages of nematode parasites of livestock. Two strains were identified with significant activity in inhibiting larval development of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta. These strains were also toxic to the adult parasitic stages of these nematode species in vitro. Adult H. contortus and O. circumcincta showed complete cessation of movement within 2 and 4 days, respectively. Trichostrongylus colubriformis adults were less affected, however, movement was still significantly reduced compared with controls. The in vitro activity against the larval stages was of a magnitude similar to or greater than that seen with the anthelmintic drugs thiabendazole and levamisole. N-terminal amino acid sequencing indicated that the two Bts contained either Cry5A and Cry5B proteins, or a Cry13 protein, and the presence of the corresponding cry5A, cry5B and cry13 genes was confirmed by PCR and sequencing. Bacillus thuringiensis spore-crystal suspensions exposed to acidic pH conditions (pH<or=3) showed greatly reduced toxicity in subsequent bioassays with nematode larvae, highlighting the need to protect the toxin from the acidic conditions of the sheep abomasum if it were to be administered per os as an anthelmintic. This study indicates that both the parasitic adult stages and the free-living larval stages of economically significant nematode parasites are susceptible to the effects of Bt, thus identifying this group of toxins as potential biocontrol agents.

An aspartyl protease inhibitor of Ostertagia ostertagi: Molecular cloning, analysis of stage and tissue specific expression and vaccine trial

Protease inhibitors are thought to protect intestinal parasitic nematodes from their hostile proteolytic environment. In a previous study, screening of Ostertagia ostertagi cDNA libraries with local antibody probes of the abomasal lymph nodes and mucus revealed a (28 kDa) aspartyl protease inhibitor (API), which was exclusively recognised by antibodies from immune calves. Here we report the molecular characterization of Oo-API (sequence analysis, developmental expression and localization) and a vaccine trial in cattle with the native and recombinant baculo-expressed antigen. The full-length open reading frame of api encodes a protein of 28 kDa. The sequence showed 82% significant homology to an Aspin homologue from Trichostrongylus colubriformis (AA034715). The cDNA encoding the full-length sequence was cloned in a bacterial pET expression vector and the pVec 35 baculovirus vector. Polyclonal rabbit serum against the Escherichia coli-expressed protein was used to develop Western Blots of extracts and ES and to localize the antigen on L3, L4 and adult worm sections. The protein was expressed in all life stages, which was confirmed by real-time polymerase chain reaction (RT-PCR), and was mainly localized in the cuticle of L3, the intestinal cells of L4, and the gut and sphincter of adult worms. Polyclonal serum was also used to affinity purify the native protein. Vaccination of calves with native Oo-API and baculovirus-expressed Oo-rbAPI in combination with QuilA resulted in no protection against Ostertagia challenge infections.

Identification of excretory-secretory products of larval and adult Ostertagia ostertagi by immunoscreening of cDNA libraries

Excretory-secretory (ES) products of Ostertagia ostertagi, an abomasal nematode of cattle, are considered to be important for the development and survival of the parasite within the host. To gain insight in the composition of these ES products of both larval (L3, L4) and adult life stages of Ostertagia cDNA libraries of the parasite were immunoscreened with polyclonal rabbit serum raised against these ES products. This approach led to the identification of 41 proteins, amongst which are structural proteins such as actin, kinesin and vitellogenin, housekeeping proteins such as those involved in protein folding, different metabolic pathways or mitochondrial functioning and proteins associated with stress (heat shock protein) or antioxidantia (thioredoxin peroxidase). A large number of the isolated proteins were similar to hypothetical proteins of the model nematode Caenorhabditis elegans. Because somatic proteins can be non-specifically released during in vitro culturing as nematodes deteriorate, it was checked if the isolated proteins are genuinely secreted. The amino acid sequences of the translated cDNAs were investigated for signal peptides and monospecific antibodies against the isolated proteins were purified and used to develop Western blots of ES and somatic extracts. In this manner it could be proven that 15 cDNAs code for genuine secreted proteins. The identification of these ES antigens allows to select proteins with potential protective capacities, which are targets for vaccine development.

Increased burdens of drug-resistant nematodes due to anthelmintic treatment

Nine groups of lambs were challenged with 500 drug-resistant (R) Ostertagia circumcincta infective-stage larvae (L3) twice-weekly for 6 weeks; 3 of the groups were also given 500 susceptible (S) L3 and another 3 given 3000 L3 twice-weekly. One week prior to parasite challenge, 1 group of each dose rate was administered ivermectin-capsules (IVM-CRCs). Following challenge, a second group from each dose rate was administered oxfendazole to remove susceptible parasites. The remaining groups received no drug treatment throughout the trial. No significant difference in faecal egg count was observed between the groups. The groups left untreated did not differ significantly in resulting worm burden. However, the percentage of the total L3 challenge recovered as 4th-stage larvae or adult worms demonstrated a density-dependent relationship and declined with increasing challenge. Those groups treated with anthelmintic to remove S worms prior to necropsy also showed density dependency as worm burdens were lower at the highest dose rate. In the groups administered IVM-CRCs, no dose-dependent effect on worm burden was observed. These differences resulted in more worms being present at the highest dose rate in the IVM-CRC-treated animals than in those animals treated orally with anthelmintic. Adult female worms from the IVM-CRC high challenge group were significantly longer and contained more eggs in utero than those in the other high challenge groups. These results demonstrate that where resistance is present, IVM-CRCs can modify the density-dependent regulation of the parasite population, resulting in the acquisition of larger resistant worm burdens than might otherwise be expected. This could accelerate the build-up of resistant worm populations and decrease the time until treatment failure.

The role of parasites in the dynamics of a reindeer population

Even though theoretical models show that parasites may regulate host population densities, few empirical studies have given support to this hypothesis. We present experimental and observational evidence for a host-parasite interaction where the parasite has sufficient impact on host population dynamics for regulation to occur. During a six year study of the Svalbard reindeer and its parasitic gastrointestinal nematode Ostertagia gruehneri we found that anthelminthic treatment in April-May increased the probability of a reindeer having a calf in the next year, compared with untreated controls. However, treatment did not influence the over-winter survival of the reindeer. The annual variation in the degree to which parasites depressed fecundity was positively related to the abundance of O. gruehneri infection the previous October, which in turn was related to host density two years earlier. In addition to the treatment effect, there was a strong negative effect of winter precipitation on the probability of female reindeer having a calf. A simple matrix model was parameterized using estimates from our experimental and observational data. This model shows that the parasite-mediated effect on fecundity was sufficient to regulate reindeer densities around observed host densities.

The population dynamics of Ostertagia gruehneri in reindeer: a model for the seasonal and intensity dependent variation in nematode fecundity

The gastrointestinal nematode Ostertagia gruehneri is a parasite of reindeer that can have a significant impact on host population dynamics. To gain a better understanding of the population dynamics of O. gruehneri, we parameterise a model for its fecundity that describes the observed seasonal and intensity dependent pattern of faecal egg counts well. The faecal egg count model is combined with a model for the seasonal faecal production rate of Svalbard reindeer to obtain quantitative estimates of the fecundity of O. gruehneri. The model is used to evaluate the relative contribution to pasture contamination of variation in the abundance of O. gruehneri and variation in reindeer densities. It is concluded that due to the intensity dependence in nematode fecundity, variation in reindeer population densities is likely to be the most important of these factors for pasture contamination.

The effect of feeding sulla (Hedysarum coronarium) or lucerne (Medicago sativa) on lamb parasite burdens and development of immunity to gastrointestinal nematodes

Two experiments investigated the efficacy of the legume Hedysarum coronarium (sulla), which contains condensed tannins (CTs), for reducing gastrointestinal nematode infections relative to lucerne. Experiment 1 was aimed to show whether the lower faecal egg count (FEC) and larval establishment previously reported in lambs grazing sulla were due to direct effects of the forage on Ostertagia circumcincta and Trichostrongylus colubriformis or were mediated through an enhanced immune response. Experiment 2 evaluated the impact of feeding sulla relative to feeding lucerne (Medicago sativa), before, at, or after larval challenge on subsequent FECs and nematode burdens. In experiment 1, 64 Romney lambs were fed either freshly cut lucerne or sulla (32 lambs per herbage) for the duration of the trial. Within each herbage there were four treatment groups (n=8 per group). Initial levels of immunity were assessed in uninfected (UN) lambs which were maintained parasite-free until challenged with 15,000 O. circumcincta and 15,000 T. colubriformis larvae on day 63, and slaughtered on day 81. The other three treatment groups were trickle-infected with each of 5000 O. circumcincta and 5000 T. colubriformis larvae three times per week from day 1 to 35. Non-steroid infected (CONTROL) and steroid-treated (STER) groups were treated with anthelmintic on day 49 and challenged with 15,000 O. circumcincta and 15,000 T. colubriformis on day 63 and slaughtered on day 81. The STER lambs were given dexamethasone trimethylacetate from day 49 to 81 to determine effects of immunity on parasite infection. From day 35 an establishment group (EST) on each herbage was fed a common pelleted lucerne diet and slaughtered on day 56 to determine nematode establishment during trickle-infection. Diet did not affect FECs but feeding lucerne increased (P<0.05) numbers of T. colubriformis in CONTROL lambs compared to those fed sulla. O. circumcincta numbers were lower (P<0.05) in UN lambs fed sulla than lucerne. The sulla diet was associated with higher (P<0.05) antibody titres against secretory-excretory antigens to adult O. circumcincta and to adult and larval T. colubriformis, so there appeared to be some immunogenic response to the sulla diet but effects upon T. colubriformis numbers were not significant. The second experiment involved 48 Romney lambs grazing conventional pasture which were infected with 10,000 each of O. circumcincta and T. colubriformis larvae either 7 days before, 7 days after, or at the time they commenced grazing either sulla or lucerne. Lambs which grazed sulla had lower (P<0.05) FEC and lower (P<0.05) O. circumcincta burdens than lambs which grazed lucerne but timing of infection had no effect on FEC or worm burdens. T. colubriformis numbers were not affected by treatment or herbage. In conclusion, the sulla diet resulted in lower O. circumcincta numbers compared to lucerne outdoors and some evidence of an immunogenic response was obtained indoors. However, neither the herbage nor the immunogenic response reduced T. colubriformis numbers in either experiment.

Effect of Ostertagia circumcincta excretory/secretory products on gastrin release in vitro

It has been suggested that parasite excretory/secretory (ES) products may be capable of direct stimulation of gastrin secretion and of contributing to the hypergastrinaemia typical of abomasal parasitism. Ostertagia circumcincta ES products were tested on an ovine antral mucosal preparation which had been developed for a pharmacological study of gastrin secretion in the sheep. Its responsiveness to chemical stimulation was established by stimulation with amino acids and amines: tryptophan (0.1-5 mM) and phenylalanine (10-100 mM) stimulated gastrin release (151-160 and 117-129%, respectively), whereas glycine (0.1-100 mM) was without effect; ammonium sulphate, but not sodium sulphate, stimulated gastrin release in concentrations from 1mM (122%) to 50mM (148%). ES products were prepared by incubation of exsheathed third-stage larvae (L3) or parasites recovered on Day 8 p.i. (L4), Day 12 p.i. (10% L4, 90% immature adults), Day 21 p.i. (5% L4, 30% immature adults, 65% adults), Day 22 p.i. (20% immature adults, 80% adults), Day 30 p.i. (adults) and Day 35 p.i. (adults), or a mixed-age parasite population. Worms were recovered from agar and incubated in either distilled water or Hank's balanced salt solution (HBSS) adjusted to pH 2.5, 3.5, 4.5, 5.0 or 7.4. HBSS pH 7.4 was also prepared with antibiotics, without glucose, and with antibiotics but without glucose. Survival of Day 21 and 35 worms and exsheathed L3 in water or in a series of HBSS adjusted to pH 2.5, 3.5, 4.5, 5.0 or 7.4 was assessed from the percentage of motile parasites. L3 slowly became immotile over several days except in HBSS pH 2.5, in which survival was reduced, whereas adult worms did not tolerate incubation at 37 degrees C in water or HBSS at pH 2.5, retained motility for about 2 days at pH 3.5, but survived well at pH 4.5 and above. Incubates prepared from all stages of O. circumcincta, both in media favourable and unfavourable for parasite survival, failed to stimulate consistently the secretion of gastrin by tissue from both parasite-naive and previously exposed sheep, whereas a considerable number of incubates were significantly inhibitory. The inhibitor may not be produced by the nematodes, but by contaminating abomasal or environmental microflora, as inhibitory activity was predominantly generated by prolonged incubation, it was less potent when glucose was omitted and was not present in media containing antibiotics. This study did not find evidence for a gastrin stimulant in O. circumcincta ES products, but did demonstrate the acid intolerance of adult worms and suggests that abomasal microbes may be capable of modulating the secretory activity of the host digestive tract.

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.

Ecology of the free living stages of cattle nematodes during summer contamination in Argentina Western Pampas

Development, migration and survival of infective larvae (L3) were studied in the Western Pampeana Region. Faeces of naturally nematode infected cattle were deposited as artificial pats on plots during mid-spring-summer of 1994/1995 and 1995/1996. Since the start and during 1995, the study coincided with a severe drought, rainfalls being 29% below the 45-year means. The predominant genera recovered were Cooperia, Ostertagia and Haemonchus. Initial and peak recovery of L3 from pats occurred 8-15 and 15-21 days later respectively. A low percentage of L3 survived from November (0.3% L3) and January (0.06% L3) to the following autumn and winter. The mean persistence of larvae detected in pats or herbage was around 200 days from deposition. The migration of L3 from faecal pats to herbage started 15 to 30 days after deposition according to rainfall occurrence. Maximum herbage recoveries of L3 from pats deposited in late summer occur during autumn rainfalls. Only, few L3 were occasionally recovered from soil. Summer conditions were associated with rapid development and translation of L3 to herbage, but also with low L3 detection after initial recoveries. Faecal pats deposited from mid-summer were the main source of autumn herbage contamination.

Evidence for a parasite-mediated inhibition of abomasal acid secretion in sheep infected with Ostertagia leptospicularis

The acid secretory capacity of the abomasal mucosa was studied in sheep experimentally infected with Ostertagia leptospicularis. The acidity of the abomasal contents, permanently recorded by a pH probe located inside the abomasum, decreased markedly to mean levels between pH 5 and 6. Subcutaneous administration of histamine or carbachol successfully stimulated acid secretion (pH 3.4). The results indicate that the abomasal mucosa harboured a population of functional parietal cells which were also identified immunohistochemically (H(+)/K(+)-ATPase). Ultrastructural investigation before stimulation revealed that the majority of these cells was in a resting state. Despite high serum gastrin levels, the acid secretion was blocked either at the level of the parietal cell or the enterochromaffin-like cell by an unknown factor, possibly mediated by the parasites. This is the first report of a parietal cell dysfunction associated with a nematode infection in the abomasum. It is suggested that the parasites induce changes in their environment which favour their survival and/or increase their reproduction.

Life-history strategies and population dynamics of abomasal nematodes in Svalbard reindeer (Rangifer tarandus platyrhynchus)

The observation that the total abundance of adult nematodes in the abomasum of Svalbard reindeer increases between October and April suggests adaptation to cope with the Arctic winter. Here we investigate the extent to which selection has led to similar life-history strategies in the 3 most numerous trichostrongyle species. The life-histories are found to differ markedly. We use flexible statistical models for the abundance and dispersion of parasites in the host population. One of the taxa, Marshallagia marshalli, was most abundant and had its highest egg output in the winter. In contrast, the abundance of the most common taxa, Ostertagia gruehneri, m. gruehneri was stable or declined from autumn to late winter, and the closely related taxa, O. gruehneri, m. arcticus, showed a similar over winter drop. The faecal egg output of these 2 taxa was highest in summer, as found in temperate trichostrongyle species. Despite the apparent contamination of summer pastures with O. gruehneri, calves showed negligible burdens until their second summer and the abundance of infection reached an asymptote within their third year. In contrast, the abundance of M. marshalli in calves showed a rapid increase over the first summer and by late winter was similar to peak levels found in adults (8000 worms). This increase could not be accounted for by the developing abomasum larvae population and is therefore evidence for transmission over the winter for this taxa. While M. marshalli showed little between-year variation, O. gruehneri showed 2-fold fluctuation in the abundance of infection. O. gruehneri may therefore play a role in the fluctuating population dynamics of the host. Since there was no apparent decline in abundance with host age in any of the 3 taxa there was no evidence of reindeer mounting an immune response.

How lambs control infection with Ostertagia circumcincta

Two of the most important questions for immunologists studying nematode infections are what effect does the host response have on the parasite and which components of the host response are responsible for these effects. The number of nematodes and the mean length of adult female Ostertagia circumcincta was measured in over 500 6-7 month old lambs of the Scottish Blackface breed. Quantitative genetic analyses indicated that there was substantial genetic variation among lambs in faecal egg counts and in worm length but the analyses provided no evidence for genetic variation in worm numbers. Separate analyses have shown a strong relationship between decreased worm length and decreased worm fecundity. Therefore, genetic resistance in lambs appears to be due to control of worm growth and not to control of worm numbers. The only immune response that is consistently associated with reduced worm length is the IgA response to fourth-stage larvae. The association is remarkably strong. After allowing for the influence of worm number on worm length (density-dependence) essentially all of the variation among deliberately infected lambs in worm length can be accounted for, in a statistical sense, by variation in the strength and specificity of the local IgA response. Therefore, the IgA mediated suppression of worm growth and fecundity appears to be the major mechanism of resistance to O. circumcincta in lambs.

The curvilinear relationship between worm length and fecundity of Teladorsagia circumcincta

The variation among sheep in fecundity of Teladorsagia (Ostertagia) circumcincta was estimated by dividing the faecal egg count by the worm number following deliberate infection of mature Scottish Blackface lambs. Fecundity was skewed and ranged from 0 to 350 eggs per worm per day. Most animals had relatively low worm fecundities, but a small number of individuals had relatively high worm fecundities. However, as fecundity is a ratio of two imprecise estimates, extreme values may be statistical artefacts. Following both deliberate and natural infection, differences in worm fecundity were associated with differences in adult female worm length. In both infections, fecundity varied with worm length to the power 0.4. This relationship should assist the measurement of fecundity in studies of host immunity, in epidemiological modelling and in estimating the influence of density-dependent relationships.

Mechanisms underlying resistance to nematode infection

Lambs show considerable genetic variation in faecal egg count following natural, predominantly Ostertagia circumcinta infection. This genetic variation is acquired and not innate. Worm length is positively associated with worm fecundity. The genetic variation in faecal egg count is a consequence of genetic variation in worm length and hence worm fecundity, and not of genetic variation in worm burdens. In contrast to lambs, mature sheep may be able to regulate both fecundity and worm numbers. In lambs, three factors account for the majority of the variation in worm length: the strength of the local IgA response against fourth-stage larvae, the specificity of this response against four molecules in particular, and the density-dependent influence of worm number.

Variation between hosts in the developmental success of the free-living stages of trichostrongyle infections of sheep

Variation between hosts of different ages and genotypes in the developmental success of trichostrongylid parasite eggs from sheep was investigated in two trials. The percentage development to infective third-stage larvae of eggs collected from lambs and adult ewes infected with Ostertagia circumcincta was compared in an indoor trial. In addition, sheep previously bred for either high or low faecal egg count and grazed outdoors on parasite contaminated pasture were sampled; egg development, faecal egg count, generic profile and faecal dry matter were measured. In both trials, development to L3 was significantly lower in eggs derived from adult ewes than from lambs and, in the field trial, from animals selected for low faecal egg count. The observed differences could not be accounted for by variations in faecal egg count, faecal dry matter content nor by differences in the generic composition of worm egg output. Although not shown conclusively, the results are consistent with an immune mechanism influencing the development of free-living stages of gastrointestinal nematodes outside the host. These results have significant implications for our understanding of parasite epidemiology, particularly as it relates to sources of pasture contamination.

Establishment and fecundity of Ostertagia circumcincta and Trichostrongylus colubriformis in lambs fed lotus (Lotus pedunculatus) or perennial ryegrass

Forty four 12-14 week old Polled Dorset ram lambs, raised helminth free from birth, were used to investigate the effects of condensed tannins (CT) in lotus (Lotus pedunculatus) on lamb growth and gastrointestinal nematode establishment and fecundity. Condensed tannins bind to proteins in the rumen and increase the flow of protein to the intestines. Lambs were allocated to either a ryegrass (Lolium perenne) or lotus diet fed ad libitum, with or without twice daily drenching of polyethylene glycol (PEG) which binds with and deactivates the CT. One week after allocation to the diets, each lamb was infected per os with 10,000 Ostertagia circumcincta and 10,000 Trichostrongylus colubriformis larvae and slaughtered 28 or 29 days later. Lambs fed lotus had lower faecal egg counts (P < 0.0001) and lower O. circumcincta burdens (P < 0.001), fewer female O. circumcincta (P < 0.0001) and higher faecal dry matter (P < 0.001) than lambs fed ryegrass, but numbers of T. colubriformis nematodes were not affected. This trial did not ascribe beneficial effects of L. pedunculatus to CT per se and the use of PEG does not seem appropriate to studies of parasitology.

Stochastic effects in a model of nematode infection in ruminants

We illustrate the importance of stochastic effects in population models of biological systems and demonstrate a number of analytic and simulation-based approaches that can usefully be applied to such models. In so doing, we compare the stochastic approach to the more usual deterministic one. The model studied represents the gastrointestinal infection of ruminants by nematodes when the hosts maintain a fixed density. The incorporation of a feedback mechanism, which accounts for the immune response of the infected animals, results in a highly nonlinear model; similar forms of nonlinearity are a feature of many plausible models in population biology. In the absence of an analytic solution to the full stochastic model we explore a number of approximations and compare them to simulations of the full stochastic process. We explore three modes of behaviour of the system. In the endemic regime the stochastic system fluctuates widely around the non-zero fixed points of the deterministic model. In the managed regime, where the system is subject to external periodic perturbation, stochastic effects are negligible. Finally, we find that in a regime in which the deterministic model predicts the long-term persistence of oscillations the stochastic model shows that extinction can occur. Of the approximation procedures we consider, the Normal approximation to the full stochastic process is the most generally applicable, and it is also the most accurate in the light of simulation results. Local linearization provides reasonably accurate prediction of the variance-covariance structure, and a transfer function approach allows calculation of the time-lagged auto- and cross-correlations in the endemic regime. Linearization of the stochastic updates themselves results in poor prediction of the population variances.

Efficacy of a pour-on formulation of eprinomectin (MK-397) against nematode parasites of cattle, with emphasis on inhibited early fourth-stage larvae of Ostertagia spp

OBJECTIVE

To evaluate efficacy of topically applied eprinomectin against inhibited early fourth-stage larvae (IL4) of Ostertagia spp in calves.

ANIMALS

4 groups (n = 6 [replicates]) for dose titration; 2 groups (n = 8 calves [replicates]) for dose confirmation.

PROCEDURE

2 dose titration studies-0, 125, 250, and 500 micrograms of eprinomectin/kg of body weight-Louisiana and Georgia- and 2 dose confirmation studies of selected therapeutic dosage (500 micrograms/kg) in Scotland and France. Monitor calves were used to determine inhibition percentage of Ostertagia IL4. Test calves were ranked by weight in replicates of 4 (titration trials) or 2 (confirmation trials) animals each, and within replicates, were randomly allocated to treatment groups. Drug treatments were done on day 0, and animals were euthanatized by replicate, with holding time between treatment and euthanasia varying among trials from 14 to 27 days.

RESULTS

Observations indicated high efficacy (> 99%) of 500 micrograms of eprinomectin/kg in removal of Ostertagia IL4. Ostertagia and Cooperia were only genera common across sites, with efficacy of aforementioned dosage against adult and larval stages of both genera consistently high (> 99%). Results of 1 or both titration studies (500 micrograms/kg) indicated > 99 to 100% efficacy against adult Haemonchus placei, Trichostrongylus axei, T colubriformis, Bunostomum phlebotomum, Dictyocaulus viviparus, and Oesophagostomum radiatum. Lower efficacy values were observed at minimal (125 micrograms/kg) dosage. In France, 500 micrograms/kg was 85% effective against Trichostrongylus spp adults; however, numbers of control calves infected with Trichostrongylus spp and degree of infection were low. Adverse reactions were not evident.

CONCLUSION

Eprinomectin given topically (500 micrograms) was highly effective against Ostertagia IL4 and other common nematodes of cattle.

Induction of traps by Ostertagia ostertagi larvae, chlamydospore production and growth rate in the nematode-trapping fungus Duddingtonia flagrans

Biological control of parasitic nematodes of domestic animals can be achieved by feeding host animals chlamydospores of the nematode-trapping fungus Duddingtonia flagrans. In the host faeces, D. flagrans develop traps that may catch nematode larvae. In experiments on agar, D. flagrans had a growth rate between 15 and 60 mm/week at temperatures between 20 and 30 degrees C. The presence of nematodes induces the fungus to produce traps. The rate of trap formation in D. flagrans has an optimum at 30 degrees C, producing 700-800 traps/cm2/2 days, when induced by 20 nematodes/cm2 on agar. Approaching 10 and 35 degrees C the ability to produce traps is gradually reduced. The response of chlamydospore production on agar to changes in temperature is the same as that for trap formation. On agar, at 10, 20 and 30 degrees C D. flagrans loses its trap inducibility after 2-3 weeks. During the ageing process, increasing numbers of chlamydospores are produced up to a certain limit. The time for reaching maximum chlamydospore concentration coincided with the time for loss of induction potential. The implications of these results in relation to biological control in faeces are discussed.

The effect of truncated infections with Ostertagia ostertagi on the development of acquired resistance in calves

The relative contribution of the third (L3), fourth (L4) and adult stages of Ostertagia ostertagi to the development of immunity was assessed in calves which were either continuously infected during 21 weeks or subjected to infections truncated by anthelmintic treatment at the L3 or L4 stage. A fourth group remained uninfected (control group). Faecal samples and blood samples were collected weekly for faecal egg counts and determination of pepsinogen and antibody levels. Only the continuously infected animals showed positive egg counts, which fell towards the end of the primary infection period. Pepsinogen and antibody levels remained high in the continuously infected group until the end of the primary infection period. At that time, they were significantly higher compared to the control calves, with intermediate values in the truncated infection groups. After the 21 weeks primary infection period all animals were dewormed. To evaluate the protection provided by the different immunisation protocols, all animals were challenged 1 week later with 156000 Ostertagia L3, spread over 12 consecutive days. The marked reduction in egg counts following challenge infection indicated a certain degree of immunity in the continuously infected calves, which was confirmed at necropsy by the reduced worm burdens, the high percentage of inhibited early L4 larvae, the reduced size of the adult worms and the higher numbers of mucosal mast cells in this group. Numbers of globule leucocytes and eosinophils were not significantly different from the control group. Infections truncated by anthelmintic treatment elicited poor development of immunity as shown by the egg output after the challenge infection and the percentages of arrested larvae and the lengths of adult worms which were intermediate to those of the continuously infected calves and control animals.

Infection of sheep with adult and larval Ostertagia circumcincta: effects on abomasal pH and serum gastrin and pepsinogen

Infection of sheep with adult or larval O. circumcincta increased serum pepsinogen and gastrin and abomasal pH. The upper limits of the normal range, calculated from over 1000 samples collected from parasite-naive sheep, were set at 2 standard deviations above the mean; these were for serum pepsinogen, 454 mU tyrosine l-1; serum gastrin, 64 pM and abomasal pH, 3.26. Five infection regimes were used: sheep previously exposed to field parasitism were infected with 30,000 larvae intraruminally (Group A), while parasite-naive sheep were administered either 50,000 larvae intraruminally (Group B), 150,000 larvae intraruminally followed by a trickle infection of 10,000 larvae thrice weekly from days 21 to 45 (Group C), 150,000 exsheathed larvae via an abomasal cannula (Group D) or 15,000 adult worms via an abomasal cannula (Group E). Whereas the presence of adult worms rapidly increased serum pepsinogen (after 8 h) and abomasal pH and serum gastrin (after about 19 h), the early infective larval stages, regardless of the infection regime, had minimal effects until the abrupt rise in all parameters 5-6 days after infection. Abomasal pH returned to near normal levels when the infections became patent and was not re-elevated by a subsequent trickle infection, whereas serum gastrin and pepsinogen remained high. The initial hypergastrinaemia was coincident with the increased abomasal pH, but was preceded by the increase in serum pepsinogen. In several sheep, serum pepsinogen increased very little during the parasitism, although there were typical effects on abomasal pH and serum gastrin. Serum gastrin was depressed when the abomasal pH exceeded about 5.5. It is suggested that an inhibitor of gastrin release is generated by proliferating abomasal microbes under these conditions and that this is a limitation to the use of elevated serum gastrin in the diagnosis of parasitism in individual sheep.

The length of strongylid nematode infective larvae as a reflection of developmental conditions in faeces and consequences on their viability

Isolates from eight gastro-intestinal nematode species of sheep, cattle and deer parasites were maintained in sheep and faecal cultures were processed at different temperatures (for four species) and moistures (for the eight species). For all the tested species, the third-stage larvae (L3) were longer at temperatures optimal for development and their length increased linearly with faecal moisture contents (FMC). These variations in length mainly concerned the volume of intestinal cells. The length of L3 had no consequence on their survival in water at room temperature (five species tested), but the short L3 migrated more slowly on agar gel than did the longer ones (verified for three species) and exsheathed more slowly (verified for two species). The establishment rate observed for short L3 of Teladorsagia circumcincta in lambs was lower than that seen for long L3 in three other lambs, but the developed worms were similar in length and fecundity. These results are relevant to our understanding of how the different species could adapt to and/or compensate for adverse conditions of development.

Viability of infective larvae of Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus colubriformis following exsheathment by various techniques

Various techniques were examined to determine optimum conditions for exsheathing infective larvae of 3 important ruminant parasites (Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus colubriformis). In repeated experiments, aliquots of 10(5)-10(6) infective larvae, 1-2 mo old, of each parasite were incubated in each of 4 exsheathing media (distilled water, Earle's balanced salt solution + carbon dioxide, nematode washing buffer + carbon dioxide, or sodium hypochlorite) for 1 or 18 hr. In each case, the percentage of larvae exsheathed and infectivity for jirds was determined. Results of these studies indicate that no single exsheathing technique of those studied is optimum for every parasite. In addition, caution must be used in drawing conclusions from in vitro studies using exsheathed larvae because techniques that routinely provide high percentages of exsheathment also appear to reduce viability.

Interaction between Ostertagia circumcincta and Haemonchus contortus infection in young lambs

Twenty-one-week-old, worm-free, pen-reared lambs were infected with either 6000 O. circumcincta L3 per week, or 3000 H. contortus L3 per week, or both (9000 L3 per week). Egg counts were monitored throughout the experiment, and worm burdens and larval establishment rates of both worm species were estimated after 4, 7, 10 and 13 weeks of infection. After 10-13 weeks of infection with H. contortus only, establishment of O. circumcincta was lower than in previously uninfected controls, demonstrating that a high level of immunity to H. contortus affords some cross-protection against O. circumcincta. Total H. contortus worm burdens and egg counts (about 2000 worms and 3000 e.p.g., respectively) in sheep infected with both worm species were less than half those observed in sheep infected with H. contortus alone (about 5000 worms and 10,000 e.p.g., respectively). Cross-protection between the two species was observed, but was probably less important than the reduction in H. contortus establishment that was caused by O. circumcincta disrupting abomasal physiology.

Description of Ostertagia ostertagi and Ostertagia leptospicularis hybrids in experimentally infected sheep

Hybrids of Ostertagia ostertagi and Ostertagia leptospicularis, derived from experimental infections in sheep, are described. Morphometrics of the hybrids were intermediate between those of parental lines for a large range of parameters (distance from apex to cervical papillae and length of esophagus for males and females, length of spicules for males, and length of vestibule, distance from vulva to the end of tail, width of tail at anus). The morphological relationship between hybrids and their parent species was assessed by discriminant analysis based on the relative values of these parameters (actual value/length of the worm). Each parental line, either bred in sheep or in the natural host, was morphologically similar and differed from hybrids.

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.

Epidemiology of Ostertagia in the Northwestern USA

The two most significant environmental factors that influence the epidemiology of Ostertagia are temperature and moisture. These factors vary more in the west and northwest than in any other part of the USA because of extreme regional differences in climate, topography, and land use. Consequently, patterns of Ostertagia transmission and inhibition also vary widely from region to region and from year to year. Recent data require revisions of previously accepted concepts of northern/southern transmission and inhibition. In particular, the flaw of liberal extrapolation of information from one region to another has now been recognized. Inhibition may not occur along the coast of the Pacific Northwest. Although not completely delineated, the transition zone between northern and southern patterns of inhibition appears to be significantly wider and more variable than previously recognized; Oregon data suggest a possible indeterminate and variable band extending north of the 45th parallel and south of the 43rd parallel. Summer inhibition has now been documented in areas of Oregon and Montana. Other than the recent Oregon and Montana studies, data on this transition zone in the Rocky Mountain region and high plains are sparse to non-existent. In contrast to previously accepted doctrine, the fall rise in egg count generally exceeds the traditionally accepted spring rise in many areas. From the Pacific Northwest to the Midwest, year-round transmission patterns have been observed. The presence of geothermal ground water sources produces microclimates that favor larval survival in many areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Mathematical models for the population biology of Ostertagia ostertagi and the significance of aggregated parasite distributions

Parasite frequency distributions are frequently aggregated. Such distributions are conveniently described using the negative binomial frequency distribution. This distribution is completely characterized by two parameters: the mean of the distribution and an exponent, k. The degree of aggregation is inversely proportional to the value of k. Aggregated parasite distributions enhance the ability of regulatory processes to maintain parasite populations at or near their equilibrium level but incorporating parasite frequency distributions in realistic models of parasite population biology is fraught with difficulty (several simplified examples are given). Indeed, it is not always possible to incorporate parasite frequency distributions and the question arises whether this compromises model performance. Trichostronglyid nematodes, including Ostertagia ostertagi, are aggregated but the estimated value of k for such populations is usually greater than 1. This is typical of populations with high population means (tens of thousands). It is shown that when the degree of aggregation is such that k > 1, the results of a model which recognizes parasite frequency distribution is not much different from the results of a model which assumes all hosts contain exactly the same number of parasites.

The role of inhibited development in the epidemiology of Ostertagia infections

Seasonal patterns of inhibited larval development have been described for Ostertagia spp. from many parts of the world; winter inhibition is found in areas where transmission of infections occurs mainly in summer and summer inhibition in areas where transmission is mainly from autumn to spring. There is no fixed regional seasonal inhibition pattern. Depending on weather and farm management, the timing and level of inhibition will vary from year to year. Moreover, differences in the propensity for inhibition have been observed between field strains of Ostertagia in cattle in Australia and in the Netherlands. Simultaneous resumption of development of large numbers of inhibited larvae can result in Type II ostertagiasis, usually in only part of the heard. For reasons as yet unknown, there appear to be differences between regions in the prevalence of this disease. Development of immunity is also involved in the onset of inhibition and the occurrence of two separate inhibited populations in one host population, "seasonal" and "immunological", has been suggested. Seasonal fluctuations in the proportion of inhibition in naturally infected animals do not necessarily imply that the main trigger for inhibition is environmental conditioning, because infection levels and thus the degree of immunity will also fluctuate seasonally. In some Ostertagia field populations during late autumn in the Netherlands, worm burdens of permanently grazed calves consist mainly of inhibited larvae, but burdens of tracer calves consist of adults. Inhibited larvae may also be involved in the development of immunity. Some protection against reinfection with Haemonchus contortus has been demonstrated in barren ewes infected 6 months earlier with a single dose of 15,000 inhibition-conditioned larvae. Such an immunogenic role may be more important in Ostertagia, because inhibited larvae are found deeper in the mucosa than those of Haemonchus.

Interbreeding in the subfamily Ostertagiinae (Nematoda: Trichostrongylidae) of ruminants

The interbreeding of 6 species of ostertagiines was studied in a sheep model. Virgin young females of selected nonpolymorphic strains of Ostertagia ostertagi, Ostertagia leptospicularis, and Teladorsagia circumcincta were mated with various male ostertagiines. Interbreeding was successful between O. ostertagi and Ostertagia lyrata, O. leptospicularis and Ostertagia kolchida, and T. circumcincta and Teladorsagia trifurcata, respectively. Their offspring were fertile and resembled one parent or the other without intermediate forms: each pair is a polymorphic species. Infertile hybrids, intermediate in form, were obtained from interbreeding between O. ostertagi and O. leptospicularis and they remain valid species.

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

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

Establishment and pathogenicity of two strains of Ostertagia ostertagi and Cooperia oncophora in calves in different locations

An experiment was carried out simultaneously in Glasgow and in Wageningen to investigate possible differences between the local strains of Ostertagia ostertagi and Cooperia oncophora. In each location calves of the local Friesian breed were infected with 100,000 larvae of either the Glasgow or Wageningen strain of O ostertagi or C oncophora. At both locations the calves received the same diet. The Glasgow strain of O ostertagi was more pathogenic than the Wageningen strain and a larger proportion of the worm burden was found in the abomasal mucosa. The number of ova per female was greater in the Wageningen strain. For C oncophora the Wageningen strain gave rise to higher worm burdens and longer worms. Differences were also present between locations. The British Friesians had higher worm burdens of C oncophora and the worms of this species were longer in this host. Compared with the Dutch Friesians the British calves had a higher proportion of O ostertagi in the mucosa. This experiment showed how difficult it is to compare data from the literature because of differences in parasite and host strains and laboratory techniques.

Observations on the output of nematode eggs in faeces and on the subsequent pasture infestation with third stage larvae produced by a herd of farmed red deer (Cervus elaphus)

More than 2900 faecal samples and 200 herbage samples were examined from January 1986 to January 1989 during a study of the host/parasite relationships of the gastrointestinal nematodes of a herd of farmed red deer in Surrey. The pattern of faecal egg output from the hinds appeared to conform to a tri-modal distribution with peaks during spring, the periparturient period and late summer. Third stage larvae were present on the herbage during every month. The new generation appeared in June but levels of larvae remained low until the autumn. The implications of these findings are discussed in relation to the farming of red deer.

Interaction of Ostertagia and Nematodirus species in sheep and the potential of serum fructosamine determination in monitoring gastrointestinal parasitism

Serum fructosamine concentration falls with an increase in plasma protein turnover. Since this increase is a feature of gastrointestinal parasite infection at all sites, a falling serum fructosamine level may be of general application in the interpretation of parasite-related events. The circulating fructosamine level was investigated in the lamb as an indicator of protein-losing gastroenteropathy associated with two parasites at different sites, Ostertagia circumcincta (abomasum) and Nematodirus spathiger (small intestine). Infection with 10,000 N spathiger infective larvae daily for seven weeks produced only slight clinical signs, and only a small change in serum fructosamine levels. 2500 O circumcincta L3 daily gave no clinical signs in most animals, but serum fructosamine was more strongly affected in this group. Concurrent infection with both organisms caused some degree of diarrhoea in all lambs, and a sustained fall in serum fructosamine, more accentuated than that observed in either of the single infection groups, supporting the value of serum fructosamine determination in monitoring gastrointestinal parasitism.

Effects of microclimatic variables on the availability and movement of third-stage larvae of Ostertagia ostertagi on herbage

Assessments were made of the influence of several microclimatic variables on the availability of third-stage larvae of Ostertagia ostertagi, on pasture herbage. Variables most closely related to recovery of larvae from the lower herbage samples were: maximum air, mat and dung temperatures. Recovery of larvae from the upper portion of the herbage was closely correlated with dung temperature, sampling-time air temperature and maximum air temperature. Bearing in mind that the moisture threshold was maintained throughout the trial the results of this study suggest that under field conditions, larval movement of third-stage O. ostertagi larvae on herbage is regulated primarily by temperature.

Teladorsagia circumcincta egg output at the onset of natural and induced lactation in ewes

Nineteen ewes maintained under 'worm-free' conditions received anthelmintic and 1 week later were dosed on 5 days each week with 500 Teladorsagia circumcincta larvae for between 10 and 12.5 weeks. Faecal egg counts were determined twice weekly. There were three groups: pregnant (P) ewes (n = 6) which each reared twin lambs, hormone-treated (H) ewes (n = 7) which were not pregnant and were given exogenous hormones (dexamethasone, oestradiol-17 beta, progesterone) for 37 days to induce udder development and milk production, and untreated barren (B) ewes (n = 6). The plasma concentrations of oestradiol-17 beta, prolactin and progesterone were measured. Starting 10-15 days before birth in Group P, there was a biphasic periparturient rise in egg count and the onset of the first peak in egg count preceded the parturient peak in plasma prolactin concentration by several days. Most Group H (5/7) and all Group B ewes remained highly resistant to Teladorsagia infection throughout, despite an induced rise in prolactin concentrations in Group H ewes. It was concluded that factors other than prolactin initiate the periparturient rise but that prolactin is one factor which maintains the response once lactation commences.

Factors influencing rain splash dispersal of infective larvae of Ostertagia ostertagi (Trichostrongylidae) from cow pats to the surroundings

Laboratory experiments were conducted to investigate rain splash dispersal of infective Ostertagia ostertagi larvae (L3) from cow pats to the surroundings during simulated rainfall. Simulated rainfall on dry cow pats resulted in dispersal of only very few L3. When cow pats were watered prior to the experiments, many infective larvae were stimulated to migrate up onto the surface of the pats, where they might be hit by water drops. When pre-watered pats were hit by falling drops, a considerable proportion of L3 was translocated. More than 90% of the translocated larvae were transported passively by splash droplets and only a minor part of the larvae migrated actively in water films or were transported passively by water run-off to the soil surrounding the pats. A reduction of the fall height of the simulated raindrops resulted in a significant reduction of the number of translocated L3. When cow pats were hit by drops of diameters between 2 and 5 mm, it was found that small raindrops were just as effective as large drops in splash dispersal of L3, provided the amount of rain was the same; but individual small drops were less effective in this respect than individual large drops. When splash droplets could travel freely, most of the splash-dispersed L3 were found within a horizontal distance of 90 cm from the pats; this applied for all sizes of drops. Most splash droplets carrying L3 were travelling within a vertical distance of 30 cm from the ground.

Induction of nematode-trapping organs in the predacious fungus Arthrobotrys oligospora (Hyphomycetales) by infective larvae of Ostertagia ostertagi (Trichostrongylidae)

Laboratory experiments were designed to study the influence of temperature, concentrations of nematodes, oxygen tension, light, and nutrient levels, on the induction of nematode-trapping hyphal nets in the predacious fungus Arthrobotrys oligospora. When induced by infective Ostertagia ostertagi larvae, a maximum number of nets was produced at 20 degrees C, at which temperature nets in surplus were produced at larval concentrations up to 1,000 larvae per cm2. A. oligospora did not produce nets in an anaerobic atmosphere containing 21% CO2 (v/v), and net induction was suppressed to a certain degree by exposure to light. The composition of the medium had an important influence on the saprophytic growth and the net-forming capability of A. oligospora as a maximum number of nets was induced at a relatively low concentration of corn meal supporting the relatively sparse mycelium. It was shown that a proportion of trapping nets in A. oligospora maintained their trapping potential for more than 7 weeks when the temperature was below 25 degrees C. Induction of nematode-trapping organs in A. oligospora is discussed in relation to control of infective nematode parasite larvae in cow pats.

Effects of trichostrongyle larval challenge on the reproductive performance of immune ewes

Ostertagia circumcincta larvae were administered to adult immune ewes either during the breeding period or around parturition to investigate whether reproductive performance was affected. Two groups of 25 ewes were given water or 12,000 ostertagia larvae three times weekly for five weeks before and five weeks after breeding to synchronised oestrus. Plasma pepsinogen levels were raised in the larval-challenged ewes during the treatment period but no significant effect of treatment was observed on ovulation rate or plasma progesterone concentration. Neither ewe live-weight nor body condition score differed between groups throughout gestation or for four weeks post partum and there was no effect from larval challenge during the breeding period on lambing rate, lamb birthweight or liveweight at four weeks old. A second experiment involved 20 twin-bearing immune ewes which were administered 17,000 ostertagia larvae three times weekly for three weeks before and three weeks after parturition. Plasma pepsinogen concentration was elevated during the larval challenge period and nematode eggs were detected in the faeces after parturition but there was no effect from treatment either on ewe liveweight and body condition score or on lamb birthweight and lamb liveweight at four weeks old. These results indicate that larval challenge with ostertagia larvae at dose rates comparable to larval intake from heavily contaminated pasture did not affect the general well being and reproductive performance of immune Greyface ewes.

Production of strains of the sheep parasite Ostertagia circumcincta by implantation of adult parasites into the abomasum of lambs

The implantation of a single pair of adult parasites of Ostertagia circumcincta via the abomasa of four lambs resulted in the production of 19, 53, 393 and 425 viable larvae after faecal culture using faeces collected from day 6 to day 20 after implantation. Implantation of a single female parasite into two lambs failed to produce larvae.