The development of protective immunity against gastrointestinal nematode and lungworm infections after use of an ivermectin bolus in first-year grazing calves

Spatiotemporal trends in cattle lungworm disease (Dictyocaulus viviparus) in Great Britain from 1975 to 2014

Background

Clinical disease caused by the bovine lungworm (Dictyocaulus viviparus) causes significant welfare and economic problems for the livestock industry. Anecdotal reports suggest that the number of clinical cases has increased, particularly in Northern England and Scotland. However, these spatiotemporal changes have not been quantified and the current impact that the disease is having across Great Britain remains unclear.

Methods

Here, we report a retrospective analysis of the spatial distribution, seasonality and age of lungworm cases reported by the Veterinary Investigation Diagnosis Analysis database from 1975 to 2014.

Results

A sharp overall increase in the dictyocaulosis diagnostic rate (DR, cases / 1000 submissions) was observed, with, for example, median 2010–2014 DR 3.5 times as high as 1980–1984 DR. Such increases were most pronounced for Scotland, which became the region with the highest proportion of cases by 2009. Cases were increasingly diagnosed during the winter months (December–February).

Conclusion

The apparent spatiotemporal changes in lungworm epidemiology pose new challenges to cattle farmers in Great Britain. Farmers and veterinarians need to remain vigilant for this disease and consider it as a possible cause for milk production losses at any time of the year. Awareness levels may have to be raised particularly in northern England and Scotland.

Biological function of Dictyocaulus viviparus asparaginyl peptidase legumain-1 and its suitability as a vaccine target

The present study characterized the biological function of the asparaginyl peptidase legumain-1 (LEG-1) of the bovine lungworm Dictyocaulus viviparus and its suitability as a recombinant vaccine against dictyocaulosis. Quantitative real-time PCR and immunoblot analysis revealed LEG-1 to be almost exclusively transcribed and expressed in parasitic lungworm stages. Immunohistochemistry localized the enzyme in the parasite's gut, which was confirmed by immunoblots detecting LEG-1 in the gut as well as male testes. LEG-1 was recombinantly (rLEG-1) expressed in the yeast Pichia pastoris and subsequently analysed in activity assays for its enzyme functions and substrate specificity. For sufficient functionality, rLEG-1 needed trans-activation through D. viviparus cathepsin L-2, indicating a novel mechanism of legumain activation. After trans-activation, rLEG-1 worked best at pH 5·5 and 35-39 °C and cleaved a legumain-specific artificial substrate as well as the natural substrates bovine collagen types I and II. In a clinical vaccination trial, rLEG-1 did not protect against challenge infection. Results of in vitro characterization, transcription pattern and localization enhance the presumption that LEG-1 participates in digestion processes of D. viviparus. Since rLEG-1 needs trans-activation through a cathepsin, it is probably involved in an enzyme cascade and therefore remains interesting as a candidate in a multi-component vaccine.

Deep insights into Dictyocaulus viviparus transcriptomes provides unique prospects for new drug targets and disease intervention

The lungworm, Dictyocaulus viviparus, causes parasitic bronchitis in cattle, and is responsible for substantial economic losses in temperate regions of the world. Here, we undertake the first large-scale exploration of available transcriptomic data for this lungworm, examine differences in transcription between different stages/both genders and identify and prioritize essential molecules linked to fundamental metabolic pathways, which could represent novel drug targets. Approximately 3 million expressed sequence tags (ESTs), generated by 454 sequencing from third-stage larvae (L3s) as well as adult females and males of D. viviparus, were assembled and annotated. The assembly of these sequences yielded ~61,000 contigs, of which relatively large proportions encoded collagens (4.3%), ubiquitins (2.1%) and serine/threonine protein kinases (1.9%). Subtractive analysis in silico identified 6928 nucleotide sequences as being uniquely transcribed in L3, and 5203 and 7889 transcripts as being exclusive to the adult female and male, respectively. Most peptides predicted from the conceptual translations were nucleoplasmins (L3), serine/threonine protein kinases (female) and major sperm proteins (male). Additional analyses allowed the prediction of three drug target candidates, whose Caenorhabditis elegans homologues were linked to a lethal RNA interference phenotype. This detailed exploration, combined with future transcriptomic sequencing of all developmental stages of D. viviparus, will facilitate future investigations of the molecular biology of this parasitic nematode as well as genomic sequencing. These advances will underpin the discovery of new drug and/or vaccine targets, focused on biotechnological outcomes.

Effects of treatments with endectocide on the weight gain of grazing cattle in a warm temperate climate

Five groups of 20 weaned beef calves were injected subcutaneously with either an ivermectin, a doramectin, an abamectin long-acting formulation, an ivermectin long-acting formulation or a saline control, at turnout and 60 and 120 days later. The animals grazed the same pasture and were sampled and weighed at turnout and 30, 60, 90, 120, 150 and 180 days later. At turnout the mean bodyweights of all the groups were similar and faecal culture showed that they had a mixed strongyle infection of Cooperia, Haemonchus, Ostertagia, Oesophagostomum and Trichostrongylus species. After 180 days, the mean bodyweight gains of each group were respectively 62.1 kg, 102.2 kg, 106.4 kg, 107.3 kg and 110.1 kg for the control, ivermectin, doramectin, ivermectin long-acting and abamectin long-acting groups. All the products significantly improved the weight gains of the cattle, and significantly reduced their faecal egg counts.

Resilience of second year grazing cattle to parasitic gastroenteritis following negligible to moderate exposure to gastrointestinal nematode infections in their first year

The influence of gastrointestinal nematode infections on performance of four groups of female Holstein Friesian calves was monitored until the end of the second grazing season (SGS). In the first year three groups were grazed and one group (G4) was permanently housed. General and grazing management during the first grazing season (FGS) was arranged such that G1 acquired moderate infections, G2 low infections and G3 very low infections with gastrointestinal nematodes. These infections were monitored through faecal egg counts, differentiation of faecal larval cultures, pasture larval counts, serum pepsinogen values, ELISA with a recombinant Cooperia oncophora protein, weight gain, tracer worm counts and sentinel worm counts. In 1998 all four groups were grazed together as one herd from 23 April to 26 October and infections were monitored with the same techniques with the exception of sentinel calves. In the FGS weight gain was higher in G4 than in the other groups and higher in G3 (28. 6kg) than in G1. Weight gain of G2 was intermediate to G1 and G3 but did not significantly differ from either group. In the SGS weight gain in G4 was far less than in any other group and the mean weight at the end of the experiment was 41.9, 38.6 and 50.9kg lower than G3, G1 and G2, respectively. Though no significant differences were observed between G1, G2 and G3 at the end of the experiment it was obvious that the weight gain advantage of G3 over G1 at the end of the FGS had disappeared. Parasitological and serological findings in the SGS indicated that G3 and G4 had build up less immunity during the FGS compared to G1 and G2. The conclusion of the experiment is that resilience to parasitic gastroenteritis in the SGS depends on the level of exposure to nematodes in the FGS. However, problems with poor weight gain only will be expected when exposure is very low in the FGS and high in the SGS.

Induction of protective immunity to Dictyocaulus viviparus in calves while under treatment with endectocides

Three groups of five parasite-naive calves were used. The treatments were: (a) Group 1 calves were weighed on Day 0 and injected with doramectin at 200 microg/kg. From Day 1 to 19 they were dosed orally with 2000 infective larvae of Dictyocaulus viviparus. On Day 28 they were again injected with doramectin, and infected with D. viviparus larvae from Days 33 to 41. They were then left untreated until Day 81 when they were infected with 20 infective larvae of D. viviparus per kg body weight. They were killed on Day 110 and lungworms were counted; (b) Group 2 calves were immunised with oral lungworm vaccine on Days 0 and 28, and infected and slaughtered as Group 1 on Days 81 and 110, respectively; (c) Group 3 calves acted as infection controls. Blood samples were taken at Days 0, 21, 49, 77 and 110 for antibody tests to D. viviparus. At autopsy there were no significant differences between the number of lungworms from Groups 1 and 2 (Means 17.4 and 31.3, respectively); Group 1 had significantly less value than Group 3 (Mean 228) (p < 0.05). Increased antibody titres to the larval sheath of the infective larvae were observed from Groups 1 and 2, showing that the larvae in Group 1 had penetrated the intestine before being killed by the circulating anthelmintic. This experiment shows that if calves are exposed to infective larvae while under systemic endectocide cover, an immune reaction is stimulated.

The effect of first season chemoprophylaxis in calves on second season pasture contamination and acquired resistance and resilience to gastrointestinal nematodes

Two groups of second grazing season cattle, which had been treated with an ivermectin-sustained-release bolus (ISRB) in their first grazing season, were monitored during consecutive years (1995 and 1996) on the same second grazing season pasture. In the preceding year (1994), this pasture had been grazed by yearlings that had not received chemoprophylaxis in their first grazing season. The objectives of the study were, firstly, to investigate whether the chemoprophylactic-treated yearlings were less resistant to gastrointestinal nematodes upon subsequent exposure, and hence excreted more strongyle eggs compared to the control yearlings; secondly, whether an increased susceptibility of the previously treated animals resulted in a yearly increase of the pasture infestation on the second grazing season pasture; and finally, whether this affected the second year weight gain of the animals. In 1996, the yearlings that had been chemoprophylactic-treated in 1995 excreted higher numbers of nematode eggs, compared to the previously 'untreated' yearlings. In addition, the proportion of Cooperia larvae was markedly higher in the faecal cultures from the chemoprophylactic treated-animals, suggesting a negative effect of preventive treatment with an ISRB on the acquired resistance of the animals. However, there was no evidence that the slightly higher egg output in the previously treated yearlings had an effect on the larval contamination of the second grazing season pasture. A significant yearly decrease in the second season average daily weight gains was observed, but it could not be inferred from the results of the parasitological parameters that the differences in second year growth were caused by different levels of resilience between chemoprophylactic-treated and -untreated animals. As the study covered three consecutive second grazing seasons, an effect of differences between years (e.g. in weather conditions or grass growth) on the results cannot be excluded.

Effects of preventive anthelmintic treatment on acquired resistance to gastrointestinal nematodes in naturally infected cattle

The objective of this study was to investigate the influence of different types of chemoprophylaxis in first season grazing calves on their resistance against a natural reinfection with Ostertagia ostertagi and Cooperia oncophora in the second grazing season. Thirty helminth-naive crossbred calves were randomly divided in three groups of 10 animals. The animals of group B received an ivermectin sustained release bolus on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group ('immune' controls). Although exposure to gastrointestinal nematodes in the first grazing season was only limited, the chemoprophylactic treatments in groups B and D resulted in three distinctly different infection levels (group C > group D > group B). At the start of the second grazing season, six helminth-naive steers (group N, 'susceptible' controls) were turned out together with the second season animals. After 3 weeks of grazing, the 'susceptible' controls were slaughtered, together with four animals from each other group. Parasitological and immunological parameters indicated that resistance to reinfection with Ostertagia was reduced in the chemoprophylactic treated animals, and was negatively related to the degree of suppression of host-parasite contact in the first grazing season (group C > group D > group B > group N). None of the groups had developed a complete resistance against Cooperia yet. A negative relationship was observed between reduction of first grazing season exposure, and weight gains early in the second grazing season. The remaining animals stayed on pasture until the beginning of November. At the end of the second grazing season, levels of acquired resistance against Ostertagia infection were similar in all groups, and all animals had become immune against Cooperia. No effect of first year chemoprophylaxis on total weight gains could be demonstrated. Because of discrepancy between pasture larval counts and tracer worm counts, it was not possible to draw firm conclusions on the effect of chemoprophylaxis on pasture infestation levels in the second year.

The effect of different infection levels on acquired resistance to gastrointestinal nematodes in artificially infected cattle

The objective of this study was to evaluate the effect of different infection levels of Ostertagia ostertagi and Cooperia oncophora in a simulated 'first grazing season' on the resistance of calves to an artificial challenge infection. The infection levels were determined by the infection schedules and the chemoprophylaxis used. Thirty six 7-11-month old Holstein-Friesian bull calves were randomly divided into four groups. The animals of group B received an ivermectin sustained release bolus (ISRB) on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group. The calves of group N were used as helminth-naive controls, while the animals of groups B, C and D were trickle infected for 24 weeks. The infection schedules were designed to simulate the expected infection pattern for each treatment group under set-stocked conditions in temperate climate areas. After the last infection, all animals were treated with oxfendazole. One week later, all animals received a challenge infection of 50,000 O. ostertagi L3 and 100,000 C. oncophora L3, spread over 10 consecutive days. During the primary infection period the faecal egg output and the serum pepsinogen and antibody levels reflected the different levels of host-parasite contact between the groups (group C > group D > group B > group N). After the challenge infection, faecal egg counts, total Ostertagia burden, size of the adult worms and abomasal globule leucocyte counts all indicated a positive relationship between the level of Ostertagia infection during the primary infection period and the level of acquired resistance. A reduction of host-parasite contact during the primary infection period, as a consequence of the infection schedule and the chemoprophylaxis used, resulted in a diminished level of resistance to the artificial challenge infection with O. ostertagi. Faecal cultures and small intestine worm counts indicated that all previously infected groups had acquired a high degree of resistance to the Cooperia challenge infection.

Effect of chemoprophylaxis with an ivermectin sustained-release bolus on acquired resistance to gastrointestinal parasites in cattle

The influence of chemoprophylaxis with an ivermectin sustained-release bolus in the first grazing season on the resistance of cattle to gastrointestinal nematodes during the following grazing season was investigated. In 1993 and 1994 dairy replacement calves were either given one bolus at the start of their first grazing season or left untreated. The two groups were grazed separately on a pasture that was divided into two similar sized paddocks. Faecal egg counts, serum pepsinogen and antibody levels were measured to evaluate host-parasite contact. Pasture infection levels were estimated by pasture larval counts and worm counts in tracer calves. After winter housing the animals were monitored during their second grazing season on a pasture that was also divided into two similar sized paddocks. Acquired resistance to gastrointestinal nematodes was evaluated by faecal egg counts and weight gains. Again, pasture infection levels were determined and pepsinogen and antibody levels were measured. During the first grazing seasons gastrointestinal nematode infections were controlled very effectively by the bolus, as shown by the greater weight gains, the negligible faecal egg counts and the low serum pepsinogen and antibody levels in the treated calves. In contrast, all parameters showed extensive parasite-host contact in the untreated animals. The efficient prophylaxis in the treated groups resulted in low levels of larval contamination on the paddocks grazed by the treated animals, compared to moderate infection levels at the end of both first grazing seasons on the paddocks grazed by the untreated animals. During the second grazing seasons (1994 and 1995) the faecal egg output was low in all groups. Although in the previously treated animals faecal egg counts were consistently higher, the differences were minimal, resulting in comparable levels of larval contamination on both paddocks. Serum pepsinogen and antibody levels were not significantly different between the groups and indicated a similar level of larval uptake on both paddocks. No negative effect of the previous chemoprophylaxis on the clinical condition and the weight gain of the second season grazing animals was observed.