Some observations on the use of the morantel sustained-release bolus in first season-grazing calves on a Belgian dairy cattle farm

Progress in the development of subunit vaccines for gastrointestinal nematodes of ruminants

The global increase in anthelmintic resistant nematodes of ruminants, together with consumer concerns about chemicals in food, necessitates the development of alternative methods of control for these pathogens. Subunit recombinant vaccines are ideally placed to fill this gap. Indeed, they are probably the only valid option for the long-term control of ruminant parasitic nematodes given the increasing ubiquity of multidrug resistance in a range of worm species across the world. The development of a subunit multicellular parasite vaccine to the point of practical application would be a groundbreaking step in the control of these important endemic infections of livestock. This review summarizes the current status of subunit vaccine development for a number of important gastrointestinal nematodes of cattle and sheep, with a focus on the limitations and problems encountered thus far, and suggestions as to how these hurdles might be overcome.

Vaccination with an Ostertagia ostertagi polyprotein allergen protects calves against homologous challenge infection

As an alternative to antihelminthic drugs, we are exploiting vaccination to control infections with the abomasal nematode Ostertagia ostertagi in cattle. Our focus for vaccine targets is excretory-secretory (ES) products of this parasite. One of the most abundant antigens in larval and adult Ostertagia ES products is a protein homologous to nematode polyprotein allergens. We found that the Ostertagia polyprotein allergen (OPA) is encoded by a single-copy gene. OPA comprises three or more repeated units, and only the 15-kDa subunits are found in ES products. The native antigen is localized in the intestinal cells of third-stage larvae and in the hypodermis and cuticle of fourth-stage larvae and adult parasites. Vaccination of cattle with native OPA (nOPA) in combination with QuilA resulted in protection against Ostertagia challenge infections. The geometric mean cumulative fecal egg counts in the nOPA-vaccinated animals were reduced by 60% compared to the counts in the control group during the 2-month course of the experiment. Both male and female adult worms in nOPA-vaccinated animals were significantly shorter than the worms in the control animals. In the abomasal mucus of vaccinated animals the nOPA-specific immunoglobulin G1 (IgG1) and IgG2 levels were significantly elevated compared to the levels in the control animals. Reductions in the Ostertagia egg output and the length of the adult parasites were significantly correlated with IgG1 levels. IgG2 titers were only negatively associated with adult worm length. Protected animals showed no accumulation of effector cells (mast cells, globular leukocytes, and eosinophils) in the mucosa. In contrast to the native antigen, recombinant OPA expressed in Escherichia coli did not stimulate any protection.

Vaccination of calves against Ostertagia ostertagi with cysteine proteinase enriched protein fractions

Cysteine proteinase enriched fractions obtained by thiol-sepharose chromatography of Ostertagia ostertagi membrane-bound protein extract (S3-thiol) or total adult excretory-secretory (ES-thiol) products were tested in a vaccination experiment to evaluate their protective efficacy against O. ostertagi in cattle. Calves were vaccinated three times and subsequently challenged with a trickled infection of 25,000 infective larvae in total over 25 days (1000 L3/day, 5 days/week). Geometric mean cumulative egg counts in the ES-thiol group were reduced by 60% during the 2-month period between the first challenge infection and necropsy, compared to the control group (P < 0.002). No reduction in egg output was observed in the S3-thiol group. At necropsy, calves immunized with ES-thiol had a significantly higher percentage of inhibited L4 larvae (9.8%) and had in total 18% less worms than the control calves, but this reduction was not statistically significant. Both the female and male adult worms were significantly smaller in the ES-thiol group than in the control group. Although no significant difference was observed in the number of eggs per female worm between the groups, there was a trend to less eggs per female worm in the ES-thiol group. Number of worms, size of adult worms and number of eggs per female worm were not significantly different between the S3-thiol group and the control group. Systemic immunization with QuilA as adjuvant induced a significant rise in Ostertagia-specific antibody levels in the abomasal mucosa. Ostertagia-specific local antibody levels showed a significant negative correlation with the size of the adult worms, the number of eggs per female worm and the cumulative faecal egg counts. However, these correlations were quite weak and did not appear to be isotype-specific.

The determination at housing of exposure to gastrointestinal nematode infections in first-grazing season calves

Various parameter estimates were assessed at housing in calves that had been exposed to gastrointestinal nematodes during a first grazing season. The analysis involved 41 groups of first grazing season (FGS) calves on 15 different farms in Belgium and comprised groups that had received chemoprophylactic treatment and untreated controls. Serum pepsinogen levels gave the clearest division between chemoprophylactic-treated calf groups (all were <2.6 U tyr), and untreated calf groups in which sub-clinical (range: 2.0-4.1 U tyr) and clinical infections (range 3.7-6.3 U tyr) occurred. There was also a tight relationship between individual pepsinogen values and adult Ostertagia burdens obtained at slaughter. In chemoprophylactic-treated groups there was a significant negative relationship between mean serum pepsinogen levels at housing and the proportion of the grazing season covered by different chemoprophylactic systems. Although only limited data on crude adult Ostertagia antigen ELISA were available, a good relationship between optical densities and estimated exposure was also found. The parasitological parameters, faecal egg counts and pasture Ostertagia larval counts at housing, and weight gain per day, gave less clear divisions among the three categories (chemoprophylaxis, sub-clinical and clinical). Distinguishing how much exposure a calf group has experienced during a first grazing season could help in designing more appropriate control measures for the FGS calves in the next year, assuring good protection and at the same time allowing sufficient exposure for the development of acquired immunity to Ostertagia, and for this serum pepsinogen is recommended.

Gastrointestinal nematode infections of first-grazing season calves in Western Europe: general patterns and the effect of chemoprophylaxis

Research on the prevention of gastrointestinal nematode infections of cattle has mainly concentrated on comparing a specific chemoprophylactic treatment system to an untreated control group on a particular farm. Here, the results from analysis of 85 studies involving over 2000 first grazing season (FGS) calves put onto pasture for at least 4 months from late spring/early summer over a 26-year period in 13 countries in Western Europe are presented. Both control and chemoprophylactic treated FGS calf groups were considered. All chemoprophylactic systems (slow- and pulse-release boli, strategic treatments) were given early in the grazing season. Two general infection levels emerged--'sub-clinical' (32 studies) and 'clinical' (53 studies). The 'sub-clinical' infections were characterised by no clinical symptoms of parasitic gastroenteritis (PGE) being observed in the control groups. Mean faecal egg counts in the 'clinical' control groups were significantly higher than those for 'sub-clinical' control groups for almost the entire season with overall peaks of 275 and 100 EPG respectively. Maximum pasture larval counts were also significantly higher in the 'clinical' control groups with 44% of 'clinical' pastures > 10,000 L3 kg(-1) dry herbage by the end of the FGS, compared to only 15% of 'sub-clinical' pastures. There was a significant positive relationship between log transformed worm burdens from tracers put onto pastures for 2 weeks and the corresponding pasture larval count. No evidence of density dependence in tracer worm burden was observed. Weight gains in the 'clinical' control groups (375 g/day) were significantly lower than those of the 'sub-clinical' control groups (530 g/day). No symptoms of PGE were observed in any of the chemoprophylactic treated groups, but in those studies with an outbreak of PGE in the control group, the treated groups had significantly higher faecal egg and pasture larval counts than treated groups in 'sub-clinical' studies. The overall weight gain in chemoprophylactic treated calves in 'clinical' studies (600 g/day) was significantly lower than the chemoprophylactic treated calves in 'sub-clinical' studies (690 g/day), and was not significantly different from the weight gain of control calves in 'sub-clinical' studies. These results indicate that on heavily infected pastures, chemoprophylaxis will prevent PGE, but calves will still suffer production losses.

Evaluation of pepsinogen, gastrin and antibody response in diagnosing ostertagiasis

Ostertagia ostertagi is widely distributed and is one of the most important parasites affecting young bovine livestock. There is, therefore, a substantial need for sensitive and specific parameters in support of diagnosis of ostertagiasis, especially for subclinical disease related to production losses. In this review, the value and application of pepsinogen, gastrin and antibody response as diagnostic tools are discussed. These three parameters are useful and comparable for confirming clinical disease in calves during their first grazing season. However, their value for detecting subclinical parasitism is questionable. Differences in the course of gastrin and pepsinogen late in the grazing season can be correlated with larval inhibition and the possibility of ostertagiasis Type II. Relatively few serological methods have been developed for the immunodiagnosis of Ostertagia and until now the indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) has been the method of choice. Antibody measuring methods have several disadvantages, most notably a lack of sensitivity and specificity, which limits their use in longitudinal epidemiological studies. Considering the necessity of cost effectiveness and ease of use, it is anticipated that additional work will result in the enhancement and quality of current immunodiagnostic methods.

Economic and production repercussions of deworming by pulse release device and oral suspension in grazing double-muscled fattening cattle

In this field trial, the repercussions of 2 administration forms of oxfendazole, namely a single administration of a front-loaded device (group 1; n = 18) and a repeated administration of a 90.6 per cent oral suspension (group 2; n = 18), were compared in first season-grazing double-muscled fattening bulls. The comparison was based on the production performances, the mean worm egg counts and the product- and labour-costs. The daily body gains determined on the whole trial period, i.e. 1.312 +/- 0.055 kg and 1.270 +/- 0.056 kg for groups 1 and 2 respectively, and mean worm egg counts per gram (on days 0 and 130:200.0 +/- 44.3 and 94.4 +/- 27.4 for group 1; 366.7 +/- 98.4 and 100.0 +/- 33.6 for group 2) did not differ significantly between the two groups. However, the total costs were lower with a front-loaded device (1,021 Belgian Francs) than with oral suspension (1,248 Belgian Francs per bull).