Effect of antihelminths with contrasting efficacy against gastrointestinal nematodes on the live-weight gain of young Nellore cattle

We estimated the losses caused by gastrointestinal nematode (GIN) infections in young Nellore cattle born in three consecutive calving seasons (Cycles I, II and III). Three groups of animals: Group 1 - free from GIN using 2.5 mg/kg of albendazole sulfoxide; Group II - free from Oesophagosomum radiatum using 0.2 mg/kg of ivermectin but infected with ivermectin-resistant Haemonchus placei and Cooperia spp.; and Group III - non-treated experimental control animals, infected with all GIN, were observed over a period of 12 months. Male and female calves were evaluated starting before weaning when the animals were an average of approximately four months of age. In Cycle I, only females were evaluated. All the animals continued to graze on pastures of Urochloa spp. (= Brachiaria). All the groups showed median faecal egg counts of fewer than 250 eggs per gram (EPG), and no clinical signs of parasitic gastroenteritis were observed. The blood variables were within the normal ranges, and no calf presented anaemia. In most of the samplings, the median EPGs were significantly lower (P < 0.05) in the group treated with albendazole. Throughout the experiment, the most prevalent parasite observed in the control group was Cooperia spp., followed in decreasing order by Haemonchus spp., O. radiatum and Trichostrongylus spp. All the groups of calves exhibited weight gain throughout the trials with control group displaying the lowest body weight gain. Body weight variables between the albendazole- and ivermectin-treated groups were not significantly different (P > 0.05). After weaning, females animals in albendazole and ivermectin treated groups exhibited higher body weights, 20.4% and 22.7%, respectively, than those of the control group. Likewise, males treated with albendazole and ivermectin exhibited 27.6% and 25.8%, respectively, more body weight gain than animals under control group. Because the main difference between the ivermectin and the control groups was the O. radiatum parasitism, most of the losses in the control group were possibly due to this nematode species. Nevertheless, the other nematodes species that occurred in relatively high intensities in control group could also have an additive effect in such losses.

An association between successful vaccination against the bovine nodular worm, Oesophagostomum radiatum and induction of eosinophilia

Immunization of 48 cattle with somatic antigen extracts of the nodular worm, Oesophagostomum radiatum, reduced faecal egg counts (FEC) by 51% and worm burden by 47%. The antibody titre of each animal was correlated to both worm burden (r = -0.40, P < 0.005) and FEC (r = -0.37, P < 0.01). The vaccinated cattle showed wide variation in their response to vaccination with worm burdens after challenge infection varying from 0 to 4060. Of these 48 vaccinated animals, eight developed sterile immunity (worm burden = 0, FEC = 0) whereas a further 10 had no protective response to immunization (worm burden > 1,000, FEC > 100). A comparison of these two sub-groups showed that the group with sterile immunity had a higher antibody titre (P < 0.05). In addition, the group with sterile immunity developed a blood eosinophilia between 21 and 29 days after challenge infection. Vaccinated, unprotected calves and control, unvaccinated calves did not develop eosinophilia.

Population biology of the parasitic phase of trichostrongylid nematode parasites of cattle and sheep

This paper reviews the previous mathematical and conceptual models for the parasitic phase of a range of trichostrongylid nematode parasites of cattle and sheep. It reassesses the results of single and trickle infection experiments and suggests as a working hypothesis that the common trichostrongylids are essentially identical with respect to the processes that determine their survivorship in the host. Parasite abundance in the parasitic phase is explained in terms of immune exclusion, which acts on recently ingested third stage larvae, and mortality of established (fifth stage) parasites. The functional forms used to describe immune exclusion and the mortality of fifth stage worms are defined, respectively, as a declining sigmoid and an asymptotic curve.

Oesophagostomum radiatum: the effect of different adjuvants on vaccination with a partially purified protective antigen

The components of a soluble extract of adult Oesophagostomum radiatum were separated into four fractions by gel filtration chromatography on a Superose-12 column. The second fraction had a molecular weight range of approximately 60,000-65,000 as judged by SDS gel electrophoresis. Vaccination of calves with this fraction significantly (P < 0.05) reduced faecal egg output after challenge infection. In addition, the packed cell volume of vaccinated calves was higher than that of control calves (P < 0.05). The effect of three adjuvants on the vaccine activity was compared. Fraction 2 presented in dextran sulfate reduced the faecal egg count by 93.6% (P < 0.05), Fraction 2 in Freund's complete adjuvant reduced the faecal egg count by 27% (P = N.S.). Quil A was ineffective as an adjuvant.

Oesophagostomum radiatum: inhibition of in vitro development by newborn calf serum

Oesophagostomum radiatum developed to fourth stage larvae after 14 days in vitro culture. However, development was totally inhibited if the standard 50% foetal calf serum in the medium was replaced by newborn calf serum. Inhibition did not occur with serum from cattle immune to O. radiatum through natural infection or experimental vaccination irrespective of the titre of specific antibodies to O. radiatum in each serum. The inhibitory action of NCS could be abolished by heat treatment at 56 degrees C for 1 h but not by dialysis or repeated freeze-thawing. The inhibition was not consistent with observed differences in the activity of 19 enzymes in the various sera or the absence of various thiol-containing stimulants of worm development.

Induction of protective immunity in calves immunized with adult Oesophagostomum radiatum somatic antigens

Oesophagostomum radiatum, the nodular worm of cattle, is a severe pathogen in previously uninfected calves. However, cattle develop a strong protective immune response upon exposure to the parasite. In order to evaluate whether soluble parasite antigens could induce protective immunity, a soluble fraction was obtained from disrupted adult worms, and this fraction was used to vaccinate calves. The vaccination protocol involved two immunizations. The first was administered intramuscularly with complete Freund's adjuvant, the second was given intraperitoneally with antigen plus alum. This immunization reduced the number of worms developing from a subsequent challenge infection by 85% and also reduced clinical signs associated with infection with adult worms. However, vaccination resulted in decreased weight gains during the larval phase of the infection. Analysis of the immune response generated in the vaccinated calves indicated that protection from infection was significantly correlated with the levels of: (1) circulating parasite-specific IgG2 antibody; (2) cellular immune reactivity as determined in a conventional parasite-specific lymphocyte proliferation assay. Serum anti-O. radiatum IgG2 antibodies from vaccinated calves were used in immunoblots to identify the major immunogens. There were five major immunogens with molecular weights ranging from 70 to 150 kDa. Fractions separated by high-pressure liquid chromatography contained immunogens that were used to immunize calves. Vaccination with these fractions was found to impart the same level of protective immunity and induced similar IgG2 antibody and cellular immune responses as the crude whole worm extract even with 100-fold less protein.

The veterinary importance of nodular worms (Olesophagostomum spp)

The nodular worms (Oesophagostomum spp) are important parasites of food animals and primates. The archaic line that parasitizes pigs appears to be less pathogenic than the parallel evolutionary lines in ruminants and primates. Morphological types of O. dentatum in pigs and an apparent new host record for O. venulosum, which normally affects sheep and wild ruminants, in cattle suggests aggressive recruitment within the genus. The same Oesophagostomum spp occur in humans and in non-human primates but it is not clear which is the natural host.

Oesophagostomum radiatum: successful vaccination of calves with high molecular weight antigens

Extracts of adult Oesophagostomum radiatum were resolved into four fractions by gel filtration chromatography on a Superose 12 column. ELISA assays on these four fractions showed that the antibodies produced by naturally infected calves predominantly reacted with the void volume fraction (VV). Three trials were conducted in which calves were vaccinated with the VV fraction of adult extract. When compared to untreated controls, vaccination with the VV of adult extract significantly (P less than 0.05) reduced worm establishment and faecal egg output after challenge infection relative to untreated controls.

The relation between the natural worm burden of steers and the faecal egg count differentiated to species

The relation between the faecal egg count and the worm burden was investigated in 104 steers of three breeds, 9-24 months of age, which were subjected to natural infection with nematode larvae from pasture at The National Cattle Breeding Station near Rockhampton in central Queensland. The worm species found were Cooperia spp., Haemonchus placei, Trichostrongylus axei, Oesophagostomum radiatum and small numbers of Bunostumum phlebotumum. The faecal egg count was found to be a reliable measure of the size of the worm burden. Steers slaughtered at 24 months of age had 90% fewer worms and 96% fewer eggs g-1 faeces (P less than 0.001) than those slaughtered at 9 months of age. Adjusted for age, the estimated faecal egg count increased 14 times (95% confidence limits 7.2, 35) for each 10-fold increase in estimated worm numbers. The proportion of each species of larvae obtained from faecal culture (larval differential count) was related to the composition of the worm burden as measured by the proportion of worms in selected maturity categories and in selected length categories for each species (P less than 0.001).

Abundance and survival of infective larvae of the cattle nematodes Cooperia punctata, Haemonchus placei and Oesophagostomum radiatum from faecal pats in a wet tropical climate

Observations were made on the abundance and survival of Haemonchus placei, Cooperia punctata and Oesophagostomum radiatum infective larvae from cattle faecal pats exposed at various times of the year in north Queensland wet tropics. Pats exposed in the hot, wet season yielded abundant larvae on herbage. In the dry season, although low numbers of infective larvae were usual, considerable numbers were produced under conditions of heavy dews on dense herbage. Irrespective of season of deposition of pats, the resulting larvae persisted generally for not longer than 10 to 12 weeks, and in large numbers for only 2 to 6 weeks. The findings suggest that prevention of contamination in the wet season, and in the dry season when light rainfalls are accompanied by heavy dews on dense herbage, will result in low levels of larval infestation on herbage. Rotational grazing in the area is suggested as a means of worm control.

Differential recoveries from faecal cultures of larvae of some gastro-intestinal nematodes of cattle

Faecal cultures were established using bovine faeces containing known numbers of eggs from either Oesophagostomum radiatum, Haemonchus placei, Cooperia pectinata or a mixture of all three. A substantially greater percentage of larvae was recovered from cultures of O. radiatum and C. pectinata than was recovered from cultures of H. placei. The same pattern was observed in mixed cultures although yields of larvae from all species in mixed cultures were significantly reduced (p less than 0.001). The lower recovery of H. placei was not associated with a lower viability of H. placei eggs. Of the three different methods of harvesting larvae, the jar and mesh recovery technique was the least effective and significantly fewer larvae were recovered with this technique than with the Baermann and inversion techniques (p less than 0.05). The results are discussed with reference to the use of faecal culture and larval differentiation in the diagnosis of mixed species nematode infections of cattle.

Protection from parasite-induced weight loss by the vaccination of calves with excretory-secretory products of larval Oesophagostomum radiatum

Excretory-secretory products (ESP) were collected from in vitro maintained Oesophagostomum radiatum larvae during the period in which the larvae molt from the third to fourth larval stage. The ESP were used to immunize 13 uninfected calves which were subsequently challenged with 1.7 X 10(4) infective O. radiatum larvae. Worm recoveries from immunized calves were reduced 23% compared to 12 unimmunized controls, while the number of intestinal nodules was 72% greater compared to unimmunized controls; however, neither difference was statistically significant. Immunized calves had enhanced serum IgG and IgA anti-ESP antibody responses upon challenge. No differences in serum IgG2 or IgM antibody or cellular immune responsiveness, as determined by in vitro antigen-induced lymphocyte proliferation, were seen. Vaccination with ESP did significantly protect calves from the weight loss seen in non-immunized calves. Unimmunized calves ceased gaining weight approximately 5 weeks after challenge and by 10 weeks after challenge had lost an average of 4 lbs. per calf. Over the same time interval (i.e., 5-10 weeks after challenge), the immunized calves gained an average of 23 lbs. per calf. These results strongly suggest that vaccination with ESP conferred an advantage to calves that is not correlated solely with the number of worms developing from challenge infection.

Oesophagostomum columbianum: gamma-irradiated third-stage larvae for immunization in lambs

40-kR gamma-irradiated third-stage larvae of Oesophagostomum columbianum were used for the immunization of Kashmir Merino lambs. Male lambs (aged from 8 to 12 weeks) were immunized in two separate experiments by two doses of irradiated larvae, given 21 days apart, and subsequently challenged with normal larvae. Judging by the establishment of worms resulting from the challenge infections in the immunized and control groups of lambs in the two experiments, a high degree of immunity was shown to develop in young lambs vaccinated with 500, followed 21 days later with 2000, 40-kR irradiated larvae. Lambs from the immunized groups showed more nodules in the intestine, a high percentage of which were positive for histotrophic stages of O. columbianum, than did controls. The importance of this finding in relation to the possible use of a vaccine for the immuno-prophylaxis of oesophagostomiasis in sheep and other animals is discussed.

The plasma cryofibrinogen of calves infected with Oesophagostomum radiatum

A cryofibrinogen complex was detected in the plasma of cattle infected with Oesophagostomum radiatum. Its formation coincided with the development of hypofibrinogenaemia and it consisted basically of fibrinogen and soluble noncross-linked fibrin in both monomer and high molecular forms. Also present in the complex, albeit in trace amounts, were cold insoluble globulin, TgG, and plasminogen. It is suggested that the complex results from thrombin activation in vivo and its role is to maintain fibrin in solution thus preventing its deposition in the vascular system.

Parasitism and calfhood diseases

That animals can and do acquire an effective immunity against helminth parasites has been demonstrated extensively experimentally, and the fact that domestic animals such as cattle, sheep, and horses become adults while maintaining good health in spite of constant exposure to reinfection long has suggested that immunity must be important to such survival. Although our attempts to date to vaccinate calves against helminth parasites have either failed or been unsatisfactory because of the pathosis induced by the experimental vaccines, the results are not surprising or discouraging. In contrast to the long history of immunization research on bacterial and viral diseases, only within a relatively short time have serious efforts been directed at exploiting hostal immunity for prevention and control of helminthic diseases. Unlike the comparatively simple structures of viruses and bacteria, helminths are complex multicellular animals with vast arrays of antigens and complicated physiological and immunological interactions with their hosts. Much more fundamental information on helminth-bovine interactions, on helminth antigens, and on cattle antibody systems must be developed before progress on control of cattle helminths by vaccination can be meaningful.

Anthelmintic treatment of young beef cattle in the Wallum region of south-eastern Queensland

An anthelmintic treatment trial on 125 Brahman-British crossbred 2 to 4 month old calves was undertaken on Wallum country in south eastern Queesland. The calves were divided into 5 experimental groups, grazed together and treated as follows for 17 months: Group 1--Untreated controls; Group 2--Monthly levamisole--niclosamide on 4 occasions; Group 3--Monthly levamisole until 1 month after weaning; Group 4--Levamisole 3 to 6 weeks after saturating rains; Group 5--No levamisole--niclosamide as for Group 2. The mean body weight gains for cattle in Groups 1 to 5 were 95, 124, 105, 121 and 97 kg respectively. Four cattle were lost from each of Groups 1 and 3 and five from Group 5. Most of these losses occurred towards the end of the second summer rainfall season. Faecal egg count maxima were recorded around weaning in untreated groups and during the summer rainfall period of both the first and second summer in all groups. The most prevalent nematode species encountered were H. placei, Cooperia spp and O. ostertagi. It is recommended that in this region cattle under 2 years of age should receive anthelmintic treatment at least in autumn and spring.