Experimental Ostertagia spp. infection of sheep: development of worm populations and lesions resulting from different dose-levels of larvae

Worm-free sheep were dosed with 8 000, 64 000 or 512 000 infective Ostertagia spp. larvae and killed 4, 7, 10, 13, 18, 24 or 66 days later. Up to day 10 the worm counts ranged from 52 to 86% of the infecting dose and results suggested no substantial reduction either in rate of development or in percentage establishment with increasing dose level. However, a reduction of worm counts, which was substantial at the higher dose-rates but comparatively small at the low rate, occurred after day 10.Gross lesions in the abomasum ranged from little more than the development of a few nodules in the low-dose sheep, to a roughened congested surface with diptheritic membranes and severe oedema in the high-dose animals at days 10–24. These effects had subsided by day 66. Histopathological changes are described.The severity and extent of the reaction was related to the parasite dose-level, but not necessarily to the numbers of worms recovered post-mortem. The rate of return to normality was quicker at the lower dose rates.     

Inhibited development of Ostertagia spp. and Cooperia spp. in naturally acquired infections in calves

Abstract

Aujeszky? disease is predominantly a nervous disease of piglets, weaners, and fatteners in which the mortality may vary from 540%. Respiratory disease is also a feature of infection with certain strains of the virus. Infection of pregnant sows may cause abortion, stillbirths, and mummification, and infertility may result in both boars and sows. Traditionally the serum neutralisation test has been used as an indicator of past infection with Aujeszky s's disease virus (ADV). However, cell-mediated immunity has recently been shown to play an important role in recovery and protection from infection with ADV and antibody-dependent cell-mediated cytotoxicity can be used as an alternative diagnostic test for detection of antibody. A number of inactivated, and live, avirulent vaccines are now available for control of the disease but their use is contraindicated in countries such as New Zealand which have a low prevalence of infection. Where possible early eradication is the best policy to follow.     

Dynamics of Ostertagia spp. and Cooperia oncophora in field-grazed cattle from weaning to 2 years old in New Zealand, with particular reference to arrested development

Gastrointestinal nematode parasite burdens were monitored in a herd of field-grazed cattle from weaning to 2 years old to allow observations to be made on the dynamics of burdens of arrested Ostertagia spp. and Cooperia oncophora. Arrested Ostertagia spp. accumulated in the herd over their first autumn and winter to reach a peak in late winter/spring (August-October). From October until late January they declined at a rate comparable to that at which they had accumulated. Numbers continued to decline at a slower rate until the following autumn (May) when they began to increase again. Observations on the decline of worm burdens in a group of animals which had been moved from pasture to worm-free conditions in October indicated that intake of infective larvae over late spring/summer contributed little to the number of arrested Ostertagia spp. in the herd. No clinical Type II ostertagiosis was observed in the field-grazed animals over the time of decline of the arrested worm burden, nor was there an increase in the number of adult Ostertagia spp. present. However, two of the animals removed from pasture to worm-free conditions developed Type II ostertagiosis approximately a month after the move. Worm burdens of successive groups of "tracers" grazed with the herd every 2 months indicated that there was a small seasonal increase in the propensity of Ostertagia spp. for arrested development. However, estimated accumulation rates of arrested larvae calculated from tracer worm burdens, suggest that this seasonal increase in propensity was not adequate in itself to account for the accumulation rate observed in "resident" animals of the herd. No comparable accumulation of arrested C. oncophora took place in resident animals over the first autumn and winter of the trial despite the fact that tracer worm burdens over this period indicated a marked seasonal increase in the propensity for arrested development by this species.     

The distribution of pepsinogen within the abomasa of cattle and sheep infected with Ostertagia spp. and sheep infected with Haemonchus contortus.

The effect of nematode infections on the production of pepsinogen by ruminants was investigated immunohistochemically and biochemically. Abomasal tissues were collected from parasite-naive cattle and sheep, from sheep infected with predominantly Ostertagia circumcincta, sheep infected experimentally with Haemonchus contortus and cattle infected with Ostertagia ostertagi. Pepsinogen was also assayed biochemically in homogenates of fundic mucosae from sheep infected with predominantly O. circumcincta. Infection with Ostertagia spp. parasites was associated mainly with nodular hyperplasia, resulting in increased numbers of cells that produce both pepsinogen and mucus. Measured biochemically, nodules contained more pepsinogen than adjacent more normal mucosa (p < 0.05), and this effect was largely attributable to the greater mass of nodules. Infection of sheep with H. contortus was associated with generalised hyperplasia, characterised by increased numbers of mucopeptic cells and in at least one animal with reductions in parietal cell numbers. At the same time, the zymogen granule content of chief cells was reduced. Similar changes were occasionally seen in sheep infected predominantly with O. circumcincta. Generalised hyperplasia is likely to be indicative of the presence of ambulatory parasitic stages as opposed to those confined to nodules. The potential for the enhanced production of pepsinogen by increased numbers of cells with a joint mucous cell and zymogenic cell phenotype may offset decreases in the numbers of chief cells or reductions in chief cell activity.     

Arrested development of bovine Ostertagia spp. and Cooperia spp. in New Zealand. Effect of temperature and duration of storage on infective larvae

Infective larvae of Ostertagia spp. and Cooperia spp. derived from naturally infected dairy calves were subjected to periods of storage of up to 16 weeks at 4 degrees C or 15 degrees C to determine if this treatment would influence their propensity for arrested development in previously worm-free calves. Results showed no significant increase in the propensity of Ostertagia spp. for arrested development in response to the treatments, but a small increase in the case of Cooperia spp.     

Termination of arrested development of the trichostrongyles of sheep in northern Nigeria.

Monthly worm counts of groups of ewes and lambs that grazed continuously and tracer lambs revealed that under the conditions existing in northern Nigeria, most of the Haemonchus contortus in sheep between November and March were arrested larvae. During the months of April and May, almost equal proportions of adults, developmental stages and arrested larvae were recovered and, by June, only adults and developmental stages were recovered in high numbers. The proportion of arrested larvae had diminished considerably. A similar pattern was recorded for Trichostrongylus spp, except that fewer larvae were involved in arrested development and very large numbers of adults were recovered throughout the duration of the study. Maturation of arrested larvae occurs in April.     

Resistance to thiabendazole in a field population of Ostertagia circumcincta from sheep.

A population of Ostertagia circumcincta from sheep has been found which, in field and laboratory trials, showed a lack of response to the recommended dose (44 mg/kg) of thiabendazole, suggesting that a degree of resistance exists to this anthelmintic. Preliminary experiments indicated a less than expected response to levamisole. This was not confirmed in a laboratory trial and therefore resistance to this anthelmintic has not been shown conclusively.     

Field evaluation of a mixture of albendazole sulphoxide and levamisole against Ostertagia and Trichostrongylus spp in sheep

The efficacy of a mixture of albendazole sulphoxide and levamisole, 3.6 and 8.25 mg/kg respectively, at single and double dose rates, was compared with the recommended dose rate of each anthelmintic alone. The comparison was conducted on groups of 6 to 14-week-old lambs on 22 farms, 16 of which had evidence of multiple resistance to benzimidazole and levamisole. A single dose of the mixture reduced mean egg counts by 95% on half the farms with multiple resistance and on all the remaining farms. Consequently, the mixture should be included in an assessment of effective anthelmintics on farms to determine its value for nematode control. A double dose rate of mixture was effective on all but 4 farms. Reductions caused by the mixture were due to the additive actions of the drugs on 18 of 22 farms; synergistic action was noted on only 3 farms. It was concluded that the mixture of albendazole sulphoxide and levamisole offered many farmers an effective anthelmintic for use in preventive control programs. Recommendations for such programs include annual rotation of effective anthelmintics as a means of delaying selection for drug resistance.     

Anti-Toxocara spp. antibodies in sheep from southeastern Brazil

The purpose of this study was to evaluate the frequency of anti-Toxocara antibodies in sheep from Presidente Prudente, southeastern Brazil. Serum samples were obtained from 365 sheep of diverse breeds and different ages. Samples were collected at a slaughterhouse and at farms located in Presidente Prudente. Three groups of animal of different ages were evaluated according to age: Group I: between 1 and 6 months old; Group II: between 7 and 10 months old; and Group III: between 11 and 15 months old. An ELISA test was carried out to detect anti-Toxocara antibodies (IgG) using the excretory-secretory antigens of Toxocara canis (TES) larvae. In total, 183 out of 365 animals (50.1%) were positive for anti-Toxocara antibodies. The frequency of antibody detection was directly proportional to the age of the animals (p<0.0001), indicating a relationship between infection and aging. In Group III, there was a higher prevalence in females (p=0.0041). The relevance of these animals to the epidemiology of toxocariasis in pets and human should be considered.     

The efficacy of levamisole, and a mixture of oxfendazole and levamisole, against the arrested stages of benzimidazole-resistant Haemonchus contortus and Ostertagia circumcincta in sheep

Sheep were allowed to graze pasture that had been seeded with benzimidazole-resistant Haemonchus contortus and Ostertagia circumcincta in order to acquire a burden of arrested larvae. Following housing, sheep were dosed orally with either oxfendazole at a dose rate of 4.7 mg/kg (to confirm the benzimidazole-resistant status of the species of nematode), levamisole at a dose rate of 7.5 mg/kg, or an oxfendazole/levamisole mixture at a dose rate of 4.6 mg/kg oxfendazole and 8.1 mg/kg levamisole. The efficacies of the treatments were assessed by estimation of the arrested larval burden in the abomasum of each sheep, either at 10 or 11 days (oxfendazole and oxfendazole/levamisole mixture), or 12 or 13 days (levamisole), after treatment. Compared to the untreated controls, the protection afforded by a single dose of either levamisole or the oxfendazole/levamisole mixture was >99% against the arrested stages of both Haemonchus contortus and Ostertagia circumcincta. Treatment with oxfendazole confirmed the benzimidazole-resistance status of the two species.     

Effect of cimetidine on abomasal pH and Haemonchus and Ostertagia species in sheep

Cimetidine, a histamine H2-receptor blocking agent which reduces gastric acid flow in simple stomach animals was administered directly into the abomasum of sheep at 100 mg kg-1 twice daily for five consecutive days and again on the eighth day. The drug caused a significant increase in the pH values of the abomasal contents and was highly effective in reducing the adult population of Haemonchus contortus (100 per cent) and Ostertagia circumcincta (70 per cent) in the abomasum of sheep. The possibility of using cimetidine as a method of treating abomasal nematode parasitism is discussed.     

Baermannization of Dictyocaulus spp. from faeces of cattle, sheep and donkeys

Faeces were collected per rectum from calves infected with Dictyocaulus viviparus (D.v.), from lambs infected with Dictyocaulus filaria (D.f.) and donkeys infected with Dictyocaulus arnfieldi (D.a.). In one experiment, the influence of storage temperature before Baermannization was investigated. Recovery rate for D.v. was approximately 80% after 24 h at 4 degrees C or 16 degrees C but only 40% at 20 degrees C. After two days at 20 degrees C the rate had fallen to 20%. Recovery rates for D.f. decreased so markedly during the first 12 h at 4, 16 and 20 degrees C that storage can not be recommended. Losses in the recovery rates of D.a. appeared insignificant after 48 h at 4 degrees C but not at 16 degrees C and 20 degrees C. In experiment II the time taken for larvae to emerge from a 10-g sample as well as the sedimentation time in Baermann tubes was investigated. The bulk of the D.v. larvae remained in the faeces for about 10 h whereas D.f. larvae emerged during the first few hours. D.a. larvae were intermediate in this respect. Sedimentation of the bulk of larvae from all three species took place within a few hours with the modified Baermann technique used.     

Haemonchus contortus and Ostertagia circumcincta: fenbendazole treatment and abomasal permeability changes in sheep

Effects of fenbendazole (7.5 mg/kg of body weight infused during 90 minutes) on abomasal transmural potential difference (PD), pH, and ionic concentrations were determined in 8 lambs fitted with permanent abomasal cannulae. Four sheep were treated before inoculation and on day 28 after inoculation, with 200,000 3rd-stage Ostertagia circumcincta larvae and 4 others were similarly inoculated with 15,000 3rd-stage Haemonchus contortus larvae. In worm-free lambs, the unique effect was an increase in Na+ concentration of the abomasal contents. The O circumcincta or H contortus-inoculated lambs had an increase in PD, pH, and Na+ concentrations. Treatment further increased these concentrations, but the effects on PD occurred and ceased earlier in sheep inoculated with O circumcincta than in those inoculated with H contortus. The results indicated that part of the changes were linked to substances produced by the parasites or by the host. The increase in PD and pH was associated with a decrease in K+ concentration and indicated that these substances stimulated HCO3- transfer.