Effect of Quil A,a saponin derivative,on the response of sheep to alum precipitatedBacteroides nodosus vaccines

Alum precipitatedBacteroides nodosus vaccines prepared from two antigens with and without the saponin derivative, Quil A, did not induce adverse tissue reactions in sheep injected subcutaneously. Vaccinated, non-infected Merino sheep had higher agglutinin antibody titres when the vaccines included Quil A. Moreover, the recovery rates in vaccinated sheep affected with foot-rot were higher when the vaccines included Quil A.     

The occurrence, prevalence and transmission of Bacteroides nodosus infection in cattle

Following reports of findings of ovine foot-rot flora in the feet of cattle, a study was undertaken to determine the prevalence of Bacteroides nodosus infection in the apparently normal cattle population. We found that 34.5 to 74.2 per cent of the animals examined on different farms had B nodosus present in one or more feet. B nodosus was not the most prevalent bacterium observed in smears from cattle. Other Gram negative species including Fusiformis necrophorus and many Gram positive cocci and coccobacilli were also present. Macroscopic lesions in the interdigital skin characterised by erosion and hyperkeratosis were usually associated with the occurrence of B nodosus. B nodosus isolated from cattle induced mild interdigital dermatitis in experimental cattle and sheep and the infection was transmitted to recipient cattle and sheep under field conditions. Virulent foot-rot of sheep was not transmitted to recipient cattle in conditions where the disease spread to susceptible sheep.     

The anthelmintic efficacy of ivermectin in experimentally infected cattle

The 22,23-dihydro derivative (ivermectin) of the major B₁ components of the avermectins was evaluated, by oral and parenteral routes, for anthelmintic activity in cattle experimentally infected with 7 gastro-intestinal nematode species and lungworm. Treatment at three dosage levels was administered when the parasites were in the L₄ developmental stage or when adult. The dosage expected to remove 95% of the nematodes (ED₉₅) by each route of administration against the various developmental stages of each species of parasite was calculated by methods of linear regression to choose dose levels to be used in subsequent developmental field trials. Parenterally, efficacy against L₄ stages of Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punctata, Oesophagostomum radiatum and Dictyocaulus viviparus exceeded 99% with treatment at 0.2 mg ivermectin/kg. Parenteral treatment of the adult parasites resulted in at least 98% reduction of worm burdens, except $\text{? 90\%}$ for T. colubriformis, with 0.2 mg/kg. Oral treatment of L₄ stages of development with 0.2 mg/kg resulted in at least a 95% reduction in worm burdens of each of the 8 species of parasite. Oral treatment of the adult worms with 0.1 mg ivermectin/kg produced at least a 98% decrease in each parasite species, except for T. colubriformis (90% reduction) for which dose-response calculations suggest 95% efficacy with oral treatment at 0.2 mg/kg.     

Prophylaxis of nematode infections in cattle with an indwelling rumino-reticular ivermectin sustained release bolus

Ivermectin delivered continuously from a rumino-reticular sustained release device was prophylactically effective in preventing establishment of nine nematode parasite species in multiply-exposed cattle. Ivermectin dosages which permitted less than or equal to 1% of infected control calf worm populations to establish ranged from less than 2.5 micrograms kg-1 day-1, which totally prevented infection with Dictyocaulus viviparus and Oesophagostomum radiatum, to approximately equal to 30 micrograms kg-1 day-1 required to suppress Nematodirus helvetianus to the same extent. Between these extremes, in decreasing order of sensitivity to enterical sustained release ivermectin, were Ostertagia ostertagi, Trichostrongylus axei, Haemonchus placei, Cooperia punctata, C. oncophora and T. colubriformis which were maximally affected at less than or equal to 10 micrograms kg-1 day-1 of ivermectin.     

Dose-titration studies of ivermectin against experimental Ancylostoma caninum and Uncinaria stenocephala infections

Dose-titration trials of ivermectin were conducted on pups with dual experimental infections of 4th-stage larvae or adult Ancylostoma caninum and Uncinaria stenocephala. Ivermectin was administered orally or subcutaneously at dosages of 0.006, 0.012, or 0.024 mg/kg of body weight. Maximal or near maximal (greater than or equal to 96% to 100%) anthelmintic effect was observed for both stages of development for each hookworm species by either route of administration at a dosage of 0.024 mg/kg. Responses for all of the aforementioned categories were linearly related to increasing log dosage of ivermectin, with common slopes (regression coefficients). Regression analysis also provided estimates of the minimal dosages required to produce maximal reduction in worm burden for each stage, species, and route of administration. The estimated ivermectin dosages for maximal efficacy ranged from a low of 0.014 mg/kg for adult A caninum by oral treatment to 0.044 mg/kg for 4th-stage larvae of U stenocephala by oral treatment.     

Effect of reticuloendotheliosis virus on the response of chickens to Salmonella typhimurium infection

Groups of 25 chickens free of maternal antibody to reticuloendotheliosis virus (REV) were inoculated with either third or seventh passage REV at either one or seven days of age. Some of the birds inoculated at day 1 with REV were inoculated with Salmonella typhimurium either concurrently or six or 13 days later while some of those inoculated with REV at day 7 were inoculated concurrently with S typhimurium. At day old, infection with S typhimurium alone caused the death of 12 of 25 chicks whereas in the dual infection, using the third passage REV, 18 of 25 birds died. Similarly no seven or 14 day old chickens died when challenged with S typhimurium alone, but previous day-old infection with REV caused a respective mortality of eight of 25 and five of 25 birds. With the seventh passage REV a similar pattern was seen. At day old S typhimurium infection alone killed seven of 25 birds whereas combined with virus the mortality was 14 of 25 and while S typhimurium alone killed none of 25 chicks infected at seven days old, the mortality in birds also infected with REV was 14 of 25. Combined virus and bacterial infections did not increase the proportion of feathering defects in birds surviving S typhimurium infections. There was a significantly higher proportion of feathering defects in birds infected with third passage virus compared with seventh passage virus. Although a higher proportion of birds had antibody responses to REV in the seventh than in the third passage group, there was no discernible difference in the effect the different viruses had on chickens' susceptibility to S typhimurium.     

Characteristics of Bacteroides nodosus isolated from cattle

Fourteen isolates of Bacteroides nodosus were cultured from cattle on six farms and examined for colony morphology, pilation, agglutinability, proteolytic activity and pathogenicity for sheep. Where sheep were also present on the farms, isolates from these were compared with those from cattle.Colonies of the bovine isolates were moderately fimbriate. Cells from these colonies were pilated, but not to the extent observed on virulent sheep isolates. The proteolytic activity of the isolates was also less than that described for virulent ovine isolates. When inoculated into sheep, B. nodosus from cattle produced only mild interdigital inflammation. There was no separation of horn characteristic of virulent foot-rot. Preliminary studies, based on agglutination tests, suggest that B. nodosus with different surface antigens may occur in cattle in the same herd and in cattle and sheep on the same farm. On one of six farms isolates from cattle and sheep were indistinguishable by the agglutination test.