Natural infection by intestinal nematodes was assessed in Santa Ines and Ile de France sheep breeds, over a five-month grazing period, with emphasis on the development of the immune response in lambs under two anthelmintic treatment regimens. Nineteen Santa Ines and 19 Ile de France male lambs were allocated into two treatment groups: animals under suppressive treatment with anthelmintics; and animals under targeted selective treatment (TST). The nematodes Trichostrongylus colubriformis and Strongyloides papillosus showed the highest infection intensity in the TST animals in both breeds. Parasite-specific immunoglobulin G levels were significantly higher and more rapidly induced in Santa Ines lambs. Additionally, these lambs had higher levels of parasite-specific immunoglobulin A in intestinal mucus. Animals under TST had higher means of mast cells and globule leukocytes in the intestinal mucosa due to longer and greater parasite challenge in comparison with the suppressive group. A breed effect (P < 0.05) was recorded for mast cells, with Santa Ines lambs presenting the highest counts. Although Santa Ines lambs had lower intestinal nematode counts than Ile de France lambs, they had shown a large variation in T. colubriformis burden, with most of them presenting a marked worm burden, despite showing an earlier and more intense immune response to intestinal nematode infection.

Knowledge regarding helminth control strategies and nematode infection of horses in Ireland is limited and only one study has been published recently. This present study was designed to investigate the current helminth control strategies followed by horse owners in Ireland. A questionnaire was formulated to collect data on general grazing, pasture management and deworming strategies including the use of fecal egg counts. Questionnaires were emailed to 700 members of the Irish Thoroughbred Breeders Association and Horse Sport Ireland. Only 78 questionnaires were returned. Respondents indicated that horses are grazed for 16–24 h day−1 during the summer and autumn (89% and 65%, respectively). Removing feces from the pasture was implemented by 37.6% of respondents. Few (22.2%) owners kept horses off pasture after worming. Overall, ivermectin and moxidectin were the most commonly administered anthelmintics in 2014 by 75% and 62% of respondents, respectively. Benzimidazole and pyrantel drugs were used by 53% and 35% of respondents, respectively. The majority of farms (81.4%) treated horses 4–5 times per year and 74.2% only estimated the weight of the horses visually. The findings of this study illustrates that many stud managers/owners do not follow best practice with regard to helminth control and more education is needed.

Weight and length profiles are presented of 3505 Ascaris worms recovered after mass anthelmintic treatment of a human community in January 1984 and, after an 11 month period of reinfection, in November 1984. Male and female worms recovered after reinfection were significantly heavier and longer than those expelled after initial treatment (P < 0·0001). Multiple regression models were employed to examine variability in parasite size. A positive influence of host body weight on the weight of parasites recovered in January, but not in November, was observed. No negative relationship was recorded at either date between worm size and the total number of worms harboured, even after controlling for host weight. Striking host age-related variability was observed in the distribution profile of weights and lengths of individual worms recovered in January. Children harboured predominantly smaller worms before initial treatment, while adults expelled mainly heavy worms. In contrast, worms expelled by both children and adults after reinfection were heavier and more homogeneous in size, particularly within the relatively heavily infected group. These patterns argue against a primary role for density- dependent or acquired resistance mechanisms in determining the size of Ascaris in humans. However, the results are consistent with a hypothesis initially suggested by Jung (1954) that established worms may inhibit the development of newly acquired Ascaris larvae, perhaps regulating their own abundance.