Eosinophil and IgA responses in sheep infected with Teladorsagia circumcincta

Infections of sheep with the gastrointestinal nematode Teladorsagia circumcincta are characterised by increased concentrations of IgA, eosinophilia and mastocytosis but the interactions between these immune responses are unclear. We investigated the kinetics of the parasite-specific IgA and eosinophil responses in controlled infections in lambs to determine if there were any associations with subsequent worm growth and survival. IgA and eosinophil responses had very similar kinetics and variation in both responses accounted for more of the variation in adult worm length than either trait alone suggesting that IgA and eosinophils interact in regulating the growth of T. circumcincta. Curiously, those animals with higher peak eosinophil responses had longer worms at slaughter emphasising the intriguing complexity of the immune responses to these parasitic infections.

A key mechanism of pathogenesis in sheep infected with the nematode Teladorsagia circumcincta

Infection of sheep with the abomasal nematode Teladorsagia circumcincta can cause a relative protein deficiency and reduce growth rate in growing lambs. A key event appears to be the destruction of junctions between epithelial cells. If the infection is heavy or prolonged, this leads to increased mucus production, hyperplasia, decreased acid production, gastrinemia, inappetance and pepsinogenemia. The severity of the infection depends upon the extent of concurrent infection, the nutritional status of the host and genetically controlled variation in the ability to mount protective immune responses.

Eosinophilia as a marker of resistance to Teladorsagia circumcincta in Scottish Blackface lambs

Faecal egg counts and peripheral blood eosinophil counts were taken from Scottish Blackface lambs following natural, predominantly Teladorsagia circumcincta infection. Peripheral eosinophil concentrations were higher in animals with lower egg counts but only in lambs that were at least 3 months of age. The reduced egg counts were due to reduced fecundity of T. circumcincta; there was no association with the number of adult T. circumcincta. Associations with the number of parasites from other species of gastrointestinal nematodes appeared to be neutral or favourable. Estimated heritabilities for eosinophil concentrations in 4- and 5-month-old lambs were 0.48 +/- 0.16 and 0.43 +/- 0.17, respectively. Therefore, under defined circumstances, eosinophil concentrations may be a useful indicator of resistance to predominantly T. circumcincta infection.

The genetic control of IgA activity against Teladorsagia circumcincta and its association with parasite resistance in naturally infected sheep

Previous studies in deliberately infected sheep have shown an association between IgA activity against 4th-stage larvae of Teladorsagia circumcincta and parasite growth, development and fecundity. The purpose of this research was to determine if these results could be confirmed in naturally infected sheep and to explore the hypothesis that plasma IgA activity could help to identify resistant lambs with shorter adult nematodes. Plasma IgA activity was skewed with most animals having relatively low levels of IgA activity. Plasma IgA activity was repeatable and highly heritable. Animals with increased IgA activity had lower egg counts and shorter adult female T. circumcincta. Therefore, under conditions of natural parasite challenge, plasma IgA activity may help to identify lambs resistant to T. circumcincta.