Phenotypic analysis of host–parasite interactions in lambs infected with Teladorsagia circumcincta

Abstract

Teladorsagia circumcincta has a widespread deleterious impact on sheep welfare and economic production. In order to devise effective methods of integrated control and selective breeding, it is necessary to understand the interaction between sheep and T. circumcincta. In this study, female Blackface lambs expected to be genetically variable for resistance to gastrointestinal nematodes were either exposed to a continuous experimental infection of T. circumcincta or sham dosed to monitor the phenotypic response to infection. As a measure of parasitism and host response, faecal eggs were counted over a three month period and post-mortem burdens ascertained. The host response to the infection was also described by differential count of white blood cells, IgA antibody level, and variation in body weight.Results suggest that nematode abundance (mean number of parasites per host) and prevalence (proportion of infected animals) were maximal shortly after the beginning of infection when virtually all the flock was infected and shed worm eggs. The host response was associated with increasing IgA antibody levels and eosinophil concentrations which, the data suggest, caused a reduction of total adult worms and an increase in the frequency of EAL4 (early arrested L4) worms.

Response to Teladorsagia circumcincta infection in Scottish Blackface lambs with divergent phenotypes for nematode resistance

“…Blackface lambs an association was found between peripheral eosinophil concentration and both FEC and worm burden (Beraldi et al, 2008), with resistant (lower FEC) animals having higher circulating eosinophils. In this study, peripheral eosinophil concentrations were not significantly different between HighFEC and LowFEC lambs.…”

“…It has been widely reported that IgA mediates the suppression of gastrointestinal nematode growth and fecundity during infection with T. circumcincta (Beraldi et al, 2008;Martínez-Valladares et al, 2005;Strain et al, 2002), with a strong IgA response often observed against 4 th -stage larvae (Stear et al, 1995b). Most of the IgA, the isotype closely associated with intestinal mucosal immune responses, in sheep blood derives from the mucosal surface of the gastrointestinal tract (Sheldrake et al, 1984), and blood and mucosal IgA levels are correlated (Henderson and Stear, 2006;Martínez-Valladares et al, 2005).…”

Immune and other factors modulating host resistance against gastrointestinal nematode parasites in sheep

“…Henderson and Stear (2006) found no relationship between numbers of adult T. circumcincta and tissue eosinophilia. At the same aspect, Beraldi et al (2008) did not observe relationship between FEC and circulating eosinophil counts. These controversy results are due to the fact that T. circumcincta causes little damage to the mucosal epithelium and eosinophils cannot interact with the parasites on the lumenal side of the intestinal epithelium (Venturina et al, 2013).…”

“…The levels of these two antibody classes are highly negatively correlated with worm length, fecundity and FEC, as both IgA and IgE are significantly increased in resistant sheep (Beraldi et al, 2008;Gossner et al, 2013).…”

“…Several experimental results have identified IgA as a major antibody against parasite infection and fecundity (Beraldi et al, 2008;Shaw et al, 2012). Many researchers support a negative correlation of serum IgA levels with infection parameters.…”