Effect of immunosupression on host-parasite interaction in sheep infected with 'Haemonchus contortus'

Abstract

It has been recently reported that immunosuppression using methylprednisolone caused greatly increased worm burdens of 'Trichostrongylus colubriformis' and 'Teladorsagia circumcinta' with little effect in sheep performance (Greer et al., 2005a;b). This indicates that the host immune response is heavily involved in the pathological effects induced by these two parasites. This fits with the Le Jambre theory of co-evolution (Love, 2005) that sheep evolved in Asia with 'Trichostrongylus' spp. and 'Teladorsagia circumsinta' as commensals rather than parasites and that immune responses against them are an unneeded consequence of the need to develop an immune response to the far more pathogenic 'Haemonchus contortus'. Results of previous studies on immunosuppression with dexamethasone and 'H. contortus' infection have found that corticosteroids increased worm burden (Adams, 1982; 1988; Adams and Davies, 1982; Presson, Gray and Burgess, 1988). While, in once case it has been reported that corticosteroids had no effect on worm burden (Adams and Davies, 1982), most of this work did not formally test effects of immunosuppression of the pathogenesis of infection with proper control groups as used by Greer and colleagues (2005a;b), prompting the following experiment.