Direct anthelmintic and immunostimulatory effects of oral dosing semi-purified phytohaemagglutinin lectin in sheep infected with Teladorsagia circumcincta and Trichostrongylus colubriformis

Lectins are plant secondary compounds that can have anthelmintic properties in vitro. In particular, the phytohaemagglutinin lectin extracted from Phaseolus vulgaris has been shown to inhibit the feeding of Trichostrongylus colubriformis and Teladorsagia circumcincta L1 larvae. However, little is known about the potential anthelmintic properties of this lectin in vivo and its suitability to control gastrointestinal parasite infections in lambs. In a 2 × 2 study, lambs were either orally dosed, or not, with 2.3mg semi-purified PHA lectin per kg live weight (LW) per day, whilst concurrently infected, or not, with 1000 T. circumcincta and 1000 T. colubriformis L3 infective larvae per day for 42 days. There were no adverse clinical effects observed with this dose of PHA lectin. Although worm burdens were similar, animals dosed with PHA lectin had reduced concentration of nematode eggs in the faeces compared with their non-lectin dosed counterparts (P=0.026), suggesting that there may be a direct effect of PHA lectin on parasite fecundity. Irrespective of infection, PHA lectin had immune-stimulatory properties with increased eosinophillia in both abomasal and small intestine tissue sections taken at slaughter on day 42 (P<0.02 for both) and a tendency for decreased ability of Teladorsagia larvae to penetrate abomasal tissue explants (P=0.06). Compared with infection alone, concurrent PHA lectin dosing and infection further increased the number of eosinophils (P<0.01), PAS-positive (mucin-producing cells) (P=0.03) and tended to increase the number of T helper cells (P=0.06). No interactions were observed for cell populations in small intestine tissue sections. These results suggest PHA lectin could have two possible modes of action against T. circumcincta and T. colubriformis, a direct anthelmintic effect on nematode fecundity and an indirect effect through enhancing local immune responses in the host.