Carbonic acid as the host signal for the development of parasitic stages of nematodes

Petronijevic T., Rogers W. P. and Sommerville R. I. 1985. Carbonic acid as the host signal for the development of parasitic stages of nematodes. International Journal for Parasitology 15: 661–667. This paper gives results on which may be based an identification of the component of the system CO 2 + H 2O ai H 2CO 3 ai H + HCO 3 − which acts as the stimulus from the animal host for some nematodes. Using infective juveniles of Nematospiroides dubius and Haemonchus contortus, the effects on exsheathment of (1) low pCO 2 values, (2) the presence of carbonic anhydrase in the stimulating medium, and (3) the inhibition of carbonic anhydrase within the juveniles have been examined. The results lead to the suggestion that it is the “readily available” undissociated H 2CO 3, or H 2CO 3 + HCO 3 − which is the critical factor in the stimulus for development. The wide range of [H +]s over which “readily available” H 2CO 3 is present in physiological environments suggests that this host signal may be important for infection with many species.