AbstractsBiology & Animal Science

Heterakis gallinae, the caecal worm of poultry, was described by Taylor (35) as "as perfect a parasite as can be found in that it does no harm to its host". In its normal host, Gallus gallus, the adult stages of the parasite are found in the lumen of the caeca. The larval stages may be found in the lumina and epithelium of the caecal glands as late as the seventh day following infection but usually no tissue invasion is present beyond the tenth day. The degree of typhlitis produced by the larval invasion is variable, depending on the degree of infection. The economic importance of the parasite came to light through the work of Graybill and Smith (19). They demonstrated that blackhead could be produced by feeding embryonated heterakid eggs to turkey poults. In the caeca this nematode acquires the protozoan Histomonas meleagridis, incriminated as the aetiological agent of infectious enterohepatitis. How the protozoa invade the caecal worm or the form taken by the protozoa in the nemic egg has not yet been explained, but in view of the volume of circumstantial evidence, the belief that these phenomena do occur is accepted by the majority of parasitologists. Not all members of this species of roundworm are capable of acting as vectors of the protozoan disease. Tyzzer (36) was able to produce a blackhead-free strain of H.gallinae. This strain was attained by passage in chicks for several generations. Connell (12) located a source of blackhead-free heterakids in Saskatchewan.[...]