The story of blackhead, insofar as scientists have deciphered its perplexing problems, is that of a unique relationship existing between a number of avian hosts, a protozoan parasite and a parasitic nematode vector. Blackhead is acknowledged to be economically the most important disease of turkeys, having forced the abandonment of turkey rearing in many parts. Fortunately, in other susceptible species of birds, the disease seldom causes serious losses. In the caeca of the chicken, and perhaps,too, in the caeca of other susceptible birds, the blackhead organism, Histomonas meleagrldis, lives and multiplies without producing clinical disease except on rare occasions. Another inhabitant of the caeca is the worm, Heterakis gallinae, which picks up Histomonas, serving as vector host of blackhead by virtue of the fact that Histomonas becomes incorporated in its eggs. It is not known how Histomonas gets into the caecal worm egg or what form the egg-borne stage of the parasite takes. There is overwhelming evidence to show that it is there, however, because when the eggs of the worms from birds carrying blackhead are embryonated and fed to susceptible turkeys, the latter develop clinical blackhead. The work leading to the discovery of the above facts, and of others relating to the subject are considered in the historical review. H. gallinae does not always carry the organism that initiates blackhead.[...]
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.123829 |
| Date | January 1949 |
| Creators | Connell, R. W. |
| Contributors | (Supervisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science. (Department of Parasitology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: NNNNNNNNN, Theses scanned by McGill Library. |
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