HEAL ▶▶▶TH
Histomoniasis a headache for poultry producers
Histomoniasis, or blackhead, is a complex disease process. Although primarily affecting turkeys with lesions in the ceca and liver, blackhead can also have a significant impact on chickens.
BY JOSE J. BRUZUAL AND COLIN ADAMS, AVIAGEN B
If blackhead is suspected, birds should be sub- mitted to a diag- nostic lab for post mortem examination.
lackhead is caused by the protozoan flagellate, Histomonas meleagridis (H. melegridis) which has a broad host range, infecting gallinaceous birds in- cluding pheasants, partridges and bobwhite quails,
in addition to chickens and turkeys. With the ban on many of the medications used to fight the disease and changes in ani- mal husbandry, such as re-using litter and increased stocking density, blackhead has re-emerged in many areas, including in North America and Europe. The focus for control of black- head is on prevention by cleaning and disinfecting, as well as controlling intermediate host and carriers and the use of new diagnostic methods to better understand how to manage and eradicate the disease.
Vectors and transmission Ingestion of adult common cecal worms (Heterakis gallinar- um) or their embryonated ova (eggs) infected with H. melea- gridis is the main culprit for blackhead. Heterakis gallinarum is the only worm known to serve as an intermediate host for blackhead. After a series of divisions, a uniquely adapted, very small form of H. meleagridis actively invades the repro- ductive tract of the cecal worm and is subsequently shed within the infected worm egg. Cecal worm eggs are extreme- ly resistant to environmental conditions and may remain in- fective for 2-3 years. There is some anecdotal or circumstan- tial evidence of a link between ground works (e.g. disturbing the litter to de-cake or during clean out) and Histomonas out- breaks, as the ground works may re-circulate buried caecal worm eggs. Transport of the infected cecal worm egg by one of several other potential disease carriers or transport hosts is also a risk. These include earthworms (which may ingest the eggs) or mechanical disease carriers, such as flies or rodents, which may simply transport the sticky eggs on their bodies.
14 ▶ POULTRY WORLD | No. 5/6, 2021
PHOTOS: AVIAGEN
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