Blackhead Disease Does Not Really Cause Black Heads By W.R. Davidson & G.L. Doster NWTF WILDLIFE BULLETIN NO.25 MITH C. S LENN G A healthy wild turkey gobbler in full strut looking for a mate. istomoniasis is caused by a protozoan parasite named Histomonas meleagridis. Often called blackhead disease, Hhistomoniasis primarily affects gallinaceous birds (chickens, grouse, partridge, peafowl, pheasants, quail, turkeys). The old name “blackhead disease” is a misnomer because the heads of birds infected with histomoniasis do not turn black. Despite the limited number of confirmed reports, histomoniasis is an important disease of wild turkeys. SIGNS OF INFECTION: Clinical signs in turkeys may include sulfur-colored droppings, lethargy, drooping wings, eyes closed, head held close to the body, weakness, or emaciation. Lesions are characterized by thickening and ulceration of the lining of the ceca and by focal necrosis in the liver. The NATIONAL WILD combination of swollen, inflamed ceca with yellow, cheesy cecal cores TURKEY FEDERATION and discrete spots of necrosis in the liver is considered indicative for his- tomoniasis. Variations in the severity and appearance of lesions are not uncommon, however, and cecal lesions without liver involvement occur occasionally. 25-1 OSTER D ARY G The cheesy core in the ceca of a turkey infected with histomoniasis. Histomoniasis appears frequent- ly in the scientific, semi-technical, and popular literature in discussions of diseases of wild turkeys; however, scientifically confirmed accounts of histomoniasis in wild turkeys are relatively few. For example, it accounted for 12% of 266 sick or dead wild turkeys from 10 south- eastern states that were submitted for diagnosis to the Southeastern Cooperative Wildlife Disease Study on the University of Georgia/Athens campus from 1972-1994. Different species of galliform birds vary greatly in their suscepti- bility to clinical disease due to his- tomoniasis. The course of infection in different host species spans the OSTER entire spectrum from a total toler- D ance without lesions to severe dis- ARY G ease with a very high death rate. The liver of a turkey infected with histomoniasis. Note the discolored, depressed lesions. Unfortunately, turkeys, either wild or domestic, almost always develop severe disease following infection. Chukar partridge, peafowl and ruffed grouse also are prone to severe disease. At the opposite end of the spectrum are species such as ring-necked pheasants, chickens and 25-2 /USFWS MENKE E AV D junglefowl which rarely become “Carrier” species, like this ring-necked WILD TURKEYS, PHEASANTS pheasant should not be introduced into sick; these species serve as carriers AND CHICKENS DON’T MIX: habitats already occupied by wild turkey of the parasite for more susceptible populations. species such as wild turkeys. These epidemiologic factors are Bobwhites, guinea fowl and important considerations in the pre- Hungarian partridge occupy inter- vention and control of histomoniasis mediate positions in which clinical under field conditions. They serve disease is common, but with fewer as the basis of the old axiom of instances of sickness or death. poultry producers “do not raise Aside from the fact that dis- chickens and turkeys together.” eased avian hosts may die and be They also form the basis for the rec- lost as a source of infection, survival ommendations in place for many of the heterakid roundworm vector decades not to introduce “carrier” in diseased ceca is extremely poor species such as pheasants or jungle- and often the worms die before the fowl into habitats occupied by wild birds do. Thus, individual birds or turkeys and not to use chicken litter species in which severe cecal lesions as fertilizer on fields or pastures fre- develop usually are not important quented by wild turkeys. sources for transmission. In con- Concepts regarding the disease trast, hosts in which cecal lesions risk posed to wild birds by the use are absent or minimal continue to of chicken litter as fertilizer were support heterakids which in turn derived long before modern produce large numbers of his- improvements in husbandry and tomonad-bearing eggs. disease control within the commer- cial poultry industry. Recent 25-3 worm, Heterakis gallinarum, which also infects the ceca of many species of galliform birds. The histomon- ads, in addition to infecting the ceca of the bird, also infect the female heterakid worms and become incor- porated within the worm’s eggs. The delicate histomonads, which do not survive direct exposure to the environment, are transmitted within the protective covering of worm eggs in the droppings of infected birds. When the histomonad-bear- ing worm eggs are ingested by a suitable host and hatch, the his- tomonads are released in the ceca OSTER where they reproduce by repeated D ARY division. Birds also may acquire G both heterakid worms and his- Adult Heterakis worms are no more than 1/2 inch long, but the females may contain several tomonads by consuming earth- hundred eggs within which the Histomonas protozoa are transmitted. worms which can serve as transport research has shown that infections ing, ulceration, and hemorrhage, hosts of heterakid larvae by ingest- with both Histomonas meleagridis which are accompanied by exten- ing heterakid larvae and in this and Heterakis gallinarum differ sive inflammation and the develop- capacity as transport hosts are an greatly among commercial broilers, ment of cheese cecal cores. important means of transmission, which are essentially free of these Histomonads from the cecal lesions especially under field conditions. parasites, present virtually no his- commonly gain entry to small veins For additional information on tomonias risk when used as fertiliz- and are carried by the blood to the this subject refer to The Wild Turkey: er on wildlife habitat. Litter from liver. In the liver the histomonads Biology and Management, edited by breeder birds or layers usually is continue reproducing and cause Jim Dickson. The book is available contaminated with both the cecal focal areas of necrosis and an for $59.95 from the National Wild roundworm and the protozoan that intense inflammatory response. A Turkey Federation, causes histomoniasis and should diagnosis of histomoniasis can best 1-800-THE-NWTF. not be used as fertilizer on wildlife be made upon examination of a habitat. It is also recommended that fresh, refrigerated carcass. However, wild turkeys be prevented from if it is not possible to deliver the using the same habitat as free-rang- carcass to a diagnostic laboratory ing “yard chickens” because these within 2 or 3 days after death, a chickens usually are infected with frozen carcass can be used. Heterakis gallinarum and are often The way that Histomoniasis carriers of histomoniasis. meleagridis is transmitted from bird The histomanads invade the lin- to bird is unusual in that it is ing of the ceca, producing thicken- dependent upon a parasitic round- 25-4.