Blackhead of Turkeys and Chickens

EVERETT E. LUND.

BLACKHEAD is caused by a microscopic, single-celled animal, Histomonas meleagridis.

It was a devastating disease in turkeys in the East and Midwest a generation or two ago. It still causes heavy losses in some flocks of turkeys and is recognized as a serious disease in chickens whose resistance is lowered by other diseases, by vaccination, or by undue exposure to adverse conditions.

The death rate in individual flocks of turkeys may run as high as 50 percent. Most of the survivors are seriously affected. Turkeys of any age may contract blackhead, but losses are usually greatest among birds 8 to 18 weeks old.

Outbreaks are most common in the spring and fall and usually are more serious in wet seasons than in dry ones. A study in Minnesota in 1951 revealed that of every 1,000 poults started, 87 died with blackhead after being placed on the range; only 6 were lost while poults were still in the brooder house. The average age of birds succumbing to blackhead on range was 17 weeks.

The symptoms of blackhead which is known also as histomoniasis and infectious enterohepatitis are quite distinct, but the name is misleading in that the head does not always turn dark. Other diseases also may cause the head to get black.

The first symptoms are not specific for blackhead but are suggestive. The birds stand with their heads tilted downward or drawn to the body. Their feathers are ruffled. The wings droop. Their eyes are partly closed. At first the birds are alert when they are disturbed, but they quickly become indifferent if they are seriously ill. Young poults may die within 2 or 3 days after the first signs of illness, but older birds may suffer for several days before dying or starting a slow recovery.

The passage of thin, sulfur-colored droppings is characteristic of blackhead, but the disease is well advanced in turkeys before this is conspicuous and it often does not appear as a symptom in chickens.

When birds that have just died from blackhead arc opened, fairly characteristic symptoms may be expected. The ceca the blind pouches are inflamed and ulcerated; they may be filled with a greenish-white material as thick as curdled milk or consolidated into cores. If the birds have been ill a long time, the cores will have become a foul-smelling, brown residue of a creamy consistency. The two ceca need not be affected equally.

By the time the sulfur-colored droppings have been passed, the liver also is visibly involved and has round, grayish-white lesions one-half inch or more in diameter. Nearby lesions may merge. Large lesions often are marked by concentric rings. Small lesions are elevated, but as they increase in size the centers flatten, and then shrink below the level of the margins, until finally the entire lesion may appear as a depressed and pox-marked area. Secondary infections sometimes set in and alter the appearance of the lesions.

The membranes covering the visceral organs and the lining of the visceral cavity sometimes become involved, and they may have a slippery feel. Peritonitis develops in extreme cases and causes death if the blackhead does not.

BLACKHEAD OCCURS when the parasites gain access to the ceca of the bird and are able to multiply in the cecal wall and in the cavity.

Occasionally the bird ingests the naked organism in contaminated feed or water or while picking gravel or preening itself. But in most instances a second parasite, the cecal worm (Heterakis gallinae), is involved. This little worm lives in the ceca of chickens, turkeys, and some other birds. Either the worm itself (which is one-third to one-half inch long and as thick as basting thread) or its egg (which is microscopic) can harbor the blackhead germ and carry it from one bird to another.

Passage by means of the worm eggs seems to be the usual method. Thus the blackhead organism, which is fragile and can live by itself outside the bird for only a few hours and which only rarely reaches its destination in a vigorous state if swallowed alone, has in the cecal worm's egg a nearly perfect means of survival outside the bird's body.

The cecal worm itself usually does little harm. But most chickens reared on the ground eventually harbor cecal worms. A great many also have histomonas, the blackhead organism. Many turkeys also become infected with cecal worms. When that happens, the danger of blackhead becomes great, for it may then be spread rapidly if the histomonad gets into the flock. In such a situation, contamination of feed, water, soil, or feathers with cecal worm eggs, now likely to be carrying histomonads, becomes a serious problem. The cecal worm egg is sturdy and may survive in the soil fora year or longer. Temperature, soil humidity, the action of micro-organisms, and probably other factors influence its survival and may account for the relative ease or difficulty experienced in controlling blackhead.

PREVENTION depends first of all on proper management. Turkeys must be kept entirely away from other fowl. Poults should never be brooded in houses that have been used by chickens, unless the buildings are of materials that can be made scrupulously clean and disinfected thoroughly. Even then they must be allowed to become entirely throughout before they are used. . Buildings with earth floors or floors that are rough and broken or of porous material are hard to make entirely safe. The litter in brooder houses must be kept clean and dry. Good ventilation will help.

Traffic between places where chickens and turkeys are kept must be held to a minimum. If one person or one vehicle or other piece of equipment must service both chicken yards and turkey yards, absolute sanitation must be practiced. Shoes, boots, the bottoms of pails, the tires of carts, and other objects that come in direct contact with the soil or litter of both chicken yards and turkey yards and houses should be rinsed freely with water before bringing them into the turkey yard or house. If they can be left to become thoroughly dry after such a rinse, that, too, will help.