Studies in chickens could lead to blackhead control in turkeys

Broiler breeders with blackhead disease could hold the answer to prevention of the disease in turkeys, Elle Chadwick, a graduate research assistant, North Carolina State University, told Poultry Health Today.

Broiler breeders are an ideal carrier for Histomonas — the cause of blackhead disease — but unlike turkeys that often die from the infection due to its impact on the liver, broiler breeders mount an immune response and survive. In fact, although a drop in weight was seen in chickens infected with Histomonas, egg production actually went up, Chadwick said.

In chickens, Histomonas becomes a normal part of the gut microflora, she explained. There appears to be a limited effect unless there’s another infection present or the birds are stressed. In that case, the immune system wanes, and chickens may experience morbidity or mortality.

People as vectors

The goal of current research is to break the life cycle of Histomonas to prevent the spread from chickens to turkeys, Chadwick said, noting that one vector can be people.

Histomonas is carried by the fecal nematode eggs of the roundworm Heterakis gallinarum. “That egg is really sticky and it can stick onto clothes. You don’t see it when it sticks,” so it can be brought from broiler breeders to turkeys, she said.

Also under study is the turkey’s ineffective immune response to Histomonas. If research can explain what’s lacking, it may eventually be possible to create a turkey that can mount an effective response. It is known that a small percentage of turkeys become resistant to Histomonas, Chadwick said.

She noted that a lot of turkey farms that have blackhead outbreaks were previously broiler farms that hadn’t thoroughly cleaned and sanitized their facilities. “If there’s improper cleaning or insects left after the clean-out, the result can be blackhead,” she said.

Asked whether Histomonas can be transmitted in feed, Chadwick said, “We have not seen transmission through the feed. Histomonas is anaerobic. It’s actually difficult to transmit orally.”

Acidity in the stomach generally kills Histomonas, although infection by oral ingestion of the protozoa is possible when the stomach is not acidic enough. Other methods of transmission are ingestion of dirt or earthworms that contain Histomonas-infected H. gallinarum eggs and a process known as “cloacal drinking” — a reflexive intake of fluids through the cloaca, according to the National Sustainable Agriculture Information Service.¹

1 Spencer T. Parasite Management for Natural and Organic Poultry: Blackhead in Turkeys. National Sustainable Agriculture Information Service. 2010.