Without an approved treatment, histomoniasis remains a growing problem among turkeys. The only realistic option for controlling the disease right now, is limiting its transmission once it enters a flock.
By Elle Chadwick, PhD
Consultant
Ag Health Consulting, LLC
LaGrange, Georgia
[email protected]
When we were able to use nitarsone, histomoniasis was well controlled. Research on the disease stopped from the 1970s until the 2000s. Since the drug was pulled from the market in the mid-2000s due to concerns about inorganic arsenic levels in treated birds, histomoniasis — commonly known as blackhead disease — has become a re-emerging disease.
Uncontrollable spread
Producers may lose only a few birds, but they can also lose an entire flock. The main issue I see in the field is uncontrollable spread of histomoniasis and the loss of entire flocks because growers don’t recognize signs of the disease.
The microscopic, single-celled protozoan parasite Histomonas meleagridis responsible for histomoniasis can infect turkeys of any age. It causes inflammation of the ceca, then liver necrosis that ultimately kills the turkey.
Cecal and liver lesions are easy to spot during necropsy, but it’s not always easy to identify living birds developing histomoniasis. To recognize the start of the disease in a flock, all mortality through grow-out would need to be necropsied to look for lesions, but this just isn’t feasible with the number of poults raised in current commercial production.
Intermediate host
H. meleagridis uses the eggs of the roundworm Heterakis gallinarum as protection to survive outside of turkeys and chickens. In other words, H. gallinarum can be considered an intermediate host for H. meleagridis. It only takes a few turkeys to eat contaminated H. gallinarum eggs to set off a histomoniasis outbreak.
The eggs of H. gallinarum need about 1 month to fully mature into worms. That’s why worms aren’t found in infected birds. Histomoniasis, however, will kill a turkey within 2 weeks. Characteristic lesions of the disease appear in the cecum as early as 4 days after infection while liver lesions are seen about 1 week later.
During the 2 weeks poults are infected but alive, they will transmit the parasite to their flockmates through cloacal contact. H. meleagridis survives for a few hours after an infected poult dies, so it’s important to remove sick and dead birds to prevent the spread of the parasite.
Prevention nearly impossible
Preventing the entry of H. m...
