Ask the Vet: Blackhead disease

With no current effective treatments, it has become increasingly important to understand the disease process and proactive measures to decrease the risk of blackhead entry into your flock.

What causes blackhead?
It is a parasitic disease caused by Histomonas meleagridis that results in clinical disease in numerous poultry species like turkeys, chickens and quail.

What does it look like?
Blackhead is a disease that primarily affects turkeys and will begin to present itself around seven to 12 days after exposure. Affected birds will have droopy wings, their head drawn towards their body, sulfur coloured droppings and appear lethargic.

Often in chronic cases the birds will begin to lose significant muscle mass. Mortality can be quite variable, but in some instances if left untreated can reach up to 100 per cent.

The necropsy lesions can be quite profound and help guide in making a quick diagnosis. There can be enlargement of the ceca with thickening of the wall and yellow caseous cores.

The liver can contain multiple target like lesions that will reach sizes of one to two centimetres in diameter. If you suspect this illness in your flock, it is very important to submit birds to your local laboratory and contact your veterinarian immediately.

How is it transmitted?
Birds can contract the disease by ingesting cecal worm eggs containing Histomonas meleagridis or by ingesting earthworms that are carrying cecal worms infected with the parasite.

The most common source of horizonal transmission within an infected flock is cloacal drinking. This is a natural process where a turkey surveys the litter environment by intaking material to help build the immune system. Unfortunately, if the turkey is sitting on Histomonas contaminated feces it will allow easy access of the parasite to the gut wall.

Another way the disease is transmitted is when birds directly ingest contaminated feces within a barn or pasture. This is an unlikely initial source of infection and often only marginally contributes to the spread within a flock.

Required actions

• Obtain a rapid diagnosis and veterinary confirmation (by gross lesions, gut scraping and microscopy).
• Use fencing to make pens in the barn with the intention of segregating the sick and healthy birds. This will also act to slow down the spread of disease within the barn.
• Cull all birds that appear depressed and lethargic. If birds are at or near market weight, plan an emergency slaughter.
• Apply hydrated lime to the litter and top dress the litter with fresh shavings.
• If possible, move the flock to a clean barn as soon as possible.
• Communicate the diagnosis to the plant for the expectation of increased liver condemnations (product is not a risk to human health for consumers or plant workers).

Follow up:

• Intensively clean and disinfect the contaminated barn.
• Increase biosecurity between flocks located on the same farm. This would include separate boots and coveralls at every barn entry.
• Work with your veterinarians to develop a deworming program.
• Apply salt to the perimeter of the barn to minimize the risk of earthworms gaining access inside and evaluate the seals of all barn entry points. This is especially important after recent rainfalls, as earthworms will prefer to move on wet cement as it will allow them to move much faster than in the dirt.

New treatment option
The Canadian Association of Poultry Veterinarians was successful in working with Health Canada to achieve an emergency drug release for Paramomycin, which is a product used in Europe to treat blackhead. The product will be held in a stockpile for veterinarians to access as needed. This process is ongoing but expect to have the product available for emergency use within the next few months.

Blackhead can be a devasting disease and hopefully by taking the necessary precautions you can lower the risk of infection on your farm.

Tom Inglis is managing partner and founder of Poultry Health Services, which provides diagnostic and flock health consulting for producers and allied industry. Please send questions for the Ask the Vet column to poultry@annexweb.com.