Histomonas/Heterakis (Turkey Blackhead)

Blackhead of Gallinaceous birds

1. A parasite within a parasite within a worm!

2. Agent of destruction: Histomonas meleagridis - the damaging parasite (a protozoan)

3. Heterakis gallinae - a (mostly) harmless cecal nematode parasite

4. Earthworm - an optional paratenic host

Terminology review

1. Direct lifecycle - parasite is transmitted directly from one (definitive) host to another, no intermediate host needed

2. Indirect lifecycle

3. Definitive host: hosts the sexually mature stage of the parasite

4. Paratentic (transport host) - NOT required for completion of lifecycle and in which NO development occurs, Usually a prey species of the definitive host

5. Vector transmits parasite, usually an arthropod

Bird cecum

1. Human appendix is a rudimentary cecum

2. Most birds have very well-developed ceca at the junction of the small and large intestine (some have 2 cecum)

Lifecycle

Histomonads multiply via binary fission. H.meleagridis uses the cecal nematode, Heterakis gallinae to protect it in the environment. Histomonads invade the nematode egg. Those eggs then are often ingested by earthworms. When the bird eats the worm, the nematode egg develops in the cecum and releases the histomonads

Species susceptibility to Histomonas meleagridis

1. Gallinaceous birds

2. TURKEYS (domestic and wild) are VERY susceptible

3. Domestic chickens are VERY resistant

Signs of blackhead

1. 7-12 days after infection

2. Listleness

3. Reduced appetite

4. Drooped wings

5. Sulfur-yellow feces, rarely cyanosis of head (combs, waddles etc)

Lesions

1. Inflammation & ulceration of ceca

2. Yellow-green exudate or cheesy pus in ceca

3. Liver necrosis - maybe focal crater-like, or involve entire liver, liver may be green or tan

Diagnosis

1. History & signs-presumptive

2. Lesions - pathognomonic (a lesion that indicates the disease)

3. Direct microscopic examination of liver or cecal scraping (look for histomonads) or PCR (definitive)

Treatment of Histomonas meleagridis

1. Specific antiprotozoal medicine not approved for food-producing animals

2. Anthelmintics (controlling the nematode, eliminates the protozoan)

3. Nothing realistic for wild birds

Control of histomonas meleagridis

1. Can cause catastrophic losses of wild turkey (over 75% mortality reported)

2. Keep domestic chickens out of wild turkey habitat

3. Partially effective vaccine available for domestic turkeys