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Blackhead -turkey vet - Histamoniasis

Blackhead Disease - Turkey vet - Avain vet 

 

Blackhead disease, or histomoniasis,

causes intermittent but severe disease in turkeys.  Losses can also occur in  chickens and  peafowl and certain other gallinaceous birds. Chickens are more resistant to the effects of the infection but may act as carriers of the disease-causing organism. Blackhead disease, is primarily a disease of young turkeys. Histomoniasis is caused by a microscopic protozoan called Histomonas Meleagridis. The name blackhead is a poor descriptive term because the heads of the birds the bird vets see  infected with this parasite are not black!. At melbourne bird vet the the protozoan causes considerable pathological damage to the liver and ceca of infected turkeys, and the untreated birds usually die.
 

the life cycle of Histomonas meleagridis - pet turkey

 

Usually by eating infected Ascarid eggs from the species Heterakis.  It was  believed that infections in turkey flocks arose only from the ingestion of embryonated eggs of the caecal worm Heterakis gallinarum, or ingestion of earthworms that were carrying larvae of the caecal worm. (turkeys eat infected earthworms, the cecal worm larvae containing the blackhead parasites are released and a blackhead infection may result.)

This mechanism did not explain the phenomenon of rapid spread of blackhead through a flock of turkeys, and led some to question whether other intermediate hosts might be involved. 

Spread in a flock also occurs by intake of liquid faeces in a process known as "cloacal drinking" – via the cloaca or vent.  The implication is that separation of sick birds becomes a primary part of stopping the spread. 
 

Where do turkeys get infections from ?

It is common that veterinarians at  bird vet  Melbourne are  unable to find Heterakis worms associated with outbreaks in turkeys.

Ringneck pheasant was the best host for caecal worms, followed by chickens and then guinea fowl. 

Caecal worm (Heterakis gallinarum) eggs, which are the only known biological vector of the blackhead organism. (Earthworms can harbour caecal worms until they are eaten by chickens or turkeys, but this is only an 'extra' reservoir of infection and not a necessary part of the life cycle).

Where did blackhead disease come from?

the pheasant re far better hosts for Heterakis than even chickens, and suffer little from the effects of histomoniasis, making them ideal as reservoirs of the disease.

 

Clinical Signs( Turkey vet)- Avain vets 

A decrease in feed consumption and loss of weight may be the first signs observed. Sick birds appear dull and depressed, and often stand by themselves with dropping trails, ruffled feathers, and a sleepy appearance.

Sulphur colored yellow droppings may be observed. Birds dying of histomoniasis have characteristic enlarged livers with circular depressed areas and enlarged ceca containing a rather dry cheesy material  Recovered birds may show swollen hard and scarred livers.

 

How is blackhead controlled by management?

Prevention of blackhead in turkeys by management is two-fold:

1.    Nitro-imadazole antibiotics like metranidazole or ronidazole or Dimetradiazole

2.    Prevention of exposure by quarantine or isolation, especially avoiding any contact with chickens or game birds,

3.    The protozoa-causing blackhead may remain infective within the in the soil for nearly three years;

4.     Young turkeys should never be reared with older turkeys or with chickens that may carry the infection. Chickens, various wild birds such as pheasant and grouse may serve as reservoirs of infection for domestic turkeys.

Also, farm owners should be aware of  workers  keeping of backyard chickens, pheasants, chukars or fighting cocks.- a source.

Could a vaccination against histomoniasis be developed? - Vet for Turkeys 

Previous investigators considered immunization an impractical approach to control of blackhead disease. Repeated infection and treatment with dimetridazole produced turkeys that were resistant to re-infection after three infection/treatment cycles. 

Recent experiments were successful in demonstrating some protection when turkey poults were given two or more inoculations with an antigen consisting of freeze/thawed cultured H. meleagridis. A single inoculation failed to offer protection when birds were challenged within a few weeks. 

More work is needed to identify the best vaccination regime, the amount of antigen needed, and the possible contribution of bacteria to the host immune response.

Does Histomonas respond to anticoccidials or antibiotics?

The answer to this is essentially no. Like some of its common relatives Trichomonas and Giardia, it is anaerobic and lacks mitochondria. These organisms make energy by an anaerobic process involving special organelles called hydrogenomes, 


Antibiotics normally have little beneficial effects on turkeys during a blackhead outbreak. Early and frequent preventive use of wormers can be of benefit in chickens because worms are the primary source of infection . In turkeys, where the infection spreads easily from bird to bird, this is probably not of value after outbreaks start.

Discussion and Conclusions

Even though losses from blackhead disease continue to be highly significant, some progress has been made in recommendations for control by management. Chickens and game birds are likely the most important source of infection for turkeys and other birds, as they are prolific in generation of infective cecal worm ova. 

The life cycle of Histomonas has been reconsidered, after the discovery that turkeys could become infected from direct contact with other birds or contaminated faeces. 

The unique structure and metabolism of Histomonas makes these organisms immune to treatment with anticoccidials and antibiotics, but antibiotics are usually considered beneficial to treat secondary bacterial infections.