Reducing Losses from Blackhead Disease: Poultry

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Poultry Site- New research from the University of Georgia reveals that chicken litter may pose a risk of transmitting blackhead to turkey flocks, while their work to vaccinate birds against the disease was unsuccessful.

Drs Robert Beckstead and Larry R. McDougald of the University of Georgia report that they used molecular techniques were used to track outbreaks of Blackhead Disease (histomoniasis), to correlate these outbreaks with specific isolates of Histomonas meleagridis, and to identify genes associated with the virulence of specific isolates.

Additionally, the project tested whether a vaccination approach could be used to protect turkeys from this disease. Isolates from outbreaks in turkeys, broiler breeder chickens, layer chickens and bobwhite quail were tested for virulence and categorised by molecular markers.

The objectives of the research, sponsored by the US Poultry & Egg Association, were to:

survey H. meleagridis field isolates from turkeys, broiler breeder pullets and other wild birds for variation in virulence
correlate virulence to molecular markers that classify H. meleagridis stains.
investigate the epidemiology of field isolates obtained from H. meleagridis outbreaks using molecular markers.
identify potential disease reservoirs and modes of transport of H. meleagridis between farms
establish and validate a molecular diagnostic test for H. meleagridis and
establish a vaccination protocol to stimulate protective immunity in turkeys.

The data from Athens confirm that there are multiple disease reservoirs and that most outbreaks of blackhead arise from distinct isolates of H. meleagridis.

Isolates varied considerably in virulence, sensitivity to nitarsone (Histostat-50) and expression of virulence genes. Variations in mortality and morbidity in outbreaks in the field was a result of the virulence of the associated isolate, particularly in chickens.

Based on this data, litter from breeder or layer pullets is likely to contain caecal worm (Heterakis galllinarum) eggs, the known vector for H. meleagridis, is the most likely source of infection in turkeys.

Although this confirms earlier work, Beckstead and McDougald stress it emphasises the increasing infection pressure resulting from overlapping areas of broiler breeder chicken farms and turkey farms.

One strain of H. meleagridis isolated from layer pullets resulted in 17 per cent mortality in chickens in the lab, highlighting the potential of this parasite to devastate chicken flocks as well as turkeys.

The researchers report they have designed a new molecular-based method to diagnosis H. meleagridis in samples obtained from tissue. This PCR-based method is specific to H. meleagridis and allows quick diagnosis without costly DNA sequencing.

Vaccination approaches using attenuated live and killed preparations tested by this group failed to produce adequate timely protection in turkeys. Although the researchers saw a delay in the onset of the disease in birds given live attenuated H. meleagridis, complete protection was never attained. While this approach was reported as successful in the literature, these results do not support the use of a vaccination to prevent blackhead.

This study is the first of its kind funded in the recent years, according to Beckstead and McDougald.

It is clear from the results that a significant part of the biology of H. meleagridis and its interaction with chickens and turkeys is poorly understood. Based on their data, there are many local reservoirs of infection in the environment, increasing the difficulty in preventing blackhead outbreaks.

Careful consideration should be taken when spreading litter from chicken farms near turkey facilities, they continue.

More research is needed to identify insects or other mechanical carriers responsible for survival and spread of the blackhead.

Identification of strains with high virulence in chickens suggests we should use caution in spreading litter from these farms near other poultry operations, Beckstead and McDougald concluded.
Further Reading

Find out more information on blackhead disease

Histamonosis, Histomoniasis, Blackhead

Introduction

Histomonas melagridis is a protozoan parasite of turkeys, and occasionally chickens, pheasants and game birds that acts together with facultative bacteria to produce the condition of Blackhead. This condition has high morbidity and mortality in turkeys. Although chickens are relatively resistant to the condition, significant disease has been seen in breeding chickens and free-range layers. The parasite is ingested in the ova of Heterakis worms or as larvae in earthworms or faeces and there is an incubation period of 15-20 days. Outwith earth worms or H. gallinae the parasite is easily destroyed. The problem is seen in high-biosecurity facilities, presumably introduced with worm eggs. Within a turkey shed transmission is rapid in spite of the fact that it is difficult to infect birds orally with unprotected parasites. It has recently been demonstrated that infection occurs readily via the cloaca when birds are on contaminated litter.
Signs

Depression.
Inappetance.
Poor growth.
Sulphur-yellow diarrhoea.
Cyanosis of head.
Blood in faeces (chickens).
Progressive depression and emaciation.

Post-mortem lesions

Enlargement of caeca.
Ulcers, caseous cores with yellow, grey or green areas.
Liver may have irregular-round depressed lesions, usually grey in colour, however they may not be present in the early stages, especially in chickens.

Diagnosis

Lesions, scrapings from fresh material.
Treatment

Historically nitro-imidazoles (e.g. dimetridazole), nitrofurans (e.g. furazolidone, nifursol) and arsenicals (e.g.nitarsone) have been used to treat this important disease of poultry. At the time of writing no products of these groups are approved for use in the European Union, and only nitarsone is approved in the USA. Arsenicals are less effective in treatment than they are in prevention. Some herbal products based on the essential oils (e.g. ‘Herban)’ have been used with some apparent success though controlled trials and formal approval for this purpose are not recorded. Intensive relittering may help reduce the level of infection, given recent new knowledge on the mechanism of transmission.
Prevention

Good sanitation, avoid mixing species, concrete floors. Use of an anti-histomonas product in feed where such products are approved but due care with respect to residue avoidance would be required. Regular worming to help control the intermediate hosts. Having both chickens and turkeys on the same property is likely to increase the risk of this disease in turkeys.

April 2014

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