Histomoniasis is a commercially significant disease of poultry, particularly of

chickens The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...

and turkeys, due to parasitic infection of a

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

n, '' Histomonas meleagridis''. The

protozoan Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

is transmitted to the bird by the

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

parasite ''

Heterakis gallinarum ''Heterakis gallinarum'' is a nematode parasite that lives in the cecum of some Galliformes, galliform birds, particularly in ground feeders such as domestic chickens and domesticated turkey, turkeys. It causes infection that is mildly pathogeni ...

''. ''H. meleagridis'' resides within the eggs of ''H. gallinarum'', so birds

ingest Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms ingesti ...

the parasites along with contaminated soil or food. Earthworms can also act as a paratenic host. ''Histomonas meleagridis'' specifically infects the cecum and liver.

Symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an disease, illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormali ...

of the infection include lethargy, reduced

appetite Appetite is the desire to eat food items, usually due to hunger. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by satiety. Appetite exists in all higher life-forms, and serves to regu ...

, poor growth, increased thirst, sulphur-yellow diarrhoea and dry, ruffled feathers. The head may become

cyanotic Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...

(bluish in colour), hence the common name of the disease, blackhead disease; thus the name 'blackhead' is in all possibility a

misnomer A misnomer is a name that is incorrectly or unsuitably applied. Misnomers often arise because something was named long before its correct nature was known, or because an earlier form of something has been replaced by a later form to which the name ...

for discoloration. The disease carries a high mortality rate, and is particularly highly fatal in poultry, and less in other birds. Currently, no

prescription drug A prescription drug (also prescription medication or prescription medicine) is a pharmaceutical drug that legally requires a medical prescription to be dispensed. In contrast, over-the-counter drugs can be obtained without a prescription. The rea ...

is approved to treat this disease. Poultry (especially free-ranging) and wild birds commonly harbor a number of parasitic worms with only mild health problems from them. Turkeys are much more susceptible to getting blackhead than are chickens. Thus, chickens can be infected carriers for a long time because they are not removed or medicated by their owners, and they do not die or stop eating/defecating. ''H. gallinarum'' eggs can remain infective in soil for four years, a high risk of transmitting blackhead to turkeys remains if they graze areas with chicken

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

in this time frame.

Symptoms

Symptoms appear within 7–12 days after infection and include depression, reduced appetite, poor growth, increased thirst, sulphur-yellow diarrhoea, listlessness, drooping wings, and unkempt feathers. Young birds have a more

acute Acute may refer to: Science and technology * Acute angle ** Acute triangle ** Acute, a leaf shape in the glossary of leaf morphology * Acute (medicine), a disease that it is of short duration and of recent onset. ** Acute toxicity, the adverse eff ...

disease and die within a few days after signs appear. Older birds may be sick for some time and become emaciated before death. The symptoms are highly fatal to turkeys, but effect less damage in chickens. However, outbreaks in chickens may result in high morbidity, moderate mortality, and extensive culling, leading to overall poor flock performance. Concurrence of ''

Salmonella ''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...

typhmurium'' and ''

E. coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'' was found to cause high mortality in broiler chickens.

Cause

A protozoan '' H. meleagridis'' is responsible for histomoniasis of

gallinaceous birds Galliformes is an order of heavy-bodied ground-feeding birds that includes turkeys, chickens, quail, and other landfowl. Gallinaceous birds, as they are called, are important in their ecosystems as seed dispersers and predators, and are often ...

ranging from chickens, turkeys,

ducks Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form t ...

, geese, grouse, guineafowl,

partridges A partridge is a medium-sized galliform bird in any of several genera, with a wide native distribution throughout parts of Europe, Asia and Africa. Several species have been introduced to the Americas. They are sometimes grouped in the Perdic ...

, pheasants, and quails. The protozoan parasite is transmitted through the eggs of a

, ''

''. The eggs are highly resistant to environmental conditions, and ''H. meleagridis'' is, in turn, highly viable inside the eggs, even for years. Birds are infected once they

the eggs of the nematode in soil, or sometimes through earthworms which had

ingested Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms inges ...

the egg-contaminated soil. Outbreak can occur rapidly from the heavily infected bird in a flock readily through normal contact between uninfected and infected birds and their droppings in the total absence of cecal worms. For this reason, infection can spread very quickly. Once inside the

digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

of the host, the

n is moved to the cecum along with the eggs of ''H. gallinarum''.

Transmission and pathology

The disease causing agent, ''Histomonas meliagridis'', is transmitted in the eggs of the worm ''Heterakis gallinarum''. Once in the environment, the eggs are carried by earthworms. When the worms are eaten and the eggs hatch in the ceca, the pathogen is released. Bird to bird transmission can also occur from cloacal drinking Visible signs of this disease are cyanosis of the head (hence, “blackhead”) and sulfur-yellow diarrhea. The pathogen causes lesions on the ceca and the liver. The ceca experience ulcerations, enlargement, and caseous masses start to form inside of them. The liver develops round, haemorrhagic, 1-2 centimeter oci that have caseous cores.

Diagnosis

Histomoniasis is characterized by blackhead in birds. ''H. meleagridis'' is released in the cecum where the eggs of the nematode undergo larval development. The parasite migrates to the

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

and

submucosa The submucosa (or tela submucosa) is a thin layer of tissue (biology), tissue in various organ (anatomy), organs of the gastrointestinal tract, gastrointestinal, respiratory tract, respiratory, and genitourinary system, genitourinary tracts. It i ...

where they cause extensive and severe

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of the tissue. Necrosis is initiated by inflammation and gradual ulceration, causing thickening of the cecal wall. The lesions are sometimes exacerbated by other pathogens such as '' Escherichia coli'' and

coccidia Coccidia (Coccidiasina) are a subclass of microscopic, spore-forming, single-celled obligate intracellular parasites belonging to the apicomplexan class Conoidasida. As obligate intracellular parasites, they must live and reproduce within an a ...

. Histomonads then gain entry into small

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

of the blood stream from the cecal lesions and migrate to the liver, causing focal necrosis. Turkeys are noted to be most susceptible to the symptoms in terms of

mortality Mortality is the state of being mortal, or susceptible to death; the opposite of immortality. Mortality may also refer to: * Fish mortality, a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock throug ...

, sometimes approaching 100% of a flock. Diagnosis can be easily performed by necropsy of the fresh or preserved carcass. Unusual lesions have been observed in other organs of turkey such as the bursa of Fabricius, lungs, and kidneys.

Prevention and treatment

Currently, no therapeutic

drugs A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via inhalat ...

are prescribed for the disease. Therefore, prevention is the sole mode of treatment. This disease can be prevented only by quarantining sick birds and preventing migration of birds around the house, causing them to spread the disease. Deworming of birds with anthelmintics can reduce exposure to the cecal nematodes that carry the protozoan. Good management of the farm, including immediate quarantine of infected birds and sanitation, is the main useful strategy for controlling the spread of the parasitic contamination. The only drug used for the control ( prophylaxis) in the United States is (

nitarsone Nitarsone is an organoarsenic compound that is used in poultry production as a feed additive to increase weight gain, improve feed efficiency, and prevent histomoniasis (blackhead disease). It is marketed as Histostat by Zoetis. Nitarsone once ...

) at 0.01875% of feed until 5 days before marketing. Natustat and nitarsone were shown to be effective therapeutic drugs. As of the end of 2015, the FDA has proscribed arsenical drugs in poultry in the US.

Nifurtimox Nifurtimox, sold under the brand name Lampit, is a medication used to treat Chagas disease and sleeping sickness. For sleeping sickness it is used together with eflornithine in nifurtimox-eflornithine combination treatment. In Chagas disease it ...

, a compound with known

antiprotozoal Antiprotozoal agents ( ATC code: ATC P01) is a class of pharmaceuticals used in treatment of protozoan infection. A paraphyletic group, protozoans have little in common with each other. For example, ''Entamoeba histolytica'', a unikont eukaryotic ...

activity, was demonstrated to be significantly effective at 300–400 ppm, and well tolerated by turkeys.

History

The disease was initially discovered in Rhode Island in the year 1893. Soon after, it was shown to have devastating effects on the turkey industry, especially in New England, dropping production from 11 million birds in 1890 to 6.6 million in 1900. However, improvements in turkey management have curbed the effects of this disease. It has since spread across the globe. It has been found in turkeys, chickens, guinea fowl, and other game birds. Bobwhite quail can also be infected.

References

External links

* * {{Authority control Protozoal diseases Poultry diseases Veterinary protozoology