Fungal Diseases of Poultry

The great majority of fungi are harmless, but a small number are capable of infecting animals and causing disease. Diseases result from: Allergic reactions to spores in mouldy litter, Poisoning as a result of toxins, Infection due to invasion by fungi of skin, lungs, or injuries/wounds.

Mycotoxins / Mycotoxicoses Aspergillosis References and Further Reading

A mycotoxicosis is a disease caused by a toxic fungal metabolite (Merck). In poultry, this usually results when fungi grow in grains and feeds.

Moulds may grow on feed (either in the standing crop or, more usually, during storage). The fungal spores that are produced when the mould reproduces may be ingested or inhaled by the animal and this may itself be harmful. Many fungi, however, also produce secondary compounds called mycotoxins. These are produced to assist the fungi in its competition with bacteria and other fungi for food and space. Some of these secondary compounds are antibiotics, and this can be beneficial to the animal. However, many of these secondary compounds are harmful to the animal as well (and to humans too). The toxicity of the mycotoxins depends on the actual mycotoxin (which will depend on the species of fungus that produced it). Different species of animal are susceptible to different mycotoxins to different degrees as well. For example, aflatoxins that may flourish on badly stored feed (such as groundnuts) are highly toxic to turkeys and ducklings, less toxic to cattle, while sheep appear to be resistant to them. Young animals are also more susceptible than adults.

Mycotoxins from different sources can can attack different parts of the body, including:

• the blood system (e.g. haemorrhaging into body tissues or from the lungs),
• the digestive system (e.g. diarrhoea, vomiting, intestinal haemorrhage),
• the respiratory system (e.g. bleeding from lungs),
• the nervous system (e.g. lack of coordination),
• the skin (e.g. rash, photosensitization),
• the urinary system,
• the reproductive system (e.g. infertility and changes to reproductive cycles),
• and may also cause suppression of the immune system.

Ensuring that feed is stored in clean, dry conditions with an adequate airflow should help prevent the development of moulds. If feed has gone mouldy, it should not be fed to livestock and care should be taken when disposing of it as the spores and toxins are often harmful to humans as well.

Mycotoxins of world-wide Importance include: the Aflatoxins, the Trichothecenes (Fusarium), Zearalenone, the Fumonisins, Ochratoxin A, and Patulin. Additional mycotoxins may be of regional importance, especially in stored crops.

For more on Mycotoxins see Contaminants and toxins in animal feeds by D’Mello, in FAO (2004)

Aflatoxicosis:

Aflatoxins are highly toxic, carcinogenic fungal metabolites produced by various species of the Aspergillus fungi. Aflatoxicosis in poultry primarily affects the liver, but immunologic and digestive functions may be involved, and the formation of red blood cells may also be affected. Weight gain, feed intake, feed conversion efficiency, pigmentation, processing yield, egg production, male and female fertility, and hatchability are likely to be affected. Some effects are a direct result of the poisoning by the toxins, while others are related to factors such as reduced feed intake (see Merck).

Fusariotoxicosis

The genus Fusarium produces many mycotoxins injurious to poultry. Fusariotoxicosis in poultry caused by the trichothecene mycotoxins produced by Fusarium species results in feed refusal, caustic injury of the oral mucosa and areas of the skin in contact with the mould, acute digestive disease, and diminished function of the bone marrow and immune system. There may also be ulceration of the oral mucosa, inflammation of the remainder of the gastrointestinal tract, discoloured liver, atrophy of the spleen and other lymph organs, and visceral haemorrhages. In laying hens, egg production may decrease, accompanied by depression, recumbency, and feed refusal (see Merck).

Ochratoxicosis

Ochratoxins are among the most toxic mycotoxins to poultry. These nephrotoxic metabolites are produced chiefly by Penicillium viridicatum and Aspergillus ochraceous , which commonly occur on numerous grains and feedstuffs. Ochratoxicosis causes primarily renal disease but also affects the liver, immune system, and bone marrow. Severe intoxication causes clinical signs of reduced spontaneous activity, huddling, hypothermia, diarrhoea, rapid weight loss, and death. Sublethal intoxication can seriously impair weight gain, feed conversion, pigmentation, carcass yield, egg production, fertility, and hatchability (see Merck).

Aspergillosis is a disease, usually of the respiratory system, of chickens, turkeys, and less ducks, and geese. In chickens and turkeys, the disease may be endemic on some farms. It is usually seen in younger birds of from 7-40 days old. Aspergillosis is caused by the spores of species of the Aspergillosus fungus that are commonly found in the environment - in soil, grain, and decaying vegetative matter. They produce a form of pneumonia that is acute in chicks and may be chronic in mature birds.

Infection may be easily prevented by good sanitation, by avoiding mouldy grain and decaying litter, and by ensuring that feeders and watering facilities are regularly cleaned. Good ventilation is important, as is keeping stress to a minimum.

Treatment of affected birds is considered useless (see Merck).