This mycotoxicosis is caused by mycotoxins produced by Aspergillus flavus, Aspergillus parasiticus or Penicillium puberulum. Four major toxins (B1, B2, G1, G2) are produced. B1 is of greatest significance and is a potent hepatotoxin. Fungi growing on peanuts, corn, wheat and several other cereal grains commonly produce the toxins. Maximum aflatoxin formation occurs under conditions related to the specific grain, its moisture content, storage temperature and humidity.
There is a marked age-related difference in susceptibility to aflatoxicosis. Young nursing or weaned growing pigs are much more susceptible than adults. When aflatoxin is ingested by a lactating dam, toxic metabolites are passed in her milk and serve as a source of exposure to the nursing pigs. These toxins reduce feed intake, average daily gain and feed efficiency. Since aflatoxins are immunosuppressive, signs of toxicosis often include an increase in previously controlled secondary diseases.
Acute aflatoxicosis is uncommon in swine. It is usually a subacute to chronic disease caused by daily ingestion of smaller amounts of aflatoxin over several weeks. Lesions often vary noticeably among pigs in the same affected group but are predominantly those of a hepatopathy. In the more acute cases there are sudden deaths, hemorrhages in multiple tissues, and icterus. The liver may be swollen, fatty, and have areas of necrosis. There may be a prolonged clotting time. With subacute to chronic hepatotoxicosis, the liver may be reduced in size, fibrotic, and ascites may be present.
Diagnosis is usually based on some combination of a history of slow growth (often accompanied by secondary diseases that seem unresponsive to treatment), an elevation of serum enzymes associated with hepatocellular damage, and gross lesions related to liver pathology. Microscopic hepatic lesions include bile duct hyperplasia and enlargement of hepatocytes. In swine, chronic aflatoxin toxicity can occur with at levels as low as 300 ppb in the feed; acute toxicity usually doesn’t occur until concentrations beyond 1000 ppb. Aflatoxin is considered to be carcinogenic in humans.