Aflatoxicosis

From Dog
Post-mortem of a dog which died from aflatoxicosis, showing fatty hepatosis and enterorrhagia[1]
Nutmeg appearance of a canine liver with chronic aflatoxin exposure[2]

Aflatoxicosis is a form of mycotoxicosis arising from toxin ingestion of spoiled feed contaminated with Aspergillus spp fungus[3] characterized by acute hemorrhagic enteritis, coagulopathy and sudden death.

Aflatoxins are often associated with groundnuts (peanuts) and corn, but they also have been found in other grains and nuts. Aspergillus spp fungi can proliferate in improperly stored grain that has a moisture content of greater than 14%, relative humidity greater than 70%, and temperature greater than 200C. These fungi also can invade grains in the field, especially when there is drought stress, insect damage, or mechanical damage.

The toxins involved include aflatoxin B1, B2 and G1, cyclopiazonic acid[4] and ochratoxins A[5] and B[6]. Toxic levels > 50 ppm are capable of inducing disease[7]. These toxins are produced as metabolic byproducts of fungal metabolic waste products and are hepatotoxic as well as highly carcinogenic[8]. Within the body, aflatoxins are metabolized by the liver to a reactive epoxide intermediate or hydroxylated to become the less harmful aflatoxin M1.

Large outbreaks can occur on farms where corn-meal are fed to dogs, or where they gain access to stores. Aflatoxicosis has also occurred from contaminated commercial dog food[9]. Outbreaks can occur as acute, subacute or chronic based on duration of exposure and volume ingested.

Affected dogs usually present within 24 hours of ingestion of contaminated meal with acute-onset anorexia, polydipsia, icterus, hematemesis, hematochezia, melena and bleeding of the skin, eye, ear and mouth. Death ensues rapidly in many cases.

Blood tests usually show signs of elevated ALT, AST and alkaline phosphatase as well as prolonged prothrombin, hyperbilirubinemia, hypocholesterolemia, hypoalbuminemia and thrombocytopenia[10].

Common complications include disseminated intravascular coagulation, hepatic encephalopathy and acute kidney injury[11].

On postmortem, a consistent, very characteristic finding was the presence of a blue-grey granular material within the bile ducts[1]. Other features include hepatocellular fatty degeneration, bile ductule proliferation and mucoid degeneration or segmental atrophy of the larger intrahepatic bile ducts[12].

A presumptive diagnosis is based on historical exposure to contaminated feed, presence of aflatoxins in food sources, vomitus, intestinal contents and characteristic histological findings[13].

A differential diagnosis would include anticoagulant rodenticides.

Supportive intravenous fluid and oxygen therapy may assist recovery.

The active toxin, aflatoxin B1 causes a dose-related hepatocyte fatty degeneration, biliary duct hyperplasia, cholestasis and, in the chronic case, hepatic fibrosis.

Despite aggressive treatment, the mortality rate with aflatoxicosis in dogs approaches 70%, suggesting that dogs with this condition have poor prognosis[14].

References

  1. 1.0 1.1 Arnot LF et al (2012) An outbreak of canine aflatoxicosis in Gauteng Province, South Africa. J S Afr Vet Assoc 83(1):E1-E4
  2. University of Pretoria
  3. Wouters AT et al (2013) An outbreak of aflatoxin poisoning in dogs associated with aflatoxin B1-contaminated maize products. J Vet Diagn Invest Feb 15
  4. Nuehring LP et al (1985) Cyclopiazonic acid mycotoxicosis in the dog. Am J Vet Res 46(8):1670-1676
  5. Dirheimer G & Creppy EE (1991) Mechanism of action of ochratoxin A. IARC Sci Publ 115:171-186
  6. Visconti A & Bottalico A (1983) High levels of ochratoxins A and B in moldy bread responsible for mycotoxicosis in farm animals. J Agric Food Chem 31(5):1122-1123
  7. Ketterer PJ et al (1975) Canine aflatoxicosis. Aust Vet J 51(7):355-357
  8. Liggett AD et al (1986) Canine aflatoxicosis: a continuing problem. Vet Hum Toxicol 28(5):428-430
  9. Stenske KA et al (2006) Aflatoxicosis in dogs and dealing with suspected contaminated commercial foods. J Am Vet Med Assoc 228(11):1686-1691
  10. Bruchim Y et al (2012) Accidental fatal aflatoxicosis due to contaminated commercial diet in 50 dogs. Res Vet Sci 93(1):279-287
  11. Greene CE et al (1977) Disseminated intravascular coagulation complicating aflatoxicosis in dogs. Cornell Vet 67(1):29-49
  12. Bastianello SS et al (1987) Pathological findings in a natural outbreak of aflatoxicosis in dogs. Onderstepoort J Vet Res 54(4):635-640
  13. Newman SJ et al (2007) Aflatoxicosis in nine dogs after exposure to contaminated commercial dog food. J Vet Diagn Invest 19(2):168-175
  14. Dereszynski DM et al (2008) Clinical and clinicopathologic features of dogs that consumed foodborne hepatotoxic aflatoxins: 72 cases (2005-2006). J Am Vet Med Assoc 232(9):1329-1337