Mycotoxicosis

Etiology

• Mycotoxins are secondary metabolites produced by certain filamentous microscopic fungi, which occur naturally in the environment and may persist in food products:
  • Aflatoxins are caused by Aspergillus spp such as Aspergillus flavus and Aspergillus parasiticus found in moldy feeds. Aflatoxin B1 is a mycotoxin and is of a concern as it is the most abundant and considered as a carcinogenic toxin for human and animals.
  • Fumonisins are caused by several species of Fusarium, although Alternaria alterna and Aspergillus niger can also produce fumonisins. The group of fumonisins include more than 10 mycotoxins. They can contaminate cereals and grains (corn, barley, wheat, rice, soybean, etc) and fruits. Corn is the most prevalent source of fumonisins all over the world.
  • Zearalenone is an estrogenic mycotoxin produced by Fusarium molds, frequently found from maize.
  • Ochratoxins are caused by species of Aspergillus and Penicillium and is a nephrotoxin.
  • Citrinin is found in moldy cereals contaminated by Aspergillus and Penicillium species. Citrinin is a nephrotoxin. In rabbits given a single oral dose of citrinin (130 mg/kg), after 8 hours, histopathological renal changes observed were cytoplasmic vacuolation of tubular epithelial cells.
  • Deoxynivalenol, also known as vomitoxin is primarily produced by Fusarium spp. This mycotoxin occurs predominantly in grains such as wheat, barley, oats, rye, and corn, and less often in rice, sorghum, and triticale. 

Predisposing factors

General

• The negative effects of different mycotoxins can be synergistic, as most of them attack similar organs such as liver or kidney.

Specific

• In one study, 50% of commercial rabbit food (containing grains) contained some mycotoxins (mainly deoxynivalenol), although in levels that can only produce chronic exposure. Other studies (again with commercial rabbit food containing grains) have shown even higher detection of mycotoxins, and 98-100% of samples had more than one type of mycotoxin.
• Feeding cereals and other grains is the most common source of mycotoxins for rabbits.

Pathophysiology

• Zearalenone in rabbits has hematotoxic, hepatotoxic, nephrotoxic and immunotoxic effects. However, some of their most important effects are in reproduction. Zearalenone also changes the microbial population of the cecum, increasing the susceptibility for dysbiosis.
• Fumonisins in rabbits cause leukoencephalomalacia, nephrotoxicity, hepatotoxicity, immunotoxicity and carcinogenesis.
• Ochratoxins in rabbits mainly affect kidneys, but also other organs with less severity. At high doses, it can have teratogenic effects on rabbit fetuses.
• Ergot alkaloids (produced by Claviceps purpurea) have been linked to tail necrosis in rabbits. They usually produce peripheral vasoconstriction.
• The fact that a product or a foodstuff contains mycotoxins does not mean it is toxic for rabbits. Adverse effects depend on the type of toxic agent, the concentration and the time of exposure.
• Mycotoxicosis also predisposes to other conditions, particularly gastrointestinal problems in rabbits.

Timecourse

• Many mycotoxins are subclinical, the result of long-term exposure.

Epidemiology

• Rarely diagnosed in pet rabbits.