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Avocado Toxicity

Learn more about this potentially dangerous fruit.
By Robert Clipsham. DMV

The subject of avocado poisoning has been a tremendous source of controversy and confusion among bird breeders and owners for as long as I can recall. This article is to clarify a few of the facts concerning the dangers of feeding avocado or offering access to avocado trees and to summarize the recent scientific literature on the subject.

Traditionally, bird owners have voiced an opinion that avocado fruit may be toxic, yet other owners have fed avocados to their birds with no abnormal incidences at all. Several recent articles in the scientific and medical journals prompted me to pursue this subject in greater depth.

Approximately half of the avocados grown in the United States go for human consumption in the form of fresh fruit or processed paste products. The remainder of the annual crop is used for a variety of products, including dog food and oil extraction for human use.

The amount of published research on the subject of avocado poisonings in humans and animals is fairly limited, but the fact is that the avocado tree can be toxic, as proven by a number of confirmed cases each year. Some scientifically designed studies have been performed in the past few years that support this conclusion.

Traditionally, veterinarians have considered the toxic chemical to be restricted to the leaves, bark, pits and skin of the avocado tree. However, more recent literature has reported health problems after fruit consumption in both humans and animals. Life threatening allergic reactions (anaphylaxis) have been documented in a surprising number of human patients via the skin scratch test after being treated for potentially life threatening episodes. 1-2

Interestingly, these reports also found a potential cross reaction to the proteins in other fruits, including cantaloupe, bananas and kiwis, as well as walnuts. This suspicion indicates that prior sensitization to avocado ingestion could be established by eating these other foods and precipitate an anaphylactic episode. These other foods with potential common antiens are common components of a balanced avian diet. Granted, birds are not people and allergies are a poorly understood phenomena, but the temptation to find out how much risk exists is not fair to your pet.

Most animals that suffer toxic side affects after eating avocado plants are horses or other livestock, especially in rural tropical climates. This includes South America, Africa and the U.S., due to the strong consumer demand for this rich fruit. Unfortunately, some animals have been intentionally fed both whole and ground avocado trees or branches as a feed supplement to clear land and save money.3

Other cases of animal poisonings have been reported in mice, rabbits, dogs and in birds.4-6 Drying of the plant does not as modify the toxic chemical(s) in avocado.

The signs associated with poisoning in to birds and mammals include edema of the throat and chest area, heart muscle failure, fluid-filled lungs and abdomen. Microscopic tissue examination revealed severe cellular damage to cardiac muscle cells and possibly the liver and kidneys. In addition, mammals have been experimentally fed dried leaves and suffered cell death of the mammary glands (noninfectious, necrotizing mastitis). This has been a commonly observed clinical finding in livestock, including goats and cattle, known to have ingested avocado plant parts. Microscopically extensive cell death and bleeding is found in the affected glands. These same test animals also sustained death of heart muscle cells at higher doses, similar to the reported bird cases.

Purification of a toxic chemical, named persin, was isolated from freeze-dried leaves.5 Persin had been previously found to be toxic to silk worms and fungi. Other investigators seeking to analyze the molecular components of avocados have found several candidates to explain the mechanism by which cells suffer from the poisons ingested. An analysis of an inhibitor of an enzyme for protein metabolism has been described as having some resemblance to a similar molecule in other plants and several animal proteinase inhibitors.7 Exactly how this protein works in animal models has yet to be determined.

Interestingly enough, the people of Mexico use the dried leaves of the Mexican avocado varieties in cooking, much as bay leaf or coriander is used in the United States, and no ill affect seems to occur. However, I am told the amount used is very small.

The treatment for a patient found to be suffering from avocado toxicity is symptomatic and nonspecific, including inducing vomiting and cathartics to eliminate the plant material from the gastrointestinal tract, followed by the use of oral-activated charcoal to absorb any remaining toxin. Shock steroids, oxygen and bronco dilators may also be necessary in more advanced cases, but their specific value is still questionable given the unknown mechanism of action persin takes.

On a practical level, it should be advocated not to offer any part of avocado trees to birds even as perches or as chewing devices. Birds should not be caged or flighted under or near avocado tree groves where falling leaves or fruit may lead to serious or fatal consequences. If the circumstance arises where the possibility of avocado poisoning exists, take your bird to your avian veterinarian as soon as possible. Have your veterinarian contact either the National Animal Poison Control Center or the Veterinary Poison Center in Urbane, Illinois, at the University of Illinois, School of Veterinary Medicine, (800) 548-2423.

Robert Clipshnm, DVM, previously owned the California Exotics Clinic. He currently writes and consults on avian medicine and surgery.

References

1. Telez-Diaz, G., et al. "Prevalence of avocado allergy among atopic patients," Allergy Proceedings, Sept.-Oct. 1995.
2. Blanco, G., et al. "Avocado hypersensitivity," Allergy, July 1994.
3. Aregheore, E.M. "A review of implications of antiquality and toxic components in unconventional feedstuffs advocated for use in intensive animal production in Nigeria," Veterinary and Human Toxicology, Feb. 1998.
4. Burger, W.P., et al. "Cardiomyopathy in ostriches (camelus) due to avocado (Persea americana var. guatemalensis) intoxication, Journal of the South African veterinary Association, 7974 Sept.
5. Oelrichs, P.B., et al. "isolation and identification of a compound from avocado (Persea americana) leaves which causes necrosis of the acinar epithelium of the lactating mammary gland and the myocardium," Natural Toxins, 1995.
6. Buoro, l.B., et al. "Putative avocado toxicity in two dogs, " Onderstepoort Journal of \/eterinary Research, March 1994.
7. Kimura, M., et al. "Primaly structure of a cysteine proteinase inhibitor from the fruit of avocado (Persea americana mill)," Biosci Biotech., Dec. 1995

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