Zoopharmacognosy

Zoopharmacognosy is a behaviour in which non-human animals apparently self-medicate by selecting and ingesting or topically applying plants, soils, insects, and psychoactive drugs to prevent or reduce the harmful effects of pathogens and toxins. The term derives from Greek roots zoo ('animal'), pharmacon ('drug, medicine'), and gnosy ('knowing'). Zoopharmacognosy is a behaviour in which non-human animals apparently self-medicate by selecting and ingesting or topically applying plants, soils, insects, and psychoactive drugs to prevent or reduce the harmful effects of pathogens and toxins. The term derives from Greek roots zoo ('animal'), pharmacon ('drug, medicine'), and gnosy ('knowing'). An example of zoopharmacognosy occurs when dogs eat grass to induce vomiting. However, the behaviour is more diverse than this. Animals ingest or apply non-foods such as clay, charcoal and even toxic plants and invertebrates, apparently to prevent parasitic infestation or poisoning. Whether animals truly self-medicate remains a somewhat controversial subject because early evidence is mostly circumstantial or anecdotal, however, more recent examinations have adopted an experimental, hypothesis-driven approach. The methods by which animals self-medicate vary, but can be classified according to function as prophylactic (preventative, before infection or poisoning) or therapeutic (after infection, to combat the pathogen or poisoning). The behaviour is believed to have widespread adaptive significance. In 1978, Janzen suggested that vertebrate herbivores might benefit medicinally from the secondary metabolites in their plant food. In 1993, the term 'zoopharmacognosy' was coined, derived from the Greek roots zoo ('animal'), pharma ('drug'), and gnosy ('knowing'). The term gained popularity from academic works and in a book by Cindy Engel entitled Wild Health: How Animals Keep Themselves Well and What We Can Learn from Them. The anti-parasitic effect of zoopharmacognosy could occur by at least two mechanisms. First, the ingested material may have pharmacological antiparasitic properties such that phytochemicals decrease the ability of worms to attach to the mucosal lining of the intestines, or chemotaxis attracts worms into the folds of leaves. Many ingested plants during purported zoopharmacognosy have a consistent physical property, e.g., the rough surface of the leaves sports many hooked and spiky hairs. So, parasites may became attached to the bristly surface or the coarse structure may function as a rasping plug, dislodging parasites from the intestines. The second possible mode of action is the material may initiate a purging response of the gastrointestinal tract by rapidly inducing diarrhoea. This substantially decreases gut transit time, causes worm expulsion and interrupts the life cycle of parasites. This, or a similar, mechanism could explain undigested grass in the faeces of various animals such as birds, carnivores and primates. Some animals ingest or apply the substance when they appear to be well, suggesting the behaviour is preventative or prophylactic. In other cases, animals ingest or apply the substance when unwell, suggesting the behaviour is therapeutic or curative. There are three methods of self-medication, namely, ingestion, absorption, or topical application.