Platypus Venom and Envenomation.

Abstract

Curiosity and controversy have surrounded the function of the crural system of the platypus since its discovery in the late 18th century. Early work on the venom confused rather than clarified the biological significance of the crural system. Many experiments gave conflicting results, especially concerning the coagulation effects of intravenous injections of venom extracts, although consistent observations were made of general vasodilation following intravenous injection into rabbits. More recent studies have shown that crural (venom) gland activity is seasonal and in synchrony with the breeding season. Secretion from the crural glands shows proteolytic activity and contains at least three major proteins, one of which has hyaluronidase activity. Subcutaneous injection of venom produced mild toxic effects whereas intravenous doses (75-90mg protein/kg) in mice were lethal. Whole venom induced local oedema after subplantar injection in rats and a 4.2kD peptide isolated from the venom caused relaxation of rat uterus in vitro. At least 16 incidents of envenomation by the platypus have been recorded in humans but no fatalities have been reported. In most human cases, envenomation resulted in immediate and severe local pain and oedema, sometimes associated with nausea, cold sweats, dull gastric pain and vomiting, hyperaesthesia and swelling of the axillary lymph nodes. Significant functional impairment of the upper limb for some weeks or months has been observed. Various treatments have been used to alleviate the symptoms of envenomation with differing successes. Envenomation has also been recorded in platypuses and dogs. The effects of these envenomations will be discussed.