Platypus venom

  The platypus is one of the few mammals to produce venom. The male has a pair of spurs on the hind limbs through which it delivers a cocktail of poisons that, while excruciatingly painful, is not lethal to most animals.

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Spur and crural gland

Venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands located in the upper thigh connected by a thin-walled duct to a calcaneus spur on each hind limb. Female platypuses, in common with echidnas, have rudimentary spur buds which do not develop (dropping off before the end of their first year) and lack functional crural glands.^[1] The spur is attached to a small bone which allows articulation; the spur can move at a right angle to the limb allowing a greater range of attack than a fixed spur would allow.^[2] The spur normally lies flat against the limb but is raised when required.^[3]

Venom

The crural gland produces a cocktail of venom, composed of over 250 different chemicals but with four major toxins. Of the four, three are defensin-like proteins (DLPs) unique to the Platypus. The different chemicals in the poison have a range of effects from lowering blood pressure to causing pain and increasing blood flow around the wound.^[2] Coagulating effects have been seen during experiments on laboratory animals, but this has not been observed consistently. Unlike snake venom, there appears to be no necrotic component in the Platypus' venom - although some muscle wastage has been observed in cases of envenomation in humans, it is likely that this is due to the inability to use the limb while the effects of the venom persist.^[3] It is unknown whether the pain caused is a result of the associated oedema around the wound or whether the venom has a component which acts directly on the pain receptors.

Although the makeup of platypus venom has a broadly similar range of effects to that of snake venom, it appears to have a different function from those poisons produced by non-mammalian species: its effects are non-life threatening but nevertheless powerful enough to seriously impair the victim. It is not used as a method of disabling or killing prey, and although it acts a defensive mechanism, only males produce venom. Since production rises during the breeding season it is theorized that it is used as an offensive weapon to assert dominance and control territory during this period.^[2]

Effect on humans

Although powerful enough to kill smaller animals,^[2] the venom is not lethal to humans. However, it produces excruciating pain which may be intense enough to incapacitate the victim. Swelling rapidly develops around the entry wound and gradually spreads outwards. Information obtained from case studies shows that the pain develops into a long-lasting hyperalgesia that can persist for months but usually lasts from a few days to a few weeks.^[3][4] A clinical report from 1992 showed that the severe pain was persistent and did not respond to morphine. There have been no reported human fatalities.^[3]

Uses

Because of the possible direct effect on pain receptors and its observed resistance to morphine the components of platypus venom are being investigated as a potential source for pain killers for conditions with chronic pain. They are also being studied as treatment for high blood pressure. ^[5]

See also

• Venomous mammals

Notes