Snakes administer bites, both as a method of hunting, and as a means of protection. Risk factors for bites include working outside with one's hands such as in farming, forestry, and construction. Snakes commonly involved in poisonings include elapids (such as kraits, cobras and mambas), vipers, and sea snakes. The majority of snake species do not have venom and kill their prey by squeezing them. Venomous snakes can be found on every continent except Antarctica. Determining the type of snake that caused a bite is often not possible. The World Health Organization says snakebites are a "neglected public health issue in many tropical and subtropical countries", and in 2017, WHO categorized snakebite envenomation as a Neglected Tropical Disease (Category A). The purpose was to encourage research, expand accessibility of antivenoms, and improve snakebite management in "developing countries".