According to this reference:
Mebendazole Official FDA information, side effects and uses. HOOKWORM, WHIPWORM AND ROUNDWORM will die off in freezing soil.
"Eggs from the worms are deposited in the soil if an infected person fails to use a toilet or bathroom. Since the eggs can live only in warm soil, they are found most often where the soil never freezes in winter. People living or traveling in areas with warm winters may have these infections. The eggs in the soil are usually carried to the mouth on food or by contact with dirty hands. In the case of hookworms a pre-adult form of the worm actually penetrates the skin (usually the foot) and burrows its way into the bloodstream. Once inside the body, they grow and breed inside the bowel. New eggs are released in the feces."