Externally they have ticks, fleas and lice. External parasites include chewing lice and feather mites. Their vectors are mostly hematophagic arthropods such as fleas, lice, ticks, and mosquitoes. In field environments, soldiers are susceptible to infestation of lice, ticks, and fleas. Fleas and lice can hide in seams. External parasites include the louse "Dahlemhornia asymmetrica" and various other lice, ticks, mites and flies. It works by disrupting the function of the neurons of lice and scabies mites. Many parasites latch onto whales, notably whale lice and whale barnacles. The exchange of body fluids is not necessary to contract an infestation of crab lice. Pubic hair can become infested with pubic lice (also known as crab lice). Wild boar may on occasion contract swine erysipelas through rodents or hog lice and ticks. At Auschwitz clothes infested with lice were treated with crystallised prussic acid. There were some issues with cleanliness, including reports of lice and crabs. The sap is used to treat acne and head lice.