HOST-RESISTANCE TO ECTOPARASITES

Examples of immunological reactions to arthropod parasites include responses by hosts to the following stimuli: excretory and secretory antigens produced by myiasis-producing larvae or skin-dwelling (mange) mites salivary antigens of blood-sucking arthropods. In many cases, these are hypersensitivity reactions, which often appear not to produce very deleterious effects on the parasites. However, some reactions - such as those induced by natural infestations with ixodid ticks and certain mange mites - damage the parasites and protect the hosts. Recently, successful vaccines have been devised to protect cattle from Boophilus microplus ticks. The antigens used, which are believed not to be introduced into the host during natural infestations, came from the midgut of the ticks. Such antigens, which are normally 'concealed' from the host, appear to induce 'novel' immunological responses which are difficult for the parasite to combat. Similar 'concealed' antigens have also been investigated in potential vaccines for use against other ectoparasitic arthropods.