Chigger Mites (Trombiculidae)

Chigger mites are parasitic hexapod larvae belonging mainly to the family Trombiculidae, which cause dermatitis (known as trombiculosis or trombiculiasis) in many animal species, including humans. Species of medical and veterinary importance belong to the genus Eutrombicula Ewing, 1938 in the Neotropics and Neartic, Neotrombicula Hirst, 1925 in the Paleartic and Leptotrombidium Nagayo et al., 1916 in the Oriental region. Species of the genus Leptotrombidium are associated with rodents, potentially acting as vectors of rickettsial disease (i.e., scrub typhus) by Orientia tsutsugamushi in humans. Chigger mites have a worldwide distribution and a low host specificity, being able to infest mostly anthropized environments. Their biological life cycle mainly occurs in the environment (i.e., eggs, prelarvae, quiescent protonymphs, active deutonymphs, quiescent tritonymphs and finally adults), with only larvae as parasitic stage on host. Species that occur in temperate regions can complete up to three generations, whereas tropical ones have continuous cycles all year round. The distribution and diversity of chigger mites is given by the environmental conditions, region and host availability. Their pathogenic effect depends on the parasitic load and on the length of the feeding structure (known as stylostome), which varies according to the species of chigger. Although not truly considered chigger mites, the family Leeuwenhoekiidae has two genera of noticeable veterinary importance (Hannemania and Straelensia). Larvae of Hannemania spp. are intradermic, typically associated with amphibians, while those of the genus Straelensia attach within the inner surface of hair follicles of dogs and Iberian ibex (Capra pyrenaica), forming intradermic solid nodules. Topical repellents are used to prevent and control trombiculiasis by avoiding mite bites. Also, the control of rodent populations is effective as a long-term measure to reduce scrub typhus. For intradermic mites, treatment can be achieved with systemic avermectins, whereas topical acaricides are not useful.