Trombiculids

Trombiculids, commonly known as trombiculid mites or chiggers, are a family of mites in the order Trombidiformes. The most notable stage for hosts is the larva, a six-legged ectoparasite that attaches to the skin and feeds on tissue fluids rather than blood. In many regions they are most active in warm, humid months and are found in tall grasses, leaf litter, and other vegetated ground cover.

Life cycle: Trombiculids undergo a four-stage life cycle—egg, larva, nymph, and adult. After hatching, the parasitic larva seeks a vertebrate host to obtain a meal. Feeding lasts several days as the larva injects saliva containing enzymes that digest host tissue and facilitate feeding. After feeding, the larva drops to the environment and molts into a non-parasitic nymph, followed by the development of an eight-legged adult.

Ecology and hosts: Adults are free-living and often predatory, while larvae are temporary ectoparasites of a wide range of vertebrates, including humans, domestic animals, and wildlife. A single species may parasitize multiple hosts, and hosts may be infested by several trombiculid species.

Medical significance: Chigger bites produce pruritic papules and intense itching, a condition known as trombiculidiasis or chigger bite dermatitis. The reaction is largely due to the host’s immune response to the mite’s saliva rather than the bite itself. Some trombiculid species, notably Leptotrombidium and related genera, can vector bacteria such as Orientia tsutsugamushi in certain regions, causing scrub typhus.

Distribution and control: Trombiculids are found worldwide, with higher prevalence in warm, humid climates and vegetated habitats. Prevention emphasizes avoiding mite-infested areas, wearing protective clothing, treating clothing with permethrin, and managing leaf litter and vegetation around human habitats.