Scrub typhus is transmitted to humans and rodents
by some species of trombiculid mites (“chiggers”,
Leptotrombidium deliense and others). The mite is very
small (0.2 – 0.4mm) and can only be seen through a
microscope or magnifying glass.
Humans acquire the disease from the bite of an
infected chigger (3,4). The bite of the mite leaves a
characteristic black eschar that is useful to the doctor
for making the diagnosis.The adult mites have a four-stage lifecycle: egg, larva,
nymph and adult. The larva is the only stage (chigger) that
can transmit the disease to humans and other vertebrates,
since the other life stages (nymph and adult) do not feed
on vertebrate animals. Both the nymph and the adult are
free-living in the soil.