Leptotrombidium chiangraiensis is a recently described chigger species which appears to be an important vector of scrub typhus.

Scrub typhus

          Scrub typhus, caused by Orientia (Rickettsia) tsutsugamushi, is transmitted by the bite of infected chiggers. This disease caused more deaths than malaria in World War II. Scrub typhus remains a significant problem throughout much of Asia and the Pacific region and presents a threat to deployed troops. The disease is greatly under-reported, because its symptoms resemble those of many other tropical diseases. A rapid, non-microscopic diagnostic test was recently developed by AFRIMS investigators working with Thai and U.S. scientists.

          In the early 1990s, AFRIMS and Thai scientists discovered and described antibiotic-resistant strains of scrub typhus that cause severe disease in northern Thailand. Current activity is focused on investigating the molecular mechanism of resistance, as well as developing diagnostic assays to detect drug resistant forms. Clinical trials to find new antibiotics capable of preventing and curing this disease are in progress.

In addition, epidemiological studies in northern Thailand have identified a new ecology for scrub typhus transmission, including the discovery of a new chigger species which appears to be an important vector. A rapid molecular method to detect and identify different scrub typhus strains has been developed by an AFRIMS scientist.

          Identification of risk factors for transmission, and possible application of vector control measures, are also research priorities.

Sagittal section of a scrub typhus infected (top panel) and uninfected (lower panel) of an adult chigger (Leptotrobidium chiangraiensis). The scrub typhus antigen stains a scarlet red color. OV = ovary; SG = salivary gland; SEG = supraoesophageal ganglion; IT = interstitial membranes; ML = midgut lobes