Metagenomic Approach to Characterizing Disease Epidemiology in a Disease-Endemic Environment in Northern Thailand

Takhampunya, Ratree; Korkusol, Achareeya; Pongpichit, Chalermpol; Yodin, Komsan; Rungrojn, Artharee; Chanarat, Nitima; Promsathaporn, Sommai; Monkanna, Taweesak; Thaloengsok, Sasikanya; Tippayachai, Bousaraporn; Kumfao, Naruemon; Richards, Allen L.; Davidson, Silas A.

Seroprevalence (IgM and IgG) for scrub typhus and rickettsiosis in UFI patients confirmed that the two diseases are highly endemic to the region, especially for scrub typhus. O. tsutsugamushi was present in all related samples studied and human exposure was clearly observed with high prevalence and titers (n = 154 with 1600, >6400 titers). Although human rickettsiosis was not detected in rodents or vectors, the levels of IgM and IgG seroprevalence for TGR and SFGR indicate the circulation of these pathogens in the area as well. Some pathogens were detected in animals and vectors but not in humans; however, seroprevalence (IgG) of the pathogens in patients indicated previous exposure in humans, such as B. henselae. It is worth noting that serological differentiation between B. henselae and B. quintana IgG antibody might not be possible since there could be some cross-reactivity between the two species. With O. tsutsugamushi, when age and sex of patients were considered, prevalence was significantly higher in 20-40 and 41-60 yearold groups, which shows the working age population having increased risk of contracting the diseases. The incidence of scrub typhus infections in humans seems to occur at higher rates during the rainy season corresponding to the time when local people start rice/corn cultivation and continues throughout the year until the harvesting season ends in October/November as the high seroprevalence in working age groups (20-60 years old) strongly supports this speculation. Moreover, the infection rate of O. tsutsugamushi in rodents and chiggers was highest in March just before the rainy season, followed by the increase of chigger indexes (number of chiggers per host) possibly leading to increased potential for disease transmission.