Risk factors analysis for neglected human rickettsioses in rural communities in Nan province, Thailand: A community-based observational study along a landscape gradient

Abstract

In this study, we estimated exposure for Scrub typhus (STG), Typhus (TG) and Spotted fever groups (SFG) rickettsia using serology at a fine scale (a whole sub-district administration level) of local communities in Nan Province, Thailand. Geographical characteristics of the sub-district were divided into two landscape types: lowland agricultural area in an urbanized setting (lowland-urbanized area) and upland agricultural area located close to a protected area of National Park (upland-forested area). This provided an ideal contrast between the two landscapes with low and high levels of human-altered habitats to study in differences in disease ecology. In total, 824 serum samples of participants residing in the eight villages were tested by screening IgG ELISA, and subsequently confirmed by the gold standard IgG Immunofluorescent Assay (IFA). STG and TG IgG positivity were highest with seroprevalence of 9.8% and 9.0%, respectively; whereas SFG positivity was lower at 6.9%. Inhabitants from the villages located in upland-forested area demonstrated significantly higher STG exposure, compared to those villages in the lowland-urbanized area (chi-square = 51.97, p < 0.0001). In contrast, TG exposure was significantly higher in those villagers living in lowland-urbanized area (chi-square = 28.26, p < 0.0001). In addition to the effect of landscape types, generalized linear model (GLM) analysis identified socio-demographic parameters, i.e., gender, occupation, age, educational level, domestic animal ownership (dog, cattle and poultry) as influential factors to explain the level of rickettsial exposure (antibody titers) in the communities. Our findings raise the public health awareness of rickettsiosis as a cause of undiagnosed febrile illness in the communities.

Habitat and Season Drive Chigger Mite Diversity and Abundance on Small Mammals in Peninsular Malaysia

“…A key recent study from Bangkok revealed an absence of O. tsutsugamushi in chiggers and rodents across seven parks in the city, despite the presence of L. deliense at four sites [ 47 ]. For human scrub typhus cases, forest cover was the single largest negative explanatory variable in Chiang Rai [ 14 ], whereas the disease was associated with forested upland habitats in Nan province [ 58 ]. However, habitat complexity was positively associated with disease incidence in Chiang Rai [ 14 ], suggesting ecotones per se, but not specific habitats, are the main drivers of disease maintenance or emergence.…”

Geography and prevalence of rickettsial infections in Northern Tamil Nadu, India: A cross-sectional study

“…In summary, this is the first sero-prevalence study conducted in 5 different districts with different geography (Ecology). We used ELISA for determining IgG antibodies to scrub typhus, spotted fever, murine typhus and Q fever, whereas the preferred assay to detect exposure to these diseases is the IFA (Chaisiri et al, 2022;De Boni et al, 2022). Further, samples from subjects staying at elevation between 1000-2000 MSL could not be performed.…”

Geography and prevalence of rickettsial infections in Northern Tamil Nadu, India: a cross-sectional study

“…In summary, this is the first sero-prevalence study conducted in 5 different districts with different geography (Ecology). We used ELISA for determining IgG antibodies to scrub typhus, spotted fever, murine typhus and Q fever, whereas the preferred assay to detect exposure to these diseases is the IFA 52 , 53 . Further, samples from subjects staying at elevation between 1000 and 2000 MSL could not be performed.…”