Seroprevalence of rickettsial infections and Q fever in Bhutan

Tshokey Tshokey, John Stenos, David N Durrheim, Keith Eastwood, Chelsea Nguyen, Stephen R Graves, Tshokey Tshokey, John Stenos, David N Durrheim, Keith Eastwood, Chelsea Nguyen, Stephen R Graves

Abstract

Background: With few studies conducted to date, very little is known about the epidemiology of rickettsioses in Bhutan. Due to two previous outbreaks and increasing clinical cases, scrub typhus is better recognized than other rickettsial infections and Q fever.

Methodology: A descriptive cross-sectional serosurvey was conducted from January to March 2015 in eight districts of Bhutan. Participants were 864 healthy individuals from an urban (30%) and a rural (70%) sampling unit in each of the eight districts. Serum samples were tested by microimmunofluorescence assay for rickettsial antibodies at the Australian Rickettsial Reference Laboratory.

Results: Of the 864 participants, 345 (39.9%) were males and the mean age of participants was 41.1 (range 13-98) years. An overall seroprevalence of 49% against rickettsioses was detected. Seroprevalence was highest against scrub typhus group (STG) (22.6%) followed by spotted fever group (SFG) rickettsia (15.7%), Q fever (QF) (6.9%) and typhus group (TG) rickettsia (3.5%). Evidence of exposure to multiple agents was also noted; the commonest being dual exposure to STG and SFG at 5%. A person's likelihood of exposure to STG and SFG rickettsia significantly increased with age and farmers were twice as likely to have evidence of STG exposure as other occupations. Trongsa district appeared to be a hotspot for STG exposure while Punakha district had the lowest STG exposure risk. Zhemgang had the lowest exposure risk to SFG rickettsia compared to other districts. People living at altitudes above 2000 meters were relatively protected from STG infections but this was not observed for SFG, TG or QF exposure.

Conclusion: This seroprevalence study highlights the endemicity of STG and SFG rickettsia in Bhutan. The high seroprevalence warrants appropriate public health interventions, such as diagnostic improvements and clinical treatment guidelines. Future studies should focus on vector profiles, geospatial, bio-social and environmental risk assessment and preventive and control strategies.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Map of Bhutan showing the…
Fig 1. Map of Bhutan showing the eight selected districts with the location of urban (U) and rural (R) primary sampling units.
(Map generated using the ESRI’s ArcMap 10.3.1 for desktop software. An electronic map of district boundaries of Bhutan in shapefile format was obtained from Global Administrative Areas database (http://www.gadm.org/country). Figure created solely for this manuscript and has not been used for any other publications or documents).
Fig 2. Overall seroprevalence of rickettsial infections…
Fig 2. Overall seroprevalence of rickettsial infections in Bhutan.
(STG, Scrub Typhus Group; SFG, Spotted Fever Group; TG, Typhus Group; QF, Q Fever).
Fig 3. Prevalence of rickettsial seropositivity in…
Fig 3. Prevalence of rickettsial seropositivity in different districts of Bhutan.
(U, Urban; R, Rural; T, Total).
Fig 4. Prevalence estimates of the four…
Fig 4. Prevalence estimates of the four infections in the urban and rural sampling units of the eight districts in Bhutan.
(Map generated using the ESRI’s ArcMap 10.3.1 for desktop software. An electronic map of district boundaries of Bhutan in shapefile format was obtained from Global Administrative Areas database (http://www.gadm.org/country). Figure created solely for this manuscript and has not been used for any other publications or documents).

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