Contrasting Spatial Distribution and Risk Factors for Past Infection with Scrub Typhus and Murine Typhus in Vientiane City, Lao PDR

Abstract

BackgroundThe aetiological diagnostic of fevers in Laos remains difficult due to limited laboratory diagnostic facilities. However, it has recently become apparent that both scrub and murine typhus are common causes of previous undiagnosed fever. Epidemiological data suggests that scrub typhus would be more common in rural areas and murine typhus in urban areas, but there is very little recent information on factors involved in scrub and murine typhus transmission, especially where they are sympatric - as is the case in Vientiane, the capital of the Lao PDR.Methodology and Principal FindingsWe therefore determined the frequency of IgG seropositivity against scrub typhus (Orientia tsutsugamushi) and murine typhus (Rickettsia typhi), as indices of prior exposure to these pathogens, in randomly selected adults in urban and peri-urban Vientiane City (n = 2,002, ≥35 years). Anti-scrub and murine typhus IgG were detected by ELISA assays using filter paper elutes. We validated the accuracy of ELISA of these elutes against ELISA using serum samples. The overall prevalence of scrub and murine typhus IgG antibodies was 20.3% and 20.6%, respectively. Scrub typhus seropositivity was significantly higher among adults living in the periphery (28.4%) than in the central zone (13.1%) of Vientiane. In contrast, seroprevalence of murine typhus IgG antibodies was significantly higher in the central zone (30.8%) as compared to the periphery (14.4%). In multivariate analysis, adults with a longer residence in Vientiane were at significant greater risk of past infection with murine typhus and at lower risk for scrub typhus. Those with no education, living on low incomes, living on plots of land with poor sanitary conditions, living in large households, and farmers were at higher risk of scrub typhus and those living in neighborhoods with high building density and close to markets were at greater risk for murine typhus and at lower risk of scrub typhus past infection.ConclusionsThis study underscores the intense circulation of both scrub and murine typhus in Vientiane city and underlines difference in spatial distribution and risk factors involved in the transmission of these diseases.

2009 A(H1N1) Seroconversion Rates and Risk Factors among the General Population in Vientiane Capital, Laos

“…The household cohort was established on the basis of a pre-existing sample constituted for the "Urbanization, Governance and Spatial Disparities of Health in Vientiane” research programme [9]–[11]. Households were recruited in 27 neighbourhoods, distributed across three zones: ( i ) the central zone; ( ii ) the inner urbanized belt and ( iii ) the outer urbanized belt, in order to reflect the variability of Vientiane's overall population [10].…”

Rickettsial Infections in Southeast Asia: Implications for Local Populace and Febrile Returned Travelers

“…[21][22][23][24] Second, when relative contributions from the 3 rickettsial groups were compared, it was found that murine typhus was more commonly reported among the urban dwelling patients and scrub typhus and SFGR infections were more prevalent among rural patients. 22,25 Geographically, as noted previously, scrub typhus was prevalent in northern and northeastern regions of Thailand, and incidence rates may be as high as 16 cases/100,000 population per year in some areas such as Chiang Mai. [26][27][28][29] Socioeconomically, agricultural, plantation, or forest workers in Thailand, Malaysia, and Indonesia were frequently affected by scrub typhus and SFGR infections.…”

Bayesian spatial modelling and the significance of agricultural land use to scrub typhus infection in Taiwan

“…Land cover is also an important factor in determining the occurrence of the disease, with higher incidence occurring in areas of secondary or transitional vegetation, presumably in relation to the preferred habitat of the rodent species on which chiggers generally feed (Traub and Wisseman, 1974). In addition, socioeconomic factors may influence transmission: higher incidence tends to occur in rural areas, with farmers at higher risk of infection, and it has been shown that increasing urbanisation and school enrolment can decrease incidence of scrub typhus (Olson and Bourgeois, 1979;Ogawa et al, 2002;Lee et al, 2006;Vallee et al, 2010;Kuo et al, 2011). Thus, we can assume that the spatial distribution of scrub typhus is determined by climatic and environmental factors (including land cover and land use), which influence the distribution of the trombiculid mites and their preferred meal sources and socioeconomic factors, which may alter the pattern of contact between humans and chiggers.…”

“…Kuo et al (2011) quantified the association of scrub typhus incidence with temperature, rainfall, and the normalized difference vegetation index (NDVI) (a measure of the greenness of vegetation derived from satellite remote sensing) in Taiwan but did not include land cover in the analyses. In Taiwan and Lao People's Democratic Republic, risk of scrub typhus infection was investigated only for a limited range of land use types (forest and degree of urbanization, respectively) (Vallee et al, 2010;Tsai and Yeh, 2013).…”