Prevalence of Melioidosis in the Er-Ren River Basin, Taiwan: Implications for Transmission

Abstract

. The objective of this study was to determine the association between the level of exposure to Burkholderia pseudomallei and the incidence rate of melioidosis and to survey the transmission modes of B. pseudomallei in the Er-Ren River Basin. The serosurveillance of melioidosis gave seropositivity rates of 36.6%, 21.6%, and 10.9%, respectively, for residents in regions A, B, and C within the Er-Ren Basin area. Culture and PCR-based detection of B. pseudomallei from soil demonstrated that the geographical distribution of this bacterium was confined to a particular site in region B. The distribution of seropositive titers was significantly associated with the incidence rate of melioidosis (120, 68, or 36 incidence cases per 100,000 population in region A, B, or C in 2005), whereas it did not correlate with the geographical distribution of B. pseudomallei within the soil. A survey of transmission modes showed that residents with seropositivity were linked to factors such as having confronted flooding and having walked barefoot on soil, which are potential risk factors associated with exposure to B. pseudomallei. Our findings indicated that the Er-Ren River Basin in Taiwan has the potential to become a high-prevalence area for melioidosis. This is the first report that documents a high prevalence of melioidosis in an area north of latitude 20°N.

Distribution of Melioidosis Cases and Viable Burkholderia pseudomallei in Soil: Evidence for Emerging Melioidosis in Taiwan

“…However, the number of melioidosis cases suddenly increased in the Er-Ren River Basin in southern Taiwan after a typhoon followed by a flood in 2005 (8,9). B. pseudomallei was isolated from agricultural crop soil, and the prevalence of B. pseudomallei-specific antibodies increased significantly among residents after the typhoon and flood incident (9). This raises the question of the extent to which B. pseudomallei is found in soil (natural environments) in Taiwan.…”

“…These cases were categorized as being acquired during prior travels to areas of endemicity overseas rather than by indigenous acquisition, because the confirmed cases were rare and the pathogens were never isolated from the environment. However, the number of melioidosis cases suddenly increased in the Er-Ren River Basin in southern Taiwan after a typhoon followed by a flood in 2005 (8,9). B. pseudomallei was isolated from agricultural crop soil, and the prevalence of B. pseudomallei-specific antibodies increased significantly among residents after the typhoon and flood incident (9).…”

“…Approximately 100 g of each sample was obtained at a depth of 30 to 60 cm, and 15 g was placed into 50 ml of Ashdown's broth in a 250-ml flask. The samples were processed, and the typical dry, wrinkled, violet-to-purple colonies of B. pseudomallei were enumerated (9). The clinical isolates (n ϭ 6) obtained from patients with melioidosis who had never traveled overseas were also analyzed (1).…”

“…The clinical isolates (n ϭ 6) obtained from patients with melioidosis who had never traveled overseas were also analyzed (1). Biochemical tests (API system; bioMérieux, Marcy l'Etoile, France) and molecular diagnostic tests (testing for the presence of the specific amplicons of the 16S RNA gene [243 and 405 bp] and flagellar gene [267 bp]) were used for confirmation of the presence of B. pseudomallei (9). The total DNA in the soil samples was isolated and purified with a soil genomic DNA extraction kit (GeneMark, Taiwan) and a purification kit (IsoQuick; ORCA Research Inc.), respectively.…”

PCR-based Methodologies Used to Detect and Differentiate theBurkholderia pseudomalleicomplex:B. pseudomallei,B. mallei, andB. thailandensis

“…Chen et al recommends the fliC method with the possible addition of another PCR method (Dharakul et al, 1999) for detection of B. pseudomallei in soil samples. In fact, two epidemiological studies used Wajanarogana et al's and Dharakul et al's assays and reported that PCR was usually inferior to serology, but superior to culture in detecting B. pseudomallei in soil samples (Su et al, 2007;Chen et al, 2010). Chen et al's epidemiological study revealed 53 soil samples that were confirmed positive by Wajanarogana et al's and Dharakul et al's tests, but were negative by culture, indicating PCR sensitivity beyond culture (Chen et al, 2010 .…”