Melioidosis results from an infection with the soil-borne pathogen Burkholderia pseudomallei, and cases of melioidosis usually cluster after rains or a typhoon. In an endemic area of Taiwan, B. pseudomallei is primarily geographically distributed in cropped fields in the northwest of this area, whereas melioidosis cases are distributed in a densely populated district in the southeast. We hypothesized that contaminated cropped fields generated aerosols contaminated with B. pseudomallei, which were carried by a northwesterly wind to the densely populated southeastern district. We collected soil and aerosol samples from a 72 km² area of land, including the melioidosis-clustered area and its surroundings. Aerosols that contained B. pseudomallei-specific TTSS (type III secretion system) ORF2 DNA were well distributed in the endemic area but were rare in the surrounding areas during the rainy season. The concentration of this specific DNA in aerosols was positively correlated with the incidence of melioidosis and the appearance of a northwesterly wind. Moreover, the isolation rate in the superficial layers of the contaminated cropped field in the northwest was correlated with PCR positivity for aerosols collected from the southeast over a 2-year period. According to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) analyses, PFGE Type Ia (ST58) was the predominant pattern linking the molecular association among soil, aerosol and human isolates. Thus, the airborne transmission of melioidosis moves from the contaminated soil to aerosols and/or to humans in this endemic area. Cases of melioidosis, an emerging disease, are usually clustered after rains or typhoons. In Taiwan, the endemic area includes rural cropped fields contaminated with B. pseudomallei in the northwest and a densely populated district in the southeast, where melioidosis-cluster is distributed. We hypothesized that contaminated cropped fields generated aerosols contaminated with B. pseudomallei, which were carried by a northwesterly wind and enveloped the southeastern densely populated district. In a prospective study, aerosols that contained B. pseudomallei-specific DNA were well distributed in the densely populated districts but were rarely found in their surrounding areas. The concentration of specific DNA in aerosols correlated with the melioidosis incidence and the northwesterly wind in this endemic area. The isolation rate in the superficial layers of the contaminated cropped field in the northwest correlated with the PCR positivity of aerosols collected from the southeastern district over a 2-year period. We used genetic typing to identify a molecular association among the soil, aerosols and human isolates. We suggest that melioidosis is airborne and is transmitted from the contaminated soils to aerosols and/or to humans in this area.

A survey for the prevalence if Burkholderia pseudomallei in soil in Taiwan found that its incidence is comparable to that in other regions of the world where melioidosis is endemic. The presence of identical genetic patterns among the clinical and environmental isolates evaluated suggested a link between the pathogens present in contaminated soil and the emergence of indigenous melioidosis.

An increase in melioidosis cases compared to other areas in Taiwan was observed in the Er-Ren River Basin, southwestern Taiwan, from November 2001 to August 2006. 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.

Prenatal exposure to lipopolysaccharide (LPS), which likely occurs due to infection or contact with environmental allergens during pregnancy, is a proposed risk factor that induces anxiety- and autism spectrum disorder-like behaviors in offspring. However, the molecular and behavioral changes in offspring after maternal immune activation have not been completely identified. We hypothesized that a subcutaneous injection of LPS in a pregnant mouse would induce changes in cerebral serotonin (5-HT) in parallel to the appearance of anxiety-like behaviors in the dam’s offspring. After LPS injections (total, 100 μg/Kg), the time spent in the central region during the open field test and the number of times that the mice moved between the light and dark boxes and between the open and closed arms on the elevated plus maze test revealed anxiety-like behaviors in offspring at 5, 6 and 9 weeks of age. The mRNA expression levels of tph2 (5-HT synthesizing enzyme) and slc6a4 (5-HT transporter) were down-regulated in both adolescent (5 weeks of age) and adult (8 weeks of age) brains. Immunohistochemistry revealed that the numbers and sizes of tph2-expressing cells were notably decreased in the raphe nuclei of the midbrain of adults. Moreover, compared with controls (phosphate-buffered saline-treated offspring), the cerebral 5-HT concentration at adolescence and adulthood in LPS-induced offspring was significantly decreased. We concluded that maternal immune activation induced by exposure to a low dose of LPS decreased cerebral 5-HT levels in parallel to the down-regulation of the tph2 and slc6a4 genes and in conjunction with anxiety-like behaviors in offspring.