No abstract

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.

. 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.

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.

BackgroundApproximately 3–5% of patients with melioidosis manifest CNS symptoms; however, the clinical data regarding neurological melioidosis are limited.Methods and FindingsWe established a mouse model of melioidosis with meningitis characterized by neutrophil infiltration into the meninges histologically and B. pseudomallei in the cerebrospinal fluid (CSF) by bacteriological culturing methods. As the disease progresses, the bacteria successively colonize the spleen, liver, bone marrow (BM) and brain and invade splenic and BM cells by days 2 and 6 post-infection, respectively. The predominant cell types intracellularly infected with B. pseudomallei were splenic and BM CD11b+ populations. The CD11b+Ly6Chigh inflamed monocytes, CD11b+Ly6Clow resident monocytes, CD11b+Ly6G+ neutrophils, CD11b+F4/80+ macrophages and CD11b+CD19+ B cells were expanded in the spleen and BM during the progression of melioidosis. After adoptive transfer of CD11b populations harboring B. pseudomallei, the infected CD11b+ cells induced bacterial colonization in the brain, whereas CD11b− cells only partially induced colonization; extracellular (free) B. pseudomallei were unable to colonize the brain. CD62L (selectin) was absent on splenic CD11b+ cells on day 4 but was expressed on day 10 post-infection. Adoptive transfer of CD11b+ cells expressing CD62L (harvested on day 10 post-infection) resulted in meningitis in the recipients, but transfer of CD11b+ CD62L-negative cells did not.Conclusions/SignificanceWe suggest that B. pseudomallei-infected CD11b+ selectin-expressing cells act as a Trojan horse and are able to transmigrate across endothelial cells, resulting in melioidosis with meningitis.