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.

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.

The development of neurologic melioidosis was linked to the elicitation of Burkholderia pseudomallei-infected L-selectinCD11b BALB/c cells in our previous study. However, whether monocytic L-selectin (CD62L, encoded by the sell gene) is a key factor remains uncertain. In the present study, after establishing multi-organ foci via hematogenous routes, we demonstrated that B. pseudomallei GFP steadily persisted in blood, splenic, hepatic and bone marrow (BM) Ly6C monocytes; however, the circulating CD16/32CD45GFP brain-infiltrating leukocytes (BILs) derived from the blood Ly6C monocytes were expanded in BALB/c but not in C57BL/6 bacteremic melioidosis. Consistent with these results, 60% of BALB/c mice but only 10% of C57BL/6 mice exhibited neurologic melioidosis. In a time-dependent manner, B. pseudomallei invaded C57BL/6 BM-derived phagocytes and monocytic progenitors by 2 d. The number of Ly6CCD62LGFP inflamed cells that had expanded in the BM and that were ready for emigration peaked on d 21 post-infection. Hematogenous B. pseudomallei-loaded sellLy6C monocytes exacerbated the bacterial loads and the proportion of Ly6CGFP BILs in the recipient brains compared to sell infected Ly6C cells when adoptively transferred. Moreover, a neutralizing anti-CD62L antibody significantly depleted the bacterial colonization of the brain following adoptive transfer of B. pseudomallei-loaded C57BL/6 or BALB/c Ly6C cells. Our data thus suggest that Ly6CCD62L infected monocytes served as a Trojan horse across the cerebral endothelium to induce brain infection. Therefore, CD62L should be considered as not only a temporally elicited antigen but also a disease-relevant leukocyte marker during the development of neurologic melioidosis.

In Taiwan, melioidosis is an emerging disease that suddenly increased in the Er-Ren River Basin, beginning in 2005 and in the Zoynan region during 2008–2012, following a typhoon. Additionally, the disease sporadically increased in a geography-dependent manner in 2016. Subcutaneous inoculation, ingestion, and the inhalation of soil or water contaminated with Burkholderia pseudomallei are recognized as the transmission modes of melioidosis. The appearance of environmental B. pseudomallei positivity in northern, central and southern Taiwan is associated with disease prevalence (cases/population: 0.03/100,000 in the northern region, 0.29/100,000 in the central region and 1.98/100,000 in the southern region). However, melioidosis-clustered areas are confined to 5 to 7.5 km2 hot spots containing high-density populations, but B. pseudomallei-contaminated environments are located >5 km northwestern of the periphery of these hot spots. The observation that the concentration of B. pseudomallei-specific DNA in aerosols was positively correlated with the incidence of melioidosis and the appearance of a northwesterly wind in a hot spot indicated that airborne transmission had occurred in Taiwan. Moreover, the isolation rate in the superficial layers of a contaminated crop field in the northwest was correlated with PCR positivity in aerosols collected from the southeast over a two-year period. The genotype ST58 was identified by multilocus sequence typing in human and aerosol isolates. The genotype ST1001 has increased in prevalence but has been sporadically distributed elsewhere since 2016. These data indicate the transmission modes and environmental foci that support the dissemination of melioidosis are changing in Taiwan.