Geographical distribution of Burkholderia pseudomallei in soil in Myanmar

Abstract

Background Burkholderia pseudomallei is a Gram-negative bacterium found in soil and water in many tropical countries. It causes melioidosis, a potentially fatal infection first described in 1911 in Myanmar. Melioidosis is a common cause of sepsis and death in South and South-east Asia, but it is rarely diagnosed in Myanmar. We conducted a nationwide soil study to identify areas where B. pseudomallei is present. Methodology/Principal findings We collected soil samples from 387 locations in all 15 states and regions of Myanmar between September 2017 and June 2019. At each site, three samples were taken at each of three different depths (30, 60 and 90 cm) and were cultured for B. pseudomallei separately, along with a pooled sample from each site (i.e. 10 cultures per site). We used a negative binomial regression model to assess associations between isolation of B. pseudomallei and environmental factors (season, soil depth, soil type, land use and climate zones). B. pseudomallei was isolated in 7 of 15 states and regions. Of the 387 sites, 31 (8%) had one or more positive samples and of the 3,870 samples cultured, 103 (2.7%) tested positive for B. pseudomallei. B. pseudomallei was isolated more frequently during the monsoon season [RR-2.28 (95% CI: 0.70–7.38)] and less in the hot dry season [RR-0.70 (95% CI: 0.19–2.56)] compared to the cool dry season, and in the tropical monsoon climate zone [RR-2.26; 95% CI (0.21–6.21)] compared to the tropical dry winter climate zone. However, these associations were not statistically significant. B. pseudomallei was detected at all three depths and from various soil types (clay, silt and sand). Isolation was higher in agricultural land (2.2%), pasture land (8.5%) and disused land (5.8%) than in residential land (0.4%), but these differences were also not significant. Conclusion/Significance This study confirms a widespread distribution of B. pseudomallei in Myanmar. Clinical studies should follow to obtain a better picture of the burden of melioidosis in Myanmar.

Environmental Factors Associated With Soil Prevalence of the Melioidosis Pathogen Burkholderia pseudomallei: A Longitudinal Seasonal Study From South West India

“…In a large environmental survey from Thailand, lower levels of organic matter, of phosphorus, potassium, calcium, magnesium, iron and salinity were correlated with the presence of B. pseudomallei in paddy soil samples (Hantrakun et al, 2016). Several additional studies also observed lower iron concentrations (Baker et al, 2015;Manivanh et al, 2017;Swe et al, 2021) and a low content of organic matter associated with B. pseudomallei presence (Baker et al, 2015;Ngamsang et al, 2015;Hantrakun et al, 2016;Manivanh et al, 2017). By comparing soil parameters of paddy field samples in Southern Iran with those of non-paddy soil samples, higher levels of available iron, manganese and organic carbon were detected in paddy soil (Azadi et al, 2021).…”

“…samples, quantitative bacterial loads were not determined (Baker et al, 2011;Suebrasri et al, 2013;Chandrakar and Dias, 2017;Swe et al, 2021). However, contradictory results were obtained, with some studies reporting higher rates of B. pseudomalleipositive samples during the dry season (Wuthiekanun et al, 1995), whereas others found higher isolation rates during the wet season (Suebrasri et al, 2013;Swe et al, 2021).…”

“…samples, quantitative bacterial loads were not determined (Baker et al, 2011;Suebrasri et al, 2013;Chandrakar and Dias, 2017;Swe et al, 2021). However, contradictory results were obtained, with some studies reporting higher rates of B. pseudomalleipositive samples during the dry season (Wuthiekanun et al, 1995), whereas others found higher isolation rates during the wet season (Suebrasri et al, 2013;Swe et al, 2021). By using a semiquantitative culture method, a study from Laos found higher B. pseudomallei isolation rates in a rice field at 60 and 90 cm compared to 5 and 30 cm, however, no clear seasonal pattern of B. pseudomallei counts could be detected (Manivanh et al, 2017).…”

“…A limitation of this resource-saving single target TTSS1 qPCR approach of our main study, is the potential underestimation of some samples with very low DNA amounts, since those samples might not be reliably detected by a single PCR assay (Gohler et al, 2017). Soil sampling at 30 cm depth was chosen, since this sampling depth has been applied in numerous studies (Wuthiekanun et al, 2005;Kaestli et al, 2007Kaestli et al, , 2009Limmathurotsakul et al, 2010;Trung et al, 2011;Hantrakun et al, 2016;Manivanh et al, 2017;Dance et al, 2018;Saengnill et al, 2020;Swe et al, 2021) and the bacterial load at this depth is less likely to be influenced by short term environmental influences such as, e.g., UV light compared to soil surface. Still a depth in the range of 30 cm is accessible during agriculture activities such as plowing and cultivating soil leading to potential human exposition.…”

“…We also evaluated various physicochemical factors in a multivariable logistic regression analysis and found the concentrations of iron, manganese and nitrogen in a reverse association with the presence of B. pseudomallei. So far, environmental studies addressing soil factors which might have an impact on B. pseudomallei presence have been based on B. pseudomallei detection by enrichment cultures (Baker et al, 2011;Suebrasri et al, 2013;Chen et al, 2014;Ngamsang et al, 2015;Hantrakun et al, 2016;Swe et al, 2021). In a large environmental survey from Thailand, lower levels of organic matter, of phosphorus, potassium, calcium, magnesium, iron and salinity were correlated with the presence of B. pseudomallei in paddy soil samples (Hantrakun et al, 2016).…”