Emergence of Human and Animal Melioidosis in Southern Africa, 2018-2021

Abstract

Melioidosis is increasingly recognised in tropical and subtropical regions worldwide as a serious and potentially fatal bacterial infection affecting humans and animals, acquired from the environment. Until now, human cases of melioidosis had not been reported in Southern Africa. Over a four-year period, we identified three human and two animal cases of melioidosis in South Africa and Namibia. Burkholderia pseudomallei isolates were investigated by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and whole-genome sequencing (WGS). Phylogenetic analysis demonstrated substantial diversity, suggesting long-term cryptic persistence of the bacterium in the Southern African region. Limited awareness of the disease and inadequate diagnostic capacity likely contribute to its apparent rarity in the region. These findings underscore the urgent need for increased surveillance, improved diagnostics, and greater awareness of melioidosis in Southern Africa to better understand its true epidemiological burden and prevent future cases.

Keywords: Burkholderia pseudomallei; Melioidosis; Namibia; South Africa; whole-genome sequencing.

Figure 1

Map showing the origin of Burkholderia pseudomallei isolates included in this study. Coloured markers indicate human (red) and ovine (blue) cases from South Africa and Namibia (created with ArcGIS Pro 2.3.0).

Figure 2

Clinical presentation of melioidosis in case-patient 2, showing a large, fluctuant swelling on the right lateral aspect of the neck, indicative of an abscess.

Figure 3

Case patient 3, chest radiology: (a) chest X-ray at first presentation showing left upper lobe consolidation and hilar lymphadenopathy. (b,c): CT transverse and sagittal plane images, showing left upper lobe consolidation (arrowhead), hilar lymphadenopathy (arrows) and small basal pleural effusion (*); nodular changes are present in both lungs. (d) Chest X-ray eight weeks later on admission, showing more extensive pneumonic infiltrates bilaterally, more on the left side.

Figure 4

Transmission electron microscopy of Burkholderia pseudomallei cultured isolate. (a) Negatively stained, lophotrichous cell. (b) Sectioned cells contained polyhydroxybutyrate inclusions (asterisks) and bacterial microcompartments/metabolosomes (arrows). (c) A delicate filigree of exopolysaccharides surrounds cells stained with a cationic dye (n = part of a nucleoid). (d) Production of extracellular vesicles (v) is another known virulence factor. Vesicle clusters appeared together with metabolosomes (arrows). Scale bars = 250 nm (a–c); 100 nm (d).

Figure 5

A maximum-likelihood phylogeny of core-genome SNPs from genomes in the Africa/America clade. Genomes shown in red were sequenced in the current study.