Environmental Surveillance of Vibrio cholerae O1/O139 in the Five African Great Lakes and Other Major Surface Water Sources in Uganda

Cholera is a major public health problem in the African Great Lakes basin. Two hypotheses might explain this observation, namely the lakes are reservoirs of toxigenic Vibrio cholerae O1 and O139 bacteria, or cholera outbreaks are a result of repeated pathogen introduction from the neighboring communities/countries but the lakes facilitate the introductions. A prospective study was conducted in Uganda between February 2015 and January 2016 in which 28 selected surface water sources were tested for the presence of V. cholerae species using cholera rapid test and multiplex polymerase chain reaction. Of 322 water samples tested, 35 (10.8%) were positive for V. cholerae non O1/non O139 and two samples tested positive for non-toxigenic atypical V. cholerae O139. None of the samples tested had toxigenic V. cholerae O1 or O139 that are responsible for cholera epidemics. The Lake Albert region registered the highest number of positive tests for V. cholerae non O1/non O139 at 47% (9/19). The peak period for V. cholerae non O1/non O139 positive tests was in March–July 2015 which coincided with the first rainy season in Uganda. This study showed that the surface water sources, including the African Great Lakes in Uganda, are less likely to be reservoirs for the observed V. cholerae O1 or O139 epidemics, though they are natural habitats for V. cholerae non O1/non O139 and atypical non-toxigenic V. cholerae O139. Further studies by WGS tests of non-toxigenic atypical V. cholerae O139 and physicochemical tests of surface water sources that supports V. cholerae should be done to provide more information. Since V. cholerae non O1/non O139 may cause other human infections, their continued surveillance is needed to understand their potential pathogenicity.

Molecular characterization of Vibrio cholerae responsible for cholera epidemics in Uganda by PCR, MLVA and WGS

Background

For almost 50 years sub-Saharan Africa, including Uganda, has experienced several outbreaks due to Vibrio cholerae. Our aim was to determine the genetic relatedness and spread of strains responsible for cholera outbreaks in Uganda.

Methodology/Principal findings

Sixty-three V. cholerae isolates collected from outbreaks in Uganda between 2014 and 2016 were tested using multiplex polymerase chain reaction (PCR), multi-locus variable number of tandem repeat analysis (MLVA) and whole genome sequencing (WGS). Three closely related MLVA clonal complexes (CC) were identified: CC1, 32% (20/63); CC2, 40% (25/63) and CC3, 28% (18/63). Each CC contained isolates from a different WGS clade. These clades were contained in the third wave of the 7^th cholera pandemic strain, two clades were contained in the transmission event (T)10 lineage and other in T13. Analysing the dates and genetic relatedness revealed that V. cholerae genetic lineages spread between districts within Uganda and across national borders.

Conclusion

The V. cholerae strains showed local and regional transmission within Uganda and the East African region. To prevent, control and eliminate cholera, these countries should implement strong cross-border collaboration and regional coordination of preventive activities.

Cholera, an acute diarrheal disease, essentially was eliminated in the western world many decades ago, but has continued to cause many deaths in sub-Saharan Africa, South America and Asia. Cholera diagnosis in most countries in sub-Saharan Africa, including Uganda, is by stool culture, serology and biochemical methods. These testing methods are unable to establish the relatedness, virulence and spread of Vibrio cholerae in region. To determine the spread, relatedness and virulence of V. cholerae responsible for the various cholera outbreaks in Uganda, we used DNA-based testing methods. We tested 63 V. cholerae isolates from samples collected in Uganda from 2014–2016. Our results showed three distinct lineages of genetically related cholera-causing bacteria. These organisms showed internal spread in Uganda and cross-border spread to neighboring countries in East Africa. These findings provide a valuable baseline and help define the context for directing control measures and technologies for cholera prevention in East Africa.