icddr,b conducts first ever household level tracking of cholera transmission in Dhaka

Farasha Bashir/icddr,b

Bangladesh’s capital – Dhaka – is classified as hyper-endemic as the city experiences two seasonal outbreaks of cholera every year. In spite of the constant threat of this disease, an exploration of the diverse V.cholerae strains percolating in this environment and its connection to the annual outbreaks were only recently examined.

Cholera is an infectious diarrhoeal disease caused by ingesting food or water contaminated with the bacteria Vibrio cholerae. It affects 1.4 billion people globally, especially in endemic countries in South Asia, Africa, and Central America. Annually, it claims over 120,000 lives when rehydration treatment is not administered imminently.

Bangladesh’s capital – Dhaka – is classified as hyper-endemic as the city experiences two seasonal outbreaks of cholera every year. In spite of the constant threat of this disease, an exploration of the diverse V.cholerae strains percolating in this environment and its connection to the annual outbreaks were only recently examined.

Researchers from icddr,b and its collaborating partners conducted whole-genome sequencing of V.cholerae, tracking the transmission of cholera at the household level across Dhaka. From 2002-2005, samples were collected from patients admitted to icddr,b’s Dhaka hospital; V.cholerae was isolated from these index patients and during a surveillance period of three weeks, additional samples were gathered from household members of the infected cholera patients. A total of 303 V.cholerae isolates were collected from 224 individuals across 103 households, specifically to analyse the prevalence of transmission among those who ate together and shared cooking utensils.

Critically, data from the research indicates there is a direct correlation between V.cholerae isolated from members of the same household, illustrating a common source for the transmission of the infection.

About 80 per cent of secondary infections were linked to the first cholera case in a particular household, suggesting the necessity to reduce exposure of V.cholerae at the household level and terminating its transmission.

Genomes of all samples were tested to determine how the cholera strains from each individual were related and compared it with strains emerging from other parts of the world between 1957 and 2014. The findings signify that not only is Dhaka part of a wider, highly connected regional transmission network but also that strains which originated from the city were discovered in outbreaks outside of South Asia, including Haiti in 2010 and parts of Africa.

The spread of cholera is closely linked to inadequate access to clean water and sanitation amenities and to tackle the rampant spread of this deadly disease, Dr Firdausi Qadri,  Scientist at icddr,b advocates for “vaccination as well as improved water, sanitation and hygiene interventions and facilities to be established in Bangladesh. This could greatly reduce the risk of cholera outbreaks not just in a particular country, but also regionally”.

This article was first published in  Global Health Insights of icddr,b