Migration Likely the Source of Yemen Cholera Outbreak

Through the use of genomic sequencing, a team of investigators has determined that the cholera strain circulating throughout Yemen entered the country via migration from Eastern Africa.

Yemen is currently experiencing the worst cholera outbreak in recorded history. The outbreak has been beating down on the nation since September 2016 featuring 2 distinct waves. So far there have been more than 1 million cases and nearly 2500 deaths since 2016.

In a letter published in Nature, investigators from the Wellcome Sanger Institute and Institut Pasteur reported that genetic sequencing can provide the ability to determine the risk of future cholera outbreaks and aid in the development of targeted interventions.

“Knowing how cholera moves globally gives us the opportunity to better prepare for future outbreaks. This information can help inform strategies for more targeted interventions with the ultimate aim of reducing the impact of future epidemics," Nick Thomson, PhD, from the Wellcome Sanger Institute and London School of Hygiene and Tropical Medicine, said in a recent statement.

To understand the nature of the outbreak strain, investigators sequenced the genomes of Vibrio cholerae from cholera samples collected in Yemen and nearby areas.

The investigators sequenced a total of 42 V cholerae samples from the 2 waves of the Yemen outbreak. The samples were collected both in the country and from a Yemeni refugee center on the Saudi Arabia-Yemen border. Additionally, the investigators collected 74 other samples from South Asia, the Middle East, and Eastern and Central Africa.

The genomic sequences were compared with a global collection of over 1000 cholera samples from the current and ongoing pandemic, which was caused by a single lineage of V cholerae called 7PET.

The team determined that the Yemen outbreak strain is related to a cholera strain that was first seen in 2012 in South Asia and has since spread globally. This particular strain caused outbreaks in Eastern Africa in 2013 and 2014 prior to its appearance in Yemen in 2016.

In addition to determining the source, the study investigators also disproved previous theories that the different waves of the cholera outbreak in Yemen were caused by 2 different strains.

Although most strains of cholera that cause epidemics are resistant to many antibiotics, the investigators found that this particular strain of V cholerae was susceptible to many antibiotics commonly used to treat cholera, including polymyxin B. Resistance to polymyxin B has previously been used as a marker of the El Tor biotype, a strain of V cholerae.

These study results could be key to understanding how cholera spreads in developing areas such as Yemen, a country with a population of 29 million, where approximately 16 million individuals do not have access to clean water and basic sanitation.

"This study illustrates again the key role of genomic microbial surveillance and cross-border collaborations in understanding global cholera spread,” Marie-Laure Quilici, PhD, a scientist in the Institut Pasteur's Enteric Bacterial Pathogens Unit and Head of the National Reference Center for Vibrios and Cholera, said in the statement. “All countries need to be aware of this and act accordingly if they are to achieve the targets set by [World Health Organization's] Global Task Force on Cholera Control, which aims to reduce the cholera death toll by 90% by the year 2030."