Scientists of the Wellcome Sanger Institute and Institut Pasteur found the strain of cholera originated in eastern Africa and was carried to Yemen by migrants according to BBC NEWS.

Yemen has experienced two waves of cholera cases since 2016.  The first epidemic was occurred from October 2016 to 26 April 2017, and 25,800 suspected cases and 129 associated death were reported.  Then 1.336 million cases and 2,641 deaths were reported on November since the second wave began on 27 April 2017.

There are two main reasons of epidemic of cholera in Yemen.  The one is civil war.  Because of it, some 16 million Yemenis lack access to safe drinking water, sanitation and basic healthcare, and 10 million do not know where their next meal comes from. The other reason is Yemen remains a transit country for people in African countries.

Researchers collected 42 cholera samples collected in Yemen and 74 other cholera samples from South Asia, the Middle East and Africa and compared more than 1,000 samples.

They found the cholera strain causing Yemen epidemic was related to one in South Asia in 2012, but it did not arrive directly from South Asia or the Middle East.  It came from these areas through eastern Africa.

Reference

BBC NEWS

https://www.bbc.com/news/world-middle-east-46746394