The paper says the study, conducted by the Netherlands-based IHE Delft Institute for Water Education and their peers from Uganda and Tanzania, found traces of 25 DNA virus families, some of which are harmful for humans.

It found that most underground water in slums in the two cities had traces of herpes virus, pox virus and papilloma virus and that the latter could be one of the causes of cancer in East Africa.

“These viruses have never been found on such a large scale in ground water. Perhaps it is because there has never been an in-depth analysis,” the paper quotes Jan Willem Foppen, one of the lead researchers and a hydrologist at the IHE Delft, as saying.