Researchers from IHE Delft Institute for Water Education and their peers from Uganda and Tanzania have found traces of 25 DNA virus families -- some of them with adverse health risk for humans -- in underground water in the slums of Kampala and Arusha.
The study, whose findings were presented at the Assembly of the European Geosciences Union in Vienna on Monday, found that most groundwater in the two slums contains traces of herpes virus, poxvirus and papilloma virus.
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," said Dr Jan Willem Foppen, one of the lead researchers and a hydrologist at the IHE Delft -- the largest graduate water education institution on the planet.
Cancer is one of the top killer diseases in East Africa, blamed for nearly 100,000 deaths every year.
According to the latest report by the International Agency for Research on Cancer, some 32,617 new cases were reported in Uganda last year, with 21,829 deaths.
In the same period, Kenya recorded 47,887 new cases and 32,987 deaths while there were 42,060 new cases in Tanzania with 28,610 deaths.
Scientists have therefore expressed concerns that the widespread use of groundwater in slums for cooking, cleaning and bathing poses a risk for the residents.
In the two-year study, the scientists analysed surface water (river and drain), spring water, wells and piezometers (groundwater from specific depth) in the three countries.
"We found 25 DNA virus families, of which 14 are from above ground hosts like frogs, mice, rats, cows, horses, monkeys and humans," Dr Foppen said.
Of the human disease causing pathogens found in the samples, herpes virus and poxviruses can lead to skin infections while the papilloma cause some types of cancers such as cervical, laryngeal and mouth.
"This could be just a tip of the iceberg. We have not found all the viruses. We found the most abundant ones," Dr Fopen said.
"Let's do something about sanitation. Let us improve our sources of drinking water and identify new pathways with communities towards sustainability."