JOHANNESBURG – Scientists say a disease destroying entire crops of cassava has spread out of East Africa into the heart of the continent. It is attacking plants as far south as Angola and now threatens to move west into Nigeria, the world’s biggest producer of the potato-like root that helps feed 500 million Africans.

“The extremely devastating results are already dramatic today but could be catastrophic tomorrow” if nothing is done to halt the Cassava Brown Streak Disease, or CBSD, scientist Claude Fauquet, co-founder of the Global Cassava Partnership for the 21st Century, told The Associated Press.

Africa, with a burgeoning population and debilitating food shortages, is losing 50 million tons of cassava a year to the disease, he said.

In Uganda, a new strain of the virus identified five years ago is destroying 45 percent of the national crop and up to 80 percent of harvests in some areas, according to a new survey, said Chris Omongo, an entomologist and cassava expert at Uganda’s National Crops Resources Research Institute.

“The new strain looks to us to be much more aggressive,” Omongo said.

Fauquet said one problem is that the virus attacks the tubers underground, so a farmer can husband his crop for up to 18 months and only realize when he goes to dig up the cassava that all his fields are infected.

“Recent estimates indicate that CBSD causes economic losses of up to $100 million annually to the African farmer, and these are probably an underestimate, as the disease has since spread into new areas,” according to a study published last year in the journal Advances in Virology.