People infected with parasitic worms may be much more susceptible to the AIDS virus, according to a study published on Tuesday that may help explain why HIV has hit sub-Saharan Africa particularly hard.

The study involving monkeys demonstrated how a type of parasitic worm that causes schistosomiasis, which affects 200 million people globally, may make HIV infection more likely.

Much lower amounts of the AIDS virus - 17 times lower - were needed to cause infection in monkeys who had the parasitic worms than in the parasite-free monkeys, the researchers said.