Malaria helps spreading AIDS in Africa by boosting the HIV in people's bodies for weeks at a time, and people weakened by HIV are, in turn, more vulnerable to malaria, in a deadly vicious circle.

Researchers from University of Washington estimated that this interaction might be responsible for thousands of HIV infections and almost a million malaria cases over two decades in just one part of Kenya. "We really need to be much more serious about what we do about malaria at the same time we're serious about what we do about HIV." said Dr. Anthony Fauci of the Kenya's National Institutes of Health.

Anti-malaria programs "assume a much, much greater imperative when you realize not only are you going to have an impact on one disease, but you might impact another disease," Fauci added.

Malaria infects up to half a billion people and kills more than 1 million every year, mostly children and mostly in Africa, which also bears the highest number of HIV infections, 24.7 million (about 2 million people died only this year).

Scientists have long suspected the two diseases help each other. HIV spreads most easily when patients have high virus levels in their blood. "A bout of malaria causes a temporary surge - a stunning sevenfold increase - in those levels," said lead researcher Laith Abu-Raddad. This surges may last 6-8 weeks. "That is longer than it takes adults in intense malaria areas, where people get the parasitic disease once or twice a year, to recover from a typical bout and feel up to sexual activity again," he said.

Moreover, weakened immune systems render HIV patients more vulnerable to malaria reinfection. The study was made in Kisumu region, Kenya, where scientists had a good monitoring of malaria and HIV cases, and even information on sexual behavior (average number of partners and sex workers). Malaria may trigger almost 5 % of HIV infections, and HIV may be behind 10 % of malaria episodes. "In Kisumu, that translated into 8,500 extra HIV infections and 980,000 extra malaria bouts over two decades". Avoiding sex for eight weeks after malarial fever would considerably lower HIV's spread but "is probably impractical to implement".

Anti-malaria programs must target HIV patients. "Increasing access to HIV medications that lower viral levels means if they do get malaria, they may not have such an infectious spike," added Abu-Raddad.