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[NAIROBI] Research in Kenya indicates that the rapid spread of HIV/AIDS across Africa could be linked to malaria.

The work has important implications for public health policies in sub-Saharan Africa, highlighting the need to tackle both diseases together.

There is considerable geographical overlap between HIV/AIDS — which infects over 40 million people in Africa — and malaria, which causes 500 million clinical infections each year.

People with both malaria and HIV/AIDS are more likely to transmit the HIV virus, according to the study published in the journal Science today (8 December). This may have promoted the rapid spread of the disease in sub-Saharan Africa.

"We have always known the relationship between [malaria and HIV/AIDS], but we did not know the impact it had on the spread: now we have a reference point," says Ayub Manya, an epidemiologist with the Kenyan National Malaria Control Programme.

When someone with HIV/AIDS contracts malaria, it creates a surge in their blood levels of HIV, making them more than twice as likely to transmit the virus to a sexual partner.

An HIV infection also makes someone more susceptible to malaria, which the researchers say may have accelerated the spread of malaria in areas where HIV is prevalent.

The team, led by Laith Abu-Raddad of the University of Washington in Seattle, United States, used a mathematical model to examine how these interactions affect the spread of both diseases.

They tested their model on data gathered from Kisumu, Kenya, and found that the interaction between the diseases was to blame for many thousands of HIV infections and almost a million malaria episodes since 1980.

"While HIV/AIDS is predominantly spreading through sexual intercourse, this biological co-factor induced by malaria has contributed considerably to the spread of HIV by increasing transmission probability per sexual act," says Abu-Raddad.

The study injects a much-needed scientific approach to the protection of vulnerable groups, and suggests that health policy should emphasise malaria prevention and early treatment strategies for HIV-infected people.

Manya says the information will help reorient treatment policy, but warns that the HIV transmission risk factor could have been higher in the 1980s before the use of condoms and anti-retroviral therapy for HIV/AIDS.

Kenya has already stepped up malaria prevention efforts, recognising that it causes HIV/AIDS patients to contract malaria in greater numbers, due to weaker immunity, says Manya.

This is why pregnant women who are HIV positive receive three times the usual dosage of the drug to protect them from malaria, he told SciDev.Net. 

However, Shahnaaz Sharif, head of Preventive and Promotive Health Services at the Kenyan Health Ministry, argues that there are many other factors that influence malaria transmission, such as male circumcision, which is thought to reduce transmission of HIV (see Male circumcision could save millions from HIV/AIDS).

"Malaria is not the only factor. If you have malaria, it increases your viral load, but even if there was no malaria, the virus would still be transmissible," says Sharif.

Link to full paper in Science

Reference: Science 314, 5805 (2006)