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In Africa, a point-of-care battle against AIDS

More than 400,000 children a year contract HIV in sub-Saharan Africa. Xuanhong Cheng creates hand-held devices that help track the virus's progress.

Medical science has not yet developed a cure or vaccination for AIDS or for the HIV virus that causes it, but efforts to combat the global AIDS epidemic appear to be having some effect.

According to UNAIDS (the Joint United Nations Program on HIV and AIDS) and the World Health Organization (WHO), the estimated number of new HIV infections reported annually has dropped 30 percent worldwide since it peaked at 3.5 million in 1996.

The number of people dying from AIDS-related diseases is also declining, the two organizations say. And new treatments are enabling persons with HIV to lead productive and, in many cases, long lives.

This encouraging news, says Xuanhong Cheng, is tempered by the tragedy of sub-Saharan Africa. Of the 33.4 million people in the world now coping with HIV, two-thirds live in sub-Saharan Africa. And more than 14 million children in the region, according to UNAIDS, have lost one or both parents to AIDS.

For Cheng, an assistant professor of materials science and engineering, one statistic stands out. More than 400,000 children each year are infected with HIV. The vast majority contract the virus through mother-to-child transmission, a phenomenon that occurs during pregnancy, labor, childbirth or breastfeeding. Preventing or decreasing the likelihood of mother-to-child transmission is a top priority of global health organizations.

HIV testing and diagnosis are critical to this effort. But in Kenya, to cite one example, an estimated 83 percent of the people with HIV remain undiagnosed because of the lack of resources in hospitals and clinics. To help overcome the shortage of facilities and staff in outlying areas, as well as difficulties in transportation, health officials are seeking to develop point-of-care diagnostics that eliminate the need to send blood samples and other specimens to laboratories for analysis. The goal is twofold: to determine if a child is infected with HIV and to monitor the progress of the disease, thus helping a doctor decide what level or type of treatment is necessary.

Tracking the progress of HIV
Cheng is part of a research team that has developed a hand-held point-of-care diagnostic device that monitors the progression of HIV by measuring the concentration of lymphocytes – a type of white blood cell – that possess a CD4 receptor on their surface in a droplet of blood.

In an infected patient, the HIV virus attaches itself to a CD4 receptor and uses the cell to make copies of itself, completely damaging the cell in the process. Because CD4 cells help initiate the body’s response to invading micro- organisms, they are a vital component of the immune system. If they are destroyed, the immune system is compromised. A CD4 count in a healthy individual is around 1,000 cells per cubic millimeter of blood. Values below this level may indicate the early stages of the disease even though the patient might not show any symptoms. Counts below 200 are a sign that the immune system has been severely weakened and the patient is then classified as having AIDS.

This CD4-counting device that Cheng helped develop is now being made commercially by Daktari Diagnostics Inc., a company based in Cambridge, Mass., that was founded by Bill Rodriguez, a former professor at Harvard Medical School. The device uses microfluidic cell chromatography to isolate cells from a blood sample without having to add chemical reagents. A droplet of the patient’s blood enters a tiny channel into an assay chamber whose walls contain antibodies that act like Velcro, capturing only the CD4+ lymphocytes. Everything else in the blood passes through. The chamber contains a simple electrical contact that is used to detect the number of captured cells.

A mission to Kenya

Cheng’s group is hoping to carry out a field test of the hand-held CD4-counting device later this year in Africa. In December 2009, to gain a better understanding of the conditions faced by African healthcare professionals, Cheng went on a weeklong fact-finding mission to Kenya. The trip was organized and funded by PATH, an international nonprofit organization dedicated to finding solutions to world health problems.

“To me, the use of this technology is straightforward, but there was no way of identifying potential problems without talking to Kenyan healthcare workers and seeing for myself the conditions in which they have to work,” says Cheng.

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Kenya’s healthcare workers are dedicated, says Cheng, but subpar facilities may require her to reconfigure her diagnostic device.