The HIV epidemic takes a heavy toll in Sub-Saharan Africa as compared to many other parts of the world – this region is home to nearly two-thirds of the world’s HIV positive people. While many external factors influence the acquisition, transmission and progression of HIV disease, VIDI fellow Dr. Ruanne Barnabas thinks that secondary infections with other pathogens prevalent in Sub-Saharan Africa may be a key factor in HIV’s increased encumbrance in that area.
Barnabas, who grew up and attended medical school in South Africa, witnessed the growth of the AIDS epidemic there first hand. To try to understand why the virus disproportionately infects so many people in Sub-Saharan Africa, Barnabas, VIDI affiliate investigator Dr. Judith Wasserheit, VIDI co-director Dr. Larry Corey and other collaborators are focusing on how HIV interacts with other infectious diseases that are also highly prevalent in those countries.
Barnabas’ research addresses whether these diseases, which include malaria, tuberculosis, and herpes, increase the HIV’s viral load, or the number of viruses circulating in an infected person’s bloodstream. It is known that higher viral load leads to higher rates of transmission. Barnabas is also looking at past studies performed around the world to determine the exact overlap between HIV and other infectious diseases in different countries.
“The hypothesis is that every infectious person infects many more susceptible people, and the epidemic spreads in areas with co-infection more quickly than in areas without co-infections,” Barnabas said.
To look at the relationship between HIV viral load and co-infection with other diseases, Barnabas and colleagues reviewed 41 past studies that looked at HIV in combination with malaria, TB, or herpes simplex virus (HSV). Her initial results from this new analysis of past research show that HIV positive persons infected with any of these three diseases, but especially malaria, tend to have higher HIV viral loads than people without co-infections. Along with former VIDI assistant member Dr. Laith Abu-Raddad and other colleagues, Barnabas has used mathematical modeling to show that higher viral loads due to greater levels of co-infection could have contributed significantly to the explosion of the HIV epidemic in Sub-Saharan Africa.
To make matters more complicated, it is known that co-infections with many secondary pathogens affect not only HIV’s transmission, but its acquisition. For example, HSV-2-infected people have an approximately 3-fold higher chance of acquiring HIV than those without herpes. Conversely, HIV infection also increases the chances of acquiring many of these secondary infections, “so this cycle is created at the population level, a reinforcing cycle between HIV and other co-infections,” Barnabas said.
Access to health care, or lack thereof, also adds to this cycle, Barnabas said. In the developed world, many of these secondary infections, such as TB or sexually transmitted infections, are much less common because infected individuals can usually access treatment quickly, before passing on the disease. Similarly, malaria is much more common in resource-poor countries as its transmission is increased by poor mosquito control. Barnabas hopes to expand her studies in the future to interactions between HIV and parasitic worms, which are often transmitted through unsanitary drinking water and are much more common in resource-poor countries than in the developed world.
The ultimate goal of Barnabas’ research is to decrease the burden of HIV in Sub-Saharan Africa. She hopes to initiate trials in the next few years to examine whether treating co-infections such as malaria will reduce HIV viral loads and thus help dampen HIV transmission in areas with high levels of co-infections. Additionally, treating co-infections may help HIV positive individuals stay healthier longer, because higher HIV viral loads means that T cell counts decrease more rapidly, and hence anti-retroviral therapy must be started earlier.
“We want to keep people well and off anti-retroviral therapy for as long as possible,” Barnabas said.
Barnabas left South Africa in 2000 to pursue a master’s and doctorate in epidemiology at the University of Oxford, where she studied the epidemiology of the human papillomavirus and its vaccine, and then moved to Seattle in 2006 for a research fellowship. She has just started a year-long clinical fellowship, and is applying for clinical instructor positions to remain in Seattle after her fellowship. Barnabas hopes to continue research focused on Sub-Saharan Africa in the future.
“Working as a junior doctor in South Africa was really eye opening because we saw many of the complications of HIV for the first time. It was a formative experience because you think there’s something that you must be able to do to stop people from getting infected in the first place,” she said. “It certainly made its stamp early on – that this was a field that I wanted to be active in and do research in.”