Competing for blood: How ecologists are solving infectious disease mysteries

Liz Fuller-Wright ・ Office of Communications

Princeton ecologists Andrea Graham, an associate professor of ecology and environmental biologist and PEI associated faculty, and Sarah Budischak examined data from an Indonesian study of 4,000 patients who were “co-infected” with malaria and hookworm. Their ecological perspective proved vital to realizing that the co-infecting species are fighting over a shared resource: red blood cells.

An international team of researchers is shining new light on “co-infections,” infectious diseases that attack the body simultaneously. The findings offer insights for treating malaria and worm infections and can help public health officials disentangle how infectious diseases compete in the human body.

By looking at malaria infections (yellow) and hookworms (gray) as competitors battling over a key resource — red blood cells — Princeton ecologists Andrea Graham and Sarah Budischak were able to explain why co-infected patients got sicker after being dewormed: without the hookworms to keep them in check, the malaria infection ran rampant. (Illustration by Matilda Luk, Office of Communications)

Princeton University ecologists Andrea Graham, an associate professor of ecology and environmental biologist and PEI associated faculty, and Sarah Budischak examined data from an Indonesian study of 4,000 patients who had two parasitic infections: malaria and hookworm. They focused on the malaria patients who also received deworming treatment and discovered previously unknown interactions between the species. Their ecological perspective proved vital to realizing that the co-infecting species are fighting over a shared resource: red blood cells.

“Co-infecting agents can interact within the ecosystem of the body just as species interact on the savannah, via resource competition, predation and all,” said Graham, co-director of Princeton’s Program in Global Health and Health Policy. “Ecologists, thinking about species interactions within the body holistically, can shed light on human health.”

When most people think of ecology, they think about the food pyramid of the rainforest or the Serengeti, said Graham, but the same resource battles that explain lion-wildebeest-grass ecosystems can apply to parasites within the human body.

By taking competition for red blood cells into account, she and her colleagues revealed that removing worms from patients who also had malaria allowed their malaria to grow to nearly three-fold higher densities. Conversely, the presence of the bloodsucking worms reduced the density of malaria parasites by over 50 percent. In other words, de-worming can exacerbate malaria infections, potentially causing more severe symptoms and increasing the risk of transmitting malaria to other people. The new study was published Feb. 8 in the journal Ecology Letters.