The researchers sought to understand what happens when the two most common malaria parasites cause infection at the same time, as they are known to attack the body in different ways.
They found that one type of parasite leads to the second species being provided with more of the resources it needs to prosper.
In people, a parasite known as P. falciparum infects red blood cells of all ages, while another – P. vivax – attacks only young red blood cells.
“Our findings also challenge ideas that one species will outcompete the other, which explains why infections involving two parasite species can pose a greater health risk to patients,” said one of the researchers Sarah Reece, Professor at University of Edinburgh in Scotland.
Experiments in mice with equivalent malaria parasites showed that the body’s response to the first infection produces more of the type of red blood cell that the second parasite needs.
In response to the first infection, millions of red blood cells are destroyed. The body responds by replenishing these cells. These fresh cells quickly become infected by the second type of parasite, making the infection worse, the researchers said.
The finding could explain why infections with both P. falciparum and P. vivax in people often have worse outcomes for patients than single infections, the team noted.
Until recently, it was unclear how two parasite species interacted during co-infections.
The study, published in the journal Ecology Letters, was carried out in collaboration with the University of Toronto.