|By uniting experimental data with mathematical modeling, Emory University researchers have uncovered the dynamics of host-parasite interactions in malaria, a poorly understood yet relatively common disease.
Using a resource-limitation model and experimental data involving the rodent malarial parasite Plasmodium chabaudi, Jacobus de Roode, PhD, Emory assistant professor of biology, and his collaborators detailed the initial dynamics of the infection in mice carrying a variety of strains, or variants, of P. chabaudi.
The study is published online in the Proceedings of the Royal Society of London Series B: Biological Sciences. Rustom Antia, PhD, Emory professor of biology, and Andrew Yates, PhD, postdoctoral fellow in Antia’s laboratory, are co-authors of the study.
"Parasites really need to get from one host to another. To do so, they have to grow inside their host and replicate in high enough numbers to get picked up by the next host, in this case, the mosquito," says de Roode. "In theory, there’s an ideal level of growth that will maximize the fitness of the parasite. That is, if the parasite doesn’t get produced in high enough numbers it won’t get transmitted to another host, but it the parasite produces too well it may kill the host before transmission can occur."
When different parasite genotypes reside in one host, competition among strains increases. As a result, those parasites that grow to higher numbers and transmit themselves more to another host are favored, explains De Roode.
"We showed that the resource-limitation model can explain the initial dynamics of infection of mice with different strains of P. chabaudi. This particular model shows that the peak parasites in the blood and the maximum loss of red blood cells (RBCs), or anaemia, are equal to the fraction of RBCs that the malaria parasite can infect," he says.
Each year, more than 500 million people become ill with malaria, and more than one million people die from the disease, according to the World Health Organization. Most cases occur in sub-Saharan Africa, but Asia, Latin America, the Middle East, and parts of Europe also are affected by the disease.
Four types of malaria infect humans: Plasmodium falciparum, P.vivax, P.malariae, and P.ovale, with P.falciparum and P.vivax the most common. De Roode and his colleagues say they will consider exploring the dynamics of acute malaria infections in other animals, including humans.
The research was supported by Emory University and the National Institutes of Health.