Malaria Makes Worms More Productive

In tropical regions, millions of people harbor intestinal worms that can linger for years and cause serious health problems. When these worm infections overlap with malaria, the outcome is not simply additive; one disease can change how the other behaves inside the host.

The Experiment

Researchers used mice to study what happens when a common intestinal roundworm, Heligmosomoides polygyrus, and the malaria parasite Plasmodium yoelii infect together. They set up several groups:

• Worm‑only mice
• Malaria → Worm mice (malaria first, then worm)
• Worm → Malaria mice (worm first, then malaria)
• Control (no infection)

Key Finding

Mice that carried both parasites produced far more worm eggs than those with only the worm. This increase was not due to a higher number of adult worms; worm counts remained similar across groups. Instead, the worms in coinfected mice adjusted their reproductive effort—each worm laid more eggs.

Immune System Dynamics

• Worms trigger a “type‑2” immune response, marked by IL‑4 and IL‑13, which helps keep worm numbers in check.
• Malaria pushes the immune system toward a “type‑1” response.
• In coinfection, type‑2 signals are dampened.

Gene activity in the spleen and cytokine levels in blood confirmed lower worm‑promoting signals (IL‑4, IL‑13) in coinfected mice.

Experimental Proof

• Blocking IL‑13: Worm‑infected mice given an IL‑13 inhibitor produced more eggs, mirroring the coinfected group.
• Adding IL‑13: Supplementing IL‑13 reduced egg output.

These results demonstrate that the worms’ reproductive boost is a direct response to the altered immune environment.

Long‑Term Impact

Over 99 days, mice with both infections shed more eggs overall and kept the worms alive longer than worm‑only mice. Even when malaria was added after the worm, the worms still benefited, indicating a lasting immune suppression effect.

Implications

In regions where malaria and worm infections overlap, people who have both diseases could unknowingly contribute more to the spread of worms. Treating malaria might therefore also reduce worm transmission, but this possibility requires careful study in human populations.