Tapeworms fight to control shared host

London: If two tapeworms infect the same host and find themselves at cross-purposes, they may actively sabotage each other in a competition to seize control, new research suggests. For the study, Nina Hafer and Manfred Milinski from the Max Planck Institute for Evolutionary Biology in Ploen, Germany, infected small crustaceans called copepods with tapeworms.

These live in copepods and then move to fish for their next life-cycle stage. The team found that when two tapeworms in the same copepod were ready to move hosts, they combined to make the copepod even more active than a single parasite would. But when an older tapeworm was sharing a host with a younger one, the older animal always won out.

The younger tapeworms failed to influence their hosts at all when in conflict with their older brethren, and did not lower the activity compared with hosts infected with only one parasite. "This suggests that the older parasite is "sabotaging" the younger one's activity," Hafer said.

The older parasite even won out when it was in competition with two younger individuals. According to Frank Cezilly, who studies host-parasite interactions at the University of Bourgogne in Dijon, France, the work is interesting. However, "it could be sabotage but it could be just that the younger parasite can't overcome [pre-existing] manipulation by the older parasite," he concluded.