Fighting parasitic infection can activate a dangerous virus

Signals from the immune system that help repel a common parasite can cause a dormant viral infection to become active again, says a new study.

The study helps illustrate how complex interactions between infectious agents and the immune system have the potential to affect illness, the researchers claimed.

The scientists identified specific signals in mice that mobilise the immune system to fight tapeworms, roundworms and other helminths, parasites that infect nearly a quarter of all humans, and found the same signals cause an inactive herpes virus infection to begin replicating again.

The researchers speculated that the virus might be taking advantage of the host response to the worm infection, multiplying and spreading when the immune system's attention is fixed on fighting the worms.

"The fact that the virus can sense' the immune reaction to a worm and respond by reactivating is a remarkable example of co-evolution," said Herbert W. Virgin from the Washington University School of Medicine in St. Louis in the US.

"We think other interactions between multiple infectious agents and the immune system will be discovered over time that we will view as similarly sophisticated or maybe even devious.

"Understanding these interactions will help us survive in a complex microbial world," he added.

Viral infections typically begin with a battle with the host's immune system.

That clash may eliminate many copies of the virus, but some can survive and hide in the nucleus of long-lived host cells without replicating, entering a phase known as latency.

Scientists have observed several examples of latent viral infections, such as tuberculosis, becoming active again after parasitic infections, such as malaria.

The new study is the first to show that this reactivation can be triggered by immune system signals, and is also the first to identify genetic elements in the virus that direct its reactivation from latency.

However, the consequences of reactivating this type of virus on human health are unclear, the researchers said.

The study was published online in the journal Science Express.