A strain of natural human proteins have been found to help ward off swine flu and other viruses including West Nile and dengue, in a discovery that could spur more effective treatments, US researchers said Thursday.

In cultured human cells, researchers lead by the Howard Hughes Medical Institute (HHMI) found that these certain proteins have powerful antiviral effects by blocking the replication of viruses.

The findings, reported Thursday in an online article from the journal Cell, "could lead to the development of more effective antiviral drugs, including prophylactic drugs that could be used to slow influenza transmission," the team said.

The influenza virus, along with the other viruses, must take over proteins in cells to sustain itself. In their study, researchers found some 120 genes that are needed by H1N1 - commonly known as swine flu.

"But in the process of figuring that out, we found this other class of genes that actually have the opposite effect, so that if you get rid of them, influenza replicates much better," according to HHMI team leader Stephen Elledge at the Harvard Medical School.

Increasing the production of the proteins therefore enables a complete blockade of the virus' replication.

"This work illustrates the important interplay between the cell innate immune response and virus replication," said Robert Lamb, a virologist at Illinois' Northwestern University, who was not part of the research team.

In a surprise discovery, the scientists who had been focused on the H1N1 virus found the proteins also blocked other viruses, such as the West Nile virus and the dengue virus.

"Making too much of these proteins might not be good for people in the long run, but we don't really know yet," Elledge said, noting that further study is needed to find if the proteins could become the basis of future antiviral therapy.

An estimated 10,000 people including 1,100 children have died of swine flu in the United States alone since the new strain of flu was first detected in April, US health authorities said earlier this month.

Thomas Frieden, head of the Centers for Disease Control and Prevention (CDC), said it was estimated there have been nearly 50 million cases and more than 200,000 hospitalizations.