(Reuters) - Arrowhead Research Corp is one step closer to achieving a cure for hepatitis B infection, Chief Executive Christopher Anzalone said.

The drug developer's stock jumped 18 percent in afternoon trading on Thursday, after the company presented positive data on its experimental antiviral therapy.

The virus is 100 times more infectious than HIV, but can be prevented with a vaccine that has been available since 1982.

However, for the 400 million people worldwide who are already chronically infected with hepatitis B, the vaccine is ineffective.

Existing hepatitis B drugs do not completely cure the infection in many cases, but tend to suppress viral replication, forcing patients to continue taking them for life.

Arrowhead's drug, ARC-520, knocked down various hep B viral components, reducing one of the key disease-causing proteins of the virus by more than 90 percent in previously treated and untreated patients, data showed.

"I think our data indicates that we are knocking down multiple viral components, and no one has been able to do that so far in hepatitis B, so I think we have a clear lead over competition," Anzalone told Reuters in an interview.

Arrowhead presented "surprisingly" positive mid-stage data on the highest dose of its therapy, compared with its previously reported data from smaller doses, analysts said.

A single 4mg/kg dose was able to achieve a peak 99 percent, or 1.9 log, reduction in a key disease-causing viral protein, and a mean reduction of 1.05 log in previously untreated patients, data showed.

"We expected it would take multiple doses to get to the 1-log threshold, so the fact that they are there with a single 4mg/kg dose is a fantastic outcome," Piper Jaffray and Co's Edward Tenthoff told Reuters.

The drug was shown to be safe and well tolerated, and data suggested the therapy may substantially disrupt additional viral functions.

These findings have pushed us to focus not only on developing ARC-520 in combination with other treatments to achieve a functional cure, but also, in particular, on previously untreated patients, Anzalone added.

Arrowhead's focus - ribonucleic acid interference (RNAi) therapy - has long lured developers as it aims to silence certain genes to curb the production of disease-causing proteins, but has met with frequent clinical failure.

Meanwhile, existing drugs work by trying to inactivate these proteins by binding to them.