LONDON (Reuters) - A new kind of experimental HIV medicine can halt one of the earliest stages of HIV infection and may lead in future to a novel class of drugs to fight other dangerous viruses, German scientists said on Wednesday.

The drug, being developed by small privately held Hannover-based firm VIRO Pharmaceuticals, is called VIR-576 and reduced the amount of HIV infection in the blood by as much 95 percent in an early-stage trial of 18 patients.

It works by preventing the virus from being able to anchor itself in human immune cells, according to the researchers, who published a study in the Science Translational Medicine journal.

“What the virus does is a bit like throwing an anchor to get hooked up to the cell,” Frank Kirchhoff, of the University Hospital of Ulm in Germany, said in a telephone interview. “This drug occupies the anchor -- which is called the fusion peptide -- and prevents its insertion into the cell membrane. So then the virus cannot get into the cell.”

Kirchhoff said VIR-576 is similar to other fusion inhibitors such as Fuzeon, sold by Trimeris and Roche, but is designed block the infection process at an earlier stage.

According to latest figures from the United Nations, an estimated 33.3 million people worldwide are infected with the human immunodeficiency virus (HIV) that causes AIDS.

The virus can be controlled with cocktails of drugs, but there is no cure and nearly 30 million people have died of HIV-related causes since the disease first emerged in the 1980s.

HIV belongs to a group of viruses known as “enveloped” viruses, which also includes influenza, mumps, measles, hepatitis B, hepatitis C, Ebola and SARS.

Kirchhoff also said the discovery that VIR-576 can fight early HIV infection suggests it may be possible in future to develop similar blockers for these other viruses.

“It’s more wishful thinking than hard evidence at the moment,” he said. “It proves the principle, but now there is a lot more work to be done.”

In this trial in HIV, Kirchhoff’s team studied 18 HIV-infected volunteers who were treated for 10 days with one of three different doses of VIR-576, which is given via injection. None of the patients was taking any other type of HIV drug and VIR-576 was the first antiretroviral drug they had received.

The results showed that at the highest dose of 5 grams per day there was a 95 percent reduction in the patients’ viral load -- a measurement of the amount of HIV in the blood. Side effects were minimal and mainly involved soreness around the injection sites, Kirchhoff said.

The researchers said the results were encouraging but stressed that the experimental drug has some drawbacks which would need further work. Because VIR-576 is a peptide and must be given through injections, it will be costly and inconvenient to use, they said, and the high dose of 5 grams a day would also make it relatively expensive.

The team’s focus now is to hunt for a small molecule that works just like just like VIR-576 but that could be made cheaply and given orally in the form of a pill.