A breakthrough in treating diseases caused by viruses was announced by medical scientists yesterday - the first drug cures of unusually metal form of viral encephalitis or brain inflammation.

The achievement was called "a major advance" by Dr. Richard Krause of the National Institutes of Health, one that should lead to successful attacks on other viruses.

The many infections diseases that attack people are mainly caused by two kind of zerms, Bacteria and viruses. Most bacteria have been successfully attacked by antibiotics since the 1940s.

But viruses have remained stubbornly resistant to these or other drugs.

Virus-caused diseases include influenza and colds, smallpox, yellow fever, measles, German measles, hepatitis, tick fever, rabies and poplio.

Some of these illnesses can be prevented by vaccines or be alleviated by various serums or treatments. By in almost all, antibiotics and other drugs have been ineffectual, and for many there is no treatment at all.

Yesterday's announcement could change that situation, doctors at a news conference at NIH agreed.

"We're somewhat at the same level as when penicillin was introduced for bacterial diseases," Dr. Charles Alford Jr. of the University of Alabama said.

He helped direct a cooperative study at 15 medical centers in which a new drug called ara-A (for adenine arabinoside) cut herpes encephalitis mortality froma usual 70 per cent to a far lesser 28 per cent.

"This is exciting news," said krause, director of NIH's National Institute of Allergy and Infectious Diseases, which organized and largely financed the effort.

"It is the first successful treatment of a serious and life-threatening virus disease," he reported." It opens up an avenue to a new form of therapy for this class of infections."

[TEXT OMITTED FROM SOURCE] antadine and ara-A - have until now been licensed by the Food and Drug Administration for use against any virus infections. Both idoxuridine and ara-A are used for patients with eye infections caused by herpes virus. Amantadine relieves and sometimes prevents flu symptoms caused by influenza A virus.

Ara-A had its origin 13 years ago when two French scientists - Drs. Michael Private de Garilhe and Jean de Rudder of the Center for Laboratory Research in Plaine-saint-Denis - were screening various plant and animal substances in a search for anticancer chemicals.

As part of their search they tested some chemicals called purine nucleosides from a Caribbean sponge called Cryptotethia crypta.

As it turned out, the nucleosides did little to retard cancer cells' growth. But the two scentists saw something else - there was no viral growth or contamination on their sponge-treated cell cultures, the kind of contamination they usually expected.

In much the same way, Dr. Alexander Fleming had noticed in 1928 that bacteria were failing to grow in a bacterial culture that had been contaminated by the common mold, Penicillin.

Other scientists eventually tried penicillin against human disease. The development of ara-A, the drug derived from the sponge nucleosides, was pursued in the laboratory by scientists at Parke, David and Ca. In Detroit.

They learned to make the substance synthetically. And this year, spurred by NIH, Drs. Richard Whitley and Aflord of the University of Alabama. Medical Center in Birmingham began their collaborative trial of ara-A in herpes encephalitis.

This disease plays havoc with braincells. When it does not kill, it commonly results in permanent central nervous system damage.

Twenty-eight patients were identified at 15 hospitals. Eighteen were treated for 10 days with ara-A, and 10-treated with a placebo, or ineffective, inert substance. Seven of these 10 died.

Of the 18 ara-A patients five died. But seven have recovered sufficiently to lead reasonably normal lives, and four of these have made a full recovery. The other six have serious brain or nerve damage, probably because the drug treatment began too late.

The cooperating doctors had originally planned to test for more patients with an ineffective placeco to mark sure of ara-A's good effect. But "in spite of our small numbers, we felt compelled" to abandon this plan, Whitley said.