AVI BioPharma Announces Publication of West Nile and Dengue Virus NEUGENE Antisense Studies in the Journal of Virology.

PORTLAND, Ore. -- AVI BioPharma, Inc. (Nasdaq:AVII), today announced the publication of two articles describing preclinical studies in which its NEUGENE(R) antisense drugs were used to inhibit dengue virus and West Nile virus (WNV) infection. The two articles were published in the April 2005 Journal of Virology, and are available online at http://jvi.asm.org/current.shtml.

"These studies are an important scientific validation of our antiviral program efforts," said Patrick L. Iversen, Ph.D., senior vice president of research and development at AVI. "Our ongoing research using NEUGENE antisense technology to inhibit viral infection represents an exciting potential alternative to current antiviral drugs."

The dengue virus study, "Inhibition of Dengue Virus Serotypes 1 to 4 in Vero Cell Cultures with Morpholino Oligomers," grew out of AVI's close collaboration with the Centers for Disease Control and Prevention (CDC). AVI has an active Cooperative Research and Development Agreement (CRADA) with the CDC for dengue virus drug development.

In the study, five NEUGENE antisense drug candidates were evaluated for their ability to inhibit replication of dengue virus in mammalian cell culture. Results showed that several NEUGENE candidates effectively inhibited dengue replication up to a millionfold, in some cases reducing the amount of virus in the cells to undetectable levels. Moreover, the viral inhibition was specific, dose-dependent and extended to all four serotypes, each of which may cause both dengue fever and dengue hemorrhagic fever. This cross-strain activity would appear to be critical for an effective clinical agent for dengue.

The West Nile virus study, "Inhibition of Flavivirus Infections by Antisense Oligomers Specifically Suppressing Viral Translation and RNA Replication," tested the ability of AVI's NEUGENE drugs to inhibit West Nile virus infection, as well as infection by other viruses of the flavivirus family. When cells infected with an epidemic strain of WNV were treated with specific NEUGENE drug candidates, viral levels were reduced substantially (up to a millionfold), without any apparent cell toxicity.

One specific NEUGENE candidate was identified that inhibited other mosquito-borne flaviviruses, and the antiviral potency correlated with the conserved RNA-targeted sequences of specific viruses. This could be very important in developing a single clinical drug candidate that could treat most of the viruses in this group. In both cases, two mechanisms of action were identified, including inhibition of viral translation and suppression of RNA replication.

"These studies represent an important component of our extensive program to develop antiviral drugs for diseases caused by RNA viruses," said Denis R. Burger, Ph.D., chairman and chief executive officer at AVI. "Our NEUGENE antisense technology is well-suited to developing rapid response therapeutics and may be used to effectively counter bioterror threats and emerging viral diseases. This could be critical for situations like the recent identification of the dengue hemorrhagic fever infectious disease in Angola and the Ebola-related strain of Marburg virus."

AVI's antiviral drug program is extensive, encompassing research on 45 viruses representing 17 viral families and involving collaborations with approximately 50 scientific investigators worldwide. Current research efforts include ongoing human clinical trials in WNV infection, animal efficacy studies in Ebola virus, and preclinical studies in hepatitis C virus, dengue virus and a variety of other RNA viruses.

About Dengue and West Nile Viruses

Dengue and West Nile viruses are both members of the flavivirus genus, a group of vector-borne (e.g., mosquito) viruses that cause significant human diseases including West Nile disease, dengue hemorrhagic fever, Japanese encephalitis, yellow fever, Murray Valley encephalitis and tick-borne encephalitis. These viruses are spherical in shape with a genome consisting of single-stranded RNA. Approximately 50 to 100 million human cases of dengue virus infection occur annually. Recent epidemics of West Nile virus caused significant morbidity and mortality in the United States. There are no drug therapies currently to treat any flavivirus infections.

About AVI BioPharma

AVI BioPharma develops therapeutic products for the treatment of life-threatening diseases using third-generation NEUGENE antisense drugs. AVI's lead NEUGENE antisense compound is designed to target cell proliferation disorders, including cardiovascular restenosis, cancer and polycystic kidney disease. In addition to targeting specific genes in the body, AVI's antiviral program uses NEUGENE antisense compounds to combat disease by targeting single-stranded RNA viruses, including West Nile virus, hepatitis C virus, dengue virus and Ebola virus. More information about AVI is available on the company's Web site at http://www.avibio.com.

"Safe Harbor" Statement under the Private Securities Litigation Reform Act of 1995: The statements that are not historical facts contained in this release are forward-looking statements that involve risks and uncertainties, including, but not limited to, the results of research and development efforts, the results of preclinical and clinical testing, the effect of regulation by the FDA and other agencies, the impact of competitive products, product development, commercialization and technological difficulties, and other risks detailed in the company's Securities and Exchange Commission filings.