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Biosecurity BriefingH5N1 Strain New to Africa; Second-Generation Zanamivir Effective with Single DoseBy Christine SooHoo, August 18, 2008 On August 11, 2008, the United Nations Food and Agriculture Organization (FAO) reported that a July outbreak of H5N1 avian influenza in Nigeria was due to a strain of the virus that is genetically different from the three strains that have caused previous outbreaks in Africa. Experts in Nigeria speculate that the strain was introduced to Africa via infected migratory birds from Europe or Central Asia or as a result of international trade.1 Laboratory results have shown that the H5N1 found in birds in Nigeria is similar to strains that have been identified in Italy, Afghanistan, and Iran. Since the most recent migration of wild birds from those regions occurred in September 2007, introduction by way of migratory birds seems less likely, and may mean that the appearance of the strain is linked to international trade.2 The possibility that the discovery of this strain of H5N1 is evidence of mutations in strains already circulating within Africa also remains. According to a FAO Animal Health Service International Wildlife Coordinator, “it remains unknown how this strain has been introduced to the continent.”2 The presence of this new strain increases the variability of the genetic pool of H5N1 strains in Africa. Consequently, greater opportunity exists for DNA reassortment of this strain with other H5N1 and non-H5N1 influenza strains, which could result in dramatic changes in the virus’ antigenicity. Changes in the H5N1 genome have the potential to alter the virus’ infectivity and transmissibility in humans. In other H5N1 news, on July 31, 2008, the pharmaceutical company, Biota Holdings Limited of Australia, issued a press release on its joint efforts with the pharmaceutical company, Daiichi-Sankyo of Japan, to develop a second-generation of the antiviral drug zanamavir. CS-8958, as it is called, is a long acting neuraminidase inhibitor (LANI) that has shown efficacy in preclinical studies against H5N1 avian influenza, influenza A, and influenza B. Phase II clinical trials involving individuals with naturally acquired influenza A or B have been completed, and Phase III clinical trials are scheduled to begin in Japan, Taiwan, Hong Kong, and Korea later this year. Phase II studies have shown that a single inhaled dose of CS-8958 is “statistically indistinguishable” from the recommended 75 mg dose of oseltamivir (TamifluTM) administered twice a day for 5 days. This treatment is advantageous because it reduces the dose and frequency of the treatment regime, facilitating patient compliance. Furthermore, when compared with current antiviral treatments, CS-8958 would reduce the amount of medication needed to treat the same number of individuals. This could allow for more doses to be stockpiled, and ultimately treatment or prophylaxis of more individuals.3 References
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