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Antimicrobial Agents and Chemotherapy, April 2001, p. 1216-1224, Vol. 45, No. 4
Department of Virology and Molecular
Biology1 and Department of Biostatistics
and Epidemiology,3 St. Jude Children's
Research Hospital, and Department of Pathology, University of
Tennessee,5 Memphis, Tennessee 38105;
Department of Chemotherapy of Infectious Diseases, Russian
Chemical and Pharmaceutical Institute, Moscow,
Russia2; and Glaxo Wellcome Research and
Development, Stevenage, Hertfordshire, United
Kingdom4
Received 31 July 2000/Returned for modification 25 October
2000/Accepted 24 January 2001
In 1997, an avian H5N1 influenza virus, A/Hong Kong/156/97
(A/HK/156/97), caused six deaths in Hong Kong, and in 1999, an avian
H9N2 influenza virus infected two children in Hong Kong. These viruses
and a third avian virus [A/Teal/HK/W312/97 (H6N1)] have six highly
related genes encoding internal proteins. Additionally, A/Chicken/HK/G9/97 (H9N2) virus has PB1 and PB2 genes that are highly
related to those of A/HK/156/97 (H5N1), A/Teal/HK/W312/97 (H6N1), and
A/Quail/HK/G1/97 (H9N2) viruses. Because of their similarities with the
H5N1 virus, these H6N1 and H9N2 viruses may have the potential for
interspecies transmission. We demonstrate that these H6N1 and H9N2
viruses are pathogenic in mice but that their pathogenicities are less
than that of A/HK/156/97 (H5N1). Unadapted virus replicated in lungs,
but only A/HK/156/97 (H5N1) was found in the brain. After three
passages (P3) in mouse lungs, the pathogenicity of the
viruses increased, with both A/Teal/HK/W312/97 (H6N1) (P3)
and A/Quail/HK/G1/97 (H9N2) (P3) viruses being found in the
brain. The neuraminidase inhibitor zanamivir inhibited viral
replication in Madin-Darby canine kidney cells in virus yield assays
(50% effective concentration, 8.5 to 14.0 µM) and inhibited viral
neuraminidase activity (50% inhibitory concentration, 5 to 10 nM).
Twice daily intranasal administration of zanamivir (50 and 100 mg/kg of
body weight) completely protected infected mice from death. At a dose
of 10 mg/kg, zanamivir completely protected mice from infection with
H9N2 viruses and increased the mean survival day and the number of
survivors infected with H6N1 and H5N1 viruses. Zanamivir, at all doses
tested, significantly reduced the virus titers in the lungs and
completely blocked the spread of virus to the brain. Thus,
zanamivir is efficacious in treating avian influenza viruses that can
be transmitted to mammals.
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.4.1216-1224.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Efficacy of Zanamivir against Avian Influenza A
Viruses That Possess Genes Encoding H5N1 Internal Proteins and Are
Pathogenic in Mammals
*
Corresponding author. Mailing address: Department of
Virology and Molecular Biology, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105-2794. Phone: (901) 495-3400. Fax:
(901) 523-2622. E-mail: Robert.Webster{at}stjude.org.
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