Drug Resistant Avian Influenza Viruses More Common in Southeast Asia Than North America

Analysis of a key protein in different subtypes of avian flu viruses shows

that resistance to the antiviral drug amantadine in H5N1 occurs worldwide, but

is especially prevalent in China, according to St. Jude

Sep 09, 2005, 01:00 ET from St. Jude Children's Research Hospital

    MEMPHIS, Tenn., Sept. 9 /PRNewswire/ -- Resistance to the antiviral drug
 amantadine is spreading more rapidly among avian influenza viruses of H5N1
 subtype in Southeast Asia than in North America, according to the study done
 by investigators at St. Jude Children's Research Hospital.
     The St. Jude team reached this conclusion by analyzing sequence data of
 the so-called M2 protein of avian influenza viruses of different subtypes
 isolated in North America and Southeast Asia during 1991-2004; and by
 evaluating the frequency of drug-resistant strains. Sequence data refers to
 the makeup of a gene coding for a particular protein, in this case, the M2
 protein. A properly functioning M2 protein is key to the virus' ability to
 replicate. The St. Jude researchers demonstrated that the largest proportion
 of Asian drug-resistant H5 and H9 avian influenza viruses occurred in China. A
 report on these findings appears in the current online edition of Virology.
     H5 influenza viruses concern world health officials because H5N1 subtype
 has been spreading throughout chicken flocks and wild birds in Southeast Asia
 since it emerged in 1997. Between late 2003 and early 2004, outbreaks of
 highly pathogenic avian H5N1 influenza occurred among poultry in eight Asian
 countries, causing the death or destruction of tens of millions of birds. As
 of August 5, 2005, 112 cases of human H5N1 infection have been confirmed in
 Indonesia, Vietnam, Thailand and Cambodia, of which 57 were fatal, according
 to the World Health Organization. Humans contract H5N1 only from close contact
 with infected birds and only one probable human-to-human transmission was
 reported in Vietnam. This has so far prevented H5N1 from becoming a major
 threat to humans.
     "However, if H5N1 variants acquire the capacity for sustained human-to-
 human transmission, the world will face the threat of a serious pandemic,"
 said Robert G. Webster, Ph.D., a member of the Infectious Diseases department
 and holder of the Rose Marie Thomas Chair at St. Jude. "Humans don't have
 resistance to H5N1, and currently vaccines to H5N1 are still being developed.
 And, the available evidence shows that the most recent strains isolated from
 humans in Asia are no longer sensitive to inhibition by the amantadine family
 of drugs."
     Resistance to the antiviral drug amantadine is caused by substitutions of
 one of five amino acids in the part of the M2 protein called the transmembrane
 domain-the part of M2 located within the coat of the influenza virus. The M2
 protein is an ion channel located in the envelope of the virus that permits
 hydrogen ions (protons) to enter the flu virion. This influx of protons allows
 the virus to shed its coat after it enters a cell-an essential step in the
 replication of the virus. Amantadine inhibits the function of the M2 protein
 and thus stops viral replication.
     "By analyzing the sequence of the transmembrane part of the M2 gene we
 were able to determine how frequently amantadine resistance occurs in avian
 influenza A subtypes isolated in various parts of the world-especially among
 those subtypes that had the potential to cause a pandemic," said Natalia A.
 Ilyushina, Ph.D., a postdoctoral fellow in the Infectious Diseases Department
 at St. Jude. First author of the Virology paper, Ilyushina did much of the
 work on this project.
     The St. Jude researchers analyzed the M2 gene sequences from 60 influenza
 viruses isolated in Southeast Asia and 74 viruses from North America that
 represented the H5, H6, H7 and H9 subtypes. The scientists also examined
 information from the National Library of Medicine's GenBank database on 408
 viruses isolated from avian hosts worldwide.
     Based on the study, the St. Jude team reported that there were no avian
 amantadine-resistant strains isolated from 1979-83 in the northeastern United
 States and Southeast Asia. However, 31 percent of H5 and 11 percent of H9
 influenza viruses from Southeast Asia isolated in 2000-04 carried M2
 mutations. Isolates of H5 and H9 subtypes from North America during that time
 remained sensitive to amantadine, while 16 percent of H7 isolates were
 resistant to this drug.
     "These data are clear and convincing," said Elena A. Govorkova, Ph.D., of
 the St. Jude Infectious Diseases department, a co-author of the paper. "The
 specific amantadine-resistance mutations in M2 that we identified can occur
 randomly throughout the world. But we now have solid proof that in Southeast
 Asia, and especially in China, these mutations are undergoing strong selective
     Selective pressure refers to the extent to which an organism has acquired
 either a beneficial genetic trait that gives it a survival advantage in a
 particular environment and therefore makes the organism more likely to survive
 and multiply; or a trait that makes it vulnerable to something in the
 environment, and therefore more likely to become extinct.
     The increasing incidence of amantadine-resistant H5N1 viruses in China
 indicates that these variants appear to have survival advantages over the
 wild, drug-sensitive strains. In addition, the infected birds die so rapidly
 there is no time for the virus to acquire a large number of mutations, among
 which could be changes in the M2 protein. Therefore, the high rate of M2
 mutations in China probably arises from some human activity that encourages
 selection of such changes, the researchers said. For example, treating
 chickens with amantadine to prevent infection with H5N1 would put selective
 pressure on the M2 gene to acquire mutations that made it resistant to this
 antiviral drug.
     "H5N1 is now endemic -- a permanent resident -- in Southeast Asia,
 including China," Webster said. "Therefore, any selective pressure on this
 virus ensures plenty of opportunity for H5N1 to acquire amantadine resistance,
 which would bring additional difficulties in controlling the pandemic."
     This concern over activities in China that might increase selective
 pressure for amantadine resistance in H5N1 has been voiced on the postings of
 ProMED over the past several months. ProMED (Program for Monitoring Emerging
 Diseases) is an electronic outbreak reporting system established by the
 International Society for Infectious Diseases to permit rapid and accurate
 monitoring of infectious disease outbreaks globally; and to serve as a central
 location for news, updates, and discussions of infectious disease outbreaks
 that threaten humans. For example, a ProMED transmission on July 6, 2005 noted
 that Joseph Domenech, the chief veterinary officer for the United Nations Food
 and Agriculture Organization commented that the use of human flu drugs by
 Chinese farmers is "a big concern."
     This work was supported in part by the National Institute of Allergy and
 Infectious Disease of the National Institutes of Health and ALSAC.
     St. Jude Children's Research Hospital
     St. Jude Children's Research Hospital is internationally recognized for
 its pioneering work in finding cures and saving children with cancer and other
 catastrophic diseases. Founded by late entertainer Danny Thomas and based in
 Memphis, Tenn., St. Jude freely shares its discoveries with scientific and
 medical communities around the world. No family ever pays for treatments not
 covered by insurance, and families without insurance are never asked to pay.
 St. Jude is financially supported by ALSAC, its fund-raising organization. For
 more information, please visit http://www.stjude.org.

SOURCE St. Jude Children's Research Hospital