M. Louise Herlocher

Influenza Viruses Resistant to the Antiviral Drug Oseltamivir: Transmission Studies in Ferrets

Three type A influenza viruses, each of which has a distinct neuraminidase-gene mutation and is resistant to the neuraminidase inhibitor oseltamivir, have been isolated. Previously, in the ferret model, an R292K mutant of a type A (H3N2) virus was not transmitted under conditions in which the wild-type virus was transmitted. This model was used to investigate whether the E119V mutant of a type A (H3N2) virus and the H274Y mutant of a type A (H1N1) virus would be transmitted under similar circumstances. Both mutant viruses were transmitted, although the H274Y mutant required a 100-fold-higher dose for infection of donor ferrets and was transmitted more slowly than was the wild type. Both the mutant and the wild-type viruses retained their genotypic characteristics.

Detection and Control of Influenza Outbreaks in Well-Vaccinated Nursing Home Populations

BACKGROUND Influenza outbreaks continue to occur in nursing homes despite high vaccination coverage among residents. Recommendations for outbreak control in institutions such as nursing homes advises use of antiviral drugs to reduce influenza transmission. METHODS Influenza surveillance was performed among elderly residents of nursing homes in Michigan during 2 influenza seasons. The antiviral drug oseltamivir was used for outbreak control at the discretion of nursing home staff once influenza transmission was confirmed by virus isolation or rapid antigen detection. RESULTS During 2000-2001, influenza was not confirmed in any of the 28 participating homes, despite transmission of types A (H1N1) and B in the community. During 2001-2002, influenza type A (H3N2) transmission was confirmed in 8 (26%) of 31 participating homes; influenza vaccine coverage among residents was 57%- 98% in outbreak-associated homes. Oseltamivir was used in all homes with influenza transmission; outbreak control varied according to the rapidity of outbreak recognition and the extent of antiviral use. Reported adverse events were primarily gastrointestinal reactions and rashes. Analysis of the usefulness of rapid antigen detection tests for outbreak recognition indicated a sensitivity of only 77% (specificity, 92%). CONCLUSIONS Oseltamivir was reasonably well tolerated, and its use, along with continued promotion of vaccination coverage among nursing home residents and staff, should be a valuable addition to institutional outbreak-control strategies.

Ferrets as a transmission model for influenza: sequence changes in HA1 of type A (H3N2) virus.

Ferrets were used as an animal model to study whether controlled transmission of type A influenza is similar to human transmission when sequence changes in HA1 are used as the outcome. Ferrets were infected initially with A/Sydney/5/97 (H3N2) or A/LA/1/87 (H3N2) intranasally, and transmission chains were established by housing infected ferrets with noninfected ferrets with no influenza antibody titer against the infecting virus. Ferrets infected with A/Sydney were seronegative for A/Sydney and A/LA; ferrets infected with A/LA were seronegative for A/LA but had hemagglutination inhibition titers against A/Sydney. Titers of naturally transmitted influenza were higher than those after direct intranasal infection, but lymphocyte counts from nasal washes diminished with transmission. Ferrets infected with A/LA had 2 amino acid differences in HA1 after transmission through 5 ferret cohorts, but those infected with A/Sydney had none. The results show the value of the ferret model. A/LA resembled the transmission of influenza in humans when under antibody pressure.

Sequence comparison of wild-type and cold-adapted B/Ann Arbor/1/66 influenza virus genes

Consensus sequences for both wt and ca B/Ann Arbor/1/66 viral PB2, PB1, PA, NP, M, and NS genes were directly determined from vRNA using a combination of chemical and chain-termination sequencing methods. There were 105 sites of difference between the wt and ca sets of these six RNA genes. The differences resulted in 26 amino acid substitutions distributed over the six proteins. The sequence changes were compared to the sequences of other known influenza type B wt viruses to pinpoint those changes that were unique to the ca B/ann Arbor/1/66 virus. Of the 26 amino acid differences, only 11 were unique to the cold-adapted virus. These unique sites were distributed among five of the six genes. The NS protein had no amino acid substitutions. The sequence changes are discussed in terms of their probable mode of origin and selection, and in terms of their importance to the cold-adapted, temperature-sensitive, and attenuation phenotypes of ca B/AA/1/66 virus. The sequence and organization of the PB2 gene and predicted protein are also given. The PB2 gene was 2396 nucleotides long, and it encoded a predicted protein of 770 amino acids with a molecular weight of 88,035 Da for the wt virus and 88,072 Da for the ca virus. Both proteins were predominantly hydrophilic, and each had an overall charge of +24.5 at pH 7.0.

Sequence comparisons of A/AA/6/60 influenza viruses: mutations which may contribute to attenuation

Influenza virus infection is a worldwide public health threat. Cold-adaptation was used to develop a vaccine line (ca A/AA/6/60 H2N2) which promised to reduce the morbidity and mortality associated with influenza and to serve as a model for other live virus vaccines. This study establishes that two distinct lines of wt A/AA/6/60 viruses exist with different phenotypic and genotypic characteristics. The two virus lines have the same parent but different passage histories. The first line is both temperature sensitive (ts) and attenuated in ferrets and the second line (after multiple passages in chick kidney cells, eggs and mice) is non-ts and virulent in ferrets. Both lines of viruses have been further differentiated by sequence analysis. We have identified point mutations common to all virulent viruses but absent from the attenuated viruses. This was accomplished by comparing the nucleotide sequences of the six internal genes in three different attenuated passages of A/AA/6/60 with those of five different virulent passages of the same virus. The corresponding nucleotides of the attenuated viruses, therefore, represent candidate attenuating lesions: 6 in the basic polymerase genes (5 in PB1, 1 in PB2), 2 in the acidic polymerase gene (PA), 1 in the matrix (M) gene, 2 in the non-structural (NS) gene, and none in the nucleoprotein (NP) gene. Two of the 5 attenuating lesions in PB1 are silent; 1/2 in PA is silent; and 1/2 in NS is silent. Further changes which might be identified by comparing nucleotide and amino acid sequences of the A/AA/6/60 viruses with those of other influenza viruses may also contribute to the attenuation of the ca virus. Our study identifies nucleotides which more precisely define virulence for this virus and suggests that growth of the virus at low temperature may have preserved a non-virulent virus population rather than attenuating a virulent one.

Assessment of Development of Resistance to Antivirals in the Ferret Model of Influenza Virus Infection

We attempted to develop in vivo resistance of influenza virus to amantadine and to zanamivir, by use of the ferret model of influenza virus infection. Resistance of influenza virus A/LosAngeles/1/87 (H3N2) to amantadine was generated within 6 days, during a single course of treatment, and mutations in the M2 gene that are characteristic of human infections were observed. In contrast, during an identical single course of treatment with zanamivir, no evidence of reduced susceptibility was demonstrated. Pooled virus shed by zanamivir-treated ferrets was used to infect another group of ferrets. Twenty virus clones grew in plaque assays containing zanamivir, indicating possible reduced susceptibility; however, none exhibited reduced susceptibility to zanamivir in neuraminidase (NA) inhibition assays. Sequencing of the NA gene of these clones revealed only a noncoding nucleotide mutation at position 685. Sequencing of the hemagglutinin gene revealed mutations at positions 53, 106, 138, 145, 166, and 186. Similar to the situation in humans, amantadine use in ferrets rapidly produces antiviral resistance, but zanamivir use does not, although nucleotide changes were observed.

Interleukin-12 cDNA skin transfection potentiates human papillomavirus E6 DNA vaccine-induced antitumor immune response.

Human papillomaviruses are associated with >90% of all cases of uterine cervical tumors. The E6 and E7 oncoproteins of human papillomavirus are potentially ideal targets of immune therapy for cervical cancer, because their expression is necessary for cellular transformation. Although both E6 and E7 proteins contain numerous predicted cytotoxic T lymphocyte (CTL) epitopes that are capable of binding to human leukocyte antigens, the majority of earlier in vivo tumor rejection studies have focused on E7. We show here that gene gun-mediated skin transfection of plasmid vector encoding the nontransforming, amino-terminal half of E6 resulted in the induction of E6-specific CTL activity and tumor rejection in a murine model. The use of recombinant murine interleukin-12 (rmIL-12) as a vaccine adjuvant has been shown to result in both an enhancement and suppression of immune responses, depending upon the doses of rmIL-12 and the experimental systems used. We demonstrate here that local expression of transgenic mIL-12 at the E6 DNA vaccination site potentiated E6-specific CTL responses and increased vaccine-induced antitumor therapeutic efficacy. Our results indicate that transfection of the mIL-12 gene at the vaccination site may represent an attractive adjuvant for cancer gene immunotherapy.

Nucleotide sequences of the PA and PB1 genes of B/Ann Arbor/1/66 virus: comparison with genes of B/Lee/40 and type A influenza viruses

The complete sequences of the PA and PB1 genome RNA segments of B/Ann Arbor/1/66 virus have been determined. The PA vRNA is 2308 bases long. Its complementary RNA has a single open reading frame of 2187 bases, capable of encoding a PA protein of 726 amino acids with a molecular weight of 83,175 Da. The predicted PA polypeptide has an overall net charge of -7.5 at pH 7.0. The PB1 vRNA is 2369 bases long. Its complementary RNA has a single open reading frame of 2277 bases, capable of encoding a PB1 protein of 752 amino acids with a molecular weight of 84,332 Da. The predicted PB1 polypeptide has an overall net charge of +18.5 at pH 7.0. Sequence homology comparisons of the PA and PB1 polypeptides from B/Ann Arbor/1/66 virus to the PA and PB1 polypeptides of type A influenza virus reveal respective homologies of approximately 38 and 60%. This high cross-type homology (61%) was previously reported for the PB1 protein of B/Lee/40 virus (Kemdirim et al., 1986). The cross-type homology for the PA protein is similar to that of other non-polymerase proteins, but is substantially lower than that seen for the PB1 protein. Thus, the high cross-type homology that exists for the PB1 gene does not appear to be a characteristic of all polymerase genes.

Influenza resistance to zanamivir generated in ferrets

Abstract Zanamivir (4-Guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid), an anti-neuraminidase drug, is highly effective in the treatment of influenza. Influenza resistance to zanamivir has proved difficult to raise. Two neuraminidase mutations leading to resistance in vitro have been identified in several viruses—glu 119 gly and arg 292 lys. Only one resistant virus (an influenza B clone) has been observed in vivo in an immunocompromised child. This series of experiments sought to develop A/LA/1/87 (H3N2) influenza clones resistant to zanamivir in a ferret model. Using this model resistance to amantadine was easily developed within 6 days of treatment. Although most ferrets treated with zanamivir shed virus in the nasal wash, all ferrets were protected from fever and illness when treated with zanamivir. When ferrets were infected with nasal wash from ferrets previously infected with A/LA/1/87 (H3N2) and treated with zanamivir, 20 clones from their nasal wash grew on MDCK cells in the presence of 1 μM zanamivir. Sequencing of the NA genes of these clones revealed no mutations at positions 119 or 292. However, a nucleotide mutation at position 685 was observed in five of the clones. Sequencing of HA1 and HA2 for all genes is underway. Although characterization of the 20 clones is not complete, we can say that resistance to zanamivir will not arise as quickly or with the same frequency as does resistance to amantadine.