Studies on the Vaccine Protection and Transmission of A(H3N2)v viruses in ferrets Open Access

Houser, Katherine Virginia (2013)

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The emergence of novel influenza A virus subtypes with the capacity to spread among humans can result in a pandemic. Multiple influenza A subtypes of zoonotic origin have resulted in human infections, but most do not display the capacity for efficient human-to-human transmission. Understanding the changes responsible for human adaptation of zoonotic influenza viruses is of vital importance for pandemic preparedness. A novel zoonotic influenza virus of the H3N2 subtype with limited human-to-human transmission capability began to emerge from the swine population in 2011.

The swine-origin H3N2 viruses continue to circulate in swine, resulting in occasional transmission from infected pigs to humans, referred to as H3N2 variant virus [A(H3N2)v] infections. To date, there have been over 300 laboratory-confirmed human cases of A(H3N2)v virus infection, however there has been no evidence of sustained human-to-human transmission. Conversely, previous studies have shown that A(H3N2)v virus transmitted efficiently in the naive ferret, an animal model that generally recapitulates the inherent ability of influenza viruses to transmit among humans. Serologic studies have shown that cross-reactive antibodies to A(H3N2)v are present at varying levels in most age groups in humans, with young adults displaying the highest frequency and young children the lowest. We investigated if the presence of cross-reactive immunity generated through seasonal influenza virus vaccination or infection could account for the limited transmission of A(H3N2)v viruses. We found that vaccination failed to substantially reduce A(H3N2)v virus shedding and subsequent transmission to naive ferrets. However, prior seasonal H3N2 virus infection resulted in reduced virus shedding following A(H3N2)v virus challenge which blunted transmission to naive ferrets. We also observed an increase in IgG and IgA antibody titers in both the sera and respiratory tracts of ferrets after prior seasonal H3N2 virus infection compared to vaccination. The data demonstrate in ferrets that the efficiency of A(H3N2)v transmission is disrupted by preexisting immunity to seasonal H3N2 virus induced by natural infection.

Table of Contents

Table of Contents


Table of Contents

List of Figures and Tables

Chapter 1. Introduction 1

1.1 Influenza History and Pathogenesis 2

1.2 Influenza A Viruses Subtypes and Host Range 3

1.3 Influenza A Virion Structure 5

1.4 The Viral Hemagglutinin 6

1.5 Influenza A Replication Cycle 8

1.6 Viral Strategies for Multiple Protein Production 12

1.7 Influenza A Mutation and Host Adaptation 13

1.8 Innate Immune Response to Influenza A 15

1.9 Adaptive Immune Response to Influenza A 20

1.10 Memory Response to Influenza A 22

1.11 Influenza A Immune Evasion 24

1.12 Influenza Vaccines and Antivirals 25

1.13 Animal Models for Influenza A Viruses 29

1.14 Influenza A Pandemic History 32

1.15 Avian Subtypes of Influenza A Virus 33

1.16 Swine Subtypes of Influenza A Virus 35

1.17 Aims of this research 38

Chapter 2. Seasonal Trivalent Inactivated Influenza Vaccine Does Not Protect against Newly Emerging Variants of Influenza A (H3N2v) Virus in Ferrets 44

2.1 Abstract 45

2.2 Introduction 46

2.3 Materials and Methods 48

2.4 Results 51

2.5 Discussion 53

2.6 Acknowledgements 53

Chapter 3. Impact of prior infection or vaccination with seasonal H3N2 influenza virus on transmission of newly emerging variants of influenza A(H3N2)v virus in ferrets 57

3.1 Abstract 58

3.2 Introduction 59

3.3 Materials and Methods 62

3.4 Results 67

3.5 Discussion 74

3.6 Acknowledgements 78

Chapter 4. Determination of the molecular mechanisms of influenza pathogenesis and transmission of avian H5N1-human H1N1 recombinant viruses 87

4.1 Abstract 88

4.2 Introduction 89

4.3 Materials and Methods 93

4.4 Results 97

4.5 Discussion 105

4.6 Acknowledgements 109

Chapter 5- Conclusions 118

References 130

List of Tables

Chapter 2

2.1 Serum Hemagglutination Inhibition (HI) antibody responses to TIV immunization in ferrets. 54

2.2 Clinical symptoms observed in TIV-immune ferrets challenged with homologous and A(H3N2)v virus. 55

Chapter 3

3.1 Clinical symptoms of inoculated and contact ferrets 79

3.2 Pre-challenge Hemagglutination-Inhibition (HI) antibody responses to immunization in ferrets 80

3.3 The effect of prior seasonal H3N2 virus infection on protection against homologous and heterologous challenge 81

3.4 Antiviral IgG and IgA antibody responses among vaccinated and previously infected ferrets 82

Chapter 4

4.1 Clinical observations following viral challenges 110

4.2 Binding preference of rgVN/04 constructs in resialation assay 111

List of Figures

Chapter 1.

1.1. Schematic diagram of an influenza A virus virion. 42

1.2. Influenza A virus replication cycle. 43

Chapter 2.

2.1 TIV vaccine efficacy following challenge with A/Perth/16/2009 (Perth/09) or A/Indiana/08/2011 (IN/11) virus. 56

Chapter 3.

3.1 Transmissibility of seasonal H3N2 and A(H3N2)v influenza viruses among naïve ferrets in the respiratory droplet model. 83

3.2 Transmission of seasonal H3N2 and A(H3N2)v viruses following vaccination with the seasonal TIV. 84

3.3 Impact of vaccination of a historical seasonal H3N2 virus on A(H3N2)v virus transmission. 85

3.4 The effect of prior seasonal H3N2 virus infection on cross-protection and transmission of A(H3N2)v virus. 86

Chapter 4.

4.1 Transmissibility of 1918HAPB2:DkNY among ferrets in the respiratory droplet model 112

4.2. In vitro and in vivo testing of rgVN/04 stock. 113

4.3. In vitro and in vivo testing of rgSI/06 stock. 115

4.4. Replication kinetics for rgVN/04 mutant viruses in Calu-3 cells from apical side 116

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