Analysis of influenza A virus reinfection in children in Japan during 1983-91

Epidemiology of repeat influenza infection in Queensland, Australia, 2005-2017

Natural infection with the influenza virus is believed to generate cross-protective immunity across both types and subtypes. However, less is known about the persistence of this immunity and thus the susceptibility of individuals to repeat infection. We used 13 years (2005–2017) of surveillance data from Queensland, Australia, to describe the incidence and distribution of repeat influenza infections. Consecutive infections that occurred within 14 days of prior infection were considered a mixed infection; those that occurred more than 14 days later were considered separate (repeat) infections. Kaplan-Meier plots were used to investigate the probability of reinfection over time and the Prentice, Williams and Peterson extension of the Cox proportional hazards model was used to assess the association of age and gender with reinfection. Among the 188 392 notifications received during 2005–2017, 6165 were consecutively notified for the same individual (3.3% of notifications), and 2958 were mixed infections (1.6%). Overall, the probability of reinfection was low: the cumulative incidence was <1% after one year, 4.6% after five years, and 9.6% after ten years. The majority of consecutive infections were the result of two type A infections (43%) and were most common among females (adjusted hazard ratio (aHR): 1.15, 95% confidence interval (CI) 1.09–1.21), children aged less than 5 years (relative to adults aged 18–64 years aHR: 1.58, 95% CI 1.47–1.70) and older adults aged at least 65 years (aHR: 1.35; 95% CI 1.24–1.47). Our study suggests consecutive infections are possible but rare. These findings have implications for our understanding of population immunity to influenza.

Epidemiology of influenza virus reinfection in Guangxi, China: a retrospective analysis of a nine-year influenza surveillance data

BACKGROUND

Epidemiological characteristics profile of the reinfection of the influenza virus has not been well described.

METHODS

Included all influenza cases of Guangxi, China from January 2011 to December 2019 recorded in National Notifiable Infectious Disease Reporting Information System (NIDRIS) within 24 hours after diagnosis.

RESULTS

A total of 53,605.6 person-months and the median time of 8.7 months were observed for reinfection. The median age at the first influenza virus infection was 4.5 (IQR=2.0-7.5) years. The cumulative reinfection incidence was 2% at 6-month, 4% at 12-month, 5% at 24-month, and 7% after 59-month. Living in the rural area (HR=1.37 [95%CI, 1.29-1.45]), age ≤6 years (HR=11.43 [95%CI, 9.47-13.80]) were independent risk factors associated with influenza reinfection. Among 49 patients experiencing twice laboratory tests, 32 patients (65.3%) were with different virus types. The interval between two consecutive laboratory-confirmed episodes of the four groups differed (p=0.148), as the maximum was 72.9 months, and the minimum was 1.2 months.

CONCLUSIONS

The reinfection of the influenza virus in Guangxi independently and positively associated with the rural area and younger age. The unusually high frequency of reinfection points to a need for further prospective longitudinal studies to better investigate sufficient impact on different subtypes.

Multiple Genome Constellations of Similar and Distinct Influenza A Viruses Co-Circulate in Pigs During Epidemic Events

Swine play a key role in the ecology and transmission of influenza A viruses (IAVs) between species. However, the epidemiology and diversity of swine IAVs is not completely understood. In this cohort study, we sampled on a weekly basis 132 3-week old pigs for 15 weeks. We found two overlapping epidemic events of infection in which most pigs (98.4%) tested PCR positive for IAVs. The prevalence rate of infection ranged between 0 and 86% per week and the incidence density ranged between 0 and 71 cases per 100 pigs-week. Three distinct influenza viral groups (VGs) replicating as a "swarm" of viruses were identified (swine H1-gamma, H1-beta, and H3-cluster-IV IAVs) and co-circulated at different proportions over time suggesting differential allele fitness. Furthermore, using deep genome sequencing 13 distinct viral genome constellations were differentiated. Moreover, 78% of the pigs had recurrent infections with IAVs closely related to each other or IAVs clearly distinct. Our results demonstrated the molecular complexity of swine IAVs during natural infection of pigs in which novel strains of IAVs with zoonotic and pandemic potential can emerge. These are key findings to design better health interventions to reduce the transmission of swine IAVs and minimize the public health risk.

Restriction of amino acid change in influenza A virus H3HA: comparison of amino acid changes observed in nature and in vitro

We introduced 248 single-point amino acid changes into hemagglutinin (HA) protein of the A/Aichi/2/68 (H3N2) strain by a PCR random mutation method. These changes were classified as positive or negative according to their effect on hemadsorption activity. We observed following results. (i) The percentage of surviving amino acid changes on the HA1 domain that did not abrogate hemadsorption activity was calculated to be ca. 44%. In nature, it is estimated to be ca. 39.6%. This difference in surviving amino acid changes on the HA protein between natural isolates and in vitro mutants might be due to the immune pressure against the former. (ii) A total of 26 amino acid changes in the in vitro mutants matched those at which mainstream amino acid changes had occurred in the H3HA1 polypeptide from 1968 to 2000. Of these, 25 were positive. We suggest that the majority of amino acid changes on the HA protein during evolution might be restricted to those that were positive on the HA of A/Aichi/2/68. (iii) We constructed two-point amino acid changes on the HA protein by using positive mutants. These two-point amino acid changes with a random combination did not inhibit hemadsorption activity. It is possible that an accumulation of amino acid change might occur without order. (iv) From the analysis of amino acids participating in mainstream amino acid change, each antigenic site could be further divided into smaller sites. The amino acid substitutions in the gaps between these smaller sites resulted in mostly hemadsorption-negative changes. These gap positions may play an important role in maintaining the function of the HA protein, and therefore amino acid changes are restricted at these locations.

Recurrent fulminant viral myocarditis with a short clinical course

A 75-year-old man recovered from an episode of acute influenza. A myocarditis with a normalized level of serum cardiac troponin T, but less than 2 weeks after recovery, he rapidly fell into cardiogenic shock and died of fulminant myocarditis. The autopsied heart showed marked inflammatory cell infiltration that mainly consisted of mononuclear cells positive for CD8, suggesting that the second bout of myocarditis was caused by viral re-infection.

Avaliação soroepidemiológica do vírus influenza em aves domésticas e silvestres no Estado do Rio de Janeiro

Estudou-se a presença de anticorpos para o vírus da influenza aviária, subtipos H1N1 e H3N2, por meio da técnica de inibição da hemaglutinação no plasma de 225 aves da Fundação RIO-ZOO, do Bwana Park e de pequenas criações do Estado do Rio de Janeiro. Entre as aves estudadas 60 (26,6%) foram soropositivas, sendo 22 (9,8%) para o subtipo H1N1, 28 (12,4%) para o subtipo H3N2 e 10 (4,4%) para os dois subtipos. Esses resultados indicam a ocorrência dos subtipos do vírus da influenza aviária investigados no Rio de Janeiro e apontam para o risco potencial de sua transmissão para a avicultura industrial e para pessoas.

Characterizing immunodominant and protective influenza hemagglutinin epitopes by functional activity and relative binding to major histocompatibility complex class II sites

In the present study the analysis of functional activity and major histocompatibility complex (MHC) binding of two adjacent MHC class II-restricted epitopes, located in the C-terminal 306-329 region of human influenza A virus hemagglutinin 1 subunit (HA1) conserved with subtype sequences and not affected by antigenic drift, was undertaken to explore the hierarchy of local immunodominance. The functional activity of two T cell hybridomas of the memory/effector Th1 phenotype in combination with in vivo immunization studies provided a good tool for investigating the functional characteristics of the T cell response. The in vitro binding assays performed with a series of overlapping, N-terminal biotinylated peptides covering the 306-341 sequence enabled us to compare the relative binding efficiency of peptides, comprising two distinct epitopes of this region, to I-Ed expressed on living antigen-presenting cells. Our studies revealed that (i) immunization of BALB/c mice with the 306-329 H1 or H2 peptides resulted in the activation and proliferation of T cells recognizing both the 306-318 and the 317-329 epitopes, while the 306-329 H3 peptide elicits predominantly 306-318-specific T cells, (ii) the 317-329 HA1 epitope of the H1 and H2 but not the H3 sequence is recognized by T cells and is available for recognition not only in the 317-329 peptide but also in the extended 306-329 or 306-341 peptides, (iii) the 306-318 and the 317-329 hemagglutinin peptides encompassing the H1, H2 but not the H3 sequence bind with an apparently similar affinity to and therefore compete for I-Ed binding sites, and (iv) the 317-341, the 317-329 peptides and their truncated analogs show subtype-dependent differences in MHC binding and those with lower binding capacity represent the H3 subtype sequences. These results demonstrate that differences in the binding capacity of peptides comprising two non-overlapping epitopes located in the C-terminal 306-329 region of HA1 of all three subtype-specific sequences to MHC class II provide a rationale for the local and also for the previously observed in vivo immunodominance of the 306-318 region over the 317-329 epitope in the H3 but not in the H1 or H2 sequences. In good correlation with the results of the binding and functional inhibition assays, these data demonstrate that in the H1 and H2 subtypes both regions are available for T cell recognition, they compete for the same restriction element with an apparently similar binding efficiency and, therefore, function as co-dominant epitopes. Due to the stabilizing effect of the fusion peptide, peptides comprising the 306-341 or 317-341 H1 sequences are highly immunogenic and elicit a protective immune response which involves the production of antibodies and interleukin-2 and tumor necrosis factor producing effector Th1 cells both directed against the 317-329 region. Based on the similarity of the I-Ed and HLA-DR1 peptide binding grooves and motifs, these results suggest that amino acid substitutions inserted to the H3 subtype sequence during viral evolution can modify the relative MHC binding capacity and invert the local hierarchy of immunodominance of two closely situated epitopes that are able to bind to the same MHC class II molecule.