Sero-epidemiologic study of influenza A(H7N9) infection among exposed populations, China 2013-2014

Mendelian randomization study on the causal effect of serum IgA levels on H7N9 avian influenza A virus susceptibility

Avian influenza A viruses (IAVs) that cross the species barrier to infect humans have the potential to initiate a new pandemic. However, the host factors influencing avian IAV infection remain poorly understood. To address this knowledge gap, we conducted a two-sample Mendelian randomization (MR) analysis by integrating our in-house genome-wide association study (GWAS) of avian IAV H7N9 susceptibility (with 217 cases and 116 controls) with the largest GWAS of serum IgA levels to date (sample size 41 263). Using the inverse-variance weighted (IVW) method, we discovered that genetically decreased serum IgA levels were associated with an increased risk of H7N9 infection (β = -2.528, 95% confidence interval [CI]: -4.572 to -0.484; p = 0.015). Consistent results were obtained from three other MR methods, including robust IVW estimation (β = -2.506, 95% CI: -4.109 to -0.902; p = 0.002), generalized summary-data-based MR (GSMR) (β = -2.238, 95% CI: -4.106 to -0.602; p = 0.019), and MR-pleiotropy residual sum and outlier (MR-PRESSO) (β = -2.528, 95% CI: -4.396 to -0.892; p = 0.026). In conclusion, our analysis provided compelling evidence support a causal relationship between genetically predicted serum IgA levels and avian IAV H7N9 susceptibility.

Biological Sex and Pregnancy Affect Influenza Pathogenesis and Vaccination

Males and females differ in the outcome of influenza A virus (IAV) infections, which depends significantly on age. During seasonal influenza epidemics, young children (< 5 years of age) and aged adults (65+ years of age) are at greatest risk for severe disease, and among these age groups, males tend to suffer a worse outcome from IAV infection than females. Following infection with pandemic strains of IAVs, females of reproductive ages (i.e., 15-49 years of age) experience a worse outcome than their male counterparts. Although females of reproductive ages experience worse outcomes from IAV infection, females typically have greater immune responses to influenza vaccination as compared with males. Among females of reproductive ages, pregnancy is one factor linked to an increased risk of severe outcome of influenza. Small animal models of influenza virus infection and vaccination illustrate that immune responses and repair of damaged tissue following IAV infection also differ between the sexes and impact the outcome of infection. There is growing evidence that sex steroid hormones, including estrogens, progesterone, and testosterone, directly impact immune responses during IAV infection and vaccination. Greater consideration of the combined effects of sex and age as biological variables in epidemiological, clinical, and animal studies of influenza pathogenesis is needed.

Anamnestic broadly reactive antibodies induced by H7N9 virus more efficiently bind to seasonal H3N2 strains

The very first influenza virus exposure in a human during infancy is known to imprint the host immune system. However, it is unclear how the memory B cells that first target virus epitopes affect antibody response to the stalk of hemagglutinin (HA) domain of influenza virus. Our study is designed to measure the cross-reactivity of antibodies induced by inactivated H7N9 virus using isolated human peripheral blood B cells. Most of the participants displayed higher levels of plasma IgG against the seasonal strains A/Vic11 and A/Cali09 than those binding to historical outbreak A/HK68 and A/PR8. H3 stalk-binding antibodies were detected in plasma at a 1:5000 dilution in 12 of 13 donors, H1 stalk-binding antibodies in all donors, indicating the existence of H3 and H1 stalk-reactive memory B cells. A moderate to high level of broadly cross-reactive antibodies was induced in memory B cells from all donors after in vitro stimulation of B cells with H7N9 virus. H3 stalk-binding antibodies were also detected in most subjects, with cross-reactivity to H1 and H7 stalk domains. The stalk-reactive antibodies bound to five H3 strains spanning 45 years and different H1, H2, H3, H5, H6, H7, H9 and B strains. Interestingly, H1- and H3-reactive IgG were much higher than H7-binding antibodies after 6 days of H7N9 stimulation. Our results demonstrate that HA stalk-reactive antibodies induced by H7N9 viruses more efficiently bound to yearly circulating both H3N2 and H1N1 strains than the boosting strain, indicating that HA stalk immunological imprint can be extended across currently circulating strains or vaccines.

Rare variant MX1 alleles increase human susceptibility to zoonotic H7N9 influenza virus

Zoonotic avian influenza A virus (IAV) infections are rare. Sustained transmission of these IAVs between humans has not been observed, suggesting a role for host genes. We used whole-genome sequencing to compare avian IAV H7N9 patients with healthy controls and observed a strong association between H7N9 infection and rare, heterozygous single-nucleotide variants in the MX1 gene. MX1 codes for myxovirus resistance protein A (MxA), an interferon-induced antiviral guanosine triphosphatase known to control IAV infections in transgenic mice. Most of the MxA variants identified lost the ability to inhibit avian IAVs, including H7N9, in transfected human cell lines. Nearly all of the inactive MxA variants exerted a dominant-negative effect on the antiviral function of wild-type MxA, suggesting an MxA null phenotype in heterozygous carriers. Our study provides genetic evidence for a crucial role of the MX1-based antiviral defense in controlling zoonotic IAV infections in humans.

Serological evidence of human infection with avian influenza A(H7N9) virus: a systematic review and meta-analysis

Background

The extent of human infections with avian influenza A(H7N9) virus, including mild and asymptomatic infections, is uncertain.

Methods

We performed a systematic review and meta-analysis of serosurveys for avian influenza A(H7N9) virus infections in humans published during 2013–2020. Three seropositive definitions were assessed to estimate pooled seroprevalence, seroconversion rate, and seroincidence by types of exposures. We applied a scoring system to assess the quality of included studies.

Results

Of 31 included studies, pooled seroprevalence of A(H7N9) virus antibodies from all participants was 0.02%, with poultry workers, close contacts, and general populations having seroprevalence of 0.1%, 0.2%, and 0.02%, respectively, based on the World Health Organization (WHO)—recommended definition. Although most infections were asymptomatic, evidence of infection was highest in poultry workers (5% seroconversion, 19.1% seroincidence per 100 person-years). Use of different virus clades did not significantly affect seroprevalence estimates. Most serological studies were of low to moderate quality and did not follow standardized seroepidemiological protocols or WHO-recommended laboratory methods.

Conclusions

Human infections with avian influenza A(H7N9) virus have been uncommon, especially for general populations. Workers with occupational exposures to poultry and close contacts of A(H7N9) human cases had low risks of infection.

Seroprevalence of H7N9 infection among humans: A systematic review and meta-analysis

In spring 2013, a novel avian-origin influenza A (H7N9) virus emerged in mainland China. The burden of H7N9 infection was estimated based on systematic review and meta-analysis. The systematic search for available literature was conducted using Chinese and English databases. We calculated the pooled seroprevalence of H7N9 infection and its 95% confidence interval by using Freeman-Tukey double arcsine transformation. Out of 16 890 records found using Chinese and English databases, 54 articles were included in the meta-analysis. These included studies of a total of 64 107 individuals. The pooled seroprevalence of H7N9 infection among humans was 0.122% (95% CI: 0.023, 0.275). In high-risk populations, the highest pooled seroprevalence was observed among close contacts (1.075%, 95% CI: 0.000, 4.357). The seroprevalence among general population was (0.077%, 95% CI: 0.011, 0.180). Our study discovered that asymptomatic infection of H7N9 virus did occur, even if the seroprevalence among humans was low.

Avian Influenza A Virus Infection among Workers at Live Poultry Markets, China, 2013-2016

We conducted a 3-year longitudinal serologic survey on an open cohort of poultry workers, swine workers, and general population controls to assess avian influenza A virus (AIV) seroprevalence and seroincidence and virologic diversity at live poultry markets (LPMs) in Wuxi City, Jiangsu Province, China. Of 964 poultry workers, 9 (0.93%) were seropositive for subtype H7N9 virus, 18 (1.87%) for H9N2, and 18 (1.87%) for H5N1. Of 468 poultry workers followed longitudinally, 2 (0.43%), 13 (2.78%), and 7 (1.5%) seroconverted, respectively; incidence was 1.27, 8.28, and 4.46/1,000 person-years for H7N9, H9N2, and H5N1 viruses, respectively. Longitudinal surveillance of AIVs at 9 LPMs revealed high co-circulation of H9, H7, and H5 subtypes. We detected AIVs in 726 (23.3%) of 3,121 samples and identified a high diversity (10 subtypes) of new genetic constellations and reassortant viruses. These data suggest that stronger surveillance for AIVs within LPMs and high-risk populations is imperative.

Identification of meteorological factors associated with human infection with avian influenza A H7N9 virus in Zhejiang Province, China

BACKGROUND

Since the first reported human infection with an avian-origin influenza A (H7N9) virus in China in early 2013, there have been recurrent outbreaks of the virus in the country. Previous studies have shown that meteorological factors are associated with the risk of human infection with the virus; however, their possible nonlinear and lagged effects were not commonly taken into account.

METHOD

To quantify the effect of meteorological factors on the risk of human H7N9 infection, daily laboratory-confirmed cases of human H7N9 infection and meteorological factors including total rainfall, average wind speed, average temperature, average relative humidity, and sunshine duration of the 11 sub-provincial/prefecture cities in Zhejiang during the first four outbreaks (13 March 2013-30 June 2016) were analyzed. Separate models were built for the 6 sub-provincial/prefecture cities with the greatest number of reported cases using a combination of logistic generalized additive model and distributed lag nonlinear models, which were then pooled by a multivariate meta-regression model to determine their overall effects.

RESULTS

According to the meta-regression model, for rainfall, the log adjusted overall cumulative odds ratio was statistically significant when log of rainfall was >4.0, peaked at 5.3 with a value of 12.42 (95% confidence intervals (CI): [3.23, 21.62]). On the other hand, when wind speed was 2.1-3.0 m/s or 6.3-7.1 m/s, the log adjusted overall cumulative odds ratio was statistically significant, peaked at 7.1 m/s with a value of 6.75 (95% CI: [0.03, 13.47]). There were signs of nonlinearity and lag effects in their associations with the risk of infection.

CONCLUSION

As rainfall and wind speed were found to be associated with the risk of human H7N9 infection, weather conditions should be taken into account when it comes to disease surveillance, allowing prompt actions when an outbreak takes place.

Influenza A(H7N9) Virus Antibody Responses in Survivors 1 Year after Infection, China, 2017

Avian influenza A(H7N9) virus has caused 5 epidemic waves in China since its emergence in 2013. We investigated the dynamic changes of antibody response to this virus over 1 year postinfection in 25 patients in Suzhou City, Jiangsu Province, China, who had laboratory-confirmed infections during the fifth epidemic wave, October 1, 2016–February 14, 2017. Most survivors had relatively robust antibody responses that decreased but remained detectable at 1 year. Antibody response was variable; several survivors had low or undetectable antibody titers. Hemagglutination inhibition titer was >1:40 for <40% of the survivors. Measured in vitro in infected mice, hemagglutination inhibition titer predicted serum protective ability. Our findings provide a helpful serologic guideline for identifying subclinical infections and for developing effective vaccines and therapeutics to counter H7N9 virus infections.

Evaluation of animal-to-human and human-to-human transmission of influenza A (H7N9) virus in China, 2013-15

A novel avian-origin influenza A(H7N9) virus emerged in China in March 2013 and by 27 September 2017 a total of 1533 laboratory-confirmed cases have been reported. Occurrences of animal-to-human and human-to-human transmission have been previously identified, and the force of human-to-human transmission is an important component of risk assessment. In this study, we constructed an ecological model to evaluate the animal-to-human and human-to-human transmission of H7N9 during the first three epidemic waves in spring 2013, winter/spring 2013-2014 and winter/spring 2014-2015 in China based on 149 laboratory-confirmed urban cases. Our analysis of patterns in incidence in major cities allowed us to estimate a mean incubation period in humans of 2.6 days (95% credibility interval, CrI: 1.4-3.1) and an effective reproduction number Re of 0.23 (95% CrI: 0.05-0.47) for the first wave, 0.16 (95% CrI: 0.01-0.41) for the second wave, and 0.16 (95% CrI: 0.01-0.45) for the third wave without a significant difference between waves. There was a significant decrease in the incidence of H7N9 cases after live poultry market closures in various major cities. Our analytic framework can be used for continued assessment of the risk of human to human transmission of A(H7N9) virus as human infections continue to occur in China.

Spatial characteristics and the epidemiology of human infections with avian influenza A(H7N9) virus in five waves from 2013 to 2017 in Zhejiang Province, China

Background

The five-wave epidemic of H7N9 in China emerged in the second half of 2016. This study aimed to compare the epidemiological characteristics among the five waves, estimating the possible infected cases and inferring the extent of the possible epidemic in the areas that have not reported cases before.

Methods

The data for the H7N9 cases from Zhejiang Province between 2013 and 2017 was obtained from the China Information Network System of Disease Prevention and Control. The start date of each wave was 16 March 2013, 1 July 2013, 1 July 2014, 1 July 2015 and 1 July 2016. The F test or Pearson’s chi-square test were used to compare the characteristics of the five waves. Global and local autocorrelation analysis was carried out to identify spatial autocorrelations. Ordinary kriging interpolation was analyzed to estimate the number of human infections with H7N9 virus and to infer the extent of infections in the areas with no cases reported before.

Result

There were 45, 94, 45, 34 and 80 cases identified from the first wave to the fifth, respectively. The death rate was significantly different among the five waves of epidemics (χ² = 10.784, P = 0.029). The age distribution (F = 0.903, P = 0.462), gender (χ² = 2.674, P = 0.614) and occupation(χ² = 19.764, P = 0.407) were similar in each period. Most of the cases were males and farmers. A significant trend (χ² = 70.328, P<0.001) was identified that showed a growing proportion of rural cases. There were 31 high-high clusters and 3 high-low clusters at the county level among the five waves and 12, 8, 2, 9 and 3 clusters in each wave, respectively. The total cases infected with the H7N9 virus were far more than those that have been reported now, and the affected areas continue to expand. The epidemic in the north of Zhejiang Province persisted in all five waves. Since the second wave, the virus spread to the south areas and central areas. There was an obvious decline in the infected cases in the urban areas, and the epidemics mostly occurred in the rural areas after the fourth wave. The epidemic was relatively dispersed since the third wave had fewer than two cases in most of the areas and showed a reinforcing trend again in the fifth wave.

Conclusions

The study revealed that there were few differences in the epidemiologic characteristics among the five waves of the epidemic. However, the areas where the possible epidemic circulated was larger than reported. The epidemic cross-regional expansion continued and mostly occurred in rural areas. Continuous closure of the live poultry market (LPM) is strongly recommended in both rural and urban areas. Illegal and scattered live poultry trading, especially in rural areas, must be forbidden. It is suggested too that a more rigorous management be performed on live poultry trade and wholesale across the area. Health education, surveillance of cases and pathogenicity should also be strengthened.

C-C Motif Chemokine Ligand 2 (CCL2) Mediates Acute Lung Injury Induced by Lethal Influenza H7N9 Virus

An avian-origin influenza A (H7N9) virus was a cause for concern in China in the spring of 2013. Most H7N9 infections resulted in acute respiratory distress syndrome (ARDS), which is a severe form of acute lung injury (ALI) that contributes to morbidity and mortality. In this study, we induced viral ALI by infecting wild-type and CCL2-deficient mice with influenza H7N9 virus. The results suggested a close association between C-C motif chemokine ligand 2 (CCL2) expressions and ALI induced by a lethal H7N9 virus strain (A/Hebei/01/2013). Elevated CCL2 levels were also detected in confirmed human cases of H7N9 and the bronchoalveolar lavage fluid (BALF) of H7N9-infected mice. Moreover, CCL2 was overexpressed in the lung tissue of infected mice. More importantly, CCL2 deficiency ameliorated H7N9-induced ALI in mice as determined by weight loss, survival rate, the wet:dry ratio of the lung, and pathology. Taken together, our findings demonstrate that CCL2 is essential for H7N9 virus infection and thus that it is a potential therapeutic target for influenza.

Sero-epidemiologic study of influenza A(H7N9) infection among exposed populations, China 2013-2014

Background

The first human infections of novel avian influenza A(H7N9) virus were identified in China in March 2013. Sentinel surveillance systems and contact tracing may not identify mild and asymptomatic human infections of influenza A(H7N9) virus.

Objectives

We assessed the seroprevalence of antibodies to influenza A(H7N9) virus in three populations during the early stages of the epidemic.

Patients/Methods

From March 2013 to May 2014, we collected sera from the general population, poultry workers, and contacts of confirmed infections in nine Chinese provinces reporting human A(H7N9) infections and, for contacts, second sera 2‐3 weeks later. We screened for A(H7N9) antibodies by advanced hemagglutination inhibition (HI) assay and tested sera with HI titers ≥20 by modified microneutralization (MN) assay. MN titers ≥20 or fourfold increases in paired sera were considered seropositive.

Results

Among general population sera (n=1480), none were seropositive. Among poultry worker sera (n=1866), 28 had HI titers ≥20; two (0.11%, 95% CI: 0.02‐0.44) were positive by MN. Among 61 healthcare and 117 non‐healthcare contacts’ sera, five had HI titers ≥20, and all were negative by MN. There was no seroconversion among 131 paired sera.

Conclusions

There was no evidence of widespread transmission of influenza A(H7N9) virus during March 2013 to May 2014, although A(H7N9) may have caused rare, previously unrecognized infections among poultry workers. Although the findings suggest that there were few undetected cases of influenza A(H7N9) early in the epidemic, it is important to continue monitoring transmission as virus and epidemic evolve.