Lack of evidence of avian-to-human transmission of avian influenza A (H5N1) virus among veterinarians, Guangdong, China, 2012

Serological evidence of human infections with highly pathogenic avian influenza A(H5N1) virus: a systematic review and meta-analysis

BACKGROUND

Highly pathogenic avian influenza A(H5N1) virus poses a global public health threat given severe and fatal zoonotic infections since 1997 and ongoing A(H5N1) virus circulation among poultry in several countries. A comprehensive assessment of the seroprevalence of A(H5N1) virus antibodies remains a gap and limits understanding of the true risk of A(H5N1) virus infection.

METHODS

We conducted a systematic review and meta-analysis of published serosurveys to assess the risk of subclinical and clinically mild A(H5N1) virus infections. We assessed A(H5N1) virus antibody titers and changes in titers among populations with variable exposures to different A(H5N1) viruses.

RESULTS

Across studies using the World Health Organization-recommended seropositive definition, the point estimates of the seroprevalence of A(H5N1) virus-specific antibodies were higher in poultry-exposed populations (range 0-0.6%) and persons exposed to both human A(H5N1) cases and infected birds (range 0.4-1.8%) than in close contacts of A(H5N1) cases or the general population (none to very low frequencies). Seroprevalence was higher in persons exposed to A(H5N1) clade 0 virus (1.9%, range 0.7-3.2%) than in participants exposed to other clades of A(H5N1) virus (range 0-0.5%) (p < 0.05). Seroprevalence was higher in poultry-exposed populations (range 0-1.9%) if such studies utilized antigenically similar A(H5N1) virus antigens in assays to A(H5N1) viruses circulating among poultry.

CONCLUSIONS

These low seroprevalences suggest that subclinical and clinically mild human A(H5N1) virus infections are uncommon. Standardized serological survey and laboratory methods are needed to fully understand the extent and risk of human A(H5N1) virus infections.

Seroprevalence of highly pathogenic avian influenza (H5N1) virus infection among humans in mainland China: A systematic review and meta-analysis

Although the effective transmission of the H5N1 virus from humans to humans has yet to be further observed, humans are at increased risk of a pandemic caused by H5N1. In order to fully evaluate the seroprevalence and risk factor of highly pathogenic avian influenza A (H5N1) virus infection among in mainland China, we performed a systematic review and meta-analysis. In this review, we searched literature on the seroprevalence of H5N1 infection among humans in mainland China from 1 January 1997 to 20 October 2018 in English and Chinese databases, including PubMed, Google scholar, Cochrane library, Clinical Trial, VIP, CNKI and WanFang database. We made a selection according to the title and the abstract of paper, and then, we excluded duplicated literature, and data incomplete literature according to the exclusion criteria we formulated. Finally, we extracted how many humans have H5N1 infection from the obtained studies to establish the seroprevalence of H5N1 infection among humans in mainland China. A total of 56 studies (including data of 35,159 humans) were compliant with our criteria. In China, the overall seroprevalence of H5N1 infection among humans was 2.45% (862/35,159), while the seroprevalence of H5N1 infection among humans from central China was 7.32% (213/2,911), higher than those in other regions of China. The seroprevalence of H5N1 infection was associated with test method, sampling time and demographic characteristics of humans. However, there was no significant difference in the effect of gender on the seroprevalence of H5N1 among humans in China. The purpose of this review was to better understand the real infection rate of H5N1 virus among humans and evaluate the potential risk factors for the zoonotic spread of H5N1 virus to humans. Sufficient epidemiological data are important to explore and understand the prevalent status of AIVs throughout the country and to disease control.

Evidence for H5 avian influenza infection in Zhejiang province, China, 2010-2012: a cross-sectional study

BACKGROUND

The first outbreak of H5N1 highly-pathogenic avian influenza (HPAI) virus associated with several human deaths occurred in 1997 in Hong-Kong, China. While H5N1 virus infection in poultry workers has been studied in some detail, little is known about the environmental risk factors of the H5 avian influenza virus infection in China.

METHODS

A cross-sectional study was performed to evaluate the environmental load of H5 viruses in poultry-contaminated environments and to explore potential risk factors associated with infection in poultry workers between October 2010 and March 2012. Serum and environmental samples were collected in Zhejiang province, China. The hemagglutination inhibition (HI) assay was used to analyze human sera for antibodies against H5N1 virus [A/Hubei/1/2010 (H5N1) and A/Anhui/1/2005 (H5N1)]. All participants were interviewed with a standardized questionnaire to collect information on exposure to poultry. H5 Avian influenza virus in the environmental samples was detected by real time RT-PCR.

RESULTS

One hundred and five of 3,453 environmental samples (3.0%) tested positive for H5 avian influenza virus. Fifty-five of 1,169 subjects (4.7%) tested seropositive for anti-H5N1 antibodies. A statistically significant difference in H5 virus detection rate was found among the different environments sampled (<0.001), with the highest showed in live bird markets (68.6%). Detection rate varied according to the source of samples, sewage (9.5%), drinking water (19.0%), feces (19.0%), cage surface (25.7%), and slaughtering chopping boards (15.2%), respectively. Direct or close contact with poultry (OR =5.20, 95% CI, 1.53-17.74) and breeding numerous poultry (OR =3.77, 95% CI, 1.72-8.73) were significantly associated with seroprevalence of antibodies to avian influenza virus A (H5N1).

CONCLUSIONS

The number of birds bred more than 1,000 and direct or close contact with poultry in the workplace or the environment would be a potential risk of H5N1 infection.

Antibodies against avian-like A (H1N1) swine influenza virus among swine farm residents in eastern China

In 2007, the avian-like H1N1 virus (A/swine/Zhejiang/1/07) was first isolated in pigs in China. Recently, it was reported that a 3-year-old boy was infected with avian-like A (H1N1) swine influenza virus (SIV) in Jiangsu Province, China. To investigate the prevalence of avian-like A (H1N1) SIV infection among swine farm residents in eastern China, an active influenza surveillance program was conducted on swine farms in this region from May 21, 2010 through April 22, 2012. A total of 1,162 participants were enrolled, including 1,136 persons from 48 pig farms, as well as 26 pig farm veterinarians. A total of 10.7% and 7.8% swine farm residents were positive for antibodies against avian-like A (H1N1) SIV by HI and NT assay, respectively, using 40 as the cut-off antibody titer. Meanwhile, all the serum samples collected from a control of healthy city residents were negative against avian-like A (H1N1) SIV. As the difference in numbers of antibody positive samples between the swine farm residents and health city residents controls was statistically significant (P = 0.002), these data suggest that occupational exposure to pigs may increase swine farm residents' and veterinarians' risk of avian-like A (H1N1) SIV infection in eastern China. This study provides the first data on avian-like A (H1N1) SIV infections in humans in China; the potential for avian-like A (H1N1) SIV entering the human population should also be taken into consideration.

Avian influenza A (H5N1) virus antibodies in pigs and residents of swine farms, southern China

BACKGROUND

Since 1997, the H5 avian influenza viruses (AIVs) circulating in China have become an international concern. Clade 2.3.2 of H5N1 AIVs is genetically distinct from the viruses isolated before 2007 and antigenically different from the vaccine strains widely used in China. Swine farms in rural China are thought to play an important role in AIVs ecology.

OBJECTIVES

A seroepidemiological study was undertaken among swine farm residents and pigs to understand the prevalence of antibodies against H5N1 AIVs in southern China.

STUDY DESIGN

During the period March 24, 2008 to December 25, 2012,serum samples were collected from 1606 swine farm residents on 40 swine farms in southern China. A total of 1980 pigs' serum samples were collected in the same swine farms where swine workers' serum samples were collected from March 2009 to March 2013. For a control group, 104 serum samples were collected from healthy city residents in Nanchang. All the serum samples were collected to perform hemagglutination inhibition (HI) and (neutralization) NT assays to investigate the prevalence of H5N1 AIV infections in southern China.

RESULTS

Sixteen human samples were positive by HI assay and 10 of these were also positive by NT assay against H5N1. No serum samples from human control and pigs were HI positive for H5N1 AIV.

DISCUSSION

Our results demonstrate minimal transmission H5N1 AIV from birds to pigs in the swine farms studied and the risk of poultry-to-human and poultry-to-pig transmission for at least clades 2.3.2 seemed very low. This study provides the first data regarding antibodies against H5N1 AIV in humans and pigs on swine farms in China. The findings of this study can serve as a baseline for additional serologic studies to assess transmission of H5N1 viruses between avian species, pigs and swine workers.

Serological surveillance of H5 and H9 avian influenza A viral infections among pigs in Southern China

Pigs are susceptible to both human and avian influenza viruses (AIV). Moreover, they are suspected of being the intermediate hosts or mixing vessels of pandemic influenza viruses. Researchers suspect that the influenza viruses are able to undergo reassortment or to adapt to various mammalian hosts while they incubate in pigs. For the present report, we conducted a serological surveillance of pigs in southern China from 2008 to 2012 to establish the prevalence of antibodies against H5N1 and H9N2 AIV. A total of one hundred pig farms from the Guangdong, Zhejiang, Fujian, and Yunnan Provinces were sampled, yielding a total of 3960 serum specimens. The haemagglutination inhibition (HI) tests revealed no evidence of H5 infection when the Clade 2.3.2 virus was used as the antigen, but a 4.6% positive rate of H9 infection was observed when using the Beijing/1/94-like virus as the antigen. The positive sera for H9 infection were further verified with neutralization tests, which confirmed a 3.7% rate of positive sera of H9 infection. In summary, the results imply that the swine populations in southern China had not been affected greatly by the H5N1 avian influenza virus. Nevertheless, these swine H9N2 influenza viruses might pose a threat to human health, and so researchers should continue to carry out swine influenza virus surveillance in China.

Epidemiological, clinical and viral characteristics of fatal cases of human avian influenza A (H7N9) virus in Zhejiang Province, China

BACKGROUND

The high mortality of avian influenza H7N9 in humans is a cause of great concern in China.

METHODS

We compared epidemiological, clinical and viral features of H7N9 influenza of 10 fatal cases and 30 survivors.

RESULTS

Increasing age (p = 0.021), smoking (p = 0.04), underlying medical background (p = 0.05) and chronic drug use (p = 0.042) had a strong relationship with death due to H7N9 infection. Serological inflammatory markers were higher in fatal cases compared to survivors. Acute respiratory distress syndrome (100%), respiratory failure (100%), co-infection with bacteria (60%), shock (50%) and congestive heart failure (50%) were the most common complications observed in fatal cases. The median time from onset of symptoms to antiviral therapy was 4.6 and 7.4 days in those who survived and those who died, respectively (p = 0.04). Viral HA, NA and MP nucleotide sequences of isolates from both study groups exhibited high molecular genetic homology.

CONCLUSIONS

Age along with a history of smoking, chronic lung disease, immuno-suppressive disorders, chronic drug use and delayed Oseltamivir treatment are risk factors which might contribute to fatal outcome in human H7N9 infection.