Serological reports of human infections of H7 and H9 avian influenza viruses in northern China

https://doi.org/10.1016/j.jcv.2008.12.014Get rights and content

Abstract

Background

H7 and H9 subtype avian influenza viruses pose a similar threat to humans as H5 virus.

Objectives

This study aims to identify the potential existence of H7 and H9 avian influenza infections in farmers and in poultry workers in northern China regions with highly pathogenic avian influenza (HPAI) H5N1 outbreaks.

Study design

Sera were collected from farmers in Xinjiang Uygur autonomous region and Liaoning province and poultry workers in Shandong province. Sera from healthy residents in Shanxi province were used as the controls. H7 and H9 virus infections were examined by hemagglutination inhibition (HI) assay using horse erythrocytes. The titer equal to or greater than 1:160 was considered positive.

Results

A total of 583 sera collected from farmers in Xinjiang were tested, and 10 (1.7%) were positive for H9 virus infection. Out of 200 sera collected from Liaoning, two (1.0%) were infected by H9 virus. No H7 virus infection was detected in the above serum samples. Neither H7 nor H9 virus infection was identified in 277 poultry workers of Shandong and in 407 residents of Shanxi.

Conclusions

Although H9 virus infection was limited in farmers from Xinjiang and Liaoning, a public health alert is needed as novel pandemic influenza strains may develop unnoticed given the presence of subclinical infections, and the possibility of re-assortment with prevailing H5N1 virus in these regions.

Introduction

Influenza A viruses are classified on the basis of two surface proteins, i.e. the hemagglutinin (HA) and neuraminidase (NA).1 Among the 16 HA subtype viruses detected in wild birds and poultry throughout the world,2 H7 and H9 subtypes have generated significant concern for potential of human infection3 besides the H5N1 viruses which have caused worldwide threat to humans.4 Different from the severe illness and high case fatality of highly pathogenic avian influenza (HPAI) H5N1 virus,5 conjunctivitis and/or mild respiratory disease were common when humans are infected with H7 and H9 subtype viruses.6, 7 However, H7 and H9 avian influenza viruses also pose a similar threat as H5 to human population because the nature of mild infections may allow the virus a greater opportunity to become more virulent through surreptitious spread and mutation or reassortment with influenza viruses of other serotypes.8, 9

As only mild manifestations presented, few cases with H7 or H9 virus infection were reported.6 The knowledge is insufficient for understanding these viruses’ ability to transmit to humans. We hypothesize that human infections with H7 and H9 influenza may occur in areas with frequently reported outbreaks of HPAI H5N1 infections in poultry, as the special territorial and social environments in these regions may have become favorable to the transmission of avian influenza viruses.

Since 2004, HPAI H5N1 outbreaks have been repeatedly reported in Xinjiang Uygur Autonomous Region of China10 and in Liaoning province.11 Human cases of HPAI H5N1 infection were diagnosed in both regions after poultry outbreaks.11, 12 In the two regions, agriculture plays a critical role in economic development and many families raise free-range domestic poultry.

In addition, since 1996, H9N2 viruses were frequently isolated from a wide range of hosts, such as chicken and swine through routine surveillance in another northern China province, Shandong.13, 14, 15 It is thought that people directly exposing to live poultry as a work-duty run high risk for infection with H7 or H9 subtype avian influenza viruses.

In this study, we conducted an epidemiological survey to detect H7 and H9 infections in farmers in Xinjiang and Liaoning where HPAI H5N1 were reported in both poultry and humans, and in professional poultry workers in Shandong. The same assay was performed in healthy residents from Shanxi, another province of northern China where no avian H5N1 outbreak occurred for comparison.

Section snippets

Study protocol and sample collection

The study was conducted in April 2006 in 2 villages around Ulumuqi, the capital city of Xinjiang, and in a village nearby a satellite city, Miquan. In February 2008, a similar survey was carried out in two villages in Liaoning, one was in Fuxin City and another was in Heishan City (Fig. 1). HPAI H5N1 outbreaks had been reported in the above five villages in December 2005.10, 11 These villages consist of a typical rural Chinese setting where the villagers usually raise various animals such as

Results

The total numbers of volunteers participating the current study were 583, 200, and 407 from Xinjiang (XJ), Liaoning (LN) and Shanxi (SX), respectively (Table 1). The age distribution in the three regions was comparable. About half of participants were female among participants in XJ and LN, and about 40% were female in SX province. The majority of volunteers from XJ and LN provinces were farmers, representing 70% and 82% of the total volunteers, respectively. On the other hand, only 30% from SX

Discussion

In the current study, human infection with H9 virus was identified in farmers from Xinjiang and Liaoning where HPAI H5N1 infection in poultry and humans have been reported. Our study indicated that H9 and H5 avian influenza viruses may co-circulate in the two regions, where both serotypes infected the human. On the other hand, there was no detectable serological evidence to suggest H7 virus infection.

The limitation of the study is that only HI assay was applied for serological test. As there is

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

We thank Dr. Jill M. Grimes-Serrano (UMass Medical School) for editing the manuscript. This study was supported by the grants of Natural Science Fund for Distinguished Young Scholars (30725032), Natural Science for Major International Joint Research Project (30810103903), China's National High-tech 863 Program (2006AA02Z457), China's National Scientific and Technical Supporting Program (2006BAD06A02), the Foundation for State Key Laboratory of Pathogen and Biosecurity (200701), a Jiangsu

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