Instituto Valenciano de Microbiología

Masía El Romeral
Ctra. de Bétera a San Antonio Km. 0.3
46117 Bétera (Valencia)
Phone. 96 169 17 02
Fax 96 169 16 37
CIF B-96337217


Influenza A virus subtype H9N2

version 7.6.13

There are three types of influenza viruses: A, B and C. Type A is subdivided into subtypes based on the antigenic differences in their surface glycoproteins: hemagglutinin (HA) and neuraminidase (NA). 16 hemagglutinin subtypes (H1 to H16) and 9 subtypes of neuraminidase (N1 to N9) that infect birds are now known. In bats it found a new subtype (H17), and a new neuraminidasaa (N10).

Of the 16 hemagglutinin subtypes that can be found in birds, three of them (H5, H7 and H9) they have caused cases of human infections. Subtype H5N1, highly pathogenic when it has infected humans, has caused an acute illness with high mortality (> 60%). The H7 subtype, low pathogenicity, in most cases, only causes clinical symptoms of conjunctivitis. H9 subtype (mainly H9N2), also low pathogenic affects poultry and wild birds, and is preferably adapted to chickens and quails been found in Asia, North America, Europe, Africa and the Pacific. This subtype causes mild signs in birds, but infections can complicate their way to secondary bacterial infections. When it has infected humans has caused flu - like symptoms.

Recently the H9 subtype circulating in China, has been concerned since the 1990s for having detected producing some human infections, in some cases adapted to interact with receptors on human cells, which could trigger a pandemic after human adaptation .

This subtype H9, unlike what happened with the H5 subtype highly pathogenic, has only caused mild infections, no consistent evidence of human transmission.

Subtype H9, had many recombinations, so that have generated 98 distinct genotypes, which would be grouped into 9 series (A to G), and would have resulted in up to 74 different lineages with marked differences as the host species and areas geographical. The genes encoding foreign proteins are closely related to H3, H4, H5M, H7, H10 and H14.

No wonder the natural host (poultry such as chickens and quails), it can be infected by H9 and H5 subtypes, which would involve the risk that the H9 subtype LPAI, could acquire genes of the H5 subtype of highly pathogenic.


This subtype H9N2, Influenza A virus is a subtype of low pathogenicity, widely distributed among poultry (chickens and quails), which currently has only caused infections flulike in China, but serologic studies have shown show that there human contact. Their coexistence in poultry with highly pathogenic H5N1 subtype could lead to recombination in which some of the genes that confer the degree of pathogenicity H5N1 subtype, was acquired by the H9N2 subtype. Some studies show that there appears to be strains that have adapted to human cell receptors through which the virus comes into contact with the cells. Therefore, international health organizations such as the World Health Organization, are monitoring the findings of this virus, but could lead to a new influenza pandemic. In our laboratory (IVAMI) we have the necessary procedures for diagnosis.


Jiang Wenming, Shuo Liu, Hou Guangyu, Li Jinping, Qingye Zhuang, Suchun Wang, Zhang Peng, Chen Jiming. Chinese and Global Distribution of Avian Influenza Viruses H9 Subtype. PlosOne 2012, 7 (12): e52671.

Guoying Dong, Jing Luo, Zhang Hong, Wang Chengmin, Duan Mingxing, Thomas Jude Deliberto, Dale Louis Nolte, Guangju Ji, Hongxuan He. Phylogenetic Diversity and genotypical Complexity of H9N2 Influenza A Viruses Revealed by Genomic Sequence Analysis. PlosOne, 2011, 6 (2): e17212.

Liu Liqi, Li Zi, Zhou Jianfang, Zhu Yun, Dong Jie, Zhao Xiang, Guo Junfeng, and Shu Yuelong. Pathogenesis and Immunogenicity of an Avian Influenza H9N2 Virus Isolated from Human. Biomed Environ Sci , 2011, 24 (5): 530-536.

Ge Fei-Fei, Jin-Ping Zhou, Jian Liu, Jian Wang, Wei-Yi Zhang, Li-Ping Sheng, Feng Xu, Hou-Bing Ju-Yun Sun Quan, and Pei-Hong Liu. Genetic Evolution of H9 Subtype Influenza Viruses from Live Poultry Markets in Shanghai, China. J Clin Microbiol 2009, 47 (10): 3294-3300.

Kim M. Pepin1, Jia Wang, Colleen T. Webb, Jennifer A. Hoeting, Mary Poss, Peter J. Hudson, Wenshan Hong, Huachen Zhu, Yi Guan, Steven Riley. Anticipating the Prevalence of Avian Influenza H5 and H9 Subtypes in Live-Bird Markets. PlosOne 2013, 8 (2): e56157.

Yu Qi, Liu Linqing, Juan Pu, Jingyi Zhao, Yipeng Sun, Guangnian Shen, Wei Haitao, Zhu Junjie, Zheng Ruifeng, Dongyan Xiong, Xiaodong Liu, and Jinhua Liu. Avian Influenza Risk Perceptions for Virus Infection Among Poultry Workers, China. Emerg Infect Dis 2013, 19 (2): 313-316.