There was less H5N1 avian influenza (AI) reported in 2017 as compared to recent years; however, the “5th wave” of H7N9 AI was nearly as large as the first four waves combined, according to information published by the Hong Kong Centre for Health Protection (CHP) of the Department of Health today.
In 2017 (as of November 20), human infections with H5N1, H5N6, H7N9 and H9N2 viruses have been reported so far.
H5N1 avian influenza
Four human H5N1 cases have been reported to the World Health Organization (WHO) in 2017, as of October 30, as compared with 10 cases and 145 cases reported in 2016 and 2015 respectively (according to onset date). The four cases occurred in Egypt (3) and Indonesia (1). Among them, two cases recovered and two cases died.
H5N6 avian influenza
One human H5N6 case has been reported by the National Health and Family Planning Commission (NHFPC) in 2017 so far. The case affected was a 33-year-old male from Guangxi with live poultry exposure before onset, and he was in serious condition at time of reporting. Since 2014, a total of 17 sporadic human cases (including at least 11 deaths) have been reported by NHFPC and all occurred in Mainland China.
H9N2 avian influenza
Four sporadic cases of human H9N2 infection have been reported by NHFPC in 2017 so far. Three cases affected young children aged less than one year while the remaining case affected a 32-year-old man. All cases presented with mild illness. Two cases reported poultry exposure prior to symptom onset.
H7N9 avian influenza
Since the emergence of human cases of H7N9 infection in Mainland China in March 2013, there have been five distinct waves of human infection. The most recent wave (fifth wave) occurred from October 2016 to September 2017. It was the most severe one among the five waves, with 766 human H7N9 cases reported globally as compared with a total of 798 cases reported during all the previous four waves combined.
In the fifth wave, Jiangsu, Zhejiang, Anhui and Guangdong were the provinces that reported the greatest numbers of cases (148, 91, 63 and 63 respectively).
The affected areas have spread to western China with eight provinces/ municipalities/autonomous regions Chongqing, Gansu, Inner Mongolia, Shaanxi, Shanxi, Sichuan, Tibet and Yunnan reported cases for the first time in this wave.
According to the United States (US) Centers for Disease Control and Prevention (CDC), based on publicly available genetic data, about 10% of viruses from the fifth wave carried genetic markers indicating reduced susceptibility to one or more neuraminidase inhibitor antiviral medications
Before the fifth wave, H7N9 viruses were known to be low pathogenic viruses in poultry and birds, and infected poultry and birds usually did not display any symptoms. In the fifth wave, outbreaks of highly pathogenic avian influenza (HPAI) A(H7N9) have occurred in multiple areas in Mainland China. The emerging HPAI viruses possessed multiple amino acid insertions at the haemagglutinin protein cleavage site and have caused high mortality in birds and poultry. In the fifth wave (as of July 14, 2017), 28 human cases of HPAI H7N9 infection (including 16 deaths) have been identified. Human infection with HPAI H7N9 was associated with exposure to sick and dead backyard poultry in rural areas. The epidemiologic characteristics and disease severity of the HPAI H7N9 case-patients were found to be similar to those observed in patients infected with low pathogenic H7N9 viruses.
Avian influenza viruses mainly affect birds and poultry. Birds and waterfowl are natural reservoirs of avian influenza viruses. Human infections with various subtypes of influenza A have occurred in the past, including H5N1, H5N6, H6N1, H7N2, H7N3, H7N7, H7N9, H9N2, H10N7 and H10N8.