Mainland China has confirmed the world’s first human case of a virulent bird flu strain, prompting Hong Kong’s Centre for Health Protection to issue an alert for the city. 
 
 The centre said health authorities confirmed this month that a 68-year-old woman in Jiangsu province had been infected with H7N4 avian influenza after developing symptoms on December 25. 
 
 The woman was admitted to hospital on New Year’s Day and was discharged on January 22. 
 
 She had contact with live poultry before she developed symptoms but no person in close contact with the woman had similar symptoms, the centre said. 
 
 The authorities in mainland China did not say whether there was an outbreak of H7N4 in poultry. 
 
 The centre said the mainland health authorities confirmed “the genes of the virus were determined to be of avian origin”. 
 
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 The centre reminded Hongkongers heading to the mainland or other affected areas for the Lunar New Year to avoid visiting wet markets, live poultry markets or farms. 
 
 “They should be alert to the presence of backyard poultry when visiting relatives and friends. They should also avoid purchasing live or freshly slaughtered poultry, and avoid touching poultry/birds or their droppings,” a spokesman for the centre said. 
 
 “They should strictly observe personal and hand hygiene when visiting any place with live poultry.” 
 
 Anybody with symptoms should notify their doctor for prompt diagnosis and treatment, the spokesman said. 
 
 Health services have been on alert for a possible human bird flu pandemic after an outbreak of the H5N1 strain in Hong Kong in 1997 infected 18 people, killing six of them. The city culled millions of poultry and imposed strict controls on markets, farms and bird imports from the mainland to try to contain the virus’s spread. 
 
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 In November that year an outbreak of H7N4 occurred in chickens at two poultry farms in northern New South Wales in Australia but nobody was infected. 
 
 From 2011 to 2016, between 10 and 145 confirmed human cases of H5N1 were reported to the World Health Organisation annually. Last year, there were three cases in Egypt and one in Indonesia. 
 
 The WHO is also closely monitoring human bird flu cases of H7N9, with a total of 1,567 human cases reported globally, including 1,564 in the past five waves, mostly on the mainland. Hong Kong reported 21 cases of H7N9, all imported from the mainland. Taiwan had five, Canada two, Macau two and Malaysia one, also imported from the mainland. 
 
 The Hong Kong centre said another strain, H5N6, had sickened 19 people since 2014, with all of the cases occurring on the mainland. The latest case was reported on January 5 this year. ||||| BEIJING (Reuters) - China has reported the first human case of the H7N4 strain of bird flu in a woman in an eastern coastal province, though she has since recovered. 
 
 The winter is traditionally the high season for bird flu infections. 
 
 In a statement late on Wednesday, the Hong Kong government’s Centre for Health Protection said it had informed of the case by mainland China’s health ministry, the National Health and Family Planning Commission. 
 
 According to the commission, this was the first case of human infection with the H7N4 strain in the world, the Hong Kong government said. 
 
 The case involved a 68-year-old woman in Jiangsu province who developed symptoms on Dec. 25, was admitted to hospital on Jan. 1 and discharged on Jan. 22. 
 
 “She had contact with live poultry before the onset of symptoms. All her close contacts did not have any symptoms during the medical surveillance period,” the Hong Kong government said. 
 
 It cited the Chinese Centre for Disease Control and Prevention as saying the virus’ genes “were determined to be of avian origin”. 
 
 The H7N9 strain is far more common in China for humans. 
 
 Since 2013, at least 600 people have died in China and more than 1,500 people have fallen sick as a result of H7N9 bird flu virus. Some 40 percent of people hospitalized with the virus die. 
 
 China recorded just a single human case of H7N9 last month. Last year 192 people contracted the H7N9 strain, 79 of whom died. ||||| A 68-year-old patient from Jiangsu province, who has since recovered, developed symptoms on Christmas Day and was admitted to hospital 
 
 A woman from eastern China has been confirmed as the first ever human case of H7N4 bird flu, according to Chinese authorities. 
 
 Officials in Hong Kong have advised citizens to avoid wet markets, live poultry markets or farms if travelling to the mainland over the week-long lunar new year holiday which starts on Thursday. 
 
 
 
 The 68-year-old patient from Jiangsu province, who has since recovered, developed symptoms on 25 December, was admitted to hospital for treatment on 1 January and was released on 22 January. 
 
 
 
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 “She had contact with live poultry before the onset of symptoms,” Hong Kong’s centre for health protection (CHP) said in an alert on Wednesday evening. “According to a report from the Chinese centre for disease control and prevention, upon analysis, the genes of the virus were determined to be of avian origin.” 
 
 A CHP spokesperson said the diagnosis had been confirmed earlier this week and added: “Travellers to the mainland or other affected areas must avoid visiting wet markets, live poultry markets or farms. They should be alert to the presence of backyard poultry when visiting relatives and friends. 
 
 “They should also avoid purchasing live or freshly slaughtered poultry, and avoid touching poultry/birds or their droppings. They should strictly observe personal and hand hygiene when visiting any place with live poultry. 
 
 “Travellers returning from affected areas should consult a doctor promptly if symptoms develop, and inform the doctor of their travel history for prompt diagnosis and treatment of potential diseases,” the CHP alert said. 
 
 
 
 According to the US government’s centers for disease control and prevention (CDC) the most frequently identified subtypes of avian influenza known to have infected human beings are the H5, H7 and H9 viruses although such transmissions are rare. There are nine known subtypes of H7 viruses, of which H7N4 is one and in most cases human infection is uncommon. 
 
 “The most frequently identified H7 viruses associated with human infection are Asian lineage avian influenza A(H7N9) viruses, which were first detected in China in 2013. While human infections are rare, these have commonly resulted in severe respiratory illness and death,” advice on the CDC website says. 
 
 “In addition to Asian lineage H7N9 viruses, H7N2, H7N3, H7N7 virus infections have been reported. These viruses have primarily caused mild to moderate illness in people, with symptoms that include conjunctivitis and/or upper respiratory tract symptoms.” 
 
 
 
 Authorities have been concerned about the possibility of a potentially devastating human bird flu pandemic in Hong Kong since late 1997 when 18 locals were infected with the H5N1 virus, six of whom died. 
 
 On Wednesday the CHP said it would “remain vigilant and work closely with the World Health Organization and relevant health authorities to monitor the latest developments”. It urged citizens “to maintain strict personal, food and environmental hygiene”. ||||| There are four types of influenza viruses: A, B, C and D. Wild aquatic birds – particularly certain wild ducks, geese, swans, gulls, shorebirds and terns – are the natural hosts for most influenza type A viruses. 
 
 Subtypes of Influenza A Viruses 
 
 Influenza A viruses are divided into subtypes on the basis of two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). There are 18 known HA subtypes and 11 known NA subtypes. Many different combinations of HA and NA proteins are possible. For example, an “H7N2 virus” designates an influenza A virus subtype that has an HA 7 protein and an NA 2 protein. Similarly, an “H5N1” virus has an HA 5 protein and an NA 1 protein. 
 
 All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats. Only two influenza A virus subtypes (i.e., H1N1, and H3N2) are currently in general circulation among people. Some subtypes are found in other infected animal species. For example, H7N7 and H3N8 virus infections can cause illness in horses, and H3N8 virus infection cause illness in horses and dogs. 
 
 Lineages of Influenza A Viruses 
 
 Avian influenza (AI) viruses – influenza viruses which infect birds –have evolved into distinct genetic lineages in different geographic locations. These different lineages can be distinguished by studying the genetic make-up of these viruses. For example, AI viruses circulating in birds in Asia, called Asian lineage AI viruses, can be recognized as genetically different from AI viruses that circulate among birds in North America (called North American lineage AI viruses). These broad lineage classifications can be further narrowed by genetic comparisons that allow researchers to group the most closely related viruses together. Thus, the North American lineage of H7N9 viruses could be further broken down into the North American ‘wild bird’ lineage versus the North American ‘poultry’ lineage. The host, time period and geographical location are often used in the lineage name to help further delineate one lineage from another. 
 
 Highly Pathogenic and Low Pathogenic Avian Influenza A Viruses 
 
 Avian influenza A viruses are designated as highly pathogenic avian influenza (HPAI) or low pathogenicity avian influenza (LPAI) based on molecular characteristics of the virus and the ability of the virus to cause disease and mortality in chickens in a laboratory setting. HPAI and LPAI designations do not refer to the severity of illness in cases of human infection with these viruses; both LPAI and HPAI viruses have caused severe illness in humans 
 
 Poultry infected with LPAI viruses may show no signs of disease or only exhibit mild illness (such as ruffled feathers and a drop in egg production) which may not be detected. Infection of poultry with HPAI viruses can cause severe disease with high mortality. Both HPAI and LPAI viruses can spread rapidly through poultry flocks. HPAI virus infection can cause disease that affects multiple internal organs with mortality up to 90% to100% in chickens, often within 48 hours. However, ducks can be infected without any signs of illness. There are genetic and antigenic differences between the influenza A virus subtypes that typically infect only birds and those that can infect birds and people. 
 
 Avian influenza viruses rarely infect people. The most frequently identified subtypes of avian influenza that have caused human infections are H5, H7 and H9 viruses. Other viruses, such as H10N8, H10N7, and H6N8, have been detected in people also, but to a lesser extent. 
 
 Influenza A H5 
 
 There are nine known subtypes of H5 virusesExternal (H5N1, H5N2, H5N3, H5N4, H5N5, H5N6, H5N7, H5N8, and H5N9). Most H5 viruses identified worldwide in wild birds and poultry are LPAI, but occasionally HPAI viruses have been detected. Sporadic H5 virus infection of humans has occurred, such as with Asian lineage HPAI H5N1 viruses currently circulating among poultry in Asia and the Middle East. Human infection of H5N1 virus infections have been reported in 16 countries, often resulting in severe pneumonia and greater than 50% mortality. 
 
 Influenza A H7 
 
 There are nine known subtypes of H7 virusesExternal (H7N1, H7N2, H7N3, H7N4, H7N5, H7N6, H7N7, H7N8, and H7N9). Most H7 viruses identified worldwide in wild birds and poultry are LPAI viruses. H7 virus infection in humans is uncommon. The most frequently identified H7 viruses associated with human infection are Asian lineage avian influenza A(H7N9) viruses, which were first detected in China in 2013. While human infections are rare, these have commonly resulted in severe respiratory illness and death. In addition to Asian lineage H7N9 viruses, H7N2, H7N3, H7N7 virus infections have been reported. These viruses have primarily caused mild to moderate illness in people, with symptoms that include conjunctivitis and/or upper respiratory tract symptoms. 
 
 Influenza A H9 
 
 There are nine known subtypes of H9 virusesExternal (H9N1, H9N2, H9N3, H9N4, H9N5, H9N6, H9N7, H9N8, and H9N9); all H9 viruses identified worldwide in wild birds and poultry are LPAI viruses. H9N2 virus has been detected in bird populations in Asia, Europe, the Middle East and Africa. Rare, sporadic H9N2 virus infections in people have been reported to generally cause mild upper respiratory tract illness; one infection has results in death.
– A year after the World Health Organization announced it was on "high alert" over outbreaks of bird flu, China has confirmed the first human case of strain H7N4. Health officials say a 68-year-old woman who fell ill in Jiangsu province on Dec. 25 was infected with the strain, though she recovered after being admitted to the hospital on Jan. 1 and was released Jan. 22, per the Guardian. Officials haven't said whether there's an outbreak of H7N4 affecting poultry, but they note the woman was in contact with live poultry before developing symptoms, reports the South China Morning Post. H7N4 is one of nine known subtypes of H7 viruses, but unlike H7N2, H7N3, H7N7, and H7N9, it has never before been seen in humans. Though still rare, H7N9 is among the most deadly strains for humans, having killed at least 600—about 40% of those hospitalized—since 2013, reports Reuters. Viruses H5 (with a mortality rate higher than 50%) and H9 (only one recorded death) have also been reported in humans, per the CDC. Alerted to the H7N4 case on Wednesday, Hong Kong's Center for Health Protection issued a travel alert ahead of a weeklong holiday for the Chinese Lunar Year, which begins Friday. Visitors to mainland China "must avoid visiting wet markets, live poultry markets, or farms," a rep says. "They should also avoid purchasing live or freshly slaughtered poultry, and avoid touching poultry/birds or their droppings."