H7N9 avian flu infects humans for the first time

The H7N9 avian influenza virus has infected humans for the first time, killing three people in China—two in Shanghai in March, and one in Hangzhou whose death was reported on 3 April. It is known to have infected a further six people in different locations across the Yangtze delta region of eastern China, all of whom are in a critical condition in hospital.

Fadela Chaib, spokesperson for the World Health Organization, said at a press conference in Geneva, “It’s the first time that H7N9 has been found in humans, so it’s of concern to WHO,” adding that, although it would be asking the health authorities in China for an update, for the time being the virus has not shown any human to human transmission.

The two deaths in Shanghai were of an 87 year old man who died on 4 March and a 27 year old man who died on 10 March. China’s National Health and Family Planning Commission announced the deaths on 31 March and at the same time disclosed that a 35 year old woman in neighbouring Anhui province who had fallen ill with the same viral infection on 9 March remained in a critical condition.

On 3 April the Chinese media reported another case of H7N9 avian flu in Hangzhou (as well as the one death). Of the four other people known to be infected so far, only one (a 45 year old woman) had worked in close contact with poultry; the source of the infection in the other three people (two women, aged 32 and 48, and a man aged 83) was not clear, state media reported.

Genetic sequencing of the virus shows that it is the reassortment of two different avian viruses, with no sign of pig or human flu virus fragments, according to Professor Malik Peiris, clinical virologist at the University of Hong Kong’s Li Ka Shing Faculty of Medicine.

Pigs were of concern because in March more than 16 000 dead pigs that had been dumped in Jiaxing, Zhejiang province, reached Shanghai via the Huangpu River, one of the city’s main drinking water sources. However, on 2 April animal health authorities in Shanghai said they had tested 34 carcasses and found no evidence of H7N9 avian flu infection.

“Although it needs to be assessed in more detail, there is also no evidence of human to human transmission, and in that respect it’s similar to H5N1 which has only very occasionally succeeded in crossing from human to human,” said Professor Peiris, who specialises in emerging virus disease at the animal-human interface.

He added, however: “There are many things we don’t know—for example, how many mild cases there are. Also, unlike H5N1, which can wipe out a poultry flock in days, infections with H7N9 in poultry are often asymptomatic or mild.

“The agricultural authorities in China have said there have been no big poultry outbreaks in China, which also fits with the genetic sequencing of the virus, but infections of H7N9 in poultry are not very dramatic. The consequence is that it becomes even more difficult to contain among poultry than H5N1, and that is hard enough.”

The H5N1 avian flu virus has killed 371 people in 15 countries since 2003 and has proved difficult to control except in environments where strict biosecurity measures can be maintained. Given the diverse levels of sophistication in poultry rearing across China, it will be a challenge to contain the H7N9 outbreak before it extends further, and there is also no vaccine for the disease, says Professor Peiris.

“Even if there were a vaccine it’s probably not feasible to vaccinate against asymptomatic disease in poultry,” he said. “Farmers won’t vaccinate poultry against a virus that is not going to have significant economic impact, so controlling H7N9 avian influenza can potentially pose a much bigger challenge to animal and human health than H5N1.”