The outbreak of the H7N9 strain of avian influenza in China has been limited to the Shanghai metropolitan area, as well as a small number of major cities in three neighboring provinces. These include Nanjing and Suqian in Jiangsu Province, Hangzhou in Zhejiang Province and Chuzhou in Anhui Province — all of which are within two or three hours by highway or high-speed rail from Shanghai.
It is my contention that almost all of the cases of avian flu in this outbreak occurred along the high-speed routes between Shanghai and Nanjing, or other proximate cities, and that the infections happened between late last month and early this month.
My guess on how this happened is that in the middle of last month, or perhaps earlier, a poultry farm in Jiangsu sent a batch of live chickens infected with the H7N9 virus to be sold for meat at farmers’ markets in several major cities, and that the outbreak started from there.
As a result, the area affected by the outbreak was limited to a few cities where live chickens could be transported to from the farm on the same day.
So far, there have been 20 cases of avian flu in humans, six of whom have died. Of these 20 cases, only four people were confirmed to have had previous contact with birds.
Furthermore, there have been no reported cases of infected birds at poultry farms, and neither the poultry farmers nor local residents have reported anything irregular.
As birds have tested positive for the H7N9 virus in several farmers’ markets, Chinese authorities have started culling infected poulty in these markets and implemented a policy of disinfecting these areas.
Based on past experience, it should not be too long before the sources of transmission are rooted out from these markets. Unfortunately, Chinese authorities have yet to discover the location of the farm where the virus originated or how the virus is transmitted.
Earlier this month, the British scientific journal Nature carried a report discussing the genetic characteristics of the H7N9 virus strain behind the current outbreak in humans.
According to the article, it is a composite of three avian flu virus strains, including the H7N9 strain found in migratory birds in Zhejiang Province, the H7N9 strain found in migratory birds in South Korea and the H9N2 strain found in domesticated ducks in China.
The article added that the H9N2 strain has an identical internal genetic segment to the H5N1 virus, and that this segment exists within the composite form of H7N9.
The implication is that the virus, having mutated into this new composite form, was then able to gestate in the bodies of human beings and certain other mammals and attack their systems.
As this new composite form of the virus has only one basic amino acid within this genetic segment, it is not pathogenic, or not very pathogenic, in domesticated or wild birds.
Experts still need to answer the question of why the virus was not transmitted to any of the several hundred individuals who have had close contact with the 20 people known to be infected.
There have been no reports of birds infected with this virus strain in Taiwan, nor of any human-to-human transmission. We cannot keep people from the areas in which the outbreak has occurred from coming to Taiwan, but if they do, they will not cause an outbreak here.
Liou Pei-pai is a former director of the Taiwan Animal Health Research Institute.
Translated by Paul Cooper
(Editor’s note: As of yesterday, China had reported 28 cases of avian flu infections in humans, including eight deaths.)