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Human to Human Transmission of H5N1Wild Bird Flu in China
Recombinomics Commentary
November 17, 2005
The first case is a 9-year-old boy from the southern province of Hunan. He was hospitalized with respiratory symptoms on 17 October and has since returned home, fully recovered.
The first is the boy's 12-year-old sister. She was hospitalized on 16 October and died the following day of severe bilateral pneumonia and acute respiratory distress syndrome.
The above description in the latest WHO report on H5N1 raises the possibility of human-to-human transmission in the first reported familial cluster in China. Although hospital admissions were just one day apart, media reports indicate the brother did nor develop symptoms until the day his sister died.
Media reports indicate that family's chickens began to die on 6 October and the sister developed symptoms a few days later. Thus, the brother did not develop symptoms until 5-10 days after his sister. This gap in disease onset dates is a common feature of human-to-human transmission, and supports boxun reports that indicate human-to-human transmission is widespread in China. Moreover, the cases cited by boxun are in the same provinces that have been reported to have H5N1 outbreaks in birds.
The H5N1 cases in China are tightly linked to migratory birds. The initial reports from China were in the spring when 519 wild birds were reported dead in the May 21 OIE report on the Qinghai Lake outbreak. The deaths involved 5 species and the H5N1 isolated from the birds was highly pathogenic, killing experimental chickens in 20 hours or less in IVPI tests.
Although the sequences contained polymorphisms found in Asia and Europe, the features characteristic of Genotype Z, including an HA cleavage site containing the poly-basic sequence RRRKKR, a 20 amino acid deletion in NA, and a 5 amino acid deletion in NS were all present in the wild bird isolates. In addition, all isolates contained the PB2 polymorphism E627K, which was found in a subset of H5N1 mammalian isolates, including humans with poor clinical outcomes.
Following the outbreak at Qinghai Lake in May were outbreaks in Xinjiang province in June. These outbreaks were under a flight path from Qinghai Lake in China to Chaney Lake in Novosibirsk, Russia, where H5N1 outbreaks began in July. These outbreaks were also found in Kazakhstan and Mongolia.
In the fall, birds began migrating to warmer regions in Europe and eastern China. In China, outbreaks were reported in Innner Mongolia, Anhui, and Hunan. These outbreaks were described in OIE reports and all indicated the outbreaks were linked to migratory birds. Recently, the number of reported outbreaks in China has increased to 1-2 per day and the reports have been geographically clustered in the eastern and western portions of China, including multiple outbreaks in Liaoning and Xinjiang provinces. The relationship with wild birds suggests that human-to-human outbreaks in one area could be expected to be repeated throughout China because of extensive migration by wild birds.
The boxun reports do show the highest number of human cases (Qinghai (143 deaths), Liaoning (69 deaths), Inner Mongolia (28 deaths), Hubei (25 deaths), Xinjiang (18 deaths), Hunan (8 deaths)) in the regions reporting wild bird linked poultry outbreaks, supporting the notion that human-to-human transmission of H5N1 in China is significantly more common than has been reported by China or mainstream media.
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