Enigmatic transmission of bird flu virus H7N9

China: Infection pathway of the H7N9 virus so far unclear

04/17/2013

The spread of bird flu infections in China is causing growing concern among experts worldwide. According to a statement by the World Health Organization (WHO), several infected persons had no contact with poultry, so that a transmission of the H7N9 virus can be excluded in this way. Also, the detection of the pathogen in a four-year-old boy who showed no symptoms suggests that the spread of the infection is less clear than previously thought.

The little-known avian flu virus H7N9 had not been found in humans before the current evidence in China. Meanwhile, according to the announcement of the official Chinese news agency „Xinhua“ 77 people have been proven to be infected with the virus. According to the Chinese Ministry of Health, the H7N9 virus has so far caused 16 deaths. Comprehensive measures have been taken to contain the infections, but as long as the origin of the pathogens and the transmission pathway have not been clarified, the risk of further spread of the H7N9 virus remains.

More than half of the infected without contact with poultry
Only about forty percent of previously reported H7N9 infections, according to the China Epidemiologist's (China Disease Prevention and Control Center) CDPCC, affect people who are in direct contact with poultry. WHO spokesman Gregory Hartl confirmed to the news agency „Reuters“, that some infected „People had no contact with poultry.“ With them, the question of the infection route remains open so far. „This is one of the puzzles that still needs to be solved“, stressed Hartl. Although there are no indications of a human-to-human transmission, this possibility should also be checked. However, the virus may also be spread through the dust to markets or another animal.

Human-to-human avian influenza not yet excluded
The renowned trade magazine „New England Journal of Medicine“ has devoted two recent articles to the H7N9 virus, expressing concerns about global expansion. In addition, Dr. Leo Poon, associate professor at the School of Public Health of the University of Hong Kong, told the news channel „CNN“, that further development is crucial „depends on whether this H7N9 virus is transmissible between humans.“ This question must be answered urgently. According to the experts, the infections of a four-year-old, who had shown no further symptoms, are particularly worrying. The pathogens were discovered here only on the basis of a routine check of relatives infected. Such unrecognized carriers of the virus could transmit the pathogens in the event of a possible human-to-human transmission, without even suspecting it. Also, the asymptomatic bird flu infection complicates the detection of H7N9 spread.

Further spread of bird flu likely
In China, a team of national experts, as well as experts from the European Union, the WHO and the US Department of Health, is working closely together to prevent the spread of H7N9 infections, identify the origin of the pathogens and determine the possible transmission pathways. Together, appropriate preventive and control measures should be developed. However, the immediate measures taken so far, such as killing thousands of birds or closing markets where live poultry were traded, have not produced the desired results. The initially limited in the region of Shanghai and the surrounding provinces recorded infections have now reached Beijing and a further spread is quite likely in the opinion of the experts. (Fp)

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Picture: Gerd Altmann