H7N9 virus

Warmer weather may be curbing spread of bird flu in China

Sharp drop in new H7N9 cases is linked to efficient measures by health authorities and the virus being sensitive to higher temperatures

PUBLISHED : Thursday, 16 May, 2013, 12:00am
UPDATED : Thursday, 16 May, 2013, 4:43am


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Government measures and favourable weather may be limiting the spread of a deadly new bird flu, as the number of reported cases has dropped sharply this month, say health experts.

As of Monday, a total of 131 human cases of H7N9 had been reported by mainland health authorities, and one case in Taiwan. But just five cases, or less than 4 per cent, have been reported this month.

At temperatures of 20 degrees [Celsius] or higher, few flu viruses can spread
Professor Lu Jiahai, Bird Flu expert

The scarcity of new cases is in sharp contrast to the spread last month. At a peak on April 16, the Chinese Centre for Disease Control and Prevention reported as many as 14 new cases in a day. A total of 57 patients recovered and were discharged from hospitals.

The mortality rate is also dropping. No one infected by the virus this month has died, according to the World Health Organisation.

The death rate of confirmed cases was 100 per cent in cases dating back to February, 40 per cent in March, and 8 per cent last month. The death toll stood at 35 on Monday.

The area of infection has also been contained to 10 municipalities and provinces on the mainland for more than a week. Although there was some cause for alarm last week in Guangdong when the virus was detected in poultry, there were no reports of human infections.

Professor Lu Jiahai , a bird flu expert with Sun Yat-sen University's School of Public Health, said that rising temperatures was good news for people concerned about the spread of the virus.

"The new bird flu could be similar to other flu viruses with a high sensitivity to temperature," he said. "It may be active in dry and cold weather conditions, but retreat with increasing temperatures and humidity.

"At temperatures of 20 degrees [Celsius] or higher, few flu viruses can spread."

But the temperature increase alone can't explain the sharp decline in reported cases, because the temperature increase in some regions was not high enough to keep the virus at bay, Lu said.

Beijing should get some credit for its quick response after first detecting the virus, with the shutting down of live poultry markets in many regions considered one of the most effective measures.

"The majority of patients were infected after contact with birds, so shutting down the poultry markets is definitely helping," Lu said.

"Some provinces such as Guangdong launched active surveillance and shut down their live poultry markets, even though they hadn't received any reports of human infection. Such measures should be encouraged and maintained."

Professor Chwan-Chuen King, an epidemiologist with National Taiwan University, agreed with Lu.

King said her previous studies on H5N1 showed that the bird flu spread when the temperature dropped sharply to near freezing, but with increasing warmth its activity decreased. The new H7N9 virus could be as vulnerable to heat as the H5N1 bird flu.

King said Beijing seemed to have learned lessons from the severe acute respiratory syndrome (Sars) outbreak in late 2002 and 2003. Beijing initially blocked reports and kept the international community in the dark about the epidemic. The then minister of health and the mayor of Beijing were later sacked for playing down the crisis in an attempt to maintain social stability.

King said she was impressed by the response to the latest bird flu. "I don't see any sign of a cover-up at all. I think they have dealt with the emergency promptly, professionally and effectively," she said.

"From the epidemiological analysis and genetic sequence they released, I can see the rise of a new generation of academic researchers and government officials who can approach an issue with competence, confidence and transparency."

However, she sounded a warning that the decline in infected cases of the latest virus could be temporary.

With temperatures falling in autumn or winter, the virus might return.

She said scientists, doctors and government officials from the mainland, Hong Kong and Taiwan should hold a meeting in August to share their experience, knowledge and draw up a plan before a possible re-emergence of the bird flu or spread of other new viruses.

"Bird flu has become a Chinese problem with global implications," she said. "Chinese communities should unite and meet the challenge jointly and with an open mind."