H7N9 avian flu kills seven and infects 23 in ChinaBMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f2222 (Published 09 April 2013) Cite this as: BMJ 2013;346:f2222
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The outbreak of H7N9 avian influenza in China had killed 17 people and infected 82 by 18 April. Thirty one cases occurred in Shanghai city, twenty five cases occurred in Zhejiang province, twenty cases occurred in Jiangsu province, three cases occurred in Anhui province, two cases occurred in Henan province and one cases occurred in Beijing city.
One child in Beijing, who displayed no symptoms and tested positive for the H7N9 virus, was considered a carrier of the strain and has been placed under observation to see if he develops symptoms. And medical teams have found that he had contact with another child, who was confirmed as Beijing’s first case of H7N9. Beijing Health Bureau deputy director Zhong Dongpo said: "This is very meaningful because it shows that the disease caused by this virus has a wide scope. It's not only limited to critical symptoms. There can also be slight cases, and even those who don't feel any abnormality at all. So we need to understand this disease in a rational and scientific way”.
The appearance of a case with no symptoms in human could make tracing more difficult, and may also mean that many people infected don’t get seriously ill and recover quickly, making the virus is less deadly than it appears.
Although there was no evidence of human to human transmission, it does not mean that human to human transmission does not occur. And experts feared the prospect of H7N9 mutating into a form easily transmissible between humans, which would have the potential to trigger a pandemic.
The World Health Organization (WHO) said last week there was as yet no evidence of human-to-human transmission of H7N9. The close contacts of the victims reported were under observation but none were reported so far to have displayed abnormal symptoms.
H7N9 strain was not previously know to infect humans before cases turned up in China. The studies from our scientists have found that a novel reassortant avian-origin influenza A (H7N9) virus was isolated from respiratory specimens obtained from all three patients and was identified as H7N9. Sequencing analyses revealed that all the genes from these three viruses were of avian origin, with six internal genes from avian influenza A (H9N2) viruses.
Substitution Q226L (H3 numbering) at the 210-loop in the hemagglutinin (HA) gene was found in the A/Anhui/1/2013 and A/Shanghai/2/2013 virus but not in the A/Shanghai/1/2013 virus. A T160A mutation was identified at the 150-loop in the HA gene of all three viruses. A deletion of five amino acids in the neuraminidase (NA) stalk region was found in all three viruses. And close contact with infected birds is a likely source of transmission. Making the H7N9 strain hard to detect is that infected poultry display slight or no symptoms, unlike the H5N1 strain which kills birds and raged across the region in the last decade.
So many cities have closed markets that sell live poultry and ban poultry trading in a move to try to halt the spread of the H7N9. In 2003 the SARS (Severe Acute Respiratory Syndrome) killed several hundred people worldwide. And the H5N1 avian flu virus has killed 371 people in 15 countries since 2003. So we should pay more attention to the spread of H7N9.
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It still remains undecided if the H7N9 avian flu is sporadic or epidemic disease in China.By 12 April, the H7N9 avian flu had infected 40 people and killed 11, including 18 in Shanghai (7 deaths),12 in Jiangsu Province(1 death),6 in Zhejiang Province(2 deaths),and 2 in Anhui Province(1 death). One 4-year-old boy in Shanghai reported by Jane Parry1 on 9 April has been discharged from the hospital on 12 April with complete rehabilitation,and one patient in Zhejiang Province was transferred to the general ward in whom H7N9 avian influenza virus was tested negative on 11 April.
“The Chinese authority not only responded rapidly in dealing with the H7N9 avian influenza, but also ensured the epidemic information instantly to Chinese public and international public”said the expert of Asia-Pacific area of Food and Agriculture Organization of the United Nation in Thailand on 11 April.
Old folks were accounted for 60% of the total infected humans,and the shortest onset of H7N9 to death was only 6 days,according to the report of Chinese media.Although there were 753 close contacts of infected patients under rigorous medical observation,only one in Shanghai was presented with signs of fever, nasal discharge,and throat itching,who was then transmitted to Shanghai Public Health Clinical Center for subsequent isolation treatment on 4 April.The suspended patient was tested negative for H7N9 avian influenza virus and was recovered well.On 12 April,there was still no evidence of human to human transmission of H7N9 avian flu.Thus rapid detection of H7N9 virus was imperative for the suspect cases so as to decrease medical cost.
In Shanghai,H7N9 Avian influenza diagnostic reagent was rapidly manufactured,by which H7N9 virus can be detected in 2 hours,reported by the media of Shanghai.This reagent is currently the only finished product for H7N9 detection in China,which has been supported for epidemic monitoring in disease prevention and control center, animal disease control center,and entry-exit inspection and Quarantine Bureau. The specific H7 and N9 gene fragments of H7N9 virus can be detected through fluorescent polymerase chain reaction (PCR) using this reagent.The positive cases discovered recently were detected by the reagent in Shanghai,Zhejiang,Jiangsu and Anhui Province.It was also applied for differential diagnosis of suspended cases.
On 10 April,the H7N9 virus was tested positive from the poultry specimens from Jiangsu,Zhejiang and Anhui,the isolated virus and that from dove samples in Shanghai were highly homologous.Thus,the poultry market was closed temporarily, all the birds inside the market were immediately killed and subsequent harmless treatment were implemented to reduce infectiosity.
The mutational gene of H7N9 avian influenza virus was generated from gene reassortment of wild birds from East Asia and poultries across Yangtze River Delta region of eastern China,according to research of the chinese academy of sciences.The evolutionary trace of the H7N9 avian flu virus has not yet been found in swine,implying that the pigs did not play a role in the virus reassortment as intermediary host.The high mortality of the virus may be ascribed to the N9 gene fragment mutation,which was observed shorter than the general N9 gene fragment.
1.Parry J. H7N9 avian flu kills seven and infects 23 in China. BMJ 2013;346:f2222. (9,April.)
Competing interests: No competing interests