Prevalence And Antigenic Variation Of Influenza A Viruses In Shanghai

Influenza viruses have threatened the human health for a long time as an important pathogen, and at the present time, epidemic surveillance and protection of high-risk population are the major measures to decrease the morbidity and mortality caused by influenza. With the help of WHO global influenza programme and the development of influenza surveillance in Shanghai, we explored the global influenza activity, especially the antigenic variation of influenza A viruses and the human condition of immune to influenza in Shanghai region. The details were as follows:Whereas the human immune condition, combining the variation of influenza viruses, can help to estimate and even forecast the trend of influenza activity, we investigated HAI antibodies of influenza A viruses in the population of Shanghai including the common population and the professional population contacting with avian or domestic animal. The results showed that the population had have strong immune barrier to A/Fujian/411/2002(H3N2) with a 52.1% positive rate of HAI antibody, while most were susceptible to A/Shanghai/7/99(H1N1) for the positive rate of HAI antibody was only 8.5%, the H5 HAI antibody was exist in the contacting population, while the H9 HAI antibody was found in both populations with higher positive rate in the contacting population, and all the positive rates of HAI antibody to H1, H3, H5, H9 were higher in contacting population than in common population.As it is helpful to master the updating influenza activity, we analyzed the general situation of global influenza in recent years with the help of WHO global influenza surveillance net, and carried out influenza virus surveillance in Shanghai region. Data showed that the epidemic of influenza was similar to the past while generally mild to moderate though reported in Africa, the Americas, Asia, Europe and Oceania, and outbreaks usually occurred from November to next March in the northern hemisphere while it came late in Shanghai from January to April; H1, H3N2 and B co-circulated, but H3N2 predominated in most countries and H1 and B viruses circulated at low levels in most time.Based on the influenza virus surveillance in Shanghai region, the phylogenetic analysis of HA segment was applied to know the antigenic variation of influenza A virus and consequently to conjecture its direction. We found that H3 viruses evolved towards multiplex directions, but showed a tend from A/Fujian/411/2002-like and A/Wyoming/3/2003-like to A/Wellington/ 1/2004-like and A/California/7/2004-like strains and then closing to A/Wisconsin/67/2005 while an emergence of the isolates distinguishable from vaccine strains. The recent H1 isolates in Shanghai were found some variation occurred on the vaccine strains A/New Caledonia/20/99-like and isolates of 2006 was distinguishing from it while was on the same cluster of the new vaccine strain A/Solomon Islands/3/2006.For human cases of H5N1 viruses are continuing to occur in recent years and to master the epidemiology of H5N1 HPAI in animals is helpful to find human cases in time and to know the updating antigenic variation of the virus, we analyzed the global H5N1 HPAI activities in recent years with the help of OIE global surveillance net and applied phylogenetic analysis to the HA segment of avian H5 isolates in Shanghai with collaborating with center for animal disease control, Shanghai. Data showed that the H5N1 virus is now endemic in the poultries in parts of some countries and has expanded its geographical range to include new countries as well as human cases continue to emerge though an efficient human-to-human transmission hasn't been established. We found the H5 isolates in Shanghai was similar to those isolated from avian in other province in China and distinguishable from the human isolates, but the isolated might break the host barrier and infect human.As showed above, we could draw the conclusion that H3 viruses could cause outbreaks or local epidemics in Shanghai for the immune of population to the new emerging antigenic drift was still unknown though there was strong immune barrier to the previous vaccine strain, H1 viruses also may caused epidemics as the population had a weak immune protection to the previous reference strains A/New Caledonia/20/99-like and part of the recent isolates were distingwishing from them and continued to evolute on the new reference strain, and H5N1 HPAI activities has expanded its geographical range thus increasing the size of the population at risk as the continuing emergence of human cases which give the virus an opportunity to evolve towards a fully transmissible pandemic strain. We should keep eyes on the human cases of avian influenza virus an its variation for the H5 isolates in Shanghai also has the possibility to infect human directly and the infection of H5, H9 viruses had previously occurred in the population especially in those contacting with animals.While carrying out the above work, the surveillance system of influenza virus and its variation of HA antigen is also consummated, and the database of HA segment is complemented, which could be used to explore the genetic evolution and antigenic variation rule of influenza A viruses. So we should continue to carry out the influenza surveillance and master the updating influenza activity so that we could study the law of antigenic variation of influenza A viruses systematically.