Friday, April 12, 2013

H7N9 in News


       Microbes come up with a lot of surprises. Many new pathogens are discovered, some potentially pathogenic and some are not. We study a lot of microbes in every category and every time there is a new infection with some mortality there is a global alert. People watch out for it and sometimes also anticipate. Sometimes a non human pathogen, shifts to human population and zoonotic disease ensues. One such virus that is always in news, is now all over the news. The H7N9 is at the top of infectious disease literature at this time. And probably the topic attracts a bit of discussion here.

     In this blog, I have talked about various aspects of Influenza multiple times. So for people who need a background discussion, refer to my earlier posts. Avian influenza is a well studied entity. From a wide range of studies it is known to us that poultry infections by avian influenza is a common feature. And such a virus making a leap to humans is also common. It is a well accepted theory that the influenza can undergo a genetic shift or drift to create a new assortent virus. Often during such process two strains recombine, to form a brand new reassortent. Almost once in 3-5 years we see a new influenza making a emergence, and takes advantage of lack of herd immunity. The virus enters population causing infections. There is a pandemic sweep, and then appears the herd immunity. Again the cycle repeats.

       So what is it that makes the news this time? Its the H7N9 reassortent virus. H stands for Haemagglutinin and Neuraminidase. There are several varieties of this, and based on the type present it is numbered. A few cases have been described for lower respiratory tract infections with varieties such as H7N2, H7N3, H9N2, or H10N7. Almost all these are case reports and has not been seen as threat. Influenza is transmitted primarily by droplets or respiratory secretions of infected persons. Influenza occurs all over the world, with an annual global attack rate estimated at 5 – 10% in adults and 20 – 30% in children. Most of the cases, It doesn't have the high fatality rate as media often hypes it.

Photo 1: H7N9 in news. Source
     In the first week of March three urban residents of Shanghai appeared with respiratory infections, it was a great deal. Cause we were expecting the H5 version to make an entry. Transmission of H7 viruses is rarely seen and these are the first cases of documented N9 cases in the world. So when the researchers saw this immediately laid hands on everything they got- PCR, sequencing and characterization. They found mutations at various points. The most interesting to me was the T160A mutation at the H3 region (150 bp loop) of HA gene and Five amino acids were deleted in the stalk region of NA residue 69 to 73. This probably has allowed the species jump. Rest of the mutations seen in other parts of the gene has possible conferred some additional fitness.

     As on April 11th 2013, i saw a report on Forbes News (Link), that reports a total of 33 cases indentified and 9 of them have died. If you are about to make a conclusion that the fatality rate is more than 25%, the hold on. We don't have a clear estimate of how many are actually infected. 33 is the identified case (not the actual number, which will be much more). so don't panic. Uyeki comments on the issue "Some of them had multi-organ failure, This is very, very severe disease, and rapidly progressive. And it's similar to H5N1 [bird flu], but it's a little hard to make comparisons based upon three cases and limited data". Source

      That brings me to the most important point. Is this the next pandemic strain? Predicting that is much difficult when compared to our previous pandemic strain H1N1. Cause this is the first time this type has been encountered in humans. We virtually know nothing about the dynamics of this new reassortent. Right now various health authorities including the WHO is keeping a close watch. By using a Global Alert and Response (GAR) (Link) strategy, we all are keeping a close watch. Vaccine represents the best option. But easily said than done, we currently don't have any.

    Probably we need to wait for some more data, but the search is on.
Uyeki, T., & Cox, N. (2013). Global Concerns Regarding Novel Influenza A (H7N9) Virus Infections New England Journal of Medicine DOI: 10.1056/NEJMp1304661

Gao, R., Cao, B., Hu, Y., Feng, Z., Wang, D., Hu, W., Chen, J., Jie, Z., Qiu, H., Xu, K., Xu, X., Lu, H., Zhu, W., Gao, Z., Xiang, N., Shen, Y., He, Z., Gu, Y., Zhang, Z., Yang, Y., Zhao, X., Zhou, L., Li, X., Zou, S., Zhang, Y., Li, X., Yang, L., Guo, J., Dong, J., Li, Q., Dong, L., Zhu, Y., Bai, T., Wang, S., Hao, P., Yang, W., Zhang, Y., Han, J., Yu, H., Li, D., Gao, G., Wu, G., Wang, Y., Yuan, Z., & Shu, Y. (2013). Human Infection with a Novel Avian-Origin Influenza A (H7N9) Virus New England Journal of Medicine DOI: 10.1056/NEJMoa1304459

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