Navigation Links
Study uncovers cause of flu epidemics
Date:3/4/2008

The exchange of genetic material between two closely related strains of the influenza A virus may have caused the 1947 and 1951 human flu epidemics, according to biologists. The findings could help explain why some strains cause major pandemics and others lead to seasonal epidemics. Until now, it was believed that while reassortment when human influenza viruses swap genes with influenza viruses that infect birds causes severe pandemics, such as the Spanish flu of 1918, the Asian flu of 1957, and the Hong Kong flu of 1968, while viral mutation leads to regular influenza epidemics. But it has been a mystery why there are sometimes very severe epidemics like the ones in 1947 and 1951 that look and act like pandemics, even though no human-bird viral reassortment event occurred.

There was a total vaccine failure in 1947. Researchers initially thought there was a problem in manufacturing the vaccine, but they later realized that the virus had undergone a tremendous evolutionary change, said Martha Nelson, lead author and a graduate student in Penn States Department of Biology. We now think that the 1947 virus did not just mutate a lot, but that this unusual virus was made through a reassortment event involving two human viruses.

So we have found that the bipolar way of looking at influenza evolution is incorrect, and that reassortment can be an important driver of epidemic influenza as well as pandemic influenza, said Nelson, whose teams findings appear in the current issue of PLoS Pathogens. We have discovered that you can also have reassortment between viruses that are much more similar, that human viruses can reassort with each other and not just with bird viruses.

Nelson and her colleagues analyzed the evolutionary patterns in the H1N1 strain of the influenza A viruses by looking at 71 whole-genome sequences sampled between 1918 and 2006 and representing 17 different countries on five continents.

Using the genome data, the researchers constructed phylogenetic trees representing evolutionary relationships across all eight genome segments of the virus.

Big differences in the shapes of these eight trees signified that reassortment events had occurred.

The swapping of genes between two closely related strains of the influenza A virus through reassortment may also have caused the 1951 epidemic, which looked and acted in many ways like a pandemic as well. Deaths in the United Kingdom and Canada from this epidemic exceeded those from the 1957 and 1968 pandemics.

Currently, there are many types of influenza virus that circulate only in birds, which are natural viral reservoirs. Though the viruses do not seem to cause severe disease symptoms in birds, so far three of these viral types have infected humans H1N1, H2N2, and H3N2.

Understanding how each strain evolves over time is crucial. H3N2 is the dominant strain and evolves much more rapidly than H1N1. So the H1N1 component of each years flu vaccine has to be updated less often. In comparison, the H3N2 component of the vaccine has been changed four times over the past seven years.

Last year the infections were dominated by H1N1 but we had no way of predicting it, said Nelson. This year the vaccine failure is due to the H3N2 mismatch because researchers picked the wrong strain.

The H1N1 virus is particularly unusual because it disappeared completely in 1957, only to mysteriously re-emerge in humans in 1977 in exactly the same form in which it had left. It is still not certain what happened to the virus during its disappearance. But since it did not evolve at all over these twenty years, the only plausible explanation is that it was some kind of a lab escape, says Nelson, who is also affiliated with Penn States Center for Infectious Disease Dynamics (CIDD).

In recent decades, flu infections in the United States have been dominated by yet another reassorted viral strain known as H3N2. This strain caused the Hong Kong flu pandemic of 1968, which killed nearly a million people.

The Penn State researcher says the study shows that the evolution of a virus is not limited to the mutation of single lineage, and that there are multiple strains co-circulating and exchanging genetic material. The H1N1 and H3N2 strains, for instance, are occasionally generating hybrid H1N2 viruses.

If we really want effective vaccines each year, our surveillance has to be much broader than simply looking at one lineage and its evolution, and trying to figure out how it is going to evolve by mutation, said Nelson. You have to look at a much bigger picture.


'/>"/>

Contact: Amitabh Avasthi
axa47@psu.edu
814-865-9481
Penn State
Source:Eurekalert

Related medicine news :

1. American College of Pediatricians Questions Validity of Spanking Study
2. Doug Flutie, Jr. Foundation Grants NAA $10,000 for Burbacher/Charleston Study
3. Kaiser Permanente Study Shows One-Third of Women Have Overactive Bladder, Incontinence or Other Pelvic Floor Disorders
4. NYU College of Nursing researcher awarded $4.1M grant to study nurses work decisions
5. Study identifies reasons patients referred late to nephrologists
6. Mouse study: Real-time imaging device may improve surgery for congenital colon disease
7. New study of targeted therapies for breast cancer -- model for global clinical trials
8. Study examines how men and women view marital and parental time pressures
9. Low-intensity exercise reduces fatigue symptoms by 65 percent, study finds
10. Leicester scientist announces unexpected and exciting advance in study of cancer type
11. UCLA launches network to study health care disparities affecting minorities
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:5/28/2017)... ... ... Viewers likely know Rob Lowe from such 80s hits as St. Elmo’s Fire and ... The West Wing and Parks and Recreation. But recently, Lowe’s leant his talents to ... on important modern-day issues that face today’s society. One of the most recent episodes ...
(Date:5/27/2017)... ... May 27, 2017 , ... Hate visiting the dentist? You should go twice per ... take care of your teeth at home. Here are some dental tips to help out: ... a small toothbrush in your work desk or a locker at school for a quick ...
(Date:5/27/2017)... ... May 27, 2017 , ... From May 21-23, hearing healthcare ... three-day event was held at the Marriott Syracuse Downtown Hotel in Syracuse, New York. ... and network of independent hearing healthcare providers to help them stay ahead in the ...
(Date:5/26/2017)... ... ... Mediaplanet is proud to announce the launch of its newest edition of ... on how to take care of all aspects of their skin. , On the ... with the Stars professional, Witney Carson, shares her journey with the disease that nearly ...
(Date:5/26/2017)... ... 26, 2017 , ... Leading CEOs from biotech, pharmaceutical, and ... 31st at The Four Seasons Hotel Boston. , The Boston CEO Conference ... exclusive access to key decision makers who influence deal making and investment. Attendees ...
Breaking Medicine News(10 mins):
(Date:5/10/2017)... CSSi, the global leader in patient recruitment, ... is proud to announce the launch of its newly ... both enriched content and a customized layout that provides ... already well-established position as the top global patient recruitment ... months of hard work, we are delighted to officially ...
(Date:5/9/2017)... 2017  Oramed Pharmaceuticals Inc. (NASDAQ: ... company focused on the development of oral drug ... Property Office has granted Oramed a patent titled, ... The patent covers Oramed,s invention of an oral ... an incretin hormone that stimulates the secretion of ...
(Date:5/8/2017)... -- Diplomat Pharmacy, Inc. (NYSE: DPLO)., has completed its acquisition ... care service center company based in Chantilly, ... management programs for leading pharmaceutical manufacturers and health care ... will join Envoy Health Management, LLC , as ... firms, and other service companies. Together, WRB and EnvoyHealth ...
Breaking Medicine Technology: