Here’s what they talked about A new flu virus was causing illness in both the US and Mexico. In Mexico, there were outbreaks of the disease in three locations, with some severe cases Appeared to be spreading rapidly and easily between humans Was this the “Big one?”
Estimated to cause between 3 and 5 million cases of severe illness every year, and between 250,000 to 500,000 deaths worldwide 1.8 million died of HIV/AIDS, a similar number from tuberculosis last year 1.5 million children died of diaorrheal diseases Why is flu such a big deal?
The flu virus has a trick up its sleeve Flu viruses, like all viruses, evolve, or mutate, constantly. Periodically, it goes through a major transformation, and a new form emerges to which people have no immunity. This new virus spreads across the world and can cause severe illness and death
The last century has seen 3 influenza pandemics 1918: H1N1- or “Spanish Flu” ( 20-40 million deaths) 1957- H2N2- “Asian flu” ( 2 million excess deaths) 1968-H3N2- “Hong Kong flu”( 1 million excess deaths) 1971-H1N1- “Russian flu” 2009 H1N1 ( Swine Flu) – less than from normal seasonal flu
Pandemics, epidemics, outbreaks Outbreak=Spread of disease, which occurs in a short period of time and in a limited geographic location (i.e., neighborhood, community, school, or hospital) Epidemic = outbreak of disease in a wider area, at levels above the ordinary Pandemic= outbreak of disease on a global scale. In the case of influenza, the global spread of a new influenza virus that has not circulated previously
Pandemic and seasonal influenza Seasonal influenza= the “normal” circulating influenza strains Pandemic= a new strain to which most people have no immunity
Image by Karsten Schneider/Science Photo Library
Classification of influenza A viruses Classified on the basis of hemagglutinin (HA) and neuraminidase ( NA). 16 subtypes of HA and 9 subtypes of NA are known to exist 3 subtypes of HA (1-3) and 2 subtypes of NA (1-2) are human influenza viruses However HA 5,7,9 and N7, predominantly found in bird viruses can also infect humans.
How have pandemics originated? The natural home of the flu virus is in aquatic birds When genes from avian influenza viruses mix with existing human viruses. Often, pigs are the “mixing bowl”, since they can be infected with both human and avian flu viruses
G Neumann et al. Nature 000, 1-9 (2009) doi:10.1038/nature08157 Genesis of swine-origin H1N1 influenza viruses.
The world of viruses took us by surprise Experts had long predicted a new pandemic, but they were looking at another virus, and at another part of the world.
May 1997, Hong Kong: first cases of human infection by H5N1- an avian influenza virus. 1999 Hong Kong: H9N2 infection: mild illness Feb. 2003, Hong Kong : 3 people who had travelled to China were infected with H5N1- two died Feb 2003, Holland: H7N7 outbreak. 89 fell ill, one died Dec 2003- major outbreaks of avian and human cases of H5N1
Currently circulating influenza A viruses in human population 1. Pandemic H1N1 (“swine flu”) 2. “old” H1N1 ( from 1971) 3. H3N2 ( from 1968 pandemic) Pandemic H1N1 appears to be causing 80- 90 percent of flu in most places, and could be displacing the other two. Will eventually become the regular seasonal flu
Prevention and treatment 1. Treatment ( once you catch the disease) is largely through anti-virals. Two anti viral drugs are effective- oseltamivir ( Tamiflu) and Zanamivir (Relenza) These drugs are neuriminidase inhibitors= they prevent the NA part of the virus from doing its work How effective are they?
Sources http://www.chp.gov.hk/en/index.html http://www.who.int/influenza/surveillance_ monitoring/en/ http://www.who.int/influenza/surveillance_ monitoring/en/ http://www.cdc.gov/flu/weekly/fluactivitysu rv.htm http://www.cdc.gov/flu/weekly/fluactivitysu rv.htm For any infectious disease outbreak: Ask yourself, are the figures any different from previous years?
For review What do the H and the N in influenza viruses mean? How do pandemics originate? What is the difference between seasonal and pandemic influenza? What are the current seasonal influenza strains? How can H1N1 be treated? How can its spread be prevented,or minimised?