Someday in the Spring, an Army private reported to the camp hospital before breakfast. He had a fever, sore, throat, headache... nothing serious. One minute later, another soldier showed up. By noon, the hospital had over a hundred cases; in a week, 500...

H1N1 FactsH1N1 Facts

Are we facing another Are we facing another deadly pandemic?deadly pandemic?

Carlos A. AguilarCarlos A. Aguilar

H1N1 FactsH1N1 Facts

IntroductionIntroduction Influenza factsInfluenza facts

GlossaryGlossaryBackground of previous Background of previous pandemicspandemics

Viral evolutionViral evolution ConclusionConclusion

GlossaryGlossary

Influenza. Colloquial flu/grippe. Acute infectious respiratory disease caused by Influenza viruses manifested by fatigue, fever and chills, a hacking cough, and body aches.

Common cold. Upper respiratory infection caused by Coronavirus or Rhinovirus, manifested with nasal congestion, sore throat, itchy eyes.

GlossaryGlossary

Influenza A. Most common type of Influenza. Strains with high propensity of mutations, partly because they can infect various animals.

Influenza virus. Mosaic of surface antigens: Hemagglutinin (19) and Neuraminidase (9) are used for nomenclature of strains. i.e. Avian strain H5N1

H1N1. Influenza A strain responsible for most seasonal outbreaks and comprises also the “Swine strain”

GlossaryGlossary

Seasonal influenza. Is a regularly recurring time period characterized by the prevalence of outbreaks of influenza during the cold half of the year in each hemisphere.

Pandemic. Disease affecting the population of an extensive region, country, continent or global

Pandemic virus in 20Pandemic virus in 20thth CenturyCentury

1918 “Spanish influenza” (H1N1) 40-50 million people died (675,000 in

US) Cedar Rapids swine show

1957 “Asian influenza” (H2N2) Disappearance of H1N1 until 1977 70,000 deaths in the US

1968 “Hong Kong influenza” (H3N2) 34,000 deaths in the US

Viral backgroundViral background

Viral adaptation to a new host species is a complex process

Influenza A (H1N1) virus overcame barriers in 1918 to emerge from an avian source simultaneously in swine and humans

1931 R. Shoppe: adult human 1931 R. Shoppe: adult human serum could neutralize the swine serum could neutralize the swine flu virus in mouse modelflu virus in mouse model

Robert B. Belshe, M.D. NEJM 353;21. Nov 24, 2005

Swine influenza in Swine influenza in humanshumans

1974: swine influenza isolation from a human, a patient with Hodgkin’s disease who lived on a pig farm

1976: Fort Dix outbreak, 230 cases/1 death triggered 40 million civilian vaccinations and 532 cases of the Guillain–Barré syndrome, including 32 deaths

Swine influenza in Swine influenza in humanshumans

1977: H1N1 reemergence in Soviet Union, Hong Kong, and northeastern China

1977 to present: Seasonal influenza predominant with 2 serotypes cocirculating: H1N1/H3N2

1979 to present: Reemergence of new swine virus 1998 triple reassortant swine influenza

virus in 17- year-old boy in Wisconsin April 2009, the first cases of S-OIV

Shanta M. Zimmer, M.D., and Donald S. Burke, M.D. NEJM; 361:279-85. Jul 16, 2009

2009 Lineage Virus2009 Lineage Virus

Descent from the 1918 virus Survivors of 1918 pandemic

protected Previous exposures to H1N1 may

provide partial protection (1947 attenuated outbreak)Importance of vaccination

Cell-mediated immunity may also play a role in competition among influenza strains

Shanta M. Zimmer, M.D., and Donald S. Burke, M.D. NEJM; 361:279-85. Jul 16, 2009

ConclusionsConclusions

Emergence of influenza A (H1N1) 91 years ago led to a disastrous global pandemic

Virus is thought to have emerged simultaneously from birds into humans and swine

ConclusionsConclusions

In contrast, S-OIV probably emerged from swine into humans

S-OIV shares three gene segments with current seasonal human influenza A (H1N1) virus and three segments with human seasonal influenza A (H3N2) virus.

By inference this outbreak may not have the same impact as 1918