User:ZayZayEM/Flupandemic

An Influenza pandemic is an epidemic of highly infective influenza that spreads on a worldwide-scale amongst the human population. While the term 'pandemic' usually refers to any large-scale epidemic, in the context of influenza the disease must spread on worldwide and must be caused by an entirely new strain of influenza virus.

The term is used to contrast with the regularly occurring incidence of influenza during the flu season. ((On average)) these annual epidemics (may) result in (upto) XX deaths per year. An influenza pandemic can be responsible for the death of millions.{{cn} ((Pandemic influenza may not necessarily be more lethal than standard influenza, but because a infection rates are tremendously higher, so too are the mortality statistics.)) The significant loss of life can result in panic and societal disorder, or even total societal collapse.

note: is not an epidemic of influenza virus. Epidemics occur to disease not disease agents. An asymptomatic epidemic really wouldn't be much would it?

note: an influenza pandemic is not an ordinary pandemic. The term has specific ramification as to the scope and CAUSE of the disease. see notes below

Lead should summarise:(i.e. the sections below)

• What it is. (a pandemic of influenza)
• What causes it. (primarily Influenza A crossing species barrier and subsequent spread through avian migrationa nd human travel)
• When it has happened before. (early non-records, modern records, Russian, Spanish, Asian, Hong Kong, H5N1)
• The ramifications of a pandemic. (cost of life, health services, further social, political, and economic impacts - past, present and predicted)
• What people are doing about. (WHO, CDC and governmental planning, industry?)

Characteristics

• Occur on a pandemic scale
• High morbidity, Variable mortality
• High final figures of death linked to high initial infection rates (not necessarily any more lethal than common flus, just infects more people in first place)
• Section: Wave nature/Phases
• Panic, social disruption, and other non-health related effects
• Section: Classifiction - detail WHO Pandmeic phases, and CDC's PSI, any other tier systems obtained ot ready.

Would like info on non-human pandemics (equine influenza, etc.)

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• Influenza pandmeic - two criteria(Webster and Laver 1972):

1. spreads throughout the world; high infection rate leading to high mortality
2. must be a new influenza virus A subtype, the HA of which is not related to that of influenza viruses circulating immediately before the outbreak, and could not have arisen from those viruses by mutation .

• Pandemic = v. big epidemic, but Flu pandemic = worldwide
• Large epidemic in warmer months = likely pandemic

• occurring at 10 to 50 years intervals

• 1729 pandemic: Distinct waves of infection were recorded; the later were more severe than the first(Brown 1932; Beveridge 1977; Patterson 1987).

Causes

• Influenza pandemics = Influenza A
• Sources of Avian influenza-human cross-species barrier changes
  • activities
  • locations
• How does influenza progress from epidemic - pandemic
  • Human travel
  • Bird travel
  • Other (malicious, other species, etc.)

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• Caused by NEW Influenza A subtype
• must be unrelated to current subtypes circulating amongst (human?) population.

  Can it be a virus that was previously endemic, but is not current. Literature reviewed so far is unclear?

• Antigenic shift variants of influenza A have been responsible for recent pandemics.
  • shift (major variation/reassortment) ≠ drift (subtle variation/mutation)
• pandemics are due to wholly new virus subtypes resulting from virus reassortment (shift)
  • must be a change that could not have happened by mutation. Otherwise not pandemic influenza.(Webster and Laver 1972).

• Mid-1970s — Researchers realize that enormous pools of influenza virus continuously circulate in wild birds.

History

The historical data available on influenza epidemics are difficult to interpret, because the symptoms can be similar to those of other diseases, such as diphtheria, pneumonic plague, typhoid fever, dengue, or typhus. Numerous commentators have attempted to identify pandemic situations throughout the entire historic period. Clear references to influenza cases can be found in scientific and lay publications since 1650, but it is only within the past three centuries that records can be considered to hold a degree of accuracy when it comes to establishing the occurence of pandemic events.

Only modern virological tools can be used to directly implicate influenza as an agent of a pandemic, and these have only become available in 20th century. However informed conclusions can be formed from records detailing plagues with global scale and high incidence of mortality. In general deadly epidemics during in Spring and Summer - outside the regular influenza season during the cooler months - indicate a pandemic event.

In the year of 1580, the first record of influenza incidence on a scale that investigators agree meets the criteria for a influenza pandemic took place. Originating in Asia, cases spread to Africa, and from Africa swept northwards through Europe. It took less than six weeks for the entire of Europe to be affected. Records from the time suggest that only 1 in 20 avoided infection. The city of Rome saw 8,000 people die from influenza, and several cities in Spain were almost wiped out.

Earlier pandemics are alluded to in history. Prior medieval records suggest wide-spread incidence of influenza during 1510 and 1557, but is not certain if these events were influenza pandemics meeting modern criteria, or just very large transcontinental epidemics.

Early modern records

By the 18th century, medical historians and investigators had access not only to data records of a higher quality, but a greater quantity of records. The records also the began to allow pandemics to be ditinguished from mere epidemics.

Of the 25 epidemics of influenza occuring during the 18th and 19th centuries, 8 or 9 might be considered pandemics in the "modern sense". In 1729 a pandemic was seen to spead from Spring-time Russia Europe over the course of 6 months. A pandmeic later emerged from China during the Autumn of 1781. The disease took the next 8 months to spread westwards beyond continental Europe by a route through Russia. Early seeding of infection has been suggested to have occured in Russia and North America, leading to later extensive outbreaks.

Another pandemic occured during 1898-1900, known as the Asiatic or Russian influenza pandemic. Resulting in at least one million deaths worldwide. But probably the most significant pandemic of that century occured earlier over 1830-1833. This pandemic showed the characteristic wave nature of a pandemic. Originating in China during the Winter of 1830, the disease swept simultaneously southwards to the Phillipines, Indonesia and Indian subcontinent, and also westwards to Russia. By 1832 North America was affected. Then later that year the Americas saw saw a resurgence of more virulent disease, as did Europe. This event has been described as the only pandemic on clear record that approaches closely to the scale of death and impact as the devastating 1918 "Spanish influenza" pandemic.

20th century

While some sources claim up to five pandemics occuring during the 20th century, most sources recognise only three actual pandemics, along with several pandemic threats.

Influenza pandemics of the 20th century

Date	Common name	Deaths	Subtype involved
1918-20	Spanish influenza	50-100 million	H1N1
1957-58	Asian influenza	1 to 1.5 million	H2N2
1968-69	Hong Kong influenza	0.75 to 1 million	H3N2

No one disputes that the most significant pandemic on record was the 1918 pandemic of "Spanish influenza". The pandemic has been likened to the Black Death in its significance in epidemiological history. Measurement and classification of pandemics and potential pandemics has been conducted in the context of the 1918 pandemic. (PSI)

Considered the first truly global pandemic, the 1918 pandemic reached remote populations on Pacific Islands and in the Arctic. Estimates from 2002 place estimates of the global death toll from the disease at 50-100 million. The pandemic occured in three waves. The first was near enough to typical seasonal figures that it was largely ignored, the second wave was so severe and violent it was questioned whether it was even caused by influenza. the most striking characteristic was that the disease was killing significant numbers of normal healthy young adults — creating the "W" mortality curve now recognised as a sign of highly pathogenic pandemic influenza.

File:Foo

I think this graph [1] depicting the impact on average life expectancy in the US by the 1918 pandemic would be an appropriate figure for this section - image should PD (work of US-govt)

The devastating impact the pandemic made influenza the number one infectious disease research priority around the globe and prompted WHO to establish global influenza surveillence by 1947. The virus responsible for the disease has been identified as H1N1, however, the exact origins of the initial outbreaks responsible for the pandemic are still not known. The pandemic was identified as a "Spanish" disease because lack of governmental censorship in Spain saw the disease receive much more media attention there than anywhere else in Europe at the time. Recent research has suggested that China may have been the source of the disease. But North America and Europe have also been suggested as places of the original outbreaks during the pandemic.

Research suggests that the strain was transmitted to humans from either an avian or porcine source (or perhaps both). The H5N1 subtype has clear indications of avian origins, and has since become endemic in swine. Ongoing research is being conducted to identify specific genetic factors responsible for the severe virulence of the virus during this pandemic.

The most recent two pandemics have been noted as having significantly lower mortality rates than the 1918 pandemic, but still possessing high morbidity (rate of severe illness). "Asian influenza" of was first isolated in Guizhou, China in 1956. From there it spread to Singapore in early 1957, then Hong Kong, and reached the US by June. The death toll in the US was estimated at 70,000. The "Hong Kong" influenza pandemic was even less lethal, killing only 33,000 in the US. However, infection rates were still high, estimated 50 million in the US were struck with disease.

A strain of avian influenza, H2N2, was identified as the agent responsible for the 1957 pandemic. Its origins are thought to be from a virus endemic to wild fowl in China, which somehow co-opted elements from a pre-existing human strain. The Hong Kong influenza was identified as H3N2, a direct descendent of the H2N2, but featuring genetic material from other viruses as well.

Recent scares and emerging threats

There have been other large-scale epidemics that have been previously identified as an influenza pandemic. Some of these have been pandemics in teh dictionary sense of a worldwide epidemic, but have not been caused by significant new emerging strain of influenza virus. For instance 1946 is sometimes identified as a pandemic year, but is now considered to be seasonal influenza that featured an unusually high incidence of mortality. Other incidents of widespread high mortality, or violent outbreaks of unidentified strains have provoked contemporary fears of a pandemic. Most recently the threat of emerging strains of highly pathogenic avian influenza capable of infecting humans has loomed over the global disease surveillance community.

The "Russian" influenza epidemic was a global spread of influenza that occured in 1977. However, the epidemic was not considered a true "influenza pandemic" as it was discovered to be subtype H1N1 — the same subtype as the Spanish influenza pandemic. The epidemic affected mostly young children, as older persons still possessed lingering immunity from the 1918 pandemic and following seasons. The epidemic spread from northern China/Russia to the United States by January 1978. Vaccines against the H1N1 subtype were not effectively circulated until the 1978/79 vaccination season.

Prior to the 1977 children's pandemic, there was an isolated outbreak of a highly pathogenic swine influenza in 1976 at Fort Dix, a US Army installation in New Jersey, USA. Alarm was raised due to the violent haemorraghic nature of the disease the virus inflicted, which brought fears that a Spanish influenza-like situation was emerging. A mass vaccination program was instituted in the United States, but hindsight suggests the virus would not have been as lethal as the Spanish influenza pandemic.

Since the late 1990s, human outbreaks of avian influenza ("bird flu") have prompted the most recent concerns regarding an imminent influenza pandemic. Experts are in strong consensus that a future pandemic is virtually inevitable.

The first outbreaks of highly pathogenic avian influenza subtype H5N1 in humans were reported in 1997. Several hundred people became infected in Hong Kong, and most worrying, the disease was more severe in young adults, just like the Spanish influenza pandemic. Spread between humans was not evident, and all cases could be tracked down as originating through human-poultry contact. In 1999, human cases of another avian influenza H9N2 in two children in Hong Kong prompted fears.

In 2003, an outbreak of subtype H7N7 in the Netherlands served to further remind health officials that Asia is not the only source of potential pandemic threats. The disease was observed to have limited human-human transmission. Affected persons included veterinarians, poultry workers and their families. In response a vaccination campaign was undertaken amongst poultry workers and their families near sites of the outbreak.

The exact mechanism and factors that contribute to viruses normally endemic to animals to undergo changes that produce viruses capable of causing influenza pandmeics amongst the human population are still not understood.

Prevention

• Commitees
• Surveillance
• Animal husbandry practices
• Vaccination

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• Pandemics cannot be predicted.
• May be planned/prepared for.

Intervention

• Vaccine distribution
• Anti-virals
• Infrastructure
• Hygeine

Global planning and preparation

• • Potential for country specific subpages - particularly USA
• International (UN, WHO, etc.)
• USA
• China
• etc.