EVERYONE in the world may have contracted it at least once in their lifetimes, but history itself shows that the flu can become more than just a yearly guest. The influenza virus—particularly Influenza A—has already caused four flu pandemics in history: that of the Spanish flu, the Asian flu, the Hong Kong flu, and this year’s A(H1N1).

The effects of these flu pandemics are greater that of their seasonal counterparts: they can cause death tolls as high as the number of casualties of world wars.

1918-1919: Spanish Flu

In an article, pathologist Jeffery Taubenberger described the influenza pandemic of 1918 to 1919 as the “mother of all pandemics,” saying that all influenza A pandemics since that time have been caused by descendants of the 1918 or Spanish flu virus. Through antigenic shifting — the abrupt and major change of influenza A virus into a more infective strain — the 1918 virus produced the subtypes of the H2N2 and H3N3 viruses that caused the subsequent Asian and Hong Kong flu pandemics.

Dr. Remedios Coronel of the UST Hospital’s Infectious Diseases department said the Spanish flu appeared during the time of the First World War and more soldiers died because of the disease than the war itself. The Twentieth Century Atlas put the death toll during the First World War at between nine and 16 million, a small number compared to the almost a hundred million victims of the Spanish flu pandemic.

The Spanish flu came in three waves from 1918 to 1919. Coronel said its disappearance may be attributed to viral mutation.

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“No new cases followed, probably because the virus may have already mutated to other strains, such as the virus responsible for the succeeding Asian and Hong Kong flu pandemics,” Coronel said.

The Spanish flu was more severe than its modern descendants. The flu-like symptoms of the disease came suddenly and progressed rapidly to hemorrhaging, respiratory failure, and in some instances, death. As a result, doctors often misdiagnosed the flu for other diseases that presented the same symptoms, like cholera or dengue fever.

Coronel said the global spread and severity of the virus could have been caused by the war and the movement and crowding of soldiers at that time.

“The lack of protective equipment and the inability to produce a vaccine may also have contributed to the spread,” Coronel said.

1957-58: Asian Flu

The Asian flu was caused by a variant of the avian or bird flu virus influenza A(H2N2) that was first identified in China, Singapore, and Hong Kong.

The book “The Bird Flu Pandemic” by Jeffrey Greene and Karen Moline said the Asian Flu was caused by an influenza virus normally found in wild ducks. The virus transferred to humans when it combined with a pre-existing human influenza strain, since influenza viruses are capable of jumping from one host species to another.

“The flu virus can re-assort its genes thus enabling easy transmission from birds to humans,” Coronel said.

Despite the high number of infected people, the symptoms of Asian flu — fever, runny nose, cough and sore throat — were known to be milder, and the death toll of one to four million was lower compared to the Spanish flu. Advancements in medical technology also helped identify the virus, allowing the creation of vaccines.

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1968-69: Hong Kong Flu

The Hong Kong Flu was first discovered in Hong Kong in July 1968, with the then British colony’s crowded city centers enabling the virus to spread rapidly.

Coronel said the influenza A(H3N2) virus killed a million people.

Still, the disease was considered to be milder compared to the Spanish and Asian flu pandemics. The Centers for Disease Control and Prevention in the United States speculated that the decreased severity of the disease’s symptoms may be because the 1968 and the 1957 viruses possessed the same “N2” antigen. This allowed those who were previously infected by the H2N2 virus to produce antibodies for the H3N2 virus, which means lesser susceptibility of those who had Asian flu to the Hong Kong flu.

2009: Influenza A(H1N1)

As of June 24, 2009, the World Health Organization has recorded a total of 55,867 confirmed cases of A(H1N1) flu in 99 countries around the world. In the Philippines alone, 727 cases have reported by the Department of Health, around a month since the first case of A(H1N1) was discovered in the country.

“The human influenza A(H1N1) is caused by a subtype of the H1N1 Influenza virus mutation of four known strains of the virus infecting humans, birds and pigs,” Coronel said.

It takes seven to 10 days for a person with the H1N1 flu to manifest symptoms such as fever, cough and muscle and joint pains.

While it is highly contagious, H1N1 flu should not be a cause for panic, Coronel said.

“The H1N1 flu is actually a very mild disease with a mortality of only 0.5 percent. Treatment for H1N1 flu is really nothing different compared to the seasonal flu,” she added.

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The H1N1 flu can be treated by antivirals such as Oseltamivir or Zanamivir, and if necessary, confinement in a negative pressure isolation room.

To prevent the spread of the disease, Coronel said it is very important for travelers to follow the quarantine guidelines prescribed by the Health department, especially if they just came from countries with confirmed cases of the H1N1 flu.

“Those with symptoms must do self-quarantine,” she added.

Coronel also stressed the importance of observing proper personal hygiene such as washing hands and covering the nose, as well as “coughing etiquette.”

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