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A viral infection that affects mainly the nose, throat, bronchi and the lungs, Influenza or Flu has the doubtful privilege of being the last uncontrolled pandemic killer of humans before AIDS. It is transmitted easily from person to person via droplets and small particles produced when infected people cough or sneeze.


Why should I be aware of this?

Influenza tends to spread rapidly in seasonal epidemics. It is in this form that influenza has acquired its deadly overtones – in the last century, there have been regular and crippling pandemics of different varieties of Flu which have resulted in thousands of fatalities. One historic measure of influenza's potential lethality is that more people died in the 1918-19 Flu pandemic than in World War I.

Even today, in the United States, between five to twenty percent of the population develops influenza. In non-pandemic years, more than 200,000 people are hospitalized from complications resulting from the disease, while 36,000 people die from it. In pandemic years, the mortality figures may exceed 100,000.

All about influenza

The symptoms of Flu sound harmless enough -- it begins with the sudden onset of high fever, aching muscles, dry cough, sore throat and dripping nose, which may last for about a week. However, even these ordinary symptoms are very distressing, especially for the very young, the elderly, and those with other serious medical conditions. It may lead to severe complications of the above symptoms, pneumonia and death.

Types of influenza

The currently circulating influenza viruses that cause human disease are divided into two groups: A and B. Together, these result in three different types of Influenza –

Influenza C does not occur in epidemics and causes mild disease.

Influenza B is only known to infect humans and seals. Its limited host range explains why there have not been any Influenza B pandemics. It also mutates at a rate two or three times slower than type A. This range of viruses causes minor symptoms, although it may develop into more severe disease in older persons.

Influenza A causes influenza in birds, humans, whales, pigs, and horses. Influenza A viruses normally seen in one species sometimes can cross over and cause illness in another species. It is responsible for devastating pandemics, including the one of 1918, and Bird Flu, which wrecks havoc in Asia practically every year.

Geographical spread and transmission

Influenza rapidly spreads around the world in seasonal epidemics. It is very contagious, especially in crowds. The Flu virus survives longer in cold and dry weather. This is why most seasonal epidemics in temperate areas appear in winter.

The influenza virus enters the body through the nose or throat. It then takes between one and four days for the person to develop symptoms. Someone suffering from influenza can be infectious from the day before they develop symptoms until seven days afterwards. Further, the type A virus is also directly transmitted from species to species, and has been, off late, especially active in countries where unhygienic butchering practices are followed.

Flu pandemics in history

Major Flu pandemics have occurred in history, usually when the Influenza A viruses have mutated. The worst pandemic was in 1918-1919, and was dubbed “Spanish Flu”. It is believed to have killed at least 40 million people, many of whom were young and otherwise healthy.

In the fifties and sixties, there were two more Influenza A pandemics -- Asian influenza in 1957 and one in Hong Kong in 1968. Both resulted in significant loss of lives, and were noted to affect healthy younger persons.

Since 2000, there have been limited outbreaks of a new subtype of Influenza A, H5N1. Since it is directly transmitted from birds to humans, it has been dubbed as Bird Flu or Avian Flu. Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. That is why its fatality rate is estimated to be over fifty per cent. The H5N1 virus that has caused human illness and death in Asia is resistant to the two antiviral medications most commonly used for influenza -- Amantadine and Rimantadine.

Prophylactic and preventive measures

In most healthy people, influenza B and C symptoms disappear in five to seven days, with the worst symptoms lasting about four days. However, since flu-related complications are so common, physicians advise influenza vaccines.

Vaccines for Influenza are of two types: the inactivated vaccine, or the “flu shot” is administered through an injection into the muscle; while the live, attenuated influenza vaccine, called LAIV, is sprayed into the nostrils. For most people influenza vaccine prevents serious influenza-related illnesses for up to one year of being admistered. Most people need one dose of influenza vaccine each year, though children under nine who are getting the vaccine for the fist time, need two doses.

The problem with flu vaccines is that they need to be updated regularly since the influenza viruses mutate very fast. Because of this, an annual vaccination is recommended. Unfortunately immunity against one strain (which is conferred by exposure or immunisation) does not protect against other strains. Even so, the prevention of virulent strains of influenza is, so far, our best bet in beating the disease.

Another way of preventing flu infection from spreading (especially in hospitals) is through the use of face masks. Health care experts seem to agree that face masks with special air filters should be an important part of the first line of defense against human-to-human transmission -- especially among first-line responders like paramedics. To see a variety of face masks and equipment that offer physical protection against the Flu, go to Influenza Virus

Once a person has contracted influenza, the few treatments that work need to be given within forty eight hours of getting infected. However, hardly anyone is diagnosed with flu so early on, and few medics even make the diagnosis of flu at that time.

Influenza drugs and treatments also change practically every year, since the strains of the virus keep mutating. The two latest antiviral drugs are Oseltamivir (better known as Tamiflu), which is taken by mouth, and Zanamivir (or Relenza), which is inhaled. Both drugs are neuraminidase inhibitors and are licensed for treatment of both the main types of influenza in humans (type A and type B). Physicians believe that these drugs would also work with Bird Flu patients, but additional studies still need to be done to demonstrate their effectiveness.

What can I do?

How to look after an influenza patient at home

Most influenza patients can be treated at home quite easily, since all they really need is rest, plenty of fluids and patience. The treatment is purely symptomatic in mild cases of influenza – paracetamol, ibuprofen or other anti-inflammatory drugs may be given to ease fevers and muscle aches, along with decongestants, cough medicines and lozenges to ease problems of the upper respiratory tract.

There are some natural remedies to alleviate flu symptoms. Here is a list of some –

  • Steam inhalations and gargles with warm saline water are very effective in alleviating cough and sore throat, without having the sedative effects of decongestant medicines.
  • Sipping warm water (adding a dash of lemon and honey is also good) is as effective as allopathic cough medicines, for relieving the non-productive cough associated with flu.
  • Chicken soup, with or without a dash of lime, is much more than comfort food – it actually helps alleviate flu symptoms.
  • A sponge down (or even a long shower) with tepid water often helps bring down the fever considerably.

For more, see Home remedies for fever.

When to call the doctor

Home care for flu patients is fine, but it is important to consult the doctor if the patient already has diabetes, lung disease, cancer, kidney or heart problems. When nursing a flu patient, if you notice any of the following danger signs, call your doctor immediately.

  • Clouded/altered consciousness
  • Breathlessness
  • Severe chest pain
  • Also, see the doctor if the flu symptoms continue unabated for more than a week, or if you seem to be improving for a few days then get much worse again.

Sometimes, during flu, a secondary infection gets in while the body's defenses are down. This is most commonly a chest infection and can be a pneumonia. The secondary infection is often caused by bacteria, and as a result is likely to respond to an antibiotic.


  • Influenza
  • Influenza Virus
  • Avian Influenza
  • Influenza (Flu)

Additional Information

  • For more on the geographical spread of Bird Flu, go to Bird Flu - BBC

See Also


Flu shots are our best protection against Influenza. However, there are some people who must NEVER be vaccinated against flu..... Read more inside