MANILA, Philippines -- Sandra, 28, was very lively that night.  After all, she was just promoted in her department.  She partied and dined.  When she returned home, she immediately went to sleep.  But the following day, she felt flattened – as if ambushed from behind – with a 39- to 40-degree fever, headache, extreme fatigue, weakness, and severe aches and pains in her muscles.  She went to the doctor.  “You’ve got flu,” she was told.

Working or playing through the flu – or influenza, to use its proper name – is impossible, unless you’re the type who can walk on hot coals and feel no pain.  You’ll probably have to take to your bed for three or more days.  But even after you recover – usually within three to seven days – you will have a dragged-down feeling that can persist for weeks and is sometimes compounded by depression.

 “Flu is an acute respiratory illness caused by a virus,” explains Jane Brody in her book, Jane Brody’s Cold and Flu Fighter.   There are three basic types of flu virus – A, B, and C – but only A and B (isolated in 1933 and 1940, respectively) are responsible for flu epidemics. New strains of the virus emerge at regular intervals and are named according to their geographic origin.

 “Flu is one of the most changeable viruses known to man,” writes Rachel Wildavsky in an article, which appeared in the American edition of Reader’s Digest.  “After we’ve been sick with one strain, it can mutate to infect us again.  We are only immune to flu viruses that our bodies have seen before.”

A flu can also “jump species” to an animal it has never infected before.  Once such flu moves into humans and if it can “learn” to pass easily between them, it can spark a pandemic — a global outbreak.

Flu, one of the oldest and most common diseases known to man, is a notorious killer. Hippocrates described flu in 412 BC and the first well-described pandemic of flu-like disease occurred in 1580.  Since that time, 31 such possible flu pandemics have been documented, with three occurring in the 20th century: In 1918, 1957 and 1968.  The disease today still affects large sections of the population each year. Its ability to kill stems from the fact that the virus can mutate quickly, often producing new strains against which human beings have no immunity. When this occurs, mortality from influenza can be staggering such as, for example, during the “Spanish Flu” pandemic of 1918-1920, where at least 20 million people died from influenza.

 In most instances, flu is dismissed as common cold.  But both differ. Symptoms of flu start 24 to 48 hours after infection and can begin suddenly.  The first clue that a person has flu is the chilly sensation.  Fever is common during the first few days, and the temperature may rise to 102-103 degrees Fahrenheit.

The main treatment for flu is to take complete rest in a warm, well-ventilated room until the disease clears up.  Staying home also avoids spreading the infection.   Drinking plenty of fluids — but do not take alcohol - may help.

 If a person is having severe symptoms but without complications, he may opt to take acetaminophen, aspirin, ibuprofen, or naproxen.  Children, however, are not advised to take aspirin since the drug may increase their risk of getting Reye’s syndrome.