Life / Health

What happens to your body when a cold or flu virus invades

You may have a cold or the flu but not know it. That’s because it can take hours to days before the associated miserable symptoms take their nasty hold, says Bryce Wylde, associate medical director of Toronto’s P3 Health and host of TV’s Wylde on Health.

Here is the inside scoop on what happens to your body when a cold or flu virus invades.

The virus finds its way in

“Whether it’s a cold or flu virus, they are spread by droplets when people sneeze, cough, share a drink or by direct contact,” said Wylde, explaining that both viruses ride on people’s mucus secretions. “You are viral many hours to days before you express symptoms.”

The attack begins

“Whether it’s cold or flu, the virus hijacks the cells in our upper respiratory tract,” Wylde said. But while a cold virus will primarily affect the nose and throat without actually killing the cells, a flu virus will often go deep into the lower part of the lungs and kill certain tissues.

Your body defends itself

“The immune system responds by signalling what are called inflammatory proteins, known technically as cytokines,” Wylde said. “This is sort of like the generals in charge of your immune system yelling out to the troops, ‘Attack, that thing is foreign.’”

And the action of cytokines is what causes you to start producing mucus, develop a fever, aches, pain, perhaps nausea and diarrhea — all in an effort to rid your body of the attacking flu virus. Milder in a cold, the immune defence reaction tends to be a runny nose and cough, but the goal is the same — eliminating the virus from the body.

“Colds can have so many different symptoms,” Wylde said. “But with flu, which is more serious, what almost always happens is fever and a bad cough, as well as aches, pains and mucus secretion. Usually with a cold, you don’t get a fever unless you’re an infant.”

You adjust your behaviour

You feel lousy — achy, tired, maybe nauseous, and you head to bed for badly needed rest. And that’s just what you should do. “Recognize that sleep is the body’s opportunity to heal itself,” said Dr. Lisa Graves, chief of the department of family and community medicine for Toronto’s St. Michael’s Hospital. “Often, the messaging we get from our bodies when we’re sick is that we’re tired and we want to rest. This is one of those times when it can be useful to listen to your body.”

And if your body says it’s not hungry, Wylde said, that’s OK, too.

“Eating causes the digestive system to use a lot of energy and can also distract the immune system.”

That said, Wylde said staying hydrated by drinking water, green tea, soup and other fluids is essential. Symptoms such as increased mucus flow, vomiting, diarrhea and perspiration means you are losing lots of important fluids.

The worst is over

“Once your fever is starting to come down unaided that’s the sort of crossover — you’re winning the battle,” Wylde said.

“Antibodies are designed by the body to recognize the virus, so as soon as it has invaded other cells, circulating antibodies give the immune system the heads up and they destroy the cell.”

Colds, however, can linger because the immune response is less intense since the threat is less deadly, Wylde said. For that reason, too, it’s hard to pinpoint when the virus has peaked.

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