The COVID-19 virus is mainly a respiratory infection that enters the body through the mouth, nose, or even the eyes. Then what happens?

Two months after America’s first confirmed case, the coronavirus has killed more than 1,000 people nationally, a toll that is increasing at an alarming rate, according to media reports.

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Among those who have died, about 65 percent were older than 70 and nearly 40 percent were over 80, according to The Washington Post, which is tracking cases.

About 5 percent were in their 40s or younger, but many more in that age group have been sick enough to be hospitalized.

Of all victims, nearly 60 percent were men, the newspaper found.

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The death toll may actually be higher because cases have been misdiagnosed as the flu or another illness and some who have died were never tested.

As the virus spreads, medical experts are continuing to learn more about how COVID-19 interacts with the human body.

They know that symptoms include fever, cough and shortness of breath and can lead to death in some, especially the elderly or those with other medical conditions.

Dr. Neal Patel, a Mayo Clinic pulmonary and critical care medicine specialist, says that, like most viruses, “many different things happen.”

“Initially, the virus can cause some damage locally where it enters. Then it moves further into the respiratory system,” he says.

“If the virus enters through your nose, you may notice typical symptoms of an upper Respiratory Tract infection, such as a runny nose or nasal congestion,” says Patel.

“The virus may stop there or may continue down the respiratory tract, where it can cause issues such as coughing.”

Once the virus is established in the body, the immune system kicks in, swarming the infection in an attempt to kill it.

“There is an initial immune response when a virus enters a body for the first time,” says the doctor.

“It’s a generic response where the immune system turns on and says: ‘You’re not supposed to be here. I’m going to try to kill you.’ It’s not a very robust response, but it is something.”

During the immune system’s response, it starts building antibodies through a process called “adaptive immunity.”

“You build an army to take down this virus,” he explains.

In some cases, the virus finds its way into the Lower Respiratory Tract where it can cause immeasurably more damage.

“Unfortunately, our body’s response to kill that virus in the lower respiratory tract can cause a lot of collateral damage. Sometimes it’s an exaggerated response, kind of like bringing an army to kill an ant.”

One of the most serious problems is deteriorating lung function.

“The ability to get oxygen in and out of the bloodstream becomes affected. Your muscles may become impaired and you get fatigued trying to inhale and exhale against lungs that aren’t working too well.”

Those who end up in intensive care unit may have developed a secondary infection, usually pneumonia, a condition where lungs fill with fluid.

“That type of patient may require some help,” says Patel.

“Mechanical ventilation, or a ventilator, is how we help that patient to rest a little bit. It allows them to get the oxygen they need so the body can work to calm this down and hopefully get rid of the virus.”

The virus also may cause gastrointestinal issues, such as diarrhea, which in itself, is not life threatening.

Check out the video below and get more information and COVID-19 coverage from the Mayo Clinic News Network.