This lesson will discuss two causes of pneumonia: viruses and fungi. We'll go over some of the main agents that cause these types of pneumonia and how viral and fungal pneumonia differ from bacterial pneumonia.
What Really Kills Us
Most of us spend our days worrying about the things in life that can hurt us from the outside. This includes cold weather, serial killers, lions, hurricanes, and so on.
Unfortunately, statistics show that something that kills us from the inside, like cancer, an endocrine disease (such as diabetes mellitus), or an infectious organism breaking down our body, is more likely going to be the cause of our eventual downfall.
Two groups of infectious organisms that can lead to our demise are viruses and fungi, and they can do this to us from a number of angles or organs that they can affect. Namely, for now, we'll talk about how they can affect the lungs.
What Is Pneumonia?
Bacteria, viruses, and fungi can all cause something known as pneumonia. Pneumonia refers to the inflammation of the alveoli in the lungs most notably as a result of a pathogenic infection. What I mean is, it's usually bugs that cause pneumonia, but do bear in mind that other things can cause pneumonia.
The alveoli referred to in the definition are the air sacs of the lungs. These are structures that help to exchange the gas entering and leaving our lungs. They're exactly like little balloons. They inflate as air comes into the lungs when you breathe in, and they deflate as you exhale.
Their inflammation and the inflammation of the rest of the airways as a result of disease can hurt the lungs and lead to fluid accumulation within the alveoli, making gas exchange quite inefficient.
While the most common cause of pneumonia - bacterial - is covered in another lesson, it's not unusual for viral pneumonia to actually predispose to a secondary bacterial infection. That's why it's important to discuss what causes this subtype of pneumonia.
Causes of Viral Pneumonia
Viral pneumonia is exactly what it sounds like. It's pneumonia caused by a virus. Some common viruses that cause this include:
- The influenza virus, the one that causes the flu. These are the most common cause of viral pneumonia.
- Respiratory syncytial virus, especially in children, but also adults.
- Parainfluenza virus, again, especially in children and infants, but less so than respiratory syncytial virus.
To help remember that these guys cause viral pneumonia, just think about their names. You know for sure that the influenza virus causes respiratory signs because I'm more than sure you've had the flu. Well, 'parainfluenza' has the name 'influenza' in it, so that should be easy to remember. And respiratory syncytial virus (RSV) is a dead giveaway since it already has the word 'respiratory' in it.
Causes of Fungal Pneumonia
Fungal pneumonia also has a lot of possible causes, including:
- Pneumocystis jiroveci pneumonia, the most common opportunistic infection in people with HIV
What I mean is that people who have a very weak immune system as a result of something like cancer or HIV/AIDS are more likely to be affected by this fungus. It's sort of a coward of a fungus. It doesn't hurt you unless you are already weak due to something else. It doesn't want to put up a fair fight and waits in the shadows to get you when you're down.
What's also interesting to note with respect to fungal pneumonia is that like pneumonia caused by bacteria, the fungi do not have to be inhaled to affect the lungs (although they most definitely can be). They can sometimes undergo hematogenous spread - that is to say via the bloodstream to the lungs from another place in the body that is affected by the fungus.
Just like you can use the airways to travel to a destination, so, too, can fungi use the air to travel into the lungs. But you can also get to your destination by using a network of roads. This network of roads within our body is our vasculature, which fungi and bacteria can use to get to your lungs from somewhere else.
Another cool tidbit is that certain fungi are more common in one place in the country versus another. Therefore, one type of fungal agent may be more likely to cause fungal pneumonia in the southwestern United States versus the Mississippi River Valley.
Telltale Signs on X-Rays
One important way to help differentiate bacterial pneumonia from viral and fungal pneumonia is via the use of X-rays. Bacterial pneumonia commonly causes something known as lobar pneumonia - that is to say only one lobe of the lung is affected. This is in contrast to fungal and viral pneumonia, both of which tend to make a diffuse interstitial pattern on the X-rays.
X-rays with fungal infection may also reveal nodules in the lungs and a miliary pattern in the lungs. This means that the radiograph looks like it has been covered in snow. It may look pretty, but it's a sign of some serious disease.
But don't think all of these signs and patterns are set in stone or that they can't be caused by other problems. It's not that simple. For example, miliary patterns can also be caused by cancer or tuberculosis.
Besides X-rays, blood tests that can indicate an infection, as well as samples of airway fluid, can help to diagnose the cause of the pneumonia.
Clinical Signs and Symptoms
Most cases of pneumonia cause very similar signs and symptoms in affected people - be they a case of viral or fungal pneumonia. This includes:
- Aches and pains
- Headache and fatigue
- Shortness of breath, a.k.a. dyspnea
- Cough, usually nonproductive in fungal and viral causes. This means it's a dry cough, one that doesn't cause a bunch of gunk to be spit up as you are coughing. This is in contrast to bacterial pneumonia, where the cough is usually full of sputum.
Treatment for fungal pneumonias includes antifungal agents, and the type that is used is dependent upon which organism has been isolated by the clinicians.
Viral pneumonia is best prevented by a vaccine for the virus if there is one, such as the flu vaccine. There are antiviral medications that can be used for some viruses that cause viral pneumonia, but their efficacy has been called into question. That is why supportive care, including lots of rest, good food, oxygen, and fever reducers are important in viral pneumonia and any other cause of pneumonia for that matter.
Hopefully, you'll never have pneumonia. Pneumonia refers to the inflammation of the alveoli in the lungs most notably as a result of pathogenic infection.
The alveoli referred to in the definition are the air sacs of the lungs.
Pneumonia can be caused by viruses, such as the influenza virus, respiratory syncytial virus, and parainfluenza virus, or by fungi, such as pneumocystic jiroveci, the most common opportunistic infection in people with HIV.
Fungi can enter the lungs when they are inhaled, or they can sometimes undergo hematogenous spread - that is to say via the bloodstream to the lungs from another place in the body that is affected by the fungus.
Signs of pneumonia include fever, shortness of breath (dyspnea), and cough, usually nonproductive in fungal and viral causes. This means it's a dry cough, one that doesn't cause a bunch of gunk to be spit up as you are coughing. This is in contrast to bacterial pneumonia, where the cough is usually full of sputum.
On X-rays, bacterial pneumonia typically causes lobar pneumonia as opposed to diffuse interstitial patterns associated with fungal and viral pneumonia.
Following this lesson, you should have the ability to:
- Define pneumonia and alveoli
- Identify the viral causes of pneumonia
- List some causes of fungal pneumonia
- Summarize the signs and symptoms of pneumonia
- Explain the treatment options for viral and fungal pneumonia