Pneumonia occurs when the air sacs and small airways in the lungs fill with liquid and cannot function properly. When this happens, the body cannot take in oxygen as it normally would. Oxygen is vital to the body’s cells, where it is needed for aerobic respiration; the breakdown of food to obtain energy for cellular work.
Causes of Pneumonia
Pneumonia can have many different causes: viral, bacterial, fungal or, in the case of aspiration pneumonia, may result from the inhalation of substances such as caustic chemicals, food or vomit.
Viral Pneumonia
Pneumonia that is caused by a viral infection causes irritation, swelling, and congestion in the lungs. Also called pneumonitis (nu-mo-NI-tis), this infectious disease occurs most often in the winter, afflicting 1 in 100 people. Viruses are the most common cause of pneumonia in children.
Cause
The viruses that most commonly cause pneumonia include:
- Influenza virus
- Respiratory syncytial virus (RSV)
- Adenoviruses
- Metapneumovirus
Course
Viral Invasion
Viruses cannot reproduce on their own, but are parasitic and must invade the cells of the host in order to reproduce. A virus typically reaches the lungs by traveling in droplets inhaled through the mouth or nose. Once in the lungs, the virus invades cells lining the airways and alveoli.
Cellular Destruction
Once invaded, cells of the lung can die due to direct killing by the virus or when the host’s immune system destroys its own infected cells. The lungs can be further damaged by the immune response to infection when white blood cells activate chemicals which cause the body’s fluid to leak into the alveoli.
This combination of cellular destruction and fluid in the lungs interferes with oxygen moving into the bloodstream.
Viral pneumonia also lowers the body's immunity, and additional illnesses, such as bacterial infection, may result leading to more serious forms of pneumonia.
Resolution of Illness
Most cases of viral pneumonia are mild and, in one to three weeks, will improve without treatment. More serious episodes may require hospitalization. Those at risk for serious viral pneumonia usually have impaired immune systems; and serious infections may result in respiratory failure, liver failure, and heart failure.
Signs & Symptoms
Symptoms are similar to those of bacterial pneumonia; the most common being headache, fever, chills, muscle aches, loss of appetite and a productive cough. Breathing may be difficult or painful. Upon physical examination, crackles may be heard when the patient’s chest is examined with a stethoscope.
Medical tests for viral pneumonia may include chest x-ray or CAT scan, arterial blood gases to check oxygen level, pleural fluid culture can be used to identify the pathogen if there is fluid in the space surrounding the lungs.
Treatment
Antibiotics, although sometimes prescribed in the treatment of viral pneumonia, are a type of medication that only kill bacteria and are not effective in treating viral pneumonia. Serious viral infections can be treated with antiviral medications.
Additional supportive care may include use of humidified air, increased fluids, and oxygen. Hospitalization may be required to prevent dehydration, assist breathing and supplement oxygen if the infection is serious.
Pneumonia Resources
For more information on types of pneumonia, see
- Mayo Clinic: Infectious Diseases
- WebMD: Pneumonia Overview
- MedlinePlue: Viral Pneumonia
This article is a summary of the causes, course, symptoms and treatment of viral pneumonia. It is not meant to be used for self-diagnosis or as a substitute for professional medical care.
Sources
Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.
