Viral pneumonia

Viral Pneumonia
Classification and external resources
Specialty	pulmonology
ICD-10	J12
ICD-9-CM	480
MedlinePlus	000073
eMedicine	emerg/468 radio/539
MeSH	D011024
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Viral pneumonia is a pneumonia caused by a virus. Viruses are one of the two major causes of pneumonia, the other being bacteria; less common causes are fungi and parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.

Symptoms of viral pneumonia include fever, non-productive cough, runny nose, and systemic symptoms (e.g. myalgia, headache). Different viruses cause different symptoms.

Common causes of viral pneumonia are:

Rarer viruses that commonly result in pneumonia include:

Viruses that primarily cause other diseases, but sometimes cause pneumonia include:

The most commonly identified agents in children are respiratory syncytial virus, rhinovirus, human metapneumovirus, human bocavirus, and parainfluenza viruses.

Viruses must invade cells in order to reproduce. Typically, a virus will reach the lungs by traveling in droplets through the mouth and nose with inhalation. There, the virus invades the cells lining the airways and the alveoli. This invasion often leads to cell death either through direct killing by the virus or by self-destruction through apoptosis.

Further damage to the lungs occurs when the immune system responds to the infection. White blood cells, in particular lymphocytes, are responsible for activating a variety of chemicals (cytokines) which cause leaking of fluid into the alveoli. The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream.

In addition to the effects on the lungs, many viruses affect other organs and can lead to illness affecting many different bodily functions. Some viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral pneumonia.

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