|Classification and external resources|
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.
Signs and symptoms
Common causes of viral pneumonia are:
- Influenza virus A and B
- Respiratory syncytial virus (RSV)
- Human parainfluenza viruses (in children)
Rarer viruses that commonly result in pneumonia include:
- Adenoviruses (in military recruits)
- Severe acute respiratory syndrome virus (SARS coronavirus) 
- Middle East respiratory syndrome virus (MERS coronavirus)
Viruses that primarily cause other diseases, but sometimes cause pneumonia include:
- Herpes simplex virus (HSV), mainly in newborns or young children
- Varicella-zoster virus (VZV)
- Measles virus
- Rubella virus
- Cytomegalovirus (CMV), mainly in people with immune system problems
- Smallpox virus
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.
In cases of viral pneumonia where influenza A or B are thought to be causative agents, patients who are seen within 48 hours of symptom onset may benefit from treatment with oseltamivir or zanamivir. Respiratory syncytial virus (RSV) has no direct acting treatments, but ribavirin in indicated for severe cases. Herpes simplex virus and varicella-zoster virus infections are usually treated with aciclovir, whilst ganciclovir is used to treat cytomegalovirus. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, adenovirus, hantavirus, parainfluenza or H1N1 virus; treatment is largely supportive.
Viral pneumonia occurs in about 200 million people a year which includes about 100 million children and 100 million adults.
- "viral pneumonia" at Dorland's Medical Dictionary[dead link]
- National Heart, Lung, and Blood Institute, U.S.A. What Causes Pneumonia?
- Table 13-7 in: Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson. Robbins Basic Pathology: With STUDENT CONSULT Online Access. Philadelphia: Saunders. ISBN 1-4160-2973-7. 8th edition.
- Ruuskanen, O; Lahti, E; Jennings, LC; Murdoch, DR (2011-04-09). "Viral pneumonia.". Lancet 377 (9773): 1264–75. doi:10.1016/S0140-6736(10)61459-6. PMID 21435708.