Viral pneumonia

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

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

Cause

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)
• Metapneumovirus
• 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 kids
• Varicella-zoster virus (VZV)
• Measles virus
• Rubella virus
• Cytomegalovirus (CMV), mainly in people with immune system problems

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

Pathophysiology

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. Viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral pneumonia.

Prevention

The best prevention against viral pneumonia is vaccination against influenza, adenovirus, chickenpox, herpes zoster, measles, and rubella.

Treatment

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) may be treated with ribavirin. 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.

Epidemiology

Viral pneumonia occurs in about 200 million people a year which includes about 100 million children and 100 million adults.

References