Viral pneumonia

Viral pneumonia is a pneumonia caused by a virus.^[1] 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. ^[2]

Features

Pneumonia
Infectious pneumonias
Bacterial pneumonia Viral pneumonia Fungal pneumonia Parasitic pneumonia Atypical pneumonia Community-acquired pneumonia Healthcare-associated pneumonia Hospital-acquired pneumonia Ventilator-associated pneumonia Severe acute respiratory syndrome
Pneumonias caused by infectious or noninfectious agents
Aspiration pneumonia Lipid pneumonia Eosinophilic pneumonia Bronchiolitis obliterans organizing pneumonia
Noninfectious pneumonia
Chemical pneumonia
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Symptoms of viral pneumonia include fever, non-productive cough, running nose, and systemic symptoms (e.g. myalgia, headache). Different viruses cause different symptoms.

Mechanism of the disease

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.

Etiology

Common causes of viral pneumonia are:

• Influenza virus A and B^[3]
• Respiratory syncytial virus (RSV)^[3]
• Human parainfluenza viruses (in children)^[3]

Rarer viruses that commonly result in pneumonia include:

• Adenoviruses (in military recruits)^[3]
• Metapneumovirus^{[citation needed]}
• Severe acute respiratory syndrome virus (SARS coronavirus) ^[4]

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

• Herpes simplex virus (HSV), mainly in newborns
• Varicella-zoster virus (VZV)
• Cytomegalovirus (CMV), mainly in people with immune system problems

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^{[citation needed]}; treatment is largely supportive.

References