Viral Pneumonia

What is viral pneumonia?

Viral pneumonia is an infection of the lungs by viruses.

Causes

Viral pneumonia most commonly occurs as a complication of seasonal flu caused by Influenza A virus.

Other viruses that can cause pneumonia:

• Parainfluenza virus
• Respiratory syncytial virus (RSV): the most common cause in children and young adults
• Adenovirus (in military recruits)
• Coronavirus
• Human metapneumovirus (in children)
• Rhinovirus (the cause of common cold; can cause pneumonia in young children)
• Varicella-zoster virus (the cause of chickenpox and shingles; spread by skin-to-skin contact)
• Rubeola virus (the cause of measles)
• Cytomegalovirus (CMV) (in individuals with bone marrow transplantation)
• Herpes simplex virus (HSV) (in impaired immunity)
• Human immunodeficiency virus (HIV)
• H1N1 Influenza virus (swine flu, 2009 pandemic)
• References: ^[1,2,3]

Is viral pneumonia contagious?

Strictly speaking, viral pneumonia is not contagious but viruses that cause it are. This means, if you are healthy and you are in close contact with someone who has, for example, viral pneumonia caused by Influenza virus, you can catch viruses from him or her but you will more likely develop the flu, rather than viral pneumonia.

Viruses that can cause pneumonia are usually spread by droplets: by coughing, sneezing, kissing or shaking hands with an infected person or touching surfaces (door knobs, bus handles) contaminated by viruses and then touching your nose and mouth. Viruses can survive on surfaces for several hours ^[3].

The incubation period for influenza virus is 1-3 days; it can be longer for other viruses ^[3].

You can more likely get it if you have one or more of the risk factors: young age (infants), old age, pregnancy or impaired immunity ^[3]. 

Symptoms and Signs

Viral pneumonia often develops as a complication of acute bronchitis, sinusitis or flu, so early symptoms can involve symptoms of those diseases: a runny nose, itchy or sore throat, headache or muscle pain. The main late symptom is a dry cough that is worse at night. In otherwise healthy individuals, viral pneumonia is usually a mild disease ^[3,4,5]. In individuals with underlying lung or heart disease and those with impaired immunity, viral pneumonia may be deadly despite treatment.

The main sign is crackling sounds during breathing detected by listening to the lungs with the stethoscope (auscultation).

In viral pneumonia, the cough is usually dry and in bacterial pneumonia productive with coughing up yellow, green or rusty mucus, but one cannot reliably distinguish between the two types of pneumonia from symptoms alone.

Diagnosis

• X-ray is needed for diagnosis of pneumonia. Usually, scattered patches in both lungs (bronchopneumonia) or, in severe cases, a dense shadow (consolidation) in one or more lung lobes (lobar pneumonia) are observed.
• Rapid antigen detection of viruses from nasal swabs has sensitivity 50-60% and specificity >90%.
• A lung biopsy is rarely needed.
• Blood, sputum or bronchoalveolar culture is rarely helpful.
• Reference: ^[6]

Differential Diagnosis

Diseases similar to viral pneumonia:

• Influenza
• Bacterial pneumonia
• Atypical (walking) pneumonia
• Fungal pneumonia
• Pneumonitis

Treatment

Treatment of viral pneumonia can involve antiviral drugs, depending on the cause:

• Influenza A virus: oseltamivir, peramivir, zanamivir, amantadine hydrochloride, rimantadine hydrochloride
• Parainfluenza and Rubeola virus (measles): ribavirin
• Adenovirus: cidofovir
• Respiratory syncytial virus (RSV): palivizumab, ribavirin
• Varicella-zoster and Herpes simplex virus: acyclovir
• Reference: ^[7]

Acetaminophen or ibuprofen can be used to lower the high temperature.

Prognosis in otherwise healthy individuals is very good ^[3]. In treated pneumonia, the recovery period is usually 3-7 days ^[8].

Complications can include secondary bacterial pneumonia, bronchiolitis, atelectasis, bronchiectasis, interstitial fibrosis, encephalitis or death.

Prevention ^[6]:

• Vaccines against influenza, measles and varicella zoster
• Palivizumab contains antibodies that protect against RSV in premature babies.
• Immune globulin

Severe Acute Respiratory Syndrome (SARS)

SARS is caused by SARS coronavirus. An outbreak has occurred in 2003 in China; no cases after 2004 are known ^[9]. SARS is contagious; it is a droplet infection that spreads from person to person by coughing or sneezing. The incubation period is 2-10 days. Symptoms can include a dry cough, high fever and chills, headache and muscle pain ^[9].

Middle East Respiratory Syndrome (MERS)

MERS is a mild or severe disease caused by Middle East Respiratory Syndrome Coronavirus (MERS-CoV). It was first detected in 2012 in Saudi Arabia. There were no known cases after 2014 in the United States ^[10].

• References

  1. Pneumonia  Encyclopaedia Britannica
  2. Learn about pneumonia  American Lung Association
  3. Mosenifar Z, Viral Pneumonia, overview  Emedicine
  4. Pneumonia  Johns Hopkins Medicine
  5. Karnath B et al, 2002, Pulmonary auscultation  Turner-White
  6. Mosenifar Z, Viral Pneumonia, workup  Emedicine
  7. Mosenifar Z, Viral Pneumonia, treatment  Emedicine
  8. Viral pneumonia  Drugs.com
  9. Severe acute respiratory syndrome (SARS)  MedlinePlus
  10. Middle East Respiratory Syndrome (MERS)  Centers of Disease Control and Prevention