Cause
Common causes of viral pneumonia are:

Influenza virus A and B
Respiratory syncytial virus (RSV)
Human parainfluenza viruses (in children)
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)Rarer viruses that commonly result in pneumonia include:

Adenoviruses (in military recruits)
Metapneumovirus
Severe acute respiratory syndrome coronavirus (SARS-CoV)
Middle East respiratory syndrome virus (MERS-CoV)
HantavirusesViruses 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
Dengue virusThe most commonly identified agents in children are respiratory syncytial virus, rhinovirus, human metapneumovirus, human bocavirus, and parainfluenza viruses. History
In the pre-antibiotic age, pneumonias had been treated with specific anti-serums of highly variable therapeutic effect and undesirable side-effects (a practice eliminated by the advent of sulfamides in 1936 and the beginning availability of penicillin in the 1940s). Viral pneumonia was first described by Hobart Reimann in 1938, in an article published by JAMA, An Acute Infection of the Respiratory Tract with Atypical Pneumonia: a disease entity probably caused by a filtrable virus. Reimann, Chairman of the Department of Medicine at Jefferson Medical College, had established the practice of routinely typing the pneumococcal organism in cases where pneumonia presented. Out of this work, the distinction between viral and bacterial strains was noticed. 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.
Herpes simplex virus and varicella-zoster virus infections are usually treated with acyclovir, whilst ganciclovir is used to treat cytomegalovirus. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, MERS coronavirus, or hantavirus. Other forms of care are largely supportive like oxygen supplementation, treatment of comorbidities, and controlling other symptoms, fever and cough, with medications. Epidemiology
There are roughly 450 million cases of pneumonia every year. Of those case, viral pneumonia counts for about 200 million cases which includes about 100 million children and 100 million adults. Viral pneumonia is more prevalent in the very young, less than 5 years old, and in the very old, more than 75 years old. Developing countries have a higher rate of incidence when it comes to viral pneumonia. On average, developing countries have an incidence rate five times higher than that of developed countries. Being pregnant can also affect the chances of developing viral pneumonia. As with all infectious diseases, viral pneumonia preys on the immunocompromised as well as individuals with one or more comorbidities especially those with:

Trauma
Severe burns
Diabetes
Malnutrition
Poverty
Environmental Exposure
Group living

References


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