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. 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. Prevention The best prevention against viral pneumonia is vaccination against influenza, chickenpox (varicella zoster), herpes zoster, measles, respiratory syncytial virus vaccine (RSV), rubella, and adenovirus vaccine. Besides vaccination there are no other ways to prevent viral pneumonia besides basic hygiene skills like covering the mouth when coughing or sneezing, staying home when sick, and washing your hands frequently. 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, or peramivir. Respiratory syncytial virus (RSV) has no direct acting treatments, but ribavirin is indicated for severe cases. Ribavirin has also been known to be used as a treatment for Parainfluenza Virus, and Adenovirus. 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