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

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 children

- "Varicella-zoster virus" (VZV)

- "Measles virus"

- "Rubella virus"

- "Cytomegalovirus" (CMV), mainly in people with immune system problems

- "Smallpox virus"

- "dengue virus"

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

The duration of the visible blistering caused by varicella zoster virus varies in children usually from 4 to 7 days, and the appearance of new blisters begins to subside after the fifth day. Chickenpox infection is milder in young children, and symptomatic treatment, with sodium bicarbonate baths or antihistamine medication may ease itching. It is recommended to keep new infants from birth up to age 6 months away from an infected person for 10 to 21 days because their immune systems are not developed enough to handle the stress it can bring on. Paracetamol (acetaminophen) is widely used to reduce fever. Aspirin, or products containing aspirin, should not be given to children with chickenpox, as it can cause Reye's Syndrome.

In adults, the disease is more severe, though the incidence is much less common. Infection in adults is associated with greater morbidity and mortality due to pneumonia (either direct viral pneumonia or secondary bacterial pneumonia), bronchitis (either viral bronchitis or secondary bacterial bronchitis), hepatitis, and encephalitis. In particular, up to 10% of pregnant women with chickenpox develop pneumonia, the severity of which increases with onset later in gestation. In England and Wales, 75% of deaths due to chickenpox are in adults. Inflammation of the brain, or encephalitis, can occur in immunocompromised individuals, although the risk is higher with herpes zoster. Necrotizing fasciitis is also a rare complication.

Varicella can be lethal to adults with impaired immunity. The number of people in this high-risk group has increased, due to the HIV epidemic and the increased use of immunosuppressive therapies. Varicella is a particular problem in hospitals, when there are patients with immune systems weakened by drugs (e.g., high-dose steroids) or HIV.

Secondary bacterial infection of skin lesions, manifesting as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children. Disseminated primary varicella infection usually seen in the immunocompromised may have high morbidity. Ninety percent of cases of varicella pneumonia occur in the adult population. Rarer complications of disseminated chickenpox include myocarditis, hepatitis, and glomerulonephritis.

Hemorrhagic complications are more common in the immunocompromised or immunosuppressed populations, although healthy children and adults have been affected. Five major clinical syndromes have been described: febrile purpura, malignant chickenpox with purpura, postinfectious purpura, purpura fulminans, and anaphylactoid purpura. These syndromes have variable courses, with febrile purpura being the most benign of the syndromes and having an uncomplicated outcome. In contrast, malignant chickenpox with purpura is a grave clinical condition that has a mortality rate of greater than 70%. The cause of these hemorrhagic chickenpox syndromes is not known.

After a chickenpox infection, the virus remains dormant in the body's nerve tissues. The immune system keeps the virus at bay, but later in life, usually in an adult, it can be reactivated and cause a different form of the viral infection called shingles (also known as herpes zoster).

The United States Advisory Committee on Immunization Practices (ACIP) suggests that every adult over the age of 60 years get the "herpes zoster" vaccine.

Shingles affects one in five adults infected with chickenpox as children, especially those who are immune-suppressed, particularly from cancer, HIV, or other conditions. Stress can bring on shingles as well, although scientists are still researching the connection. Shingles are most commonly found in adults over the age of 60 who were diagnosed with chickenpox when they were under the age of 1.

Bacteria are the most common cause of community-acquired pneumonia (CAP), with "Streptococcus pneumoniae" isolated in nearly 50% of cases. Other commonly isolated bacteria include "Haemophilus influenzae" in 20%, "Chlamydophila pneumoniae" in 13%, and "Mycoplasma pneumoniae" in 3% of cases; "Staphylococcus aureus"; "Moraxella catarrhalis"; "Legionella pneumophila" and Gram-negative bacilli. A number of drug-resistant versions of the above infections are becoming more common, including drug-resistant "Streptococcus pneumoniae" (DRSP) and methicillin-resistant Staphylococcus aureus (MRSA).

The spreading of organisms is facilitated when risk factors are present. Alcoholism is associated with "Streptococcus pneumoniae", anaerobic organisms, and "Mycobacterium tuberculosis"; smoking facilitates the effects of "Streptococcus pneumoniae", "Haemophilus influenzae", "Moraxella catarrhalis", and "Legionella pneumophila". Exposure to birds is associated with "Chlamydia psittaci"; farm animals with "Coxiella burnetti"; aspiration of stomach contents with anaerobic organisms; and cystic fibrosis with "Pseudomonas aeruginosa" and "Staphylococcus aureus". "Streptococcus pneumoniae" is more common in the winter, and should be suspected in persons aspirating a large amount of anaerobic organisms.

Community-acquired pneumonia (CAP) is acquired in the community, outside of health care facilities. Compared with health care–associated pneumonia, it is less likely to involve multidrug-resistant bacteria. Although the latter are no longer rare in CAP, they are still less likely.

Developing countries are more severely affected by TORCH syndrome.

The U.S. Centers for Disease Control and Prevention (CDC) publishes a journal "Emerging Infectious Diseases" that identifies the following factors contributing to disease emergence:

- Microbial adaption; e.g. genetic drift and genetic shift in Influenza A

- Changing human susceptibility; e.g. mass immunocompromisation with HIV/AIDS

- Climate and weather; e.g. diseases with zoonotic vectors such as West Nile Disease (transmitted by mosquitoes) are moving further from the tropics as the climate warms

- Change in human demographics and trade; e.g. rapid travel enabled SARS to rapidly propagate around the globe

- Economic development; e.g. use of antibiotics to increase meat yield of farmed cows leads to antibiotic resistance

- Breakdown of public health; e.g. the current situation in Zimbabwe

- Poverty and social inequality; e.g. tuberculosis is primarily a problem in low-income areas

- War and famine

- Bioterrorism; e.g. 2001 Anthrax attacks

- Dam and irrigation system construction; e.g. malaria and other mosquito borne diseases

TORCH syndrome can be prevented by treating an infected pregnant person, thereby preventing the infection from affecting the fetus.

Varicella zoster virus (VZV) has a high level of infectivity and has a worldwide prevalence. Shingles is a re-activation of latent VZV infection: zoster can only occur in someone who has previously had chickenpox (varicella).

Shingles has no relationship to season and does not occur in epidemics. There is, however, a strong relationship with increasing age. The incidence rate of shingles ranges from 1.2 to 3.4 per 1,000 person‐years among younger healthy individuals, increasing to 3.9–11.8 per 1,000 person‐years among those older than 65 years, and incidence rates worldwide are similar.

This relationship with age has been demonstrated in many countries, and is attributed to the fact that cellular immunity declines as people grow older.

Another important risk factor is immunosuppression. Other risk factors include psychological stress. According to a study in North Carolina, "black subjects were significantly less likely to develop zoster than were white subjects." It is unclear whether the risk is different by gender. Other potential risk factors include mechanical trauma and exposure to immunotoxins.

There is no strong evidence for a genetic link or a link to family history. A 2008 study showed that people with close relatives who had had shingles were twice as likely to develop it themselves, but a 2010 study found no such link.

Adults with latent VZV infection who are exposed intermittently to children with chickenpox receive an immune boost. This periodic boost to the immune system helps to prevent shingles in older adults. When routine chickenpox vaccination was introduced in the United States, there was concern that, because older adults would no longer receive this natural periodic boost, there would be an increase in the incidence of shingles.

Multiple studies and surveillance data, at least when viewed superficially, demonstrate no consistent trends in incidence in the U.S. since the chickenpox vaccination program began in 1995. However, upon closer inspection, the two studies that showed no increase in shingles incidence were conducted among populations where varicella vaccination was not as yet widespread in the community. A later study by Patel "et al." concluded that since the introduction of the chickenpox vaccine, hospitalization costs for complications of shingles increased by more than $700 million annually for those over age 60. Another study by Yih "et al". reported that as varicella vaccine coverage in children increased, the incidence of varicella decreased, and the occurrence of shingles among adults increased by 90%. The results of a further study by Yawn "et al". showed a 28% increase in shingles incidence from 1996 to 2001. It is likely that incidence rate will change in the future, due to the aging of the population, changes in therapy for malignant and autoimmune diseases, and changes in chickenpox vaccination rates; a wide adoption of zoster vaccination could dramatically reduce the incidence rate.

In one study, it was estimated that 26% of those who contract shingles eventually present complications. Postherpetic neuralgia arises in approximately 20% of people with shingles. A study of 1994 California data found hospitalization rates of 2.1 per 100,000 person-years, rising to 9.3 per 100,000 person-years for ages 60 and up. An earlier Connecticut study found a higher hospitalization rate; the difference may be due to the prevalence of HIV in the earlier study, or to the introduction of antivirals in California before 1994.

Rodent control in and around the home remains the primary prevention strategy, as well as eliminating contact with rodents in the workplace and campsite. Closed storage sheds and cabins are often ideal sites for rodent infestations. Airing out of such spaces prior to use is recommended. Avoid direct contact with rodent droppings and wear a mask to avoid inhalation of aerosolized rodent secretions.

HFRS is primarily a Eurasian disease, whereas HPS appears to be confined to the Americas. The geography is directly related to the indigenous rodent hosts and the viruses that coevolved with them.

The rash and pain usually subside within three to five weeks, but about one in five people develop a painful condition called postherpetic neuralgia, which is often difficult to manage. In some people, shingles can reactivate presenting as "zoster sine herpete": pain radiating along the path of a single spinal nerve (a "dermatomal distribution"), but without an accompanying rash. This condition may involve complications that affect several levels of the nervous system and cause many cranial neuropathies, polyneuritis, myelitis, or aseptic meningitis. Other serious effects that may occur in some cases include partial facial paralysis (usually temporary), ear damage, or encephalitis. During pregnancy, first infections with VZV, causing chickenpox, may lead to infection of the fetus and complications in the newborn, but chronic infection or reactivation in shingles are not associated with fetal infection.

There is a slightly increased risk of developing cancer after a shingles infection. However, the mechanism is unclear and mortality from cancer did not appear to increase as a direct result of the presence of the virus. Instead, the increased risk may result from the immune suppression that allows the reactivation of the virus.

Although shingles typically resolves within 3–5 weeks, certain complications may arise:

- Secondary bacterial infection

- Motor involvement, including weakness especially in "motor herpes zoster"

- Eye involvement: trigeminal nerve involvement (as seen in herpes ophthalmicus) should be treated early and aggressively as it may lead to blindness. Involvement of the tip of the nose in the zoster rash is a strong predictor of herpes ophthalmicus.

- Postherpetic neuralgia, a condition of chronic pain following shingles

Viral encephalitis is a type of encephalitis caused by a virus.

It is unclear if anticonvulsants used in people with viral encephalitis would prevent seizures.

Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy. Both causes may be present with similar symptoms.

MVD is caused by two viruses Marburg virus (MARV) and Ravn virus (RAVV)family Filoviridae

Marburgviruses are endemic in arid woodlands of equatorial Africa. Most marburgvirus infections were repeatedly associated with people visiting natural caves or working in mines. In 2009, the successful isolation of infectious MARV and RAVV was reported from healthy Egyptian rousettes ("Rousettus aegyptiacus") caught in caves. This isolation strongly suggests that Old World fruit bats are involved in the natural maintenance of marburgviruses and that visiting bat-infested caves is a risk factor for acquiring marburgvirus infections. Further studies are necessary to establish whether Egyptian rousettes are the actual hosts of MARV and RAVV or whether they get infected via contact with another animal and therefore serve only as intermediate hosts. Another risk factor is contact with nonhuman primates, although only one outbreak of MVD (in 1967) was due to contact with infected monkeys. Finally, a major risk factor for acquiring marburgvirus infection is occupational exposure, i.e. treating patients with MVD without proper personal protective equipment.

Contrary to Ebola virus disease (EVD), which has been associated with heavy rains after long periods of dry weather, triggering factors for spillover of marburgviruses into the human population have not yet been described.

Possible causes of lymphocytic interstitial pneumonia include the Epstein-Barr virus and Human Immunodeficiency Virus.

Prognosis is generally poor. If a patient survives, recovery may be prompt and complete, or protracted with sequelae, such as orchitis, hepatitis, uveitis, parotitis, desquamation or alopecia. Importantly, MARV is known to be able to persist in some survivors and to either reactivate and cause a secondary bout of MVD or to be transmitted via sperm, causing secondary cases of infection and disease.

Of the 252 people who contracted Marburg during the 2004–2005 outbreak of a particularly virulent serotype in Angola, 227 died, for a case fatality rate of 90%.

Although all age groups are susceptible to infection, children are rarely infected. In the 1998–2000 Congo epidemic, only 8% of the cases were children less than 5 years old.

Aspiration pneumonia is often caused by a defective swallowing mechanism, often due to a neurological disease or as the result of an injury that directly impairs swallowing or interferes with consciousness. Examples of the former are stroke, Parkinson's disease, and multiple sclerosis, and examples of the latter are some types of dementia, seizures, intoxication, and general anaesthesia. For many types of surgical operations, patients are therefore instructed to take nothing by mouth (nil per os, abbreviated as NPO) for at least four hours before surgery.

Sixty percent of people with acute interstitial pneumonitis will die in the first six months of illness. The median survival is 1½ months.

However, most people who have one episode do not have a second. People who survive often recover lung function completely.

BFL symptoms improve in the absence of the bird proteins which caused the disease. Therefore, it is advisable to remove all birds, bedding and pillows containing feathers from the house as well as washing all soft furnishings, walls, ceilings and furniture. Certain small mammals kept as pets have the same or similar proteins in their fur and feces and so should be removed. Peak flow measurements will indicate a lung condition however a spirometric test on lung capacity and patients ability to move air in and out of the lungs plus in more advanced cases an X-ray test or CT scan is available to confirm whether someone has the disease or not. Steroid inhalers similar to those used for asthma are effective or in cases where the patient finds inhaling difficult high dosages of steroids combined with bone density protecting drugs are used to treat a person with BFL, reducing the inflammation and hopefully preventing scarring. Recovery varies from patient to patient depending on what stage the condition was at when the patient consulted the doctor, the speed of diagnosis and application of the appropriate treatment to prevent residual damage to the lungs and many make a full recovery. However, BFL may reoccur when in contact with birds or other allergens.

An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g. Severe acute respiratory syndrome, HIV/AIDS) that may have evolved from a known infection (e.g. influenza) or spread to a new population (e.g. West Nile fever) or to an area undergoing ecologic transformation (e.g. Lyme disease), or be "reemerging" infections, like drug resistant tuberculosis. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics. Many emerging diseases are zoonotic - an animal reservoir incubates the organism, with only occasional transmission into human populations.

A preceding antigenic challenge can be identified in approximately two-thirds of people. Viral infections thought to induce ADEM include influenza virus, enterovirus, measles, mumps, rubella, varicella zoster, Epstein Barr virus, cytomegalovirus, herpes simplex virus, hepatitis A, and coxsackievirus; while the bacterial infections include Mycoplasma pneumoniae, Borrelia burgdorferi, Leptospira, and beta-hemolytic Streptococci. The only vaccine proven to induce ADEM is the Semple form of the rabies vaccine, but hepatitis B, pertussis, diphtheria, measles, mumps, rubella, pneumococcus, varicella, influenza, Japanese encephalitis, and polio vaccines have all been implicated. The majority of the studies that correlate vaccination with ADEM onset use small samples or case studies. Large scale epidemiological studies (e.g., of MMR vaccine or smallpox vaccine) do not show increased risk of ADEM following vaccination. In rare cases, ADEM seems to follow from organ transplantation. An upper bound for the risk of ADEM from measles vaccination, if it exists, can be estimated to be 10 per million, which is far lower than the risk of developing ADEM from an actual measles infection, which is about 1 per 1,000 cases. For a rubella infection, the risk is 1 per 5,000 cases. Some early vaccines, later shown to have been contaminated with host animal CNS tissue, had ADEM incident rates as high as 1 in 600.

Hypersensitivity pneumonitis may also be called many different names, based on the provoking antigen. These include:

Of these types, Farmer's Lung and Bird-Breeder's Lung are the most common. "Studies document 8-540 cases per 100,000 persons per year for farmers and 6000-21,000 cases per 100,000 persons per year for pigeon breeders. High attack rates are documented in sporadic outbreaks. Prevalence varies by region, climate, and farming practices. HP affects 0.4–7% of the farming population. Reported prevalence among bird fanciers is estimated to be 20-20,000 cases per 100,000 persons at risk."

Acute interstitial pneumonitis occurs most frequently among people older than forty years old. It affects men and women equally. There are no known risk factors; in particular, smoking is not associated with increased risk.