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Viral pneumonia is a
pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severit ...
caused by a
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...
. Pneumonia is an infection that causes inflammation in one or both of the lungs. The
pulmonary alveoli A pulmonary alveolus (plural: alveoli, from Latin ''alveolus'', "little cavity"), also known as an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where oxygen is exchanged for carbon dioxide. Al ...
fill with fluid or pus making it difficult to breathe. Pneumonia can be caused by
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
, viruses, fungi or parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.


Signs and symptoms

Symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...
s of viral pneumonia include
fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...
, non-productive
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...
,
runny nose Rhinorrhea, rhinorrhoea, or informally runny nose is the free discharge of a thin mucus fluid from the nose; it is a common condition. It is a common symptom of allergies ( hay fever) or certain viral infections, such as the common cold or COV ...
, and systemic symptoms (e.g.
myalgia Myalgia (also called muscle pain and muscle ache in layman's terms) is the medical term for muscle pain. Myalgia is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another li ...
,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
). Different viruses cause different symptoms.


Diagnosis

Diagnosis, like with any infection, relies on the detection of the infectious cause. With viral pneumonia, samples are taken from the upper and/or lower respiratory tracts. The samples can then be run through
polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...
(PCR), allowing for amplification of the virus as that allows better detection if present in the sample. Other ways for a diagnosis to be obtained is by ordering a
chest x-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in me ...
, blood tests,
pulse oximetry Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading o ...
, and a medical/family history to see if there are any known risks or previous exposures to a person with viral pneumonia. If the person is in serious condition and in the hospital there are more invasive studies that can be run to diagnosis the person.


Cause

Common causes of viral pneumonia are: * ''
Influenza virus ''Orthomyxoviridae'' (from Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' 'mucus') is a family of negative-sense RNA viruses. It includes seven genera: ''Alphainfluenzavirus'', ''Betainfluenzavirus'', '' Gammainfluenzavirus'', ' ...
'' A and B * ''
Respiratory syncytial virus Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a common, contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus. ...
'' (RSV) * ''
Human parainfluenza viruses Human parainfluenza viruses (HPIVs) are the viruses that cause human parainfluenza. HPIVs are a paraphyletic group of four distinct single-stranded RNA viruses belonging to the '' Paramyxoviridae'' family. These viruses are closely associated wit ...
'' (in children)Table 13-7 in: 8th edition. *''
Severe acute respiratory syndrome coronavirus 2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...
'' (SARS-CoV-2) Rarer viruses that commonly result in pneumonia include: * ''
Adenovirus Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...
es'' (in military recruits) * ''
Metapneumovirus ''Metapneumovirus'' is a genus of viruses in the family ''Pneumoviridae''. The genus contains two species: * Avian metapneumovirus Avian metapneumovirus (aMPV), also known as turkey rhinotracheitis or swollen head syndrome, causes a variety o ...
'' * ''Severe acute respiratory syndrome coronavirus'' (SARS-CoV) * ''Middle East respiratory syndrome virus'' (MERS-CoV) * ''
Hantavirus ''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA viruses in the family '' Hantaviridae'' within the order ''Bunyavirales''. Members of this genus may be called orthohantaviruses or simply hantaviruses. Orthohantav ...
es'' Viruses that primarily cause other diseases, but sometimes cause pneumonia include: * ''
Herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names '' Human alphaherpesvirus 1'' and ''Human alphaherpesvirus 2'', are two members of the human ''Herpesviridae'' family, a set of viruses that produce viral in ...
'' (HSV), mainly in newborns or young children * ''
Varicella-zoster virus Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chil ...
'' (VZV) * ''
Measles virus ''Measles morbillivirus'' (MeV), also called measles virus (MV), is a single-stranded, negative-sense, enveloped, non-segmented RNA virus of the genus '' Morbillivirus'' within the family '' Paramyxoviridae''. It is the cause of measles. Human ...
'' * '' Rubella virus'' * ''
Cytomegalovirus ''Cytomegalovirus'' (''CMV'') (from ''cyto-'' 'cell' via Greek - 'container' + 'big, megalo-' + -''virus'' via Latin 'poison') is a genus of viruses in the order '' Herpesvirales'', in the family '' Herpesviridae'', in the subfamily '' Betah ...
'' (CMV), mainly in people with immune system problems * ''
Smallpox virus Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
'' *''
Dengue virus ''Dengue virus'' (DENV) is the cause of dengue fever. It is a mosquito-borne, single positive-stranded RNA virus of the family '' Flaviviridae''; genus '' Flavivirus''. Four serotypes of the virus have been found, a reported fifth has yet to ...
'' The most commonly identified agents in children are ''respiratory syncytial virus'', '' rhinovirus'', ''human metapneumovirus'', ''human
bocavirus ''Bocaparvovirus'' is a genus of viruses in the subfamily ''Parvovirinae'' of the virus family ''Parvoviridae''. Humans, cattle, and dogs serve as natural hosts. There are 28 species in this genus. Diseases associated with this genus include, in ...
'', 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 Hobart Ansteth Reimann (1897–1986) was an American virologist and physician. Reimann made contributions to medicine with his 1938 landmark article on atypical pneumonia (the "first description of virus pneumonia"); and articles on periodic ...
in 1938, in an article published by
JAMA ''The Journal of the American Medical Association'' (''JAMA'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of biom ...
, ''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 Thomas Jefferson University is a private research university in Philadelphia, Pennsylvania. Established in its earliest form in 1824, the university officially combined with Philadelphia University in 2017. To signify its heritage, the un ...
, 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 In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
and
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passe ...
with
inhalation Inhalation (or Inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
. There, the virus invades the cells lining the airways and the
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
. This invasion often leads to cell death either through direct killing by the virus or by self-destruction through
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes ( morphology) and death. These changes in ...
. Further damage to the lungs occurs when the immune system responds to the infection.
White blood cell White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
s, in particular
lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...
s, are responsible for activating a variety of chemicals (
cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...
s) 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
organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...
s 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 Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptom ...
, chickenpox (varicella zoster),
herpes zoster Shingles, also known as zoster or herpes zoster, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or fac ...
,
measles Measles is a highly contagious infectious disease caused by measles virus. Symptoms usually develop 10–12 days after exposure to an infected person and last 7–10 days. Initial symptoms typically include fever, often greater than , cough, ...
, respiratory syncytial virus vaccine (RSV),
rubella Rubella, also known as German measles or three-day measles, is an infection caused by the rubella virus. This disease is often mild, with half of people not realizing that they are infected. A rash may start around two weeks after exposure and ...
, and
adenovirus Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...
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 Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
, or
peramivir Peramivir (trade name Rapivab) is an antiviral drug developed by BioCryst Pharmaceuticals for the treatment of influenza. Peramivir is a neuraminidase inhibitor, acting as a transition-state analogue inhibitor of influenza neuraminidase and th ...
.
Respiratory syncytial virus Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a common, contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus. ...
(RSV) has no direct acting treatments, but
ribavirin Ribavirin, also known as tribavirin, is an antiviral medication used to treat RSV infection, hepatitis C and some viral hemorrhagic fevers. For hepatitis C, it is used in combination with other medications such as simeprevir, sofosbuvir, pe ...
is indicated for severe cases.
Ribavirin Ribavirin, also known as tribavirin, is an antiviral medication used to treat RSV infection, hepatitis C and some viral hemorrhagic fevers. For hepatitis C, it is used in combination with other medications such as simeprevir, sofosbuvir, pe ...
has also been known to be used as a treatment for Parainfluenza Virus, and
Adenovirus Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...
.
Herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names '' Human alphaherpesvirus 1'' and ''Human alphaherpesvirus 2'', are two members of the human ''Herpesviridae'' family, a set of viruses that produce viral in ...
and
varicella-zoster virus Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chil ...
infections are usually treated with
acyclovir Aciclovir (ACV), also known as acyclovir, is an antiviral medication. It is primarily used for the treatment of herpes simplex virus infections, chickenpox, and shingles. Other uses include prevention of cytomegalovirus infections following t ...
, whilst
ganciclovir Ganciclovir, sold under the brand name Cytovene among others, is an antiviral medication used to treat cytomegalovirus (CMV) infections. Ganciclovir was patented in 1980 and approved for medical use in 1988. Medical use Ganciclovir is indicated ...
is used to treat
cytomegalovirus ''Cytomegalovirus'' (''CMV'') (from ''cyto-'' 'cell' via Greek - 'container' + 'big, megalo-' + -''virus'' via Latin 'poison') is a genus of viruses in the order '' Herpesvirales'', in the family '' Herpesviridae'', in the subfamily '' Betah ...
. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, MERS coronavirus, or
hantavirus ''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA viruses in the family '' Hantaviridae'' within the order ''Bunyavirales''. Members of this genus may be called orthohantaviruses or simply hantaviruses. Orthohantav ...
. 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


External links

{{DEFAULTSORT:Viral Pneumonia Pneumonia