Viral pneumonia
Encyclopedia
Viral pneumonia is a pneumonia
caused by a virus
.
Viruses are one of the two major causes of pneumonia, the other being bacteria
; less common causes are fungi and parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.
s of viral pneumonia include fever
, non-productive cough
, running nose, and systemic symptoms (e.g. myalgia
, headache
). Different viruses cause different symptoms.
Rarer viruses that commonly result in pneumonia include:
Viruses that primarily cause other diseases, but sometimes cause pneumonia include:
The most commonly identified agents in children are respiratory syncytial virus, rhinovirus
, human metapneumovirus, human bocavirus
, and parainfluenza viruses.
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 cell
s, in particular lymphocyte
s, are responsible for activating a variety of chemicals (cytokine
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
s and can lead to illness affecting many different bodily functions. Viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral pneumonia.
, influenza, chickenpox, herpes zoster
, measles
, rubella
, and SARS.
or zanamivir. Respiratory syncytial virus
(RSV) may be treated with ribavirin
. Herpes simplex virus
and varicella-zoster virus infections are usually treated with aciclovir
, whilst ganciclovir
is used to treat cytomegalovirus
. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, adenovirus, hantavirus
, parainfluenza or H1N1
virus ; treatment is largely supportive.
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
caused by a virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
.
Viruses are one of the two major causes of pneumonia, the other being bacteria
Bacterial pneumonia
Bacterial pneumonia is a type of pneumonia caused by bacterial infection.-Sign and symptoms:*Fever*Rigors*Cough*Dyspnea*Chest pain*Pneumococcal pneumonia can cause Hemoptysis-Gram positive:...
; less common causes are fungi and parasites. Viruses are the most common cause of pneumonia in children, while in adults bacteria are a more common cause.
Signs and symptoms
SymptomSymptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s of viral pneumonia include fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, non-productive cough
Cough
A cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...
, running nose, and systemic symptoms (e.g. myalgia
Myalgia
Myalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections...
, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
). Different viruses cause different symptoms.
Cause
Common causes of viral pneumonia are:- Influenza virus A and B
- Respiratory syncytial virusHuman respiratory syncytial virusHuman respiratory syncytial virus is a virus that causes respiratory tract infections. It is the major cause of lower respiratory tract infections and hospital visits during infancy and childhood. A prophylactic medication exists for preterm birth infants and infants with a congenital heart...
(RSV) - Human parainfluenza virusesHuman parainfluenza virusesHuman parainfluenza viruses are a group of four distinct serotypes of enveloped single-stranded RNA viruses belonging to the paramyxovirus family.Parainfluenza viruses can be detected via cell culture, immunofluorescent microscopy, and PCR....
(in children)
Rarer viruses that commonly result in pneumonia include:
- Adenoviruses (in military recruits)
- MetapneumovirusMetapneumovirusHuman metapneumovirus is a negative single-stranded RNA virus of the family Paramyxoviridae and is closely related to the avian metapneumovirus subgroup C. It was isolated for the first time in 2001 in the Netherlands by using the RAP-PCR technique for identification of unknown viruses growing...
- Severe acute respiratory syndrome virusSevere acute respiratory syndromeSevere Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...
(SARS coronavirus)
Viruses that primarily cause other diseases, but sometimes cause pneumonia include:
- Herpes simplex virusHerpes simplex virusHerpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
(HSV), mainly in newborns - Varicella-zoster virus (VZV)
- Measles virusMeaslesMeasles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
- Rubella virusRubella virusRubella virus is the pathogenic agent of the disease Rubella, and is the cause of congenital rubella syndrome when infection occurs during the first weeks of lunacy.Humans are the only known host of this virus....
- CytomegalovirusCytomegalovirusCytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...
(CMV), mainly in people with immune system problems
The most commonly identified agents in children are respiratory syncytial virus, rhinovirus
Rhinovirus
Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose...
, human metapneumovirus, human bocavirus
Bocavirus
Bocavirus is a genus in the family Parvoviridae, subfamily Parvovirinae.The type species is bovine bocavirus.-Genome:Like the other members of this family bocaviuses have two open reading frames - ORF1 and 2. Uniquely among parvoviruses, the bocaviruses they contain a third open reading frame...
, and parainfluenza viruses.
Pathophysiology
Viruses must invade cells in order to reproduce. Typically, a virus will reach the lungs by traveling in droplets through the mouthMouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
and nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
with inhalation
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
. 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
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
.
Further damage to the lungs occurs when the immune system responds to the infection. White blood cell
White blood cell
White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...
s, in particular lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s, are responsible for activating a variety of chemicals (cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
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 (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
s and can lead to illness affecting many different bodily functions. 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 pneuonia is vaccination against adenovirusAdenovirus vaccine
An adenovirus vaccine is a vaccine against Adenovirus.It was used by the United States military from 1971 to 1999, but was discontinued when the only manufacturer stopped production. This vaccine elicited immunity to serotypes 4 and 7. On March 16, 2011, the U.S. Food and Drug Administration...
, influenza, chickenpox, herpes zoster
Varicella vaccine
The varicella vaccine is a live virus that protects against the viral disease commonly known as chickenpox caused by Varicella Zoster Virus . Varicella vaccine is marketed as Varivax in the U.S. by Merck...
, measles
Measles vaccine
Measles vaccine is a highly effective vaccine used against measles. The measles-mumps-rubella-varicella combo vaccine has been available since 2005...
, rubella
Rubella vaccine
Rubella vaccine is a vaccine used against rubella.One form is called "Meruvax"....
, and SARS.
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 oseltamivirOseltamivir
Oseltamivir INN , an antiviral drug, slows the spread of influenza virus between cells in the body by stopping the virus from chemically cutting ties with its host cell; median time to symptom alleviation is reduced by 0.5–1 day. The drug is sold under the trade name Tamiflu, and is taken orally...
or zanamivir. Respiratory syncytial virus
Human respiratory syncytial virus
Human respiratory syncytial virus is a virus that causes respiratory tract infections. It is the major cause of lower respiratory tract infections and hospital visits during infancy and childhood. A prophylactic medication exists for preterm birth infants and infants with a congenital heart...
(RSV) may be treated with ribavirin
Ribavirin
Ribavirin is an anti-viral drug indicated for severe RSV infection , hepatitis C infection and other viral infections. Ribavirin is a prodrug, which when metabolised resembles purine RNA nucleotides...
. Herpes simplex virus
Herpes simplex virus
Herpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
and varicella-zoster virus infections are usually treated with aciclovir
Aciclovir
Aciclovir or acyclovir , chemical name acycloguanosine, abbreviated as ACV,is a guanosine analogue antiviral drug, marketed under trade names such as Cyclovir, Herpex, Acivir, Acivirax, Zovirax, and Zovir...
, whilst ganciclovir
Ganciclovir
Ganciclovir INN is an antiviral medication used to treat or prevent cytomegalovirus infections.Ganciclovir sodium is marketed under the trade names Cytovene and Cymevene . Ganciclovir for ocular use is marketed under the trade name Vitrasert...
is used to treat cytomegalovirus
Cytomegalovirus
Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...
. There is no known efficacious treatment for pneumonia caused by SARS coronavirus, adenovirus, hantavirus
Hantavirus
Hantaviruses are negative sense RNA viruses in the Bunyaviridae family. Humans may be infected with hantaviruses through rodent bites, urine, saliva or contact with rodent waste products...
, parainfluenza or H1N1
Swine flu
Swine influenza, also called pig influenza, swine flu, hog flu and pig flu, is an infection by any one of several types of swine influenza virus. Swine influenza virus or S-OIV is any strain of the influenza family of viruses that is endemic in pigs...
virus ; treatment is largely supportive.