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Microbiology
Table of Contents
Unit 22 Overview: Respiratory System Infections
22.1 Anatomy and Normal Microbiota of the Respiratory Tract
22.2 Bacterial Infections of the Respiratory Tract
22.3 Viral Infections of the Respiratory Tract
22.4 Respiratory Mycoses

🦠microbiology review

22.3 Viral Infections of the Respiratory Tract

Citation:

Viral respiratory infections range from the common cold to severe influenza. These infections affect millions worldwide, causing symptoms like coughing, sneezing, and fever. Understanding their characteristics and transmission is crucial for prevention and treatment.

Influenza viruses, particularly type A, can lead to serious complications and pandemics. Other respiratory viruses, such as RSV and adenoviruses, can cause severe illness in certain populations. Some respiratory infections may even result in systemic effects, including skin rashes.

Viral Respiratory Infections

Characteristics of viral respiratory infections

  • Common cold (rhinovirus, coronavirus)
    • Symptoms include runny nose, sneezing, sore throat, cough, and mild fever
    • Self-limiting infection lasting 7-14 days
  • Influenza (influenza viruses)
    • Symptoms include high fever, chills, headache, muscle aches, cough, sore throat, and fatigue
    • Can lead to complications such as pneumonia, especially in high-risk individuals (elderly, immunocompromised)
  • Respiratory syncytial virus (RSV)
    • Most severe in infants and young children
    • Symptoms include runny nose, decreased appetite, coughing, sneezing, fever, and wheezing
  • Parainfluenza viruses
    • Cause croup in children characterized by barking cough, hoarseness, and difficulty breathing
    • In adults, symptoms resemble the common cold
  • Adenoviruses
    • Symptoms include fever, sore throat, cough, conjunctivitis (pink eye), and diarrhea
    • Can cause pneumonia in immunocompromised individuals

Comparison of influenza virus types

  • Influenza A
    • Most severe type responsible for seasonal epidemics and pandemics
    • Undergoes antigenic drift (minor changes) and antigenic shift (major changes) in surface proteins
    • Infects humans and animals (birds, pigs) allowing for genetic reassortment
    • Transmitted through respiratory droplets and contact with contaminated surfaces (viral transmission)
  • Influenza B
    • Less severe than influenza A but can still cause significant illness
    • Undergoes antigenic drift but not antigenic shift
    • Primarily infects humans
    • Transmitted through respiratory droplets and contact with contaminated surfaces
  • Influenza C
    • Mildest form rarely causing significant illness
    • Antigenically stable does not undergo antigenic drift or shift
    • Infects humans and pigs
    • Transmission is not well understood but likely similar to influenza A and B

Systemic effects of respiratory viruses

  • Some viral respiratory infections can cause systemic effects due to viremia (presence of virus in the blood)
  • Viremia allows the virus to spread to other organs and tissues including the skin
  • Examples of viral respiratory infections causing skin rashes:
    • Measles (rubeola)
      • Caused by measles virus (paramyxovirus)
      • Characteristic red maculopapular rash appearing 3-5 days after initial symptoms
    • Rubella (German measles)
      • Caused by rubella virus (togavirus)
      • Fine pink maculopapular rash starting on the face and spreading to the body
    • Varicella (chickenpox)
      • Caused by varicella-zoster virus (herpesvirus)
      • Itchy vesicular rash appearing in crops later forming scabs
  • Skin rashes can be an important diagnostic tool for identifying the causative virus in respiratory infections

Viral infection process

  • Upper respiratory tract (nose, pharynx, larynx) is often the initial site of infection
  • Lower respiratory tract (trachea, bronchi, lungs) may become involved in more severe cases
  • Incubation period varies depending on the specific virus
  • Viral replication occurs within host cells, leading to cell damage and immune response
  • Immune system activation results in inflammation and production of antibodies to fight the infection

Key Terms to Review (85)

Adenovirus: Adenovirus is a type of DNA virus that commonly causes respiratory, eye, and gastrointestinal infections. It is also used as a vector in gene therapy due to its ability to deliver genes to host cells.
Alveoli: Alveoli are tiny air sacs located in the lungs where gas exchange occurs between the air and the blood. They play a critical role in respiration by allowing oxygen to enter the bloodstream and carbon dioxide to be expelled.
Antigen drift: Antigen drift is the gradual accumulation of mutations in the genes that code for viral surface proteins, leading to changes in their antigenic properties. This process can result in new virus strains that evade the immune system.
Antigenic shift: Antigenic shift is a process in which two or more different strains of a virus, or viruses from different species, combine to form a new subtype with a mixture of surface antigens. This can lead to sudden and major changes in the virus's antigenic properties.
Bronchi: The bronchi are major air passages that branch off from the trachea into the lungs. They play a crucial role in conducting air to and from the respiratory zones of the lungs.
Cell-mediated immune response: Cell-mediated immune response is a type of immune response that does not involve antibodies but rather the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. It is crucial for defense against intracellular pathogens such as viruses and some bacteria.
Chickenpox: Chickenpox is a highly contagious viral infection caused by the varicella-zoster virus, characterized by an itchy rash and red spots or blisters. It primarily affects children but can occur in individuals of any age.
Common cold: The common cold is a viral infection primarily affecting the upper respiratory tract, characterized by symptoms such as sneezing, coughing, and a runny nose. It is most commonly caused by rhinoviruses but can also be due to other viruses like coronaviruses.
Conjunctivitis: Conjunctivitis, commonly known as pink eye, is an inflammation or infection of the conjunctiva, the transparent membrane that lines your eyelid and covers the white part of your eyeball. It can be caused by bacteria, viruses, allergens, or irritants.
Coronavirus: Coronavirus is a type of virus that primarily infects the respiratory tract, causing illnesses ranging from the common cold to more severe diseases such as COVID-19. It is characterized by its crown-like spikes on its surface.
Cytokine storm: A cytokine storm is an excessive and uncontrolled release of pro-inflammatory cytokines, often resulting from an overactive immune response. It can lead to severe inflammation and tissue damage, particularly in the respiratory system.
Cytokines: Cytokines are small proteins released by cells, especially those of the immune system, that have a specific effect on interactions and communications between cells. They play crucial roles in regulating immune responses and inflammation.
Endemic disease: An endemic disease is a disease that is consistently present within a specific geographic area or population group. It exhibits predictable patterns and does not require external factors to maintain its presence.
Encephalitis: Encephalitis is the inflammation of the brain, typically caused by viral infections. It can result in symptoms ranging from mild flu-like signs to severe neurological damage.
German measles: German measles, also known as rubella, is a contagious viral infection characterized by a red rash and mild fever. It primarily spreads through respiratory droplets and can cause serious complications in pregnant women.
Hemagglutinin protein: Hemagglutinin protein is a surface glycoprotein found on the influenza virus that facilitates viral entry into host cells. It binds to sialic acid receptors on the surface of respiratory epithelial cells to initiate infection.
Incubation period: The incubation period is the time interval between exposure to a pathogen and the appearance of the first symptoms. It is a critical phase in understanding disease transmission and prevention.
Influenza pandemic: An influenza pandemic is a global outbreak of a new influenza A virus that spreads easily from person to person, causing widespread illness. These pandemics occur when a novel virus emerges against which humans have little to no immunity.
Influenza B virus: Influenza B virus is one of the primary types of viruses responsible for causing seasonal flu in humans. Unlike Influenza A, it primarily affects humans and is less likely to cause pandemics.
Influenza C virus: Influenza C virus is a type of influenza virus that primarily infects humans and swine. It generally causes mild respiratory illness and is less common than Influenza A and B viruses.
Influenza: Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It can lead to mild to severe illness and even death in extreme cases.
Influenza virus: Influenza virus is an RNA virus that causes the contagious respiratory illness known as the flu. It primarily infects the nose, throat, and occasionally the lungs, leading to symptoms like fever, cough, and body aches.
Influenza A virus: Influenza A virus is a highly contagious virus that causes respiratory illness in humans and animals. It is known for its ability to mutate rapidly, leading to seasonal epidemics and occasional pandemics.
Influenza vaccine: The influenza vaccine is an immunization designed to protect against the influenza virus, commonly known as the flu. It stimulates the immune system to produce antibodies specific to the virus, reducing the risk of infection.
Koplik’s spots: Koplik's spots are small, white lesions with a bluish center found on the buccal mucosa. They are a pathognomonic sign of measles infection.
Live attenuated vaccine: A live attenuated vaccine uses a weakened form of the virus, which can still replicate but does not cause disease. It stimulates a strong immune response by mimicking a natural infection.
MERS: MERS (Middle East Respiratory Syndrome) is a viral respiratory illness caused by the MERS-CoV coronavirus. It leads to severe respiratory symptoms and has a high mortality rate.
MMR: MMR stands for Measles, Mumps, and Rubella, which are three highly contagious viral infections affecting the respiratory system. The MMR vaccine provides immunity against these diseases.
Orthomyxovirus: Orthomyxovirus is a family of RNA viruses that includes the influenza viruses, which cause respiratory infections in humans. These viruses are characterized by their segmented genome and ability to undergo genetic reassortment.
Oseltamivir: Oseltamivir is an antiviral medication used to treat and prevent influenza A and B. It works by inhibiting the neuraminidase enzyme, which is essential for viral replication.
Parainfluenza virus: Parainfluenza virus is a group of RNA viruses that primarily cause respiratory infections, especially in children. They are significant pathogens leading to illnesses such as croup, bronchiolitis, and pneumonia.
Peramivir: Peramivir is an antiviral drug used to treat influenza. It is a neuraminidase inhibitor that prevents the virus from spreading in the respiratory tract.
Pregnancy: Pregnancy is the condition of carrying one or more embryos or fetuses in the uterus. It typically lasts around 40 weeks from the last menstrual period to childbirth.
Respiratory syncytial virus: Respiratory Syncytial Virus (RSV) is a common respiratory virus that causes infections of the lungs and respiratory tract. It is particularly dangerous for infants, elderly adults, and immunocompromised individuals.
Reye syndrome: Reye syndrome is a rare but serious condition that causes swelling in the liver and brain. It most commonly affects children and teenagers recovering from a viral infection, often the flu or chickenpox.
Rubella: Rubella is a contagious viral infection characterized by a red rash and mild fever. It is caused by the rubella virus and can have serious consequences if contracted during pregnancy.
SARS: SARS (Severe Acute Respiratory Syndrome) is a viral respiratory illness caused by the SARS-associated coronavirus (SARS-CoV). It emerged in 2002-2003, causing a global outbreak with significant mortality and morbidity.
Sialic acid receptor: Sialic acid receptors are specific binding sites on the surface of host cells that interact with sialic acid-containing molecules. These receptors play a crucial role in the attachment and entry of certain viruses, including influenza, into host cells.
Spanish flu: Spanish flu, caused by the H1N1 influenza A virus, was a pandemic that occurred in 1918-1919. It disproportionately affected young adults and led to severe respiratory complications.
Shingles: Shingles, also known as herpes zoster, is a viral infection caused by the reactivation of the varicella-zoster virus (VZV), which also causes chickenpox. It is characterized by a painful rash that typically appears on one side of the body or face.
Syncytia: Syncytia are large, multinucleated cells formed by the fusion of individual infected cells. They are a hallmark of certain viral infections and can disrupt normal tissue function.
Teratogenic: Teratogenic refers to any agent or factor that causes malformation of an embryo or fetus. Teratogens can lead to severe congenital abnormalities and developmental issues.
Viral pneumonia: Viral pneumonia is an infection of the lungs caused by various viruses, leading to inflammation and fluid buildup in the alveoli. It often results in symptoms like cough, fever, and shortness of breath.
Varicella: Varicella, commonly known as chickenpox, is a highly contagious viral infection caused by the varicella-zoster virus (VZV). It primarily affects the respiratory tract and subsequently spreads to the skin, causing an itchy rash with red spots and blisters.
Viral neuraminidase: Viral neuraminidase is an enzyme present on the surface of influenza viruses that facilitates the release of newly formed viral particles from infected cells. It cleaves sialic acid residues, aiding in viral spread within the host.
Varicella-zoster virus: Varicella-zoster virus (VZV) is a highly contagious virus responsible for causing both varicella (chickenpox) and herpes zoster (shingles). It belongs to the Herpesviridae family and establishes lifelong latency in the host.
Viremia: Viremia is the presence of viruses in the bloodstream, which allows them to be spread throughout the body. It can lead to systemic infections and is a crucial step in the pathogenesis of many viral diseases.
Zanamivir: Zanamivir is an antiviral medication used to treat and prevent influenza A and B. It works by inhibiting the enzyme neuraminidase, which is essential for the virus's replication.
Adenoviruses: Adenoviruses are a group of DNA viruses that can infect a variety of host cells, including those in the respiratory tract. They are commonly associated with respiratory illnesses and have also been utilized in the development of gene therapy techniques.
Oseltamivir: Oseltamivir is an antiviral medication used to treat and prevent influenza (flu) infections. It works by inhibiting the activity of the neuraminidase enzyme, which is essential for the release and spread of influenza viruses within the body, thereby reducing the duration and severity of flu symptoms.
Measles: Measles is a highly contagious viral disease that primarily affects the respiratory system and can lead to serious complications. It is characterized by a distinctive red rash and is a significant public health concern globally, particularly in areas with low vaccination rates.
Immune Response: The immune response is the body's defense mechanism against foreign pathogens, such as viruses, bacteria, and other harmful microorganisms. It involves a complex network of cells, tissues, and organs that work together to recognize, neutralize, and eliminate threats to the body's health and well-being.
Incubation Period: The incubation period refers to the time between when an individual is exposed to an infectious agent and when they begin to show symptoms of the resulting disease. This period is crucial in understanding the progression and transmission of infectious diseases across various contexts.
Endemic: Endemic refers to a disease or condition that is consistently present within a specific geographic location or population. It describes a situation where a particular infectious agent or disease is native to a certain area and is maintained at a baseline level within that region.
Pandemic: A pandemic is a global outbreak of a disease that affects a large number of people across multiple countries or continents. It is characterized by the rapid and widespread transmission of an infectious agent, often a novel virus, that can lead to significant morbidity and mortality worldwide.
Cytokines: Cytokines are a diverse group of small proteins secreted by various cells, primarily immune cells, that act as signaling molecules to coordinate and regulate immune responses, inflammation, and other physiological processes. They play a crucial role in cellular defenses, pathogen recognition, inflammation, adaptive immunity, and various immune-related disorders and conditions.
Rubella: Rubella, also known as German measles, is a highly contagious viral infection that primarily affects the respiratory system. It is characterized by a red, itchy rash and can have serious complications, especially for pregnant women and their unborn babies. Rubella is a significant focus in the context of both vaccine development and viral infections of the respiratory tract.
Respiratory Syncytial Virus: Respiratory syncytial virus (RSV) is a highly contagious virus that primarily infects the respiratory tract, causing a range of illnesses from mild cold-like symptoms to severe pneumonia, especially in young children and older adults. This virus is a major focus in the context of polyclonal and monoclonal antibody production, as well as viral infections of the respiratory tract.
Conjunctivitis: Conjunctivitis is an inflammation or infection of the conjunctiva, the transparent membrane that covers the white part of the eye and the inner surface of the eyelids. It can be caused by various factors, including bacterial or viral infections, allergies, and irritants, and is commonly known as 'pink eye.'
Croup: Croup is a respiratory condition characterized by a distinctive barking cough, hoarseness, and difficulty breathing, typically caused by viral infections affecting the upper airway. It is a common childhood illness that can cause significant distress and concern for parents.
Viral Transmission: Viral transmission refers to the process by which viruses are spread and transmitted from one host to another. It is a crucial concept in understanding the epidemiology and spread of viral infections, particularly in the context of respiratory tract infections.
Alveoli: Alveoli are the tiny, air-filled sacs located at the end of the respiratory tree within the lungs. They are the primary site of gas exchange, where oxygen is taken in and carbon dioxide is expelled, and are crucial for the respiratory system's normal function and microbiota.
Pneumonia: Pneumonia is a respiratory infection that causes inflammation in the lungs, leading to the alveoli (air sacs) to fill with fluid or pus. This can make breathing difficult and impair the lungs' ability to deliver oxygen to the bloodstream effectively. Pneumonia is a serious condition that can be caused by various pathogens, including viruses, bacteria, and fungi, and can range in severity from mild to life-threatening.
Paramyxoviridae: Paramyxoviridae is a family of enveloped, negative-sense, single-stranded RNA viruses that primarily infect the respiratory tract. These viruses are known for their ability to cause significant respiratory illnesses in both humans and animals.
Orthomyxoviridae: Orthomyxoviridae is a family of viruses that primarily infect the respiratory tract, causing diseases such as influenza. These viruses have a segmented, single-stranded, negative-sense RNA genome and are known for their ability to undergo frequent genetic changes, leading to the emergence of new viral strains.
Influenza Viruses: Influenza viruses are a group of RNA viruses that primarily infect the respiratory tract and cause the common illness known as the flu. These viruses are responsible for seasonal outbreaks and occasional global pandemics that can have significant public health implications.
Upper Respiratory Tract: The upper respiratory tract refers to the anatomical region of the respiratory system that includes the nose, nasal cavity, paranasal sinuses, pharynx, and larynx. This area is responsible for the initial processing and filtering of inhaled air before it reaches the lower respiratory tract.
Coronavirus: Coronavirus is a type of virus that primarily infects the respiratory tract, causing a range of illnesses from the common cold to more severe diseases like COVID-19. These viruses are named for the crown-like spikes on their surface, which give them a distinctive appearance under a microscope.
Varicella: Varicella, commonly known as chickenpox, is a highly contagious viral infection caused by the varicella-zoster virus (VZV). It primarily affects the respiratory tract and causes a characteristic itchy, blister-like rash that can spread throughout the body.
Zanamivir: Zanamivir is an antiviral medication used to treat and prevent influenza (flu) infections. It works by inhibiting the neuraminidase enzyme, which is essential for the influenza virus to replicate and spread within the body, making it an important tool in managing viral infections of the respiratory tract.
Lower Respiratory Tract: The lower respiratory tract refers to the portion of the respiratory system that includes the trachea, bronchi, bronchioles, and alveoli. This region is responsible for the exchange of gases, primarily the intake of oxygen and the removal of carbon dioxide, which is essential for sustaining life.
Laryngitis: Laryngitis is a condition characterized by inflammation of the larynx, the part of the throat that contains the vocal cords. This inflammation can lead to hoarseness, a raspy voice, and difficulty speaking or swallowing.
Rhinitis: Rhinitis is a condition characterized by inflammation and irritation of the nasal passages, often resulting in symptoms such as nasal congestion, runny nose, and sneezing. It is a common occurrence in the context of viral infections affecting the respiratory tract.
Viral Culture: Viral culture is the process of growing and propagating viruses in living cells or tissues, which is essential for the diagnosis, research, and understanding of viral infections. It involves isolating and cultivating viruses in a controlled laboratory environment to study their characteristics, replication, and interactions with host cells.
Viral Replication: Viral replication is the process by which a virus makes copies of itself inside the host cell. It is a complex multi-step process that is essential for the propagation and spread of viruses, including those that infect the respiratory tract.
Dyspnea: Dyspnea is the medical term for shortness of breath or difficulty breathing. It is a common symptom that can occur in various respiratory tract infections, including those caused by viruses.
Parainfluenza Viruses: Parainfluenza viruses are a group of RNA viruses that primarily cause respiratory tract infections, particularly in young children. These viruses are closely related to but distinct from the influenza viruses, hence the name 'parainfluenza'.
Bronchi: The bronchi are the primary airway branches that extend from the trachea and carry air into and out of the lungs. They are a critical component of the respiratory system, playing a vital role in both the anatomy and function of the respiratory tract.
Viremia: Viremia refers to the presence of virus particles in the bloodstream. It is a crucial aspect of viral infections, as it allows the virus to circulate and potentially infect various tissues and organs throughout the body.
Wheezing: Wheezing is a high-pitched whistling sound that occurs during breathing, often as a result of obstruction or inflammation in the airways. It is a common symptom associated with various respiratory conditions, particularly those affecting the lungs and bronchial tubes.
Interferons: Interferons are a group of signaling proteins produced by the body's cells in response to the presence of pathogens, such as viruses, bacteria, and parasites. They play a crucial role in the immune system's defense against viral infections, including those that affect the respiratory tract.
PCR (Polymerase Chain Reaction): PCR, or Polymerase Chain Reaction, is a powerful molecular biology technique used to amplify specific DNA sequences exponentially. It is a fundamental tool employed across various fields, including microbiology, genetics, forensics, and diagnostics, to study and detect the presence of genetic material from a wide range of organisms, including prokaryotes, viruses, fungi, and protozoa.
Antigenic Drift: Antigenic drift is a gradual, continuous process of genetic changes that occur in the surface proteins of viruses, particularly influenza viruses, leading to the emergence of new viral strains. This evolutionary mechanism allows the virus to evade the host's immune system and cause recurring infections.
Rhinovirus: Rhinoviruses are a group of small, non-enveloped RNA viruses that are the primary causative agents of the common cold. They are closely associated with infections of the upper respiratory tract and play a significant role in viral infections discussed in the context of the anatomy and normal microbiota of the respiratory tract, as well as viral infections of the respiratory tract.
Antigenic Shift: Antigenic shift is a major, abrupt, and unexpected change in the surface antigens of a virus, particularly in influenza viruses. This phenomenon results in the emergence of a new viral strain that is significantly different from previous strains, often leading to the potential for widespread outbreaks and pandemics.