Viral Respiratory Tract Infections

Which virus is the most common cause of the common cold?

Rhinovirus

What family does the rhinovirus belong to?

Picornaviridae

Name a non-enveloped, +ssRNA virus that replicates best at 33-35°C in the upper respiratory tract

Rhinovirus

What receptor does rhinovirus use to enter host cells?

ICAM-1

Why is vaccine development difficult for rhinovirus?

Because it has over 100 serotypes with high antigenic variability.

How is rhinovirus primarily transmitted?

By aerosols and direct contact, including contaminated hands and fomites

Which symptoms are typical of rhinovirus infection?

Nasal congestion, rhinorrhea, sneezing, sore throat, and mild cough; fever is usually absent or low-grade

Rhinovirus replicates best at 33-35°C. What clinical relevance does this have?

It explains why it mainly infects the upper respiratory tract and rarely causes lower respiratory infections

How is rhinovirus infection usually diagnosed?

Clinically, based on symptoms; lab tests like PCR are not routinely needed

What is the mainstay of treatment for infections caused by rhinovirus?

Supportive care including hydration, rest, and symptom relief

Which immune response is most important in controlling rhinovirus infection?

Innate immunity, particularly interferon production

Name a virus from the Picornaviridae family that causes common cold symptoms but does not have a vaccine

Rhinovirus

What family does adenovirus belong to?

Adenoviridae

Which virus is a non-enveloped, double-stranded DNA virus that can cause respiratory illness, conjunctivitis, and gastroenteritis?

Adenovirus

Which virus can cause pharyngoconjunctival fever, especially in children and young adults?

Adenovirus

What type of genome does adenovirus have?

dsDNA

How is adenovirus primarily transmitted?

Respiratory droplets, fecal-oral route, and direct contact with contaminated surfaces

Which virus can cause outbreaks in close-contact settings such as military recruits and daycare centers?

Adenovirus

Which receptor does adenovirus use to enter host cells?

Coxsackie-adenovirus receptor (CAR)

Adenovirus can cause epidemic keratoconjunctivitis. What does this mean?

It is a highly contagious eye infection causing conjunctivitis

Is there a vaccine available for adenovirus? If yes, who is it used for?

Yes, a live oral vaccine is available for military recruits to prevent respiratory disease caused by adenovirus types 4 and 7

What is the typical clinical presentation of adenovirus respiratory infection?

Fever, sore throat, cough, and sometimes pneumonia

How is adenovirus infection diagnosed?

PCR, viral culture, or antigen detection from respiratory secretions or stool

What is the treatment for adenovirus infections?

Supportive care; no specific antiviral therapy is routinely used

What family do coronaviruses belong to?

Coronaviridae

Which type of genome do coronaviruses have?

Positive-sense single-stranded RNA

Name a virus family characterized by enveloped viruses with spike proteins forming a crown-like appearance under electron microscopy

Coronaviruses

Which coronavirus caused the SARS outbreak in 2002-2003?

SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus)

Which coronavirus caused the COVID-19 pandemic?

SARS-CoV-2

How are coronaviruses primarily transmitted?

Respiratory droplets, aerosols, and fomites

What receptor does SARS-CoV-2 use to enter host cells?

ACE2 (Angiotensin-converting enzyme 2)

Which symptoms are common in coronavirus infections?

Fever, cough, shortness of breath, fatigue; can range from mild cold-like symptoms to severe pneumonia

Which human coronaviruses usually cause mild upper respiratory infections, like the common cold?

HCoV-229E, HCoV-NL63, HCoV-OC43, and HCoV-HKU1

How is coronavirus infection diagnosed?

RT-PCR from respiratory specimens

What treatments are available for coronavirus infections?

Supportive care for mild disease; antivirals, corticosteroids, and monoclonal antibodies for severe COVID-19

Are vaccines available for coronaviruses?

Yes, vaccines are available for SARS-CoV-2 (COVID-19)

What family does the influenza virus belong to?

Orthomyxoviridae

What type of genome does influenza virus have?

-ssRNA, segmented

Which influenza virus proteins are responsible for viral entry and release from host cells?

Hemagglutinin (HA) for entry and Neuraminidase (NA) for release

What is the main difference between influenza A and B viruses?

Influenza A infects humans and many animals and causes pandemics

Influenza B primarily infects humans and causes seasonal outbreaks.

Which influenza virus subtype caused the 1918 Spanish flu pandemic?

H1N1

How does antigenic shift differ from antigenic drift in influenza viruses?

Antigenic shift is a major change due to reassortment of genome segments; antigenic drift is minor point mutations over time

How is influenza primarily transmitted?

Respiratory droplets and aerosols

Which clinical symptoms are typical of influenza infection?

Fever, chills, cough, myalgia, headache, and fatigue

How is influenza diagnosed?

Rapid antigen tests, PCR from respiratory specimens, or viral culture

What is the mainstay of treatment for influenza?

Supportive care and antivirals like oseltamivir, zanamivir

Who should receive the annual influenza vaccine?

Everyone older than 6 months, especially high-risk groups (elderly, children, pregnant women, chronic illness)

Why do influenza vaccines need to be updated annually?

Because of antigenic drift causing changes in HA and NA proteins

What family does parainfluenza virus belong to?

Paramyxoviridae

What type of genome does parainfluenza virus have?

-ssRNA

Which respiratory tract diseases are commonly caused by parainfluenza viruses?

Croup (laryngotracheobronchitis), bronchiolitis, and pneumonia

How many major types of human parainfluenza viruses are there?

4

Which parainfluenza virus type is most commonly associated with croup?

1

How is parainfluenza virus primarily transmitted?

Respiratory droplets and direct contact

What is a characteristic clinical feature of croup caused by parainfluenza virus?

Barking cough and inspiratory stridor

Does parainfluenza virus have an envelope?

Yes, it is an enveloped virus

Which viral surface proteins are important for parainfluenza virus infectivity?

Hemagglutinin-neuraminidase (HN) and fusion (F) proteins

How is parainfluenza virus infection diagnosed?

PCR or viral culture from respiratory secretions

What is the treatment for parainfluenza virus infections?

Supportive care (humidified air, hydration); no specific antiviral treatment

Can parainfluenza virus cause disease in adults?

Yes, especially in immunocompromised patients and elderly

What family does Respiratory Syncytial Virus (RSV) belong to?

Paramyxoviridae

What type of genome does RSV have?

-ssRNA

Is RSV an enveloped virus?

Yes

What age group is most commonly affected by severe RSV infection?

Infants under 2 years old.

Which respiratory diseases are typically caused by RSV in infants?

Bronchiolitis and pneumonia

How is RSV transmitted?

Respiratory droplets and direct contact with contaminated surfaces

What is the characteristic histopathological finding in RSV infection?

Syncytia (multinucleated giant cells) formation

Which viral surface proteins are important for RSV entry and fusion?

Fusion (F) protein and attachment (G) protein

How is RSV infection diagnosed?

PCR, antigen detection, or viral culture from respiratory secretions

What is the primary treatment for RSV infection?

Supportive care, including oxygen and hydration

Is there a vaccine available for RSV?

No widely used vaccine yet, but monoclonal antibody prophylaxis (palivizumab) is available for high-risk infants

Can RSV cause reinfection throughout life?

Yes, reinfections are common but usually milder in older children and adults

A 25-year-old woman presents with a 2-day history of nasal congestion, sneezing, sore throat, and mild cough. She reports no fever or systemic symptoms. The symptoms began after she spent time in a crowded indoor event during a cool day. On exam, her nasal mucosa is inflamed but lungs are clear. No lab tests are done.

Key points:

Most common cause of the common cold

Non-enveloped, positive-sense ssRNA virus (Picornaviridae)

Replicates best at 33-35°C (upper respiratory tract)

Transmitted via aerosols and direct contact

No vaccine or antiviral treatment; supportive care only

Rhinovirus

A 10-year-old boy develops fever, sore throat, conjunctivitis with red eyes, and mild diarrhea. He attends a day camp where several kids have similar symptoms. Physical exam reveals pharyngitis and conjunctival injection. PCR testing from a throat swab confirms a DNA virus.

Key points:

Non-enveloped, double-stranded DNA virus (Adenoviridae)

Causes respiratory illness, conjunctivitis, and gastroenteritis

Transmitted via respiratory droplets, fecal-oral route, and contact

Pharyngoconjunctival fever is a classic syndrome

Live oral vaccine exists for military recruits (types 4 & 7)

Adenovirus

A 40-year-old man presents with fever, dry cough, fatigue, and shortness of breath. Symptoms started 5 days ago after traveling to an area with recent viral outbreaks. Chest X-ray shows bilateral infiltrates. Nasopharyngeal PCR confirms a positive-sense RNA virus with spike proteins.

Key points:

Enveloped, positive-sense ssRNA virus (Coronaviridae)

Causes mild URIs to severe pneumonia (e.g., SARS, MERS, COVID-19)

Transmitted by respiratory droplets and aerosols

Uses ACE2 receptor (SARS-CoV-2) for cell entry

Diagnosed by RT-PCR; vaccines available for SARS-CoV-2

Coronavirus

A 65-year-old woman with diabetes presents in winter with abrupt onset of high fever, chills, myalgia, headache, and dry cough. Her unvaccinated status and the recent local outbreak raise suspicion. Rapid antigen testing confirms a segmented RNA virus infection.

Key points:

Enveloped, negative-sense segmented ssRNA virus (Orthomyxoviridae)

Hemagglutinin (HA) and Neuraminidase (NA) are key surface proteins

Causes seasonal flu with systemic symptoms

Transmitted by respiratory droplets

Annual vaccine needed due to antigenic drift; antivirals available

Influenza virus

A 2-year-old boy presents with a barking cough, hoarseness, and inspiratory stridor worsening at night. His mother notes a preceding runny nose and low-grade fever. He attends daycare where several children had similar symptoms. PCR confirms a negative-sense RNA virus.

Key points:

Enveloped, negative-sense ssRNA virus (Paramyxoviridae)

Causes croup (laryngotracheobronchitis), bronchiolitis, pneumonia

Type 1 is most commonly linked to croup

Transmitted via respiratory droplets and contact

Supportive treatment; no specific antivirals

Parainfluenza VIrus

A 6-month-old infant is brought to the emergency room with wheezing, cough, and difficulty breathing. The infant had mild upper respiratory symptoms 3 days ago. On exam, subcostal retractions and diffuse wheezes are noted. RSV antigen test is positive.

Key points:

Enveloped, negative-sense ssRNA virus (Paramyxoviridae)

Most severe in infants <2 years, causing bronchiolitis and pneumonia

Causes syncytia formation in infected cells

Transmitted by droplets and contact with fomites

Supportive care; palivizumab for high-risk infants

Respiratory Syncytial Virus