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Which of the following pathogens is most likely responsible for these symptoms?
Dr. Shoaib Ahmad Baig
January 04, 2025
🔍 Question of the day
A toddler is initially seen for fever, nasal congestion, and a sore throat. The symptoms are mild, and supportive care is advised. However, two days later, the child develops a persistent fever, harsh barking cough, difficulty breathing, and stridor, prompting a visit to the emergency department.
Which of the following pathogens is most likely responsible for these symptoms?
A. Rhinovirus
B. Paramyxovirus
C. Togavirus
D. Parvovirus
E. Calicivirus
Correct Answer 🎯: B. Paramyxovirus
⚙️
🧠 Initial Infection
Paramyxovirus (Parainfluenza virus) → Infects respiratory epithelial cells
⬇
Viral replication in respiratory mucosa
⬇
Local inflammation & cytokine release (↑ IL-1, TNF-α)
⬇
Mucosal edema and infiltration of immune cells
🧠 Edema in Subglottic Region
Subglottic narrowing (critical area of the larynx in children)
⬇
Inspiratory airflow obstruction
⬇
Stridor (high-pitched sound during inspiration)
⬇
Worsening with crying or agitation
Symptoms Explained 🔧
🧠 Systemic Symptoms
Fever, runny nose, sore throat
⬇
Viremia uncommon; symptoms localized
🧠 Brassy Cough (Seal-like)
Viral damage to vocal cords → Impaired vibration
⬇
Harsh “barking” cough typical of croup
🧠 Narrowing of the subglottic space (like squeezing a straw) 🥤
⬇
Inspiratory airflow obstruction → Stridor
Like trying to blow air through a straw while it’s partially blocked.
⚖️ Explanation of Other Differentials
Differential ⚖️ | Mechanism ⚙️ | Why Incorrect? 🔴 |
|---|---|---|
🔍 Rhinovirus | ⚙️ Infects nasal and pharyngeal mucosa, causing runny nose and mild cough. | Lacks stridor or airway narrowing. |
🔍 Togavirus | 🧠 Associated with rash diseases like rubella (German measles). • Rash > respiratory symptoms. | No airway involvement → Rule out. |
🔍 Parvovirus | 🧠 Think slapped cheeks disease. • Mainly causes a rash, anemia (in severe cases) | no significant upper airway findings. |
🔍 Calicivirus ( | ⚙️ Infects GI tract → vomiting and diarrhea | No respiratory symptoms. |
📝 Flashcards
Stay Hungry, Stay Curious!
Your Brother In This Struggle
Dr. Shoaib Ahmad
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