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Viral Respiratory Infections

Viral Respiratory Infections
Many viruses can cause multiple illnesses; the type and degree of illness often depends on host factors, including immune status and age.
Respiratory viruses often have systemic effects. Although they primarily target respiratory tissues, these effects are due to inflammation, impairment of lung function, etc.
Upper respiratory infections, specifically, are the most common infectious disease; though often self-limiting, they can have serious complications and may progress to involve the lower respiratory tract.
Respiratory viruses are transmitted in respiratory droplets, aerosols, saliva, and via the hands and other hard surfaces.
Key respiratory structures
Nasal and oral cavities are continuous with the pharynx.
Pharynx opens to the larynx; recall that the pharynx also opens to the esophagus of the digestive tract.
Trachea leads to the bronchial tree.
Lungs; bronchial tree delivers air to the sac-like alveoli.
Paranasal sinuses are spaces within the skull; they can become inflamed and sore.
Upper Respiratory Tract Infections
Common Cold
Viruses:
Rhinovirus accounts for most cases of the cold, followed by Coronavirus, Adenovirus, Respiratory syncytial virus (referred to as RSV from here on), Parainfluenza virus, and Human metapneumovirus.
These viruses invade the respiratory epithelial tissue and trigger inflammation, which produces redness and edema.
Signs and Symptoms:
Individuals with the cold typically have the following symptoms: – Congested and/or runny nose, cough, and sore throat. – Aches and pains are possible.
The common cold is self-limiting, and lasts approximately 7 to 10 days.
Fever is rare, but complications, such as sinusitis and pneumonia, can occur; complications are more likely in the elderly and others with immune deficiencies.
Pharyngitis (Sore Throat)
Viruses:
Caused by adenovirus and herpes simplex virus. It is also associated cold and flu viruses.
Signs and Symptoms:
Pharyngitis is characterized by infected and inflamed tonsils, which produces a scratchy throat and, possibly, difficulty swallowing.
Herpangina
Caused by Coxasackievirus A; it is characterized by small whitish patches spread over the upper palate and throat. This infection is most common in children.
Infections of both Upper & Lower Respiratory Tracts
Laryngotracheobronchitis (Croup)
Viruses:
Most often attributed to Parainfluenza virus, type 1, followed by RSV and Adenovirus; Influenza A and B viruses can also cause croup.
Signs and Symptoms:
Affected adults are likely to experience hoarseness.
Children are more often affected, particularly between the ages of 6 months to three years; croup is a common infection in this age group.
Croup in small children is characterized by inspiratory stridor, which produces a "squeak"-like sound, and/or tachypnea, which is often referred to as a "seal bark" cough; these are the result of swelling in the trachea, larynx, and bronchi. X-rays often show a "steeple sign" (sometimes called "wine bottle" sign), caused by subglottic narrowing of the trachea.
Influenza
Viruses:
Caused by Influenza viruses A and B;
Signs and Symptoms:
Patients experience aches and chills, with possible fever, as well as fatigue, respiratory symptoms (cough, sinus congestion), sore throat, and, especially in children, vomiting and diarrhea.
Complications, including sinusitis, pneumonia, and inflammation of key organ systems, can occur.
Lower Respiratory Tract Infections
Bronchiolitis
Most common in children under two years of age.
Viruses:
Most often caused by RSV, though rhinovirus and parainfluenza virus can also cause bronchiolitis.
Bronchiolitis occurs when the small bronchial tubes become inflamed, necrotic, and, subsequently, narrowed by mucus and debris. As a result, some alveoli collapse because air cannot be delivered to them, whereas low-oxygen air is trapped in other alveoli.
Signs and Symptoms:
Infants can experience fever, congestion or runny nose, coughing, and wheezing. Cyanosis, particularly of the lips and nail beds, can occur as the result of reduced oxygen levels.
Other signs of bronchiolitis include: rapid, shallow breathing and/or apnea, with wheezing and crackling.
Infants struggling to breath may grunt and, as a result of accessory muscle involvement, retractions may be observed – look for "sucking in" of the skin around the base of the neck as the infant struggles to bring in air.
Due to congestion and obstructed breathing, infants may also have difficulty bringing in foods and liquids, which can lead to dehydration.
Pneumonia
Infection and inflammation of the lung parenchyma.
Viruses:
Be aware that, due to antibacterial vaccines and other factors, viral causes of pneumonia are increasingly common.
Children: RSV is a significant cause of viral pneumonia in children, followed by parainfluenza and influenza viruses.
Adults: Influenza viruses are the most significant cause of viral pneumonia in adults, followed by RSV, parainfluenza viruses, adenovirus, and rhinovirus (rhinovirus-induced pneumonia is most common in elderly and/or immunocompromised individuals).
Signs and Symptoms:
Patients may experience fever, chills, and aches, as well as chest pains, shortness of breath, and rapid heart rate; sputum is often yellow or green from mucus, or even red, from blood.
Vomiting and diarrhea are possible, as is confusion.

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