Parainfluenza

Parainfluenza refers to infections caused by human parainfluenza viruses (HPIVs), a group of enveloped, single-stranded RNA viruses in the Paramyxoviridae family. There are four types, HPIV-1 through HPIV-4, that commonly infect humans and cause respiratory tract illnesses.

Transmission occurs via respiratory droplets, direct contact with contaminated surfaces, or inhalation of aerosols. After exposure, symptoms typically appear within 2 to 6 days. Infections can be confined to the upper airways or extend to the lower respiratory tract, producing conditions such as croup, bronchiolitis, pneumonia, and tracheobronchitis.

Clinical features vary by age and type. Croup characterized by a barking cough and stridor is common with HPIV-1 and HPIV-2. HPIV-3 is a frequent cause of bronchiolitis and pneumonia in infants; HPIV-4 tends to cause milder illnesses, often indistinguishable from a common cold.

Diagnosis is usually clinical, supported by laboratory testing when needed. RT-PCR or viral culture from throat or nasal swabs can identify HPIV. Most infections are self-limited.

Treatment is supportive: fluids, rest, fever reducers, and humidified air as needed. For croup, guidelines support short courses of dexamethasone and, in moderate to severe cases, nebulized epinephrine. Antibiotics are not routinely used unless bacterial co-infection is suspected. Antivirals and vaccines are not generally available; ribavirin may be considered in severe, immunocompromised cases.

Prevention relies on standard infection control measures and hand hygiene.

Epidemiology: HPIVs are a leading cause of pediatric respiratory illness worldwide. Infected adults can also experience illness, usually milder. There is no licensed vaccine as of now.