A young adult presenting with swelling of the parotid glands is likely suffering from which disease?

Swelling of the parotid glands is a hallmark sign of mumps, which is a viral infection caused by the mumps virus. This condition typically presents with parotitis, characterized by painful swelling of one or both parotid glands, often accompanied by fever, fatigue, and malaise.

The mumps virus primarily targets the salivary glands, leading to their inflammation. The presentation aligns with mumps being predominantly recognized for this symptom, especially in children and young adults who are unvaccinated or under-vaccinated. Given the context of the question and the specific symptom of parotid gland swelling, mumps is the most relevant diagnosis.

Other options are less likely to be associated with parotid swelling. Rubella generally presents with a rash and mild lymphadenopathy, and congenital rubella syndrome involves a range of congenital anomalies rather than parotid swelling. Measles does not typically involve salivary gland swelling and is characterized more by its distinctive rash and systemic symptoms.