Mumps, also known as epidemic parotitis, is an acute respiratory infectious disease caused by the mumps virus. It is clinically characterized by non-suppurative inflammation of the parotid glands, leading to swelling and pain in the parotid region. Other salivary glands, various glandular tissues, and the nervous system may also be involved.
Etiology
The mumps virus is a single-stranded RNA virus belonging to the genus Rubulavirus in the family Paramyxoviridae. Its antigenic structure is stable, and there is only one serotype. The virus particles are spherical, with varying sizes of approximately 100–200 nm, and possess an envelope. The surface of the virus contains two key components, hemagglutinin-neuraminidase protein and fusion protein, both of which play a crucial role in viral virulence. This virus is sensitive to physical and chemical factors, and agents such as lysol and formalin can inactivate it within 2–5 minutes. It also loses viability under ultraviolet radiation or heating to 56°C for 20 minutes.
Epidemiology
Patients and asymptomatic carriers act as the sources of infection. Viral shedding in saliva begins 7 days before parotid gland swelling and continues until 9 days after the swelling onset. Transmission occurs primarily through airborne droplets or direct contact. Cases can occur year-round, with a peak incidence in winter and spring.
Pathogenesis
The virus enters the body via the mouth and nose and replicates in the epithelial and lymphoid tissues of the upper respiratory tract, triggering localized inflammation and immune responses. It then enters the bloodstream, causing viremia, and spreads to the parotid glands and other organ systems. The virus may also reach the parotid glands through the salivary duct. After infecting monocytes, it can invade the central nervous system via the choroid plexus, where it replicates in the choroid plexus and ependymal cells. Infected cells may shed into the cerebrospinal fluid, leading to meningoencephalitis. Specific IgM antibodies begin to appear by the second day of illness and persist for approximately 3 months. Specific IgG antibodies are detectable by the end of the first week, peak after 3 weeks, and provide lifelong immunity. The mumps virus also induces cell-mediated immune responses.
Pathology
The hallmark pathological feature is non-suppurative inflammation in affected glands, with congestion, edema, pinpoint hemorrhage, lymphocytic infiltration, and necrosis of glandular cells. Swelling of ductal cells within the affected glands and accumulation of necrotic cells and exudate within ductal lumens obstruct glandular secretion. Increased levels of amylase in saliva enter the bloodstream via the lymphatic system, leading to elevated blood and urinary amylase levels. In cases of meningoencephalitis, degenerative or necrotic brain cells and inflammatory cell infiltration are observed.
Clinical Manifestations
The incubation period ranges from 12 to 25 days, with an average of 18 days. Initial symptoms are often nonspecific, including headache, fatigue, and fever, followed by swelling and pain of the parotid glands. The parotid gland progressively enlarges, creating a saddle-shaped swelling centered around the earlobe and accompanied by hypersensitivity, distension pain, and mild tenderness. Redness and swelling may be observed at the opening of the parotid duct.
Unilateral parotid swelling typically occurs first, with the other side becoming involved within a few days. The swelling generally subsides within 4–5 days, and the entire process lasts about 6–10 days. Other salivary glands, such as the submandibular glands, may also enlarge. Patients may experience varying degrees of fever, typically lasting 3–7 days. Approximately 20% of patients maintain a normal body temperature throughout the illness.
Due to the tropism of the mumps virus for glandular and nervous tissues, complications involving the central nervous system, other glands, and organs may occur.
Meningoencephalitis
Meningoencephalitis is the most common complication in children and often occurs during the peak of mumps. Clinical signs include fever, headache, vomiting, neck stiffness, and positive Kernig's sign. Cerebrospinal fluid exhibits changes consistent with aseptic meningitis. The prognosis is generally good, with recovery within 2 weeks.
Orchitis
Orchitis is the most common complication in male patients, often unilateral. It usually occurs 4–5 days after the onset of mumps and as parotid swelling begins to subside. Symptoms include testicular pain, followed by swelling and severe tenderness. Epididymitis, hydrocele, and scrotal edema may also occur. Systemic symptoms, such as high fever and chills, are common. Orchitis typically resolves within about 10 days. Around 30–50% of affected patients develop varying degrees of testicular atrophy, and bilateral involvement may result in infertility.
Oophoritis
Oophoritis is observed in about 5–7% of adolescent females, with symptoms often mild. It may present as lower abdominal pain, tenderness, and menstrual irregularities. Fertility is generally unaffected.
Pancreatitis
Severe acute pancreatitis is rare and typically occurs a few days after parotid swelling. Clinical manifestations include severe upper abdominal pain and tenderness, along with fever, chills, nausea, and repeated vomiting. Since mumps infection can elevate blood and urinary amylase levels, pancreatitis diagnosis should be supported by serum lipase testing.
Hearing loss
Hearing loss results from involvement of the auditory nerve. The incidence is low, and most cases are unilateral. The condition may be difficult to detect promptly and is challenging to treat, potentially leading to permanent hearing loss.
Other Complications
Myocarditis is relatively common, whereas nephritis, mastitis, thymitis, thyroiditis, dacryoadenitis, keratitis, thrombocytopenia, and arthritis are rare but possible.
Laboratory Examinations
Measurement of Blood and Urinary Amylase
Serum and urinary amylase levels exhibit mild to moderate elevation in approximately 90% of patients during the early stages of the illness, typically returning to normal within two weeks. Simultaneous elevation of blood lipase levels can aid in the diagnosis of pancreatitis.
Serological Testing
Positive serum-specific IgM antibodies indicate a recent infection. A fourfold or greater increase in specific IgG antibody titers in paired serum samples has diagnostic significance.
Pathogen Detection
Isolation of the mumps virus from saliva, blood, cerebrospinal fluid, or urine confirms the diagnosis. Specific antibodies can be used to rapidly detect the virus in culture samples. Additionally, RT-PCR can be utilized to detect virus-specific nucleic acid fragments.
Diagnosis and Differential Diagnosis
Diagnosis is typically based on epidemiological history, clinical symptoms, and physical examination. For suspected cases, serological testing and viral isolation may be performed to confirm the diagnosis. Differential diagnoses include suppurative parotitis, acute lymphadenitis, and other causes of parotid gland swelling, such as leukemia, lymphoma, Sjögren's syndrome, or parotid gland tumors.
Treatment
There is no specific antiviral treatment, and management is primarily symptomatic.
During the acute phase, patients should rest adequately, maintain oral hygiene, and ensure sufficient hydration and nutrition with a soft or liquid diet while avoiding acidic foods. Antipyretics or physical cooling methods may be used to manage high fever. For severe parotid swelling and pain, analgesics can be administered. When testicular pain and swelling occur, a scrotal support strap may provide relief.
Prevention and Prognosis
Patients should remain isolated until parotid swelling has fully resolved. In group settings, children with contact history should be monitored for three weeks. Active immunization can be achieved with the live attenuated mumps vaccine, typically administered as part of the measles-mumps-rubella (MMR) combination vaccine included in immunization programs. This approach has demonstrated strong protective efficacy.
The prognosis of mumps is generally favorable, with most patients making a full recovery.