Common symptoms The incubation period, the time between the start of infection and when symptoms begin to show, is about 7–25 days, averaging 16–18 days. 20–40% of infections are asymptomatic or are restricted to mild respiratory symptoms, sometimes with a fever. Over the course of the disease, three distinct phases are recognized: prodromal, early acute, and established acute. The prodromal phase typically has non-specific, mild symptoms such as a low-grade fever, headache, malaise, muscle pain, loss of appetite, and sore throat. In the early acute phase, as the<unk>  virus spreads throughout the body, systemic symptoms emerge. Most commonly, parotitis occurs during this time period. During the established acute phase, orchitis, meningitis, and encephalitis may occur, and these conditions are responsible for the bulk of<unk>  morbidity. The parotid glands are salivary glands situated on the sides of the mouth in front of the ears. Inflammation of them, called parotitis, is the most common<unk>  symptom and occurs in about 90% of symptomatic cases and 60–70% of total infections. During<unk>  parotitis, usually both the left and right parotid glands experience painful swelling, with unilateral swelling in a small percentage of cases. Parotitis occurs 2–3 weeks after exposure to the virus, within two days of developing symptoms, and usually lasts 2–3 days, but it may last as long as a week or longer. In 90% of parotitis cases, swelling on one side is delayed rather than both sides swelling in unison. The parotid duct, which is the opening that provides saliva from the parotid glands to the mouth, may become red, swollen, and filled with fluid. Parotitis is usually preceded by local tenderness and occasionally earache. Other salivary glands, namely the submandibular, and sublingual glands, may also swell. Inflammation of these glands is rarely the only symptom. Complications Outside of the salivary glands, inflammation of the testes, called orchitis, is the most common symptom infection. Pain, swelling, and warmness of a testis appear usually 1–2 weeks after the onset of parotitis but can occur up to six weeks later. During<unk>  orchitis, the scrotum is tender and inflamed. It occurs in 10–40% of pubertal and post-pubertal males who contract<unk> . Usually,<unk>  orchitis affects only one testis but in 10–30% of cases both are affected.<unk>  orchitis is accompanied by inflammation of the epididymis, called epididymitis, about 85% of the time, typically occurring before orchitis. The onsent of<unk>  orchitis is associated with a high-grade fever, vomiting, headache, and malaise. In prepubertal males, orchitis is rare as symptoms are usually restricted to parotitis. A variety of other inflammatory conditions may also occur as a result of<unk>  virus infection, including: * Mastitis, inflammation of the breasts, in up to about 30% of post-pubertal women * Oophoritis, inflammation of an ovary, in 5–10% of post-pubertal women, which usually presents as pelvic pain * Aseptic meningitis, inflammation of the meninges, in 5–10% of cases and 4–6% of those with parotitis, typically occurring 4–10 days after the onset of symptoms.<unk>  meningitis can also occur up to one week before parotitis as well as in the absence of parotitis. It is commonly accompanied by fever, headache, vomiting, and neck stiffness. * Pancreatitis, inflammation of the pancreas, in about 4% of cases, which causes severe pain and tenderness in the upper abdomen below the ribs * Encephalitis, inflammation of the brain, in less than 0.5% of cases. People who experience<unk>  encephalitis typically experience a fever, altered consciousness, seizures, and weakness. Like meningitis,<unk>  encephalitis can occur in the absence of parotitis. * Meningoencephalitis, inflammation of the brain and its surrounding membranes.<unk>  meningoencephalitis is commonly accompanied by fever 97% of the time, vomiting 94% of the time, and headache 88.8% of the time. * Nephritis, inflammation of the kidneys, which is rare because kidney involvement in<unk>  is usually benign but leads to presence of the virus in urine * Inflammation of the joints (arthritis), which may affect at least five joints (polyarthritis), multiple nerves in the peripheral nervous system (polyneuritis), pneumonia, gallblader without gallstones (acalculous cholecystitis), cornea and uveal tract (keratouveitis), thyroids (thyroiditis), liver (hepatitis), retina (retinitis), and corneal endothelium (corneal endothelitis), all of which are rare * Recurrent sialadenitis, inflammation of the salivary glands, which is frequent A relatively common complication is deafness, which occurs in about 4% of cases.<unk>  deafness is often accompanied by vestibular symptoms such as vertigo and repetitive, uncontrolled eye movements. Based on electrocardiographic abnormalities in the infected, MuV also likely infects cardiac tissue, but this is usually asymptomatic. Rarely, myocarditis and pericarditis can occur. Fluid buildup in the brain, called hydrocephalus, has also been observed. In the first trimester of pregnancy,<unk>  may increase the risk of miscarriage. Otherwise,<unk>  is not associated with birth defects. Other rare complications of infection include: paralysis, seizures, cranial nerve palsies, cerebellar ataxia, transverse myelitis, ascending polyradiculitis, a polio-like disease, arthropathy, autoimmune hemolytic anemia, idiopathic thrombocytopenic purpura, Guillain–Barré syndrome, post-infectious encephalitis encephalomyelitis, and hemophagocytic syndrome. At least one complication occurs in combination with the standard<unk>  symptoms in up to 42% of cases.<unk>  has also been connected to the onset of type 1 diabetes, and, relatedly, the<unk>  virus is able to infect and replicate in insulin-producing beta cells. Among children, seizures occur in about 20–30% of cases involving the central nervous system.
Mumps
Chickenpox
Smallpox
Larva currens
Cowpox
Sealpox
Scabies
Malaise