Mumps : Virus Characteristics, Pathology and Pathogenesis

Mmps is an ssRNA virus, a Pleomorphic virus with a lipoprotein envelope. It Belongs to the paramyxoviridae family- Genus Rubulavirus. It has a Single stereotype with 12 known genotypes. Humans are the only natural hosts, and there is no other reservoir. No carrier state is produced in this. It has two important surface proteins as mentioned below:

• HN protein ( Hemagglutin-Neuraminidase) helps in attaching viruses to host cells.
• F protein (fusion) is used for the entry/fusion of viruses to host cells.

Antibodies are formed against both proteins and are found to be protective.

Epidemiology And Mode Of Spread of Mumps

• Most common age: is 5 to 15 years. In the prevaccine era, the commonly affected age group was between 5 to 19, but it does not discuss the age groups in the current scenario. Infants are protected due to transplacental maternal antibodies. More cases occur in winter and spring. Secondary attack rate:40 to 80%. One infection gives lifelong protection. Mode of spread: respiratory droplets, Fomites. Communicable period: Virus in saliva 7 days before to 7 days after the onset of parotitis. In this period, Maximum infectivity is seen in 1 to 2 days before to 5 days after the onset of parotid swelling. Mumps is one of the most common causes of aseptic meningitis in children (India).

Q. What is the overall communicable period of the virus?

A. 7 before or 7 days after the onset of parotitis.

Q. When is the maximum infectivity seen?

A. 1 to 2 days before to 5 days after the onset of parotid swelling.

Pathology and Pathogenesis of Mumps

In case of infections, the mumps virus replicates in epithelial cells of the oral cavity/airway tract. It will also spread to regional lymph nodes. After replication, the virus will show a phase called viremia. They reach a certain organ system, first salivary glands.

• CNS 
• Testes 
• Pancreas/thyroid

Pathology Of Mumps

Most infected tissues 

1. Cellular Necrosis 
2. Intense Lymphocytic Infiltrate 

• Tests → Focal infarcts 
• CNS → CSF Pleocytosis is prominent even in asympt. cases 

In mumps viruses, most infected tissues have two pathologies in common. They produce cellular necrosis and Intense lymphocytic infiltrate  In addition, when the virus reaches the testes, it produces a focal infarct. CNS will show CSF pleocytosis prominent even in asymptotic cases.

Clinical Features Of Mumps

The incubation period is from 16 to 18 days. Some infections are asymptomatic or show mild, non-specific illness. Features of typical infection include:

• Fever: initial symptom associated with headache, vomiting, and body pains.
• Parotitis: Develops 2 days after the onset of fever.
• Initially unilateral, it becomes bilateral in 70% of cases.
• Painful swelling is associated with dry mouth, difficulty in chewing, and I/L ear pain.
• Stevenson duct openings are red and edematous.
• Sour or acidic foods exacerbate pain.
• As swelling increases, the angle of the jaw is obscured, and the earlobe is pushed upwards and outwards.
• The fever lasts for 3 to 5 days.
• Swelling peaks in 4 days and subsides in 7 days.
• Sometimes, submandibular salivary glands may also be involved.
• A morbilliform rash may also be present in some.
• Edema over the sternum is found due to lymphatic obstruction.

If an unimmunized individual gets an infection, it is less severe, and parotitis is absent.

Virus Characteristics

• ssRNA virus, Pleomorphic virus with a lipoprotein envelope. Belongs to the paramyxoviridae family- Genus Rubulavirus. Single stereotype with 12 known genotypes. Humans are the only natural host, no other reservoir. No carrier state is produced. Two important surface proteins- HN protein ( Hemagglutin-Neuraminidase) helps in attaching viruses to host cells. F protein (fusion) is used for the entry/fusion of viruses to host cells. Antibodies are formed against both proteins and are found to be protective.

Epidemiology And Mode Of Spread

• Most common age: is 5 to 15 years. In the prevaccine era, the commonly affected age group was between 5 to 19, but it does not discuss the age groups in the current scenario. Infants are protected due to transplacental maternal antibodies. More cases occur in winter and spring. Secondary attack rate:40 to 80%. One infection gives lifelong protection. Mode of spread: respiratory droplets, Fomites. Communicable period: Virus in saliva 7 days before to 7 days after the onset of parotitis. In this period, Maximum infectivity is seen in 1 to 2 days before to 5 days after the onset of parotid swelling. Mumps is one of the most common causes of aseptic meningitis in children (India).

Q. What is the overall communicable period of the virus?

A. 7 before or 7 days after the onset of parotitis.

Q. When is the maximum infectivity seen?

A. 1 to 2 days before to 5 days after the onset of parotid swelling.

Pathology And Pathogenesis

• In case of infections, the mumps virus replicates in epithelial cells of the oral cavity/airway tract. It will also spread to regional lymph nodes. After replication, the virus will show a phase called viremia. They reach a certain organ system, first salivary glands- CNS , Testes, Pancreas/thyroid. In mumps viruses, most infected tissues have two pathologies in common. They produce cellular necrosis, Intense lymphocytic infiltrate. In addition, when the virus reaches the testes, it produces a focal infarct. CNS will show CSF pleocytosis  prominent even in asymptotic cases.

Clinical Features Of Mumps

• The incubation period is from 16 to 18 days. Some infections are asymptomatic or show mild, non-specific illness. Features of typical infection Fever: initial symptom associated with headache, vomiting, and body pains. Parotitis: Develops 2 days after the onset of fever. Initially unilateral, it becomes bilateral in 70% of cases. Painful swelling is associated with dry mouth, difficulty in chewing, and I/L ear pain. Stevenson duct openings are red and edematous. Sour or acidic foods exacerbate pain. As swelling increases, the angle of the jaw is obscured, and the earlobe is pushed upwards and outwards. The fever lasts for 3 to 5 days. Swelling peaks in 4 days and subsides in 7 days. Sometimes, submandibular salivary glands may also be involved. A morbilliform rash may also be present in some. Edema over the sternum is found due to lymphatic obstruction.
• If an unimmunized individual gets an infection, it is less severe, and parotitis is absent. The child suffers from unilateral parotitis with swelling and redness on the cheeks.

Complications of Mumps

Overall, the most common complication is meningitis, with or without encephalitis. In children, the most common is meningitis, with or without encephalitis. In adolescents it is orchitis.

Meningitis and encephalitis 

Mumps virus is neurotropic and enters the CNS via the choroid plexus. It Produces aseptic meningitis, with or without encephalitis. CNS involvement can happen before, with, or after the onset of parotitis. However, in most cases, meningitis develops 5 days after the onset of parotitis. Symptoms may resolve in 7 to 10 days. Rarely is there also the presence of transverse myelitis, Acute disseminated encephalomyelitis, aqueductal stenosis, facial palsy, and sensorineural hearing loss.

• Features of Aseptic Meningitis - It includes increased cells( predominantly lymphocytic ) and proteins, the cell culture is sterile, and the CSF glucose level is normal (15% of patients may have low CSF glucose transiently as well).
• Sensory neural hearing loss - The cause of this in mumps is damage to the 8th cranial nerve. However, this is a rare case. Damage is transient.
• Nelson says that symptomatic CNS involvement occurs in 10 to 30% of infected individuals, but CSF pleocytosis has been found in 40-60% of patients with mumps parotitis.

Orchitis and oophoritis 

It is the most common complication in adolescents and adults in around 30-40% of males. It begins within 3 to 5 days after parotitis. Fever, chills, and painful testicular swelling are observed. In 70% of cases, it is bilateral, and in 30% of cases unilateral. Atrophy of the testis is common, but sterility is rare/not seen. Oophoritis in females may occur but is less common than orchitis.

Other Complications:

• Pancreatitis mumps can precipitate insulin-dependent diabetes mellitus(type 1 diabetes mellitus).
• Myocarditis is also seen with some endocardial fibroelastosis.
• Arthritis within 3 weeks but is mild and self-limited.
• Recurrent thyroiditis can progress to clinical hypothyroidism.

Investigations 

• Leukopenia with relative lymphocytosis. Serum amylase is elevated in almost 90% of patients. Serologic testing - Serum IgM can be detected via ELISA  (investigation of choice) . A significant increase in serum mumps IgG antibodies between acute and convalescent serum specimens can be demonstrated.  All serological tests are difficult to interpret in a vaccinated child.
• Virus detection and isolation.Cell culture is used for isolation. Viral antigen detection by DIF.Viral nucleic acid detection by PCR ( Positive only for 3 days after the onset of parotitis.)

Treatment Of Mumps

There is no specific treatment for mumps. Conservative management is to control the disease.

• Adequate hydration.
• Analgesic and fever control.
• A soft, bland diet 
• Warm saline mouthwashes.

The role of steroids in the treatment of mumps is symptomatic relief is seen in orchitis and arthritis, but it does not alter the course of the disease.

Period of isolation in Mumps 

AAP recommends Isolation for 5 days after the onset of the parotid swelling. Indian setting OP GHAI 9th edition recommends isolation in mumps is recommended till the parotid swelling subsides.