Mumps and Measles

Question 1

Mumps and measles

Type of Virus

Answer 1

Paramyxoviruses

Question 2

Paramyxoviruses

Answer 2

Brief review of structure of paramyxoviruses:
• Enveloped virion
• Nucleocapsid has helical symmetry
• Genome consists of single molecule of RNA
• RNA genome is minus-stranded
• Virion carries a RNA polymerase
• Virion hemagglutinate red cells

Question 3

Genetic Structure of Mumps & Measles

Paramyxoviruses

Answer 3

• The minus-stranded viral RNA is in one piece
• Genetic reassortment is impossible.
• This is in contrast to Influenza (orthmyxovirus) that undergoes genetic reassortment

Question 4

Mode of Infections

Influenza & Parainfluenza

Answer 4

Influenza (orthomyxovirus) and parainfluenza (paramyxovirus) viruses generally cause local, nonsystemic, nonviremic infections.

Question 5

Mode of Infections

Mumps & Measles

Answer 5

Mumps and measles are paramyxoviruses that cause systemic infections with viremia as an essential step in pathogenesis

Question 6

Consequence of Viremia in Mumps and Measles

Answer 6

a. Incubation period is longer for mumps and measles because cycles of multiplication in several sites in succession are required.
b. Lifelong immunity occurs in individuals who have had the disease. Obligatory viremia allows neutralization by IgG.

Question 7

Mumps

Answer 7

Mumps is caused by a paramyxovirus that is antigenically related to the parainfluenza viruses.
There is one serotype of mumps virus and humans
are the sole reservoir of mumps.

Question 8

Mumps Pathogenesis

Answer 8

Mumps is transmitted via respiratory droplets. After
an average incubation period of typically around 18-21 days a prodromal period of fever, malaise & anorexia is quickly followed by unilateral or bilateral swelling of the parotid gland. The usual presenting clinical symptom is PAROTIDITIS.

Question 9

Parotiditis

Mumps

Answer 9

Mumps virus grows in the enlarged painful
parotid salivary glands and is excreted in saliva
several days before and after swelling of the salivary
gland begins. Parotiditis begins about 18-21 days after infection (3 week incubation period).
Pain arises only from pressure within organs in tight capsules, e.g. parotid gland and testis (orchitis) after puberty. Most infections are symptomatic (only 30% are asymptomatic)

Question 10

Transmission of Mumps

Answer 10

Transmission occurs by respiratory exposure with saliva droplets containing mumps virus.
Primary virus multiplication is in respiratory epithelium and local lymph nodes. This results in viremia that infects salivary glands and other organs.
The virions produced int he salivary glands go down the duct to the mouth and provide most of the infectious virions spread by coughs and sneezes.

Question 11

Orchitis

Mumps

Answer 11

It’s seen inabout 30% of infected males past puberty. Orchitis is quite painful inflammation of the testicles.
Unilateral orchitis resolves with no other complications.
Bilateral orchitis can result in sterility or subferterlity, although this outcome is uncommon.

Question 12

Other organs infected

Mumps

Answer 12

Other organs affected include the pancreas, the ovary (both uncommon) and, much more commonly, the meninges (aseptic meningitis). All have a generally benign course.

Question 13

Immunity

Mumps

Answer 13

Immunity is generally lifelong even after subclinical infection.

Question 14

Treatment

Mumps

Answer 14

There is no antiviral therapy for mumps.

Question 15

Immunization

Mumps

Answer 15

Immunization uses a live attenuated vaccine. The mumps vaccine is a component of the MMR pediatric vaccine that is given twice to confer protection without serious side effects.
The incidence of infection has fallen markedly in developed countries because of childhood immunization.

Question 16

Measles

Answer 16

Measles is caused by a paramyxovirus. It is antigenically unrelated to any other paramyxovirus of humans.

Question 17

Measles (General Info)

Answer 17

Measles is probably the most contagious disease known.
Also, in contrast to most other viruses, it almost never causes subclinical infections. Before the vaccine era there were local epidemic generally every three years, in winter.

Question 18

Measles Epidemics

Answer 18

a. The measles virus causing the epidemic is antigenically the same measles virus (epidemics occur with no antigenic variation).
b. The number of nonimmune susceptibles increases because of new births.
c. When the concentration of nonimmune susceptibles is sufficient to break down herd immunity, measles virus can be introduced
and is rapidly disseminated in the population causing a new epidemic.

Question 19

Transmission of Measles

Answer 19

a. Measles virus is efficiently transmitted via respiratory droplets. Measles virus infects via respiratory tract and initially multiplies in epithelium and local lymph nodes (also conjunctiva).
b. Asymptomatic infections are rare/unknown.

Question 20

Symptoms of Measles

Answer 20

Before the rash, various PRODROMAL SYMPTOMS (prodromal symptoms are those nonspecific symptoms that appear before the definitive symptoms) appear: fever, cold-like symptoms, runny nose, red eyes.
Just prior to the definitive symptoms of the measlesrash, Koplik spots (bright red lesions with a
white central spot on the buccal mucosa) are seen
and is predictive of the measles rash appearing in a
day or two (Koplik’s spots = measles). Along with the appearance of the measles rash, fever, runny nose, coughing/sneezing, conjunctivitis, and photophobia are common symptoms.

Question 21

Measles Rash

Answer 21

The rash begins after a 14-day incubation period.
The measles rash is described as a generalized
maculopapular erythematous rash. The immune response plays a role in the genesis of the rash.

Question 22

Measles Virus Shedding

Answer 22

Virus excretion from respiratory tract and in tears and urine for a few days before and after appearance of the rash.

Question 23

Measles Prognosis

Answer 23

• 0.1 - 0.3 death rate from Measles in the USA
• 5-25% death rate in developing countries
• In developed countries, 1 in 20 cases result in pneumonia
• Otitis media is frequent
• Acute encephalitis (1-2 in 1000 cases) leading to 500 deaths and 1500 retarded survivors per in USA in 195–1960 before immunization

Question 24

Treatment for Measles

Answer 24

• There are no treatments for measles

* Immune response ultimately eliminates viral excretion and confers life long immunity

Question 25

Measles Pathology

Answer 25

• Measles virus infects a tissue
• The viral antigen enters the membrane of the first infected cell
• Cell fusion spreads the infection to adjacent cells
• The final result is a multinucleate giant cell

Question 26

Anergy in Measles

Answer 26

• Infection with the measles virus profoundly suppresses cell mediated immunity.
• For example: Delayed hypersensitivity skin tests (such as the tuberculin test) become negative for a few weeks or even months in a child who was positive before contracting measles.
• This transient loss of cell mediated immunity is called “ANERGY”.
• Some of the measles deaths, primarily in developing countries, are caused by secondary infections acquired during this period of anergy.

Question 27

Measles Epidemiology

Answer 27

a. Measles virus needs a large, concentrated human population to survive. There is one serotype and humans are the sole reservoir. Since the virion is enveloped and unstable, it must be growing in some individual somewhere at all times.
b. Measles virus disappears from small isolated populations because continuous transmission is blocked by immunity or herd immunity. Study of these populations shows:
(1) that life-long measles immunity (resulting from infection) does not require restimulation by contact with exogenous virus and
(2) that immune individuals do not excrete
infectious measles virus.

Question 28

GIANT-CELL PNEUMONIA

Answer 28

Rare lethal GIANT-CELL PNEUMONIA
without any measles rash when cell-mediated
immunity is defective. Proof that cell-mediated immunity plays a role in the genesis of the rash.

Question 29

Measles Vaccines

Answer 29

An injected live attenuated vaccine gives excellent long term protection. The live measles vaccine is one of the components of the MMR pediatric vaccine which is given twice.
Due to the high infectivity of measles, it is more difficult to establish and suspend herd immunity.

Question 30

Measles Erradication

Answer 30

Measles has been eradicated in the USA but imported cases are still common and around 50-100 cases occur every year.

Question 31

Challenges of Measles Erradication

Answer 31

The challenge(s) of measles eradiation. In developing countries, many cases of measles occur before age 12 months, making immunization extremely difficult because of maternal antibody. Steady progress is being made in the world-wide eradication of measles