Measles virus

Highly contagious virus that causes a triad of cough, coryza, and conjunctivitis

Background

Enveloped RNA Morbillivirus in the Paramyxoviridae family
- Family includes parainfluenza, RSV, measles, mumps
Eight structural proteins: F, C, H (haemagglutination), L (large), M (matrix), N (nucleoprotein), P (phosphopolymerase), and V
- N, P, and L complex with RNA
- C and V interact with cellular proteins and regulate replication
- M, H, and F are viral envelop proteins
- H helps with host cell attachment, and F helps with spread between cells

Airborne droplets can remain in the air up to 2 hours after a person with measles has coughed
- It is droplet, but just very small droplet
Innoculated through respiratory mucosa, enters lymphoid cells via SLAM receptor
- SLAM (CDw150) is present on lymphocytes and antigen-presenting cells
Spreads to entire respiratory systems, as well as intestines, bladder, skin, and spleen, lymph nodes, liver, conjunctiva, and brain
Propagates within T and B lymphocytes and monocytes, but also endothelial, epithelial, and dendritic cells
Host response success causes disappearance of serology and appearance of rash
- Possibly the rash represents a hypersensitivity reaction to the virus mediated by cellular immunity

Infection confers lifelong immunity, though vaccination may not
Worldwide distribution
Prior to vaccination, there were epidemics every 2 to 5 years lasting 3 to 4 months
Vaccine hesitancy is becoming more common
- Parts of Europe

Incubation period 10-14 days (range up to 21 days), followed by several days of prodrome that includes fever, anorexia, cough, coryza, and conjunctivitis
- Can be mistaken for common cold or for Kawasaki disease
- Koplik spots appear at end of prodrome
  - Bluish gray specks on a red base in the oral mucosa ("like grains of sand")
Rash follows Koplik spots
- Spreads from face to body, including palms and soles
- Fevers resolve soon after rash appears
- Rash is erythematous and maculopapular, and my desquamate as it begins to heal
- Usually lasts 5 days, clearing in the same pattern that it appeared
The rash disappears about 7 to 10 days after late prodromal period, with cough being the last symptom to disappear

Respiratory involvement, either as primary infection of with bacterial superinfection
- Otitis media, pneumonia (on CXR, even if uncomplicated)
Acute encephalitis, which can have sequelae
- Blindness, corneal scarring
Hepatitis
Complications are more common in adults who are infected

Degenerative neurological condition caused by persistent CNS infection despite immune response
5-10 years after infection
Higher risk if infection before age 2 years
Inevitably ends in death

Patients with passive immunity to measles may present with a milder form
- Babies with mom's immunoglobulin, or patients who have received immune globulin
The prodrome, Koplik spots, and rash are often absent, and it is sometimes subclinical

Patients with prior immunization with killed vaccine (no longer on market, since 1960s) may have an atypical presentation
Prodrome of fever and pain for 1 to 2 days
Rash follows, but moves peripherally to centrally, and have varied form (urticarial, maculopapular, hemorrhagic, vesicular)
- Can mimic vaicella, RMSF, HSP, drug eruption, or toxic shock syndrome
Fever continues, with edema, interstitial pneumonia, hepatitis, and occasionally pleural effusion
More prolonged course, with very high antibody titres

Chemotherapy, transplantation, AIDS, and congenital cellular immunodefieciency are all risk factors for severe measles
- Possibly also malnutrition
Can develop giant cell pneumonia, without rash, as well as a chronic encephalitis
- Can detect measles RNA in brain tissue

Most infectious just before rash; quickly becomes non-infectious after end of prodrome
Supportive care
Vitamin A can be given, especially if the child is deficien
- In children >1 year, vitamin A 200,000 IU daily for 2 days
- If 6-12 months old, use 100,000 IU for 2 days
- Less than 6 months, use 50,000 IU
- If deficient, give another dose at 2 to 4 weeks
Ribavirin unhelpful but sometimes given

Infectious period is 5 days prior to rash and 4 days after, in general, though infectiousness starts with respiratory involvement
Need to do contact tracing, including people up to two hours after any room they were in
All contacts should be quarantined at home regardless of symptoms

Indications for passive immunization with immune globulin
- High risk for severe or fatal measles and are susceptible
- Includes children with malignancy, cell-mediated immunodeficiency (including AIDS), and possibly babies <1 year
- Must be given within 6 days of exposure
- Infants <1 year: IMIg 0.25 mL/kg once
- Other children: IMIg 0.5 mL/kg once (maximum of 15 mL)
Immunization for post-exposure prophylaxis can be done in other, immunocompetent patients
- Can shorten the time to rash, suggesting a shorter period of infectiousness

Live vaccine given in MMR at 12-15 months, with a booster later in childhood
Don't vaccinate for 5-6 months after receiving immune globulin
No adverse effects of revaccination
Rates need to be >95% to prevent imported cases from causing outbreaks
Rates less than 80% allow endemic transmission with cyclical outbreaks every 3-5 years
Vaccination is contraindicated in AIDS, other cell-mediated immunodeficiency, and in pregnancy
- Wait 3 months after chemotherapy
- Don't use MMRV, since no safety data are available
Can be associated with anaphylaxis in patients with true egg allergy