Infectious Disease: Measles

Question 1

Definition

Answer 1

Highly contagious airborne infection caused by RNA paramyxovirus (measles virus) and only occurs in humans

It is the most infectious of all diseases transmitted through the respiratory route with a basic reproduction number (R0) between 15-20 people infected in a totally susceptible population.

Question 2

Epidemiology

Answer 2

Rare since the introduction of widespread MMR (measles, mumps, and rubella) vaccination

Close contract with infected persons
Absence/incomplete MMR vaccination record
Infants
Pregnancy/immunocompromised: more severe

Question 3

Pathophysiology

Answer 3

Virus inhaled from droplets and infects the respiratory epithelium and immune cells of the respiratory tract . There are four distinct phases of measles infection:

1. Incubation : approximately 10-14 days
2. Prodromal : initial localised inflammation with patients experiencing the 3 C’s: coryzal symptoms, cough, conjunctivitis.
3. Exanthem : as viraemia develops, patients become pyrexial and can develop Koplik spots on their buccal mucosa. Once the virus has disseminated, perivascular and lymphocytic infiltration occurs, leading to the development of a generalised maculopapular rash that classically starts behind the ears before spreading to the entire body
4. Recovery : fever and rash resolve, however, the cough may persist for up to two weeks

Infection with the measles virus can lead to induced immunosuppression which can last for weeks to even years. This is thought to be due to the replacement of immune memory cells with measles-specific lymphocytes, leading to an “immune amnesia”. This leads to an increased susceptibility to secondary infection, causing the majority of measles-related deaths.

Question 4

Signs and symptoms

Answer 4

Prodromal phase (4-7 days):
- fever
- malaise
- cough
- rhinorrhoea
- conjunctivitis

Exanthem phase (~ 7 days):
- maculopapular rash which may become confluent
- classically apppears on the face and behind the ears first
- high fever
- Koplik spots

Recovery phase:
- resolution of rash and fever
- cough may persist for up to 2 weeks

Question 5

Diagnosis

Answer 5

It is a notifiable disease and the local health protection team must be informed

FIRST LINE = Oral fluid (OF sample) minimal invasive and can be tested for measles IgM/IgG and measles RNA.
- OF sample should be taken from all patients with suspected measles
- measles IgM usually detectable in the first few days following infection, whereas IgG takes approximately 7-10 days to become detectable
- OF samples for IgM are more sensitive and specific than serum, particularly in the first few days after the rash

Consider:
- Mouth/Throat swabs: can be used for PCR testing for measles RNA if collected within 6 days of the onset of the rash

Question 6

Treatment

Answer 6

FIRST LINE =
- Conservative management: rest, oral fluids and paracetamol/ibuprofen from symptomatic relief
- school/work absence: patients are advised to stay away from school/work for 4 days after the initial development of the rash and avoid contact with susceptible people
- notifying the health protect team: all suspected cases of measles need to be discussed with the local health protection team

Question 7

Complications

Answer 7

• Increased susceptibility to opportunistic infection for several weeks after the person has recovered due to induced immunosupression
  = Otitis media
  = Respiratory involvement: pneumonia is the most common cause of measles-related mortality
• Blindness
• Acute encephalitis
• Subacute sclerosis panencephalitis: rare but serious complication due to persistent measles infection
• Febrile convulsions