MFF0088: Measles virus and measles


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Australian Society for Infectious Diseases

Last week, I received a little bump from the Australian Society for Infectious Diseases. The Society published its September issue of ASID ASIDES which focuses on member activities. This issue had a couple of pages on The Medical Fun Facts Podcast.

I’ve been an ASID member for as long as I can remember. The Society welcomes members from many professional groups including specialist microbiologists, infectious diseases physicians, public health physicians, infection prevention and control practitioners, medical laboratory scientists and other suitably qualified persons with an interest in infectious diseases. If you’re interested in knowing more about ASID and becoming a member, please visit the ASID website.

Measles virus

Welcome to The Medical Fun Facts Podcast, it’s Monday 16 October 2017. Tonight, I wanted to talk about the Measles virus (MeV).

The Measles virus is a single-stranded RNA virus in the genus Morbillivirus. As far as I know, the Measles virus only infects humans. I can also infect some other primates experimentally.

It would appear that Measles virus and the animal pathogen, Rinderpest virus have a common ancestry. Within the species, there are currently 8 clades and about 23 subtypes.

When the Measles virus infects humans, it causes the disease measles. I remember having measles as a child. I recall the distinctive maculopapular rash and feeling generally miserable while missing out on school.

Measles

Measles is a contagious infectious disease which is generally regarded as a respiratory illness but in some patients, it progresses to a neurological disease with a fatality rate that is sadly too high given measles the disease can be eradicated and the Measles virus can be safely contained.

Clinical features of measles include:

  • An early fever, conjunctivitis, coryza, cough and in some cases spots on the mucous membrane inside your mouth near where you find your molars, these are known as Koplik spots.
  • A red blotchy rash usually starts on the face around the third to seventh day and then spreads around the body. The rash can last between four and seven days. The peripheral blood white cell count often drops.
  • Complications, resulting from viral replication or bacterial superinfection, may occur up to 4 weeks after the rash. Death can result from neurological infection and severe secondary bacterial infections which causes a severe consolidating or necrotising pneumonia depending on the bacterial cause.
  • The complications include middle ear infection, pneumonia, laryngotracheobronchitis (croup), diarrhoea, febrile seizures, and brain infection (encephalitis). In about 1 in 100,000 cases, Subacute Sclerosing Panencephalitis (SSPE) may develop years after the infection. SSPE has a very high fatality rate and patients endure a painful terrible death.

Diagnosis can be made clinically when fever, maculopapular rash and cough, coryza, or conjunctivitis are present. It is recommended that clinical diagnoses are confirmed by medical testing by medical laboratory scientists and pathologists. The detection of IgM antibody or a four-fold rise in IgG titre or the detection of Measles virus RNA by PCR in blood, urine, and nasopharyngeal specimens will confirm a diagnosis. As always, isolated IgM detection in the absence of typical symptoms should be interpreted very cautiously. In this situation, PCR of a nasopharyngeal specimen is recommended.

Measles generally occurs in populations where vaccination does not occur or the vaccination rate is low. Vaccination campaigns in many countries have clearly demonstrated that measles can be avoided in communities. In parts of Asia and Africa, >100,000 children died of measles. It’s remarkable that people who hesitate about the safety and value of vaccination sometimes are heard to say that measles is a harmless childhood disease. Improved vaccine coverage in Asia and Africa brought the number of deaths in 2000 which was >500,000 to just over 150,000 in 2011.

The average incubation period for measles is 14 days with a range of 7 to 21 days. Measles virus is transmitted by droplet and direct contact with nasal and throat secretions. Measles is widely regarded as one of the most communicable of infectious diseases. Patients are infectious from 4 days prior to the onset of rash to 4 days after the appearance of the rash. That said, the communicability diminishes quite a lot two days after the appearance of the rash.

If you’ve never had measles and if you’ve never been immunised, you’re susceptible to infection. Most people require at least two doses of vaccine for successful immunisation.

Questions for listeners

Have you had measles?

Have you been immunised against measles?

Have you had your children immunised against measles?

Please leave your answers in the comments section of the show notes or on the Facebook page or on YouTube.

That’s episode 88 in the can.

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Medical Fun Facts is available in Anchor, the Apple Podcasts app, and on Stitcher. You’ll find the links in the show notes.

If you have any questions or comments please let me know. If I’ve said anything incorrect I welcome correction.

I’ll catch you next week for episode 89. Something beginning with the letter N. Send me suggestions.

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Thank you, and good night.

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