Outbreak of Scarlet Fever in the UK

There is an outbreak of scarlet fever occurring in the UK. What makes this different from a regular Strep sore throat (caused by Streptococcus pyogenes) is that the strains of Strep causing these outbreaks encode a gene that allows them to produce a superantigen-exotoxin. This causes the non-specific activation of T helper cells, and creates the characteristic signs and symptoms of a sandpaper rash, and strawberry tongue.

But it is interesting how the signs and symptoms develop. First comes the typical Strep sore throat signs, a sore throat and a fever. Then, 12-48 hours after the first signs develop, the effect of the exotoxin becomes apparent, causing the effects of activation of non-specific T helper cells (the superantigen exotoxin binds outside of the antigen-binding site on the MHC class II molecule, allowing TCRs on T helper cells to non-specifically interact with these MHC molecules, and become activated.

The other thing to note, is that the effects of this toxin are relatively mild, and the threat to the child is the same as that of a regular Strep sore throat. In a patient under the age of 18, it should be treated immediately with antibiotics to prevent the Strep sore throat sequelae: Rheumatic fever or kidney failure, that occurs as a consequence of mounting an antibody response to specific strains of Streptococcus pyogenes.

 

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