Marcus is 32 years old and presents to the GP with a one week history of fever, malaise and myalgia. His eyes also feel sticky and look red. He returned from Barbados 8 days ago where he had been working as a vet on a one month placement. He reports feeling well whilst abroad and had checked guidance that no malaria prophylaxis was necessary prior to travel. His bowels are opening as normal and there is no blood in his stool or urinary symptoms. Past medical history is unremarkable.
Chest and abdomen examination today is unremarkable, and his observations are stable. You note bilateral conjunctival ingestion and eye movements are normal with no photophobia.
What is the likely diagnosis?