Girl (4) wasn't immunised in country of birth
One of the patients diagnosed with measles in the current outbreak is just four years old and had not been immunised against the virus.
A Tralee-based GP was the first to identify a case of measles in his area, which is linked to the outbreak.
Dr David O'Brien, who practises alongside his mother, Dr Bridget O'Brien, treated a little girl who presented with "textbook symptoms" of the virus in May. Dr O'Brien said he knew straight away that it was a case of measles - despite the fact that he had never seen a case of the disease before.
The child is a non-Irish national who has moved to Ireland in the past year and was not immunised in her country of birth.
It is understood that she did not require hospitalisation.
Members of at least two families in the area have contracted the disease.
"It's not something we would see that often and it's the first case that I'd ever seen.
"The classical signs are the rash - which you would often see with other viral illnesses - and other signs include conjunctivitis or spots in the mouth," Dr O'Brien said.
He advised the patient to remain at home in order to avoid transmitting the virus to anyone else as it is airborne.
"For the most part it is a self-limiting virus but in rare cases, about one in 5,000, there can be swelling in the brain or the possibility of contracting viral pneumonia," he said.
Since the first case in May, Dr O'Brien has also seen some of the other people who have contracted measles, some of whom he suspects may have contracted the virus before it was identified.
Local newspaper 'The Kerryman' has reported that parents of children attending the Christian Brothers School in Tralee were warned that people may have been exposed to measles at a First Holy Communion in a local church on May 14.