.
Authorities are now searching for anyone who has been in contact with them during their stay.
This includes all those on board the Air France flight that took the family to Costa Rica on February 18.
VACCINES COMPULSORY
France only made measles vaccines compulsory for the first time last year.
Most other developed countries insist on children being vaccinated against the disease - including the UK through the MMR injections.
Measles was officially wiped out in the UK in 2016 thanks to the jab, the World Health Organisation (WHO) confirmed.
According to the WHO, the measles vaccine prevented 21 million deaths worldwide between 2000 and 2017.
But a rise in imported cases to the UK and outbreaks across Europe suggest the tide is turning in the fight against the virus.
In 2016 there were more than 500 measles cases in England.
ANTI-VAX MYTHS
Health officials blame the rise of the so-called "anti-vax" movement for contributing to outbreaks.
Anti-vaxxers wrongly believe that vaccines are more harmful to their children - including unfounded claims linking the MMR jab to autism.
Such misinformation is leading to a resurgence of potentially life-threatening infections, health chiefs fear.
An official report released last year claimed measles cases were 30 per cent higher worldwide in 2017 than the previous year.
Martin Friede, WHO’s director of immunisation, vaccines and biologicals, said at the time: "We are actually regressing in the fight against measles."
He added that "supposed experts making accusations against the vaccine without any evidence" have had a negative impact on parents’ decisions.
Rash move: How common is measles?
THE World Health Organization confirmed that the UK eliminated measles in 2016.
This is because the MMR vaccine is highly effective and vaccine uptake has been very high in the UK for many years.
But this doesn't mean that measles has disappeared. Measles is common in many countries around the world, and currently there are several large measles outbreaks across Europe.
We'll continue to see imported measles cases in the UK, and anyone who hasn't had 2 doses of the MMR vaccine can catch it.
In 2016 there were more than 500 measles cases in England, many in teenagers and young people attending summer festivals who'd missed out on their MMR vaccine in childhood.
Source: NHS
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