People travelling to countries affected by malaria have been warned to take proper medication and medical advice.
There have been six recent cases of the disease, including two deaths, in Britain; the six people had all recently returned from the Gambia in west Africa.
The Health Protection Surveillance Centre (HPSC) warned that potential visitors should take the appropriate precautions.
Dr Paul McKeown of the HPSC, a specialist in public health medicine, said none of the people recently affected in Britain had taken anti-malarial medication.
"Malaria is a common and serious tropical disease passed on to humans by mosquito bites. There have been more than 40 cases so far this year in Ireland, in people who contracted the disease abroad. There are about half a billion cases each year globally," he said.
"The best defence against malaria is to avoid getting bitten by infected mosquitoes by staying away from areas where mosquitoes gather and by protecting your skin using clothing, anti-mosquito sprays and mosquito nets. There are also effective prophylactic medications that can be taken to prevent the development of the disease."
Dr McKeown said failure to take the right medication is one of the commonest reasons for developing malaria.
"Anyone who becomes ill during or following a visit to a country where malaria is common should seek immediate medical advice and let their doctor know about their recent travel. Doctors should be suspicious of a fever or flu-like illness in such travellers, and should assume malaria until proven otherwise."
He said there were few side effects from a course of tablets taken to prevent malaria.