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Q Our practice nurse says patients have immunity to malaria for two years after leaving their country but then lose it. Is this true?
A People who live and remain in malarious areas develop immunity against the disease after repeated infections. At highest risk are children under five years of age.
Of particular concern are patients who, having lived in a particular malarious area, leave to become immigrants, or refugees in a non-malarious area. As they are no longer exposed to mosquito bites, over time they lose immunity.
It is not possible to give a precise time when such immunity is lost. By two years, one should expect for the immunity to have been practically lost, but in some instances this has been observed after six months. When we see such travellers in primary care travel clinics, we cannot estimate the degree of the individual's immunity.
Quite often, these travellers believe they have retained some immunity, having lived at their destination, and thus do not seek pre-travel health advice and do not take prophylaxis (chemoprophylaxis and/or bite prevention measures). But they are in fact often at a higher risk than another traveller who stays only in an air-conditioned hotel, as the immigrant traveller back home will expose himself to a higher rate of transmission.
Further, they might have left home at a time when malaria transmission was relatively low, only to return years later when transmission is high.
I had a case of a man who, having lived and worked in the UK for 25 years, retired and decided to spend the first three months of his retirement back home in Nigeria. He refused chemoprophylaxis and on his return he presented intermittently with 'flu-like illness'. When I first saw him he'd already had three negative blood tests for malaria and was not prepared to have any more blood tests.
I insisted on remaining suspicious of malaria and it was his fifth blood tests that finally showed Plasmodium falciparum present.
The safest rule for your practice nurse is to always advise malaria chemoprophylaxis and mosquito bite prevention to all immigrants visiting their home country, irrespective of the time they have been away. Pay particular attention to children accompanying them.
Dr George Kassianos, immunisation spokesman for the RCGP and a GP in Bracknell, Berkshire