A key malaria treatment has failed for the first time in patients being treated in the UK, doctors say.

The drug combination was unable to cure four patients, who had all visited Africa, in early signs the parasite is evolving resistance.

A team at the London School of Hygiene and Tropical Medicine said it was too early to panic.

But it warned things could suddenly get worse and demanded an urgent appraisal of drug-resistance levels in Africa.

Malaria parasites are spread by bites from infected mosquitoes.

It is a major killer of the under-fives with one child dying from the disease every two minutes.

Between 1,500 and 2,000 people are treated for malaria in the UK each year - always after foreign travel.

Most are treated with the combination drug: artemether-lumefantrine.

But clinical reports, now detailed in the journal Antimicrobial Agents and Chemotherapy, showed the therapy failed in four patients between October 2015 and February 2016.

All initially responded to therapy and were sent home, but were readmitted around a month later when the infection rebounded.

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All of the patients were eventually treated using other therapies.

But the detailed analysis of the parasites suggested they were developing ways of resisting the effects of the front-line drugs.

Two of the cases were associated with travel to Uganda, one with Angola and one with Liberia - suggesting drug-resistant malaria could be emerging over wide regions of the continent.

The malaria parasites all seemed to be evolving different mechanisms rather than there being one new type of resistant malaria parasite spreading through the continent.

The type of resistance is also clearly distinct from the form developing in South East Asia that has been http://www.bbc.co.uk/news/health-37859264" rel="nofollow - causing huge international concern.