Two bottles, a box and envelopes containing pills of a new potentially cheap and effective malaria treatment that combines existing drugs. British doctors are warning travellers using last-minute-deal websites to seek anti-malarial drugs in advance. (Ricardo Moraes/Associated Press)

Travel websites that offer last-minute deals should inform people about the risks of malaria, infectious disease experts say.

In a letter published in this week's British Medical Journal, doctors said they were concerned about three recent cases of imported malaria in U.K. travellers returning from Gambia, a popular winter sun destination where malaria is endemic.

The letter was authored by John Widdrington, an infectious disease specialist at James Cook University Hospital, in Middlesbrough, U.K., and his colleagues.

Increasing use of websites to make cheaper last-minute holiday bookings means that more and more travellers are not getting a prescription for anti-malarial drugs in time to prevent the infectious disease, the authors said.

All three of the Gambia patients used the same travel website. Two made a late booking and failed to take the preventative drugs. The third also failed to take adequate medical advice before travelling and take such medication.

Within two weeks of returning home, they were all admitted to hospital with severe malaria. No further information was provided because of patient confidentiality restrictions.

"Many travel websites and holiday brochures, including the website used by our patients, make no specific reference to the risk of contracting malaria," the doctors wrote.

"Travel websites need to include explicit messages about taking medical advice and effective chemoprophylaxis before travelling to malaria-endemic areas. Advice on allowing sufficient time to organize this might reduce the particular risk to people making late bookings."

Chemoprophylaxis is the use of drugs to prevent the development of an infectious disease.