An emergency blood test showed that he had contracted potentially fatal falciparum malaria. Rapid diagnosis helped save Malcolm's life, but he still spent over five days in hospital being treated with quinine and antibiotics. Malcolm has learnt the hard way that even when you seek advice on protection, and take the tablets religiously, there's no guarantee of immunity. On two subsequent trips he used mefloquine again with no ill effects. If the mosquito is buzzing it has not yet landed.
Mosquitoes detect specific substances in human sweat with their antennae.
As different people have different metabolism, they give out slightly different amounts of these chemicals in their sweat. So if two people are in close proximity, the mosquitoes will home in on the one they find most attractive. But it is also likely that one person isn't reacting to the bites, not that they aren't being bitten. Don't let the apparent lack of bites make you complacent. There is no excuse for not taking your anti-malaria medication.