Dogs have such exquisitely sensitive noses that they can detect bombs, drugs, citrus and other contraband in luggage or pockets. Is it possible that they can sniff out even malaria? And when might that be useful? A small pilot study has shown that dogs can accurately identify socks worn overnight by children infected with malaria parasites even when the children had cases so mild that they were not feverish. In itself, such canine prowess is not surprising. Since 2004, dogs have shown that they can detect bladder cancer in urine samples, lung cancer in breath samples and ovarian cancer in blood samples. Trained dogs now warn owners with diabetes when their blood sugar has dropped dangerously low and owners with epilepsy when they are on the verge of a seizure. Other dogs are being taught to detect Parkinsons disease years before symptoms appear. The new study ... does not mean that dogs will replace laboratories. But for sorting through crowds, malaria-sniffing dogs could potentially be very useful. Some countries and regions that have eliminated the disease share heavily trafficked borders with others that have not. For example, South Africa, Sri Lanka and the island of Zanzibar have no cases but get streams of visitors from Mozambique, India and mainland Tanzania. And when a region is close to eliminating malaria, dogs could sweep through villages, nosing out silent carriers people who are not ill but have parasites in their blood that mosquitoes could pass on to others.