New research by Dr. Eli Schwartz of Tel Aviv University and his co-workers sheds some light on why this is so. In nearly half of the cases of malaria that appeared after travelers returned home (usually despite careful use of anti-malaria drugs), the disease developed after a delay of many months. It turned out that the malaria parasites had quietly taken up residence in the liver of the infected patient, where they were protected against the medicines we use to zap them. Present medications only act on malaria parasites in the bloodstream; we need new products that can attack malaria in the liver as well.