Isolated malaria outbreak in Somalia: role of chloroquine-resistant Plasmodium falciparum demonstrated in Balcad epidemic.

A study was conducted in Balcad in December 1988 during a reported outbreak of malaria in order to investigate possible factors contributing to the outbreak. The slide positivity rate of 71% among fever patients, which was significantly higher than the usual rate, suggests the existence of a fresh malaria outbreak in the area. High parasite densities together with the pronounced malaria symptoms among both resident children and adult immigrants indicated little, if any, malaria experience in these patients. This outbreak could not be explained by gross climatic changes, e.g. unusual rainfalls. The in-vivo response of P. falciparum to the standard therapeutic regimen of chloroquine showed a high degree of resistance, with 31 of 36 patients showing resistance, including five RI responses and 26 RII-RIII responses. Micro in-vitro tests for chloroquine susceptibility showed resistance in 33 out of 37 isolates with a mean EC50 and EC99 of 1.50 and 10.97 X 10(-6) mol l-1 blood, respectively, indicative of a high degree of chloroquine resistance. All isolates tested against sulphadoxine/pyrimethamine showed a sensitive response. The frequent presence (78%) of detectable chloroquine levels prior to treatment did not apparently alter the in-vitro parasite growth. This is a sign of widespread use of this drug resulting in a high 'drug pressure' in the area. The proportion of sensitive parasites was inversely related to the pretreatment chloroquine concentration providing evidence of the selection of resistant parasites by the previous drug intake.(ABSTRACT TRUNCATED AT 250 WORDS)