Surveillance of urinary thiocyanate concentration after epidemic spastic paraparesis in Mozambique

A large epidemic of spastic paraparesis in Mozambique during a drought was attributed to cyanide exposure from cassava. Active surveillance in one of the villages most affected by the epidemic detected four new cases in the first year after the epidemic, and none in the second year. In apparently healthy schoolchildren in the same village, surveillance of urinary thiocyanate concentration, an indicator of cyanide exposure, showed high peak values of 1175 and 673 mumols l-1 in succeeding years, with a gradual return to near-normal values in the third year. A marked seasonal variation in thiocyanate concentration was present, with the highest value coinciding with the dry season, the period of the epidemic, and the cassava harvest. Lower values were found in the neighbouring unaffected semi-urban centre. As cassava cultivation increases in many drought-affected countries, we recommend monitoring urinary thiocyanate concentration to estimate cyanide exposure and identify populations at risk for spastic paraparesis epidemics.