Sowda-type onchocerciasis in Guatemala.

The usual pattern of onchocercal dermatitis in Africans and Guatemalans is a generalized and symmetrical dermatitis located on legs, arms and trunk. These patients appear to be anergic, with depressed immune responses and numerous microfilariae in the skin. In contrast, "sowda" is an unusual type of onchocercal dermatitis found in Yemenites and in a minority of African patients. Here the dermatitis is localized and asymmetrical - typically confined to one limb or one region of the body. Patients with sowda appear to be hypergic, with active humoral and cellular immune responses; microfilariae are rare or absent. This study describes two Guatemalan patients with sowda-type dermatitis. The diagnosis in these two patients is based on the asymmetrical papular pruritic dermatitis, rare or absent microfilariae, a positive Mazzotti reaction, and histopathologic changes characteristic of the sowda-type onchocercal dermatitis.