Causative agent of loaosis (loiasis, Loa loa filariosis, African eyeworm)
Occurrence, life cycle, and epidemiology. Thirteen million people are infected with this filarial species in the tropical rainforest areas of Africa (western and central Africa, parts of Sudan) (WHO, 1995).
The adult and pre-adult parasites (Table 10.4) live in and migrate through the subcutaneous connective tissues. The microfilariae appear in a periodic pattern during the day in peripheral blood (Table 10.4, Fig. 10.17). Accordingly, the intermediate hosts are diurnally active horsefly species (Tabanidae: Chry-sops species). The prepatent period is five to six months. In some cases, mi-crofilariae do not appear in the blood even in older cases of infection. The adult filariae live for several years.
Pathogenesis and clinical manifestations. Clinical symptoms can occur two to 12 months after the infection. They are probably mainly allergic in nature. The filariae migrating through the connective tissues cause edematous swellings in the limbs, face, and body ("Calabar swellings") and itching nodules (Fig. 10.16b). The infection is often accompanied by blood eosinophilia. Migration of a parasite beneath the conjunctiva causes lacrimation, erythema, and other symptoms.
Diagnosis, therapy, and prevention. Diagnosis involves observation of typical symptoms, adult parasites in subcutis or conjunctiva and microfilariae in peripheral blood (in blood specimens sampled during the day!) (Table 10.4, Fig. 10.17). The drug of choice is diethylcarbamazine that kills microfilariae and damages macrofilariae after long-term therapy (N.B.: possible side effects).
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