STUDIES ON FILARIASIS AMONGST ORANG ASLI IN PENINSULAR MALAYSIA, WITH SPECIAL REFERENCE TO CHEMOTHERAPY

Abstract

Filarial infections and its chemotherapy in Orang Asli were studied. Chemotehrapeutic drug trials with the laevorotatory isomer of tetramisole or 2,3,5,6 – tetrrahydro – 6 – imidazo (2, 1-b) thiazole and diethylcarbamazine citrate (DEC) in rural Wuchereria bancrofti, periodic and subperiodic Brugia malayi microfilaraemic patients and laboratory models of Brugian filariasis were carried out. Microfilarial rates of 0.7%, 1.7%, 3.7% and 0.2% due to rural W. bancrofti, periodic B. malayi, subperiodic B. malayi and a mixed infection of W. bancrofti and B. malayi respectively were seen in the 2,645 Orang Asli examined. The mean microfilarial rate was 6.3%. Microfilarial densities were low with 86.1% having counts below 50/60 mm3 peripheral blood film. There was no sex difference in microfilarial rates which were found to increase steadily from birth to late teens and then stabilized. The transmission of the disease among Orang Asli was discussed. 79 microfilaraemic patients were put on drug trials with various oral levamisole hydrochloride total dosage regimes of 150-3,150 mg/kg body weight and total oral DEC of 36 and 126 mg/kg body weight. Complementary drug trials in cats infected with B. malayi and B. pahangi confirmed the effectiveness of these two drugs. The optimum dosage regime with levamisole hydrochloride recommended for treatment of microfilaraemic patients is 100 mg stat and then 100 mg twice daily for 10 days. This dosage regime was as effective as a total oral dosage of DEC at 36 or 126 mg/kg body weight. Side reactions were dose dependent, transient and mild. Fever was the commonest side reaction seen. One patient developed fits after a single oral dose of 150 mg levamisole hydrochloride. The patho-physiology of these side reactions was discussed and the use of levamisole hydrochloride at the dosage suggested her as an alternative drug for the treatment of patent and occult filariasis should be under close supervision. The Indirect Fluorescent Antibody Technique (IFAT) using papain-treated and non-treated whole microfilarial antigens of subperiodic B. malayi, B. pahangi and Dirofilaria repens was shown to be useful in the detection of filarial antibodies. A titre of 1:10 and above, and 1:80 and above using non-treated and papain-treated antigens respectively were considered positive titres. Treatment of microfilaraemic patients signifantly lowered the percentage of positive IFAT titres.