Studies on Filariasis in Malaya: Treatment ofWuchereria MalayiFilariasis with Diethylcarbamazine in Single Daily Doses

Antifilarial activity of diterpenoids from Taxodium distichum

BACKGROUND

Lymphatic filariasis caused by Wuchereria bancrofti, Brugia malayi and B. timori, is a debilitating disease with an adverse social and economic impact. The infection remains unabated in spite of treatment with existing antifilarial drugs diethylcarbamazine (DEC) and ivermectin which are chiefly microfilaricides. There is therefore, need for macrofilaricides, embryostatic agents and better microfilaricides. In the present study we explored the antifilarial potential of crude extract and its molecular fractions of the plant Taxodium distichum using in vitro assay systems and rodent models of B. malayi infection.

METHODS

Ethanolic extract (A001) of aerial parts of T. distichum was solvent fractionated and sub-fractionated. Four molecules, 3-Acetoxylabda-8(20), 13-diene-15-oic acid (K001), Beta-sitosterol (K002), labda-8(20),13-diene-15-oic acid (K003) and Metasequoic acid A (K004) were isolated from the fractions and their structure determined by spectroscopic analysis. The extract, subfractions and molecules were evaluated for antifilarial activity against B. malayi by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) reduction and motility assays in vitro and in two animal models, Meriones unguiculatus and Mastomys coucha, harbouring B. malayi infection.

RESULTS

A001 was effective in killing microfilariae (mf) and adult worms in vitro. The diterpenoid K003 produced 100 % reduction in motility of both mf and adult worms and > 80 % inhibition in MTT reduction potential of adult female worms. In B. malayi-M. unguiculatus model, A001 killed all the adult worms in > 80 % of infected animals. K003 was embryostatic (> 95 %) in this model. In the B. malayi-M. coucha model, K003 killed ~54 % of adult worms (macrofilaricidal activity) and rendered > 36 % female worms sterile; it also stopped any further rise in microfilaraemia after day 42 post-initiation of treatment.

CONCLUSION

Ethanolic extract of aerial parts of the plant T. distichum possesses potent antifilarial activity and the active principle was localised to K003 which showed significant macrofilaricidal activity and late suppression of peripheral microfilaraemia and some embryostatic activity. These findings indicate that labdane diterpenoid molecule(s) may provide valuable leads for design and development of new macrofilaricidal agent(s). To the best of our knowledge, this is the first report on antifilarial efficacy of products from the plant T. distichum.

Diagnosis and treatment of lymphatic filariasis

The lymphatic filariases, Wuchereria bancrofti, Brugia malayi, and B. timori, infect nearly 100 million people throughout the tropics, but mainly in Africa and southeast Asia. Over 900 million people live in endemic, areas at risk to the infection. The filarial parasites reproduce slowly, whereas their mosquito vectors are quickly-reproducing opportunists. Thus, although vector control can reduce the risk of transmission, the parasite itself would seem a more vulnerable target for prolonged attack. In this article, Felix Partono discusses the clinical diagnosis of f lariasis and argues that the disease can be effectively controlled by attacking the parasites in infected communities, using diethyl-carbamazine (DEC) as the drug of choice.

Drug trials with levamisole hydrochloride and diethylcarbamazine citrate in Bancroftian and Malayan filariasis

Seventy-eight microfilaraemic patients with Wuchereria bancrofti and Brugia malayi infections were treated with various oral levamisole hydrochloride total dosage regimes of 150 to 3,150 mg and total diethylcarbamazine citrate (DEC) of 36 and 126 mg per kg body-weight. Significant microfilaricidal and probable macrofilaricidal effects were seen at total levamisole hydrochloride dosages of 300 to 3,150 mg and the DEC dosages. The optimum dosage regime with levamisole hydrochloride recommended for treatment of microfilaraemic patients is 100 mg initially followed by 100 mg twice daily for 10 days. This dosage regime was as effective as a total oral dosage of DEC at 126 mg per kg body-weight. Side reactions were dose-dependent, mild and transient, with fever being the most common. One patient developed fits after 150 mg levamisole hydrochloride. The pathophysiology of these side reactions is discussed and it is recommended that levamisole hydrochloride, as a probable alternative for the treatment of patent and occult filariasis, should be used only under close medical supervision.

Effectiveness Of Diethylcarbamazine In The Mass Treatment Of Malayan Filariasis With Low Dosage Schedule

A series of 250 patients with filariasis due to periodic type of Brugia malayi was selected for the mass treatment with diethylcarbamazine from two areas in Cheju-Do. Two types of dosage schedules have been employed: the one was the conventional dosage schedule (uninterrupted dose of 6 mg/kg once daily 6 times repeated with an interval of one or two month totaling 72 mg/kg), and the other was the low dosage schedule (uninterrupted dose of 0.5, 1, 2, 4, 6 mg/kg body weight given once a day with an additional 6 mg/kg once daily totaling the maximum 37.5 mg/kg). The relative effectiveness of those two schedules was evaluated under the basis of the effects on microfilaria counts and the results of analysis of side-reactions observed. The results obtained in this experiment are summarized as it follows. In the conventional dosage treatment, 118 out of 141 microfilaria positives treated (83.7%) became negative and microfilaria reduction rate was about 99%. However, in the low dosage treatment, 35 out of 43 positives treated (85.4%) became negative and reduction rate of microfilaria, 99.5% in average. Total dose and duration of treatment were 72 mg/kg and about 60 days in the former schedule but it were maximum 37.5 mg/kg and 10 days in the latter. The recurrence of filariasis after treatment in both conventional and low dosage was negligible. Comparative analyses regarding the resulting side-reactions between the two schedules were made on their frequency, severity, onset and duration and relationship with microfilaria density. The febrile reaction was most frequently observed in 80.5% in the conventional, 43.9% in the low dosage schedule. The main side-reactions usually appeared within 6 to 10 hours and lasted 48 to 72 hours in the former threament, however they occurred in 7 to 8 hours and lasted 24 to 43 hours in the latter dosage schedule. It is assumed that the side-reactions are not directly related with the microfilaria count. However, the febrile reaction seems to be correlated with microfilaria density if it is above a certain limit. The presence of adult worm in a lymphnode involved with local reaction was ascertained from the biopsy specimens performed and local reactions such as lymphangitis and lymphadenitis after drug administrations were assessed from clinical and pathological point of view. It was conclusively indicated that the chemotherapeutic response to low dosage schedule within shorter length of treatment was equal to that of larger doses in long term medication from the point of the reduction in microfilaria, and particularly the resulting side-reactions were also reduced in the low dosage schedule.