Effects of Amodiaquine against Litomosoides carinii in Gerbils and Cotton Rats

Abstract

In searching for alternative antifilarial drugs, amodiaquine was found to be active against adult forms of Litomosoides carinii in Mongolian gerbils but not directly active against circulating microfilariae. Oral doses of 100, 50, or 25 mg/kg/day X 5 had significant activity. Female worms were more susceptible to the drug than males. In contrast, oral doses of 100 mg/kg/day X 5 had only feeble activity against the same strain of L. carinii in cotton rats. The generally unsatisfactory state of chemotherapy in filariasis encourages the development of alternative drugs (World Health Orgranization, 1967). Therefore, new types of antifilarial agents are being sought in these laboratories, mainly through the use of Litomosoides carinii in gerbils. The antimalarial drug amodiaquine (Camoquin?) was found to be active in this program. This report deals with its effects against adult and microfilarial stages of L. carinii in gerbils and cotton rats. MATERIALS AND METHODS Mongolian gerbils (Meriones unguiculatus, males) were purchased as weanlings from Tumblebrook Farms. Cotton rats (Sigmodon hispidus, juveniles of both sexes) were raised in the laboratory under conditions precluding natural infection. They were infected with Litomosoides carinii through a modification of the tank exposure method of Hawking and Sewell (1948) approximately 8 weeks before use. Briefly, this entailed allowing a large number of mites to feed on a gerbil or cotton rat with a patent L. carinii infection for 2 weeks and then allowing the mites to feed during an additional 2 weeks on the test animals. This schedule encompassed well the 2to 3-week incubation period in mites. The entire operation was carried out at 24 to 27.5 C. The animals used in an experiment were exposed concomitantly in the same tank. When placed on test, the gerbils weighed 70 to 100 g and the cotton rats weighed 140 to 200 g. Examination for microfilariae were made in Giemsa-stained thick films of blood drawn from the retro-ocular sinus. Films were prepared by spreading 20 mm3 of blood on a 25 by 15 mm area of a slide. Counts were made in 10 fields (100 X magnification). Multiplication of this count by 0.645 gave the approximate number of microfilariae/mm3 of blood. These examinations were started early in patency, 7 weeks after the 1st day of the 2-week exposure period, and were Received for publication 29 March 1968. continued at intervals of 1 to 4 days until the animals were examined for adult worms. Surviving animals were killed and examined for adult worms on day 15 by searching the pleural and peritoneal cavities. The thorax was excised intact, transferred to a petri dish containing heparinized physiologic saline, and dissected so as to permit a thorough search of the pleural cavity. The peritoneal cavity, which only occasionally contained worms, was carefully inspected. The numbers of live worms were scored or counted, as indicated. The numbers of dead worms were scored throughout since they could not be counted accurately owing to encapsulation and degeneration. Amodiaquine [ 4-[ 7-chloro-4-quinolylamino] -adiethylamino-o-cresol, dihydrochloride, dihydrate] was administered by gavage as solutions in aqueous 1% hydroxyethyl cellulose and 0.1% Tween 80 (volumes of 5 ml/kg). Doses were expressed in terms of the free base. The daily dose was given in two subdoses, approximately 6 hr apart. The controls were sham-dosed. The Mann-Whitney U test (Siegel, 1956) was used to test for significant differences (a = 0.05) between numbers of male or female worms in treated and control groups and between numbers of males and numbers of females within a group. Microfilarial counts were subjected to a 2-factor analysis of variance with repeated measures and, subsequently, the Neuman-Keuls procedure for testing differences between means (Winer, 1962).