Quantitative Oogram Method in Cebus Monkeys Experimentally Infected with Schistosoma mansoni

Abstract

Quantitative oogram studies were conducted on four Cebus monkeys experimentally infected with Schistosoma mansoni, using rectal biopsy and mucosal curettage. The latter technique was recommended because it is easier to perform and gave a higher mean and a smaller variation in the number of eggs per gram of tissue. At least four rectal snips should be taken for quantitative evaluation of candidate schistosomicidal compounds. In experimental chemotherapy of schistosomiasis, monkeys are widely used for preclinical trials and, by rectal biopsy and mucosal curettage, schistosome eggs may be detected in the rectum wall (Pellegrino et al., 1965), providing a good criterion for the evaluation of drug activity. Active drugs produce an interruption of egg laying at the intestinal wall. According to the drug and dose, this stoppage may be permanent or temporary. In the latter case, that is, when relapse occurs, it is not possible to detect any reduction of worm population. Therefore, a quantitative method would be desirable. Can9ado et al. (1964) recently described a technique for a quantitative oogram in fragments from rectal biopsy and mucosal scraping in humans. The results obtained with this quantitative oogram method in four Cebus monkeys experimentally infected with S. mansoni are presented in this paper. MATERIAL AND METHODS Four Cebus apella macrocephalus Spix, 1823, were exposed, by percutaneous route, to 150 cercariae of S. mansoni shed by laboratory-infected Biomphalaria glabrata (L.E. strain kept at the Instituto de Biologia). For the collection of rectal snips two devices previously described (Pellegrino et al., 1965) were used. Rectal biopsy and mucosal curettage were performed from 199 to 355 days after infection, at a spot 5 to 10 cm distant from the anus. For quantitation a technique similar to that described by Cancado et al. (1964) was used. Glass Received for publication 30 September 1965. * This study has been supported by a research grant from the NIH, Bethesda, Maryland (AI 05917-02 TMP). t Fellow from CAPES, Brazil. Address: Instituto Nacional de Endemias Rurais, C. Postal 1743. Belo Horizonte, Brazil. slides and cover slips were previously weighed on a balance of 0.1 mg sensitivity. The biopsy fragments were transferred to one of the slides and the curetted snips to another. After covering the slides with their respective slips and pressing them, the preparations were weighed again. The weight of each fragment was then calculated. The slides were microscopically examined under low magnification. All viable eggs were counted and classified according to the criteria previously described (Prata, 1957; Pellegrino et al., 1962) and the number of eggs per gram of tissue was estimated. To study the daily as well as the spatial variation of the number of eggs, four fragments were collected, by rectal biopsy and mucosal curettage, from different sites of the rectal wall, on 4 successive days. Analysis of variance of the number of eggs per gram of tissue was made by using logarithmic transformation of the data.