Seasonal abundance of trematode cercariae in Bulinus truncatus in a small focus of schistosomiasis in the Nile Delta*

420 BRIEF COMMUNICATIONS/NOTES ......4 Fig. 2. Cyst of Entamoeba co/i stained with modified MIF solution (x500). Chilomastix mesnili, cysts and trophozoites; Dientamoeba fragilis, trophozoites; Endolimax nana, trophozoites; Entamoeba histolytica, cysts and trophozoites; E. hartmanni, cysts; E. coli, cysts and trophozoites; Giardia lamblia, cysts and trophozoites; and Iodamoeba butschlii, cysts. Little difference was detected between specimens stained with the two solutions. The modified MF solution was used to preserve 1 330 stool samples for several months; the results were comparable to those observed when the origi- nal MF solution was used. REFERENCES Sapero, J. J. et al. (1951). Science, 114, 550-551 Sapero, J. J. & Lawless, D. K. (1953) Amer. J. trop. Med. Hyg., 2, 613-619 Seasonal abundance of trematode cercariae in Bulinus truncatus in a small focus of schistosomiasis in the Nile Delta* K. Y. CHU,1 ISMAIL K. DAWOOD,' & H. A. NABI a Abstract Bulinus truncatus was most numerous from June to August, and echinostome cercariae, present in 19.3 % ofsnails, were the most prevalent ofthe 4 types of trematode cercariae found. The echinostomes occurred throughout the year, other cercariae only * From the Schistosomiasis Control Pilot Project and Training Centre, El Saraya, Alexandria, Egypt. The project is partly supported by WHO. 1 WHO malacologist. Present address: Inter-regional Research Project on Schistosomiasis Control in man-made Lakes, P.O. Box M190, Accra, Ghana. 'Agricultural engineer and malacologist. Agricultural engineer and assistant malacologist. in certain months. Double infections were uncommon. The findings suggest that echinostome cercariae exer- cise some biological control of Schistosoma haema- tobium in the area studied. El-Gindy & Rushdi (1962) found 8 types of trema- tode cercaria in Bulinus truncatus, the intermediate host of Schistosoma haematobium, in Egypt. How- ever, the relative and seasonal abundance of the different types of cercaria in the snail has not been examined. The present report summarizes a 1-year study in a well-known focus of schistosomiasis near Alexandria. 2910 SCHISTOSOME CERCARIAE IN EGYPT Materials and methods A small area surrounding Tamama, a village about 30 km from Alexandria, was selected for the study. The prevalence of S. haematobium infection among the local population is approximately 40%. No antischistosomal control measures have been applied. To collect snail specimens, 900 scoop samples were taken at monthly intervals in 18 selected streams from October 1968 to September 1969. On being taken back to the laboratory, Bul. truncatus snails were crushed for detection and identification of cer- carial infections. A number of specimens of Biom- phalaria alexandrina and Physa acuta were also examined. Results The results of the study are presented in Table 1. The collections showed that there was a high density of Bul. truncatus from June to August, and a low density in September, October, January, and May. Four types of cercaria were found: an echinostome, an amphistome, a schistosome, and a xiphidiocer- caria. The cercarial infection rate over the whole year in Bul. truncatus was 19.3% for the echino- stome, 5.5% for the amphistome, 0.4% for the schistosome, and 0.1 % for the xiphidiocercaria. The echinostome cercariae were prevalent throughout the year, the amphistomes only in cold months. Schistosome cercariae were found only in November, December, February, and June, and xiphidiocer- cariae only in June. Double infections were uncommon. A combin- ation of echinostome and amphistome cercariae was found in only 3 cases, and no other combinations were detected. Discussion The results show that Bul. truncatus is an ideal intermediate host for the echinostome and amphi- stome cercariae as well as the schistosomes. Echino- stome and amphistome cercariae were also found in Biom. alexandrina, but in very small numbers and at a low intensity of infection. Echinostome cysts were found in Bul. truncatus, Biom. alexandrina, and P. acuta. If cysts are included in the rate of Table 1. Monthly rate of trematode cercarial infection in Bulinus truncatus in and near Tamama village Snails infected with No. of schisto- Month snails some echinostome cercariae amphistome cercariae xiphidio- examined cercariae No. % No. % cercariae No. No. 1968 Oct. 103 0 18 17.5 6 5.8 0 Nov. 147 2 6 4.1 13 8.8 0 Dec. 153 2 24 15.7 13 8.5 0 1969 Jan. 104 0 14 13.5 3 2.9 0 Feb. 156 3 3 1.9 34 21.8 0 March 174 0 31 17.8 15 8.6 0 April 133 0 25 18.8 5 3.8 0 May 99 0 10 10.1 0 0 0 June 317 1 42 13.3 0 0 2 July 277 0 163 58.9 1 0.4 0 Aug. 248 0 41 16.5 1 0.4 0 Sept. 98 0 10 10.2 0 0 0 Total 2 009 8 387 19.3 91 5.5 2 421 422 BRIEF COMMUNICATIONS/NOTES echinostome infection in Bul. truncatus, the annual rate is 31.5%. Of the 8 types of trematode cercaria found in Bul. truncatus by El-Gindy & Rushdi (1962), we found only 4. In a nearby area, we found a longi- furcate holostome cercaria also mentioned by El- Gindy & Rushdi (op. cit.). Little is known of the prevalence of echinostomes in Egypt, although Abdel-Azim (1930) found that this type of cercaria (Echinostomum recurvatum) was present in large numbers of Bul. truncatus (= Bul. contortus, Bul. dybowski, and Bul. innesi) in the Cairo area. The final hosts of the echinostome are not known. Laboratory white mice were quite sus- ceptible to infection when they were fed with natural- ly and experimentally encysted Biom. alexandrina and Bul. truncatus. Echinostome eggs started to appear in the faeces of mice 8-9 days after cysts had been eaten, and collar spines were well developed in adult worms in the fifth week after infection. Recent evidence (Lie et al., 1965, 1966, 1967) shows that echinostome cercariae are antagonistic to the development of larvae of other trematode species in the same host. Lie et al. (1968) also suggested that competing echinostome larvae might be used to control other trematodes, i.e., by intro- ducing echinostomes into an area to suppress the target species, a schistosome. Judging from the results obtained at Tamama and reported here, nature is already exercising some biological control of S. haematobium, and hence of urinary schistoso- miasis, by means of echinostomes in one area in Egypt. The effect of such natural control on the endemicity of urinary schistosomiasis is as yet un- clear. It may foreshadow the possibility of also using echinostomes for the biological control of intestinal schistosomiasis in the Nile Delta. REFERENCES Abdel-Azim, M. (1930) Ann. trop. Med. Parasit., 24, 189 El-Gindy, M. S. & Rushdi, M. Z. (1962) In: Wolsten- holme, G. E. W. & O'Connor, M., ed., Bilharziasis, London, Churchill, pp. 81-102 (Ciba Foundation Symposium) Lie, K. J. et al. (1965) Nature (Lond.), 206, 422 Lie, K. J. et al. (1966) J. Parasit., 52, 454 Lie, K. J. et al. (1967) J. Parasit., 53, 1205 Lie, K. J. et al. (1968) Trans. roy. Soc. trop. Med. Hyg., 62, 299 Laboratory evaluation of the molluscicidal potency of a butanol extract of Phytolacca dodecandra (endod) berries S. S. BAALAWY 1 Abstract The effect of butanol extracts of endod against Biomphalaria choanomphala, B. pfeifferi, andBulinus (Physopsis) nasutus was tested at different concentra- tions andfor different exposure periods. Exposure to 19-25 ppm for 6 hours or to 6-7 ppm for 24 hours caused about 100 % mortality. A number of substances of vegetable origin have been found to have molluscicidal activity. Mozley (1939, 1952) reported that the fruits of Balanites aegyptiaca, Sapindus saponaria, and Swartzia mada- gascarensis were among the most promising natural 1 East African Institute for Medical Research, Mwanza, Tanzania. molluscicides. An investigation of the molluscicidal properties of the fruits of Sapindus saponaria on the snail Bulinus (Physopsis) africanus was made by Msangi & Zeller (1965). In many developing countries in the tropics, schistosomiasis is endemic and the snails that trans- mit the disease are widespread. Therefore, large-scale schistosomiasis control programmes based on the control of snails by means of conventional mollusci- cides may be expensive. Further studies on the pos- sibilities of using vegetable molluscicides are there- fore desirable. Dried berries of Phytolacca dodecandra (endod) are widely used in Ethiopia instead of soap for washing clothes. It was observed that in natural bodies of water where endod had been used there 2911