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The Use of Cercariae Infec­tion of the Bulinus Truncatus Snail for Evaluation of Schistosomiasis Control in Iran

Ali Farahnak, Iraj Mobedi, Mohammad Reza Eshraghian

How to cite this article:

A Farahnak, I Mobedi, MR Eshraghian, The Use of Cercariae Infec­tion of the Bulinus Truncatus Snail for Evaluation of Schistosomiasis Control in Iran. 2008; 28(1): 59-59


To the Editor: Urinary schis­tosomiasis caused by Schistosoma haematobium has been reported from many countries in Africa and Asia.1 Many studies have been con­ducted on the distribution, ecology, biology and host-parasite relation­ships of the snail in Khuzestan during the 1970s by the staff of the Schistosomiasis Control Project.2-5 Because of political changes in the neighboring country of Iraq where urinary schistosomiasis was preva­lent, and because of the constant travel of Iraqi citizens to these areas, local and national health authorities wanted an evaluation of the current situation of the disease from the viewpoint of parasite transmission from snails to the local inhabitants.6 Therefore, the present study was conducted to determine the pres­ence of Schistosoma cercariae in local Bulinus snails as criteria for evalua­tion of the schistosomiasis control program in the rural area of the southwest of Iran.


A total of 2400 B. truncatus snails were randomly collected from southern and eastern districts of the Dezful region and transferred to a health research centre. Collected snails were examined for shedding cercariae by using artificial light, leaving over night or by crushing snails in a glass plate. Cercariae were identified by systematic key references.7 Of the total of Bulinus snails examined for schistosome cercariae, 52 (2%) were found to be infected with Amphistome cercariae, and 15 (0.05%) with Strigea cer­cariae (Figures 1, 2, 3). Not a single Schistosoma cercaria was obtained from the snails.


Evaluation of the progress of schistosomiasis control programs, by case detection, when the infec­tion rate becomes extremely low, is expensive, time consuming and difficult. For these reasons, the method of examination of the snail intermediate host for the presence of cercariae of the parasite can be used as a new approach for evalu­ation of the transmission status of the infection. The abundance of snail hosts in this area, as well as the visiting of Iraqi citizens who may come from schistosomiasis-infested areas of Iraq, may cause reinfection of the local snails with the parasite. Various cercariae species including Strigea cercariae and Amphistome cercariae obtained from B. truncatus by shedding or crushing methods, can be easily distinguished from cercariae of schistosomes, which has no pharynx.


During the summer, Khuzestan province is very hot. For this reason, people, especially children, swim and play in the rivers or canals, which are used for agricultural pur­poses. In addition, many young chil­dren work on the agricultural farms without any protection on their hands or feet where S. haemato­bium as well as animal schistosome cercariae can readily penetrate the skin.8 Lack of S. haematobium cercariae in our samples in this region revealed that snails are free from this parasite and support the theory that transmission of schistosomes cecaria does not occur in the districts and therefore this disease is still under control, which is good news for in­habitants of the region as well as for local health authorities. Because of the presence of Bulinus in the other parts of province, use of this proto­col for evaluating the transmission status of S. haematobium by finding cercariae of the parasite among local B. truncatus is recommended.


This study was supported by a grant (240/802) from the School of Public Health and the Institute of Public Health Research at Medical Sciences/ University of Tehran. Special thanks to Professor Freidon Arfaa for review and his comments on the article. The authors would like to thank the Mr. R. Pourshojaei and Mr. M. Jahanbani for collection of snails. Thanks also Miss M. Rohnavaz for maintaining of snails in the lab.



1. WHO Expert Committee. Prevention and control of schistosomiasis and soil-transmitted helminthiasis. World Health Organ Tech Rep Ser 2002;912:1-57.

2. Chu KY, Massoud J, Arfaa F. Distribution and ecology of Bulinus truncatus in Khuzestan, Iran. Bull World Health Organ 1968; 39:607-37.

3. Chu KY, Massoud J, Sabbaghian H. Host-parasite relationship of Bulinus truncatus and Schis­tosoma haematobium in Iran. 4. Effect of month of infection on cercarial-incubation periods of S. haematobium and S. bovis. Bull World Health Or­gan 1966; 34:135-40.

4. Chu KY, Arfaa F, Massoud J. The survival of Bulinus truncatus buried in mud under experimen­tal outdoor conditions. Ann Trop Med Parasitol 1967;61:6-10.

5. Massoud J, Arfaa F, Farahmandian I, Ardalan A, Mansoorian A. Progress in the national schis­tosomiasis control programme of Iran. Bull World Health Organ 1982; 60:577-82.

6. Youssef AR, Cannon JM, Al Juburi AZ, Cockett AT. Schistosomiasis in Saudi Arabia, Egypt, and Iraq. Urology 1998;51(5A Suppl):170-4.

7. Schell S.C. The trematodes. Wm.C.Brown Com­pany Publishers. 1970:18-34.

8. Farahnak A, Essalat M. A study on cercarial der­matitis in Khuzestan province, south western Iran. BMC Public Health 2003; 3. www.biomedcentral. com/1471-2458/3/35 .


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