Saudi Journal of Gastroenterology
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Year : 2000  |  Volume : 6  |  Issue : 3  |  Page : 157-160
Formol-ether concentration method in the diagnosis of active schistosoma mansoni in patients with detectable IHA

1 Dr. Al Mofarreh Polyclinic, KKUH, Riyadh, Saudi Arabia
2 Department of Medicine, KKUH, Riyadh, Saudi Arabia

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Date of Submission09-Jun-1999
Date of Acceptance30-May-2000


Schistosomiasis is a world wide human infection. In Saudi Arabia there are multiple endemic foci. Various methods have been used to diagnose Schistosoma mansoni. We studied 1410 patients coming from S. mansoni endemic areas with detectable antibodies by indirect hemagglutination (IHA). Stool specimens were tested for S. mansoni ova by direct smear and formol-ether concentration (FEC) methods. The objective of the study was to identify patients with active schistosomiasis using FEC method and a single direct smear. Twenty percent of IHA positive patients had active infection detected by FEC, while a single direct stool smear diagnosed only 2.4% (P<0.0001). The percentage of positive FEC was significantly increasing in linear trend with IHA level. This trend wasn't observed with direct smear examination. The current data suggest that FEC is helpful to diagnose active schistosomiasis, therefore it is recommended in IRA positive individuals.

Keywords: Schistosoma mansoni, Indirect hemagglutination, formol-ether concentration.

How to cite this article:
Al Mofarreh MA, Al Akwaa AM, Hasan SW, Al Mofleh IA. Formol-ether concentration method in the diagnosis of active schistosoma mansoni in patients with detectable IHA. Saudi J Gastroenterol 2000;6:157-60

How to cite this URL:
Al Mofarreh MA, Al Akwaa AM, Hasan SW, Al Mofleh IA. Formol-ether concentration method in the diagnosis of active schistosoma mansoni in patients with detectable IHA. Saudi J Gastroenterol [serial online] 2000 [cited 2023 Jan 29];6:157-60. Available from:

Schistosomiasis is caused by the trematodes Schistosome. Schistosoma mansoni, hematobium, Japonicum and intercalatum are the four main species responsible for human infection. World­ wide, over 200 million individuals are infected in more than 70 countries [1] . In Saudi Arabia multiple endemic foci of S. mansoni and S. hematobium are scattered over the country (e.g. Al-Baha, Hail, Taif, Bisha, Najran) [2],[3],[4] . Overall prevalence of 6.5% has been reported in 1984 [4] . A decade later a prevalence as low as 0.4 % had been reported [5],[6] . S. mansoni predominantly affects the colon, where the presence of ova produces macroscopic lesions such as mucosal granularity, erythema and superficial ulcerations. Progressive fibrosis in the intestinal wall frequently leads to rigidity and stricture formation. Early detection and treatment of schistosomiasis is important for preventing irreversible complications. Indirect hemagglutination is a quite sensitive and fast screening method [7] . However, it is not useful for differentiating active infection from previous exposure. Demonstration of ova is important for a definitive diagnosis. This however, can be difficult in mild and chronic infection with a low parasite burden. In such instances direct stool smear examination which is practiced in several clinics and institutions often fail to demonstrate ova [8] . In contrast FEC is more useful with a higher detection rate [9],[10].

The objective of this study was to utilize FEC for optimal detection of active Schistosoma mansoni infection among individuals with detectable antibodies by IHA.

   Patients and Methods Top

The medical records of adult patients originating from schistosomiasis endemic areas (e.g. Al-Baha, Hail, Taif, Bisha, Najran, Jizan, Mahael, Abha, Madinah, Riyadh) [2],[3] , who attended Dr. Al-Mofarreh Polyclinic in Riyadh during a period of six years from 1413-1418 H (1993-1998) were retrospectively analyzed.

Cellognost® Schistosomiasis Reagent (Code No. OTGN10/11 Bearing, Germany) was used to test blood for detection and estimation of antibody levels by IRA. A titer of > 1:16 was considered diagnostically significant for scishstosomiasis [11] . With every batch of IAH test a positive and negative control were included to verify the validity of the test results. Stool specimens were examined by a single direct smear and FEC methods. In the direct examination a small piece of fresh stool was placed on a microscope slide and a drop of saline was added. Both stirred into an oven suspension, covered with cover glass and scanned for Schistosoma mansoni and other parasites for a minimum of five minute before reporting negative. A modified Ritchiefs method was used for FEC by fixing one gram of feces in seven ml of 10% formol-saline for 10 minutes and large fecal particles were removed by straining.The filtrate was mechanically shaken vigorously with 3ml of diethyl ether followed by centrifugation at 2000 rpm for 2 minutes. After discarding all the three layers of supernatant the sediment was transferred to a glass slide for microscopic examination. Schitosoma mansoni ova were counted under low power objective and their viability was confirmed by using high-power objective [12],[13] Both methods were performed by a ten-year experienced microbiologist. The results of IHA were correlated with the results of direct smear and FEC for all patients. Active infection was considered in the presence of viable ova which was estblished by finding a well defined fully developed miracidium or flickering of excretory flame cells in unfixed fresh ova [14],[15] .

Chi-Square, z-test and linear correlation trend were used for statistical analysis. P values of <0.05 were considered significant.

   Results Top

The total number of patients with detectable IHA (> 1:16) was 1410. Three hundred fifty nine patients (25%) had history of treated scishstosomiasis. The age ranged from 16-87 (mean 45) years with 3:1 male to female ratio. Active infection was detected in 280 patients (20%) by FEC method, whereas direct smear detected only 34 (2.4%) which was simultaneously detected by FEC [Figure - 1]. A significant linear trend of positive FEC in correlation with increasing level of IRA titer was noted. The higher the antibody titer the more the percentage of positive FEC (P<0.001). This correlation was not observed with direct smear [Table - 1].

A high percentage of positive FEC (40%) were encountered in patients with titer of 1 > 2048 compared to 18% in those with lower titers.

   Discussion Top

Schistosoma infection is a worldwide disease. It is found in parts of South America some Carabian islands, Africa, Middle East, along the Nile Valley countries, Yemen and parts of Saudi Arabia [1],[2],[3],[4],[5],[6] . Although the infection is frequent and some times universal in endemic areas, the progression to symptomatic disease is relatively uncommon and depends on a number of factors including duration and intensity of infection [16] . Liver involvement may induce fibrosis and portal hypertension associated with a major morbidity and mortality. The diagnosis of Schistosoma mansoni is established by identification of ova in stool by a variety of techniques including direct smear, sedimentation method, Kato and FEC [12],[13],[17] . Because of its simplicity, and specificity, the direct smear has been the most widely used technique [18] . However it lacks sensitivity. This could be amplified by repeating the examination 4-6 times [18],[19] . This may be inconvenient for the patients and time consuming for laboratory personnel. In mild infections, ova may not be detected in the stool by direct smear. However, additional use of FEC significantly (P<0.0001) increases the yield of detection as has been observed in this study.

In the current study Schistosoma mansoni ova were detected by direct smear in only in 2.4% this was markedly lower than those reported in the literature ranging between 30-45% [8],[10],[19],[20],[21] .This marked difference could be due to a low parasite burden in the examined population. It could also be due reduction of infection rates as a result of successful eradication programs [4],[5].

In our series FEC was significantly superior to the direct stool technique (P<0.0001) which concords with other reports [23],[25],[26].

In endemic areas few studies have reported FEC sensitivity ranging between 25 and 75% [16],[18]. Our results fell in the lower range. Although FEC method is accurate it is time consuming and requires more expertise.

Many serological tests have been applied for the diagnosis of Schistosoma infestation for instance intradermal test (IDT), circumoval precipitin test (COPT), cercaria-Hullen reaction, miracidia immobilization test, hemagglutination test (IHA), fluorescent antibody test, enzyme linked immunosorbent assay (ELISA). These tests are not well standardized and differ in sensitivity and specificity. A positive test may indicate a present or past infection. The sensitivity for the majority of the current tests has been greater than 90% [16] . Indirect hemagglutination has been utilized in epidemiological studies in endemic areas and in diagnosis of recent infection in non-endemic or in visitors to endemic areas [7],[22],[24] . Varying sensitivities and specificities have been reported in the range 25-95% [7],[9],[10],[11],[21],[24] . This may be attributed to the purity and type of the antigens used. It has been reported to be reliable method for screening and diagnosis of chronic schistosomiasis especially in association with high titer (≥1:512) [25] . Therefore it was used as a screening test for our study population. There was a significant linear increase in FEC detection rate with increase in antibody level. This correlation has been reported previously [25],[26] .

In conclusion the current data indicate that FEC is helpful in differentiating active from non-active infection in individuals with detectable antibodies by IHA. The positivity increases significantly in linear trend with the antibody levels.

   References Top

1.Theodore EN. Schistosomiasis: In Isselbacher (Eds.) Fauci, et al 14th edition volum 1. International edition 1998;1:1217-22.  Back to cited text no. 1    
2.Arafaa F. Schistosomiasis control Programs in the Kingdom of Saudi Arabia. WHO Assignment Report. 1984;EM/SCHIS/89, SAA/ MPD/ 002.  Back to cited text no. 2    
3.Sebai ZA, Schistosomiasis in Saudi Arabia. Ann Saudi Med 1988;8:169-74.  Back to cited text no. 3    
4.Ahmed SA, El Zaher F, Gbolahan 00. Intestinal parasite infetation in Saudis and non Saudis in the Armed Forces Hospital, Riyadh. Saudi Med J 1994;16:242-7.  Back to cited text no. 4    
5.Weekly epidemiological records, WHO, No. 39 September 1995.   Back to cited text no. 5    
6.Al-Madani AA. Schistosomiasis control in Saudi Arabia with special reference to the period 1983-1988. Public Health 1990; 104:261-6.  Back to cited text no. 6  [PUBMED]  
7.Rabello Al. Parasitological diagnosis of Schistosoma mansoni: fecal examination and rectal biopsy. Mem Inst Oswalob Cruz 1992;87:325-31.  Back to cited text no. 7    
8.Truant AL, Elliott SH, Kelly MI, Smith JH. Comparison of formalinethyl ether Sedimentation, formalin ethyl acetate sedimentation and zinc sulfate flotation technique for detection of intestinal parasite. J Clin Mic 1981;13:882-4.  Back to cited text no. 8    
9.Dos-Santos JG, Watson B. Direct wet mounts versus concentration for routine parasitologic examination are both necessary. Am J Clin Pathology 1988;89:389-91.  Back to cited text no. 9    
10.Elliott EE. Schistosomiasis pathophysiology, diagnosis and treatment. Gastroenterol Clin Nrt Am 1996;25:599-625.  Back to cited text no. 10    
11.Abdel Wohab MF. Schistosomiasis in Egypt. Baca Raton FL: CRC Press, 1982.  Back to cited text no. 11    
12.Chatterjee KD. Parasitology, Protozoology and Helmintology in relation to clinical Medicine. Twelfth edition Calcutta, Sree Saraswaty Press 1980;142-4.  Back to cited text no. 12    
13.Ellen JoB, Peterson LR, FineGold SM. Diagnostic microbiology Ninth edition page 1988;786-7.  Back to cited text no. 13    
14.Monica C. Medical Laboratory mannual for tropical countries 2 nd edition, Churchill living stone, London, 1991;1:333.  Back to cited text no. 14    
15.Feldmeler H, Bienzle U, Dietrich M, Slevertsen HJ. Combination of availability test and a quantification method for Schistosoma hematobium eggs. Trop Med Parasitol 1979;30:417-22.  Back to cited text no. 15    
16.Mahmoud AAF. Schistosomiasis. In Saunders (ed): Cecil text book of Medicine Vol. 2. Philadelphia 1992;2000-6.  Back to cited text no. 16    
17.Abdel Wahab MF. Schistosoma mansoni in Egypt. Clin Trop Med Corns Dis 1987;2:371-95.  Back to cited text no. 17    
18.Rabello Al, Rocha RS, de oliveira JP, Katz N, Lambertucci JR. Stool examination and rectal biopsy in the diagnosis and evaluation of therapy of Schistosoma mansoni. 1992;34:601-8.  Back to cited text no. 18  [PUBMED]  
19.Azab M, Al Zayat EA. Evaluation of purified antigens in hemagglutination test for determination of cross reactivities in diagnosis of foscioliasis and schistosomiasis. J Egpt Soc Parasitol 1996;26:677-85.  Back to cited text no. 19    
20.Germillion DH, Kuntz RE, Geckler RW. Intestinal parasites and commensals in Saudi Arabian military recruits in Texas based on examination by the MIF and FE techniques. J Parasitol 1983;69:434-6.  Back to cited text no. 20    
21.Baretlett MS, Harper K, Smith N, Verbanc P, Smith JW. Comparative evaluation of a modified zinc sulfate flotation technique. J Clin Microbiol 1978;7:524-8.  Back to cited text no. 21    
22.Wilson M, Fried J. Mc Quay RM, Sulzer AJ. Evaluation of the indirect immunofluresence and complement fixation tests for diagnosis of Schistosomiasis. Amr J Trop Med Hyg 1977;26:1159-63.  Back to cited text no. 22    
23.Khalil H. M, Abdel Baki MH, Ahmed MM, Saleh SM, Abbas MM, Amir EA. Evaluation of direct and indirect methods in diagnosis of chronic intestinal schistosomiasis in Menoufia Govemorate. J Egpt Soc Parasitol 1993;23:55-61.  Back to cited text no. 23    
24.Felmeier H, Zwingenberger K. Immunodiagnosis of schistosomiasis. Arztl Lab 1988;34:287-99.  Back to cited text no. 24    
25.Al Sabah A, Al Teimi I, Al Maghawry I, Al Dosoqi R, Laajam M. Reliability of hemaglutination test for diagnosis of schistosomiasis compared with parasitological diagnosis. Fourth annual meeting of the Saudi Gastroenterology Association, Riyadh. 1996.  Back to cited text no. 25    
26.Hossain A, Bolbol AS, Chowdhury MNH, Mahgoub ES, Mofleh IA, Rajapakse DA. Serologic diagnosis of schistosomiasis. J Med 1986;17:3-4.  Back to cited text no. 26    

Correspondence Address:
Mohammad A Al Mofarreh
Consultant Physician & Gastroenterologist, Dr. Al Mofarreh Polyclinic, P.O. Box 9889, Riyadh 11423
Saudi Arabia
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Source of Support: None, Conflict of Interest: None

PMID: 19864711

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