Manal B. Jamjoom and Abdul Elah A. Banaja. Department of Medical Parasitology, Faculty of Medicine, King Abdul Aziz University 2

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1 World Journal of Medical Sciences 2 (2): , 2007 ISSN IDOSI Publications, 2007 "Comparative Studies on e Susceptible and Non-Susceptible Biomphalaria alexandrina e Intermediate Snail Host of Schistosoma mansoni in Western Saudi Arabia" 1 2 Manal B. Jamjoom and Abdul Elah A. Banaja 1 Department of Medical Parasitology, Faculty of Medicine, King Abdul Aziz University 2 Director of Taif University Abstract: Schistosomiasis is an important parasitic disease at infects humans. Among e main species of schistosomes infecting humans is Schistosoma mansoni and S. haematobium. Snails of various genera, such as Biomphalaria alexandrina and Bulinus truncates, act as intermediate hosts and play a major role in e transmission of schistosomes. Transmission from human to snail is under e influence of e ciliated miracidium larvae at hatch from e eggs of e parasite voided in e faeces or urine. After a period of asexual multiplication in e snail, a second aquatic larval stage, e cercaria, emerges and infects human by direct penetration of e skin. The present work was carried out on Biomphalaria alexandrina snails, e intermediate host of Schistosoma mansoni. Snails were collected from various sites in sou western Saudi Arabia. Their progeny were reared in e laboratory under standard conditions. Different biological experiments were carried out to determine e susceptibility level in e various populations of snail. The miracidia were obtained by isolating viable ova of e hatching parasite from faeces of infected individuals (human and mice). Different sets of regulated experimental infection of snails wi e miracidia of Schistosoma mansoni were preformed. The effect of miracidial density, water temperature, miracidial age, size of snails, as well as light and darkness were investigated. The study revealed at e infection rate increased as e number of miracidia used increased (1, 60%; 2, 60%; 3, 70%; 5, 80%; 15, 90%; and 20, 90%). No significant increase of infection rate was achieved at higher water temperatures (at 15 C: 65% wi newly hatched miracidia; 75%, wi 15 minutes miracidia; 85% wi 30 minutes miracidia; 95% wi 45 minutes miracidia and 100% wi 60 minutes miracidia. At 20 C: 75% wi newly hatched miracidia; 80%, wi 15 minutes miracidia; 90%, wi 30 minutes miracidia; 95% wi 45 minutes miracidia and 100% wi 60 minutes miracidia). Similar results were obtained at 25 C and 30 C. However, e infection rate decreased in relation to snail size increase. At snail size 2-4 mm e infection rate was 90%, e rate decreased to 85% at 4-6 mm and 6-8 mm size, while at 8-10 mm size e rate was 80%. At mm and mm size e rate dropped to 75%. Light and dark conditions had a significant difference on e infection rate (40% in darkness and 90% in light). Laboratory observations also indicated at some of e snails exposed to infection wi miracidia of e respective parasite developed infection and produced cercariae, while e rest remained uninfected. Key words: Biomphalaria alexandrina intermediate host susceptible snails non-susceptable snails Schistosomiasis Schistosoma mansoni miracidia Saudi Arabia INTRODUCTION schistosomes infecting humans are Schistosoma mansoni and S. haematobium. Biomphalaria alexandrina Schistosomiasis is a disease caused by infection and Bulinus truncatus are e intermediate hosts for wi various species of e genus Schistosoma. Some S. mansoni (agent for intestinal schistosomiasis) and 200 million people are probably infected and S. haematobium (agent for urinary schistosomiasis). million more are exposed to infection [1]. The infection Urinary and intestinal schistosomiasis is endemic in is transmitted by specific aquatic snails in a wide Saudi Arabia. In 2004, e prevalence of schistosomiasis variety of fresh water habitat. Among e species of was 2.9/100,000 persons (0.0029%) according to e Corresponding Auor: Dr. Manal B. Jamjoom, Department of Medical Parasitology/ Female section, King AbdulAziz University, P.O. Box 42806, Jeddah 21551, Saudi Arabia 108

2 Saudi Arabia Ministry of Heal Statistic Book, paraensei wi e ability of secretory excretory ( products (SEP) derived from sporocysts of is parasite According to e source, a total of persons were to interfere wi e spreading behavior of host examined, 639 were infected (0.05%). The prevalence hemocytes in an in vitro assay. Some studies did not among Saudis was 61.2% and non Saudis 38.8%. Males detect strain differences [17-20] Guillou et al. [21] stated have higher infection rate (82%) an females (18%). The e presence of susceptibility or resistance of B. rate of infection was higher among e year-old glabrata to e trematode Echinostoma caproni. age group (53.7%). The highest prevalence was Mascara et al. [22] carried out artificial selection of reported in Jazan, Bishah, Aseer and Al-Bahah. Urinary Biomphalaria tenagophila snails for susceptibility schistosomiasis is prevalent in Jazan, Aseer and to infection by Schistosoma mansoni (Brazilian SJ Bishah, whereas intestinal schistosomiasis is prevalent strain) from natural populations. Occasionally, nonin Taif, Al-Bahah, Aseer, Bishah, Najran, Makkah Al- susceptible snails outbreed e susceptible ones and Mukarramah, Al-Medina and Hail. A total of water replace em [23,24]. sources were examined in different localities in e The detection of Biomphalaria snails infected wi above mentioned areas in e year 2004 and 778 (~2.3%) S. mansoni was usually performed by cercariae shedding were found to be contaminated. Limited studies have induced by artificial light exposure or by squeezing snails been conducted to explore e susceptibility and between two glass slides. However, ese meods are none- susceptibility among snails in Saudi Arabia. not able to detect e parasite neier in dead snails nor in Lwambo et al. [2] studied e infectivity of miracidia of e pre-patent period. Accordingly, infection diagnosis is e Saudi Arabian isolate of S. mansoni in Biomphalaria only possible after e parasite has completed its life cycle arabica and found at e snails are influenced by (3 to 4 weeks after infection), when cercariae release is several factors such as miracidial dose, water temperature started [4]. and salinity. Arfaa et al., [3] assessed e potential role The aim of is study was to investigate e of ree species of Bulinus in e transmission of susceptibility of Biomphalaria snails exposed to Schistosoma haematobium in Saudi Arabia, on e experimental infection wi S. mansoni influenced by basis of eir susceptibility to experimental infection, different factors including: miracidial density, water eir geographical distribution and numbers and type temperature, miracidial age, size of snails, as well as of habitats in which ey were found. miracidial invasion in light and dark conditions. The Previous studies showed at some snails at were existence of susceptible and non-susceptible strains of exposed to infection wi miracidia of schistosomes snails will be assessed. Such investigations are important developed infection and produced cercariae, while e implication for field control studies. Hence, it will be oers remained uninfected. Many documented data valuable to breed non-susceptible snails in large scale and indicated at many external and internal factors introduce em into e field. Natural selection would influence e number of trematode larvae produced furer act to increase e proportion alleles for by eir intermediate snail hosts wi special reference to insusceptibility and eventually provide some mean of schistosomes [4]. Among e variables studied are e biological control for schistosomiasis in natural temperature [2,5,6], host nutritional status [7], genetic populations. differences wiin e parasite population [8], e life span of e snail [9] and e size of e snails [4,6]. Studies also MATERIALS AND METHODS showed at e susceptibility of snails to schistosome s infection depends on e metabolic status of e snail Snails and parasites: itself. One of e metabolic activities depends upon e (a) Rearing of snail intermediate hosts: 100 snails were production of reactive oxygen species by hemocytes collected from different localities and habitats (irrigation from e snail [10,11]. Professional phagocytes play a canals and drains, current stream, ponds, dry canals etc...) crucial ruole in host defense against paogens. Their in Souwestern region of Saudi Arabia and examined arsenal includes e ability to initiate a respiratory burst individually for cercarial production. Snails were reared [12,13]. The generation of reactive oxygen species is singly in eier a 250 ml or 400 ml beaker wi a Petri dish apparently essential for efficient killing of bacteria and cover at an ambient temperature at 26 C. Tap water fungi [14,15]. DeGaffé and Loker [16] correlated e aerated for at least 24 hours was used and snails were susceptibility of e snail Biomphalaria glabratato to fed dried oven or fresh lettuce 2 or 3 times a week. infection wi e digenetic trematode Echinostoma Reproduction was by self-fertilization. Rooms, in which 109

3 snails were maintained and experiments were conducted, were kept at a temperature of about 26 C. Eggs were laid by adult snails of e first generation. Each snail progeny to be isolated from rearing was numbered from "1" on maturity is based on onset of egg lying. Each snail s progeny were maintained under standard laboratory conditions as described above to give e second and ird generation of snails which were subjected to e same biological studies. 3- Size dependent host susceptibility to infection: Snails of varying shell sizes (2-4, 4-6, 6-8, 8-10, and mm) were exposed to 10 miracidia, average age of 30 min, in 5 ml of water at 26 C for a period of 1 hour under conditions of light. Twenty snails from each size group were exposed. Snails were examined from e 27 day up to e 50 days to assess wheer or not ey had acquired infection rough e observation of cercaria shedding. (b) Production of miracidia: Snails were exposed to 4- Illumination and darkness and e rate of miracidia hatched from eggs in e faeces of mice and/or infection: Twenty snails of mm (shell diameter) human infected wi trematodes. Fresh faeces were were exposed individually to 5 miracidia. The infection comminuted in aerated tap water, allowed to settle for was carried out in e presence of electric lamp (100 watt) 5 minutes en fresh water was added. The procedure for 10 hours. Similarly, anoer twenty snails of being repeated until e supernatant was clear. The mm were exposed in complete darkness. After sediment was en examined under e dissecting miracidial exposure, each group was transferred to a microscope and as miracidia hatched ey were labeled plastic container and maintained under same transferred individually by pipette to e snail containers. laboratory conditions. Snails were monitored for a total period of 50 days for cercarial shedding starting Experimental Meods: by e 27 day after infection. 1- Miracidial density and e rate of infections: Single snails of mm shell diameter were exposed in 5 ml of RESULTS water at 26 C for a period of 30 min to a range of miracidial densities (1, 2, 3, 5, 15 and 20 miracidial / 5ml). The Out of e 100 field collected snails only 15 miracidia used in ese experiments have an average age snails were naturally infected wi Schistosoma of 30 minutes, twenty snails were used for each of ese mansoni (15%). miracidial densities. After exposure, snails were removed, placed in rectangular plastic container (45 x 28 x 13 cm) 1- Miracidial density and e rate of infections: The and kept for days later to assess wheer or not infection rate of snails exposed to different miracidial ey had acquired infection rough e observation of density is summarized in Table 1. Alough e results cercaria shedding. showed at e rate of infection increases as e number of invading miracidia increase yet it was 2- Temperature, miracidial age and miracidial infectivity: statistically insignificant. However, e value of P = 0.9 Freshly hatched miracidia were pipetted into dishes (not significant). and left to age under a range of temperatures. The miracidial age dependent infectivity was carried out at 2- Temperature and miracidial age effect on e following temperatures: 15 C, 20 C, 25 C and 30 C. infectivity: The results obtained from exposing snails At each regulated temperature, e miracidia infectivity to different aged miracidia at different temperature are were estimated using 5 different age groups of miracidia summarized in Table 2. Generally, temperature and (freshly hatched, 15, 30, 45 and 60 min). Five miracidia of miracidial age had an insignificant effect on snail a given identical age were randomly chosen and placed in infectivity rate. However, snails exposed to e freshly 5 ml of regulated water container. One snail of mm hatched, 15 and 30 minutes aged miracidia displayed in diameter was en added to e experimental vessel and higher infection at 15 C and 20 C. Higher temperatures exposed to infections for 2 hours. A total of 20 snails (25 C and 30 C) generated e same infection rate. were used for each miracidial age. After exposure, e Snails exposed to 45 and 60 minutes aged miracidia snails were transferred to rectangular plastic containers showed e same infection rate at e different at 26 C constant temperature. From e 27 to e 50 day, temperature tested. snails were examined for infections rough e observation of cercaria shedding. Snails at fail to 3- Size dependent host susceptibility to infection: The shed cercariae by e 50 day after exposure were crushed results obtained from exposing different sized snails to e and examined microscopically for infection. same number of miracidia (10) are shown in Table

4 Table 1: Miracidial density in relation to e rate of infection of snails Total number (No.) of snails used 120 snails (20 snails each) Miracidial densities No. of susceptible snails No. of non-susceptible snails Rate of infection (%) 60 % 60 % 70 % 80 % 90 % 90 % Table 2: Number of infected snails wi different ages of miracidia at different temperature 100 snails (20 snails each) No. of total Age of miracidia snails used Freshly Water temperature hatched 15 min. 30 min. 45 min 60 min. Number of snails infected at 15 C (65 %) (75 %) (85 %) (95 %) (100 %) Number of snails infected at 20 C (75 %) (80 %) (90 %) (95 %) (100 %) Number of snails infected at 25 C (75 %) (80 %) (90 %) (95 %) (100 %) Number of snails infected at 30 C (75 %) (80 %) (90 %) (95 %) (100 %) Table 3: The infection rate in relation to snail size Number of 120 snails (20 snails each) exposed snails Size of snails 2-4mm 4-6mm 6-8mm 8-10mm 10-12mm 13-15mm No. of infected snails Rate of infection (%) 90 % 85 % 85 % 80 % 75 % 75 % Table 4: Rate of infection of snails exposed to miracidia at light and dark periods 40 snails (20 snails each) Number of total snails Illumination Light Darkness Number of infected snails 18 8 Rate of Infection (%) 90 % 40 % Results indicated at e smaller e snail size e higher e infection rate. This was also non-significant statistically. 4- Illumination and darkness and e rate of infection: The results obtained from exposing snails to e same number of miracidia (5) under light and dark periods are shown in Table (4). Results showed at e infection rates were significantly higher in light condition an in e dark. DISCUSSION Schistomiasis occurs in Saudi Arabia (Saudi Arabia Ministry of Heal Statistic Book, 2004, / Default.html). The present work was intended to investigate e susceptibility and non-susceptibility of e Biomphalaria snails, e intermediate host of Schistosoma mansoni, to experimental infection in relation to different external variables which may affect its rate of infection wi e parasite. The infection rate among e snails collected from e field was (15%). Snail susceptibility to infection was confirmed only when each snail was tested individually for production of cercariae, usually from e 27 to e 50 day (~3-7 weeks) after infection us allowing enough time for e parasite to completed its life cycle. The suggestion of susceptible and non-susceptible snails to infection was expressed by a number of auors [10-18,20-23,25-27]. The relation between snail s infectivity and e density of miracidia is well documented. Previous studies reported higher infection rate as miracidial dose increased [28,29,6]. The results obtained from is study also showed at e snail s infection rate increased as e number of miracidia was increased, in spite of being not statistically significant. Loker [30] exposed laboratory-reared Lymnaea catascopium snails individually to different numbers of Schistosomatium douitti miracidia. Increasing e exposure dosage from 3 to 10 miracidia generally increased infection rates, in some age classes up to 100%. Snail s susceptibility to infection affected by miracidial age under different degrees of temperatures regulated water. Infection occurred at all miracidial ages influenced by different water temperatures. Regardless, of being statistically insignificant; e lowest infection rate was encountered among e freshly hatched miracidium exposed at 15 C; while e rate of infection was among e (60 minutes) aged miracidium at e different temperature examined (15, 20, 25 and 30 C). Anderson et al. [5] reported at e dea rate of miracidia declined exponentially wi age where lifeexpectancy was maximal (approximately 16 h) at 15 C. Infectivity also declined rapidly wi larval age but, in contrast to larval survival, e rate of infection was at its maximum at 25 C. Lwambo et al. [2] found at water temperature during exposure had an influence on e mortality, infection rate and cercarial production in Biomphalaria arabica exposed to S. mansoni miracidia. 111

5 The infection rate was highest in snails exposed at 28 natural habitats. Finally, it would be beneficial to select and 34 C. No infection of Biomphalaria arabica non-susceptible snails and mass culture em to increase occurred at e temperature of 10 C. Shoukry et al. [6] e proportion of e alleles of insusceptibility as a indicated at snails 4-6 mm in diameter exposed to 5 possible means for biological control of schistosomiasis freshly hatched miracidia under light and in water at in natural population. Furer investigation is needed to 25 C were e optimum conditions for infection of elucidate e reason of susceptibility and insusceptibility Biomphalaria alexandrina. in snails. Age and size-dependent susceptibility was presented by earlier workers [4,6,29-32]. The present REFERENCES work suggested at snail s susceptibility to be nonsignificantly correlated wi its size. This data confirm and 1. Webbe, G., The six diseases of WHO. extend earlier work on snail s susceptibility and indicate Schistosomiasis: some advances. Brit. Med. J. at e susceptibility declined wi increased snail (Clin. Res. Ed.), 283: 1-8. size. The infection rate was at its highest among snails 2. Lwambo, N.J., E.S. Upaam, M. Kruatrachue and 2-4 mm in diameter exposed to 20 snails. This may be V. Viyanant, The host-parasite relationship related to e ability of larger snails to kill invading between e Saudi Arabian Schistosoma mansoni miracidia, or e possibility of a nutritional competition and its intermediate and definitive hosts. 1. between parasite and snail. Such competition for S. mansoni and its local snail host Biomphalaria nutrients has been studied mostly in association wi arabica. Soueast. Asian J. Trop. Med. Public a reduction in egg laying during invasion of e Heal., 18(2): hepatopancreas by secondary sporocysts [33]. 3. Arfaa, F., E. Mahboubi, M. Al-Jeffri, A. Selim and Anderson et al. [5] indicated at snail susceptibility G. Russell, The potential role of various was shown to be more closely correlated wi host species of intermediate hosts of Schistosoma size raer an host age. The susceptibility declined haematobium in Saudi Arabia. Trans. R. Soc. Trop. exponentially wi increased host size. Size-dependent Med. Hyg., 83(2): susceptibility was shown to generate concave age- 4. Niemann, G.M. and F.A. Lewis, Schistosoma prevalence curves for infection wiin snail populations, mansoni: Influence of Biomphalaria glabrata size where e maximum prevalence is generated in snails of on susceptibility to infection and resultant cercarial intermediary age. Niemann and Lewis [4] used production. Exp. Parasitol., 70(3): Biomphalaria glabrata snails of e same age, but 5. Anderson, R.M., J.G. Mercer, R.A. Wilson and different sizes, to determine size-related susceptibility N.P. Carter, Transmission of Schistosoma to Schistosoma mansoni miracidial infection and e mansoni from man to snail: experimental studies of influence of snail size on total cercarial production. Snails miracidial survival and infectivity in relation to larval wi shell diameters from <5 to >17 mm were individually age, water temperature, host size and host age. exposed to miracidia. The percentage of snails which Parasitology., 85(Pt 2): developed infections was lower in snails wi larger 6. Shoukry, N.M., F.M. El-Assal, G.N. Soluman and shell sizes. N.S. Mansour, Susceptibility of ree The current work also showed at snail s successive snail generations from positive and susceptibility was higher under light conditions which negative laboratory bred Biomphalaria alexandrina was also previously reported by Shoukry et al. [6]. from different localities in Egypt to infection wi In conclusion, is work demonstrated differences Schistosoma mansoni from Giza. J. Egypt. Soc. in Biomphalaria snail s susceptibility in relation to Parasitol., 27(2): various biological factors. Insusceptibility to infection 7. Coles, G.C., The effect of diet and crowding wi Schistosoma mansoni could be a heritable on e shedding of Schistosoma mansoni cercariae character. Joubert et al. [34] proposed e use of by Biomphalaria glabrate. Ann. Trop. Med. insusceptible snails as a possible meod of controlling Parasitol., 67: schistosomiasis. He also suggested at to change e 8. Cohen, L.M. and L.K. Eveland, Schistosoma susceptibility of natural snail populations from being mansoni: characterization of clones maintained by predominantly susceptible to a non-susceptible state microsurgical transplantation of sporocysts. J. was, rough e release of refractory snails into Parasitol., 74:

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