[A Retrospective Study on Planorbarius metidjensis and Its Role as a Potential Intermediate Host in the Transmission of Schistosoma haematobium in the Souss-Massa Region (Morocco)]. / Étude rétrospective sur Planorbarius metidjensis et son rôle comme hôte intermédiaire potentiel dans la transmission de Schistosoma haematobium dans la région du Souss-Massa (Maroc).

A retrospective research study was carried out by our team on Planorbarius metidjensis to highlight its epidemiological role as a potential host snail of Schistosoma haematobium in the Souss-Massa region. Contrary to the habitats colonized by Bulinus truncatus, the main host snail, those of P. metidjensis are located at the altitude of above 300 m. The best results of the experimental infections with S. haematobium were obtained using juvenile planorbids of 2 to 3 mm in diameter and a dose of five miracidia per snail. No snail naturally infected with the parasite was found when dissecting 3,457 adult bulinids and 2,470 adult planorbids. Despite the location of its habitats in altitude, P. metidjensis is a potential intermediate host of S. haematobium and it is important to follow these populations, as those of B. truncatus, in the future to avoid possible reoccurrence of indigenous cases of the disease.

Une étude rétrospective des travaux de notre équipe sur Planorbarius metidjensis a été réalisée afin de souligner son rôle épidémiologique comme mollusque hôte potentiel de Schistosoma haematobium dans la région du Souss-Massa. À l'inverse des habitats colonisés par Bulinus truncatus, le principal mollusque hôte, ceux de P. metidjensis sont localisés en altitude (plus de 300 m). Les meilleurs résultats de l'infestation expérimentale avec S. haematobium ont été obtenus en utilisant des planorbes juvéniles de 2 à 3 mm en diamètre et une dose de cinq miracidiums par individu. Aucun individu infesté naturellement par le parasite n'a été trouvé lors de la dissection de 3 457 bulins adultes et de 2 470 planorbes adultes. Malgré la localisation de ses habitats en altitude, P. metidjensis est un hôte intermédiaire potentiel de S. haematobium, et il importe de surveiller dans l'avenir ces populations, comme celles du bulin, afin d'éviter la réapparition éventuelle de cas autochtones de la maladie.

Oxidative stress responses in bivalves (Scrobicularia plana, Cerastoderma edule) from the Oued Souss estuary (Morocco).

The aim of this work was to study the responses of oxidative-stress biomarkers (catalase: CAT, thiobarbituric acid reactive substances: TBARS) in bivalves (Scrobicularia plana and Cerastoderma edule) from the Oued Souss estuary (Morocco). This estuary, subjected to large amounts of sewage discharges and industrial effluents, do not receive since November 2002 any waste outlets due to their connection to a wastewater purification plant. High CAT and TBARS values were recorded in both species collected before the implantation of wastewater treatment. These results confirm that these bivalves were submitted to various contaminants generating oxidative stress and membrane lipid peroxidation. The diminution of these two biomarkers following the setting up of the purification plant indicates probably a reduction in contaminants in the Oued Souss estuary. We recommend the use of CAT and TBARS as oxidative-stress biomarkers in S. plana and C. edule.

[Bulinus truncatus, Planorbarius metidjensis and endemic bilharziosis in the southwestern Morocco]. / Bulins, planorbes et endémie bilharzienne dans le sud-ouest marocain.

Since Planorbarius metidjensis was recently found to be an experimental intermediate host of Schistosoma haematobium in the South-West of Morocco, a study on planorbid and B. truncatus was carried out from 1997 to 2005. Eleven planorbid populations were identified in 1997 in the Agadir province, all living at high altitude (from 340 to 1380 m). In contrast, most of the seven bulinid populations inhabited low-lying zones. Three annual generations of P. metidjensis (April-July June-September, and August-March) were noted in two populations (living in perennial bodies of water) in Imouzzer so that juvenile snails were present throughout the year. The dissection of numerous snails collected from these 18 populations between 1999 and 2005 revealed the absence of natural infections with S. haematobium. As most cases of human bilharziosis detected in the Agadir region between 1993 and 1997 are located in highlands, P. metidjensis might be the principal intermediate host of S. haematobium in districts at 500 m above sea level.

Wastewater toxicity of tannin- versus chromium-based leather tanneries in Marrakesh, Morocco.

The toxicity of leather tanning wastewater from a traditional tannery (TT), which is based on vegetable tannin (VT), was compared with wastewater from a tannery combining the use of chromium-based tanning (CT) with VT-based tanning operations. Wastewater samples from a TT and a CT plant as well as from five sewer sampling points were collected in Marrakesh, Morocco, and the concentrations of VT and some selected inorganics were measured. A set of bioassays were used to test wastewater toxicity in sea urchin (Paracentrotus lividus) embryos and sperm, in Daphnia magna, and in marine microalgae (Dunaliella tertiolecta). Toxicity end points included: (1) developmental defects, embryonic mortality, sperm fertilization success, and offspring damage in sea urchins; (2) D. magna immobilization; and (3) algal growth rate inhibition. Toxicity tests on TT and CT effluents (TTE and CTE) were run at dilutions ranging from 0.1% to 2% (sea urchins and algae) or up to 12% in D. magna. Parallel bioassays were run on VT extract (VTE) at nominal tannin concentrations ranging from 0.1 to 10 mg l(-1). The results showed higher toxicity of CTE compared with TTE. CTE toxicity in sea urchins and algae showed concentration-related trends, whereas TTE exerted hormetic effects at levels of 0.1% to 0.2% and toxic effects at levels >or=1%. The same trends were observed for VTE, suggesting a prevailing role of tannin in TTE-associated effects. The moderate wastewater toxicity of VT-based tanneries might prompt interest in the VT tanning process.

Habitats of Bulinus truncatus and Planorbarius metidjensis, the intermediate hosts of urinary schistosomosis, under a semiarid or an arid climate.

Since Bulinus truncatus and Planorbarius metidjensis are the intermediate hosts of Schistosoma haematobium in southwestern Morocco, five rivers were investigated to identify sites colonized by either of both species and determine the characteristics of their habitats via the study of 12 physicochemical parameters in running water. P. metidjensis was observed in the upper valleys of three rivers, whereas B. truncatus was found in sites of lower altitude. A component analysis demonstrated that altitude (from 4 to 1,380 m), water pH (from 5.9 to 9.2), and electric conductivity (from 120 to 6,020 microS/cm) were the main descriptors of environment. A multiple correspondence analysis showed that P. metidjensis was associated to Ancylus fluviatilis, high altitude, and possibly low electric conductivity. B. truncatus was associated to Melanoides tuberculata and was found in lower altitude sites with medium electric conductivity in water. Using logistic regressions, the main characteristics were altitude and dissolved oxygen for B. truncatus, and chlorides and CaCO3 for P. metidjensis. As the habitats of both S. haematobium intermediate hosts differed from each other by altitude and the frequency of snails, which cohabited with them, these findings may be used to detect the presence of either of both intermediate hosts in numerous spring heads which are present on the western slope of the Anti Atlas mountains and the corresponding valleys.

Tolerance and biomarkers as useful tools for assessing environmental quality in the Oued Souss estuary (Bay of Agadir, Morocco).

The aim of this study was to assess aquatic environmental quality of Oued Souss (Agadir, Morocco). This estuary has been subjected for a long time to large amounts of sewage discharges and industrial effluents. Since November 2002, no waste outlets have been discharged in this site due to their connection to a wastewater purification plant. Firstly, we have compared metal tolerance of the annelid polychaete (Nereis diversicolor) originating from Oued Souss and a relatively clean site (Oualidia, Morocco). Secondly, we have evaluated with a multi-marker approach (acetylcholinesterase [AChE], glutathione-S-transferases [GSTs], catalase, thiobarbituric acid reactive substances [TBARs]) responses of worms to the pollution gradient. Results have shown that worms from Oued Souss have acquired tolerance to copper and zinc due to a long-term sub-lethal metal exposure and this metal tolerance was maintained in spite of the end of wastewater discharges in this site. Higher catalase, GSTs and TBARs values have been observed in worms from Oued Souss sampled before implantation of wastewater treatment. The multi-marker approach confirms that these worms have been submitted to various contaminants. In contrast, high inhibition in AChE activities measured in worms from Oued Souss could be explained by the continuous agricultural influence of nearest areas. The level of contamination was probably maintained since biomarker values were generally higher in worms from Oued Souss when compared to Oualidia.

In situ relationship between energy reserves and steroid hormone levels in Nereis diversicolor (O.F. Müller) from clean and contaminated sites.

The aim of this study was to investigate, in situ, the temporal effects of urban effluent discharge on energy reserves and steroid hormone levels in the intrasedimentary worm Nereis diversicolor. Results have shown no differences in energy reserves (glycogen, lipids) in organisms originating from a contaminated site (Oued Souss) and a comparatively clean site (Oualidia). Both sites are located on the Moroccan Atlantic coast. In contrast, steroid hormone (progesterone, testosterone, and 17beta-estradiol) levels were significantly decreased in animals from Oued Souss. The differences in the responses suggest that organisms from the polluted site have been exposed to endocrine disruptors.

Effect of a short period of desiccation during the patent period on cercarial shedding of Schistosoma haematobium from Planorbarius metidjensis.

Planorbarius metidjensis infected with Schistosoma haematobium were subjected, from the first day of shedding, to a 5- or 10-day period of desiccation in order to study its effect on the cercarial release occurring after reactivation of snails in water. These results were compared to those of infected controls that were not subjected to desiccation. Compared to controls, the duration of shedding following reactivation was shorter and the total number of cercariae shed by each infected snail was smaller in the 5- and 10-day groups. The rhythm occurring in the daily cercarial production of the 5-day group was shorter (11 days only) at the beginning of the shedding period and lengthened to 17-18 days at the end of the patent period. In the 10-day group, no rhythm was found. These results could be explained by the length of the desiccation period and its consequences on the development of S. haematobiumsporocysts in the body of snails.

Schistosoma haematobium: comparative studies on the characteristics of infection in three populations of Planorbarius metidjensis from the Agadir province in South Morocco.

Planorbarius metidjensis measuring 2 or 3 mm in diameter and originating from three populations in the Agadir province (Ida Ou Gnidif, Imouzzer, and Sidi Belkacem) were experimentally infected with Schistosoma haematobium to determine if the complete larval development of the parasite might be ensured by any snail population of the Agadir province and to compare the general characteristics of infection. No significant difference between the three populations was noted in the survival rates of snails when the first shedding occurred or in the prevalence of infection. The mean duration of the shedding period was significantly higher in the Imouzzer population (111 days versus 53-58 days). The total number of cercariae shed per mollusc was significantly lower in the Ida Ou Gnidif planorbids (1,398/snail versus 3,346 and 3,343/snail in the other 2 groups). The same rhythm in daily cercarial production was noted in the three snail groups, with the periodicity being 18-20 days. Despite some differences in parasite development between the three snail populations, the different populations of P. metidjensis can ensure the complete development of S. haematobium and maintain local transmission in the South of Morocco.

Schistosoma haematobium: comparative studies on prevalence and cercarial shedding according to the shell diameter of Planorbarius metidjensis at miracidial exposure.

Experimental infections of Planorbarius metidjensis by Schistosoma haematobium were carried out under controlled conditions to determine whether there was a size limit after which the snail could not longer sustain Schistosoma infection. Snails measuring 1-6 mm in diameter were exposed to two miracidia each and were raised at 24-26 degrees C until their death. The frequency of snails with cercarial shedding was 63% in the 2.1- to 3-mm group. In the other groups the frequencies were lower, decreasing to 2.8% in the 5.1- to 6-mm group. The periodicity of S. haematobium cercarial shedding was not modified by the snail diameter at miracidial exposure.

Schistosoma haematobium: influence of the number of miracidia on several characteristics of infection in newborn Planorbarius metidjensis.

Newborn Planorbarius metidjensis (less than 72 h of life) were individually exposed to one, two, or five miracidia of Schistosoma haematobium to assess how the quantity of miracidia would affect the shedding of cercariae. The infection rate of snails increased as the number of miracidia increased (from 17% to 87% at 24-26 degrees C). The prepatent period was significantly shorter in planorbids exposed to a single miracidium (38 days) than in the two groups infected with two or five miracidia per snail (51-53 days). No significant difference was noted between the mean values recorded for the three groups in terms of the patent-period duration (48-70 days), the total number of cercariae (1,570-1,935/snail), and size at snail death (5.4-6 mm). A rhythm was detected in the daily production of cercariae from P. metidjensis; however, its periodicity differed according to the snail group (15-16, 20-23, and 25-27 days for the groups infected with one, two, and five miracidia, respectively.

A comparative study of the shedding of cercariae of Schistosoma haematobium in newborn Bulinus truncatus.

A comparative study of the shedding of cercariae of Schistosoma haematobium was performed in Bulinus truncatus and Planorbarius metidjensis individually exposed to 5 miracidia in their first 72 h of life. No significant difference was noted between the mean values of the two snail groups concerning the prepatent period duration (53-57 days at 24 degrees-26 degrees C), the patent period duration (41 days for B. truncatus, 70 days for P. metidjensis), or the total number of cercariae (1,499 per B. truncatus, 1,935 per P. metidjensis). Successive periods of heavy and low production were encountered in the shedding of cercariae; however, the periodicity was identical in the two snail species (25-27 days) and the emergence of cercariae peaked between 11 a.m. and 1 p.m.

Field observations concerning infection of Lymnaea palustris by Fasciola hepatica.

Fasciola hepatica miracidia were experimentally introduced into five sites colonized by Lymnaea palustris over a period of 4 or 6 years. In the first four ponds, a progressive increase in the prevalence of the spring-generation juvenile snails was observed (from 0.4 to 18.1%), with a corresponding increase in the shell height of infected snails (from 3.6 to 7.8 mm). In the fifth habitat, the pond dried in 1990 causing the prevalence to drop as compared with the initial values and to subsequently increase in 1991-1992.

Redial generations of Fasciola gigantica in the pulmonate snail Lymnaea truncatula.

Lymnaea truncatula, 4 mm in height, were subjected to infection by a single miracidium of Fasciola gigantica, then raised at 23 degrees C until day 60 of the experiment. Histological study of these snails demonstrated a mean redial burden of 34 parasites at day 60, of which one third were degenerating forms. The mean number of living independent rediae did not exceed 5 for the first and second generations. Conversely, in subsequent generations there were as many as 18 rediae per snail at day 60. The first living redia of the first generation in particular gave rise to daughter rediae. Mature rediae appeared at day 35 and especially concerned the first and second generations at day 60. The authors conclude that development of the first and second redial generations occurs during the same period, and that the forms of the first cohort of the second generation are produced from the first redia of the first generation which originated from the sporocyst.