Description of two new cercariae [an echinostome cercaria and a xiphidiocercaria] procured from biomphalaria pfeifferi [Krauss] from Nigeria

During parasitological examination of Biomphalaria pfeifferi snails obtained from Niger state [Nigeria], 2 new types of cercariae were found. They are identified to the level of referring to the major group and described here for the first time. They were examined viable and stained with vital stains as well as fixed in 70% alcohol. They were drawn with a camera lucida and photographed. They are identified as an echinostome cercaria and a xiphidiocercaria. The echinostome is characterized by having a ventral sucker almost double in size the oral one. It has a semicircular structure located beyond the oral sucker. Three pairs of penetration glands are found at the anterior portion of the body. The number of collar spines is relatively large [44-46]. The flame cells are 17x2 in number. Two main lateral excretory ducts extend anteriorly, form two typical echinostome loops then pass posteriorly to open together in a diverticulat-ed excretory vesicle. Its tail is relatively long and flattened with 3 fin folds. The tail [640 microm] is longer than the body [475microm].The xiphidiocercaria belongs to the [ornatae] group. It is relatively small [180.5x110microm] with a long stylet [3'0nm]. Its oral sucker is one and half times the size of the ventral sucker. Two excretory ducts extend posteriorly in both sides and become dilated and unite to open in a circular excretory vesicle. Tail is slender shorter than the body and has a dorso-ventral fin fold. Key words: Echinostome cercaria, xixphidiocercaria, Biomphalaria pfeifferi

Schistosoma mansoni cercarial host location and infection under simulated natural conditions in Egypt

This study was performed in water ditches under simulated natural conditions in Egypt to elucidate the effect of various environmental factors on Schistosoma mansoni cercarial host location and infection of the definitive host [using albino mice]. Evaluation of these factors was dependent on both infection rate of exposed mice as well as the schistosome worm load under the same experimental conditions. The seasonal water temperature proved to be a very important factor and this was proven by the infection rate of mice and the worm load recovered were lower in January and April [16°C and 22°C midday water temperature] and much higher in July and October [29°C and 25°C]. The daytime factor is similarly important as temperature illustrated by the schistosome infection of mice groups exposed at 8-10 am was much higher than in groups exposed between 1pm and 3pm [p<0.001]. The greatest infection rate of mice and worm load were obtained when the shedding snails were close to the exposed group of mice. Both criteria increased with the increase of cercarial density in the water. The length of exposure period is also an extremely important factor for schistosome infection, being highest 87.5% [p<0.001] in3 hours exposure period. Infection rate was found to be 88.2% and 55.6% of shedding snails were located at water surface and midway to the bottom, respectively, and no infection occurred when located at the bottom. The schistosome infection of mice decreased in presence of increasing density of the floating plant Eichhornia crassipes in the ditch water, but low condensation of the submersed plant Ceratophyllum demersum appeared to have stimulating effect

Experimental evaluation of Candonocypris novaezelandiae (Crustacea: Ostracoda) in the biocontrol of Schistosomiasis mansoni transmission

<p><b>OBJECTIVE</b>To test Candonocypris novaezelandiae (Baird) (C. novaezelandiae), sub-class Ostracoda, obtained from the Nile, Egypt for its predatory activity on snail, Biomphalaria alexandrina (B. alexandrina), intermediate host of Schistosoma mansoni (S. mansoni) and on the free-living larval stages of this parasite (miracidia and cercariae).</p><p><b>METHODS</b>The predatory activity of C. novaezelandiae was determined on B. alexandrina snail (several densities of eggs, newly hatched and juveniles). This activity was also determined on S. mansoni miracidia and cercariae using different volumes of water and different numbers of larvae. C. novaezelandiae was also tested for its effect on infection of snails and on the cercarial production.</p><p><b>RESULTS</b>C. novaezelandiae was found to feed on the eggs, newly hatched and juvenile snails, but with significant reduction in the consumption in the presence of other diet like the blue green algae (Nostoc muscorum). This ostracod also showed considerable predatory activity on the free-living larval stages of S. mansoni which was affected by certain environmental factors such as volume of water, density of C. novaezelandiae and number of larvae of the parasite.</p><p><b>CONCLUSIONS</b>The presence of this ostracod in the aquatic habitat led to significant reduction of snail population, infection rate of snails with schistosme miracidia as well as of cercarial production from the infected snails. This may suggest that introducing C. novaezelandiae into the habitat at schistosome risky sites could suppress the transmission of the disease.</p>

Experimental studies of effect of chaetogaster limnaei [oligochaeta: annelida] on Schistosoma mansoni transmission in aquatic habitats

This study assessed the effect of association between the oligochaete Chaetogaster limnaei and the snail Biomphalaria alexandrina on schistosomiasis transmission in aquatic habitats. This experimental study included factors affecting the oligochaete / snail association such as water volume and snail species and size. The effect of Chaetogaster on snail survivorship, growth and reproduction, life of the free - living larval stages of Schistosorna mansoni and on infection of the snail with miracidia were also studied. Results show that there was a positive correlation between snail size and infestation intensity of the oligochaete. The infestation of B. alexandrina by Chaetogaster had no effect on the survival and growth of snails, but led to a remarkable reduction in egg production. Chaetogaszer proved to have predatory activity on S. mansoni miracidia and cercariae and the number of predated organisms increased with the increase of prey density. Introducing one Chaetogaster per snail after exposure to S. mansoni miracidia showed no effect on infection rate of snails and length of incubation and shedding periods but reduced significantly the total periodic cercarial production of the parasite. This study gives indication that Chaetogaster may play a significant role in reducing the population of the medically important snail B. alexandrina via suppressing its productivity, as well as reducing schistosome transmission

Schistosomiasis in newly reclaimed areas in Egypt 2- patterns of transmission

The distribution, abundance and seasonality of infected Biomphalaria alexandrina and Bulinus truncatus were studied for two years [1992-1994] in two newly reclaimed areas; namely, El-Manayef and El- Morra located on both sides of Suez Canal near Ismailia City. The results confirmed the occurrence of transmission of both Schistosoma mansoni and S. hematobium since infected snails of both species were recovered in these areas. Consequently, this proved that reclamation of parts of the desert utilizing Nile water had led to the spread of Schistosomiasis to these areas. Analysis of the Delta showed that the infected snails, especially B. alexandrina, was found clustered in a relatively few number of transmission sites. Furthermore, the greater majority of these sites were found to be located within a less number of transmission foci. This pattern of focality was clearly demonstrated by geographical information system [GIS] produced maps

Biomphalaria glabrata: a new threat for schistosomiasis transmission in Egypt

Identification of Biomphalaria glabrata [the snail host of Schistosoma mansoni in the new world] was based on morphometry of the shell, shape of the radular lateral teeth and the presence of the characteristic renal ridge. B. glabrata snails collected from natural water courses in Egypt proved to be susceptible to a local strain of S. mansoni. These snails were infected by 52% versus 75% for Biomphalaria alexandrina [the only local host] under the same laboratory conditions. Meanwhile, the periodic total cercarial production was higher in B. glabrata than in B. alexandrina [252+110 cercariae/snail versus 203+86 cercariae/snail, respectively]. Differences in infection rate, length of schistosome incubation period, duration of cercarial shedding and cercarial production in various sizes of the two snail species were reported and discussed

Filtration, centrifugation and mouse exposure for the detection of schistosome cercariae in water

Three methods for the detection of Schistosome cercariae in water were studied under laboratory and simulated field conditions in Egypt. Water samples tested by filtration and centrifugation, quantitatively, reflected the density of cercariae in moderately turbid canal water [30 nephelometry Turbidity Unites, NTU]. When tested in waters of increasing turbidity, the centrifuge gave more consistent results than the filtration system. The centrifugation technique was more efficient in processing the water samples and took almost half the time of filtration and mouse exposure was useful in detecting cercariae, but was not quantitative. However, there was a significant improvement in worm recovery when mice were more close together in the floatation device. Mouse exposure was also expensive and cumbersome to use. The present results concluded that centrifugation may be considered the technique of choice for further cercariometric work under the Egyptian conditions

Cercariometry in the study of schistosoma mansoni transmission in Egypt

The recovery of Schistosoma mansoni cercariae was studied in experimental ditches and natural irrigation canals using a continuous operating centrifuge and a water suction sampling technique. Recovery of cercariae from static water in the ditches where caged infected Biomphalaria alexandrina snails were placed showed that cercariae recovered were more with increase of infected snails and decrease of water volume and were most abundant in the proximity of the snails which produced them. Shade or heavy vegetation cover reduced the recovery of cercariae. Results suggested also strong seasonal differences in diurnal patterns of cercarial recovery. In early morning peak with large number of cercariae occurred during hot weather while in cooler seasons cercariae appear in fewer numbers but persist for most of the day. Obtained information, beside contributing to knowledge of cercarial behavior, should help to optimize taking water sample and consequently to increase efficiency of cercariometry techniques. In the natural irrigation system, cercariometry was significantly more sensitive in detecting transmission foci than snail sampling by a dip net

Ecology of biomphalaria alexandrina the snail vector of schistosoma mansoni in Egypt

The patterns of spreading and seasonal variation of population density of Biomphalaria alexandrina, the snail vector of Schistosoma mansoni in Egypt, in correlation with some environmental parameters were studied for 1988-1990 in four irrigation canals in Giza and Qalyoubia governorates. Results showed that the spreading patterns of snails along canals are changeable because of water current and irrigation activities. The snail population density showed two peaks, different in height, in April-May and November-December separated by two bottoms following the "Winter Closure" and during the hot summer season. The height of the peaks appears to be dependent on the extent of the "Winter Closure" and the prevailing water temperature. Two snail sampling tools; the dip-net and drag scoop, were used concurrently in this study. No considerable difference in sampling efficacy was recognized between these tools in the case of Biomphalaria. However, the dip-net appears to be more efficient in sampling other pulmonates while the drag scoop is more efficient in sampling prosobranchs. It is also realized that double sampling of 50% of sampling sites the next day should be satisfactory as a quality control system in snail population studies

Helisoma duryi: its present range of distribution and implications with schistosomiasis snails in Egypt

The range of distribution of Helisoma duryi, a potential competitor to schistosomiasis snail vectors in Egypt, was determined in the south of Nile Delta. Results showed that H. duryi was found in the River Nile, Geziret El-Kerateyeen banks, Damietta and Rosetta Branches, Tawfiky and Menoufy Canals and their branches and Bassoussiya, Bahadiya and Sheshaa Canals and their branches. Helisoma was found in all categories of canals and drains coexisting in various degrees with other snail species including schistosomiasis vectors [Bulinus truncatus and Biomphalaria alexandrina]. The population density of H. duryi and associated B. truncatus, B. alexandrina and Physa acuta were studied for one year in three channels. Statistical analysis of results showed that Helisoma has a significantly negative correlation with schistosomiasis vectors in these channels. Helisoma population showed a major peak in the warmest months of the year [July-August], thus showed recovery in population after "Winter Closure" later than Bulinus, Biomphalaria and Physa. Helisoma proved to be free of any natural trematode infection

Population dynamics and schistosomal infection of biomphalaria alexandrina in four irrigation canals in Egypt

The natural growth, reproductivity, mortality and schistosomal infection of Biomphalaria alexandrina, the snail vector of Schistosoma mansoni in Egypt, were studied for one year in four irrigation canals, namely El-Khassa and Radwan [Giza Governorate] and Sendebis and Sanafeer [Qalyoubiya Governorate]. Radwan canal contains a considerably dense Biomphalaria population and three generations of Snails [parents generation and autumn and spring generations] were recognized .Two phases of growth were distinguished in both autumn and spring generations, a faster phase followed by a slower one. The faster phase extends from January to May and from March to August in the autumn and spring generations, respectively. The daily mortality rate of snails was highest in the hot season [June - September] and lowest in the cold months [December - April]. Continuous reproductivity of Biomphalaria snails was observed allover the year with highest values of reproduction index from November to March .Biomphalurza snails collected from El Khassa and Radwan canals were free of S. mansoni infection, while snail of sanafeer canal carried patent infection and September and October. Prepatent infection was also found in Sanafeer canal in July at September and in sendebis canal in September

Distinguishing heliscma [seminolina] Duryi from biomphalaria Alexandria in Egypt

A relationship between the height [H] and diameter [D] was extracted for distinguishing the shells of Helisoma duryi and Biomphalaria Alexandrina, which are similar in general appearance. This relation is expressed as follows: In juvenile snails: H. duryi [H = 0.44 D + 1.7] and B. Alexandrina [H = 0.3 D + 0.7]. In older snails: H. duryi [H = 0.3 D + 2.5] and B. alexandrina [H = 0.2 D + 1.54]. The difference in structure is also given