Six lots of 18 B. glabrata from: La Victoria, Turmero, Cagua in Aragua state; Caserío El 25 in Carabobo state, Chabasquén in Portuguesa state and Humocaro Bajo in Lara state, were experimentally infected with miracidia of SM, C5 and C6 strains of Schistosoma mansoni (18 snails/Schistosoma mansoni strain). The averages of the intramolluscal period (IMP) obtained for the S. mansoni strains were very similar and comprised between 35.4 and 36.1 days. No significative statistical differences in the IMP were found according to the S. mansoni strain and the size of snails: < 7 mm and 7 mm. However, significative statistical differences in the IMP were found, in relation to the B. glabrata strain and between the snails classifiel in two groups according to the S. mansoni dose (5 miracidia/snail and 10 miracidia/snail). The higher percentages of infection (PI) were found for the following parasite-snail combinations: C6-Cas. El 25 (80.7%), SM-La Victoria (73.1%) and C5-Cagua (62%). No significative statistical differences were found for the PI a) between the snail classifiel in two groups according to the size (<7 mm and 7 mm), b) in relation to the miracidium dosification (5 and 10 miracidia/ snail and c) in accord to the S. mansoni strain. However, significative statistical differences were found for the PI obtained with different strains of the snail.

Snails of the genus Biomphalaria from Venezuela were subjected to morphological assessment as well as polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis. Morphological identification was carried out by comparison of characters of the shell and the male and female reproductive apparatus. The PCR-RFLP involved amplification of the internal spacer region ITS1 and ITS2 of the RNA ribosomal gene and subsequent digestion of this fragment by the restriction enzymes DdeI, MnlI, HaeIII and MspI. The planorbids were compared with snails of the same species and others reported from Venezuela and present in Brazil, Cuba and Mexico. All the enzymes showed a specific profile for each species, that of DdeI being the clearest. The snails were identified as B. glabrata, B. prona and B. kuhniana.

Nine lots of 32 B. glabrata snails (5-7mm in diameter) from the following strains from the endemic area: Cagua, Valencia Lake (Puerta Negra Sector), Ingenio Bolívar (Aragua State), Mariara, Caserío El 25 and Güigüe (Carabobo state), and from the non-endemic area: Anzoátegui (Lara state), Chabasquén (Portuguesa state) and Caripe (Monagas state) were experimentally infected (5 miracidiums/snail) with C5 Schistosoma mansoni strain. The intramolluscal prepatent period oscillated between 23 and 25 days for the nine strains. The duration of intramolluscal infection varied a lot, from 20 days in the case of the Chabasquén strain to 93 days for the Güigüe strain. The average cercariae production in the 3rd day of emission varied from X = 74.4 for the Mariara strain to 591.7 in the case of the Chabasquén strain. Significant statistical differences were found in relation to the total number of emitted cercariae in the 3rd day (H = 97.4; P < 0.05), with significant statistical differences detected among most of the 36 strain combinations, except for the following: Mariara/Ingenio Bolívar, Cagua/Cas. El 25, Valencia Lake/Güigüe and Güigüe/Caripe. The strains of Valencia Lake (88.8%), Cagua (85.2), Chabasquén (82.6%) and Caripe (82.6%) showed the highest rates of self-cure, whereas the Güigüe strain showed the lowest: 21.4%.

Se infectaron experimentalmente 9 lotes de 32 caracoles B. glabrata (de 5 a 7mm de diámetro) con miracidios de la cepa C5 de Schistosoma mansoni a razón de 5 miracidios por caracol, pertenecientes a las siguientes cepas: En el área endémica de transmisión de Esquistosomiasis mansoni a) Sector Puerta Negra, Lago Valencia, b) Cagua c) Ingenio Bolívar (Estado Aragua) d) Mariara e) Caserío El 25 f) Güigüe (Estado Carabobo). Fuera del área endémica de transmisión g) Anzoátegui (Estado Lara), h) Chabasquén (Estado Portuguesa), i) Sector La Elvira, Caripe (Estado Monagas). El período prepatente intramolusco, osciló entre 23 y 25 días, para las 9 cepas evaluadas. La duración total de la infección fue muy variable desde 20 días para la cepa Chabasquén, hasta 93 días para la de Güigüe.La producción total promedio de cercarias al tercer día de iniciada la emisión varió desde X = 74,4 para la cepa de Mariara, hasta X = 591,7 para la cepa de Chabasquén. Se evidenció la existencia de diferencias estadísticamente significativas (H = 97,4, P < 0,05) en la producción total de cercarias al tercer día de iniciada la emisión, detectándose diferencias estadísticamente significativas para casi todas las 36 combinaciones, excepto para las cuatro siguientes: Mariara/Ingenio Bolívar, Cagua/Caserío El 25, Lago de Valencia/Güigüe y Güigüe/Caripe.En lo que respecta al porcentaje de caracoles que presentaron cura espontánea, los valores mas elevados se obtuvieron en las cepas del Lago de Valencia (88,8%), Cagua (85,2%), Chabasquén (82,6%), Caripe (82,6%) y Anzoátegui (80%). Mientras que el porcentaje mas bajo se obtuvo para la cepa de Güigüe (21,4%).

By mean of the silver impregnation of a lot of 47 cercariae belonging to C5 venezuelan Schistosoma mansoni strain, a polymorphism of size was evidenced. The morph was conformed by the greatest cercariae (between 152.9µm to 218.4µm). This group was ever present in the population of cercariae in less percentage (29.8%). The length of the normal cercariae was comprised between 119µm to 152µm. This group was the dominant in the population: 70.2%. The comparison between the length of both lots of cercariae resulted with significative statistical differences (t = 5.5; P < 0.001). For the total studied cercariae the average of the length was X = 143.9µm and for the wide X = 68.6µm. It was found a positive significative correlation between the wide and the length of the cercariae r = 0.83 (P < 0.001).

Mediante la impregnación con nitrato de plata, de un lote de 47 cercarias de la cepa C5 de Schistosoma mansoni (Venezuela), se evidenció un polimorfismo de tallas. El morfo estaría conformado por las cercarias mas grandes (entre 152,9 y 218µm), este grupo siempre presente en la población de cercarias en menor porcentaje (29,8%). El grupo constituido por las cercarias de talla normal, menores de 152,8µm es dominante en la población de cercarias (70,2%). La comparación entre el largo de ambos lotes de cercarias resultó con diferencias estadísticamente significativas (t = 5,5; P < 0,001). Para el total de las cercarias estudiadas, el largo promedio del cuerpo cercariano resultó de 143,9µm y el ancho de 68,6µm. Se detectó una correlación positiva y significativa entre el ancho y el largo de las cercarias de l a cepa objeto de estudio (r = 0,83; P < 0,001).

A total of 113254 individuals from 100 venezuelan municipalities were studied by mean of Kato-Katz coprological examination and the geohelminth prevalences were established. The national prevalences of T. trichiura, A. lumbricoides and Anquilostomideos were 32.6%, 26.9% and 5.6% respectivelly. For T. trichiura the highest values were obtained for the following municipalities: Arévalo González (54.6%) in Miranda state, Urama (76.9%) in Carabobo state and Punta de Piedra (78.4%) in Sucre state. For A. lumbricoides the highest values were determined in Punta de Piedra (63%), Tunapuy (61.9%) in Sucre state and Arévalo González (62,7%) in Miranda state. For hookworm the highest values were detected in El Amparo (39.5%) and San Camilo (35.9%) in the state of Apure. In relation to the age, the highest prevalence of Ascariosis and Trichuriosis were determined in pre-school and school children and for hookworm in adolescents and adults. A high variability between the municipalities belonging to the same state for the three geohelminths was observed.

El examen coproparasitológico (técnica de Kato-Katz) de un total de 113.254 personas, pertenecientes a 100 municipios de Venezuela, permitió establecer las siguientes prevalencias a nivel nacional: Ascaris lumbricoides: 26,9%, Trichuris trichiura: 32,6% y Anquilostomideos: 5,6%. Además se determinaron los valores de la prevalencia para los mencionados geohelmintos en los 100 municipios considerados observándose una gran variabilidad. Para T. trichiura los valores máximos se obtuvieron en los municipios Arévalo González (54,6%), en el Estado Miranda, Urama (76,9%) en el Estado Carabobo y Punta de Piedra (78,4%) en el Estado Sucre. Para A. lumbricoides, en los municipios Punta de Piedra (63%) y Tunapuy (61,9%), en el Estado Sucre y Arévalo González (62,7%) en el Estado Miranda. Mientras que para los Anquilostomideos las prevalencias máximas se detectaron en los municipios El Amparo (39,5%) y San Camilo (35,9%) en el Estado Apure. En cuanto a la edad las prevalencias más altas se determinaron en niños de edad pre-escolar y escolar, para A. lumbricoides y T. trichiura y en adolescentes y adultos para anquilostomideos.