Fasciola gigantica: larval productivity of three different miracidial isolates in the snail Lymnaea truncatula

Bimiracidial infections of Lymnaea truncatula with three isolates of Fasciola gigantica, originating from China, Egypt and Madagascar, were carried out to determine the effect of geographic origin of the parasite on the larval productivity of redial generations. The prevalences of experimental infections in snails exposed to strains from Madagascar, China and Egypt were 20.8%, 60.0% and 80.0%, respectively. At day 49 post-exposure (p.e.), the total number of free rediae in snails infected with the Egyptian isolate was significantly higher than that recorded in the Madagascan group. On the other hand, at day 49 p.e., the majority of cercariae in the Chinese and Egyptian groups were produced by R2a rediae (70.6% and 66.6% of cercariae produced by all live rediae), while, in the Madagascan group, the cercariae were produced mainly by the first redial generation. Snails infected with the Egyptian isolate of miracidia developed more live rediae and, consequently, could produce a higher number of cercariae. As a result, L. truncatula snails were highly adapted to infections with the Egyptian and Chinese isolates of F. gigantica.

Cercarial productivity of redial generations in single-miracidium infections of Lymnaea truncatula with Paramphistomum daubneyi or Fasciola hepatica

Single-miracidium infections of Lymnaea truncatula with Paramphistomum daubneyi or with Fasciola hepatica were carried out under laboratory conditions to count free rediae, their germinal embryos, and to determine the cercarial productivity of each redial generation. In snails infected by P. daubneyi, the cercariae were produced by the first (8.7 cercariae per redia) and second (8.9 per redia) generations. At day 63 post-exposure, they corresponded, respectively, to 53.9% and 46.1% of cercariae produced by all rediae. In snails infected by F. hepatica, the majority of cercariae were produced by the R2a group (18.2 cercariae per redia) and corresponded to 66.0% of cercariae produced all rediae. The cercariae produced by the other redial groups were more limited in number: 17.5 per redia in the R1b group (28.7%) and 2.0 per redia in the R2b/R3a group (5.3%). Cercarial productivity of P. daubneyi until day 63 post-exposure was more limited in number than that of F. hepatica: a total of 145 cercariae per snail versus 427 per snail.

The Life-Cycle and Morphology of Stemmatostoma-Pearsoni, Gen Et Sp-Nov, With Notes on the Morphology of Telogaster-Opisthorchis Macfarlane (Digenea, Cryptogonimidae)

Stemmatostoma pearsoni, gen. et sp. nov., is described from the intestine of Leiopotherapon unicolor (Gunther) and Macquaria novemaculeata (Steindachner) in Queensland. Stemmatostoma is placed within the Neochasminae and is distinguished by its long oesophagus, compact ovary, short caeca, pre-ovarian vitellaria, simple gonotyl and funnel-shaped oral sucker. The diagnosis of the Neochasminae is emended excluding Parspina Pearse. Telogaster opisthorchis Macfarlane is recorded from the intestine of Anguilla reinhardtii Steindachner from Victoria. The spinose oral suckers of S. pearsoni and T. opisthorchis are capable of being retracted into tegumental pockets. It is postulated that this arrangement may be widespread amongst spinose cryptogonimids. The first intermediate host of S. pearsoni is Posticobia brazieri (Smith), a prosobranch snail. The second intermediate hosts are freshwater fish: Hypseleotris galii (Ogilby), H. compressus (Krefft), Mogurnda mogurnda (Richardson), M. adspersa (Castelnau), Philypnodon grandiceps (Krefft), Gobiomorphus australis (Krefft), and Pseudomugil signifer Kner. Within the snail there is a mother sporocyst generation, a redial generation and a cercarial generation. Development of the mother sporocyst is similar to that described for other opisthorchioids. Cryptogonimid cercariae are characterized by 16 flame-cells, pre-vesicular penetration glands, dorso-ventral caudal finfolds and absence of body pigmentation. On the basis of cercarial and adult morphology it is proposed that Pseudexorchis Yamaguti be excluded from the Cryptogonimidae.