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1.
This paper focuses on the geographical distribution and habitats of Lymnaea truncatula, the intermediate, snail host of the liver fluke, Fasciola hepatica, as reflected by the 723 samples in the database of the National Freshwater Snail Collection, Potchefstroom, South Africa. The 221 different loci (1/16-degree squares) on record reflect an extensive but discontinuous distribution, except in Lesotho and in parts of the Mpumalanga, Gauteng and North West provinces of South Africa. Although recorded from 12 different types of waterbody, it was mostly (42.0%) recovered from swamps. Most samples (45.8%) were collected in habitats with slow-flowing water. A muddy substratum was recorded for 62.5% of the samples. Most samples (86.3%) were collected in habitats with a mean annual air temperature of 10-20 degrees C, and more than 69% came from localities with a mean annual rainfall of 600-900 mm. An integrated decision tree constructed from the data indicated that temperature and types of waterbody play a decisive role in determining the presence of L. truncatula in a given area. A temperature index calculated for all mollusc species ranked L. truncatula second in a total of 53 species according to its association with low temperatures. It remains to be established whether its distribution is indeed discontinuous, and whether its preference for a particular habitat, amphibious habits and ability to aestivate could have resulted in some populations having been overlooked during surveys.  相似文献   

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Radiolabeled metacercariae of Fasciola hepatica were obtained in vivo by incubating infected Lymnaea columella snails with 20 muCi radioselenomethione (75Se-M) per snail in 5 ml of water for 5 h, or in vitro by incubating a batch of unlabeled F. hepatica metacercariae with 75Se-M for 24 h. Radioassay showed that only 5% of the 75Se-M was incorporated into maritas (juvenile flukes) from the in vivo labeled metacercariae. The inner cyst wall of in vivo labeled metacercariae contained 46% of the total activity, of which 21% was dissolved in the excysting medium. The outer, tan-colored cyst wall contained 49% of the radioactivity. Through diffusion/attachment, maritas from in vitro labeled metacercariae could occasionally be labeled with 0.4% of the total radioactivity. However, the activity was lost after inoculation into the body of mice. The outer and inner cyst walls of in vitro labeled metacercariae contained 92% and 7.6%, respectively, of the total activity. Microautoradiography demonstrated that 75Se-M was evenly distributed in the body of marita and the cyst wall of inner and outer layers from an in vivo labeled metacercaria. A 9 X 4 micron rectangularly-shaped aggregate of Ag degree grains was present on the outer periphery of the inner cyst wall. Microautoradiography of in vitro labeled metacercariae demonstrated a significant concentration of Ag degree grains on the cyst walls. The ventral plug contained fewer Ag degree grains per unit area compared to the other portion of the inner cyst wall. Uptake and distribution of 75Se-M in the snail host were also studied. It appeared that rediae and cercariae tended to concentrate the label in the foot, the mantle and the digestive gland. Little or no radioactivity was present in the areas where F. hepatica larvae were not found.  相似文献   

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The southern border of the European endemic area of Echinococcus multilocularis runs along the alpine crest. This endemic transition area was analysed in the canton Grisons on a small spatial scale. A total of 543 foxes originating from 10 areas north and 4 areas south of the main alpine divide were investigated. Parasites were isolated using the sedimentation and counting technique on intestinal contents. The mean prevalence of E. multilocularis was 6.4% with significant differences between different areas. In the southern valleys, only foxes from the Val Müstair were infected (14.3%). On the northern side of the main alpine divide, prevalences varied between 0 and 40%. The predation habits of foxes on potential intermediate hosts was investigated by means of stomach content analyses (n=530). Rodents of the genera Microtus/Pitymys were found in 19.6% of fox stomachs, Clethrionomys glareolus in 8.0% and Arvicola terrestris in 0.4%. A small scale analysis based on a 10 x 10 km grid suggested that the predation rate on the genera Microtus/Pitymys significantly correlated with the prevalence of E. multilocularis in foxes (Spearman's r = 0.51). Hence, E. multilocularis appears to occur in the alpine study area on a very small spatial scale. These local sources of infection may persist for decades. This may partly explains why, during the last 34 years, some human cases of alveolar echinococcosis occurred in areas of the Canton Grisons where the parasite is presently endemic in foxes. No such human cases have been recorded in other areas free of E. multilocularis.  相似文献   

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A commercially available ELISA for detecting antibodies to liver fluke was evaluated for use in Australia. Milk and serum samples from cattle and sheep in which infection with Fasciola hepatica was confirmed by detection of eggs in faeces were used to estimate sensitivity. Similar samples collected from cattle and sheep outside the F. hepatica-endemic area were used to estimate specificity. The ELISA was also evaluated for detecting antibodies to F. hepatica in milk from sheep and antibodies to Fasciola gigantica in sera from cattle and buffaloes, but with small numbers of samples. In cattle, the sensitivity and specificity of the ELISA were 98.2% and 98.3% using serum and 97.7% and 99.3% using milk. In infected herds, 41.4% and 41.5% of animals were positive in the serum and milk ELISAs, respectively, whereas F. hepatica eggs were found in faecal samples from 26.5% of animals. In sheep, the sensitivity of the ELISA was 96.9% and the specificity was 99.4%. In infected flocks, 60.2% of animals were positive in the serum ELISA and F. hepatica eggs were found in faecal samples 52.2% of animals. There was perfect agreement in the ELISA between paired serum and milk samples collected from ewes. The assay detected antibodies in sera from cattle and buffaloes with natural and experimental F. gigantica infections. In the experimentally infected animals, antibodies were detected 2 weeks post-infection. We conclude that the ELISA will be a valuable tool for diagnosing F. hepatica infections in cattle and sheep. The assay may also be useful for diagnosing F. gigantica infections but further studies are required to establish sensitivity and specificity.  相似文献   

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Mixed breed goats were infected with metacercariae of Fasciola hepatica and the resulting worm burdens were quantitated after primary and secondary exposure of the goats to the parasite. Mean length and width of the parasite recovered after all primary exposures were 1.91 +/- 0.2 cm and 0.91 +/- 0.2 cm, respectively. A mean of 71.8 +/- 5.9% of the flukes were recovered from all of the primary infections. In the secondary infections, the mean length and width of the flukes from the physically smaller population was 0.88 +/- 0.27 cm and 0.53 +/- 0.19 cm, respectively. A mean of 67 +/- 6.7% of the flukes were recovered from this secondary infection. It appears that the goat is susceptible to challenge infections with F. hepatica and that its response to this infection is much like that of sheep.  相似文献   

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The climatic variables that were most useful in classifying the infection status of Queensland cattle herds with bluetongue virus were assessed using stepwise linear discriminant analysis. A discriminant function that included average annual rainfall and average daily maximum temperature was found to correctly classify 82.6% of uninfected herds and 72.4% of infected herds. Overall, the infection status of 74.1% of herds was correctly classified. The spatial distribution of infected herds was found to parallel that of the suspected vector,Culicoides brevitarsis. This evidence supports the role of this arthropod species as a vector of bluetongue viruses in Queensland.The effect of potential changes in temperature and rainfall (the so-called global warming scenario) on the distribution of bluetongue virus infection of cattle herds in Queensland was then investigated. With an increase in both rainfall and temperature, the area of endemic bluetongue virus infection was predicted to extend a further 150 km inland in southern Queensland. The implications of this for sheep-raising in Queensland are discussed.Abbreviations AGID agar gel immunodiffusion  相似文献   

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Field surveys were carried out in the Lismore and Casino area for the presence of fresh water snails potentially responsible for the transmission of trematodes in ruminants. Although the North American snail, Lymnaea columella has previously only been reported from metropolitan areas, large populations of the snail were found east of Lismore. Natural infection with F. hepatica was detected in some of the snails and laboratory studies showed that this snail species was highly susceptible to infection with miracidia of F. hepatica and produced viable metacercariae. Three species of planorbid snails, Helicorbis australiensis, Pygmanisus pelorius and Gyraulus gilberti were also found. The first 2 planorbid species were infected with paramphistomid cercariae.  相似文献   

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In adultFasciola hepatica glucose is broken down to volatile fatty acids, carbon dioxide and lactate. In the cytosol glucose is converted into malate and lactate and malate is metabolized further in the mitochondrial compartment via a dismutation. The dismutation of malate can proceed under anaerobic conditions. To a limited extent oxygen can function as terminal electron acceptor.It is shown that the reaction catalysed by fumarate reductase is a reversible reaction. The direction of the reaction depends on the relative concentrations of fumarate and succinate.Mechanisms of ATP production and electron transport under aerobic and anaerobic conditions are discussed. It is concluded that the energy metabolism of the adult liver fluke is adapted to the life in an environment with a low oxygen content.
Kurzfassung Beim adultenFasciola hepatica wird Glucose in flüchtige Fettsäuren, Kohlendioxid und Laktate gespalten. Im Zytosol wird die Glucose in Malate und Laktate gespalten und Malate werden im Mitochondrienbereich durch Redox-Dismutation weiter verstoffwechselt. Die Dismutation der Malate kann unter anaeroben Bedingungen ablaufen. In gewissem Ausmass kann Sauerstoff terminal Elektronen binden.Es wird gezeigt, dass die Reaktion, die durch Fumaratreduktase katalysiert wird, reversibel ist. Der Ablauf der Reaktion hängt von den relativen Konzentrationen der Fumarate und Succinate ab.Ferner werden die Mechanismen der ATP-Produktion und des Elektronentransports unter aeroben und anaeroben Bedingungen diskutiert. Zusammenfassend wird festgestellt, dass der Energiestoffwechsel des adulten grossen Leberegels an ein Leben in einer sauerstoffarmen Umwelt adaptiert ist.

Resume Chez les douves adultes le glucose est dégradé en acides gras volatil, gaz carbonique et lactate. Dans le cytosol le glucose est convertit en malate et en lactate et le malate est métabolisé ensuite dans la mitochondrie selon un phénomène de transformation biochimique. La transformation biochimique du malate peut se réaliser dans des conditions anaérobies. Dans une certaine mesure l'oxygène peut fonctionner comme un accepteur terminal d'électrons.Il est démontré que la réaction catalysée par la fumarate réductase est réversible. Le sens de la réaction dépend de la concentration relative en fumarate et succinate.Le mécanisme de production de l'ATP, du transport des électrons dans des conditions aérobies et anaérobies est discuté. Il est retenu que le métabolisme énergétique de la douve adulte est adapté à la vie dans un environnement pauvre en oxygène.

Riassunto Negli adulti diFasciola hepatica il glucosio si scinde in acidi grassi volatili, biossido di carbonio e lattato. Nel citosol il glucosio è convertito in malato e lattato, ed il malato è ulteriormente metabolizzato nel comparto mitocondriale attraverso un processo di dismutazione. La dismutazione del malato può proseguire in condizioni di anaerobiosi. In misura limitata l'ossigeno può agire come accettore terminale di elettroni.E'stato dimostrato che la reazione catalizzata dalla fumarato-reduttasi è una reazione reversibile. La direzione della reazione dipende dalle concentrazioni relative di fumarato e di succinato.Vengono discussi i meccanismi di produzione di ATP e del trasporto di elettroni in condizione di aerobiosi e di anaerobiosi. Si conclude che il metabolismo energetico dell'adulto diFasciola hepatica è adattato alla vita in un ambiente con bassi livelli di ossigenazione.
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Freshly excysted Fasciola hepatica possess an outer glycocalyx which on incubation at 37 degrees C is rapidly shed. Using an ELISA technique the release of this parasite antigen was shown to be temperature-dependent and to occur in both normal bovine serum as well as in serum free conditions. The ELISA failed to detect the antibody--antigen complexes that occurred when flukes were incubated in immune serum. Release of specific parasite antigen fell slowly with in vitro cultured flukes, but increased with in vivo cultured flukes. Using a fluorescence inhibition assay, antigens with high ELISA titres inhibited surface fluorescence of the parasite suggesting that the ELISA was detecting surface antigens as well as other parasite metabolic products. Several metabolic blocking agents and commercial antihelminthics were titrated against juvenile F. hepatica to screen for inhibition of the surface--tegument shedding: there was little selective inhibition of surface shedding without a significant loss of motility.  相似文献   

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We described the transmission dynamics of Fasciola hepatica at its southern distribution range. Studies of prevalence and egg output in cattle and population dynamics and infection in snails were performed in a farm in the Andean Patagonian valleys, Argentina, between December 1998 and February 2002. Snail surveys were conducted from spring to autumn. Infection was diagnosed coprologically in the whole herd at the beginning and end of the study, and in a cohort of heifers at the beginning and end of 2001. A twice-a-year anthelmintic treatment was implemented in 1999. The relationship of the variables mentioned above with temperature and rainfall was determined. Lymnaea viatrix showed a life-span of about 15 months and an annual pattern of population dynamics. Specimens were frequently found in temporary environments and lagoons, and rarely in streams. Snail abundance and soil-water availability were directly related in temporary environments and inversely related in lagoons. Overall prevalence in L. viatrix was 0.67% (range: 0.9-14%) and infection was detected in summer and autumn. At the beginning of the study, calves were the least infected age group (15%). Prevalences and median egg counts in grazing animals were similar at the beginning (heifers: 81%, 3.3 epg; cows: 60%, 1.3 epg) and end of the study (heifers and cows: around 51%, 1 epg). Likewise, the prevalence in the cohort of heifers remained similar (around 40%) between surveys. Transmission to cattle was highly effective despite of the short activity period and the low infection rate of snails, and the regular anthelminthic treatment. There would be two seasonal transmission peaks, one in summer-autumn, when infected snails were present, and the other in early spring due to overwintering metacercariae. Some recommendations based on the climatic conditions of the region are provided to minimize snail infection and ultimately to reduce the incidence of fasciolosis in cattle.  相似文献   

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The influence of Fasciola hepatica and Fasciola gigantica infection on serum glucose and beta-hydroxybutyrate (beta-HOB) in sheep was evaluated. This was done by setting up two groups of sheep. The first group (n=13) was split in two sub-groups, one experimentally infected with F. hepatica (n=9) and the other (n=4) as uninfected control. A second group consisting of a sub-group experimentally infected with F. gigantica (n=9) the other sub-group (n=6) left as uninfected control was also set up. The results of weight gain, parasitological and serum liver enzymes activity (glutamate dehydrogenase [GLDH] and gamma glutamyltransferase [gamma-GT]) used in monitoring the infection showed that all infected animals developed fasciolosis. It was observed that a reduction in serum glucose levels was significantly lower (p<0.05) in F. hepatica infected sheep than in uninfected control sheep starting from 5 weeks post-infection (wpi) to the end of the experiment. Similar reduction was recorded in F. gigantica infected sheep between 8 and 19 wpi. In contrast, serum beta-HOB levels were elevated in F. hepatica infected sheep between 6 and 16 wpi and in F. gigantica infected sheep between 7 and 15 wpi. It would appear from these serum glucose and beta-HOB levels that fasciolosis does lead to energy deficiency (low glucose) and ketosis (increased beta-HOB). The decrease in serum glucose and increase in serum beta-HOB levels in infected sheep may help in understanding the interaction between fasciolosis and nutritional status of infected ruminants especially in young growing animals.  相似文献   

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