Geographic distribution modelling for ruminant liver flukes (Fasciola hepatica) in south-eastern Europe

Maximum entropy ecological niche modelling was utilised to predict the geographic range for fluke genotypes and haplotypes in south-eastern Europe, using the Maxent program. The lowest (0.832) and the highest (0.947) area under the curve values were observed in the models for the haplotypes CtCmt1 and CtCmt2.2, respectively. Precipitation and temperature contribute equally to model building of the genotypes based on the 28S rDNA gene. In regard to the mtDNA gene region, precipitation is the most important factor in modelling the CtCmt1 haplotype range, while temperature appears to be the most important factor in modelling the CtCmt2.1 and CtCmt2.2 haplotype ranges. The highest level of probability for the geographic distribution of Fasciola hepatica genotypes and haplotypes covered the regions of southern Bulgaria and central and northern Greece which contain a high concentration of potential ruminant hosts.     

Parasiticidal effects of peroxynitrite on ovine liver flukes in vitro

Peroxynitrite (ONOO-) is a cytotoxic anion, produced by interaction between nitric oxide and superoxide in vivo in some inflammatory cells. This study investigated its effects on Fasciola hepatica and Dicrocoelium dendriticum isolated from ovine livers and kept in bile at room temperature. Peroxynitrite was synthesized using a quenched flow reactor and assayed spectrophotometrically. It was applied at different concentrations (10(-3.5) to 10(-2.3 M)) to the flukes kept in bile. The viability of the peroxynitrite-treated flukes was compared with a control group (n=5-7 per group). Control F. hepatica and D. dendriticum lived for 226+/-11and 208+/-14min, respectively. Life times were decreased by peroxynitrite at all concentrations used (P<0.001). At the highest concentration of peroxynitrite, F. hepatica and D. dendriticum lived only for 6.1+/-0.4 and 4.1+/-4.1+/-0.2min, respectively. Correlation between peroxynitrite concentration and parasite viability was significant in the case of F. hepatica (r= -0.842; P= 0.0035). A single application of peroxynitrite can decrease the life span of ovine liver flukes. A failure in the activation of hepatic macrophages in infected animals may lead to a decreased production of free radicals and, thus, peroxynitrite. Such a failure is likely to deprive the body of a defence tool against multicellular parasites.     

Use of Geographic Information Systems in the development of prediction models for onchocerciasis control in Ethiopia

A risk assessment model was developed for onchocerciasis distribution and its control in Ethiopia using Geographic Information System (GIS) methods. GIS data analysis was done to generate 3 separate risk models using selected environmental features of (1) earth observing satellite data on Normalized Difference Vegetation Index (NDVI) and midday Land Surface Temperature (LST) prepared from AVHRR sensor data of the Global land 1-km project for the years 1992 and 1995, (2) FAO agroclimatic databases from the Crop Production System Zone (CPSZ) of the Intergovernmental Authority on Development (IGAD) sub-region of East Africa, and (3) a climate-based forecast index based on the growing degree days (GDD) and water budget concepts. Parasitological data used for the analysis were published and unpublished reports of onchocerciasis surveillance made between 1969 and 2000 in various parts of the country. Analysis of queries based on 1992 and 1995 annual wet and dry season data of the Global land 1-km project resulted in a predictive value of 95.1%, 94.0% and 96.3%, respectively, using data values extracted from buffers centered on sites above 5% prevalence. The model based on CPSZ data predicted an endemic area that best fit the distribution of sites over 5% prevalence; the query was based on CPSZ values of average altitude (442-2134 m), annual mean temperature (18-28 degrees C), annual rainfall (822-1980 mm), annual potential evapotranspiration (1264-1938 mm), rain minus potential evapotranspiration (-124 - 792 mm), average NDVI x 100 (2000-5000) and average terrain percent slope (9-34). The climate-based model based on GDD and water-budget predicted high risk to severe risk areas in the western and southwestern parts of the country. All three of the models predicted suitable areas for the transmission of onchocerciasis outside known endemic areas, suggesting the need for ground-based validation and potential application to current community-directed treatment programs with ivermectin (CDTI) for control of onchocerciasis in Ethiopia.     

Mathematical models of Neospora caninum infection in dairy cattle: transmission and options for control

The transmission and control of Neospora caninum infection in dairy cattle was examined using deterministic and stochastic models. Parameter estimates were derived from recent studies conducted in the UK and from the published literature. Three routes of transmission were considered: maternal vertical transmission with a high probability (0.95), horizontal transmission from infected cattle within the herd, and horizontal transmission from an independent external source. Putative infection via pooled colostrum was used as an example of within-herd horizontal transmission, and the recent finding that the dog is a definitive host of N. caninum supported the inclusion of an external independent source of infection. The predicted amount of horizontal transmission required to maintain infection at levels commonly observed in field studies in the UK and elsewhere, was consistent with that observed in studies of post-natal seroconversion (0.85-9.0 per 100 cow-years). A stochastic version of the model was used to simulate the spread of infection in herds of 100 cattle, with a mean infection prevalence similar to that observed in UK studies (around 20%). The distributions of infected and uninfected cattle corresponded closely to Normal distributions, with S.D.s of 6.3 and 7.0, respectively. Control measures were considered by altering birth, death and horizontal transmission parameters. A policy of annual culling of infected cattle very rapidly reduced the prevalence of infection, and was shown to be the most effective method of control in the short term. Not breeding replacements from infected cattle was also effective in the short term, particularly in herds with a higher turnover of cattle. However, the long-term effectiveness of these measures depended on the amount and source of horizontal infection. If the level of within-herd transmission was above a critical threshold, then a combination of reducing within-herd, and blocking external sources of transmission was required to permanently eliminate infection.     

Seasonal and Geographic Variation of Southern Blue Whale Subspecies in the Indian Ocean

Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four “acoustic populations” occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.     

The complete mitochondrial genomes of the liver flukes Opisthorchis felineus and Clonorchis sinensis (Trematoda)

The complete mitochondrial genomes of the parasitic trematodes Opisthorchis felineus and Clonorchis sinensis (family Opisthorchiidae) were fully sequenced in order to develop markers for DNA diagnostics of the liver flukes infection, molecular ecology, population and phylogenetic studies. The complete sequences of mitochondrial genomes of these species comprise 14,277 and 13,875 bp, respectively, and are thus the shortest trematode mitochondrial genomes sequenced to date. The gene content and arrangement are identical to that of Fasciola hepatica. ATG and GTG are used as the start-codons and TAG and TAA are used as the stop-codons. The stop-codon TAG of the C. sinensis nad1 gene overlap by 1 nt with the downstream tRNA-Asn gene. Alternative structures for the Ser(UCN) tRNAs were found for both species. The noncoding control regions are separated into two parts by the tRNA-Gly gene and contain neither tandem repeats, which are characteristic for trematode control regions, nor secondary structures. In conclusion, the complete mitochondrial DNA sequences of O. felineus and C. sinensis will serve as a resource for comparative mitochondrial genomics and systematic studies of parasitic trematodes.     

Comparison of adult liver flukes from highland and lowland populations of Bolivian and Spanish sheep

A morphological study of adult liver flukes and eggs from sheep in a human fascioliasis endemic zone in the Northern Bolivian Altiplano showed that they belong to the species Fasciola hepatica. An exhaustive morphometric comparison with a F. hepatica population from Spanish sheep was made using image analysis and an allometric model: (y2m-y2)/y2 = c(y1m-y1)/y1[b, where y1 = body surface or body length, y2 = one of the measurements analyzed, y1m, y2m = maximum values towards which y1 and y2 respectively tend, and c, b = constants. Only slight allometric differences in worms were observed despite the geographic distance between both Spanish and Bolivian sheep populations and the very high altitude of the Bolivian Altiplano.     

Microsatellite-based parentage control in cattle

As a new approach to parentage control we developed two multiplex coamplification polymerase chain reaction (PCR) systems containing a total of six different short tandem repeat (STR) loci; the microsatellite polymorphisms were visualized by automated fluorescence detection on the Applied Biosystems 373 DNA Sequencer with 672 Genescan Analysis software. Allele frequency data were determined from 238 animals. Thirty-five bovine parentage control cases not solvable by conventional blood typing could be solved.     

Geospatial analysis of giant liver flukes among moose: effects of white-tailed deer

Natural infections of giant liver flukes (Fascioloides magna) occur primarily in cervids and bovids. In northeastern North America, a common definitive host for giant liver flukes is the white-tailed deer (Odocoileus virginianus). Giant liver flukes cannot reproduce in moose (Alces alces) and eventually die, but only after causing extensive tissue damage in the liver. We used data on the occurrence of giant liver flukes in adult moose collected between 1972 and 2000 from northeastern Minnesota, USA. These data were recorded by 93 km² sampling units (square grid of 9.66 km on each side). Sample sizes varied between 0 and 45 adult moose examined per sampling unit. We fitted a second-order global polynomial model to adjust for trends in the occurrence of flukes across the study area, modeled the de-trended data using a circular semi-variogram model, and finally kriged our data, arriving at a predicted response surface for the occurrence of liver flukes in moose. Correlational analyses indicated that the occurrence of liver flukes in moose was influenced more by the density of white-tailed deer based on rates of hunter harvest (r?=?0.54) than was the proportion of wetland habitats (r?=?0.25). Ordinary least-squares multiple regression (R _adj?=?0.29, AIC_c?=?795.3) documented a strong relationship between the occurrence of liver flukes in moose and population density of white-tailed deer (p?<?0.001) but a weaker relationship for wetland habitats (p?=?0.16). A geographically weighted multiple regression produced a stronger relationship (R _adj?=?0.60, AIC_c?=?765.7). Disease maps, as we developed here, are a useful geospatial tool that has relevance for understanding disease processes in moose that may be extended to other mammals.     

Geographic variation of blood and liver proteins in cricket frogs

Population and species structure of the cricket frogs, Acris crepitans and A. gryllus, were examined in terms of protein variation throughout their geographic ranges. Eight hundred and fifty animals, collected from 32 populations in 20 states, were processed to obtain electrophoretic evidence on 20 blood and liver proteins. Molecular data confirm the reproductive isolation of the two species. They had different albumins, transferrins, and hemoglobins; frogs with hybrid protein patterns were not found in regions where the two species are sympatric. Within A. crepitans eight proteins were invariant across the species range; twelve exhibited one or more variant phenotypes. The genetic integrity of the species was illustrated by the uniformity of the albumin, plasma esterases, liver LDH, GOT, GDH, MDH-NADP, NADP-reductase, and hemoglobin polypeptide 4. Its polytypic nature, with geographic divergence into Plains, Delta, and Appalachian groups, was suggested by the presence of specific hemoglobin, transferrin, and liver esterase variants in animals of certain regions. Within-population polymorphism was exhibited by the transferrins, MDH-NAD, and three complexes of liver esterases; heterozygosity was greater in central than in peripheral populations. Biochemical evidence supports the hypothesis that the two species diverged during a Pleistocene disjunction of proto-Acris populations in Florida and Mexican refuges. With the recession of the glaciers, A crepitans presumably moved from its Mexican refuge northward and northeastward, to become adapted both to grassland and deciduous forest biomes and to attain contact and overlap with A. gryllus in southeastern United States.Supported by National Science Foundation Grants GB 3124 and GB-7294X to HCD and by Grants in-aid from Sigma Xi to Nevo.Laboratory of Genetics, The Hebrew University, Jerusalem, Israel. Work done while on a traineeship with the Committee on Evolutionary Biology at the Museum of Comparative Zoology, Harvard University.     

The zoonotic,fish-borne liver flukes Clonorchis sinensis,Opisthorchis felineus and Opisthorchis viverrini

Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini are the three most important liver flukes involved in human health, infecting more than 45 million people worldwide. Both C. sinensis and O. viverrini, and possibly O. felineus, can induce human cholangiocarcinoma as well as inducing other hepatobiliary pathology. Although the life cycles of all three species are similar, only that of O. felineus in Europe remains predominantly zoonotic, while O. felineus in Asia and C. sinensis have a stronger mixture of zoonotic and anthroponotic components in their life cycles. Opisthorchis viverrini from the Mekong area of southeastern Asia is predominantly anthroponotic. Here we discuss the comparative epidemiology of these three taxa comparing in detail the use of first, second and final animal hosts, and consider the potential role of humans in spreading these pathogens. In addition we discuss the genetic structure of all three species in relation to potentially cryptic species complexes.     

Geographic distribution of the invasive cattle tick Rhipicephalus microplus, a country-wide survey in Benin

The cattle tick Rhipicephalus microplus is currently invading the West African region, and little information is available on the spread of this exotic tick in this region. We set out a country-wide field survey to determine its current distribution in Benin. Ticks were collected on cattle from 106 farms selected by random sampling covering all regions of the country. Rhipicephalus annulatus was found on 70?% of all farms, R. decoloratus on 42?%, R. geigyi on 58?%, and R. microplus on 49?%. There is a clear geographic separation between the indigenous Rhipicephalus species and R. microplus. Rhipicephalus annulatus occurs mainly in the northern departments, but it was also observed in lower numbers in locations in the south. The presence of R. decoloratus is limited to the northern region, and in most locations, this tick makes up a small proportion of the collected ticks. The tick R. geigyi tends to be dominant, but occurs only in the four northern departments. The observations concerning R. microplus are entirely different, this species occurs in the southern and central region. The results of this survey confirm the invasive character and displacement properties of R. microplus, since in less than a decade it has colonized more than half of the country and has displaced indigenous ticks of the same genus in many of the sampled locations.     

Host resistance in cattle tick control

Cattle ticks are an important constraint on the livestock industry, particularly in tropical and subtropical areas, mainly because of the diseases they transmit and the costs of control. Conventional control is by means of acaricides; although there are still serious drawbacks, these can be minimized by a strategic approach. In this review Julio de Castro and Robin Newson look at alternatives. One is to make use of the host's innate abilities. In the simplest situation, where no control measures are applied, the animals develop their own protective immunity against ticks and tick-borne diseases (TBDs). Alternatively, breeds of cattle with naturally high resistance to ticks can be used, enhanced by selection. Methods of immunizing cattle against ticks are also under development. Ideally, ticks should be managed at an economically acceptable level by a combination of techniques, supported where necessary by vaccination against TBDs.     

Seroprevalence of Neospora caninum infection in dairy cattle of Southern China

A seroepidemiological survey of Neospora caninum infection in dairy cattle was carried out in China's southern Guangdong Province between July 2009 and March 2010. A total of 370 serum samples of dairy cattle was collected from 5 farms and examined for antibodies to N. caninum by enzyme-linked immunosorbent assay. The overall seroprevalence of N. caninum in dairy cattle was 18.9% (70/370). The seroprevalence of N. caninum in aborting cows (22.7%) was higher than that in nonaborting cows (16.3%), but the difference was not statistically significant (P > 0.05). Five-yr-old dairy cattle had the highest seroprevalence (27.8%), followed by those that were 6-yr-old (20.4%). Dairy cattle with 4 pregnancies had the highest seroprevalence (29.2%). There was no apparent association of N. caninum seropositivity with age or number of pregnancies (P > 0.05). The results of the present survey indicated that the infection with N. caninum is prevalent in dairy cattle of all ages in southern China, which may be one of the causes of bovine abortion. This is the first report of seroprevalence of N. caninum in dairy cattle in southern China.