Seasonal dynamics of Fasciola hepatica burdens in grazing Timahdit sheep in Morocco

Intra- and interspecies variation and population dynamics of Fasciola gigantica among ruminants in Sudan

Fasciola gigantica is a widespread parasite that causes neglected disease in livestock worldwide. Its high transmissibility and dispersion are attributed to its ability to infect intermediate snail hosts and adapt to various mammalian definitive hosts. This study investigated the variation and population dynamics of F. gigantica in cattle, sheep, and goats from three states in Sudan. Mitochondrial cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 1 (ND1) genes were sequenced successfully to examine intra and interspecific differences. ND1 exhibited higher diversity than COI, with 15 haplotypes and 10 haplotypes, respectively. Both genes had high haplotype diversity but low nucleotide diversity, with 21 and 11 polymorphic sites for ND1 and COI, respectively. Mismatch distribution analysis and neutrality tests revealed that F. gigantica from different host species was in a state of population expansion. Maximum likelihood phylogenetic trees and median networks revealed that F. gigantica in Sudan and other African countries had host-specific and country-specific lineages for both genes. The study also indicated that F. gigantica-infected small ruminants were evolutionarily distant, suggesting deep and historical interspecies adaptation.

Effects of temperature on the life history traits of intermediate host snails of fascioliasis: A systematic review

BACKGROUND

The impact of climate change has led to variations in various biological processes, leading to altered transmission dynamics of infectious diseases, including snail-borne diseases (SBDs). Fascioliasis is one of the neglected zoonotic tropical snail-borne diseases caused by the trematode of the genus Fasciola. This review focused on laboratory experimental and model studies that evaluate the potential effect of temperature change on the ecology and biology of the intermediate host snails (IHS) of Fasciola.

METHODS

A literature search was conducted on Google Scholar, EBSCOhost, and PubMed databases using predefined medical subject heading terms, Boolean operators, and truncation symbols in combination with direct keywords: Fasciolosis AND Temperature, Lymnaea OR Austropeplea OR Radix OR Galba OR Fossaria OR Pseudosuccinea AND growth, fecundity, AND survival at the global scale. Other search terms used were (Fascioliasis AND Temperature), (Lymnaea AND Temperature), (Austropeplea AND Temperature), (Fossaria AND Temperature), (Galba AND Temperature), (Pseudosuccinea AND Temperature), and (Radix AND Temperature).

RESULTS

The final synthesis included thirty-five published articles. The studies reviewed indicated that temperature rise may alter the distribution, and optimal conditions for breeding, growth, and survival of IHS, ultimately resulting in changing the transmission dynamics of fascioliasis. The literature also confirmed that the life history traits of IHS and their interaction with the liver fluke parasites are driven by temperature, and hence climate change may have profound outcomes on the population size of snails, parasite density, and disease epidemiology.

CONCLUSION

We concluded that understanding the impact of temperature on the growth, fecundity, and survival of IHS may broaden our knowledge of the possible effects of climate change and hence inform fascioliasis control programs.

Potential Hybridization of Fasciola hepatica and F. gigantica in Africa-A Scoping Review

The occurrence of Fasciola gigantica and F. hepatica in Africa is well documented; however, unlike in Asia, there is a paucity of information on the existence of hybrids or parthenogenetic species on the continent. Nonetheless, these hybrid species may have beneficial characteristics, such as increased host range and pathogenicity. This study provides evidence of the potential existence of Fasciola hybrids in Africa. A literature search of articles published between 1980 and 2022 was conducted in PubMed, Google Scholar, and Science Direct using a combination of search terms and Boolean operators. Fasciola species were documented in 26 African countries with F. hepatica being restricted to 12 countries, whilst F. gigantica occurred in 24 countries, identified based on morphological features of adult Fasciola specimens or eggs and molecular techniques. The co-occurrence of both species was reported in 11 countries. However, the occurrence of potential Fasciola hybrids was only confirmed in Egypt and Chad but is suspected in South Africa and Zimbabwe. These were identified based on liver fluke morphometrics, assessment of the sperms in the seminal vesicle, and molecular techniques. The occurrence of intermediate host snails Galba truncatula and Radix natalensis was reported in Ethiopia, Egypt, South Africa, Tanzania, and Uganda, where F. hepatica and F. gigantica co-occurrences were reported. The invasive Pseudosuccinea columella snails naturally infected with F. gigantica were documented in South Africa and Egypt. In Zimbabwe, P. columella was infected with a presumed parthenogenetic Fasciola. This suggests that the invasive species might also be contributing to the overlapping distributions of the two Fasciola species since it can transmit both species. Notwithstanding the limited studies in Africa, the potential existence of Fasciola hybrids in Africa is real and might mimic scenarios in Asia, where parthenogenetic Fasciola exist in most Asian countries. In South Africa, aspermic F. hepatica and Fasciola sp. have been reported already, and Fasciola hybrids have been reported? in Chad and Egypt. Thus, the authors recommend future surveys using molecular markers recommended to identify Fasciola spp. and their snail intermediate hosts to demarcate areas of overlapping distribution where Fasciola hybrids and/or parthenogenetic Fasciola may occur. Further studies should also be conducted to determine the presence and role of P. columella in the transmission of Fasciola spp. in these geographical overlaps to help prevent parasite spillbacks.

Genetically 'pure' Fasciola gigantica discovered in Algeria: DNA multimarker characterization, trans-Saharan introduction from a Sahel origin and spreading risk into north-western Maghreb countries

Fascioliasis is a freshwater snail-borne zoonotic helminth disease caused by two species of trematodes: Fasciola hepatica of almost worldwide distribution and the more pathogenic F. gigantica restricted to parts of Asia and most of Africa. Of high pathological impact in ruminants, it underlies large livestock husbandry losses. Fascioliasis is moreover of high public health importance and accordingly included within the main neglected tropical diseases by WHO. Additionally, this is an emerging disease due to influences of climate and global changes. In Africa, F. gigantica is distributed throughout almost the whole continent except in the north-western Maghreb countries of Morocco, Algeria and Tunisia where only F. hepatica is present. The present study concerns the DNA multimarker characterization of the first finding of F. gigantica in sheep in Algeria by the complete sequences of rDNA ITS-1 and ITS-2 and mtDNA cox1 and nad1 genes. Sequence comparisons and network analyses show sequence identities and similarities suggesting a south-north trans-Saharan geographical origin, with introduction from Ghana, through the Sahel countries of Burkina Faso and Mali into Algeria. This way perfectly fits with nomadic pastoralism according to interconnecting intranational and transborder herd transhumance routes traditionally followed in this western part of Africa from very long ago. The risk for further spread throughout the three north-western Maghreb countries is multidisciplinarily analysed, mainly considering the present extensive motorization of the intranational transhumance system in Algeria, the lymnaeid snail vector species present throughout the north-western Maghreb, the increasing demand for animal products in the growing cities of northern Algeria and the continued human infection reports. Control measures should assure making anti-fasciolid drugs available and affordable for herders from the beginning and along their transhumant routes and include diffusion and rules within the regional regulatory framework about the need for herd treatments.

Molecular Confirmation of a Fasciola gigantica × Fasciola hepatica Hybrid in a Chadian Bovine

Fascioliasis is a zoonotic infection of humans and, more commonly, ruminants. It is caused by 2 liver fluke species, Fasciola hepatica and Fasciola gigantica, which differ in size. The traditional morphological methods used to distinguish the 2 species can be unreliable, particularly in the presence of hybrids between the 2 species. The development of advanced molecular methods has allowed for more definitive identification of Fasciola species, including their hybrids. Hybrids are of concern, as it is thought that they could acquire advantageous traits such as increased pathogenicity and host range. In 2013, we collected flukes from Fasciola-positive cattle, sheep, and goats slaughtered in 4 Chadian abattoirs. DNA from 27 flukes was extracted, amplified, and analyzed to identify species using the ITS1+2 locus. Twenty-six of the 27 flukes were identified as F. gigantica, while the remaining fluke showed heterozygosity at all variable sites that distinguish F. hepatica and F. gigantica. Cloning and sequencing of both alleles confirmed the presence of 1 F. hepatica and 1 F. gigantica allele. To our knowledge, this is the first unambiguous, molecular demonstration of the presence of such a hybrid in a bovine in sub-Saharan Africa.

Molecular identification and seasonal infections of species of Fasciola in ruminants from two provinces in China

We determined the prevalence and seasonality of infections by Fasciola of goats and bovine species (cattle and water buffalo) in Hubei and Anhui provinces of China. Faecal samples were collected at 2- to 3-month intervals from 200 goats in Hubei province and from 152 bovine species in Anhui province. All faecal samples were examined for the presence of parasites. We determined the nucleotide sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2) of the nuclear ribosomal DNA (rDNA) of 39 Fasciola worms from Anhui province. The prevalence of Fasciola infection in goats ranged between 3.5 and 37.0%, with mean eggs per gram (EPG) ranging between 29.0 and 166.0. Prevalence and EPG exhibited downward trends over time with significant differences. The prevalence of Fasciola infection in cattle ranged between 13.3 and 46.2% (mean EPG, 36.4-100.0), and that of water buffalo ranged between 10.3 and 35.4% (mean EPG, 25.0-89.6), with a higher prevalence of infection and EPG from June to October compared with December to March. Analysis of ITS-1 and ITS-2 sequences revealed that F. hepatica and F. gigantica were present in all bovine species of Anhui province and that F. gigantica mainly infected water buffalo. This is the first demonstration of Fasciola infection in Hubei province and detection of F. hepatica and F. gigantica in Anhui province. The present study of Hubei province shows that mass treatment of livestock with closantel sodium injections in April and August/September controlled Fasciola infection effectively.

Direct, immunological and molecular techniques for a fasciolosis survey in a rural area of San Luis, Argentina

Fasciolosis is a zoonosis caused by the trematode Fasciola hepatica, prevalent in cattle, that is actually emerging as a cause of disease in humans. The goal of this work was to describe the characteristics of fasciolosis in arroyo El Juncal region, La Toma, San Luis province, Argentina. In order to get this objective, a transversal, quantitative study was carried out by a fieldwork that allowed the collection of data, human, animal, and environmental samples. The materials were processed by direct, immunological and/or molecular diagnostic techniques. According to the geographical characteristics and in presence of all the definitive and intermediate hosts, reservoirs, and sources of infection, it was possible to describe the persistence of fasciolosis in the area. The prevalence was 11.90 % in humans (by serology), 5.26 % in cattle (by coprological analysis) and 61.76 % in snails (by PCR). The situation that was found for this area indicates that any measure of intervention for the control of this zoonosis should be adopted by multidisciplinary teams.

Risk factors and geospatial modelling for the presence of Fasciola hepatica infection in sheep and goat farms in the Greek temperate Mediterranean environment

Risk factors related to herd and farmer status, farm and pasture management, and environmental factors derived by satellite data were examined for their association with the prevalence of F. hepatica in sheep and goat farms in Thessaly, Greece. Twelve farms (16·2%) and 58 farms (78·4%) of 74 had evidence of infection using coproantigen and serology respectively. The average normalized difference vegetation index (NDVI) of farm location for 12 months before sampling was the most significant environmental risk factor for F. hepatica infection based on high seropositivity. The risk of infection increased by 1% when the value of NDVI increased by 0·01 degree. A geospatial map was constructed to show the relative risk (RR) of Fasciola infection in sheep and goat farms in Thessaly. In addition, geospatial maps of the model-based predicted RR for the presence of Fasciola infection in farms in Thessaly and the entire area of Greece were constructed from the developed model based on NDVI. In conclusion, this study demonstrated that Thessaly should be regarded as an endemic region for Fasciola infection and it represents the first prediction model of Fasciola infection in small ruminants in the Mediterranean basin.

Epidemiology of fasciolosis affecting Iberian ibex (Capra pyrenaica) in southern Spain

Between 1995 and 2006, we surveyed the presence of Fasciola hepatica in Iberian ibex (Capra pyrenaica) from Andalucía (southern Spain) by both necropsy (n = 2,096) and coprological approaches (n = 380). Most of the samples came from the Sierra Nevada mountain range (n = 1,884 and 267, respectively), and all positive cases involved animals from this location. The prevalence reached 0.53% by necropsy and 1.87% by faecal examination. Taking into account both diagnostic methodologies and the total number of animals affected (n = 14), we obtained a yearly prevalence of 0.7 +/- 0.3%. The infection with F. hepatica was found not to be related to host sex, climatology or to co-infection with Sarcoptes scabiei (the most important parasite affecting Iberian ibex, with a prevalence of 49.27 +/- 7.90% in the examined animals). The prevalence of fasciolosis decreased significantly during the period under study and this would be explained by an increase of ibex resistance to this fluke as a result of a reduction of the parasite abundance in the area and/or a reduction of the host infection rate. There was no statistical difference between the two diagnostic methods for the examination of fasciolosis during the period in which both methods were used. Therefore, examination of faecal samples as a non-invasive procedure may provide a useful approach for monitoring fasciolosis in wild ungulate populations. The results of the present study provided foundation for the effective control of F. hepatica infection in Iberian ibex.

PCR diagnosis of Fasciola hepatica in field-collected Lymnaea columella and Lymnaea viatrix snails

Fasciolosis, caused by the trematode Fasciola hepatica, is a zoonosis of economic importance in livestock that is emerging as a chronic disease in humans. The intermediate hosts are lymnaeid snails, in which diagnosis of infection is traditionally based on cercarial shedding, tissue sectioning and crushing. We developed a PCR assay for the sensitive and specific detection of F. hepatica in field-collected Lymnaea sp. snails. A primer pair was designed to amplify a 405 bp fragment of the cytochrome c oxidase subunit 1 gene of F. hepatica. The PCR assay showed a limit of detection of 10 pg of genomic F. hepatica DNA. No cross-reactions were observed with samples from other related trematode species or from the snail hosts Lymnaea columella and Lymnaea viatrix. DNA sequencing of the amplicon showed 100% homology with F. hepatica, and 75-89% homology with other trematodes on regions that did not include the entire set of primers. Two samples from Argentina were analysed. For snails in sample 1 (n = 240), identified as L. columella, the infection rate was 17.5 and 51.3% by direct examination and PCR, respectively. For snails in sample 2 (n = 34), identified as L. viatrix, the infection rate was 2.9 and 61.8% by direct examination and PCR, respectively. Differences in infection rates between these diagnosis methods were significant for both samples. Our PCR technique showed to be effective for detecting specific F. hepatica infections of low intensity in the intermediate host, and hence it could be used to study the epidemiological situation in a given area, as well as to assess host suitability for the parasite.

The prevalence of Fasciola hepatica in its snail intermediate host determined by DNA probe assay

Accurate snail intermediate host infection prevalence data have the potential to be extremely useful in determining seasonal transmission dynamics of Fasciola hepatica. Because the microscopic techniques currently used lack the sensitivity and specificity necessary to obtain meaningful infection prevalence data, we developed a highly accurate and efficient DNA probe assay. The assay has a sensitivity of 100%, a specificity of > 99%, easily detects a single miracidia and does not cross-hybridize with DNA of Fascioloides magna, Paramphistomum liorchis or Heterobilharzia americana, trematodes that share the same intermediate host and enzootic range as Fasciola hepatica. Using this assay, we determined the prevalence of F. hepatica in its snail intermediate host, Fossaria cubensis, during the second year of a 2-year study on the epizootiology of Fasciola hepatica in Florida. The overall infection prevalence of snails assayed in this study (n = 5246) was 1.5% and ranged from 0.1% to 3.1% for individual cattle ranches. Additionally, infection prevalence differed significantly for successive size groupings of snails, varying from 0% for 1-mm snails to 18.5% for 9- and 10-mm snails. The accuracy and efficiency of the DNA probe assay reported here for determining snail infection prevalence offers an inexpensive alternative to tracer animal studies for determining the epizootiology of F. hepatica.

Approaches to the control of fasciolosis in ruminants

Approaches to the control of fasciolosis in ruminants are compared for developed countries, and for developing countries with particular reference to regions growing irrigated rice. In all environments problem definition and investigation are based on one or more of observation, abattoir surveys, faecal egg counts, tracer animals and snail studies. In developed countries each husbandman grazes a large number of animals, controls access to pasture and water, and markets high value products. Strategic and tactical treatments control fasciolosis in these circumstances and will continue to do so while anthelmintics remain effective. In many developing countries subsistence families possess small numbers of animals, feed and water sources are shared by many families, and the products are mainly draft power, fertiliser and meat for local consumption. Consequently the agricultural cycle, and the life cycles of the parasite and intermediate host, are closely interrelated and there is some scope for controlling infection by modifying husbandry practices. Anthelmintics are not affordable. Recent observations of a major fasciola resistance gene with substantial dominance, in Indonesian Thin Tail sheep infected with Fasciola gigantica, suggest that parasite control by breed substitution, or cross-breeding and selection, is feasible. Such control would be inexpensive to implement, and sustainable.

A repetitive DNA probe for the sensitive detection of Fasciola hepatica infected snails

Epizootiologic studies on F. hepatica frequently use microscopic techniques for the detection of infected snails, however, the poor efficiency, sensitivity, and specificity associated with these techniques limit their usefulness. A DNA-based test for the identification of snails infected with larval stages of F. hepatica would solve these problems and enable a level of detection accuracy previously unavailable. We have cloned and sequenced a 124 bp fragment of repetitive DNA from F. hepatica which hybridizes specifically with DNA of F. hepatica but not with DNA of its snail intermediate hosts Fossaria cubensis and Pseudosuccinea columella, or with DNA of Fascioloides magna and Paramphistomum liorchis, ruminant trematodes which share the same intermediate host and same enzootic range as F. hepatica. Using this 124 bp fragment as a probe, infection in snails was detected immediately following miracidial penetration, thus a sensitivity equivalent to the minimum biologic unit of the parasite was achieved. This 124 bp repeated sequence belongs to a large family of 124 bp repeats that share a high level of sequence identity and constitute approximately 15% of the F. hepatica genome. We also report here the development of a quick and inexpensive DNA extraction protocol for use in field-collected snails. Thus, we have developed both a highly sensitive and specific DNA probe and a means to use the probe in a large epizootiologic study of F. hepatica where thousands of field-collected snails need to be assayed for infection.

Effects of an anthelmintic treatment programme on sheep productivity in the Middle Atlas, Morocco

This study evaluated the production advantages of the strategic anthelmintic treatment of both lambs and ewes in an area endemic for gastro-intestinal nematodes, lungworms and liver flukes. The liver fluke infections were generally chronic. The lambs were treated with albendazole (SmithKline Beecham), fenbendazole (Hoechst Roussel) or a vitamin supplement and their weight gains were followed over the next 7 months. The control group, which received a vitamin supplement only, gained 6.67 kg from July to January. The group that received fenbendazole, an anthelmintic with no activity against liver flukes, gained 10.42 kg over the study period. The third group which received albendazole, an anthelmintic with efficacy against liver flukes, gained 13.07 kg over the same period. Lamb deaths apparently due to liver flukes were 12, 4, and zero for the control, fenbendazole and albendazole groups, respectively. Similar advantages were observed in the ewes. Deaths were 16, 8, and zero in the control, fenbendazole and albendazole groups, respectively. The lambing rate in the control group was significantly lower than that in either of the 2 treated groups. The number of services per conception was significantly lower in the albendazole treated group than that in either of the other groups. These studies demonstrated the advantages of anthelmintic treatment in sheep in a helminth endemic area. While removing gastro-intestinal nematodes and lungworms improved production, the additional removal of liver flukes enhanced production gains as well as reducing deaths.