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      Human fascioliasis infection sources, their diversity, incidence factors, analytical methods and prevention measures

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      Parasitology
      Cambridge University Press (CUP)

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          Abstract

          Human fascioliasis infection sources are analysed for the first time in front of the new worldwide scenario of this disease. These infection sources include foods, water and combinations of both. Ingestion of freshwater wild plants is the main source, with watercress and secondarily other vegetables involved. The problem of vegetables sold in uncontrolled urban markets is discussed. Distinction between infection sources by freshwater cultivated plants, terrestrial wild plants, and terrestrial cultivated plants is made. The risks by traditional local dishes made from sylvatic plants and raw liver ingestion are considered. Drinking of contaminated water, beverages and juices, ingestion of dishes and soups and washing of vegetables, fruits, tubercles and kitchen utensils with contaminated water are increasingly involved. Three methods to assess infection sources are noted: detection of metacercariae attached to plants or floating in freshwater, anamnesis in individual patients, and questionnaire surveys in endemic areas. The infectivity of metacercariae is reviewed both under field conditions and experimentally under the effects of physicochemical agents. Individual and general preventive measures appear to be more complicated than those considered in the past. The high diversity of infection sources and their heterogeneity in different countries underlie the large epidemiological heterogeneity of human fascioliasis throughout.

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          Development of a rational scale to assess the harm of drugs of potential misuse.

          Drug misuse and abuse are major health problems. Harmful drugs are regulated according to classification systems that purport to relate to the harms and risks of each drug. However, the methodology and processes underlying classification systems are generally neither specified nor transparent, which reduces confidence in their accuracy and undermines health education messages. We developed and explored the feasibility of the use of a nine-category matrix of harm, with an expert delphic procedure, to assess the harms of a range of illicit drugs in an evidence-based fashion. We also included five legal drugs of misuse (alcohol, khat, solvents, alkyl nitrites, and tobacco) and one that has since been classified (ketamine) for reference. The process proved practicable, and yielded roughly similar scores and rankings of drug harm when used by two separate groups of experts. The ranking of drugs produced by our assessment of harm differed from those used by current regulatory systems. Our methodology offers a systematic framework and process that could be used by national and international regulatory bodies to assess the harm of current and future drugs of abuse.
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            Fascioliasis and other plant-borne trematode zoonoses.

            Fascioliasis and other food-borne trematodiases are included in the list of important helminthiases with a great impact on human development. Six plant-borne trematode species have been found to affect humans: Fasciola hepatica, Fasciola gigantica and Fasciolopsis buski (Fasciolidae), Gastrodiscoides hominis (Gastrodiscidae), Watsonius watsoni and Fischoederius elongatus (Paramphistomidae). Whereas F. hepatica and F. gigantica are hepatic, the other four species are intestinal parasites. The fasciolids and the gastrodiscid cause important zoonoses distributed throughout many countries, while W. watsoni and F. elongatus have been only accidentally detected in humans. Present climate and global changes appear to increasingly affect snail-borne helminthiases, which are strongly dependent on environmental factors. Fascioliasis is a good example of an emerging/re-emerging parasitic disease in many countries as a consequence of many phenomena related to environmental changes as well as man-made modifications. The ability of F. hepatica to spread is related to its capacity to colonise and adapt to new hosts and environments, even at the extreme inhospitality of very high altitude. Moreover, the spread of F. hepatica from its original European range to other continents is related to the geographic expansion of its original European lymnaeid intermediate host species Galba truncatula, the American species Pseudosuccinea columella, and its adaptation to other lymnaeid species authochthonous in the newly colonised areas. Although fasciolopsiasis and gastrodiscoidiasis can be controlled along with other food-borne parasitoses, fasciolopsiasis still remains a public health problem in many endemic areas despite sustained WHO control programmes. Fasciolopsiasis has become a re-emerging infection in recent years and gastrodiscoidiasis, initially supposed to be restricted to Asian countries, is now being reported in African countries.
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              Chapter 2. Fasciola, lymnaeids and human fascioliasis, with a global overview on disease transmission, epidemiology, evolutionary genetics, molecular epidemiology and control.

              Fascioliasis, caused by liver fluke species of the genus Fasciola, has always been well recognized because of its high veterinary impact but it has been among the most neglected diseases for decades with regard to human infection. However, the increasing importance of human fascioliasis worldwide has re-launched interest in fascioliasis. From the 1990s, many new concepts have been developed regarding human fascioliasis and these have furnished a new baseline for the human disease that is very different to a simple extrapolation from fascioliasis in livestock. Studies have shown that human fascioliasis presents marked heterogeneity, including different epidemiological situations and transmission patterns in different endemic areas. This heterogeneity, added to the present emergence/re-emergence of the disease both in humans and animals in many regions, confirms a worrying global scenario. The huge negative impact of fascioliasis on human communities demands rapid action. When analyzing how better to define control measures for endemic areas differing at such a level, it would be useful to have genetic markers that could distinguish each type of transmission pattern and epidemiological situation. Accordingly, this chapter covers aspects of aetiology, geographical distribution, epidemiology, transmission and control in order to obtain a solid baseline for the interpretation of future results. The origins and geographical spread of F. hepatica and F. gigantica in both the ruminant pre-domestication times and the livestock post-domestication period are analyzed. Paleontological, archaeological and historical records, as well as genetic data on recent dispersal of livestock species, are taken into account to establish an evolutionary framework for the two fasciolids across all continents. Emphasis is given to the distributional overlap of both species and the roles of transportation, transhumance and trade in the different overlap situations. Areas with only one Fasciola spp. are distinguished from local and zonal overlaps in areas where both fasciolids co-exist. Genetic techniques applied to liver flukes in recent years that are useful to elucidate the genetic characteristics of the two fasciolids are reviewed. The intra-specific and inter-specific variabilities of 'pure'F. hepatica and 'pure'F. gigantica were ascertained by means of complete sequences of ribosomal deoxyribonucleic acid (rDNA) internal transcribed spacer (ITS)-2 and ITS-1 and mitochondrial deoxyribonucleic acid (mtDNA) cox1 and nad1 from areas with only one fasciolid species. Fasciolid sequences of the same markers scattered in the literature are reviewed. The definitive haplotypes established appear to fit the proposed global evolutionary scenario. Problems posed by fasciolid cross-breeding, introgression and hybridization in overlap areas are analyzed. Nuclear rDNA appears to correlate with adult fluke characteristics and fasciolid/lymnaeid specificity, whereas mtDNA does not. However, flukes sometimes appear so intermediate that they cannot be ascribed to either F. hepatica-like or F. gigantica-like forms and snail specificity may be opposite to the one deduced from the adult morphotype. The phenotypic characteristics of adults and eggs of 'pure'F. hepatica and F. gigantica, as well as of intermediate forms in overlap areas, are compared, with emphasis on the definitive host influence on egg size in humans. Knowledge is sufficient to support F. hepatica and F. gigantica as two valid species, which recently diverged by adaptation to different pecoran and lymnaeid hosts in areas with differing environmental characteristics. Their phenotypic differences and ancient pre-domestication origins involve a broad geographical area that largely exceeds the typical, more local scenarios known for sub-species units. Phenomena such as abnormal ploidy and aspermic parthenogenesis in hybrids suggest that their separate evolution in pre-domestication times allowed them to achieve almost total genetic isolation. Recent sequencing results suggest that present assumptions on fasciolid-lymnaeid specificity might be wrong. The crucial role of lymnaeids in fascioliasis transmission, epidemiology and control was the reason for launching a worldwide lymnaeid molecular characterization initiative. This initiative has already furnished useful results on several continents. A standardized methodology for fasciolids and lymnaeids is proposed herein in order that future work is undertaken on a comparable basis. A complete understanding of molecular epidemiology is expected to help greatly in designing global actions and local interventions for control of fascioliasis.
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                Author and article information

                Journal
                Parasitology
                Parasitology
                Cambridge University Press (CUP)
                0031-1820
                1469-8161
                November 2018
                July 11 2018
                November 2018
                : 145
                : 13
                : 1665-1699
                Article
                10.1017/S0031182018000914
                29991363
                7a8bde33-c0b9-42fd-80e5-ae35d0da54fd
                © 2018

                Free to read

                http://creativecommons.org/licenses/by/4.0/

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