Climate change effects on trematodiases, with emphasis on zoonotic fascioliasis and schistosomiasis

Predicting impacts of climate change on Fasciola hepatica risk

Fasciola hepatica (liver fluke) is a physically and economically devastating parasitic trematode whose rise in recent years has been attributed to climate change. Climate has an impact on the free-living stages of the parasite and its intermediate host Lymnaea truncatula, with the interactions between rainfall and temperature having the greatest influence on transmission efficacy. There have been a number of short term climate driven forecasts developed to predict the following season's infection risk, with the Ollerenshaw index being the most widely used. Through the synthesis of a modified Ollerenshaw index with the UKCP09 fine scale climate projection data we have developed long term seasonal risk forecasts up to 2070 at a 25 km square resolution. Additionally UKCIP gridded datasets at 5 km square resolution from 1970-2006 were used to highlight the climate-driven increase to date. The maps show unprecedented levels of future fasciolosis risk in parts of the UK, with risk of serious epidemics in Wales by 2050. The seasonal risk maps demonstrate the possible change in the timing of disease outbreaks due to increased risk from overwintering larvae. Despite an overall long term increase in all regions of the UK, spatio-temporal variation in risk levels is expected. Infection risk will reduce in some areas and fluctuate greatly in others with a predicted decrease in summer infection for parts of the UK due to restricted water availability. This forecast is the first approximation of the potential impacts of climate change on fasciolosis risk in the UK. It can be used as a basis for indicating where active disease surveillance should be targeted and where the development of improved mitigation or adaptation measures is likely to bring the greatest benefits.

Cathepsins B1 and B2 of Trichobilharzia SPP., bird schistosomes causing cercarial dermatitis

Trichobilharzia regenti and T. szidati are schistosomes that infect birds. although T. regenti/T. szidati can only complete their life cycle in specific bird hosts (waterfowl), their larvae-cercariae are able to penetrate, transform and then migrate as schistosomula in nonspecific hosts (e.g., mouse, man). Peptidases are among the key molecules produced by these schistosomes that enable parasite invasion and survival within the host and include cysteine peptidases such as cathepsins B1 and B2. These enzymes are indispensable bio-catalysts in a number of basal biological processes and host-parasite interactions, e.g., tissue invasion/migration, nutrition and immune evasion. Similar biochemical and functional characteristics were observed for cathepsins B1 and B2 in bird schistosomes (T. regenti, T. szidati) and also for their homologs in human schistosomes (Schistosoma mansoni, S. japonicum). Therefore, data obtained in the research of bird schistosomes can also be exploited for the control of human schistosomes such as the search for targets of novel chemotherapeutic drugs and vaccines.

Potential role of hares in the spread of liver fluke in the Netherlands

Hares (Lepus europeanus) sharing pasture with cattle from six locations in the Netherlands were examined for the presence of liver fluke (Fasciola hepatica) and shown to have prevalences of infection ranging from 0 to 41%. The mitochondrial haplotypes of liver flukes present in the hare populations were determined and compared with those found in cattle from a farm where triclabendazole resistance has been reported. Phylogenetic analysis indicated that the flukes present in the hares belonged to the same clades as those present in the cattle. A consideration of the life cycle of the liver fluke and the seasonal breeding pattern and ecology of hares supports the suggestion that hares may act as a refugia for liver fluke and as a vector for the spread of drug-resistant genotypes.

Parasitological and molecular study of the furcocercariae from Melanoides tuberculata as a probable agent of cercarial dermatitis

Cercarial dermatitis is caused by animal schistosomes in many parts of the world including Iran. Various stages of the parasites have been studied in intermediate and definitive hosts in northern and southwestern Iran; however, no molecular investigation for species identification and classification of these agents has been carried out, so far. In the present study, more than 3,800 aquatic snails were collected from water sources of Khuzestan, southwest Iran. The snails were identified as Lymnaea gedrosiana, Radix auricularia, Melanoides tuberculata, Melanopsis sp. and Physa acuta. They were examined for schistosome cercariae. Two specimens of M. tuberculata were infected with ocellate furcocercariae belonging to the family Schistosomatidae. Molecular studies were carried on these schistosomatid samples. Both samples belong to an unknown schistosome species and genus in sister position to Gigantobilharzia-Dendritobilharzia clade. They differ from other species in their ITS sequence region as well as in their intermediate host specificity--This is one of the first reports on schistosome cercariae from M. tuberculata and the first including molecular data. Due to adaptability and invasiveness of this snail species, this new schistosome species, as a potential causative agent of cercarial dermatitis in humans, needs to be studied further.

Population dynamics of the liver fluke, Fasciola hepatica: the effect of time and spatial separation on the genetic diversity of fluke populations in the Netherlands

An evaluation of the genetic diversity within Fasciola hepatica (liver fluke) may provide an insight into its potential to respond to environmental changes, such as anthelmintic use or climate change. In this study, we determined the mitochondrial DNA haplotypes of > 400 flukes from 29 individual cattle, from 2 farms in the Netherlands, as an exemplar of fasciolosis in a European context. Analysis of this dataset has provided us with a measure of the genetic variation within infrapopulations (individual hosts) and the diversity between infrapopulations within a herd of cattle. Temporal sampling from one farm allowed for the measurement of the stability of genetic variation at a single location, whilst the comparison between the two farms provided information on the variation in relation to distance and previous anthelmintic regimes. We showed that the liver fluke population in this region is predominantly linked to 2 distinct clades. Individual infrapopulations contain a leptokurtic distribution of genetically diverse flukes. The haplotypes present on a farm have been shown to change significantly over a relatively short time-period.

Liver fluke β-tubulin isotype 2 binds albendazole and is thus a probable target of this drug

Albendazole is a benzimidazole drug which can be used to treat liver fluke (Fasciola hepatica) infections. Its mode of action is believed to be the inhibition of microtubule formation through binding to β-tubulin. However, F. hepatica expresses at least six different isotypes of β-tubulin, and this has confused, rather than clarified, understanding of the molecular mechanisms of benzimidazole drugs in this organism. Recombinant F. hepatica β-tubulin proteins were expressed in, and purified from, Escherichia coli. These proteins were then used in pull-down assays in which albendazole was covalently linked to Sepharose. β-Tubulin isotype 2 was pulled down in this assay, and this interaction could be reduced by adding competing albendazole. Molecular modelling of β-tubulin isotypes suggests that changes in the side change conformations of residue 200 in the putative albendazole binding site may be important in determining whether, or not, a particular isotype will bind to the drug. These results, together with previous work demonstrating that albendazole causes disruption of microtubules in the liver fluke, strongly suggest that β-tubulin isotype 2 is one of the targets of this drug.

Malaria resurgence risk in southern Europe: climate assessment in an historically endemic area of rice fields at the Mediterranean shore of Spain

BACKGROUND

International travel and immigration have been related with an increase of imported malaria cases. This fact and climate change, prolonging the period favouring vector development, require an analysis of the malaria transmission resurgence risk in areas of southern Europe. Such a study is made for the first time in Spain. The Ebro Delta historically endemic area was selected due to its rice field landscape, the presence of only one vector, Anopheles atroparvus, with densities similar to those it presented when malaria was present, in a situation which pronouncedly differs from already assessed potential resurgence areas in other Mediterranean countries, such as France and Italy, where many different Anopheles species coexist and a different vector species dominates.

METHODS

The transmission risk was assessed analysing: 1) climate diagrams including the minimum temperature for Plasmodium falciparum and Plasmodium vivax development; 2) monthly evolution of the Gradient Model Risk (GMR) index, specifying transmission risk period and number of potential Plasmodium generations; 3) ecological characteristics using remote sensing images with the Eurasia Land Cover characteristics database and the monthly evolution of the Normalized Difference Vegetation Index (NDVI); 4) evaluation of A. atroparvus population dynamics.

RESULTS

Climatological analyses and GMR index show that a transmission risk presently exists, lasting from May until September for P. falciparum, and from May until October for P. vivax. The GMR index shows that the temperature increase does not actually mean a transmission risk increase if accompanied by a precipitation decrease reducing the number of parasite generations and transmission period. Nevertheless, this limitation is offset by the artificial flooding of the rice fields. Maximum NDVI values and A. atroparvus maximum abundance correspond to months with maximum growth of the rice fields.

CONCLUSIONS

The Ebro Delta presents the ecological characteristics that favour transmission. The temperature increase has favoured a widening of the monthly potential transmission window with respect to when malaria was endemic. The combined application of modified climate diagrams and GMR index, together with spatial characterization conforms a useful tool for assessing potential areas at risk of malaria resurgence. NDVI is a good marker when dealing with a rice field area.

Proteomic analysis of in vitro newly excysted juveniles from Fasciola hepatica

Fasciolosis is a world-wide distributed zoonotic disease affecting several herbivores, and represents an important factor of economic loss in animal meat producing industries. In addition, specific risk factors and geographic areas for Fasciola hepatica human infection have been heavily reported recently. Several aspects related with this disease, e.g., drug resistance and prevention through vaccination, have yet to be solved. After ingestion, the infective stage for the vertebrate host-metacercariae - hatch in duodenum and the newly excysted juveniles (NEJ) penetrate the intestinal wall. The identification of proteins expressed by NEJ and specifically those found in the host-parasite interface could help understanding the first steps of animal and human infection by F. hepatica. Here we use a proteomic approach to identify a set of proteins enriched at the host-parasite interface from in vitro NEJ by applying liquid chromatography and tandem mass spectrometry (LC-MS/MS) analysis. Using this approach, we identified numerous proteins related with several biological processes of the parasite. In addition, we characterize one of the identified molecules, the 14-3-3z protein, and demonstrate its association with the outer structures of NEJ and its presence in both somatic and secretory components from the parasite. The NEJ proteins described here, together with those previously described by others, could provide new insights into the biology of the parasite and its relationship with the vertebrate host at the beginning of the infection.

Methodical approaches in the identification of areas with a potential risk of infection by bird schistosomes causing cercarial dermatitis

Larval stages (cercariae) of schistosomatid flukes represent the causative agents of swimmer's itch (cercarial dermatitis), a waterborne allergic disease. Cercariae of bird schistosomes are the most frequently reported agent. Recent studies on parasite behaviour in mammals showed that infections by cercariae can be linked to more than skin syndromes. Despite the failure of complete development in mammals, bird schistosomes can escape from the skin and migrate transitorily in the hosts. These findings brought novel insights into the fate and potential pathogenic effect of the parasites in non-compatible hosts, including humans. Cercarial dermatitis occurs globally and recently is considered to be re-emerging; however, there are no data on the number of afflicted persons per year. This might be explained by a relatively low interest in human skin infections arising after bathing in fresh water. In addition, the real occurrence of bird schistosomes in the field is known only for a few areas. The paucity of epidemiological/biogeographical data is probably caused by difficulties associated with detection of the parasites in intermediate and definitive hosts. Therefore, based on personal experience and data available in the literature, we have summarized methodological approaches enabling the detection of bird schistosomes in various hosts and environments.