Intermediate Host Populations Research Articles

Temporal dynamics of parasite populations and communities of blue sea catfish Ariopsis guatemalensis (Günther, 1864), in a eutrophic coastal lagoon from Mexican Pacific

ABSTRACT The temporal dynamics of parasite populations and communities of blue sea catfish Ariopsis guatemalensis from a tropical eutrophic coastal lagoon was studied during an annual cycle. A total of 620 adult fishes were collected between January and December 2019. Eleven taxa of parasites were identified, three of monoxenous (single-host life cycle), and eight of heteroxenous (multi-host life cycle) parasites. The infection levels of two monoxenous (Neotetraonchus vegrandis and Ergasilus sp.) and five heteroxenous (Austrodiplostomum sp. Pseudoacanthostomum panamense, Pseudoleptorhynchoides lamothei, Contracaecum sp. and Hysterothylacium perezi) parasite species varied between sampling months and/or climatic seasons. The infection dynamics of these group of parasites were influenced by environmental changes generated by the dry/rainy cycle, which can affect the availability of intermediate host populations, and the feeding and reproductive behaviour of the host. Although the species composition of the parasite communities remains quite stable over time, its structure registers important changes mainly during the rainy season. Some host traits such as the feeding and reproductive behaviour, body size, physical condition, and sex of the host, as well as the temporal replacement of numerically dominant parasite species, were the main factors responsible for variations in the parasite community structure.

Prevalence of Neospora caninum and associated risk factors in semi-intensive female water buffaloes reared in Greece, using an ELISA kit on milk samples

Neospora caninum is an apicomplexan (family: Sarcocystidae) protozoan parasite with a global distribution. In the N. caninum life cycle, dogs and other related canids are the definitive hosts, while other animals such as water buffaloes (Bubalus bubalis) constitute the intermediate host for this parasite. In many countries, the water buffalo is of high economic importance, providing valuable high-quality products for human needs. Although knowledge concerning the prevalence of this parasite in intermediate animal host populations is crucial, data from water buffalo are scarce. Keeping this in mind, the aim of this study was to examine the presence and assess the prevalence rates of N. caninum infection in water buffaloes in Northern Greece, where this animal husbandry sector started to raise, as well as to determine associated risk factors, with the application of a commercially available Neospora ISCOM ELISA test kit, developed for the detection of antibodies against N. caninum in milk samples The study was conducted during January–June 2023 in a total of 172 individual raw milk samples, collected from dairy buffaloes, reared under a semi extensive system, in three different farms. Information on the status of N. caninum infection in buffaloes from Greece was so far unknown with a lack of epidemiological or risk factors associated. For the detection of N. caninum, the commercially available Neospora ISCOM ELISA test kit (SANOVIR ®, Svanova Biotech AB, Uppsala, Sweden) was utilized. Results demonstrated the presence of N. caninum in water buffaloes from Greece for the first time. All positive N. caninum animal were asymptomatic, with absence of any disease signs. The overall prevalence of infection was 22.10%, whereas the main risk factors include the presence of dogs as well as the low biosecurity measures.

Parasite-mediated predation determines infection in a complex predator-prey-parasite system.

The interplay of host-parasite and predator-prey interactions is critical in ecological dynamics because both predators and parasites can regulate communities. But what is the prevalence of infected prey and predators when a parasite is transmitted through trophic interactions considering stochastic demographic changes? Here, we modelled and analysed a complex predator-prey-parasite system, where parasites are transmitted from prey to predators. We varied parasite virulence and infection probabilities to investigate how those evolutionary factors determine species' coexistence and populations' composition. Our results show that parasite species go extinct when the infection probabilities of either host are small and that success in infecting the final host is more critical for the survival of the parasite. While our stochastic simulations are consistent with deterministic predictions, stochasticity plays an important role in the border regions between coexistence and extinction. As expected, the proportion of infected individuals increases with the infection probabilities. Interestingly, the relative abundances of infected and uninfected individuals can have opposite orders in the intermediate and final host populations. This counterintuitive observation shows that the interplay of direct and indirect parasite effects is a common driver of the prevalence of infection in a complex system.

Identification, Pathogenicity, Public Health, and Economic Importance of Tapeworms of Poultry

Tapeworms of poultry are a group of cestodes that parasitize the intestinal tract of chickens and other birds. They cause economic losses due to reduced production, growth retardation, weight loss, and mortality. In Ethiopia, several species of tapeworms have been reported in poultry, especially in free-range systems and low land areas. The most common genera are Davainea, Hymenolepis, Amoebotaenia, Choanotaenia, and Raillietina. These tapeworms have complex life cycles that require arthropod or other invertebrate intermediate hosts, such as snails, beetles, ants, and earthworms. The birds become infected by ingesting these intermediate hosts that contain the infective larval stage of the tapeworms. The larvae then attach to the mucosa of the intestine and change themselves to adult tapeworms that produce eggs or proglottids that are passed in the feces. Tapeworm infections can cause various clinical signs and pathological lesions in poultry, depending on the species, number, and location of the worms. Some of the common signs are diarrhea, anorexia, emaciation, weakness, ruffled feathers, slow movement, and rapid breathing. Some tapeworms can also cause intestinal blockage, hemorrhage, nodular growth, and catarrhal enteritis. Tapeworm infections can also predispose the birds to other diseases by impairing their immunity and nutrition. However, other chicken diseases may have similar symptoms and effects like tapeworm infections, so deferential diagnosis should be done at the laboratory level or post-mortem examination. The treatment and control of tapeworm infections in poultry are challenging because of the presence of intermediate hosts that serve as sources of infection. Prevention of birds from contact with intermediate hosts is the most important step that should be taken in the control of tapeworm infection. This can be achieved by improving the hygiene and sanitation of the poultry houses and yards, providing clean water and feed, preventing access to wild birds and rodents that may carry intermediate hosts, and using insecticides or biological agents to reduce intermediate host populations. Tapeworms of poultry are a significant problem in Ethiopia and other tropical countries where free-range systems and low land areas are common. They cause economic losses and affect the health and welfare of poultry. Therefore, more attention should be given to their identification, pathogenicity, public health, and economic importance.

Seasonal and environmental dynamics of intra-urban freshwater habitats and their influence on the abundance of Bulinus snail host of Schistosoma haematobium in the Tiko endemic focus, Mount Cameroon region.

Urogenital schistosomiasis (UGS) caused by Schistosoma haematobium is endemic in the South West Region of Cameroon. An understanding of the abundance and distribution of the Bulinus snail, intermediate host can inform strategic snail control programmes at a local scale. This study investigated seasonal dynamics and environmental factors influencing occurrence and abundance of freshwater snail intermediate hosts in Tiko, a semi-urban endemic focus in the Mount Cameroon area. A longitudinal malacological field survey was conducted between December 2019 and December 2020 in the Tiko municipality. Snails were collected for one year monthly at 12 different human water contact sites along a stretch of the Ndongo stream using a standardized sampling technique. Freshwater snails were identified using shell morphological features. In addition, water temperature, pH, electrical conductivity, total dissolved solutes, salinity, water depth, width and flow velocity were measured, and vegetation cover as well as substrate type were determined. Bayesian regression models were used to identify the main environmental factors affecting the occurrence and abundance of Bulinus intermediate host. In total, 2129 fresh water snails were collected during the study period. Physa (51.4%) was the most abundant genus followed by Melanoides (28.6%) then, Bulinus (15.5%), Lymnaea (4.2%), Indoplanorbis (0.2%) and Potadoma (0.1%). Seasonality in abundance was significant in Bulinus sp as well as other genera, with greater numbers in the dry season (peaks between December and February). Water temperature, a rocky or sandy substrate type associated positively with Bulinus sp, meanwhile a higher water flow rate and medium vegetation negatively influenced the snail intermediate host population. These findings underscore the importance of timing behavioural and snail control interventions against schistosomiasis as well as increase vigilance of other trematode diseases in the study area. The continuous spread of planorbid snail hosts is a major concern.

Parasite communities of the golden snapper Lutjanus inermis (Perciformes: Lutjanidae): inter-annual variations during strange climatic events.

Strange oceanographic events such as El Niño and La Niña may have indirect effects on the local transmission processes of intestinal parasites due to the reduction or increase in populations of potential intermediate or definitive hosts. A total of 713 individuals of Lutjanus inermis (Peters) were collected over an 8-year period (October 2015 to July 2022) from Acapulco Bay, Mexico. Parasite communities in L. inermis were quantified and analysed to determine if they experienced interannual variations in species composition and structure as a result of local biotic and abiotic factors influenced by oceanographic events, such as El Niño-Southern Oscillation (ENSO), or La Niña, the cool phase of the ENSO climate pattern. Twenty-six taxa of metazoan parasites were recovered and identified: two Monogenea, eight Digenea, two Acanthocephala, four Nematoda, one Cestoda, seven Copepoda, and two Isopoda. Species richness at the component community level (8 to 17 species) was similar to reported richness in other species of Lutjanus Bloch. Parasite communities of L. inermis exhibited high inter-annual variation in the abundance of component species of parasite. However, the species richness and diversity were fairly stable over time. Climatic episodes of El Niño and La Niña probably generated notable changes in the structure of local food webs, thus indirectly influencing the transmission rates of intestinal parasite species. Changes in species composition and community structure of parasites possibly were due to variations in feeding behaviour during the events and differences in the host body size.

Infection patterns of helminth community in black rockcod Notothenia coriiceps in West Antarctica over a 6-year term.

Patterns of the rockcod Notothenia coriiceps infection with helminths were analysed to understand the dynamics of parasite communities in this Antarctic fish and to test their stability over time. The study was performed using helminth samples collected from 183 N. coriiceps in 2014-2015 and 2020-2021 in the vicinity of the Ukrainian Antarctic station (UAS) "Akademik Vernadsky", Galindez Island, Argentine Islands, West Antarctica. Overall, 25 helminth taxonomical categories (nine trematodes, four cestodes, five nematodes, and seven acanthocephalans) were subjected to analysis. A direct comparison of the helminth population characteristics showed that nine species significantly changed their infection parameters during the 6years between the samples. Seven of them (Pseudoterranova sp., Contracaecum sp., Ascarophis nototheniae, monolocular metacestodes, bilocular metacestodes, Metacanthocephalus rennicki, and Diphyllobothrium sp.) were found to have a significant impact on the differences between helminth infracommunities in 2014-2015 and 2020-2021. Most studied patterns of helminth component community appeared to show a stable tendency, and observed fluctuations were close to the steady trend. Slight but significant changes in the infection patterns observed in this study might have been caused by changes in the populations of intermediate, paratenic, and definitive hosts of helminths (marine invertebrates, mammals, and birds), which participate in helminth transmission in Antarctic ecosystems.

Inertia of parasite infection versus host biomass fluctuation

Infection by parasites with complex life cycles such as trematodes depends on many environmental factors which may result in a time-lag between host biomass fluctuations and parasite density in hosts. A cockle (marine bivalve, second intermediate host) population and its associated parasite community were monitored over 15 years. A time-shift correlation analysis suggests that trematode abundance in cockles responds to cockle biomass after a long delay (8 year time-lag). Thus, these parasites can sustainably support a deficit of their intermediate host.

Angiostrongylus vasorum, Aelurostrongylus abstrusus, Crenosoma vulpis and Troglostrongylus brevior Infections in Native Slug Populations of Bavaria and Baden-Wuerttemberg in Germany.

Angiostrongylus vasorum, Crenosoma vulpis, Aelurostrongylus abstrusus and Troglostrongylus brevior can cause severe cardiovascular and pulmonary symptoms in companion animals and wildlife. Recently, these nematodes were reported to spread within Europe and South America. The reasons behind this are still unknown, but obligate gastropod intermediate host populations might play a role. Therefore, lungworm infections in terrestrial slug populations in selected geographic areas of the Federal States of Bavaria and of Baden-Wuerttemberg, Germany, were studied. In total, 517 slugs (462 Arion spp., 51 Deroceras reticulatum, one Limax maximus, and three unknown slug species) were collected in the summer and autumn seasons, artificially digested and microscopically and molecularly analyzed for the presence of metastrongyloid lungworm larvae. Overall, gastropods showed a prevalence of 11.61% (60/517) for A. vasorum, 1.74% (9/517) for A. abstrusus, 0.77% (4/517) for C. vulpis and 0.97% (5/517) for T. brevior infections, respectively. In Obrigheim (Baden-Wuerttemberg), a hyperendemic focus of canine angiostrongylosis was identified. Here, gastropod infection rates rose from 13.60% (17/125) to 62.96% (34/54) within a few months. In total, 25.61% (84/328) of analysed terrestrial gastropods from Baden-Wuerttemberg were positive for metastrongyloids. In contrast, Bavarian gastropods showed a much lower prevalence of 4.76% (9/189). For the first time, the presence of T. brevior was confirmed for Arion spp. in Baden-Wuerttemberg via molecular analyses. Overall, the current data confirm that canine angiostrongylosis occurs in hyperendemic foci in certain geographic areas with high infection rates in intermediate host populations. As a result, the prevalence for a specific region can rise remarkably within a short period of time. Thus, for a better understanding of lungworm epidemiology in Germany and to protect dogs from angiostrongylosis in hyperendemic foci, it seems mandatory to enhance current efforts on Metastrongyloidea-targeted monitoring on a geographical and time span-related level.

Modeling schistosomiasis transmission: the importance of snail population structure

BackgroundSchistosomiasis is a neglected tropical disease endemic in 54 countries. A major Schistosoma species, Schistosoma mansoni, is sustained via a life cycle that includes both human and snail hosts. Mathematical models of S. mansoni transmission, used to elucidate the complexities of the transmission cycle and estimate the impact of intervention efforts, often focus primarily on the human host. However, S. mansoni incurs physiological costs in snails that vary with the age of the snail when first infected. Snail demography and the age of snail infection could thus affect the force of infection experienced by humans, which is frequently used to predict the impact of various control strategies.MethodsTo address how these snail host and parasite interactions influence model predictions, we developed deterministic models of schistosomiasis transmission that include varying complexity in the snail population age structure. Specifically, we examined how model outputs, such as schistosome prevalence in human and snail populations, respond to the inclusion of snail age structure.ResultsOur models suggest that snail population age structure modifies the force of infection experienced by humans and the relationship between snail infection prevalence and corresponding human infection prevalence. There are significant differences in estimated snail infection, cercarial density and mean worm burden between models without snail population dynamics and those with snail populations, and between models with a homogeneous snail population and those with age stratification. The variation between finely age-stratified snail populations and those grouped into only juvenile and adult life stages is, however, minimal.ConclusionsThese results indicate that including snails and snail age structure in a schistosomiasis transmission model alters the relationship between snail and human infection prevalence. This highlights the importance of accounting for a heterogeneous intermediate host population in models of schistosomiasis transmission where the impact of proposed control measures is being considered.Graphical

Mathematically modeling spillovers of an emerging infectious zoonosis with an intermediate host.

Modeling the behavior of zoonotic pandemic threats is a key component of their control. Many emerging zoonoses, such as SARS, Nipah, and Hendra, mutated from their wild type while circulating in an intermediate host population, usually a domestic species, to become more transmissible among humans, and this transmission route will only become more likely as agriculture and trade intensifies around the world. Passage through an intermediate host enables many otherwise rare diseases to become better adapted to humans, and so understanding this process with accurate mathematical models is necessary to prevent epidemics of emerging zoonoses, guide policy interventions in public health, and predict the behavior of an epidemic. In this paper, we account for a zoonotic disease mutating in an intermediate host by introducing a new mathematical model for disease transmission among three species. We present a model of these disease dynamics, including the equilibria of the system and the basic reproductive number of the pathogen, finding that in the presence of biologically realistic interspecies transmission parameters, a zoonotic disease with the capacity to mutate in an intermediate host population can establish itself in humans even if its R0 in humans is less than 1. This result and model can be used to predict the behavior of any zoonosis with an intermediate host and assist efforts to protect public health.

Seasonal prevalence of zoonotic trematode parasites in commercial catfish species in the Ho Chi Minh City area

An epidemiological study of fishborne zoonotic trematodes (FZT) infecting three major catfish species, hybrid catfish (Clarias sp.), river catfish (Pangasianodon hypopththalmus) and black-spotted catfish (Pangasius larnaudii), produced locally in Ho Chi Minh City, Vietnam, was conducted during 2017-2018. The impact of seasonal changes associated with the wet and dry seasons was assessed. The only species of FZT found was Haplorchis pumilio, a new host record for black-spotted catfish. Farm prevalence of H. pumilio was highest for black-spotted catfish (20.0 %) and hybrid catfish (16.7 %), and lowest for farms producing river catfish (5.0 %). The FZT prevalence in hybrid catfish (N = 300 per season) was higher in the wet season (2.0 %) than in the dry season (0.3 %); however, it was not significantly different (P > 0.05). For all three catfish species (N = 550 per season), seasonal prevalence was significantly higher (P < 0.05) in the wet season than in the dry season (1.5 % versus 0.2 %). These results demonstrate that, overall, most aquaculture farmers in this area employed management practices that were effective in lowering the risk of parasite infection in grow-out catfish compared with prevalence data for catfish reported from the Mekong Delta. However, the basis for the seasonal effect is not clear. The increase in snail intermediate host populations and pond contamination with parasites eggs from surface run-off are risk factors, generally, but the significantly higher impact on hybrid catfish production requires further investigation.

Small snails, high productivity? Larval output of parasites from an abundant host

AbstractHow energy is transformed and distributed within ecosystems is a fundamental question in ecology. Parasites have been shown to play an essential role in these processes. In particular, the larval stages of trematodes, that is, cercariae, appear to contribute significantly to biomass and productivity in aquatic systems.Overall, ecosystem‐wide studies on parasite productivity remain scarce and have typically investigated systems with large hosts and high parasite infection rates. These studies may thus represent isolated cases of exceptionally high parasite contribution to ecosystem energetics, potentially overestimating the importance of parasite biomass.Here, we quantified the productivity of trematode cercariae from a small but hyper‐abundant snail intermediate host with only moderate trematode prevalence (i.e., proportion of infected individuals) in an entire lake ecosystem. We assessed individual larval output from snails and calculated the overall trematode productivity in the ecosystem.Average output of individual trematode species ranged from 3 to 62 cercariae per snail per day and correlated negatively with individual cercarial size. Cercarial productivity was not uniformly distributed across trematode taxa, but dominated by the most common species that accounted for more than 80% of the productivity.Total cercarial productivity amounted to 1.85 g m−2, which falls within the ranges of previous studies from freshwater systems. Small but abundant snail populations may thus support a considerable productivity of parasites. However, total annual cercarial productivity in the study system amounted to 5.9 kg, which constituted just 1.2% of the standing stock snail biomass, suggesting that intermediate host populations are potentially underexploited by their parasites. Moreover, comparisons with previous studies revealed contrasting patterns of parasite productivity and biomass contribution across different habitats, showing that impacts of parasites on ecosystem energetics can vary widely.Overall, we are still far away from having a complete picture of the dynamics of parasite productivity and biomass in many ecosystems. It therefore remains critical to quantify the contribution of parasites to the flow and distribution of energy and nutrients within and across habitats, to better understand their impacts on fundamental ecological principles, such as food‐web structure and ecosystem energetics.

The helminth community component species of the wood mouse as biological tags of a ten post-fire-year regeneration process in a Mediterranean ecosystem.

Serra Calderona Natural Park, a Mediterranean ecosystem, has been in post-fire regeneration for 10years. To elucidate which helminth community component species of the wood mouse, Apodemus sylvaticus, can be considered biological tags of this process, the influence of intrinsic (host density; host sex and age) and extrinsic factors (site, year, and period of capture; vegetation recovery) on their prevalence and abundance has been analysed, comparing a burned and an unburned area. A total of 564 wood mice (408 from the burned and 156 from the unburned area), from the 2nd to the10th post-fire year, was included in this helminthoecological study. The results suggest that the area in post-fire regeneration is still more vulnerable to periodic environmental changes than the unburned area as deduced from the analysis of the helminth populations of Pseudocatenotaenia matovi, Skrjabinotaenia lobata, Trichuris muris, Eucoleus bacillatus and Aonchotheca annulosa. The intermediate and definitive host populations presented a greater variability to these environmental changes in the burned area (Taenia parva, P. matovi, S. lobata, A. annulosa, Syphacia stroma and S. frederici). In the regenerating area, some behavioural changes in certain populations determined by the host sex are taking place (T. parva, Helgimosomoides polygyrus and S. frederici). During the last years studied, a greater similarity in the populational development of some component species between both areas can be appreciated (H. polygyrus and S. stroma). The role of the wood mouse and its helminth parasites as biological tags of the post-fire regeneration process in Mediterranean ecosystems has been confirmed.

Regional surveillance of parasitic infections in wild Northern Bobwhite Quail (Colinus virginianus) utilizing a mobile research laboratory platform

AbstractNorthern bobwhite quail (Colinus virginianus), a popular gamebird among hunters, have been declining over recent decades in the Rolling Plains ecoregion. Investigations in the past few years have revealed a high prevalence of eyeworms (Oxyspirura petrowi) and caecal worms (Aulonocephalus pennula) in this ecoregion, prompting a need to better understand their host–parasite interaction and other factors that influence infection. In this study, the efficiency of a mobile laboratory was tested by deploying it to three field sites in the Rolling Plains between July and August of 2017 and collecting cloacal swabs from bobwhites. The DNA was extracted from swabs for quantitative PCR and was run in the mobile and reference laboratory to specifically detectA. pennulaandO. petrowiinfection. When compared with the Wildlife Toxicology's reference laboratory, the mobile laboratory had a 97 and 99% agreement forA. pennulaandO. petrowi, respectively. There were no significant differences in infection levels between field sites. Due to its efficiency, it is proposed that the mobile laboratory would be an effective way to monitor infection levels, in addition to factors that may affect infection such as climate, diapause, and intermediate host populations.

The Pine marten (Martes martes) and the Stone marten (Martes foina) as possible wild reservoirs of Toxoplasma gondii in the Baltic States.

Toxoplasma gondii is an important zoonotic parasite that infects a wide spectrum of mammals. Moreover, its presence in wild carnivores is indicative of environmental contamination by the parasite. A total of 186 marten (152 pine marten; 34 stone marten) meat juice samples from Latvia and Lithuania were tested for T. gondii seroprevalence. Samples were tested for T. gondii specific antibodies by a commercial ELISA and antibodies were found in 121 (65.1%) samples. Higher prevalence (67.8%) occurred in pine martens compared to that of stone martens (52.9%). Adult pine martens had a 2.0 (95% CI 0.9-4.7) times higher odds ratio to test seropositive than juvenile Pine martens. In addition, a significant positive correlation (r=0.75; P=0.05) was observed between T. gondii seroprevalence in martens and the number of estimated Eurasian lynx as a possible definitive host within the game administrative unit. The present study suggests that the high seroprevalence of T. gondii in Pine and Stone martens could indicate a high incidence of the parasite in the intermediate and definitive host population and in the environment.

Molecular identification of cryptic cysticercosis: Taenia ovis krabbei in wild intermediate and domestic definitive hosts.

The complex life cycle of taeniids represents an ideal model of a multi-host system. The complexity of these parasites can therefore cover the epidemiological issues of the interface between wild and domestic animals, especially once spatial overlap between wild and domestic definitive and intermediate hosts occurs. Here we use the occurrence of Taenia ovis krabbei in two model areas as an example of this epidemiological complexity. In two contiguous areas in the Italian northern Apennines, two hunted roe deer (Capreolus capreolus) showed numerous cysticerci in the muscles of their whole body and an adult tapeworm was recorded in a semi-stray dog (Canis lupus familiaris). Through molecular typing of the mitochondrial cytochrome c oxidase I (cox1) gene, cysticerci and the adult tapeworm of T. krabbei were identified. Taenia krabbei cysticercosis was recorded for the first time in Italy. Although the role of dogs in the parasite's life cycle emerges, the overlap between wild and domestic definitive hosts and the increase of wild population densities raise concerns about the temporal (old or new) introduction and the spread of this parasite by one of these canid species (wolf (Canis lupus) or dog). Although T. krabbei is not a public health issue, economic concerns emerged for hunters and meat producers, related to the damage of carcasses by cysticerci. Therefore, there is a need to evaluate the spread of T. krabbei in the intermediate and definitive host populations, and to ensure the relevant sanitary education for hunters in order to avoid practices that could favour the spread and maintenance of its life cycle.

Effect of National Schistosomiasis Control Programme on Taenia solium taeniosis and porcine cysticercosis in rural communities of Tanzania

Taenia solium is found throughout sub-Saharan Africa and co-endemic with schistosomiasis in many regions. Taenia solium leads to taeniosis and neurocysticercosis - the leading cause of preventable epilepsy globally. This study aimed to assess the effects of the National Schistosomiasis Control Programme on prevalence of taeniosis and porcine cysticercosis over a four year period in Tanzania. School-based mass drug administration (MDA) of praziquantel was carried out based on schistosomiasis endemicity. Four human and five porcine cross-sectional surveys were carried out from 2012 to 2015 in Mbozi and Mbeya district in Tanzania. Three rounds of school-based MDA of praziquantel were delivered in Mbozi and two in Mbeya. The prevalence of taeniosis and porcine cysticercosis was estimated annually. Stool samples were collected from humans and prevalence of taeniosis estimated by copro-Ag-ELISA. Blood samples from pigs were collected to estimate cysticercosis prevalence by Ag-ELISA. “Track-and-treat” of taeniosis cases was carried out after each survey. In total 12082 stool samples and 4579 porcine serum samples were collected. Significantly fewer children (≤15) from Mbozi were infected throughout the study than children from Mbeya who showed a significant decrease in copro-Ag prevalence after the first treatment only. During the final survey in Mbozi the prevalence of taeniosis in adults (1.8%) was significantly lower (p=0.031, OR 0.40, CI: 0.17–0.89), compared to baseline (4.1%). The prevalence of porcine cysticercosis (8%) had also dropped significantly (p=0.002, OR 0.49, CI: 0.32–0.76) in this district compared to baseline (13%), whereas no significant difference was seen in Mbeya compared to baseline. The study suggests that three rounds of MDA targeting schistosomiasis in school-aged children combined with ‘track-and-treat’ contributed to a reduction in prevalence of T. solium in this population, and also had a spillover effect on adults in treated areas as well as reducing the prevalence of T. solium in the intermediate pig host population. Elimination of T. solium in this area would require a One Health approach.

Strong neutral genetic differentiation in a host, but not in its parasite

The genetic diversity and population structure of a parasite with a complex life cycle generally depends on the dispersal by its most motile host. Given that high gene flow is assumed to hinder local adaptation, this can impose significant constraints on a parasite's potential to adapt to local environmental conditions, intermediate host populations, and ultimately to host-parasite coevolution. Here, we aimed to examine the population genetic basis for local host-parasite interactions between the eye fluke Diplostomum lineage 6, a digenean trematode with a multi-host life cycle (including a snail, a fish, and a bird) and its second intermediate host, the three-spined stickleback Gasterosteus aculeatus L. We developed the first microsatellite primers for D. lineage 6 and used them together with published stickleback markers to analyse host and parasite population structures in 19 freshwater lakes, which differ in their local environmental characteristics regarding water chemistry and Diplostomum abundance. Our analyses suggest that one parasite population successfully infects a range of genetically differentiated stickleback populations. The lack of neutral genetic differentiation in D. lineage 6, which could be attributed to the motility of the parasite's definitive host as well as its life cycle characteristics, makes local host-parasite co-adaptations seem more likely on a larger geographical scale than among the lakes of our study site. Our study provides a suitable background for future studies in this system and the first microsatellite primers for a widespread fish parasite.

Trophic ecology, behaviour and host population dynamics in Echinococcus multilocularis transmission

The life cycle of the cestode Echinococcus multilocularis primarily involves canids and small mammals (rodents, lagomorphs) as definitive and intermediate hosts, respectively. Several surveys have identified marked temporal and geographical variations at different scales in the parasite’s prevalence in both types of hosts, suggesting variations in the biological and ecological factors that control transmission processes. The parasite transmission from intermediate to definitive hosts is determined by the predator–prey relationship, which theoretically depends on prey population dynamics and the complex dietary response of predators to varying densities of prey species and other food items. Parasite eggs are transmitted to intermediate hosts via carnivore faeces, whose distribution in the environment is driven by the defecating behaviour of final hosts. We reviewed field-based studies that address issues related to the trophic ecology and behaviour of definitive hosts, interactions between definitive and intermediate hosts, and E. multilocularis transmission both in wild and domestic animals in rural and urban environments. Two density-dependent mechanisms control the transmission dynamics in definitive hosts: one is based on the variations in the availability of intermediate hosts, and the other is based on the variations in the density of the definitive host and its faeces. Non-linearity and the direct and delayed responses of definitive host contamination in relation to intermediate host population variations were recorded. The dietary response of the red fox was shown to be complex when abundant alternative resources were available (anthropogenic food, multiple intermediate host prey species). Micro-local hotspots of parasite transmission to intermediate hosts in a landscape, as well as areas of higher risk for human contamination in village and urban settings, may be explained by the definitive hosts’ activity patterns and defecation behaviour.