Joanne Cable

The development and implementation of diagnostic tools for the detection of Schistosoma in freshwater snail vectors were added to the World Health Organization’s guidelines on the control and elimination of human schistosomiasis in 2022. However, there are few documented examples of their application in schistosomiasis elimination settings. The current study validated a high-throughput polymerase chain reaction–based diagnostic protocol for the detection of Schistosoma haematobium (causing urogenital schistosomiasis) and S. bovis (causing bovine schistosomiasis) DNA in Bulinus spp. in the elimination setting of Pemba (Zanzibar, United Republic of Tanzania). Bulinus were collected and screened for patent schistosome infections across 4 malacological surveys (2017–2018) from 52 human–freshwater contact sites (i.e. freshwater bodies) located in 8 shehias (small administrative regions). Shehias varied from high (persisting) to low (declining) human urogenital schistosomiasis prevalence. Of the 9430 Bulinus spp. screened for patent schistosome infections using the standard parasitological shedding method, 0.11% (10/9430) S. haematobium and 0.02% (2/9430) S. bovis patent infections were observed. Using the molecular diagnostic, of the 5465 snails screened, 2.73% (149/5465) S. haematobium and 0.24% (13/5465) S. bovis DNA-positive snails were identified. Xenomonitoring detected >12× more S. haematobium presence in Bulinus spp. than conventional shedding methods, demonstrating a higher sensitivity for identifying parasite presence. Xenomonitoring positives suggest that S. bovis transmission occurs in several focal areas in Pemba, with a wider distribution than previously thought. Identification of human and bovine schistosome DNA in both low and high prevalence settings shows the feasibility of using xenomonitoring assays for transmission/elimination surveillance.

Skin is a multifunctional organ essential for maintaining body homeostasis, regulating functions and providing protection from environmental stressors. In fish, skin is immune active, containing antimicrobial proteins acting as the first line of defence against infectious pathogens. The gills function similarly, as a key mucosal immunity site, where pathogens induce both innate and adaptive immune responses. In this study, proteomic analysis identified differentially expressed proteins in the skin and gills of ectoparasite Gyrodactylus turnbulli infected guppies (Poecilia reticulata) at two timepoints post-infection (Days 13 and 17). These fish were provided with a health-promoting additive, aimed to boost immunocompetency and reduce ectoparasite infections. Different proteomes were evidenced based on infection status of fish (susceptible, responding, or resistant) and in-feed supplementation. In skin tissue, susceptible fish showed no evidence of immune response, reflecting their high parasite load. Responding fish employed biological processes like apoptosis, reducing the gyrodactylid niche. In resistant fish, up-regulated innate and adaptive immunity explained the low parasite load on the host over the entire infection trajectory. Overall, fish protein expression in the skin and gills was affected both by the dietary supplement and gyrodactylid infection burden, highlighting the role of natural immunostimulants in aquatic infectious disease prophylaxis, control and treatment.

Social networks influence the spread of parasites through populations. Although we know how parasites are transmitted as a product of social interactions, we have a limited understanding of how social networks are affected by parasites over time. Host–parasite interactions and the networks they form, are typically examined as static networks, and while topological descriptions at a specific time point are useful, both behaviour and the infection process are dynamic. By monitoring replicate populations of Trinidadian guppies ( Poecilia reticulata ) daily before and during infection with the ectoparasite Gyrodactylus turnbulli , we show how parasitism drives social network dynamics. Specifically, infected individuals increased their connections in networks affected by parasitism. In contrast, uninfected control shoals showed no change in network metrics. The structure of subnetworks (motifs) and networks, however, did not change in response to infection status. These findings provide further evidence of reciprocal host behaviour–parasite feedback mechanisms, and highlight that infected fish alter their interactions in order to ‘off-load’ their parasites. Understanding how these reciprocal interactions affect the structure and function of natural systems, as well as understanding how these interactions may alter with future environmental change, are key areas of future research.

Cystic echinococcosis (hydatidosis) is a world-wide zoonotic disease of mainly humans, livestock and dogs, caused by Echinococcus granulosus. The disease can negatively impact food production and animal welfare and causes socio-economic hardship. Here, we aimed to identify the local bovine hydatid cyst fluid (BHCF) antigen for developing a sero-diagnostic assay to be used for the pre-slaughter screening of food animals. In total, 264 bovines approved for slaughter in Pakistan were subjected to serum collection and post-mortem screening for hydatid cysts. These cysts were assessed microscopically to assess fertility and viability, and by PCR for molecular confirmation of species. A BHCF antigen was identified from positive sera via SDS-PAGE, confirmed by Western blot, and quantified via a bicinchoninic acid (BCA) assay. The quantified crude BHCF antigen (iEg67 kDa) was then used in ELISA screening to test all sera collected from known positive and negative animals based on hydatid cyst presence/absence. Of the 264 bovines examined, 38 (14.4%) showed hydatid cysts during post-mortem examination. All of these individuals, plus an additional 14 (total: 52; 19.6%) tested positive based on less time-consuming ELISA examination. Based on ELISA, occurrence in females (18.8%) was significantly higher than in males (9.2%) and was higher in cattle (19.5%) compared to buffalo (9.5%). The infection rate increased with age in both host species: cumulatively, 3.6% in animals aged 2–3 years, 14.6% in 4–5-year-olds and 25.6% in 6–7-year-olds. The occurrence of cysts in cattle was significantly higher in the lungs (14.1%) compared to their livers (5.5%), whereas the opposite was true in buffalo (6.6% livers, 2.9% lungs). For both host species, most cysts in the lungs were fertile (65%), while the majority in the liver were sterile (71.4%). We conclude that the identified iEg67 kDa antigen is a strong candidate for the development of a sero-diagnostic screening assay for the pre-slaughter diagnosis of hydatidosis.

Background: Mathematical modelling of host-parasite systems has seen tremendous developments and broad applications in theoretical and applied ecology. The current study focuses on the infection dynamics of a gyrodactylid-fish system. Previous experimental studies have explored the infrapopulation dynamics of co-infecting ectoparasites,Gyrodactylus turnbulliandG. bullatarudis, on their fish host,Poecilia reticulata, but questions remain about parasite microhabitat preferences, host survival and parasite virulence over time. Here, we use more advanced statistics and a sophisticated mathematical model to investigate these questions based on empirical data to add to our understanding of this gyrodactylid-fish system.Methods: A rank-based multivariate Kruskal-Wallis test coupled with its post-hoc tests and graphical summaries were used to investigate the spatial and temporal parasite distribution of different gyrodactylid strains across different host populations. By adapting a multi-state Markov model that extends the standard survival models, we improved previous estimates of survival probabilities. Finally, we quantified parasite virulence of three different strains as a function of host mortality and recovery across different fish stocks and sexes.Results: We confirmed that the captive-bredG. turnbulliand wildG. bullatarudisstrains preferred the caudal and rostral regions respectively across different fish stocks; however, the wildG. turnbullistrain changed microhabitat preference over time, indicating microhabitat preference of gyrodactylids is host and time dependent. The average time of host infection before recovery or death was between 6 and 14 days. For this gyrodactylid-fish system, a longer period of host infection led to a higher chance of host recovery. Parasite-related mortalities are host, sex and time dependent, whereas fish size is confirmed to be the key determinant of host recovery.Conclusion: From existing empirical data, we provided new insights into the gyrodactylid-fish system. This study could inform the modelling of other host-parasite interactions where the entire infection history of the host is of interest by adapting multi-state Markov models. Such models are under-utilised in parasitological studies and could be expanded to estimate relevant epidemiological traits concerning parasite virulence and host survival.Graphical

Intensification of fish farming practices is being driven by the demand for increased food production to support a rapidly growing global human population, particularly in lower-middle income countries. Intensification of production, however, increases the risk of disease outbreaks and thus the likelihood for crop losses. The microbial communities that colonise the skin mucosal surface of fish are poorly understood, but are important in maintaining fish health and resistance against disease. This skin microbial community is susceptible to disruption through stressors associated with transport, handling and the environment of intensive practices, and this risks the propagation of disease-causing pathogens. In this study, we characterised the microbial assemblages found on tilapia skin — the most widely farmed finfish globally — and in the surrounding water of seven earthen aquaculture ponds from two pond systems in distinct geographic regions in Malawi. Metabarcoding approaches were used to sequence the prokaryotic and microeukaryotic communities. We found 92% of prokaryotic amplicon sequence variants were common to both skin and water samples. Differentially enriched and core taxa, however, differed between the skin and water samples. In tilapia skin, Cetobacterium, Paucibacter, Pseudomonas and Comamonadaceae were enriched, whereas, the cyanobacteria Cyanobium, Microcystis and/or Synechocystis , and the diatom Cyclotella , were most prevalent in pond water. Ponds that clustered together according to their water prokaryotic communities also had similar microeukaryotic communities indicating strong environmental influences on prokaryotic and microeukaryotic community structures. While strong site-specific clustering was observed in pond water, the grouping of tilapia skin prokaryotes by pond site was less distinct, suggesting fish microbiota have a greater buffering capacity against environmental influences. The characterised diversity, structure and variance of microbial communities associated with tilapia culture in Malawi provide the baseline for studies on how future intensification practices may lead to microbial dysbiosis and disease onset. Highlights: Fish skin and pond water communities differ structurally, but share common taxa Pond locations have a stronger influence on water versus fish skin microbiome community structure Selected skin-associated taxa could be used to monitor dysbiotic events in aquaculture Taxa with opportunistic pathogen potential were identified at low abundance

Natural host populations differ in their susceptibility to infection by parasites, and these intrapopulation differences are still an incompletely understood component of host‐parasite dynamics. In this study, we used controlled infection experiments with wild‐caught guppies (Poecilia reticulata) and their ectoparasite Gyrodactylus turnbulli to investigate the roles of local adaptation and host genetic composition (immunogenetic and neutral) in explaining differences in susceptibility to infection. We found differences between our four study host populations that were consistent between two parasite source populations, with no indication of local adaptation by either host or parasite at two tested spatial scales. Greater values of host population genetic variability metrics broadly aligned with lower population mean infection intensity, with the best alignments associated with major histocompatibility complex (MHC) “supertypes”. Controlling for intrapopulation differences and potential inbreeding variance, we found a significant negative relationship between individual‐level functional MHC variability and infection: fish carrying more MHC supertypes experienced infections of lower severity, with limited evidence for supertype‐specific effects. We conclude that population‐level differences in host infection susceptibility probably reflect variation in parasite selective pressure and/or host evolutionary potential, underpinned by functional immunogenetic variation.

The polyopisthocotylean Discocotyle sagittata is a blood-feeding monogenean that infects the gill lamellae of rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta. The ultrastructure of their alimentary tract, at different stages of the life cycle, was previously unknown. Here, we show that the gastrodermis of the oncomiracidium, subadult, and adult D. sagittata follows the same structural organization as that of other blood-feeding polyopisthocotyleans, being composed of digestive cells alternating with a connecting syncytium. Digestive cells of the oncomiracidium are found in three developmental forms: undifferentiated, developing differentiated, and differentiated (presumably functioning) cells whereas those of adult and subadult are present in a single functioning state with variable size and content. The apical cytoplasm of adult digestive cells forms conical outgrowths, a feature which is absent in the oncomiracidium. The connecting syncytium of the oncomiracidium has no evidence of metabolic activity, while that of adult and subadult is metabolically active. The lamellae of the connecting syncytium of adults and subadults are more numerous and larger, and their terminal portions are expanded, compared with those of the oncomiracidium. Parallel, tubular, membranous structures are characteristic of the apical cytoplasm of the connecting syncytium of the oncomiracidium. Luminal lamella in the oncomiracidium, subadult, and adult form balloon-like structures enclosing some luminal contents, but those of the oncomiracidium are larger, bounded by nucleated cytoplasmic layer, and enclose more luminal contents. The possible functions of these structures and mechanism of digestion in both oncomiracidium and adult are discussed.

Rivers have been subject to the construction of numerous small‐scale anthropogenic structures, causing the alteration and fragmentation of habitats. Despite their impact on fish habitat selection, migration, and swimming performance, more hydraulic structures are being added to riverine systems. These mainly have the purpose of harnessing renewable energy or mitigating the impact of flooding, as in the case of leaky barriers that are widely used for natural flood management. By providing a sustainable and cost‐effective supplement to traditional hard engineering flood risk management methods, these channel‐spanning wooden barriers are constructed using sustainable, local materials, intended to slow down surface water and groundwater flow, reduce flood peaks, and attenuate the flow reaching downstream communities. Despite their increasing popularity, little is known about the design implications on fish movement or hydrodynamics. Using scaled laboratory flume experiments we investigate how the physical design of four leaky barriers varying in porosity, length, provision of overhead cover, and color, impact on fish movement and spatial usage, and the channel hydrodynamics. Our fish behavioral analysis reveals that juvenile rainbow trout (Oncorhynchus mykiss) movement reduces with barrier presence. Upstream passage increases with barrier color but not cover, for shorter rather than longer leaky barriers, and for a non‐porous barrier compared to its porous counterpart. Barrier‐specific flow alterations appear to play a secondary role compared to barrier color. Our study showed that physical barrier design and leaky barrier presence alter fish movement, and therefore care needs to be taken during the design of such natural flood management structures.