Infectious diseases of humans and wildlife are increasing globally but the contribution of novel artificial anthropogenic entities such as nano-sized plastics to disease dynamics remains unknown. Despite mounting evidence for the adverse effects of nanoplastics (NPs) on single organisms, it is unclear whether and how they affect the interaction between species and thereby lead to ecological harm. In order to incorporate the impact of NP pollution into host-parasite-environment interactions captured in the “disease triangle”, we evaluated disease outcomes in the presence of polystyrene NP using an ecologically-relevant host-parasite system consisting of a common planktonic cyanobacterium and its fungal parasite. NP at high concentrations formed hetero-aggregates with phytoplankton and inhibited their growth. This coincided with a significant reduction in infection prevalence, highlighting the close interdependency of host and parasite fitness. Lower intensity of infection in the presence of NP indicates that reduced disease transmission results from the parasite’s diminished ability to establish new infections as NP formed aggregates around phytoplankton cells. We propose that NP aggregation on the host’s surface acts as a physical barrier to infection and, by reducing host light harvesting, may also hamper parasite chemotaxis. These results demonstrate that the consequences of NP pollution go well beyond toxic effects at the individual level and modulate the intensity of species interactions, thereby potentially eliciting diverse cascading effects on ecosystem functioning.

The present paper reports on the interrelationships of fish, parasites and the bioaccumulation of hazardous organic compounds in the Zemplínska Šírava water reservoir in eastern Slovakia, which is heavily polluted with polychlorinated biphenyls (PCBs). The concentrations of these contaminants were measured in various fish matrices (dorsal and abdominal muscle tissues, hepatopancreas, intestine wall and adipose tissue) of the freshwater bream, Abramis brama (Cyprinidae), and in its intestinal parasite Caryophyllaeus laticeps (Cestoda), which was used for the first time as a model for a PCB bioaccumulation study. Regarding the fish, the highest concentrations of PCBs were found in the intestine, followed by hepatopancreas and muscle tissues. The amounts of PCBs were higher in abdominal muscles than in their dorsal parts. Concentrations of ∑PCBs above the limits set by European regulations were detected in both muscle parts in the fish, confirming the persistent unfavorable conditions in this locality and high risk for biota and humans. Based on bioconcentration factor values (BCFs), PCBs reached much higher levels in cestodes compared to bream matrices. Some significant differences in PCB amounts between infected and uninfected bream were determined. Fulton's condition factor (CF) significantly differed in infected and non-infected fish (p ˂ 0.05), with CF values surprisingly lower in fish free of parasites compared to parasitized fish, which suggests a “mutualistic” relationship between the parasite and its host.

Metal pollution is a growing concern that affects the health of humans and animals globally. Copper is an essential insect micronutrient required for respiration, pigmentation and oxidative stress protection but can also act as a potentially toxic trace element. While several studies have focused on the negative fitness effects of copper on the aquatic larvae of mosquitoes, the effects of larval copper exposure on adult mosquito fitness (i.e., survival and fecundity) and their ability to transmit parasites (i.e., vector competence) remains unclear. Here, using a well-studied model vector-parasite system, the mosquito Aedes aegypti and parasite Dirofilaria immitis, we show that sublethal copper exposure in larval mosquitoes alters adult female fecundity and vector competence. Specifically, mosquitoes exposed to copper had a hormetic fecundity response and mosquitoes exposed to 600 μg/L of copper had significantly fewer infective parasite larvae than control mosquitoes not exposed to copper. Thus, exposure of mosquito larvae to copper levels far below EPA-mandated safe drinking water limits (1300 μg/L) can impact vector-borne disease dynamics not only by reducing mosquito abundance (through increased larval mortality), but also by reducing parasite transmission risk. Our results also demonstrated that larval copper is retained through metamorphosis to adulthood in mosquitoes, indicating that these insects could transfer copper from aquatic to terrestrial foodwebs, especially in urban areas where they are abundant. To our knowledge this is the first study to directly link metal exposure with vector competence (i.e., ability to transmit parasites) in any vector-parasite system. Additionally, it also demonstrates unequivocally that mosquitoes can transfer contaminants from aquatic to terrestrial ecosystems. These results have broad implications for public health because they directly linking contaminants and vector-borne disease dynamics, as well as linking mosquitoes and contaminant dynamics.

This paper is a part of a multi-disciplinary research “Application of Decentralized On-Site Water Treatment System in Egypt for Use in Agriculture and Producing Safe Fish and Animal Proteins”.The project aimed to investigate the environmental impact of implementing sewage water before and after treatment using the effluent of the on-site decentralized Japanese' Johkasou system, in agriculture and producing fish protein. The aim is to establish such system in Egypt to strengthen the sanitary conditions of water resources. In the present study, the impact of the sewage pollution in some fish farms at El-Fayyum, Port Said and El-Dakahlia governorates in Egypt was carried out. Water and fish (Oreochromis niloticus and Mugil cephalus) samples were collected from private fish farms of such localities. Bacteriological and chemical examination of water samples revealed the existence of coliforms and many other bacterial species of significant human health hazards. The chemical parameters of water showed a marked deviation from normal levels while examination of fish flesh specimens indicated contamination with Streptococcus Sp., Staphylococcus Sp., and Salmonella in all examined localities. Other bacterial isolates of human health importance (Morganella morganii, Pseudomonas cepacia and Enterococcos durans) were identified. The parasitological examination revealed the presence of encysted metacercariae (EMC); Diplostomatidae, Prohemistomatidae and Heterphyidae. Moreover, two protozoan parasites (Mxyoboulus tilapiae and Ichthyophthirius multifilis) were also recorded. The histopathological examination revealed mild tissue reaction in case of bacterial infection and severe pathological lesions in different organs in case of EMC infection. Lamellar hyperplasia and mononuclear cell infiltration in branchial tissue was common findings. In skeletal muscles, atrophy of muscle fibres, myolysis and myophagia were detected.

It is a common method to analyse physiological mechanisms of organisms – commonly referred to as biomarkers – to indicate the presence of environmental pollutants. However, as biomarkers respond to a wide range of stressors we want to direct the attention on natural stressors, i.e. on parasites. After two years maintenance under controlled conditions, roach (Rutilus rutilus) revealed no influence on levels of metallothionein by the parasite Ligula intestinalis. The same was found for Gammarus fossarum infected with Polymorphus minutus. However, the heat shock protein (HSP70) response was affected in both host-parasite systems. While the infection of roach resulted in reduced levels of HSP70 compared to uninfected roach, the infection in G. fossarum led to higher levels of HSP70. We also analysed the effect of a 14 days Cd exposure (4 μg/L) on the uninfected and infected gammarids. The exposure resulted in induced levels for both, metallothionein and HSP70 whereas the combination of stressors, parasite and exposure, revealed a decrease for levels of HSP70 in comparison to the metal exposure only. Accordingly, parasites as natural parts of aquatic ecosystems have to be considered in ecotoxicological research.

Microsporidia parasites are commonly found in amphipods, where they are often asymptomatic, vertically-transmitted and have several effects on host sexuality and behaviour. As amphipods are often used as models in ecotoxicological studies, we investigated the effect of microsporidian infections on energy reserves and defence capacities of Gammarus roeseli under cadmium stress. Only females were infected by two microsporidia parasites: Dictyocoela roeselum or Dictyocoela muelleri. In physiological conditions, microsporidia had no major effect on energy reserves and defence capacities of G. roeseli, while under cadmium exposure, energy reserves and antioxidant defence were weaker in infected females. Moreover, higher malondialdehyde levels detected in infected females revealed that they suffered more cellular damages. Our results suggest that microsporidia may affect gammarid fitness in stressful conditions, when parasitic stress cannot be compensated by the host. Consequently, microsporidia parasites should be a factor necessary to take into account in ecotoxicology studies involving amphipods.

Here we evaluated the potential for trace metal accumulation of two parasitic species, Hysterothylacium sp. (Nematoda) and Phyllodistomum sp. (Digenea), found parasitizing Hoplias malabaricus, a characiform fish also known as trahira, collected from two neotropical rivers, Jacaré-Pepira and Jacaré-Guaçú, in southeastern Brazil. Fish were collected between July 2017 and July 2019, totaling 90 fish specimens analyzed, 45 from each river. From fish, we take samples of three different tissues: muscle, intestine and liver. Along with the parasite samples taken from fish hosts, tissue samples were analyzed by an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) for obtaining the trace metal (Al, Cr, Mn, Fe, Ni, Cu, As, Cd e Pb) concentrations. All elements were found in statistically higher concentrations in the parasites, both nematodes and digeneans, than in the host tissues, but in comparison, was observed that Hysterothylacium sp. had higher concentrations than those obtained in Phyllodistomum sp. We also found that uninfected fish had statistically higher concentrations of metals than infected ones. And in those who are infected, the size of the parasitic infrapopulations correlated negatively with the concentrations of trace metals obtained in the hosts tissues, that is, the concentrations in fish showed a tendency to decrease as the parasitic infrapopulations increased, or vice versa. In addition, our results show that the influence of the parasitic infrapopulations on metal concentrations in the fish host is not affected in cases of mono-infection or co-infection.

We assessed the performance of taxonomic and several functional trait-based approaches in the assessment of spatial and temporal patterns of dusky flounder (Syacium papillosum) parasite assemblages along the Yucatan shelf to determine their potential as bioindicators of marine chemical pollution. Fish specimens were collected throughout three research cruises that took place in 2015, 2016 and 2018. In addition to the traditional taxonomic approach, four trait-based approaches were performed including community-weighted means (CWM), functional trait niche (FTN), functional groups (FGs), and Rao's functional diversity (FD). Significant spatial and temporal variations in parasite communities were detected using the taxonomic approach. In general, these variations were also reflected in the four trait-based approaches performed, indicating that changes in taxa composition and abundance also resulted in functional composition shifts. Resemblance matrices of both taxonomic and functional trait approaches were significantly correlated. Variations in taxonomic and trait-based composition using the four approaches were significantly correlated with depth, and at least one chemical pollutant variable. Feeding mode, transmission, life stage and attachment structure displayed spatial variability and significant correlations with predictor variables, which indicates that this set of attributes functions as a good surrogate for assessing variations in the functional composition of flatfish parasite communities in relation to pollution. FTN and CWM were the approaches that best detected spatio-temporal variation. CWM and FD were best suited for detecting pollution gradients. These results reveal the feasibility of using trait-based approaches to assess marine parasite communities as bioindicators of chemical pollution. Functional traits of marine metazoan parasites are as good indicators of the effect of oil pollution as taxonomic diversity. This may be a time-saving and cost-effective approach to performing environmental assessments.

Dichlorvos (2,2-dichlorovinyl-dimethylphosphate), an organophosphorus pesticide used for indoor insect and livestock parasite control, is among the most common commercially available pesticides. However, there are significant concerns over its toxicity, especially due to its relative stability in water, soil, and air. Zebrafish, an important developmental model, has been used for studying the effects of toxic compounds. The aim of this study was to evaluate the exposure to dichlorvos at early life stages (1 h postfertilization - 7 days postfertilization) in the zebrafish and its toxicological effects during the development, through morphological (7 days postfertilization), locomotor and social behavior analysis (7, 14, 30, 70, and 120 days postfertilization). Dichlorvos (1, 5, and 10 mg/L) exposure reduced the body length and heartbeat rate at 7 days postfertilization (dpf), as well as the surface area of the eyes (5 and 10 mg/L). The avoidance behavior test showed a significant decrease in escape responses at 7 (1, 5, and 10 mg/L) and 14 (5 and 10 mg/L) dpf zebrafish. The evaluation of larval exploratory behavior showed a reduction in distance traveled, mean speed (1, 5, and 10 mg/L) and time mobile (10 mg/L) between control and dichlorvos groups. In addition, the analysis performed on adult animals showed that the changes in distance traveled and mean speed remained reduced in 30 (1, 5, and 10 mg/L) and 70 dpf (5 and 10 mg/L), recovering values similar to the control at 120 dpf. The social behavior of zebrafish was not altered by exposure to dichlorvos in the early stages of development. Thus, the exposure to organophosphorus compounds at early stages of development induces an increased susceptibility to behavioral and neuronal changes that could be associated with several neurodegenerative diseases.