A growing body of research implicates inflammation as a potential pathway in the aetiology and pathophysiology of some mental illnesses. A systematic review was conducted to determine the association between parasitic infection and mental illnesses in humans in Africa and reviewed the state of the evidence available. The search focused on publications from Africa documenting the relationship between parasites from two parasite groups, helminths and protozoans, and four classifications of mental illness: mood affective disorders, neurotic and stress-related disorders, schizotypal disorders and unspecified mental illnesses. In the 26 reviewed papers, the prevalence of mental illness was significantly higher in people with parasitic infection compared to those without infection, i.e., 58.2% vs 41.8% (P < 0.001). An overall odds ratio found that the association of having a mental illness when testing positive for a parasitic infection was four times that of people without infection. Whilst the study showed significant associations between parasite infection and mental illness, it also highlights gaps in the present literature on the pathophysiology of mental illness in people exposed to parasite infection. This study highlighted the importance of an integrated intervention for parasitic infection and mental illness.

Wild mammals, especially rodents, can participate in the life cycle of Schistosoma mansoni; however, the impact of these parasite strains on the severity of schistosomiasis remains unclear. The aim of this study was to comparatively evaluate the parasitological and immunopathological alterations induced by an S. mansoni strain isolated from the wild rodent Holochilus sciureus (HS strain) and a parasite strain isolated from a human (LE strain) in experimentally infected mice. Male BALB/c mice were subcutaneously infected with 50 cercariae/mouse of either the HS or the LE strain and were evaluated for 12 weeks. In the experimental groups, the parasite burden was estimated by worm and egg (feces and tissues) count, and immunopathological alterations were evaluated in the liver and intestines. Compared to experimental infection with the LE parasite strain, HS-infected mice showed reduced number of parasite worms but higher fecundity rate, significant reduction in IL-5, IL-10 and IL-13 concentrations, lower EPO-activity in liver homogenate and higher concentrations of TNF-α, IFN-γ, IL-12 and IL-17 in the small intestine homogenate. Moreover, HS infection resulted in higher concentrations of NO end-products in both the liver and intestine, suggesting a predominance of the Th1/Th17 immune response. HS-infected mice also showed higher plasma transaminase levels, formed larger granulomas, and had a higher mortality rate in comparison with LE-infected mice. Data indicate that BALB/c mice infected with the HS strain of S. mansoni showed reduced susceptibility to the parasite but stronger tissue inflammation and high disease severity.

Sarcocystis neurona, Neospora spp. and Toxoplasma gondii are related protozoans; they were considered the same parasite until 1970s. Two of these parasites, S. neurona and Neospora spp. are associated with a neurological syndrome in horses, called equine protozoal myeloencephalitis (EPM). The diagnosis and treatment of EPM are difficult. Most cases of EPM are related to S. neurona while only a few are due to Neospora spp. infections. There are two species of Neospora, Neospora caninum that has a wide host range and Neospora hughesi that has been found only in horses. Currently, T. gondii is not considered as a cause of EPM in horses, although it causes neurological illness in many other hosts, including humans. The present review provides an update on history, life cycle, diagnosis and treatment of these three infections in horses.

Human toxocariasis is a neglected tropical disease, which is actually global in distribution and has a significant impact on global public health. The infection can lead to several serious conditions in humans, including allergic, ophthalmic and neurological disorders such as epilepsy. It is caused by the common roundworm species Toxocara canis and Toxocara cati, with humans becoming accidentally infected via the ingestion of eggs or larvae. Toxocara eggs are deposited on the ground when infected dogs, cats and foxes defecate, with the eggs contaminating crops, grazing pastures, and subsequently food animals. However, transmission of Toxocara to humans via food consumption has received relatively little attention in the literature. To establish the risks that contaminated food poses to the public, a renewed research focus is required. This review discusses what is currently known about food-borne Toxocara transmission, highlighting the gaps in our understanding that require further attention, and outlining some potential preventative strategies which could be employed to safeguard consumer health.

The prevalence rates of trypanosomes, including those that require cyclical transmission by tsetse flies, are widely distributed in Africa. Trypanosoma brucei and Trypanosoma congolense are actively maintained in regions where there are no tsetse flies although at low frequencies. Whether this could be due to an independent evolutionary origin or multiple introduction of trypanosomes due to continuous movement of livestock between tsetse-free and -infested areas is not known. Thus, the aim of the study was to carry out microsatellite genotyping to explore intra-specific genetic diversity between T. (Trypanozoon), T. congolense and Trypanosoma vivax from the two regions: tsetse infested and tsetse free. Microsatellite genotyping showed geographical origin-based structuring among T. (Trypanozoon) isolates. There was a clear separation between isolates from the two regions signalling the potential of microsatellite markers as diagnostic markers for T. brucei and Trypanosoma evansi isolates. Trypanosoma vivax isolates also clustered largely based on the sampling location with a significant differentiation between the two locations. However, our results revealed that T. congolense isolates from Northern Kenya are not genetically separated from those from Coastal Kenya. Therefore, these isolates are likely introduced in the region through animal movement. Our results demonstrate the occurrence of both genetic connectivity as well as independent evolutionary origin, depending on the trypanosome species between the two ecologies.

Nosema apis and N. ceranae are the two causative agents of Nosema disease in adult honey bees (Apis mellifera L.). Nosema apis has been a recognized parasite for over a century and its epizootiology is well known. In contrast, N. ceranae is an emerging parasite of honey bees, which is now globally prevalent and the dominant Nosema spp. in many parts of the world. Despite this, many gaps in our knowledge exist regarding this species. For example, we do not fully understand all of the routes of transmission of N. ceranae among bees, or how long this parasite is capable of surviving in honey bee colonies. Here we investigated the viability and infectivity of N. ceranae spores in water and 2 M sucrose over time after storage at 33, 20, −12 and −20°C. Spores in both 2 M sucrose and water maintained high viability, except in water at −20°C over the course of the 6-week experiment. Infectivity was variable for spores after storage at all four temperatures, but all were infective at the last time point. The results provide evidence for cold tolerance and suggest that both water and 2 M sucrose (fall bee feed) could act as routes of transmission for N. ceranae. This work also contains information that may help influence management recommendations for the parasite.

Fish (Elasmobranchia and Actinopterygii) inhabit the majority of aquatic habitats globally. They are crucial for human nutrition but they may be negatively affected by parasitic protists and metazoan parasites. Fish parasites are also an extraordinary group of animals because of their ecological and evolutionary importance and unique adaptations to parasitism. They also play a key role in ecosystem functioning. In the present special issue, 13 review and research articles on major groups of fish parasites are provided to document the current advancement in our understanding of different aspects of their biology, ecology and associations with their fish hosts. The existing gaps in our knowledge of these peculiar animals are mapped and future trends in their research outlined.

Parasite transmission is the ability of pathogens to move between hosts. As a key component of the interaction between hosts and parasites, it has crucial implications for the fitness of both. Here, we review the transmission dynamics of Gyrodactylus species, which are monogenean ectoparasites of teleost fishes and a prominent model for studies of parasite transmission. Particularly, we focus on the most studied host–parasite system within this genus: guppies, Poecilia reticulata, and G. turnbulli/G. bullatarudis. Through an integrative literature examination, we identify the main variables affecting Gyrodactylus spread between hosts, and the potential factors that enhance their transmission. Previous research indicates that Gyrodactylids spread when their current conditions are unsuitable. Transmission depends on abiotic factors like temperature, and biotic variables such as gyrodactylid biology, host heterogeneity, and their interaction. Variation in the degree of social contact between hosts and sexes might also result in distinct dynamics. Our review highlights a lack of mathematical models that could help predict the dynamics of gyrodactylids, and there is also a bias to study only a few species. Future research may usefully focus on how gyrodactylid reproductive traits and host heterogeneity promote transmission and should incorporate the feedbacks between host behaviour and parasite transmission.

Arginine methylation is a post-translational modification involved in gene transcription, signalling pathways, DNA repair, RNA metabolism and splicing, among others, mechanisms that in protozoa parasites may be involved in pathogenicity-related events. This modification is performed by protein arginine methyltransferases (PRMTs), which according to their products are divided into three main types: type I yields monomethylarginine (MMA) and asymmetric dimethylarginine; type II produces MMA and symmetric dimethylarginine; whereas type III catalyses MMA only. Nine PRMTs (PRMT1 to PRMT9) have been characterized in humans, whereas in protozoa parasites, except for Giardia intestinalis, three to eight PRMTs have been identified, where in each group there are at least two enzymes belonging to type I, the majority with higher similarity to human PRMT1, and one of type II, related to human PRMT5. However, the information on the role of most of these enzymes in the parasites biology is limited so far. Here, current knowledge of PRMTs in protozoan parasites is reviewed; these enzymes participate in the cell growth, stress response, stage transitions and virulence of these microorganisms. Thus, PRMTs are attractive targets for developing new therapeutic strategies against these pathogens.

The incidence rate of inflammatory bowel diseases is increasing in developed countries. As such there is an increasing demand for new therapies. The aim of this systematic review was to investigate whether there is evidence to support the use of helminth therapy for the management of Crohn's disease and ulcerative colitis. Four databases (PubMed, Embase, Medline and the Cochrane Central Register of Control Trials) were searched for primary evidence in the form of clinical studies. Nine studies were suitable for inclusion: five double-blind randomized control trials and four open-label studies. This review divided the results of the studies into two categories: (a) the efficacy of helminth therapy and (b) the safety of helminth therapy. Results regarding the efficacy were mixed and a conclusive answer could not be reached, as there was not enough evidence to rule out a placebo effect. More research is needed, particularly studies with control groups to address the possibility of a placebo effect. Despite this, all nine studies concluded helminth therapy was safe and tolerable, and therefore there is currently no evidence against further exploration of this treatment option.

The current systematic review and meta-analysis demonstrate the genotypic distribution of canine echinococcosis worldwide. Studies published from the inception until 21 May 2021 were screened, relevant articles were selected and the random-effect model was used to draw forest plots with 95% confidence intervals (CIs). Totally, 44 articles were included, mostly examined dogs (37 records), followed by wolf (8 records), jackal (7 records), fox (3 records), pump fox (3 records) and coyote (1 record). Echinococcus granulosus sensu stricto (G1–G3) and G6/7 cluster of Echinococcus canadensis were the most common genotypes among canids. Most studies were conducted in Asia and Europe with 17 and 15 datasets, respectively. Exclusively, Iran possessed the highest number of studies (10 records). Meta-analysis showed that the pooled molecular prevalence of echinococcosis was 33.82% (95% CI 24.50–43.83%). Also, the highest and lowest prevalence of canine echinococcosis was calculated for South America (66.03%; 95% CI 25.67–95.85%) and Europe (19.01%; 95% CI 9.95–30.16%). Additionally, there were statistically significant differences between the global prevalence of echinococcosis in canines and publication year, continent, country, sample type, host and molecular test. These findings will elevate our knowledge on the poorly known canine echinococcosis worldwide.

Transmission mode is a key factor that influences host–parasite coevolution. Vector-borne pathogens are among the most important disease agents for humans and wildlife due to their broad distribution, high diversity, prevalence and lethality. They comprise some of the most important and widespread human pathogens, such as yellow fever, leishmania and malaria. Vector-borne parasites (in this review, those transmitted by blood-feeding Diptera) follow unique transmission routes towards their vertebrate hosts. Consequently, each part of this tri-partite (i.e. parasite, vector and host) interaction can influence co- and counter-evolutionary pressures among antagonists. This mode of transmission may favour the evolution of greater virulence to the vertebrate host; however, pathogen–vector interactions can also have a broad spectrum of fitness costs to the insect vector. To complete their life cycle, vector-borne pathogens must overcome immune responses from 2 unrelated organisms, since they can activate responses in both vertebrate and invertebrate hosts, possibly creating a trade-off between investments against both types of immunity. Here, we assess how dipteran vector-borne transmission shapes the evolution of hosts, vectors and the pathogens themselves. Hosts, vectors and pathogens co-evolve together in a constant antagonistic arms race with each participant's primary goal being to maximize its performance and fitness.

Foodborne trematodes (FBTs) have a worldwide distribution (with particular prevalence in south-east Asia) and are believed to infect almost 75 million people, with millions more living at risk of infection. Although mortality due to trematodiasis is low, these infections cause considerable morbidity and some species are associated with the development of cancer in hyperendemic regions. Despite this, FBTs are often side-lined in terms of research funding and have been dubbed neglected tropical diseases by the World Health Organisation. Thus, the aim of this special issue was to provide an update of our understanding of FBT infections, to shine a light on current work in the field and to highlight some research priorities for the future. With contributions from leading researchers, many from endemic regions, we review the major FBT species. In doing so we revisit some old foes, uncover emerging infections and discover how outbreaks are being dealt with as a result of new approaches to parasite control. We also report advances in our understanding of the interactions of FBTs with their mammalian hosts and uncover new interplay between trematodes and host microbiome components. We hope that this article collection will stimulate discussion and further research on the FBTs and help raise them from their neglected status.

Climate change effects on host–parasite interactions have been poorly studied in arid or semi-arid habitats. Here, we conducted an experiment aimed to increase the temperature inside European roller Coracias garrulus nest boxes located in a semi-arid habitat on different nest-site types to look for effects on different ectoparasite abundances and nestling growth. Average nest temperature was slightly higher in heated nests than in control nests, although differences were not statistically significant. However, relative humidity was significantly lower at night in heated nests as compared to control nests. The abundance of sand flies, mites and carnid flies was significantly higher in heated, less humid, nests while biting midge abundance was significantly lower in heated nests. Other ectoparasites were not significantly affected by treatment. Relative humidity was high even in heated nests, reaching more than 60%. Sand fly abundance was higher in nests located in sandstone walls, while mite abundance was higher in isolated farmhouses. In addition, sand fly prevalence was higher in nests located in isolated farmhouses and sandstone walls. Heat treatment, nest-site type or ectoparasite abundances did not affect the nestling body mass, wing length or their growth at different nestling ages.

From a systematic review framework, we analysed the clinical evidence on the effectiveness and safety of monotherapy and combination chemotherapy for Chagas disease (ChD) treatment. The research protocol was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and patient, intervention, comparison and outcome strategy. Only randomized controlled trials (RCT) were retrieved from Embase, Medline, Scopus and Web of Science databases. Diagnostic tools, treatment protocols, seroconversion rates and adverse events were investigated. Fifteen RCT mainly concentrated in endemic countries were identified. ChD diagnosis was mainly based on haemagglutination, immunofluorescence, enzyme-linked immunosorbent assay and polymerase chain reaction. Benznidazole (BNZ), nifurtimox, fosravuconazole, posaconazole, allopurinol and thioctic acid were the identified drugs. The best negative seroconversion results (100, 96, 94 and 91.3%) were, respectively, based on BNZ (5 mg kg day−1, 200 mg day−1, 150 mg day−1 and 2.5 mg kg−1) administration for 60 days. Negative seroconversion was not achieved with allopurinol (300 mg day−1 for 60 days). Adverse reactions ranged from 5 to 73% in patients receiving antiparasitic chemotherapy. Treatment discontinuation (1.5–57%) was mainly associated with gastrointestinal, cutaneous and neurological manifestations. Current RCT-based evidence indicates that BNZ is the most viable option for ChD treatment. However, new protocols need to be developed to mitigate side effects and increase patient adherence to antiparasitic chemotherapy. Therefore, shorter regimens, lower concentrations and treatments combining BNZ with posaconazole, fosravuconazole or ravuconazole may be viable to ensure comparable efficacy to BZN-based monotherapy, contributing to reduce dose- and time-dependent toxicity reactions.

Although infections with Cyclospora cayetanensis are prevalent worldwide, many aspects of this parasite's life cycle remain unknown. Humans are the only known hosts, existing information on its endogenous development has been derived from histological examination of only a few biopsy specimens. In histological sections, its stages are less than 10 μm, making definitive identification difficult. Here, confirmation of cyclosporiasis in a duodenal biopsy specimen from an 80-year-old man without any recognized immunodeficiency patient is reported. Asexual forms (schizonts) and sexual forms (gamonts) were located within enterocytes, including immature and mature schizonts, an immature male gamont and a female gamont. Merozoites were small (<5 μm × 1 μm) and contained two rhoptries, subterminal nucleus and numerous micronemes and amylopectin granules. These parasite stages were like those recently reported in the gallbladder of an immunocompromised patient, suggesting that the general life-cycle stages are not altered by immunosuppression.

This study focuses on the role of the population structure of Leishmania spp. on the adaptive capacity of the parasite. Herein, we investigate the contribution of subpopulations of the L. (V.) braziliensis Thor strain (Thor03, Thor10 and Thor22) in the profile of murine macrophages infection. Infection assays were performed with binary combinations of these subpopulations at stationary phases. The initial interaction time showed major effects on the combination assays, as demonstrated by the significant increase in the infection rate at 5 h. Based on the endocytic index (EI), Thor10 (EI = 563.6) and Thor03 (EI = 497) showed a higher infection load compared to Thor22 (EI = 227.3). However, the EI decreased in Thor03 after 48 h (EI = 447) and 72 h (EI = 388.3) of infection, and showed changes in the infection level in all Thor10/Thor22 combinations. Assays with CellTrace CFSE-labelled Thor22 promastigotes indicated an increase (~1.5 fold) in infection by this subpopulation in the presence of Thor10 when compared to the infection profile of Thor03/Thor22 combinations in the same proportions. In addition, the potential of these subpopulations, alone or in binary combinations, to modulate the expression of cytokines and nitric oxide (NO) in vitro was investigated. Lower NO and tumour necrosis factor-α production levels were observed for all Thor10/Thor22 combinations at 24 h compared to these subpopulations alone. In contrast, Thor03/Thor22 combination assays increased IL-10 production at this time. Collectively, these results provide in vitro evidence on the potential of L. (V.) braziliensis population structure to play a relevant role in a host infection by this parasite.

This research aims to determine whether the combination of epidemiological and clinical features can predict malaria. Diagnostic investigation detected 22.3% of individuals with Plasmodium vivax (P. vivax) malaria, with significant predominance of the male gender. The malaria triad (fever, chills and headache) had a more expressive frequency (81.1%) in individuals with positive thick blood than those with negative thick blood smear (65.1%), although there was no statistical significance. Among the variables analysed as predictive for positive thick blood smear, it was observed that personal history of travel to an endemic malaria area and past malaria infection (PMI) were significantly associated with malaria, even in multiple logistic regression. Fever had the higher sensitivity (94.6%) and past malaria history had the greater specificity (68.2%), with accuracy of 23.5% and 67.5%, respectively. In combined analysis, fever with chills had the highest sensitivity (91.9%), but low accuracy (38.5%). High specificity (91.5%) was found in the association of malaria triad, PMI and history of travel to endemic malaria area (which along with anorexia, was higher 94.6%), with good accuracy (80.7%), suggesting that the screening of patients for performing thick blood smear can be based on these data. The epidemiological features and the malaria triad (fever, chills and headache) can be predictors for identification of malaria patients, concurring to precocious diagnosis and immediate treatment of individuals with malaria.

Infection by malaria parasites (Plasmodium spp.) remains one of the leading causes of morbidity and mortality, especially in tropical regions of the world. Despite the availability of malaria control tools such as integrated vector management and effective therapeutics, these measures have been continuously undermined by the emergence of vector resistance to insecticides or parasite resistance to frontline antimalarial drugs. Whilst the recent pilot implementation of the RTS,S malaria vaccine is indeed a remarkable feat, highly effective vaccines against malaria remain elusive. The barriers to effective vaccines result from the complexity of both the malaria parasite lifecycle and the parasite as an organism itself with consequent major gaps in our understanding of their biology. Historically and due to the practical and ethical difficulties of working with human malaria infections, research into malaria parasite biology has been extensively facilitated by animal models. Animals have been used to study disease pathogenesis, host immune responses and their (dys)regulation and further disease processes such as transmission. Moreover, animal models remain at the forefront of pre-clinical evaluations of antimalarial drugs (drug efficacy, mode of action, mode of resistance) and vaccines. In this review, we discuss commonly used animal models of malaria, the parasite species used and their advantages and limitations which hinder their extrapolation to actual human disease. We also place into this context the most recent developments such as organoid technologies and humanized mice.