Recent epidemiologic and clinical importance of Toxoplasma gondii infections in marine mammals: 2009-2020

Evaluating the Risk Landscape of Hawaiian Monk Seal Exposure to Toxoplasma gondii

Toxoplasmosis is a disease of primary concern for Hawaiian monk seals (Neomonachus schauinslandi), due to its apparently acute lethality and especially heavy impacts on breeding female seals. The disease-causing parasite, Toxoplasma gondii, depends on cats to complete its life cycle; thus, in order to understand how this pathogen infects marine mammals, it is essential to understand aspects of the terrestrial ecosystem and land-to-sea transport. In this study, we constructed a three-tiered model to assess risk of Hawaiian monk seal exposure to T. gondii oocysts: (1) oocyst contamination as a function of cat population characteristics; (2) land-to-sea transport of oocysts as a function of island hydrology, and (3) seal exposure as a function of habitat and space use. We were able to generate risk maps highlighting watersheds contributing the most to oocyst contamination of Hawaiian monk seal habitat. Further, the model showed that free-roaming cats most associated with humans (pets or strays often supplementally fed by people) were able to achieve high densities leading to high levels of oocyst contamination and elevated risk of T. gondii exposure.

Assessing the impact of preventative measures to limit the spread of Toxoplasma gondii in wild carnivores of Madagascar

Novel multihost pathogens can threaten endangered wildlife species, as well as humans and domestic animals. The zoonotic protozoan parasite Toxoplasma gondii is transmitted by members of Felidae and can infect a large number of animal species, including humans. This parasite can have significant health consequences for infected intermediate hosts and could further endanger wild carnivore populations of Madagascar. Building on an empirical characterization of the prevalence of the pathogen in local mammals, we used mathematical models of pathogen transmission in a multihost community to compare preventative measures that aim to limit the spread of this parasite in wild carnivores. Specifically, we examined the effect of hypothetical cat vaccination and population control campaigns on reducing the risk of infection by T. gondii in wild Eupleridae. Our model predicted that the prevalence of exposure to T. gondii in cats would be around 72% and that seroprevalence would reach 2% and 43% in rodents and wild carnivores, respectively. Reducing the rodent population in the landscape by half may only decrease the prevalence of T. gondii in carnivores by 10%. Similarly, cat vaccination and reducing the population of definitive hosts had limited impact on the prevalence of T. gondii in wild carnivorans of Madagascar. A significant reduction in prevalence would require extremely high vaccination, low turnover, or both in the cat population. Other potential control methods of T. gondii in endangered Eupleridae include targeted vaccination of wild animals but would require further investigation. Eliminating the threat entirely will be difficult because of the ubiquity of cats and the persistence of the parasite in the environment.

Whole genome enrichment approach for genomic surveillance of Toxoplasma gondii

Pathogenic bacteria, viruses, fungi, and protozoa can cause food and waterborne diseases. Surveillance methods must therefore screen for these pathogens at various stages of water distribution and of food from production to consumption. Detection using nucleic acid amplification methods offer rapid identification, but such methods have limited utility for characterizing populations, variant types or virulence traits of pathogens. Whole genome sequencing (WGS) can be used to determine this information. However, pathogens must be isolated and cultured to yield sufficient DNA for WGS, which is laborious or not feasible for certain stages of parasites like oocysts of Toxoplasma gondii. We previously developed the Circular Nucleic acid Enrichment Reagent (CNER) method to make whole genome enrichment (WGE) baits for difficult-to-grow bacterial pathogens. WGE using CNERs facilitates direct sequencing of pathogens from samples without the need to isolate and grow them. Here, we made WGE-CNERs for T. gondii to demonstrate the use of the CNER method to make baits to enrich the large genomes of water and foodborne protozoan pathogens. By sequencing, we detected as few as 50 parasites spiked in an oyster hemolymph matrix. We discuss the use of WGE-CNERs for genomic surveillance of food and waterborne pathogens.

Detection of Toxoplasma gondii and Sarcocystis sp. in the meat of common minke whale (Balaenoptera acutorostrata): A case of suspected food poisoning in Japan

A case of suspected food poisoning related to the consumption of raw meat from a common minke whale (Balaenoptera acutorostrata) was reported in Tokyo, Japan, in June 2020. Microscopic analysis revealed tissue cysts of Toxoplasma gondii and sarcocysts of Sarcocystis sp. in whale meat. The SAG2 and ITS1 region sequences of T. gondii were detected in the DNA extracted from the meat. Genotyping of the multilocus nested PCR-RFLP using the genetic markers SAG1, SAG2 (5'- SAG2, 3'-SAG2, and alt. SAG2), SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico revealed that the genotype of T. gondii was type II, with a type I pattern for the L358 locus. In the phylogenetic analyses of the six loci (GRA6, GRA7, SAG1, HP2, UPRT1, and UPRT7), these sequences clustered into haplogroup 2. Moreover, the sequences of the virulence-related genes ROP5 and ROP18 of T. gondii isolated from whale meat were similar to those of the type II ME49 reference strain. Sequence analyses of the mtDNA cox1 gene, 18S rRNA gene, and ITS1 region indicated the highest similarity of sarcocyst isolated from whale meat to Sarcocystis species that infect birds or carnivores as intermediate hosts; however, the species could not be identified. To our knowledge, this is the first report of T. gondii and Sarcocystis spp. being detected in same whale meat ingested by patients involved in a suspected food poisoning case in Japan.

Toxoplasma gondii Infection in the Eurasian Beaver (Castor fiber) in Switzerland: Seroprevalence, Genetic Characterization, and Clinicopathologic Relevance

Toxoplasma gondii is a coccidian parasite able to infect all warm-blooded animals and humans. Rodents are one of the most important intermediate hosts for T. gondii, but little is known about infection in beavers and its clinical relevance. Toxoplasmosis was not considered an important waterborne disease until recently, but with increased outbreaks in humans and animals this perspective has changed. Serum samples from 247 Eurasian beavers (Castor fiber) collected from 2002 to 2022 were tested for antibodies to T. gondii by a commercial ELISA. Antibodies to T. gondii were found in 113 (45.8%) beavers. Higher weight and proximity to urban areas were found to be significant predictors for seropositivity. Additionally, T. gondii DNA was detected in 23/41 brain tissue samples by real-time PCR. Histopathologic examination of brain sections revealed inflammatory changes in 26/40 beavers, mainly characterized by encephalitis, meningitis, choroid plexitis, or a combination of them. In six of these cases the lesions were in direct association with parasitic stages. With an adapted nested PCR multilocus sequence typing and in silico restriction fragment length polymorphism analysis approach, three different T. gondii genotypes were detected in brain samples: the clonal Type II strain (ToxoDB 1), a Type II variant (ToxoDB 3), and a novel genotype exhibiting both Type II and I alleles in a further animal. Toxoplasma gondii infections in beavers have epidemiologic and clinical significance. The high seroprevalence indicates frequent contact with the parasite, and as competent intermediate hosts they may play an important role, contributing to maintaining the life cycle of T. gondii in semiaquatic habitats. In addition, although most beavers appear to develop subclinical to chronic disease courses, acute and fatal outcomes, mainly characterized by encephalitis and generalized infection, do also occur.

Putting infection on the map: Using heatmaps to characterise within- and between-host distributions of trematode metacercariae

The location of parasites within individual hosts is often treated as a static trait, yet many parasite species can occur in multiple locations or organs within their hosts. Here, we apply distributional heat maps to study the within- and between-host infection patterns for four trematodes (Alaria marcianae, Cephalogonimus americanus, Echinostoma spp. and Ribeiroia ondatrae) within the amphibian hosts Pseudacris regilla and two species of Taricha. We developed heatmaps from 71 individual hosts from six locations in California, which illustrate stark differences among parasites both in their primary locations within amphibian hosts as well as their degree of location specificity. While metacercariae (i.e., cysts) of two parasites (C. americanus and A. marcianae) were relative generalists in habitat selection and often occurred throughout the host, two others (R. ondatrae and Echinostoma spp.) were highly localised to a specific organ or organ system. Comparing parasite distributions among these parasite taxa highlighted locations of overlap showing potential areas of interactions, such as the mandibular inner dermis region, chest and throat inner dermis and the tail reabsorption outer epidermis. Additionally, the within-host distribution of R. ondatrae differed between host species, with metacercariae aggregating in the anterior dermis areas of newts, compared with the posterior dermis area in frogs. The ability to measure fine-scale changes or alterations in parasite distributions has the potential to provide further insight about ecological questions concerning habitat preference, resource selection, host pathology and disease control.

Migratory Wild Birds as Potential Long-Distance Transmitters of Toxoplasma gondii Infection

Toxoplasma gondii is a worldwide distributed zoonotic protozoan capable of infecting a wide range of mammals (including humans) and birds as intermediate hosts. Migratory wild birds, through interconnecting countries along their flyways, can play a role in the spatial spread of T. gondii and could contribute to its sylvatic cycle. Additionally, hunted wild birds used for meat consumption could represent a further source of human infection. To determine the presence of T. gondii in wild birds, a total of 50 individuals belonging to the Anseriformes and Charadriiformes orders were sampled during the 2021–2022 hunting season in Northern Italy. Cardiac muscle samples of three Northern shovelers (Anas clypeata), two wild mallards (A. platyrhynchos), one Eurasian teal (A. crecca), and one Northern lapwing (Vanellus vanellus) were positive for the molecular detection of T. gondii based on a targeted amplification of the B1 gene. A 14% (7/50) overall positivity was observed in the sampled population. Results from this study suggest a moderate exposure of wild aquatic birds to T. gondii, highlighting the importance of a further characterization of T. gondii in its wildlife hosts.

Estimations of the number people with mental diseases associated with toxoplasmosis and identification of risk factors by continent

Strong evidence exists based on metanalysis of the relationship between toxoplasmosis and many psychiatric diseases: schizophrenia, bipolar disorder, and suicidal behavior. Herein, we estimate the number of cases based on the attributable fraction due to toxoplasmosis on these diseases. The population attributable fraction of mental disease associated with toxoplasmosis was 20,4% for schizophrenia; 27,3% for bipolar disorder; and 0,29% for suicidal behavior (self-harm). The lower and upper estimated number of people with mental disease associated with toxoplasmosis was 4'816.491 and 5'564.407 for schizophrenia; 6'348.946 and 7'510.118,82 for bipolar disorder; and 24.310 and 28.151 for self-harm; for a global total lower estimated number of 11'189.748 and global total upper estimated number of 13'102.678 people with mental disease associated with toxoplasmosis for the year 2019. According to the prediction through the Bayesian model of risk factors for toxoplasmosis associated with mental disease, these varied in importance geographically; thus, in Africa, the most important risk factor was water contamination and in the European region, the cooking conditions of meats. Toxoplasmosis and mental health should be a research priority given the enormous potential impact of reducing this parasite in the general population.

Is the incidence of congenital toxoplasmosis declining?

Prenatal infection with the protozoan parasite Toxoplasma gondii can cause congenital toxoplasmosis (CT), an often fatal or lifelong-disabling condition. Several studies of human populations have reported temporal decreases in seroprevalence, suggesting declining CT incidence. However, the consistency of this trend among diverse populations remains unclear, as does its implication for prenatal screening programmes, the major intervention against CT. Using temporally resolved data on the seroprevalence of T. gondii in various countries, we discuss how the parasite's changing epidemiology may affect trends in CT incidence in varying and counterintuitive ways. We argue that parasite stage-specific serology could be helpful for understanding underlying causes of secular changes in seroprevalence. Furthermore, we highlight the importance of updating cost-effectiveness estimates of screening programmes, accounting for neuropsychiatric sequelae.

Terrestrial runoff influences the transport and contamination levels of Toxoplasma gondii in marine organisms

There is a growing concern regarding the potential adverse impact of Toxoplasma gondii contamination of the marine environment on marine wildlife and public health. Terrestrial runoff is a significant route for dissemination of T. gondii oocysts from land to sea. Yet, the influence of terrestrial runoff on T. gondii prevalence in marine animals in China is largely unknown. To address this concern, we examined the presence of T. gondii in marine oysters Crassostrea spp., rockfish Sebastes schlegelii (S. schlegelii), fat greenling fish Hexagrammos otakii (H. otakii), and Asian paddle crab Charybdis japonica (C. japonica) using a PCR assay targeting T. gondii B1 gene. A total of 1920 samples were randomly collected, in Jan-Dec 2020, from terrestrial runoff areas (TRA, TRB, and TRC) and non-terrestrial runoff area (Grape bay) in Weihai, China. T. gondii prevalence in TRB and TRC was 6.04 % and 5.83 %, respectively, which was higher than 2.29 % detected in the non-terrestrial runoff area. The highest prevalence was detected in Crassostrea spp., and a correlation was observed between T. gondii prevalence and weight of Crassostrea spp. The temperature, but not precipitation, significantly correlated with T. gondii prevalence. Understanding the fate of T. gondii delivered to oceans by terrestrial runoff is critical for predicting future disease risks for marine wildlife and humans.

Exploiting the Macrophage Production of IL-12 in Improvement of Vaccine Development against Toxoplasma gondii and Neospora caninum Infections

Toxoplasmosis and neosporosis are major protozoan diseases of global distribution. Toxoplasma gondii is the cause of toxoplasmosis, which affects almost all warm-blooded animals, including humans, while Neospora caninum induces neosporosis in many animal species, especially cattle. The current defective situation with control measures is hindering all efforts to overcome the health hazards and economic losses of toxoplasmosis and neosporosis. Adequate understanding of host-parasite interactions and host strategies to combat such infections can be exploited in establishing potent control measures, including vaccine development. Macrophages are the first defense line of innate immunity, which is responsible for the successful elimination of T.gondii or N. caninum. This action is exerted via the immunoregulatory interleukin-12 (IL-12), which orchestrates the production of interferon gamma (IFN-γ) from various immune cells. Cellular immune response and IFN-γ production is the hallmark for successful vaccine candidates against both T. gondii and N. caninum. However, the discovery of potential vaccine candidates is a highly laborious, time-consuming and expensive procedure. In this review, we will try to exploit previous knowledge and our research experience to establish an efficient immunological approach for exploring potential vaccine candidates against T. gondii and N. caninum. Our previous studies on vaccine development against both T. gondii and N. caninum revealed a strong association between the successful and potential vaccine antigens and their ability to promote the macrophage secretion of IL-12 using a murine model. This phenomenon was emphasized using different recombinant antigens, parasites, and experimental approaches. Upon these data and research trials, IL-12 production from murine macrophages can be used as an initial predictor for judgment of vaccine efficacy before further evaluation in time-consuming and laborious in vivo experiments. However, more studies and research are required to conceptualize this immunological approach.

Prevalence and genotype of Toxoplasma gondii in stranded Hawaiian cetaceans

Toxoplasma gondii is a significant threat to endangered Hawaiian wildlife including birds and marine mammals. To estimate the prevalence of T. gondii in stranded cetaceans from 1997 to 2021 in Hawai'i, we tested tissues from 37 stranded spinner dolphins Stenella longirostris and 51 stranded individuals that represented 18 other cetacean species. DNA from cetacean tissue extracts were screened using a nested polymerase chain reaction (PCR) assay targeting the Toxoplasmatinae internal transcribed spacer 1 of the nuclear ribosomal DNA. A positive result was obtained in 9 tissues examined for each of 2 spinner dolphins out of 525 tissue samples analyzed by PCR. The PCR-positive spinner dolphins had disseminated acute toxoplasmosis with necrosis, inflammation, and intralesional protozoal cysts and tachyzoites in multiple organs. Discrete positive immunostaining for T. gondii was observed in all tissues tested including the adrenal gland, brain, liver, and lung. Both positive spinner dolphins were negative for cetacean morbillivirus. The T. gondii genotyping was performed by restriction fragment length polymorphism (PCR-RFLP) based on 10 genetic markers. The PCR-RFLP analysis revealed the T. gondii belonged to PCR-RFLP-ToxoDB genotype #24, previously detected in wild pig Sus scrofa in O'ahu, bobcats Lynx rufus from Mississippi, USA, and chickens Gallus gallus from Costa Rica and Brazil. These cases represent the first report of this genotype in aquatic mammals and the second and third reports of fatal disseminated T. gondii infection in stranded spinner dolphins from Hawai'i. Nearshore species, like spinner dolphins, may be at increased risk of mortality from this parasite in marine coastal waterways via sewage systems, storm water drainage, and freshwater runoff.

Detection of Toxoplasma gondii oocysts in soil and risk mapping in an island environment in the Northeast of Brazil

Toxoplasmosis is an emerging and re-emerging infectious disease that can be transmitted through a contaminated environment. Environmental contamination is an emergency health issue, and determining its occurrence is fundamental to a One Health approach. In this study, we addressed the extent of environmental contamination and viability of Toxoplasma gondii oocysts in soil in different environments on Fernando de Noronha Island, Brazil. In addition, we performed species distribution modelling to predict the environmental suitability for coccidia persistence in the studied area. Soil samples were collected in 14 neighbourhoods of the Island and in the four main squares, creating a total of 95 soil samples (five samples per site). The samples were analyzed by the polymerase chain reaction (PCR) technique for the presence of the 18S ribosomal DNA gene of Apicomplexan protozoa, followed by genetic sequencing. We obtained 4.2% (4/95) positive soil samples with 100% similarity for T. gondii sequences. Two out of four positive sites on PCR showed viability of T. gondii oocysts through the mouse bioassay technique. As a result of the application of the species distribution modelling, environmental adequacy for the coccidia was observed throughout the Island. The results confirm the contamination of the soil in this insular environment by T. gondii oocysts and the environmental suitability by modelling application. These findings are an alert for the possibility of infection in animals and humans by contaminated soil, and for contamination of the maritime environment in addition to water resources for consumption by the local population.

Toxoplasma gondii Genetic Diversity in Mediterranean Dolphins

Toxoplasma gondii constitutes a major zoonotic agent but also has been frequently identified as an important cause of clinical disease (e.g., abortion, pneumonia, encephalitis) in wildlife; specifically, T. gondii has been associated with neurological disease in cetaceans. This study investigated the genetic diversity of T. gondii strains involved in infections in dolphins found stranded in the Mediterranean coastlines of Italy. Tissue samples from 16 dolphins (Stenella coeruleoalba and Tursiops truncatus species) positive for T. gondii-DNA presence by PCR were examined by histology and subjected to further genetic characterization of strains detected by PCR-RFLP and multilocus PCR-sequencing assays. According to fully genotyped samples, the genotypes ToxoDB#3 (67%) and #2 (22%) were detected, the latter being reported for the first time in cetaceans, along with a mixed infection (11%). Subtyping by PCR-seq procedures provided evidence of common point mutations in strains from southwestern Europe. Despite evidence of T. gondii as a cause of neurological disease in dolphins, sources of infections are difficult to identify since they are long-living animals and some species have vast migration areas with multiple chances of infection. Finally, the genetic diversity of T. gondii found in the dolphins studied in the Mediterranean coastlines of Italy reflects the main genotypes circulating inland in the European continent.

Toxoplasma gondii Infection in Marine Animal Species, as a Potential Source of Food Contamination: A Systematic Review and Meta-Analysis

PURPOSE

Many marine animals are infected and susceptible to toxoplasmosis, which is considered as a potential transmission source of Toxoplasma gondii to other hosts, especially humans. The current systematic review and meta-analysis aimed to determine the prevalence of T. gondii infection among sea animal species worldwide and highlight the existing gaps.

METHODS

Data collection was systematically done through searching databases, including PubMed, Science Direct, Google Scholar, Scopus, and Web of Science from 1997 to July 2020.

RESULTS

Our search strategy resulted in the retrieval of 55 eligible studies reporting the prevalence of marine T. gondii infection. The highest prevalence belonged to mustelids (sea otter) with 54.8% (95% CI 34.21-74.57) and cetaceans (whale, dolphin, and porpoise) with 30.92% (95% CI 17.85-45.76). The microscopic agglutination test (MAT) with 41 records and indirect immunofluorescence assay (IFA) with 30 records were the most applied diagnostic techniques for T. gondii detection in marine species.

CONCLUSIONS

Our results indicated the geographic distribution and spectrum of infected marine species with T. gondii in different parts of the world. The spread of T. gondii among marine animals can affect the health of humans and other animals; in addition, it is possible that marine mammals act as sentinels of environmental contamination, especially the parasites by consuming water or prey species.

Development of a droplet digital polymerase chain reaction tool for the detection of Toxoplasma gondii in meat samples

Toxoplasmosis is a zoonotic disease caused by the protozoan parasite Toxoplasma gondii. Infection in humans has usually been related to the consumption of raw, undercooked or cured meat. The aim of this study was to develop a droplet digital polymerase chain reaction (ddPCR)-based assay for the detection and quantification of T. gondii in meat samples. To optimize the ddPCR, T.gondii reference DNA aliquots at five known concentrations: 8000 cg/µl, 800 cg/µl, 80 cg/µl, 8 cg/µl were used. Moreover, results obtained by ddPCR and quantitative PCR (qPCR) were compared using 80 known samples (40 positive and 40 negative), as well as 171 unknown diaphragm tissue samples collected at slaughterhouses. The ddPCR showed a sensitivity of 97.5% and a specificity of 100%, with a detection limit of 8 genomic copy/µl of T. gondii. A nearly perfect agreement (κ = 0.85) was found between results obtained by ddPCR and qPCR for both positive and negative known samples analysed. On the 171 diaphragm tissue samples from field, 7.6% resulted positive by ddPCR and only 1.2% by qPCR. Therefore, this innovative method could be very useful for the detection of T. gondii in meat samples, aiming to prevent human infections.

A systematic review, meta-analysis and meta-regression of the global prevalence of Toxoplasma gondii infection in wild marine mammals and associations with epidemiological variables

Toxoplasma gondii infection in wild marine mammals is a growing problem and is associated with adverse impacts on marine animal health and public health. This systematic review, meta-analysis and meta-regression estimates the global prevalence of T. gondii infection in wild marine mammals and analyzes the association between T. gondii infection and epidemiological variables. PubMed, Web of Science, Science Direct, China National Knowledge Infrastructure, and Wanfang Data databases were searched until 30 May 2021. Eighty-four studies (n = 14,931 wild marine mammals from 15 families) were identified from literature. The overall pooled prevalence of T. gondii infection was 22.44% (3,848/14,931; 95% confidence interval (CI): 17.29% - 8.04%). The prevalence in adult animals 21.88% (798/3119; 95% CI: 13.40 -31.59) was higher than in the younger age groups. North America had a higher prevalence 29.92% (2756/9243; 95% CI: 21.77 - 38.77) compared with other continents. At the country level, the highest prevalence was found in Spain 44.26% (19/88; 95%CI: 5.21 - 88.54). Regarding climatic variables, the highest prevalence was found in areas with a mean annual temperature >20°C 36.28% (171/562; 95% CI: 6.36 - 73.61) and areas with an annual precipitation >800 mm 26.92% (1341/5042; 95% CI: 18.20 - 36.59). The subgroup and meta-regression analyses showed that study-level covariates, including age, country, continent, and mean temperature, partly explained the between-study heterogeneity. Further studies are needed to investigate the source of terrestrial to aquatic dissemination of T. gondii oocysts, the fate of this parasite in marine habitat and its effects on wild marine mammals. This article is protected by copyright. All rights reserved.

Seroprevalence of Toxoplasma gondii in Pinnipeds under Human Care and in Wild Pinnipeds

Toxoplasma gondii infection has been reported in numerous species of marine mammals, some of them with fatal consequences. A serosurvey for T. gondii infection was conducted in pinnipeds from an oceanographic park in Portugal (n = 60); stranded pinnipeds on the Portuguese coast (n = 10); and pinnipeds captured in Lorenzensplate, Germany (n = 99). Sera from 169 pinnipeds were tested for the presence of antibodies to T. gondii by the modified agglutination test with a cut-off titre of 25. An overall seroprevalence of 8.9% (95% confidence interval: 5.1–14.2) was observed. Antibody titres of 25, 50, 100, 1600 and ≥3200 were found in five (33.3%), two (13.3%), five (33.3%), one (6.7%) and two (13.3%) animals, respectively. Pinnipeds under human care had a seroprevalence of 20.0% (12/60), in contrast to 2.8% (3/109) in wild pinnipeds (p < 0.001). General results suggest a low exposure of wild pinnipeds to T. gondii, while the seroprevalence found in pinnipeds under human care highlights the importance of carrying out further studies. This is the first serological survey of T. gondii in pinnipeds in Portugal and the first infection report in South African fur seal (Arctocephalus pusillus pusillus).

Evidence of Hearing Loss and Unrelated Toxoplasmosis in a Free-Ranging Harbour Porpoise (Phocoena phocoena)

Simple Summary

Evidence of hearing impairment was identified in a female harbour porpoise (Phocoena phocoena) on the basis of inner ear analysis. The animal live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. Ultrastructural examination of the inner ear revealed evidence of sensory cell loss, which is compatible with noise exposure. In addition, histopathology also revealed multifocal necrotising protozoal encephalitis. A diagnosis of toxoplasmosis was confirmed by positive staining of tissue with anti-Toxoplasma gondii antibodies; however, T. gondii tachyzoites were not observed histologically in any of the examined tissues. This is the first case of presumptive noise-induced hearing loss and demonstration of T. gondii cysts in the brain of a free-ranging harbour porpoise from the North Sea.

Abstract

Evidence of hearing impairment was identified in a harbour porpoise (Phocoena phocoena) on the basis of scanning electron microscopy. In addition, based on histopathology and immunohistochemistry, there were signs of unrelated cerebral toxoplasmosis. The six-year old individual live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. The most significant gross lesion was multifocal necrosis and haemorrhage of the cerebrum. Histopathology of the brain revealed extensive necrosis and haemorrhage in the cerebrum with multifocal accumulations of degenerated neutrophils, lymphocytes and macrophages, and perivascular lymphocytic cuffing. The diagnosis of cerebral toxoplasmosis was confirmed by positive staining of protozoa with anti-Toxoplasma gondii antibodies. Tachyzoites were not observed histologically in any of the examined tissues. Ultrastructural evaluation of the inner ear revealed evidence of scattered loss of outer hair cells in a 290 µm long segment of the apical turn of the cochlea, and in a focal region of ~ 1.5 mm from the apex of the cochlea, which was compatible with noise-induced hearing loss. This is the first case of concurrent presumptive noise-induced hearing loss and toxoplasmosis in a free-ranging harbour porpoise from the North Sea.

Exposure of pelagic seabirds to Toxoplasma gondii in the Western Indian Ocean points to an open sea dispersal of this terrestrial parasite

Toxoplasma gondii is a protozoan parasite that uses felids as definitive hosts and warm-blooded animals as intermediate hosts. While the dispersal of T. gondii infectious oocysts from land to coastal waters has been well documented, transmission routes to pelagic species remain puzzling. We used the modified agglutination test (MAT titre ≥ 10) to detect antibodies against T. gondii in sera collected from 1014 pelagic seabirds belonging to 10 species. Sampling was carried out on eight islands of the Western Indian Ocean: Reunion and Juan de Nova (colonized by cats), Cousin, Cousine, Aride, Bird, Europa and Tromelin islands (cat-free). Antibodies against T. gondii were found in all islands and all species but the great frigatebird. The overall seroprevalence was 16.8% [95% CI: 14.5%-19.1%] but significantly varied according to species, islands and age-classes. The low antibody levels (MAT titres = 10 or 25) detected in one shearwater and three red-footed booby chicks most likely resulted from maternal antibody transfer. In adults, exposure to soils contaminated by locally deposited oocysts may explain the detection of antibodies in both wedge-tailed shearwaters on Reunion Island and sooty terns on Juan de Nova. However, 144 adults breeding on cat-free islands also tested positive. In the Seychelles, there was a significant decrease in T. gondii prevalence associated with greater distances to cat populations for species that sometimes rest on the shore, i.e. terns and noddies. This suggests that oocysts carried by marine currents could be deposited on shore tens of kilometres from their initial deposition point and that the number of deposited oocysts decreases with distance from the nearest cat population. The consumption of fishes from the families Mullidae, Carangidae, Clupeidae and Engraulidae, previously described as T. gondii oocyst-carriers (i.e. paratenic hosts), could also explain the exposure of terns, noddies, boobies and tropicbirds to T. gondii. Our detection of antibodies against T. gondii in seabirds that fish in the high sea, have no contact with locally contaminated soils but frequent the shores and/or consume paratenic hosts supports the hypothesis of an open-sea dispersal of T. gondii oocysts by oceanic currents and/or fish.

Potential Risk of Three Zoonotic Protozoa (Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii) Transmission from Fish Consumption

In recent decades, worldwide fish consumption has increased notably worldwide. Despite the health benefits of fish consumption, it also can suppose a risk because of fishborne diseases, including parasitic infections. Global changes are leading to the emergence of parasites in new locations and to the appearance of new sources of transmission. That is the case of the zoonotic protozoa Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii; all of them reach aquatic environments and have been found in shellfish. Similarly, these protozoa can be present in other aquatic animals, such as fish. The present review gives an overview on these three zoonotic protozoa in order to understand their potential presence in fish and to comprehensively revise all the evidences of fish as a new potential source of Cryptosporidium spp., Giardia duodenalis, and Toxoplasma gondii transmission. All of them have been found in both marine and freshwater fishes. Until now, it has not been possible to demonstrate that fish are natural hosts for these protozoa; otherwise, they would merely act as mechanical transporters. Nevertheless, even if fish only accumulate and transport these protozoa, they could be a "new" source of infection for people.