key: cord-0025871-cgsenbk1
authors: Ahmadpour, Ehsan; Rahimi, Mohamad Taghi; Ghojoghi, Altin; Rezaei, Fatemeh; Hatam-Nahavandi, Kareem; Oliveira, Sónia M. R.; de Lourdes Pereira, Maria; Majidiani, Hamidreza; Siyadatpanah, Abolghasem; Elhamirad, Samira; Cong, Wei; Pagheh, Abdol Sattar
title: Toxoplasma gondii Infection in Marine Animal Species, as a Potential Source of Food Contamination: A Systematic Review and Meta-Analysis
date: 2022-01-17
journal: Acta Parasitol
DOI: 10.1007/s11686-021-00507-z
sha: bf9f4842801d6ac090dbcdce4f6b1ee6df00991e
doc_id: 25871
cord_uid: cgsenbk1

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. GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11686-021-00507-z.

Marine species constitute a very diverse group of animals with global distribution, mostly along coastal regions or habitat [1] . The human population density in coastal areas greatly increased during the recent decades and zoonotic pathogens can be transmitted to humans directly or indirectly from marine animals [2] . Thus, the health of marine mammals can substantially influence human's well-being. Toxoplasmosis, caused by the intracellular protozoan Toxoplasma gondii, is a zoonotic infection with felids as definitive hosts, and a wide range of homoeothermic vertebrates as intermediate hosts [3, 4] . Pregnant women and immunocompromised patients are at a higher risk for developing the clinical disease with harsh outcomes, including congenital toxoplasmosis (hydrocephalus, chorioretinitis, and cerebral calcifications) and lifethreatening encephalitis [5] [6] [7] . Understanding T. gondii transmission routes in wild, free-ranging marine mammals is problematic. There are three possible routes by which marine animals could become infected with T. gondii, including: ingestion of oocysts, ingestion of bradyzoites in tissue cysts of other intermediate hosts or vertically. Oocysts are shed via cat feces into the environment, which can readily infect several animal species [8, 9] . Small T. gondii oocysts show remarkable resistance to common disinfectants and remain alive in moist surroundings, even when exposed to a vast range of salinity and temperature conditions. This environmental tolerance leads to in fast and extensive dispersal of infection, particularly following heavy rain falls. The runoff originated from rainfalls alongside wastewater outfalls being likely contaminated with stray/feral cat fecal material make a huge depot of infective oocysts, which are usually discharged into a water body, i.e., sea and ocean, posing potential risk of T. gondii infection in those species dwelling in marine habitats [10] . In another way, marine animals acquired infection through ingestion of T. gondii protozoal cyst containing numerous bradyzoites. In areas where definitive hosts are rare and the viability of oocysts are likely limited due to freezing conditions, such as the Canadian Arctic, this could explain how animals are exposed to T. gondii. A number of investigators have pointed out that oocysts and bradyzoites of T. gondii are concentrated by oysters, clams and mussels during filter-feeding activity. It is noteworthy that the role of vertical transmission of toxoplasmosis in marine animals is unknown [9] . These are highly promising findings, but the precise mode of transmission is still open to question. Experimentally, oocyst sporulation occurs in seawater, remaining infective for animals for 6-24 months, depending on the temperature [11, 12] .

During the last decades, a number of studies have reported T. gondii infection in marine animals, such as cetaceans, pinnipeds, sirenians, and sea otters (Enhydra lutris) [13] [14] [15] [16] . Disseminated clinical disease has also been documented in adult or sometimes neonate marine mammals from Europe, USA, and Australia [17] [18] [19] , with some degree of morbidity observed, for example, in the sea otters [13, 20, 21] and in the Pacific harbor seal (Phoca vitulina richardsi) [22, 23] . Furthermore, it seems that some species have been threatened and endangered in part due to toxoplasmosis [3, 24] .

The increasing amount of anthropogenic toxicants discharged into the marine environment, as well as morbillivirus infection, can suppress the immunity of marine mammals and give rise to clinical toxoplasmosis susceptibility, yet in others cases, no links to concurrent disease have been identified [25, 26] . Since T. gondii is a pronounced hallmark of aquatic pollution and marine species are superb sentinel animals in marine life [27] [28] [29] , it would be beneficial to assess the status of T. gondii infection in these animals. Thus, the current systematic review and meta-analysis aimed to investigate the prevalence of T. gondii infection among marine animal species worldwide and highlight the existing gaps.

This study was prepared and performed in accordance with the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) statement [30] . Data were systematically searched and collected from English language databases including PubMed, Science Direct, Google Scholar, Scopus, ISI Web of Science, published from inception to 1 January, 2020 by two investigators (FR and ASP).

The search process was performed using the following keywords and medical subject headings (MeSH) terms: "Toxoplasma gondii", "Toxoplasmosis", "T. gondii" in combination with "fishes", "marine mammals"; "oyster", "Shellfish", "mussels", "dolphin", "shark", "crab", "seal", "sea lion", "whale", "sea otter", "porpoise", "shrimp", "Manatees", "Walruses", "Eel", "crayfish", and "turtle". To avoid missing of any paper, the reference list of relevant papers was screened manually.

For the first screening, the two independent authors (ASP and FR) surveyed the title and the abstract of all papers returned from the search process. To ensure the eligibility for inclusion to the systematic review, full texts of papers were also reviewed by investigators (ASP and FR), and any disagreement on articles selected was resolved.

Selected articles were assessed according to a checklist used in previous studies [31] . This checklist was based on contents of the strengthening the reporting of observational studies in epidemiology (STROBE) checklist containing questions about various methodological aspects such as type of study, sample size, study population, data collection approaches and tools, sampling methods, variables estimation status, methodology, research objectives and demonstration of results according to the objectives [32] . For each question, a score was attributed and articles with a score of at least seven were selected articles. In addition, any disagreements with selected papers were reviewed by another author.

Papers were included in the meta-analysis with the following criteria: (1) original articles; (2) studies in English language;

(2) articles available in full-text; (3) studies that evaluated the prevalence of T. gondii infection in marine animals. On the other hand, the exclusion criteria entailed: case reports, review articles, letter to the editor, unclear or not technically acceptable diagnostic criteria, insufficient information, congress articles, as well as those with unavailable full-text. After reviewing all articles, papers without sufficient information and that did not obtain the minimum quality score were excluded.

In this study, a forest plot was used to visualize the summarized results and heterogeneity among the included studies. The size of every square indicated the weight of every study as well as crossed lines presented confidence intervals, CI. To assess heterogeneity index, Cochran's Q test and I 2 statistics were applied. Additionally, a funnel plot was designed to determine the small study effects and their publication bias, based on Egger's regression test. The meta-analysis was conducted using Stats Direct statistical software (http:// www. stats direct. com). A P value less than 0.05 was considered statistically significant. Additional meta-analysis was performed based on the type of host, location and diagnostic method.

A total of 5175 papers were analyzed by exploration of PubMed, Science Direct, Scopus, Google Scholar, and ISI Web of Science databases, and finally 55 records were found to be eligible for the current systematic review and metaanalysis. The searching and study selection procedures are illustrated in Fig. 1 . Based on Continent, the highest number of investigations was from Europe (30 studies) with a total prevalence of 12.99%, and marine mustelids were the most infected group with 53.12%. It is also worth noting that 24 studies from North America were included in this systematic review, indicating a total prevalence of 21.15%, and an exceptionally high infection rate among cetaceans was observed in this continent (80.85%). In Asian countries, a low prevalence rate of 1.78% was reported and the pinnipeds were the most infected group with 29.2%. In South America, Fig. 1 Flowchart describing the study design process a pooled prevalence of 8.03% was reported with the highest infection in cetaceans (30.35%). In Oceania, the pooled prevalence was 17.73% and cetaceans were the most infected species (26.12%). In addition, the pooled prevalence rate in Antarctica was 39.21% in pinnipeds. On the other hand, no reports were found for the North Pole and the African continent (Fig. 2) .

According to Table 1 , T. gondii infection was detected in dolphins (45 entries), whales (29 entries), seals (31 entries), sea lions (5 entries), sea otters (10 entries), porpoise (3 entries), oysters/mussels/shellfish (11 entries), fishes (4 entries), shrimp (2 entries), manatees (2 entries), walruses, eel and crayfish (single record for each) using serological and/or molecular techniques. Most reports were from the USA and Brazil with 24 records for each country, followed by Scotland (15 records), Italy (13 records), China (10 records), Spain (9 records), Canada and United Kingdom (8 records for each), Mexico (5 records), Norway and Russia (4 records for each), New Zealand (3 records), Japan (2 records) as well as single records from Iran, Turkey, Portugal, Netherlands, Peru, Australia and Solomon Islands. Altogether, eight serological methods were employed to determine T. gondii infection among marine animals. These include the modified agglutination test (MAT) as the most used technique (41 records), followed by immunofluorescence antibody test (IFA) (30 records) and immunohistochemistry (IHC) (21 records). Moreover, 17 entries used conventional polymerase chain reaction (PCR), being this the most used molecular technique, followed by nested-PCR (7 records) and quantitative PCR (qPCR) (4 records). Subgroup analysis ( Table 2) showed that most studies were focused on cetaceans (whale, dolphin and porpoise) (36 studies), whereas the highest prevalence rate of T. gondii infection belonged to marine mustelids (sea otter, 10 studies) with 54.8% (95% CI 34.21-74.57%). Pooled proportion of T. gondii infection in dolphin species was of 51.07%. According to Egger's test, the prevalence rates in cetaceans (P value = 0.0489) and pinnipeds (P value = 0.0004) were statistically significant.

The present systematic review and meta-analysis aimed to determine the prevalence rate of T. gondii infection worldwide. The obtained data were categorized based on the species of marine animals, continents, and diagnostic techniques. Among marine animals, the prevalence of T. gondii infection was higher in the population of sea otters (54.8%). In a study, Miller et al. [33] suggested that coastal freshwater runoff is a risk factor for toxoplasmosis in southern sea otters Esmerini et al. [82] (Enhydra lutris nereis) in southern California. Furthermore, it has been shown that exposure to T. gondii among sea otters was highly influenced by individual animal prey choice and habitat use [34] . Toxoplasmosis had considerable morbidity and mortality rates in the sea otter [35] . T. gondii encephalitis in sea otters causes high mortality rate and is responsible for slow population recovery, particularly for the endangered Southern sea otter [27] . In addition, cetaceans were the most infected animals in North America, South America, and Oceania.

Modified agglutination test (MAT) was the most applied diagnostic assay for T. gondii detection in marine animals. This technique is widely employed in research of toxoplasmosis in humans and in all species of animals because it is considered as a rapid and simple approach without the requirement for special facilities [36] . Molecular methods, particularly polymerase chain reaction (PCR) and nested PCR, were used in marine animals usually as a food source for humans like fishes, shrimp, oysters, and crayfish, amongst others. Some studies indicate that consumption of contaminated raw shellfish and mussels can be considered a IHC immunohistochemistry, IFA immunofluorescence antibody test, DAT direct agglutination test, LAT latex agglutination test, HRM real time PCR/high-resolution melting analysis, IHAT indirect hemagglutination test significant health danger due to their ability to infect a wide variety of hosts such as other marine animals and humans. However, they are particularly at risk for T. gondii infection, and therefore, they can be considered a bioindicator for monitoring waterborne pathogens [37, 38] . The high prevalence rate of T. gondii in the examined marine species may indicate that the nearby terrestrial environment in the studied area was heavily contaminated by T. gondii, and consequently, contamination was transferred to the aquatic environment. Furthermore, marine hosts may associate with T. gondii infection as paratenic hosts in some area [39] . Hence, contamination of marine animal species is an important bioindicator for contamination of aquatic environments. Each cat, as final host for T. gondii, shed over 3-810 million oocysts. The sporulation of the oocysts takes 1-5 days, and they can remain infective in the soil for up to 18 months [40] . Furthermore, experiments showed that oocysts of T. gondii can sporulate in sea water and survive at 4 °C for 24 months and then infect mice [12] . One important factor in infected hosts is the strain of the parasite, which plays a major role in the toxoplasmosis prognosis. So far, the genotypes T. gondii were classified as classical types I, II, III, mix/recombinant atypical, and African lineages [41] . Comparison between T. gondii genotypes from the marine and terrestrial environments would help clarify routs and mechanisms of land-sea transmission. Type I strains, which are highly virulent and pathogenic, can lead to acquired ocular toxoplasmosis in individuals with disseminated congenital form of T. gondii [42, 43] . Aksoy et al. [37] reported T. gondii type 1 infection in Mytilus galloprovincialis (Mediterranean mussel), one of the most consumed shellfish in Turkey. The authors suggested that these types of contaminated seafood may be involved in the transmission of the parasite to humans and other hosts. Type II T. gondii strains are the vast majority of human infections and have a worldwide distribution. Type II strains are causative agents for numerous asymptomatic toxoplasmosis cases in Europe, it can be pathogenic for two important categories of subjects, namely immature fetuses and immunocompromised individuals [43] . On the basis of a previous study, Dubey et al. [44] showed Type II T. gondii from a striped dolphin (Stenella coeruleoalba) in Costa Rica. It is noteworthy that Type III T. gondii in mice are classified as avirulent strain. Study carried out by Hancock et al. [45] showed the first report of type III T. gondii in a Hawaiian monk seal. This genotype was determined to be restriction fragment length polymorphisms (RFLP) of the SAG2 gene. On the other hand, it has previously been shown that Type X strains of T. gondii are virulent for southern sea otters from coastal California [27] . Additionally, one interesting study has demonstrated Type X strains of T. gondii in canids, coastal-dwelling felids, nearshore-dwelling sea otters, and marine bivalve. It is assumed that contaminated runoff to feline faecal rapidly reaches sea from lands, and otters could be infected with T. gondii via the consumption of filter-feeding marine invertebrates [46] . The prevalence rate of marine T. gondii infection in various regions of the world was very different, and ranged from 0 to 100%. These differences may originate from different types of marine animals, sample sizes, and diagnostic approaches in the reviewed studies. Regarding continents, North America showed the highest T. gondii infection in marine animals that may suggest the level of fecal contamination of the soil and water reservoirs. Our analysis also showed that there is either no available data (Africa) or very limited literature (Antarctica, Oceania, and South America) on the prevalence of T. gondii infection in significant parts of the globe. Therefore, it is essential to conduct more studies to determine the putative role of T. gondii on marine species. The main limitation expressed in the included studies regarding prevalence of T. gondii infection in marine animal species was related to the use of different diagnostic methods with varying sensitivity and specificity due to their great impact on the results. The use of an accurate and reliable technique can help to correctly interpret the results of T. gondii prevalence in marine species in different parts of the world.

The results of current study indicated that the global prevalence rate of T. gondii infection was high in marine animals. It is well demonstrated that T. gondii parasite has a very successful adaptation in aquatic environments. Despite the worldwide range and broad marine animals host record of T. gondii infection, there was no evidence regarding toxoplasmosis in these animals in most parts of the world. Therefore, it is necessary to develop surveillance for detection of T. gondii in aquatic animals in different regions with appropriate molecular and serological techniques. It is also important to know the ecology of this parasite in aquatic environment to design appropriate strategies for monitoring, controlling, and prevention of the transmission of toxoplasmosis to humans or other hosts.

The online version contains supplementary material available at https:// doi. org/ 10. 1007/ s11686-021-00507-z.

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