Molecular characterization of Cryptosporidium molnari reveals a distinct piscine clade

First Epidemiological Report on the Prevalence and Associated Risk Factors of Cryptosporidium spp. in Farmed Marine and Wild Freshwater Fish in Central and Eastern of Algeria

PURPOSE

The present study aimed to estimate the prevalence and molecular characterization of Cryptosporidium spp. in six different fish species both from marine and freshwater environments.

METHODS

During a period of 2 years (2018-2020), a total of 415 fecal samples and 565 intestinal scrapings were collected in seven provinces from the central and eastern Algeria. From those, 860 fish belonged to six different species, two of which are cultured marine and four are wild freshwater fish. All samples were screened for Cryptosporidium spp. presence using molecular techniques. Nested PCR approach was performed to amplify partial sequences of the small subunit ribosomal RNA (SSU rRNA) and 60-kDa glycoprotein (GP60) genes for Cryptosporidium genotyping and subtyping. Detailed statistical analysis was performed to assess the prevalence variation of Cryptosporidium infection according to different risk factors.

RESULTS

Nested PCR analysis of SSU gene revealed 173 Cryptosporidium positive fish, giving an overall prevalence of 20.11% (17.5-23.0). Cryptosporidium spp. was detected in 8.93% (42/470) of cultured marine fish and 33.58% (131/390) of wild freshwater fish. Overall, the prevalence was affected by all studied risk factors, except the gender. Molecular characterization and subtyping of Cryptosporidium isolates showed occurrence of IIaA16G2R1 and IIaA17G2R1 subtypes of C. parvum in the fish species Sparus aurata.

CONCLUSION

The present study provides the first epidemiological data on the prevalence and associated risk factors of Cryptosporidium spp. in farmed marine and wild freshwater fish and the first molecular data on the occurrence of zoonotic C. parvum in fish from North Africa (Algeria).

Molecular Characterization of Cryptosporidium spp. in Cultivated and Wild Marine Fishes from Western Mediterranean with the First Detection of Zoonotic Cryptosporidium ubiquitum

Fish not only harbor host-specific species/genotypes of Cryptosporidium, but also species like zoonotic C. parvum or anthroponotic C. hominis, which can pose a risk for fish consumers. This study aims to investigate fish cryptosporidiosis in an important aquaculture and fishery area of the Western Mediterranean (Comunidad Valenciana, Spain). We analyzed 404 specimens belonging to the following three groups: cultivated fish (N = 147), wild synanthropic fish (N = 147) and wild fish from extractive fisheries (N = 110). Nested PCR targeting the 18S rRNA gene, followed by sequencing and phylogenetic analysis, were performed. Positive isolates were also amplified at the actin gene locus. An overall prevalence of 4.2% was detected, with the highest prevalence in the synanthropic group (6.1%). C. molnari was identified in thirteen specimens from seven different host species. Zoonotic C. ubiquitum was detected in two European sea bass (Dicentrarchus labrax). One isolate similar to C. scophthalmi was detected in a cultivated meagre (Argyrosomus regius), and one isolate, highly divergent from all the Cryptosporidium species/genotypes described, was identified from a synanthropic round sardinella (Sardinella aurita). This study contributes to increasing the molecular data on fish cryptosporidiosis, expanding the range of known hosts for C. molnari and identifying, for the first time, zoonotic C. ubiquitum in edible marine fishes, pointing out a potential health risk.

Prevalence and Molecular Epidemiology of Cryptosporidium Infection in Clarias gariepinus Fish in Egypt

PURPOSE

This study investigated the prevalence and molecular detection of Cryptosporidium spp. in catfish (Clarias gariepinus).

METHODS

A total of 300 Carias gariepinus fish were collected from two freshwater sources: the Nile River (180) and drainage canals (120). The stomach and intestine epithelium of each individual fish sample were screened by modified Ziehl-Neelsen (mZN) staining technique for the detection of Cryptosporidium oocysts followed by the serological survey for detection of Cryptosporidium antibodies using Enzyme-Linked Immunosorbent Assay (ELISA) and molecular characterization using complemented DNA polymerase chain reaction (cPCR).

RESULTS

ELISA showed higher prevalence of 69.3% than that prevalence obtained by mZN, 64% for the total examined Clarias gariepinus fish. Also, higher prevalence of Cryptosporidium infection 65.5% and 75.8% obtained by ELISA than 61.1% and 68.3% by mZN, in both fish groups from Nile River and Drainage canal, respectively. PCR analysis revealed the expected positive bands at 1056 bp. DNA sequencing and phylogenetic analysis proved that the positive-PCR Cryptosporidium isolate identified in the present study was Cryptosporidium molnari.

CONCLUSION

Freshwater fishes (Clarias gariepinus) are subjected to a high infection rate with Cryptosporidium spp.; the drainage canals obtained fishes showed higher prevalence than that collected from Nile River which indicates an important public health problem and a potential risk of drainage canals in Egypt. ELISA showed higher prevalence of cryptosporidiosis than mZN, for the total examined Clarias gariepinus fish and phylogenetic analyses confirmed this protozoal organism to be a novel species of Cryptosporidium molnari.

A review of the current status of Cryptosporidium in fish

Species of the genus Cryptosporidium (phylum Apicomplexa) infect the epithelium of the gastrointestinal tract of several vertebrate hosts, including humans and domestic and wild animals. In the past 20 years, several studies have focused on Cryptosporidium in fish. To date, a total of four piscine-host-specific species (Cryptosporidium molnari, Cryptosporidium huwi, Cryptosporidium bollandi and Cryptosporidium abrahamseni), nine piscine genotypes and more than 29 unnamed genotypes have been described in fish hosts. In addition, Cryptosporidium species and genotypes typical of other groups of vertebrates have also been identified. This review summarizes the history, biology, pathology and clinical manifestations, as well as the transmission, prevalence and molecular epidemiology of Cryptosporidium in wild, cultured and ornamental fish from both marine and freshwater environments. Finally, the potential role of piscine hosts as a reservoir of zoonotic Cryptosporidium species is also discussed.

Cryptosporidium in fish: Implications for aquaculture and beyond

Aquaculture industries are expanding worldwide and control of Cryptosporidium is of great importance. Cryptosporidiosis is a serious waterborne/foodborne disease, responsible for infectious outbreaks globally. Current knowledge on the Cryptosporidium species in the aquatic environment and their occurrence in piscine hosts is steadily increasing since the Cryptosporidium species have been detected in marine, freshwater, cultured, captive and ornamental fish in a wide range of geographical regions. The zoonotic potential of these parasites and their pathological impact on piscine hosts have been increasingly reported and the fishborne zoonotic risk from Cryptosporidium spp. is of major importance from a public health point of view. Zoonotic subtypes in fish have been described in various studies and are probably related to water contamination from animal and human wastes. This review critically evaluated existing scientific data, related to Cryptosporidium species in piscine hosts, emphasizing transmission routes and the potential impact of piscine cryptosporidiosis in aquaculture. This knowledge will facilitate consumers, authorities and water industries such as fisheries and aquaculture, the prevention and control of waterborne and fishborne cryptosporidiosis in fish products.

Cryptosporidium abrahamseni n. sp. (Apicomplexa: Cryptosporidiiae) from red-eye tetra (Moenkhausia sanctaefilomenae)

The morphological, biological, and molecular characterisation of Cryptosporidium piscine genotype 7 from red-eye tetras (Moenkhausia sanctaefilomenae) are described, and the species name Cryptosporidium abrahamseni n. sp. is proposed. Histological analysis of intestinal tissue identified large numbers of Cryptosporidium organisms along the epithelial lining of the intestine. Sequence and phylogenetic analysis at 18S rRNA (18S) and actin loci conducted on intestinal scrapings revealed that C. abrahamseni n. sp. was genetically distinct from other Cryptosporidium species. At the 18S locus, it was most closely related to C. huwi (3.2% genetic distance) and exhibited genetic distances ranging from 5.9 to 6.5% (C. molnari) to 14.9% (C. scolpthalmi) from all other Cryptosporidium species. At the actin locus, the genetic distances were larger and C. abrahamseni n. sp. exhibited 10.3% genetic distance from C. huwi, and 17.6% (C. molnari) to 28% (C. canis) genetic distance from other Cryptosporidium spp. Phylogenetic analysis of concatenated 18S and actin sequences confirmed that C. abrahamseni n. sp. shares the closest genetic relationship with C. huwi (6.7% genetic distance), while the genetic distance between C. abrahamseni n. sp. and other Cryptosporidium spp. ranged from 12.1% (C. molnari) to 20.4% (C. canis). Based on genetic and histological data, C. abrahamseni n. sp. is validated as a separate species.

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.

Molecular Characterization of Novel Cryptosporidium Fish Genotypes in Edible Marine Fish

Current knowledge of Cryptosporidium species/genotypes in marine fish is limited. Following phylogenetic analysis at the 18S rDNA locus, a recent study identified six new genotypes of Cryptosporidium colonizing edible fish found in European seas. Of these, five grouped in a clade together (#Cryptofish 1-5) and one grouped separately (#Cryptofish 7). In the present study, after phylogenetic analyses of #Cryptofish1, #Cryptofish2, #Cryptofish4, #Cryptofish5 and #Cryptofish7 at the actin locus, the presence of two major clades was confirmed. In addition, when possible, longer 18S amplicons were generated. In conclusion, the small genetic distances between these genotypes designated as a novel marine genotype I (#Cryptofish 1-5) suggest that they may be genetic variants of the same species, while the designated novel marine genotype 2 (#Cryptofish 7) is clearly representative of a separate species.

Cryptosporidium bollandi n. sp. (Apicomplexa: Cryptosporidiiae) from angelfish (Pterophyllum scalare) and Oscar fish (Astronotus ocellatus)

The species name Cryptosporidium bollandi n. sp. is proposed for Cryptosporidium piscine genotype 2 based on morphological, biological and molecular characterisation. Phylogenetic analyses of 18S rRNA (18S) sequences revealed that C. bollandi n. sp. was most closely related to piscine genotype 4 (5.1% genetic distance) and exhibited genetic distances of 10.0%, 12.2% and 25.2% from Cryptosporidium molnari, Cryptosporidium huwi and Cryptosporidium scophthtalmi, respectively. At the actin locus, C. bollandi n. sp. was again most closely related to piscine genotype 4 (6.8% genetic distance) and exhibited 15.5% (C. molnari), 18.4% (C. huwi), 22.9% (C. scophthalmi) and up to 27.5% genetic distance from other Cryptosporidium spp. (Cryptosporidium felis). Phylogenetic analysis of concatenated 18S and actin sequences showed that C. bollandi n. sp. exhibited 12.9% (C. molnari) to 21.1% (C. canis) genetic distance from all other Cryptosporidium spp. Genetic data as well as previous histological analysis clearly supports the validity of C. bollandi n. sp. as a separate species.

Are molecular tools clarifying or confusing our understanding of the public health threat from zoonotic enteric protozoa in wildlife?

Emerging infectious diseases are frequently zoonotic, often originating in wildlife, but enteric protozoa are considered relatively minor contributors. Opinions regarding whether pathogenic enteric protozoa may be transmitted between wildlife and humans have been shaped by our investigation tools, and have led to oscillations regarding whether particular species are zoonotic or have host-adapted life cycles. When the only approach for identifying enteric protozoa was morphology, it was assumed that many enteric protozoa colonized multiple hosts and were probably zoonotic. When molecular tools revealed genetic differences in morphologically identical species colonizing humans and other animals, host specificity seemed more likely. Parasites from animals found to be genetically identical - at the few genes investigated - to morphologically indistinguishable parasites from human hosts, were described as having zoonotic potential. More discriminatory molecular tools have now sub-divided some protozoa again. Meanwhile, some infection events indicate that, circumstances permitting, some "host-specific" protozoa, can actually infect various hosts. These repeated changes in our understanding are linked intrinsically to the investigative tools available. Here we review how molecular tools have assisted, or sometimes confused, our understanding of the public health threat from nine enteric protozoa and example wildlife hosts (Balantoides coli - wild boar; Blastocystis sp. - wild rodents; Cryptosporidium spp. - wild fish; Encephalitozoon spp. - wild birds; Entamoeba spp. - non-human primates; Enterocytozoon bieneusi - wild cervids; Giardia duodenalis - red foxes; Sarcocystis nesbitti - snakes; Toxoplasma gondii - bobcats). Molecular tools have provided evidence that some enteric protozoa in wildlife may infect humans, but due to limited discriminatory power, often only the zoonotic potential of the parasite is indicated. Molecular analyses, which should be as discriminatory as possible, are one, but not the only, component of the toolbox for investigating potential public health impacts from pathogenic enteric protozoa in wildlife.

Prevalence, Molecular Identification, and Risk Factors for Cryptosporidium Infection in Edible Marine Fish: A Survey Across Sea Areas Surrounding France

Cryptosporidium, a zoonotic pathogen, is able to infect a wide range of hosts including wild and domestic animals, and humans. Although it is well known that some parasites are both fish pathogens and recognized agents of zoonosis with a public health impact, little information is available concerning the prevalence of Cryptosporidium in wild aquatic environments. To evaluate the prevalence of Cryptosporidium spp. in commercially important edible marine fish in different European seas (English channel, North sea, Bay of Biscay, Celtic sea and Mediterranean sea), 1,853 specimens were collected as part of two surveys. Nested PCR followed by sequence analysis at the 18S rRNA gene locus was used to identify Cryptosporidium spp. The overall prevalence of Cryptosporidium spp. in sampled fish reached 2.3% (35 out of 1,508) in a first campaign and 3.2% (11 out of 345) in a second campaign. Sequence and phylogenetic analysis of positive samples identified Cryptosporidium parvum (n = 10) and seven genotypes which exhibited between 7.3 and 10.1% genetic distance from C. molnari, with the exception of one genotype which exhibited only 0.5–0.7% genetic distance from C. molnari. Among 31 analyzed fish species, 11 (35.5%) were identified as potential hosts for Cryptosporidium. A higher prevalence of Cryptosporidium spp. was observed in larger fish, in fish collected during the spring-summer period, and in those caught in the North East Atlantic. Pollachius virens (saithe) was the most frequently Cryptosporidium positive species. In fish infected by other parasites, the risk of being Cryptosporidium positive increased 10-fold (OR: 9.95, CI: 2.32–40.01.04, P = 0.0002). Four gp60 subtypes were detected among the C. parvum positive samples: IIaA13G1R1, IIaA15G2R1, IIaA17G2R1, and IIaA18G3R1. These C. parvum subtypes have been previously detected in terrestrial mammals and may constitute an additional source of infection for other animals and in particular for humans. Microscopical examination of histological sections confirmed the presence of round bodies suggestive of the development of C. parvum within digestive glands. We report herein the first epidemiological and molecular data concerning the detection of Cryptosporidium in edible marine fish in European seas surrounding France broadening its host range and uncovering potential novel infection routes.

Identification of a novel piscine Cryptosporidium genotype and Cryptosporidium parvum in cultured rainbow trout (Oncorhynchus mykiss)

This study reports for the first time the presence and molecular characterization of Cryptosporidium in farmed rainbow trout (Oncorhynchus mykiss Walbaum, 1792). A total of 360 fish, with no apparent clinical signs of disease, were collected and classified into groups according to their size. Cryptosporidium oocysts were detected by immunofluorescence microscopy in 33 specimens (9.2%), which were located in pyloric caeca samples (42.4%), intestinal scrapings (39.4%), or at both locations (18.2%). In the smallest (youngest) fish group, a higher percentage of positive samples were detected in the pyloric caeca relative to the intestinal location (58.8 vs. 17.6%; P = 0.01), including a cluster with more than 10 oocysts observed in the pyloric caeca of one specimen. PCR amplification and sequencing of fragments of SSU-rDNA and hsp70 genes identified a novel Cryptosporidium piscine genotype (genotype 9) in two specimens and Cryptosporidium parvum in seven fish, including the specimen in which the oocyst cluster was observed. Moreover, Cryptosporidium oocysts were detected in farm water samples (41.7 and 16.7% from influent and effluent, respectively). Although Giardia was not found in gastrointestinal samples, Giardia cysts were observed in 50.0 and 33.3% of the influent and effluent water samples, respectively. The results support the existence of natural infections by C. parvum in freshwater cultured fish, suggesting that the rainbow trout could shed infectious oocysts in aquatic environments and it may be a potential source of human infection when this edible fish is handled.

Cryptosporidium in fish: alternative sequencing approaches and analyses at multiple loci to resolve mixed infections

Currently, the systematics, biology and epidemiology of piscine Cryptosporidium species are poorly understood. Here, we compared Sanger ‒ and next-generation ‒ sequencing (NGS), of piscine Cryptosporidium, at the 18S rRNA and actin genes. The hosts comprised 11 ornamental fish species, spanning four orders and eight families. The objectives were: to (i) confirm the rich genetic diversity of the parasite and the high frequency of mixed infections; and (ii) explore the potential of NGS in the presence of complex genetic mixtures. By Sanger sequencing, four main genotypes were obtained at the actin locus, while for the 18S locus, seven genotypes were identified. At both loci, NGS revealed frequent mixed infections, consisting of one highly dominant variant plus substantially rarer genotypes. Both sequencing methods detected novel Cryptosporidium genotypes at both loci, including a novel and highly abundant actin genotype that was identified by both Sanger sequencing and NGS. Importantly, this genotype accounted for 68·9% of all NGS reads from all samples (249 585/362 372). The present study confirms that aquarium fish can harbour a large and unexplored Cryptosporidium genetic diversity. Although commonly used in molecular parasitology studies, nested PCR prevents quantitative comparisons and thwarts the advantages of NGS, when this latter approach is used to investigate multiple infections.

Molecular characterisation of a disseminated Cryptosporidium infection in a Koi carp (Cyprinus carpio)

Cryptosporidium is a protozoan parasite that infects a wide range of hosts, yet relatively little is known about the epidemiology of cryptosporidiosis in fish. Here we report a disseminated Cryptosporidium infection in a male Koi carp (Cyprinus carpio), with parasite stages identified deep within the epithelium of the intestine, kidneys, spleen, liver and gills causing severe granulomatous inflammatory lesions. Molecular characterization at two loci; 18S ribosomal RNA (rRNA) and actin, revealed this to be a novel Cryptosporidium genotype, most closely related to Cryptosporidium molnari.

Public health significance of zoonotic Cryptosporidium species in wildlife: Critical insights into better drinking water management

Cryptosporidium is an enteric parasite that is transmitted via the faecal-oral route, water and food. Humans, wildlife and domestic livestock all potentially contribute Cryptosporidium to surface waters. Human encroachment into natural ecosystems has led to an increase in interactions between humans, domestic animals and wildlife populations. Increasing numbers of zoonotic diseases and spill over/back of zoonotic pathogens is a consequence of this anthropogenic disturbance. Drinking water catchments and water reservoir areas have been at the front line of this conflict as they can be easily contaminated by zoonotic waterborne pathogens. Therefore, the epidemiology of zoonotic species of Cryptosporidium in free-ranging and captive wildlife is of increasing importance. This review focuses on zoonotic Cryptosporidium species reported in global wildlife populations to date, and highlights their significance for public health and the water industry.

Genetic diversity of Cryptosporidium in fish at the 18S and actin loci and high levels of mixed infections

Cryptosporidium is an enteric parasite that infects humans and a wide range of animals. Relatively little is known about the epidemiology and taxonomy of Cryptosporidium in fish. In the present study, a total of 775 fish, belonging to 46 species and comprising ornamental fish, marine fish and freshwater fish were screened for the prevalence of Cryptosporidium by PCR. The overall prevalence of Cryptosporidium in fish was 5.3% (41/775), with prevalences ranging from 1.5 to 100% within individual host species. Phylogenetic analysis of these Cryptosporidium isolates as well as 14 isolates from previous studies indicated extensive genetic diversity as well as evidence for mixed infections. At the 18S locus the following species were identified; Cryptosporidium molnari-like genotype (n=14), Cryptosporidium huwi (n=8), piscine genotype 2 (n=4), piscine genotype 3-like (n=1), piscine genotype 4 (n=2), piscine genotype 5 (n=13), piscine genotype 5-like (n=1) and five novel genotypes (n=5). At the actin locus, species identification agreed with the 18S locus for only 52.3% of isolates sequenced, indicating high levels of mixed infections. Future studies will need to employ both morphological characterization and deep sequencing amplicon-based technologies to better understand the epidemiological and phylogenetic relationships of piscine-derived Cryptosporidium species and genotypes, particularly when mixed infections are detected.

Cryptosporidium huwi n. sp. (Apicomplexa: Eimeriidae) from the guppy (Poecilia reticulata)

The morphological, biological, and molecular characteristics of Cryptosporidium piscine genotype 1 from the guppy (Poecilia reticulata) are described, and the species name Cryptosporidium huwi n. sp. is proposed to reflect its genetic and biological differences from gastric and intestinal Cryptosporidium species. Oocysts of C.huwi n. sp. over-lap in size with Cryptosporidium molnari, measuring approximately 4.4-4.9 µm (mean 4.6) by 4.0-4.8 µm (mean 4.4 µm) with a length to width ratio of 1.04 (0.92-1.35) (n = 50). Similar to C.molnari, C.huwi n. sp. was identified in the stomach only and clusters of oogonial and sporogonial stages were identified deep within the epithelium. However, phylogenetic analysis of 18S rRNA sequences indicated that C. huwi n. sp. exhibited 8.5-9.2% and 3.5% genetic distance from C.molnari isolates and piscine genotype 7 respectively. At the actin locus, the genetic distance between C.huwi n. sp. and C.molnari was 16.6%. The genetic distance between C.huwi n. sp. and other Cryptosporidium species at the 18S locus was 13.2%-17% and at the actin locus was 18.9%-26.3%. Therefore C. huwi n. sp. is genetically distinct from previously described Cryptosporidium species.

Cryptosporidiumspecies in humans and animals: current understanding and research needs

Cryptosporidiumis increasingly recognized as one of the major causes of moderate to severe diarrhoea in developing countries. With treatment options limited, control relies on knowledge of the biology and transmission of the members of the genus responsible for disease. Currently, 26 species are recognized as valid on the basis of morphological, biological and molecular data. Of the nearly 20Cryptosporidiumspecies and genotypes that have been reported in humans,Cryptosporidium hominisandCryptosporidium parvumare responsible for the majority of infections. Livestock, particularly cattle, are one of the most important reservoirs of zoonotic infections. Domesticated and wild animals can each be infected with severalCryptosporidiumspecies or genotypes that have only a narrow host range and therefore have no major public health significance. Recent advances in next-generation sequencing techniques will significantly improve our understanding of the taxonomy and transmission ofCryptosporidiumspecies, and the investigation of outbreaks and monitoring of emerging and virulent subtypes. Important research gaps remain including a lack of subtyping tools for manyCryptosporidiumspecies of public and veterinary health importance, and poor understanding of the genetic determinants of host specificity ofCryptosporidiumspecies and impact of climate change on the transmission ofCryptosporidium.

Cryptosporidiosis and Cryptosporidium species in animals and humans: a thirty colour rainbow?

Parasites of the genus Cryptosporidium (Apicomplexa) cause cryptosporidiosis in humans and animals worldwide. The species names used for Cryptosporidium spp. are confusing for parasitologists and even more so for non-specialists. Here, 30 named species of the genus Cryptosporidium are reviewed and proposed as valid. Molecular and experimental evidence suggests that humans and cattle are the hosts for 14 and 13 out of 30 named species, respectively. Two, four and eight named species are considered of major, moderate and minor public health significance, respectively. There are at least nine named species that are shared between humans and cattle. The aim of this review is to outline available species information together with the most commonly used genetic markers enabling the identification of named Cryptosporidium spp. Currently, 28 of 30 named species can be identified using the complete or partial ssrRNA, serving as a retrospective 'barcode'. Currently, the ssrRNA satisfies the implicit assumption that the reference databases used for comparison are sufficiently complete and applicable across the whole genus. However, due to unreliable annotation in public DNA repositories, the reference nucleotide entries and alignment of named Cryptosporidium spp. has been compiled. Despite its known limitations, ssrRNA remains the optimal marker for species identification.

Looking for Cryptosporidium: the application of advances in detection and diagnosis

The protozoan Cryptosporidium is a major public and animal health concern. Young children, immunocompromised people, and pre-weaning animals are especially vulnerable, but treatment options are limited and there is no vaccine. A laboratory diagnosis is required to confirm cases of cryptosporidiosis, and species and genotype determination is essential in distinguishing human from non-human sources, understanding transmission, and strengthening the epidemiological evidence for causative links in outbreaks. However, testing is not consistent, as demonstrated by investigation of a significant increase in cases in some European countries during 2012. Many methods employed are laborious and time-consuming; recent advances, translated into diagnostic assays, can improve testing and facilitate typing to support clinical and environmental investigations.

Additional novel Cryptosporidium genotypes in ornamental fishes

Current knowledge on the prevalence and genotypes of Cryptosporidium in fishes is still limited. This study investigated the prevalence of Cryptosporidium species in 171 ornamental fishes, belonging to 33 species, collected from 8 commercial aquariums around Perth, Western Australia. All samples were screened by nested PCR targeting the 18S rRNA locus. A total of 6 positives were identified by PCR at the 18S locus from 4 different species of fishes (red eye tetra, Moenkhausia sanctaefilomenae; gold gourami, Trichogaster trichopterus; neon tetra, Paracheirodon innesi; goldfish, Carassius auratus auratus), giving an overall prevalence of 3.5% (6/171). Four different genotypes were identified, only one of which has been previously reported in fish; piscine genotype 4 in a neon tetra isolate, a rat genotype III-like isolate in a goldfish, a novel genotype in three isolates from red eye (piscine genotype 7) which exhibited a 3.5% genetic distance from piscine genotype 1 and a piscine genotype 6-like from a gold gourami (1% genetic distance). Further biological and genetic characterisation is required to determine the relationship of these genotypes to established species and strains of Cryptosporidium.

Detection of Cryptosporidium molnari oocysts from fish by fluorescent-antibody staining assays for cryptosporidium spp. affecting humans

Three direct fluorescent-antibody staining assay kits for the detection of zoonotic Cryptosporidium species were used to detect Cryptosporidium molnari from Murray cod, and the cryptosporidia were characterized by using small-subunit (SSU) ribosomal DNA (rDNA). To facilitate rapid diagnosis of infection, this study demonstrated that all three kits detected fresh C. molnari and two kits detected formalin-fixed oocysts.