Short communicationAdditional novel Cryptosporidium genotypes in ornamental fishes
Introduction
Cryptosporidium is an obligate, intracellular, protozoan parasite which undergoes endogenous (internal) development resulting in the production of an encysted stage that is excreted in the faeces of the host (Fayer et al., 2000). The parasite causes self-limiting diarrhoea in immunocompetent individuals but may be chronic and life-threatening to those that are immunocompromised (Hunter et al., 2007). Humans can acquire Cryptosporidium infections through various transmission routes, such as direct contact with infected persons (person-to-person transmission) or animals (zoonotic transmission) and ingestion of contaminated food (foodborne transmission) and water (waterborne transmission) (Xiao, 2010). Molecular data indicates that seven Cryptosporidium species/genotypes are responsible for most human cryptosporidiosis cases, including Cryptosporidium hominis, Cryptosporidium parvum, Cryptosporidium meleagridis, Cryptosporidium felis, Cryptosporidium canis, Cryptosporidium ubiquitum and Cryptosporidium cuniculus (Xiao and Feng, 2008, Xiao, 2010, Chalmers et al., 2011) with C. parvum and C. hominis by far the most common species in humans worldwide (Xiao, 2010).
Relatively little is known about the taxonomy, epidemiology, pathology, host range or zoonotic potential of Cryptosporidium in fishes (Zanguee et al., 2010). Cryptosporidium infections are known to cause emaciation, poor growth rates, coelomic distention, anorexia, spiralling, listlessness and increased mortality in various fish hosts (Alvarez-Pellitero and Sitja-Bobadilla, 2002, Alvarez-Pellitero et al., 2004, Ryan et al., 2004, Murphy et al., 2009, Zanguee et al., 2010).
Currently only two species of Cryptosporidium are recognised in fishes; Cryptosporidium molnari in gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labarx), and Cryptosporidium scophthalmi in turbot (Psetta maxima, sny. Scophthalmus maximus) (Alvarez-Pellitero and Sitja-Bobadilla, 2002, Alvarez-Pellitero et al., 2004). C. molnari has recently been characterised genetically (Palenzuela et al., 2010), but currently no genetic sequences are available for C. scophthalmi. In addition to the two accepted species, a total of nine species/genotypes have been identified in fishes: piscine genotype 1 from a guppy (Poecilia reticulate) (Ryan et al., 2004); piscine genotype 2 from a freshwater angelfish (Pterophyllum scalare) (Murphy et al., 2009), piscine genotype 3 from a sea mullet (Mugil cephalus) (Reid et al., 2010); piscine genotype 4 from a golden algae eater (Crossocheilus aymonieri), a kupang damsel (Chrysiptera hemicyanes) and an oscar fish (Astronatus ocellatis); piscine genotype 5 from an angelfish (P. scalare), a butter bream (Monodactylidae) and a golden algae eater (C. aymonieri); piscine genotype 6 from a guppy (P. reticulate) (Zanguee et al., 2010), and C. parvum, Cryptosporidium xiaoi and pig genotype II in whiting (Sillago vittata) (Reid et al., 2010).
A recent study of Cryptosporidium in ornamental fishes collected from aquariums in Perth, Western Australia reported a high prevalence of infection (10.5%) and identified three novel genotypes (piscine genotypes 4–6) (Zanguee et al., 2010). The high prevalence of potentially pathogenic Cryptosporidium found in ornamental fishes in that study is potentially of much wider significance than its effects on the ornamental fish industry, because if these fishes are released, they may constitute a major threat to the highly endemic and threatened freshwater fish fauna of Western Australia. The aim of this present study was to expand our knowledge and understanding of Cryptosporidium species infecting ornamental fishes in Western Australia by screening additional fish species using PCR and sequence analysis.
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Sampling
A total of 171 ornamental fishes, belonging to 33 species, were collected from 8 commercial aquariums across the Perth metropolitan area in Western Australia (Table 1). Fishes were collected live to preserve tissues. All fishes were euthanized in an ice slurry upon arrival at the laboratory. They were then weighed and measured (length and width) and dissected using a fresh scalpel blade for each fish. The intestine and stomach were placed in a 1.5 mL eppendorf tube and enough PCR grade water was
Prevalence of Cryptosporidium in fish hosts
Of the 171 samples screened, only 6 were positive by PCR at the 18S locus, giving an overall prevalence of 3.5% (0.8–6.3% CI). This is lower than the prevalence of 10.5% found in ornamental fishes in Western Australia by Zanguee et al. (2010), but considerably higher than the prevalence of 0.8% for Cryptosporidium reported in 709 cultured, wild marine and wild freshwater fishes in Western Australia (Reid et al., 2010). The six positives were identified in four species of fishes; red eye tetra (
Discussion
Of the four genotypes that were identified in this study, only one (piscine genotype 4 identified in the neon tetra) has been previously reported in fishes. The goldfish-derived isolate is likely a variant of rat genotype III, but sequencing at the actin locus is required to confirm this. This is the first time that rat genotype III has been identified in a fish host. Little is known about rat genotype III and its zoonotic potential is unknown, however it has not been reported in humans to date
Acknowledgements
We would like to thank all the aquariums that were involved with the project, Susan Kueh for her help with the fish dissections and Naomi Sleep for her fish expertise.
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