Cryptosporidium

Zahedi, Alireza, Paparini, Andrea, Jian, Fuchun, Robertson, Ian & Ryan, Una, 2016, Public health significance of zoonotic Cryptosporidium species in wildlife: Critical insights into better drinking water management, International Journal for Parasitology: Parasites and Wildlife 5 (1), pp. 88-109 : 99-100

3.3. Cryptosporidium in fi sh and marine mammals

Cryptosporidium has been described in both fresh and marine water piscine species with parasitic stages located either on the stomach or intestinal surface, or deep within the epithelium ( Table 4). The first account of Cryptosporidium in a piscine host was Cryptosporidium nasorum , identified in a Naso tang , a tropical fish species ( Hoover et al., 1981). However, currently only three species are recognized; C. molnari , C. scophthalmi and C. huwi (previously known as piscine genotype I) (Alvarez-Pellitero and Sitja-Bobadilla, 2002; Alvarez-Pellitero et al., 2004; Palenzuela et al., 2010; Costa et al., 2015; Ryan et al., 2015), none of which have been reported in humans. In fish hosts, Cryptosporidium fish species and genotypes are typically located either in the stomach or intestine and the parasite can cause clinical manifestations, such as emaciation, decrease in growth rate, anorexia, whitish faeces, abdominal swelling, and ascites ( Alvarez-Pellitero et al., 2004; Ryan et al., 2015). Most studies on Cryptosporidium in fish have been reported in farmed or aquarium fish ( Table 4) and little data are currently available regarding the molecular identification of Cryptosporidium species and genotypes in wild fish populations and, in particular, in edible fish ( Palenzuela et al., 2010; Reid et al., 2010; Barugahare et al., 2011; Gibson-Keuh et al., 2011; Koinari et al., 2013; Certard et al., 2015).

In addition to the three recognized species of Cryptosporidium in piscine hosts, numerous Cryptosporidium species and genotypes have been reported in fish including; piscine genotypes 2 to 8, unnamed novel genotypes (n = 5), rat genotype III, C. parvum , C. hominis , C. xiaoi and C. scrofarum ( Table 4). Of these, only C. parvum , C. hominis and C. scrofarum are of public health interest. Cryptosporidium scrofarum was identified in a whiting ( Reid et al., 2010); C. parvum was found in School whiting, Nile tilapias, a Silver barb, Arctic char and European whitefish and C. hominis was reported in Mackerel scad ( Reid et al., 2010; Gibson-Kueh et al., 2011; Koinari et al., 2013; Certad et al., 2015). In one of the most recent studies, C. parvum was identified in freshwater fish from Lake Geneva ( Lac Ĺeman) by both histology and molecular analysis ( Certad et al., 2015). In that study, the overall prevalence of Cryptosporidium was 36.6% (15/41); the prevalence of C. parvum and C. molnari was 86.7% (13/15) and 6.7% (1/15), respectively, while 6.7% (1/15) were mixed C. parvum and C. molnari infections ( Certad et al., 2015). Histological analysis identified C. parvum developmental stages in the stomach and intestine suggesting that C. parvum was infecting the fish, rather than being passively carried which has important public health implications.

Subtyping of Cryptosporidium isolates in fish has identified C. parvum subtype IIaA18G3R 1 in School whiting from Australia ( Reid et al., 2010), three C. parvum subtypes (IIaA14G2R1, IIaA15G2R1 and IIaA19G4R1) in Nile tilapia, silver barb and mackerel scad and a C. hominis subtype (IdA15G1) in mackerel scad in Papua New Guinea ( Koinari et al., 2013), and C. parvum subtypes IIaA15G2R1, IIaA16G2R1 and IIaA17G2R 1 in Arctic char and European whitefish from France ( Certad et al., 2015). All of these C. parvum subtypes are zoonotic and commonly found in cattle and humans ( Xiao, 2010). The identification of the C. hominis subtype probably reflects human sewage contamination of the water. Clearly further studies in this area are required to better understand the transmission dynamics of Cryptosporidium in fish.