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

3.2. Cryptosporidium in birds

The mobility of migratory birds, together with their distribution and ability to form large colonies, makes them potentially suitable to spread pathogens. Due to their easy access to drinking water catchments and other water sources, wild birds are believed to be a potential risk to drinking water safety. The epidemiology of avian cryptosporidiosis, in particular zoonotic Cryptosporidium species infecting birds is therefore of public health importance. Currently only three avian Cryptosporidium spp . are recognised; C. meleagridis , C. baileyi and C. galli ( Table 3) ( Ryan and Xiao, 2014).

3.2.1. C. meleagridis

C. meleagridis infects the intestinal (small and large intestine and bursa) epithelial cells of a wide range of birds ( Table 3) ( Ryan and Xiao, 2014). It was first detected in a wild turkey ( Meleagris gallopavo ) by Tyzzer in 1929, but named as a valid Cryptosporidium species in 1955 ( Slavin, 1955). C. meleagridis oocysts have been experimentally infected into broiler chickens, ducks, turkeys, calves, pigs, rabbits, rats and mice ( Darabus and Olariu, 2003; Ryan and Xiao, 2014). It has also been reported as one of the most commonly detected human-infectious Cryptosporidium species in wastewater ( Feng et al., 2007, 2011a; Li et al., 2012).

Molecular analysis has revealed that C. meleagridis has relatively low host specificity, and many C. meleagridis subtypes at other loci have been found in both birds and humans and both anthroponotic and zoonotic transmission routes have been suggested ( Cama et al., 2003; Elwin et al., 2012; Silverlås et al., 2012). Subtyping at the gp60 locus has identified seven subtype families (IIIa ‾ IIIg) and the likely occurrence of cross-species transmission of C. meleagridis between birds and humans ( Wang et al., 2014). Human volunteer studies have shown that healthy adults can be infected and become ill from ingestion of C. meleagridis oocysts ( Chappell et al., 2011). In the study by Chappell et al., five volunteers were challenged with 10 5 C. meleagridis oocysts and monitored for six weeks for faecal oocysts and clinical manifestations. Four volunteers had diarrhoea; three had detectable faecal oocysts; and one infected volunteer remained asymptomatic. All infections were self-limited and oocysts were cleared within Ý 12 days of challenge ( Chappell et al., 2011).

3.2.2. Cryptosporidium baileyi

C. baileyi is generally associated with the respiratory form of cryptosporidiosis in birds and has been predominantly reported in broiler chickens. Compared to C. meleagridis , C. baileyi is capable of infecting a larger spectrum of avian hosts ( Table 3), targeting various sites of infection mostly associated with digestive and respiratory tracts ( Ryan and Xiao, 2014). Experimental cross-transmission of C. baileyi to other birds has been successfull, however there has been no reports of cross-transmission between birds and other vertebrates ( Lindsay and Blagburn, 1990; Cardozo et al., 2005), except for a single unsubstantiated report of human infection with C. baileyi which did not include any molecular analysis ( Ditrich et al., 1991). Therefore, C. baileyi is not considered to be of public health significance.

3.2.3. Cryptosporidium galli

Unlike other avian species, C. galli is a gastric species with endogenous developmental stages occurring in the glandular epithelial cells of the proventriculus (Pavĺasek, 1999, 2001; Ryan et al., 2003; Ng et al., 2006; Ryan and Xiao, 2014). It predominantly infects birds of the family Spermestidae, Fringilidiae and domestic chickens ( Gallus gallus ), and seems to be more prevalent among songbirds ( Table 3). Successful experimental cross-transmission of C. galli to other chickens have been reported, however the full extent of its host range is still unknown ( Ryan, 2010). It has not been reported in humans.

3.2.4. Other Cryptosporidium species and genotypes reported in birds

In addition to C. meleagridis , other zoonotic species of Cryptosporidium reported in birds include C. hominis , C. parvum , C muris and C. andersoni (Zylan et al., 2008; Jellison et al., 2009; Ryan, 2010; Reboredo-Fernandez et al., 2015; Gomes et al., 2012). In addition, twelve genotypes; avian genotypes I ‾ V, the black duck genotype, the Eurasian woodcock genotype and goose genotypes I ‾ V have been reported ( Table 3). To date, there is no evidence of human cryptosporidiosis caused by these genotypes.