An overall 3.4% prevalence (37/1,081 samples) of cryptosporidiosis was seen in domestic rabbits. This is higher than rates reported for wild rabbits in previous studies but at the lower end of rates reported for farmed, laboratory, and pet rabbits (13
). Differences in techniques used for the detection of infection and in the management and age of animals probably contributed to the observed variations in the prevalence of cryptosporidiosis in rabbits. In the present study, Cryptosporidium
oocysts were detected in many rabbits on two farms (farms 2 and 8), and animals of 1 to 3 months of age had much higher infection rates than those in other age groups (Table ).
In this study, only the Cryptosporidium
rabbit genotype was identified in rabbits. Sequence similarity analysis revealed that the 18S rRNA, actin, and COWP gene sequences obtained in this study were identical to each other at each locus and had 100% identity to the Cryptosporidium
rabbit genotype isolates from rabbits and humans found in previous studies (4
); only sequences of the HSP70 gene had minor differences, which were seen in the copy number of a minisatellite repeat. Prior to this study, only five publications, representing four studies, characterized Cryptosporidium
spp. in rabbits. Thus, only a single nucleotide sequence each is available for the actin and COWP loci, and five very short sequences (<400 bp) are available for the HSP70 locus (13
). The Cryptosporidium
rabbit genotype has nucleotide sequences very similar to those of C. hominis
at the 18S rRNA (only four nucleotide substitutions compared to sequence AJ849462 [within a 787-bp region]), COWP (no substitution compared to sequence DQ388389 [within a 535-bp region]), and actin (only one nucleotide substitution compared to sequence EF591784 [within a 1,066-bp region]) loci. More nucleotide substitutions were seen in the HSP70 gene, especially at the 3′ end of the sequence (11 to 13 substitutions in the 1,920-bp sequence obtained in this study). At this locus, C. hominis
has 12 or 13 copies of the 12-bp minisatellite sequence, whereas the rabbit genotype has only 9 or 10 copies. There is a need for further studies of the taxonomic relationship between C. hominis
and the Cryptosporidium
rabbit genotype to establish the validity of the name Cryptosporidium cuniculus
, previously used to describe the parasite in rabbits.
Sequence analysis of the gp60 gene is useful for investigating transmission dynamics, for identification and differentiation of outbreaks, and for tracking infection sources (23
). In recent studies, several Cryptosporidium
rabbit genotype isolates from humans and rabbits were subtyped at the gp60 locus. Thus far, two subtype families have been identified, including the Va subtype family, in humans (VaA18 and VaA22) and rabbits (VaA18) in the United Kingdom, and the Vb subtype family, in rabbits in the Czech Republic (VbA19) and China (VbA29) (4
). In this study, the gp60 sequence analysis revealed that the isolates of this study belonged to three subtypes (VbA29, VbA35, and VbA36) in the Vb subtype family, which has thus far not been seen in humans.
In conclusion, the Cryptosporidium rabbit genotype is a common parasite infecting farmed rabbits in Henan, China. Although there has not been any reported human infection with the parasite in China, its genetic similarity to C. hominis and the recent finding of the parasite in humans in the United Kingdom indicate that rabbits can be a potential reservoir of zoonotic cryptosporidiosis. More systematic biologic characterizations of the parasite are needed to understand the taxonomic status of the Cryptosporidium rabbit genotype and its public health significance.