A low-virulence Eimeria intestinalis isolate from rabbit (Oryctolagus cuniculus) in China: molecular identification, pathogenicity, and immunogenicity

Abstract

An Eimeria intestinalis isolated from a rabbit in China was first identified by amplifying the 18S small subunit (SSU) ribosomal RNA gene. The size of the amplified fragment was 1521 bp. The 18S SSU RNA gene of the E. intestinalis isolate shared 99 % sequence identity with E. intestinalis isolates from France and the Czech Republic, with 100 and 96 % coverage, respectively. Then, the pathogenicity and immunogenicity of the E. intestinalis isolate were evaluated in specific pathogen free (SPF) rabbits. In the pathogenicity assay, SPF rabbits in four groups were infected with 5 × 10³, 5 × 10⁴, 5 × 10⁵, and 0 sporulated oocysts, respectively. Clinical signs including diarrhoea, constipation, loss of appetite, and reduction of body weight gain were observed in rabbits inoculated with 5 × 10⁴ and 5 × 10⁵ oocysts. And one rabbit (25 %) inoculated with 5 × 10⁵ oocysts died 15 days after the inoculation. In the immunogenicity assay, SPF rabbits in five groups (named B1, B2, B3, B4, and B5) were immunised with 5 × 10¹, 5 × 10², 5 × 10³, 0, and 0 sporulated oocysts, respectively. All rabbits but the B5 group were challenged with 1 × 10⁶ oocysts. After the challenge, no or slight clinical signs were seen in rabbits of the B2 and B3 groups. Compared with the control, a 69.6 and 84.5 % reduction of oocyst output was observed in the B2 and B3 groups, respectively. The body weight gain of the two groups was obviously higher than that of the challenge control group. All the results show that the E. intestinalis isolate has low virulence but immunogenicity in rabbit.