Pathogenesis of Eimeria praecox in chickens: variability in virulence of field strains compared with that of laboratory strains of E.praecox and E.acervulina
Résumé
The pathogenesis in chickens of the apicomplexan Eimeria praecox was compared with that of E. acervulina, using intestinal lesions, mucosal integrity, body weight gain (BWG) and feed conversion ratio (FCR) as criteria. Characteristics of each species were described by combinations of polymerase chain reaction (PCR) assays and classic parasitological signs. There were considerable overlaps in lengths, breadths, shape indices and volumes of the oocysts of each species. Both species caused statistically significant reductions in BWG at the lowest inocula tested (500,000 sporulated oocysts per bird of E. praecox and 250,000 of E. acervulina). E. praecox was observed for the first time to cause actual body weight loss and marked increases in FCR, as did E. acervulina. E. acervulina caused gross, white pathognomonic lesions, but E. praecox caused micro-lesions visible in fresh tissue only with a dissecting microscope. Occasionally, lesions of the Houghton strain of E. acervulina were observed to be rounded, rather than typically “ladder-like”. Both species caused villous erosion and atrophy. No mortalities occurred in birds receiving up to one million sporulated oocysts each of either species. Using BWG and FCR as criteria, the virulences of recent field strains of E. praecox from Wales (Tynygongl) and the USA (Raleigh) were compared with English laboratory strains of E. praecox (Houghton) and E. acervulina. (Houghton). E. praecox (Tynygongl) was markedly more virulent than E. acervulina (Houghton), which was more virulent than E. praecox (Raleigh) and E. praecox (Houghton).
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