Polymerase Chain Reaction Directed to Eimeria ITS1 rDNA or a Single-Copy Orthologue Corroborates Standard Micro-oocyst Analysis of Intestinal Tissue from Chickens Infected with E. acervulina , E. maxima , or E. tenella .

The purpose of this study was to compare micro-oocyst counts of Eimeria to PCR analysis of intestinal DNA from smears of duodenum, jejunum/ileum, and cecum of chickens infected with Eimeria acervulina , Eimeria maxima , or Eimeria tenella oocysts. Broiler chicks were infected in triplicate with various doses of E. acervulina , E. maxima , or E. tenella oocysts and were necropsied 5-6 days later to recover duodenal, jejunal, or cecal tissue for micro-oocyst count and for DNA recovery. Micro-oocyst counts were done independently by three individuals. Micro-oocyst counts and PCR directed to ITS1 rDNA or to a single-copy orthologue (SCO 5995) displayed a linear relationship with oocyst dose for each Eimeria species. A strong correlation was found between mean micro-oocyst counts and both PCR assays for E. acervulina ( r = 0.78-0.94), E. maxima ( r = 0.79-0.91), and E. tenella ( r = 0.85-0.96). There was good agreement between ITS1 and SCO 5995 PCR assays: E. acervulina ( r = 0.92), E. maxima ( r = 0.79), and E. tenella ( r = 0.93). However, only ITS1 PCR analysis corroborated micro-oocyst counts of Eimeria oocyst DNA recovered from Eimeria -infected broiler chickens submitted to a poultry diagnostic laboratory. These findings suggest that ITS1 PCR or SCO PCR can validate traditional micro-oocyst counts used in quantifying Eimeria infection in chickens. Additional studies may provide a method for estimating the relative abundance of each Eimeria species in a natural infection.