Development and field evaluation of a nested polymerase chain reaction-restriction fragment length polymorphism (nPCR-RFLP) analysis to identify A. marginale-infected and A. centrale-vaccinated cattle

A nested polymerase chain reaction-restriction fragment length polymorphism (nPCR-RFLP) assay based on the amplification of the Anaplasma spp. highly conserved msp5 gene and posterior digestion with HindIII endonuclease was developed and evaluated in field samples. Results were compared using an nPCR specific for Anaplasma marginale (nPCR-Am) based on the msp1 beta gene and an nPCR specific for A. centrale (nPCR-Ac) based on the msp2 operon (msp2-o) gene. Amplicons dilutions of msp1 beta and msp5 of A. marginale and msp2-o and msp5 of A. centrale and dilutions of parasited erythrocytes (PE) with A. marginale and A. centrale were used to determine the detection limits. The results were 20 DNA copies/reaction and 30 PE for A. marginale and A. centrale by nPCR-RLFP and nPCR-Am/Ac. A mix of msp5-Am and msp5-Ac was used to evaluate the interference of msp5 from one species for the detection of the other. Co-amplification of the DNA from both species was observed up to a 1:7 ratio of one species to the other. Field samples positive for Anaplasma spp. antibodies (n = 260) from 32 herds were evaluated. Strength of agreement between results by nPCR-RFLP and nPCR-Am or nPCR-Ac was 78% (kappa = 0.44) and 94% (kappa = 0.85), respectively. Thirty-four samples were positive for A. marginale by nPCR-RFLP but negative by nPCR-Am. msp1 beta amplicons of 10 samples from 5 herds with discrepancies between nPCR-Am and nPCR-RFLP results were cloned and sequenced. The analysis of the msp1 beta sequence showed several mutations in the target region of the internal forward primer that would explain the failure in the amplification. Only 10 of the 20 coinfections identified by nPCR-Ac/nPCR-Am were detected by nPCR-RFLP. nPCR-RFLP is a sensitive, low-cost and accessible molecular method for low-complexity laboratories. More studies are needed to establish in which circumstances coinfections can be underestimated.