Abstract
Avian coccidiosis is a disease caused by members of the genus Eimeria. Huge economic losses incurred by the global poultry industry due to coccidiosis have increased the need for cost-effective and easily available recombinant vaccines. Microneme protein 2 (MIC2) and surface antigen 1 (SAG1) of E. tenella have been recognised as potential vaccine candidates. However, the genetic diversity of the antigens in field isolates, which affects vaccine efficacy, has yet to be largely investigated. Here, we analysed genetic diversity and natural selection of etmic2 and etsag1 in Korean E. tenella isolates. Both genes exhibited low levels of genetic diversity in Korean isolates. However, the two genes showed different patterns of nucleotide diversity and amino acid polymorphism involving the E. tenella isolates obtained from different countries including China and India. These results underscore the need to investigate the genetic diversity of the vaccine candidate antigens and warrant monitoring of genetic heterogeneity and evolutionary aspects of the genes in larger numbers of E. tenella field isolates from different geographical areas to design effective coccidial vaccines.
Highlights
Avian coccidiosis is an enteric disease caused by infections due to Eimeria spp
Nested polymerase chain reaction (PCR) trials to amplify etmic2 and etsag1 from the samples revealed that 156 etmic2 and 101 etsag1 fragments were successfully amplified from 231 E. tenella-positive samples
The co-ding region of each gene was annotated by deleting non-coding internal introns manually based on the reference sequences, E. tenella Houghton strain etmic2 (XM_013377912.1) and etsag1 (AJ586531.2)
Summary
Avian coccidiosis is an enteric disease caused by infections due to Eimeria spp. The annual loss of the global poultry industry due to coccidiosis has been estimated at GBP10.36 billion based on total production losses and approximate costs of prophylaxis and treatment [1]. Seven different species of Eimeria, namely, E. acervulina, E. tenella, E. maxima, E. mitis, E. praecox, E. brunetti, and E. neacatrix, are known to infect domestic chicken and cause avian coccidiosis, with varying levels of fecundity, pathogenicity, and sites of replication within the chicken gut [3]. E. tenella is one of the most virulent species and is economically important worldwide [4,5,6] Anticoccidial compounds such as ionophores have been widely used in chemoprophylaxis to control Eimeria infection [7,8]. The residual anticoccidial drugs in poultry products such as meat and eggs have been concerned as potential risks that may affect human health. In this respect, the development of effective and economic coccidial vaccines is imperative
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