Integrated diagnostic strategy for Theileria equi in camels: combining real-time PCR and cELISA for molecular and...

Theileria equi is a globally significant tick-borne pathogen causing equine piroplasmosis, yet its occurrence in dromedary camels (Camelus dromedarius) is an understudied phenomenon. This study provides an integrated molecular and serological characterization of T. equi in dromedary camels in Egypt. A total of 210 blood samples were collected from apparently healthy slaughtered camels in Giza, Sharqia, and Cairo governorates and subjected to an integrated diagnostic approach comprising microscopic examination, conventional PCR (cPCR), species-specific cPCR, real-time PCR (rtPCR), and competitive ELISA (cELISA). Microscopic examination identified 16/210 (7.6%, 95% CI: 4.7-11.9%) positive samples, while universal cPCR targeting the Babesia/Theileria 18 S rRNA gene yielded a prevalence of 12.4% (26/210, 95% CI: 8.4-17.8%). Species-specific cPCR increased the detection rate to 28.6% (95% CI: 22.7-35.3%), while rtPCR demonstrated superior sensitivity, identifying T. equi DNA in 43.3% (95% CI: 36.8-50.1%) of samples indicating a high carrier state. In contrast, serological analysis via cELISA revealed a markedly low antibody prevalence of 2.4% (95% CI: 1.0-5.5%), likely reflecting the inadequate validation of the commercial equine-specific assay for camelid immunoglobulins rather a true absence of exposure. Phylogenetic analysis based on the partial 18 S rRNA gene of two camel isolates (deposited in GenBank accession numbers PZ014470.1 and PZ014471.1) demonstrated that both clustered tightly within the T. equi genotype A, sharing 98-100% nucleotide identity with equine T. equi strains from geographically diverse regions. Pairwise alignment and genetic distance analyses confirmed minimal divergence between camel-derived and equine-derived isolates, while clear separation was observed from other Theileria and Babesia species. These findings provide unequivocal molecular evidence that Egyptian dromedary camels act as carriers of T. equi strains genetically indistinguishable from those infecting equids, strongly suggesting that camels may act as incidental hosts the epidemiology of equine piroplasmosis. This study underscores the critical need for inclusion of camels in surveillance programmes and tick-borne disease control strategies in endemic regions and the development of camel-specific diagnostic tools.