Characterisation of field tropical Theileriosis and associated risk factors in two bioclimatic areas of Algeria.

ABSTRACT

Tropical theileriosis (TT) is a tick-borne disease caused by Theileria annulata and commonly infects cattle in tropical and subtropical regions, including Algeria. It is a significant obstacle to cattle breeding programs established to improve production in Algeria. The present investigation aimed to estimate the current molecular prevalence, risk factors, and genetic characterisation of T. annulata in two bioclimatic areas of Algeria. In a cross-sectional study, 679 blood samples (629 from healthy cattle selected on farms and 50 from diseased cattle identified by veterinarians) were collected from the humid (n = 307+50) and semi-arid (n = 322) areas and screened by blood smear examination followed by polymerase chain reaction targeting cytochrome oxidase subunit 3 (cox III) mitochondrial and the 18S ribosomal RNA (18S rRNA) genes for Theileria spp. Seventy-six positive samples (56 clinically healthy and 20 with clinical signs) for Theileria spp. were confirmed to be T. annulata by the merozoïtes surface antigen-1 (Tams1) gene showing a rate of 8.9 % in clinically healthy and 40.0 % in suspected cattle. Among the 307 bloods samples collected from healthy cattle in the humid area, 25 cattle (8.1 %) were positive for T. annulata. Of the 322 healthy cattle from the semi-arid site, 31 (9.6 %) were carriers of T. annulata DNA. In subclinical population, demographic and environmental parameters analysis indicated that T. annulata infection was higher in adult crossbred cattle raised in the intensive and semi-intensive system (P<0.001). The multiple logistic regression analysis showed that age, breed, farming system, and bioclimatic area are potential risk factors for T. annulata infection in cattle (P<0.05). Multiple alignments of cox III sequences of T. annulata showed high heterogeneity with 25 polymorphic sites (nucleotide diversity π = 0.02402), resulting in two haplotypes with a low genetic diversity index (Hd) of 0.533. The 18S rRNA sequence alignment revealed only one T. annulata genotype with 100 % identity to the strains isolated from cattle and ticks in Mediterranean and Asian countries. Our preliminary results will serve as a basis for further studies on the genetic diversity and molecular epidemiology of T. annulata.