A Comparative Genomic Study of Attenuated and Virulent Strains of Babesia bigemina

Bernardo Sachman-Ruiz,Carmen Rojas,Luis Lozano,Grecia Martínez,José J Lira,J Antonio Álvarez,Julio V Figueroa

doi:10.3390/pathogens10030318

Abstract

Cattle babesiosis is a socio-economically important tick-borne disease caused by Apicomplexa protozoa of the genus Babesia that are obligate intraerythrocytic parasites. The pathogenicity of Babesia parasites for cattle is determined by the interaction with the host immune system and the presence of the parasite’s virulence genes. A Babesia bigemina strain that has been maintained under a microaerophilic stationary phase in in vitro culture conditions for several years in the laboratory lost virulence for the bovine host and the capacity for being transmitted by the tick vector. In this study, we compared the virulome of the in vitro culture attenuated Babesia bigemina strain (S) and the virulent tick transmitted parental Mexican B. bigemina strain (M). Preliminary results obtained by using the Basic Local Alignment Search Tool (BLAST) showed that out of 27 virulence genes described and analyzed in the B. bigemina virulent tick transmitted strain, only five were fully identified in the attenuated laboratory strain. In all cases, the identity and coverture of the identified genes of the wildtype strain were higher than those of the laboratory strain. This finding is putatively associated with the continuous partial loss of virulence genes in the laboratory strain after several passages of the parasite population under optimal in vitro growth conditions. The loss of virulence factors might be reflected in the absence of symptoms of the disease in cattle inoculated with the attenuated strain despite the presence of infection in the bovine host cells.

Highlights

Bovine babesiosis is caused by Babesia bovis and Babesia bigemina in Mexico
The presentation of bovine babesiosis caused by B. bigemina is 12–16 days after the ticks feed on the bovine, coinciding with the presence of the intraerythrocytic parasite in the peripheral blood
The genome sequencing and assembly analysis elucidated that the attenuated Babesia bigemina laboratory strain contained a 9,180,241 pb and a wildtype 11,852,459 pb, which represented a 22.545% difference (Table 1)

Summary

Introduction

Bovine babesiosis is caused by Babesia bovis and Babesia bigemina in Mexico. The disease is distributed in tropical areas and is considered to be one of the most important diseases transmitted by Rhipicephalus microplus and R. annulatus ticks [1]. The absence of a reversion to virulence of the attenuated B. bigemina S strain was demonstrated after three successive passages in susceptible cattle and it was confirmed that the parasites maintained in the in vitro culture lost the ability to multiply in the vector tick during a second pass by sub-inoculation in susceptible cattle [26]. This was evidenced by the absence of kinetes in the hemolymph of ticks fed in cattle with patent parasitemia. The list of genes associated with the virulence of B. bigemina is called the virulome of B. bigemina

Results and Discussion

Parasites

Genomic DNA Extraction

Data Accession