Abstract
Bovine babesiosis, caused by Babesia bovis, is an economically significant tick-borne disease that imposes restrictions to livestock production worldwide. Current methods to control bovine babesiosis have severe limitations and novel approaches, including transmission-blocking vaccines, are needed. Members of the widely conserved CCp family are multidomain adhesion proteins containing LCCL motifs, which are differentially expressed on gametocytes of apicomplexans, including Babesia spp. and Plasmodium spp. While Plasmodium parasites contain 6 distinct CCp genes, only three members (CCp 1-3) were previously identified in B. bovis. In this study, we describe the identification and characterization of two novel non-canonical members of the CCp gene family in B. bovis, named CCp5 and FNPA. The genes were identified in silico by TBLASTN using P. falciparum CCp family domains as queries. Unlike CCp1-3, the B. bovis CCp5 and FNPA proteins lack the LCCL canonical domain but contain other typical multidomain adhesion motifs which are present in classical CCp proteins. In addition, the B. bovis CCp5 and FNPA are in synteny with known CCp genes in related apicomplexans. Sequence analysis of these two proteins demonstrated high sequence conservation among B. bovis different isolates. Transcription, immunoblot, and immunofluorescence analyses demonstrated expression of CCp5 and FNPA in blood and in vitro induced sexual stages of B. bovis. The FNPA, in contrast to CCp5, has a predicted transmembrane domain, suggesting that it might be expressed in the surface of sexual stage parasites. Altogether, finding of this study support FNPA as a possible target of a transmission-blocking vaccine against B. bovis.
Highlights
Babesia bovis, which is transmitted by Rhipicephalus spp. ticks, is a hemoparasite responsible for bovine babesiosis, a disease that causes enormous economic losses to the cattle industry in tropical and subtropical regions worldwide
Database searches on the B. bovis genome using TBLASTN with the P. falciparum CCp family domains as queries resulted in the identification of two additional and previously unnoticed CCp-like genes, which we termed here as CCp5 and FNPA
We describe the presence of two additional single gene-copy CCp-related genes (CCp5 and FNPA) in the genome of B. bovis and B. bigemina, as previously described in Plasmodium spp. [16, 31]
Summary
Babesia bovis, which is transmitted by Rhipicephalus spp. ticks, is a hemoparasite responsible for bovine babesiosis, a disease that causes enormous economic losses to the cattle industry in tropical and subtropical regions worldwide. Babesia parasites have a complex lifecycle that includes the development of asexual stages in vertebrate hosts and sexual stages inside their definitive tick vectors [1–3]. Sporozoites, the infectious form of B. bovis, are introduced via tick saliva into the bovine host by infected Rhipicephalus spp., where they invade and reproduce asexually as merozoites in red blood cells (RBC). Babesia bovis acute infection in cattle results in high fever, anorexia, inappetence, and severe intravascular hemolytic anemia. B. bovis expresses proteins that facilitate cytoadhesion of infected RBCs to capillaries, causing neurological symptoms and general organ failure, leading to rapid death of cattle, especially in immunologically naïve adult (more than one-year old) animals [3, 8, 9]
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