The Babesia bovis hap2 gene is not required for blood stage replication, but expressed upon in vitro sexual stage induction

• Published in: PLoS neglected tropical diseases Vol. 11; no. 10; p. e0005965
• Main Authors: Hussein, Hala E, Bastos, Reginaldo G, Schneider, David A, Johnson, Wendell C, Adham, Fatma K, Davis, William C, Laughery, Jacob M, Herndon, David R, Alzan, Heba F, Ueti, Massaro W, Suarez, Carlos E
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 06.10.2017; Public Library of Science (PLoS)
• Subjects: Animal diseases; Animals; Arachnid Vectors - parasitology; Arachnids; Asexual reproduction; Babesia; Babesia bovis - drug effects; Babesia bovis - genetics; Babesia bovis - growth & development; Babesia bovis - physiology; Babesiosis; Biological fertilization; Biology and Life Sciences; Blood; Bovidae; BSD gene; Cattle; Cattle - parasitology; Disease control; Disease transmission; Erythrocytes; Erythrocytes - parasitology; Female; Fertilization; Funding; Gene expression; Genes; Genes, Protozoan; Genetic aspects; Genomics; Health; Human diseases; Life cycle; Life cycle engineering; Life Cycle Stages; Life cycles; Malaria; Medicine and Health Sciences; Midgut; Parasites; Parasitology; Pathology; Peptide Elongation Factor 1 - genetics; Plasmids; Plasmodium; Promoter Regions, Genetic; Promoters (Genetics); Proteins; Protozoan Proteins - genetics; Protozoan Proteins - metabolism; Red blood cells; Replication; Reproduction (biology); Reproduction - drug effects; Reproduction - genetics; Research and Analysis Methods; Rhipicephalus - parasitology; Sexual reproduction; Sexual stages; Software; Strain; Supervision; Theileria; Transcription (Genetics); Transmission; Tropical diseases; Vaccines; Vector-borne diseases; Xanthurenates - pharmacology; Xanthurenic acid; United States > US
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0005965

Babesia bovis, is a tick borne apicomplexan parasite responsible for important cattle losses globally. Babesia parasites have a complex life cycle including asexual replication in the mammalian host and sexual reproduction in the tick vector. Novel control strategies aimed at limiting transmission of the parasite are needed, but transmission blocking vaccine candidates remain undefined. Expression of HAP2 has been recognized as critical for the fertilization of parasites in the Babesia-related Plasmodium, and is a leading candidate for a transmission blocking vaccine against malaria. Hereby we identified the B. bovis hap2 gene and demonstrated that it is widely conserved and differentially transcribed during development within the tick midgut, but not by blood stage parasites. The hap2 gene was disrupted by transfecting B. bovis with a plasmid containing the flanking regions of the hap2 gene and the GPF-BSD gene under the control of the ef-1α-B promoter. Comparison of in vitro growth between a hap2-KO B. bovis clonal line and its parental wild type strain showed that HAP2 is not required for the development of B. bovis in erythrocytes. However, xanthurenic acid-in vitro induction experiments of sexual stages of parasites recovered after tick transmission resulted in surface expression of HAP2 exclusively in sexual stage induced parasites. In addition, hap2-KO parasites were not able to develop such sexual stages as defined both by morphology and by expression of the B. bovis sexual marker genes 6-Cys A and B. Together, the data strongly suggests that tick midgut stage differential expression of hap2 is associated with the development of B. bovis sexual forms. Overall these studies are consistent with a role of HAP2 in tick stages of the parasite and suggest that HAP2 is a potential candidate for a transmission blocking vaccine against bovine babesiosis.