Coinfection with Antigenically and Genetically Distinct Virulent Strains of Babesia bovis Is Maintained through All Phases of the Parasite Life Cycle

Abstract

Antigenic polymorphism is a defining characteristic of the Babesia bovis variable merozoite surface antigen (VMSA) family. Sequence analysis strongly suggests that recombination between virulent strains contributes to VMSA diversity. While meiosis during the aneuploid stage of the parasite's life cycle in the tick vector Rhipicephalus (Boophilus) microplus is the most probable source of interstrain recombination, there is no definitive evidence that coinfection of the mammalian host or R. microplus ticks with more than one virulent strain occurs. Using allele-specific real-time quantitative PCR, we tested the hypotheses that cattle could support coinfection of two antigenically variant virulent tick-transmissible strains of B. bovis and that R. microplus ticks could acquire and transmit these two divergent strains. The results indicate that both calves and ticks can support virulent B. bovis coinfection through all phases of the hemoparasite's life cycle. Neither strain dominated in either the mammalian or invertebrate host, and larval tick progeny, which could be coinfected individually, were also able to transmit both strains, resulting in virulent babesiosis in recipients. While coinfection of the tick vector provides the context in which allelic antigenic diversity can be generated, recombination of VMSA genes could not be confirmed, suggesting that VMSA allelic changes are slow to accumulate.

Genetic polymorphism of Babesia bovis merozoite surface antigens-2 (MSA-2) isolates from bovine blood and Rhipicephalus annulatus ticks in Israel

“…The mixtures of B. bovis genotypes present in cattle and ticks were previously described by Berens et al (2007), who showed that cattle could support co-infection of two antigenically variant tick-transmissible virulent strains of B. bovis, and that R. microplus ticks could acquire and transmit these two strains. Similarly, in another study, Lau et al (2010) suggested that the recombination between isolates would most likely occur during the tick's acquisition of blood meals from the co-infected mammalian hosts: the infected ticks could transmit new variants that might cause clinical outbreaks in vaccinated herds that already had developed herd immunity (Lau et al, 2010).…”

“…The B. bovis VMSA family, expressed from multiple different alleles. Homologous recombination, between or within isolates contributes to VMSA diversity (Allred et al, 2000;Berens et al, 2007;Lau et al, 2010). The different MSA-2 genotypes present simultaneously in the examined samples may arise within the individual animal and ticks through infection with another genotype resulting in co-infection.…”

High within-host genetic variation of the nematode Spirocerca lupi in a high-density urban dog population

“…If within host variation is an important determinant of virulence as suggested by theory (Frank, 1996;Berens et al, 2007;Restif, 2009), the more frequent amalgamation of infrapopulations (Eppert et al, 2002) in urban areas should lead to a more virulent parasite population. It may be interesting to compare virulence between such populations.…”

Piroplasmids and ticks: a long-lasting intimate relationship

“…While the same is probably true for Babesia sp. parasites, its experimental demonstration is still pending (32). In addition, selection of piroplasmid subpopulations from heterogeneous field isolates is likely to happen during the tick life cycle stages.…”