Bovine babesiosis is a tick-borne disease of cattle caused by the protozoan parasites of the genus Babesia. Babesia bovis, Babesia bigemina and Babesia divergens are considered by International health authorities (OIE) as the principal species of Babesia that cause bovine babesiosis. Animals that recover from a babesial primo infection may remain as persistent carriers with no clinical signs of disease and can be the source of infection for ticks that are able to acquire Babesia parasites from infected cattle and to transmit Babesia parasites to susceptible cattle. Several procedures that have been developed for parasite detection and diagnosis of this infectious carrier state constitute the basis for this review: A brief description of the direct microscopic detection of Babesia-infected erytrocytes; PCR-based diagnostic assays, which are very sensitive particularly in detecting Babesia in carrier cattle; in-vitro culture methods, used to demonstrate presence of carrier infections of Babesia sp.; animal inoculation, particularly for B. divergens isolation are discussed. Alternatively, persistently infected animals can be tested for specific antibabesial antibodies by using indirect serological assays. Serological procedures are not necessarily consistent in identifying persistently infected animals and have the disadvantage of presenting with cross reactions between antibodies to Babesia sp.

The instrumentation of the in vitro culture system has allowed researchers to learn more about the metabolic and growth behavior of Babesia spp. The various applications for in vitro cultivation of Babesia include obtaining attenuated strains for vaccination or pre-munition, the selection of pure lines with different degrees of virulence, studies on biological cloning, ultrastructure, antigen production for diagnostics, drug sensitivity assessments, and different aspects of parasite biology. Although there are different types of vaccines that have been tested against bovine babesiosis, so far, the only procedure that has offered favorable results in terms of protection and safety has been the use of live attenuated vaccines. In countries, such as Australia, Argentina, Brazil, Uruguay and Israel, this type of vaccine has been produced and used. The alternative to live vaccines other than splenectomized calf-derived biological material, has been the in vitro cultivation of Babesia bovis and B. bigemina . The development of in vitro culture of Babesia spp. strains in a defined medium has been the basis for the initiation of a source of parasites and exoantigens for a variety of studies on the biochemistry and immunology of babesiosis. The use of live immunogens from attenuated strains derived from in vitro culture is highlighted, which has been proposed as an alternative to control bovine babesiosis. In several studies performed in Mexico, this type of immunogen applied to susceptible cattle has shown the induction of protection against the experimental heterologous strain challenge with both, Babesia -infected blood and animal exposure to confrontations on tick vector-infested farms. The combination of transfection technologies and the in vitro culture system as integrated methodologies would eventually give rise to the generation of genetically modified live vaccines. However, a greater challenge faced now by researchers is the large-scale cultivation of Babesia parasites for mass production and vaccine distribution.

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The objective of this study was to evaluate in native cattle the use of an in vitro derived attenuated live vaccine (Babesia bovis-Babesia bigemina). Three commercial farms located in a tropical region in Chiapas State, Mexico were included. For each ranch, 40 animals were selected as negative to Babesia spp. by using an immunofluorescent antibody test (IFAT) and PCR. Animals were distributed in four groups with 10 animals each: (i) <9 months, (ii) 9-18, (iii) 18-36 and (iv) >36 months old. From each group, two subgroups were formed with five animals each; one subgroup was vaccinated and the other served as control without vaccination. Monitoring and sampling were carried out initially at vaccination (day 0), at day 7 and then every 4 weeks for 12 months. During the study rectal temperature ( degrees C), packed cell volume (Ht %) and percentage of erythrocytes parasitized were registered, furthermore IFAT and PCR were performed. Prevalence rate at the beginning of the study was 83% by IFAT. During the survey, 26 non-vaccinated of the 120 selected animals (43%) showed clinical symptoms of babesiosis, confirmed by stained smears versus only four (6.6%) of the vaccinated ones. All Babesia-affected animals required specific treatment. Vaccinated cattle showed titres of up to 1 : 1840 and 1 : 1027 for B. bovis and B. bigemina, respectively by IFAT. Protection conferred by vaccination was about 93%. We propose that this vaccine should not only be used in cattle coming from babesiosis free zones, but also in native cattle kept in hyperendemic areas.