Seasonal Variation and Frequency Distribution of Ectoparasites in Crossbreed Cattle in Southeastern Brazil

Ticks and antibodies: May parasite density and tick evasion influence the outcomes following immunization protocols?

Ticks are a major concern to human health and livestock worldwide, being responsible for economic losses that go beyond billions of US dollars per year. This scenario instigates the development of vaccines against these ectoparasites, emphasized by the fact that the main method of controlling ticks still relies on the use of acaricides, what increases costs and may affect the environment as well as human and animal health. The first commercial vaccines against ectoparasites were produced against the tick Rhipicephalus microplus and their efficacy were based on antibodies. Many additional attempts have been conducted to produce protective immune responses against ticks by immunization with specific antigens and the antibody response has usually been the main target of evaluation. But some controversy still populates the roles possibly performed by humoral responses in tick-mammalian host relationships. This review focuses on the analysis of specific aspects concerning antibodies and ticks, especially the influence of parasite density and evasion/modulation. The immunization trials already described against R. microplus were also compiled and analyzed based on the characteristics of the molecules tested, protocols of immunization and tick challenge. Within these issues, it is discussed if or when antibody levels can be directly correlated with the development of tick resistance, and whether anti-tick protective immune responses generated by infestations may become ineffective under a different tick density. Also, higher titers of antibodies can be correlated with protection or susceptibility to tick infestations, what may be altered following continuous or repeated infestations and differ greatly comparing hosts with distinct genetic backgrounds. Regarding evasion, ticks present a sophisticated mechanism for dealing with antibodies, including Immunoglobulin Binding Proteins (IGBPs), that capture, transport and inject them back into the host, while keeping their properties within the parasite. The comparison of immunization protocols shows a total of 22 molecules already tested in cattle vaccination trials against R. microplus, with the predominance of concealed and dual antigens as well as marked differences in tick challenge schemes. The presence of an antibody evasion apparatus and variable levels of tick resistance when facing different densities of parasites are concerns that should be considered when testing vaccine candidates. Ultimately, more refinement may be necessary to effectively design a cocktail vaccine with tick molecules, which may be needed to be altered and combined in non-competing immune contexts to be universally secure and protective.

Dynamics of natural infection by Babesia bovis and Babesia bigemina in dairy cattle from an enzootic instability area in Northeastern Brazil

This study aimed to determine the dynamics of natural infection in the transmission of Babesia spp. to cattle in an enzootic instability area in Northeastern Brazil. Blood samples were collected from 30 calves located on two dairy farms to determine the packed cell volume (PCV) and the timing of the primo-infection using polymerase chain reaction (PCR) and their association with climatic factors and management practices. On Farm A, the determination of primo-infection was observed on average at 249.4 (±24.42) days of age for B. bigemina and at 252.6 (±17.07) days of age for B. bovis; there was no significant difference between the times of infection (P> 0.05). The infection coincided with a period of high rainfall in the region. On Farm B, primo-infection infection was not observed. There was no infection by Babesia spp. on Farm B due to the intensive use of acaricides that led to an absence of ticks. There was no significant difference between the average PCV of animals from Farms A and B (P> 0.05). The management practices on the properties, in addition to the weather conditions influenced the exposure of the animals to disease vectors and may have contributed to the maintenance of this enzootic area in Northeastern Brazil.

Off-host development and survival of Rhipicephalus (Boophilus) microplus in the Brazilian semiarid

Rhipicephalus (Boophilus) microplus is the most economically important tick of the world, including Brazil. Whereas the epidemiology of R. microplus is well known in most of the Brazilian land, virtually nothing is known from the Brazilian semiarid region, the Caatinga biome. Considering the relevance of R. microplus for the cattle industry within the Caatinga, this study aimed to evaluate for the first time the off-host development of this tick species under natural conditions of the Caatinga. During 2011-2015, engorged females of R. microplus were exposed to field conditions of native Caatinga, where female oviposition, egg incubation and hatching, and larval survival were quantified. In parallel, counterpart ticks (control group) were evaluated under optimal conditions in the laboratory. During the study, nearly 100% of the engorged females of the control group successfully oviposited fertile egg masses, from which most of the eggs yielded larvae (mean % hatching usually>90%). Under field conditions, while almost 100% of the engorged females oviposited, in most of the times no larvae hatched from these eggs. Furthermore, when larvae hatched, mean % hatching was most of the times <50%. Soil temperatures did not oscillate drastically through the study, with mean temperature between 30 and 35°C in most of the time. In contrast, rainfall was irregular throughout the study. Correlation analyses indicated that either the number of egg masses that yielded larvae, or the mean % hatching of the egg masses were positively associated with higher rainfall months. Our results showed that in most of the time, field conditions were unfavorable for R. microplus, indicating that cattle would have a low exposure to R. microplus infestations when raised in Caatinga fields like those of the present study.