Control of Rhipicephalus microplus on taurine cattle with fluralaner in a subtropical region.

BACKGROUND: In Rio Grande do Sul, Brazil, a region with a subtropical climate, Rhipicephalus microplus is present in taurine cattle raised for beef and milk. In addition, ticks resistant to multiple acaricides are present in this region. Recently, fluralaner (isoxazoline) was launched on the market. Thus, there is a need to evaluate the effects of fluralaner for the control of R. microplus on taurine cattle. In addition, occurrence of myiasis by Cochliomyia hominivorax larvae after tick parasitism and weight gain of cattle during the experimental period were evaluated. METHODS: Thirty naturally infested cattle were divided into two experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on; T02, control. T01 received fluralaner on Days 0 (early summer in January), 42 and 84 (early autumn), whereas T02, a control group, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of R. microplus females and calculation of the efficacy of fluralaner were performed on Days 3, 7, 14, 28, 35, 42, 56, 70, 84, 98, 112 and 126. The occurrence of myiasis was assessed throughout the study period. In addition, the weight, weight gain and daily weight gain of the animals were evaluated. RESULTS: In the 12 evaluations performed, the parasitic load of T01 was near zero. Fluralaner showed 99.5% efficacy on the 3rd day after the first treatment and 100% efficacy from Day 7 to Day 126. Cochliomyia hominivorax larvae (n = 6; p = 0.0251) were found only in the control group (T02). At the end of the study, the animals subjected to treatments with fluralaner gained 32.8 kg more than the animals in the control group. CONCLUSIONS: Application of fluralaner in summer and autumn, with 42-day intervals between treatments, was effective to control R. microplus on taurine cattle, which also gained more weight than control cattle. Additionally, no cases of myasis were documented in animals treated with fluralaner.

Can herd seroprevalence be used as an indicator of enzootic stability for bovine anaplasmosis? Insights from a case-control field study in Brazil.

Bovine anaplasmosis presents a significant challenge to livestock production in tropical, subtropical, and temperate regions. For many years, the concept of enzootic stability/instability (initially established for babesiosis) and herd seroprevalence as an indicator of outbreak risks have been applied to anaplasmosis. However, this model has never been definitively validated for Anaplasma marginale. The objective of this study was to examine the relationship between herd immunity (seroprevalence) and the occurrence of anaplasmosis outbreaks in Southern Brazil. A case-control study was conducted, categorizing farms into two groups: cases (farms with a history of clinical anaplasmosis) and controls (those without anaplasmosis). Thirteen farms were identified as "cases", while 23 were identified as "controls". A substantial difference in seroprevalence distribution between the two groups was observed. The majority of "control" farms exhibited over 75% of animals with antibodies to A. marginale in both calves and heifers, whereas the majority of "case" farms had a seropositive cattle percentage below 75%. Additionally, twelve months after cattle serology tests, we conducted a prospective follow-up survey to identify any clinical cases of anaplasmosis. Statistical associations (P < 0.05) were found between both retrospective and prospective anaplasmosis outbreaks and the hypothetical threshold of herd seroprevalence (75%). We hypothesize that herd seroprevalence may be an indicator of the risk of occurrence of clinical anaplasmosis. It appears that the epidemiology of cattle anaplasmosis, at least in our conditions, aligns with the well-known model of enzootic stability/instability originally applied to bovine babesiosis.

Does parity order or cow antibody level influence the humoral immunity of calves for cattle anaplasmosis?

Anaplasmosis is a widely distributed vector-borne disease of cattle caused by the bacteria Anaplasma marginale, which may lead to severe losses in beef and dairy cattle production. Anecdotal information among farmers suggested that some cows may deliver calves more resilient to anaplasmosis. To investigate this, we tested two hypotheses: (i) whether the parity order or (ii) cow antibody levels may influence the humoral immunity of pre-weaning calves against cattle anaplasmosis. For this study, we sampled 170 cattle (Bos taurus taurus, Angus breed) on a farm in Southern Brazil, comprising 85 cows (50 multiparous and 35 primiparous) and their 85 calves (50 days old). Antibodies against A. marginale were investigated using iELISA. Eighty percent of the animals were considered seropositive (100% of the cows and 60% of the calves). There was no significant difference in seroprevalence between calves from primiparous and multiparous cows. However, calves from multiparous cows exhibited higher antibody levels. To address the second question, we classified cows based on their antibody levels to A. marginale (high or low). Calves from cows with high antibody levels also showed elevated antibody levels against A. marginale. Furthermore, calves from cows with high antibody levels had approximately four times greater odds of being seropositive for A. marginale at 50 days old than those born to mothers with low antibody levels. In conclusion, the calf's antibody level against A. marginale appears to be related to the cow's parity order and the mother's antibody level.