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Evaluation of the efficacy of ivermectin against Theileria orientalis infection in grazing cattle.

ABSTRACT:

Background

Raising cattle on pastures is known to be beneficial for animal welfare and cost reduction. However, grazing is associated with the risk of contracting tick-borne diseases, such as theileriosis. Here, the efficacy of ivermectin against these diseases and associated clinical symptoms were evaluated.

Results

A total of 68 cattle from a grazing cattle farm were selected and divided into two groups: the control group (17 cattle) with no preventive treatment and the ivermectin-treated group (51 cattle) in which cattle were treated with pour-on ivermectin prior to grazing. The infection rates of Theileria orientalis and the red blood cell (RBC) profile (e.g., RBC count, hematocrit value, and hemoglobin concentration) were compared in the spring (before grazing) and summer (during grazing) between the two groups. Based on PCR amplification of the major piroplasm surface protein (MPSP) gene, 12 cattle were positive for T. orientalis infection. Phylogenetic analysis revealed that the isolates identified in this study consisted of three MPSP types (1, 2, and 7). The T. orientalis infection rate in the control group during grazing was 3-fold higher than that in the ivermectin-treated group. Moreover, differences in RBC parameters during grazing were greater in the control group than in the ivermectin-treated group. In particular, the hematocrit value was significantly reduced in the control group.

Conclusions

The results of this study demonstrated that ivermectin had protective effects against T. orientalis infection and RBC hemolysis in grazing cattle.

SUBMITTER: Park J

PROVIDER: S-EPMC6697941 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionTheileria orientalis, an economically significant tick-borne hemoparasite, infects cattle globally. The T. orientalis Ikeda genotype, transmitted by Haemaphysalis longicornis ticks, is associated with clinical manifestations characterized by anemia, abortions, and mortality, although subclinical infections prevail. Despite the common occurrence of subclinical infections, therapeutic interventions targeting T. orientalis Ikeda in such cases are currently lacking, impeding effective parasite control measures. To address this critical knowledge gap, we assessed the efficacy of buparvaquone (BPQ) in eliminating the T. orientalis Ikeda, US isolate, in sub-clinically infected cattle.MethodsTwelve sub-clinically infected calves, identified by the presence of T. orientalis in peripheral blood alongside the absence of fever and anemia, were enrolled in the study. Six calves received two treatments of the BPQ label dose (2.5 mg/kg) at a 48-h interval, while additional three calves received the drug at a dosage of 6 mg/kg following the same regimen. Three untreated calves served as controls.Results and discussionEndpoint and quantitative PCR analyses revealed that BPQ exerted a transient effect on T. orientalis parasitemia. Parasites remained undetectable in peripheral blood until weeks 4 and 11 post-treatment in animals administered 2.5 mg/kg and 6 mg/kg of BPQ, respectively. Intriguingly, following recrudescence, administering 6 mg/kg to animals previously treated with 2.5 mg/kg did not result in a reduction in parasite load. Pharmacokinetic analysis data suggested that escalating the dosage led to a less than proportional increase in serum concentrations of BPQ. Moreover, a significant yet reversible decrease (p < 0.05) in blood urea nitrogen was observed in animals treated with the drug, irrespective of the dosage. Despite parasitemia relapse, animals treated with 6 mg/kg BPQ exhibited a noteworthy decrease (p < 0.05) in IgG levels specific to the T. orientalis major piroplasm surface protein compared to controls and animals treated with 2.5 mg/kg of the drug.ConclusionBPQ did not demonstrate efficacy in clearing subclinical T. orientalis Ikeda infection. Future investigations are warranted to explore innovative therapeutic modalities that, in synergy with vaccines and diagnostic assays, can facilitate the development of comprehensive programs aimed at controlling and eradicating this parasite.

Project description:BackgroundBovine theileriosis, caused by the haemoprotozoan Theileria orientalis, is an emerging disease in East Asia and Australasia. Previous studies have demonstrated transplacental transmission of various Theileria spp. but molecular confirmation of transplacental transmission of T. orientalis has never been confirmed in the field. In this study, cow-calf (< 48 h old) pairs were sampled across 3 herds; opportunistic samples from aborted foetuses or stillborn calves were also examined. Molecular (multiplex qPCR) and serological (ELISA) methods were used to determine infection prevalence and the presence of anti-Theileria antibodies in each herd. In addition, pregnant heifers and foetal calves were sampled at abattoir and tested for the presence of T. orientalis by qPCR.ResultsThe qPCR results indicated that, even though there was a high prevalence of T. orientalis infection in cows, the rate of transplacental transmission to their calves was low, with only one newborn calf from one herd and one foetus from the abattoir testing positive for T. orientalis DNA. Five aborted foetuses and stillborn calves, 3 of which were derived from a herd experiencing a high number of clinical theileriosis cases at the time of sampling, all tested negative for T. orientalis by qPCR. This suggests that in utero infection of calves with T. orientalis may not be a major driver of abortions during theileriosis outbreaks. Temporal monitoring of 20 calves born to T. orientalis-positive mothers indicated that T. orientalis was detectable in most calves between 10 and 27 days post-partum, consistent with prior field studies on adult cattle introduced to Theileria-affected herds. There was a positive correlation between the ELISA ratio of newborn calves and their mothers within 48 h of calving; however, maternal antibodies were only detectable in some calves and only for 4-4.5 weeks post-partum. All calves displayed high parasite loads peaking at 4-8 weeks post-partum, with only some calves subsequently mounting a detectable adaptive antibody response.ConclusionsThese findings indicate transplacental transmission of T. orientalis appears to play only a minor role in persistence of T. orientalis infection in the field; however calves are highly susceptible to developing high level T. orientalis infections at 4-8 weeks of age regardless of whether maternal antibodies are present post-partum.