Abstract
BackgroundBovine besnoitiosis, an emerging disease in Europe that can be transmitted by vectors, is caused by the apicomplexan Besnoitia besnoiti. Bovine besnoitiosis is difficult to control due to the complexity of its diagnosis in the acute stage of the disease, poor treatment success and chronically asymptomatic cattle acting as parasite reservoirs. When serological prevalence is low, detection and specific culling of seropositive cattle is feasible; however, economic considerations preclude this approach when serological prevalence is high. The aims of this study were to evaluate the accuracy of detection of super-spreaders in highly infected herds and to test their selective elimination as a new control strategy for bovine besnoitiosis.MethodsPrevious real-time PCR analyses performed on skin tissues from 160 asymptomatic animals sampled at slaughterhouses showed that the tail base was the best location to evaluate the dermal parasite DNA load. All seropositive animals (n = 518) from eight dairy or beef cattle farms facing a high serological prevalence of besnoitiosis were sampled at the tail base and their skin sample analysed by real-time PCR. A recommendation of rapid and selective culling of super-spreaders was formulated and provided to the cattle breeders. Subsequent serological monitoring of naïve animals was used to evaluate the interest of this control strategy over time.ResultsAmong the 518 seropositive animals, a low proportion of individuals (14.5%) showed Cq values below 36, 17.8% had doubtful results (36 < Cq ≤ 40) and 67.8% had negative PCR results. These proportions were grossly similar on the eight farms, regardless of their production type (beef or dairy cattle), size, geographical location or history of besnoitiosis. Within two weeks of the biopsy, the rapid culling of super-spreaders was implemented on only three farms. The numbers of newly infected animals were lower on these farms compared to those where super-spreaders were maintained in the herd.ConclusionsReal-time PCR analyses performed on skin biopsies of seropositive cattle showed huge individual variabilities in parasite DNA load. The rapid culling of individuals considered as super-spreaders seems to be a new and encouraging strategy for bovine besnoitiosis control.
Highlights
Bovine besnoitiosis, an emerging disease in Europe that can be transmitted by vectors, is caused by the apicomplexan Besnoitia besnoiti
Mean Quantification cycle (Cq) values in skin samples ranged from 15.0 to 20.0 but no significant difference was observed between the lower body parts
When the serological prevalence is below 10% in a cattle herd, the rapid detection and subsequent culling or separation of all seropositive individuals is currently the most effective way to prevent the within-herd spread of besnoitiosis [14]
Summary
An emerging disease in Europe that can be transmitted by vectors, is caused by the apicomplexan Besnoitia besnoiti. Bovine besnoitiosis is a re-emerging protozoan disease in Europe caused by the cyst-forming apicomplexan parasite Besnoitia besnoiti [1, 2]. The tachyzoite and bradyzoite stages of the parasite develop in the cattle host and are respectively responsible for the acute and chronic phases of this disease. The subsequent chronic phase, which can last several years, is characterized by massive skin alterations resulting from the formation of numerous cysts containing thousands of bradyzoites. This chronic and debilitating disease is responsible for heavy economic losses in cattle, and sometimes death. In most infected and seropositive cattle, no obvious clinical signs are observed
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