Vector-borne transmission of Besnoitia besnoiti by blood-sucking and secretophagous flies: epidemiological and clinicopathological implications

Abstract

BackgroundBovine besnoitiosis has been recently diagnosed in a three-parted herd of 796 Aubrac and Charolais beef cattle in Hungary. A large scale serological, histological and molecular survey was initiated in order to uncover important factors in the local epidemiology of the disease.FindingsBlood samples were collected (three times from the whole herd, and repeatedly from selected animals) for serological screening by ELISA. In addition, various organs from aborted fetuses and newborn calves, skin and colostrum samples of seropositive heifers/cows, and ticks collected from the cattle were histologically and/or molecularly analysed for the presence of Besnoitia besnoiti.All fetal and calf tissues, as well as colostrum and tick samples from cows were PCR negative. Based on ELISA results, only very few local cows seroconverted after mating with imported, infected bulls, and not necessarily as a consequence of this event. Among calves that were born to seropositive, imported cows and stayed with their mother until weaning at seven months of age, seroprevalence decreased significantly, but remained high. At the same time, 28 calves born from seropositive cows, but separated from their dams immediately after receiving colostrum, were successfully reared and remained uninfected.Following a second herd-level screening, all Aubrac cattle (except for heifer calves) and all seropositive Charolais cows and bulls were culled. Manifestation of the disease is currently sporadic. Among chronically affected heifers two types of skin lesions were noted, and histological evaluation indicated marked distension of sweat gland ducts with membrane-bound structures (resembling cystozoites) in their contents.ConclusionsTransmission through natural mating, as well as transplacental, colostral and tick-borne transmission of B. besnoiti was either unlikely or did not occur. However, the risk for spreading of the infection was high, when calves stayed with their mother during suckling, and if animals were kept in the same stable (although physically separated) during the main fly season. Herd replacement and generation exchange (i.e. early weaning and artificial feeding) appear to be the successful strategies for the local eradication of bovine besnoitiosis. Adding to the already known mechanical transmission of B. besnoiti by blood-sucking flies, results of the present study suggest that secretophagous flies should also be evaluated as potential vectors of this coccidium species.

Vascular wall injury and inflammation are key pathogenic mechanisms responsible for early testicular degeneration during acute besnoitiosis in bulls

“…Vascular lesions can cause a lack of irrigation, hindering the cooling of the testicle at the level of the pampiniform plexus aggravated by the presence of tissue cysts that may occlude the lumen of the vessel [33]. On the other hand, fibroplasia, hyperkeratosis and ectasias of sweat glands would hinder the cooling of the testicle [34]. During chronic besnoitiosis, there is a lack of heat exchange in the testicle due to thickening of the scrotum, which may contribute to permanent infertility [35].…”

Bovine besnoitiosis (Besnoitia besnoiti) in an Irish dairy herd

“…Given the patterns of occurrence of clinical cases during the warmer months in this herd, it is reasonable to assume that vectors are playing a role in the intra‐herd disease transmission. A recent study, examining the local epidemiology of besnoitiosis transmission in beef cattle in Hungary, investigated a number of different transmission routes including vectors (biting flies and ticks), transplacental transmission, colostral transmission, as well as the importance of close contact for transmission (Hornok and others 2015b). These authors found that venereal, transplacental, colostral and tickborne transmission of B. besnoiti was unlikely or did not occur.…”

Seroprevalence and risk factors of Besnoitia besnoiti infection in Korean cattle – short communication

“…Besnoitia besnoiti (Apicomplexa: Sarcocystidae) is an obligate intracellular parasite that causes bovine besnoitiosis (Cortes et al, 2014). In contrast to other coccidian parasites, the main route of spreading of B. besnoiti between animals is mechanical transmission by flies as vectors (Hornok et al, 2015). The clinical signs of besnoitiosis in cattle differ according to the stage of infection.…”

“…In the chronic stage, severely lichenified and alopecic skin is observed, and the bulls can develop orchitis, resulting in infertility (Schares et al, 2013). Generally, while bovine besnoitiosis is associated with a high morbidity and low mortality, not all infected animals develop clinical signs (Jacquiet et al, 2010;Hornok et al, 2015).…”