Development of a protocol testing the ability of Stomoxys calcitrans (Linnaeus, 1758) (Diptera: Muscidae) to transmit Besnoitia besnoiti (Henry, 1913) (Apicomplexa: Sarcocystidae)

Abstract

Cattle besnoitiosis due to the cyst-forming coccidian parasite Besnoitia besnoiti has recently been reported in expansion in Europe since the end of the twentieth century. The B. besnoiti life cycle and many epidemiological traits are still poorly known. Hematophagous flies, including the worldwide-distributed Stomoxys calcitrans, could be mechanical vectors in the contamination of mouthparts after the puncture of cutaneous cysts or ingestion of infected blood. In this study, a protocol is presented to assess more deeply the role of S. calcitrans, reared in laboratory conditions, in parasite transmission. A preliminary trial showed that stable flies could transmit tachyzoites from bovine artificially parasite-enriched blood to B. besnoiti-free blood using glass feeders. Evidence of transmission was provided by the detection of parasite DNA with Ct values ranging between 32 and 37 in the blood recipient. In a second time, a B. besnoiti-infected heifer harboring many cysts in its dermis was used as a donor of B. besnoiti. An interruption of the blood meal taken by 300 stable flies from this heifer was performed. Immediately after the blood meal was interrupted, they were transferred to a glass feeder containing B. besnoiti-free blood from a non-infected heifer. Quantitative PCR and modified direct fluorescence antibody test (dFAT) were used to detect B. besnoiti DNA and entire parasites, respectively, in the blood recipient, the mouthparts, and the gut contents of S. calcitrans at two time intervals: 1 and 24 h after the interrupted blood meal. Parasite DNA was detected at both time intervals (1 and 24 h) in all samples (blood recipient, mouthparts, and gut contents of stable flies) while entire parasites by dFAT were only found in the abdominal compartment 1 h after the interrupted blood meal. Then, S. calcitrans were able to carry B. besnoiti from chronically infected cattle to an artificial recipient in the conditions of the protocol.

Fig. 1

Diagrams of the experimental design. a Experiment 1: control group. b Experiment 2: experimental transmission with tachyzoite-enriched blood as a source of parasites. c Experiment 3: experimental transmissions with long exposure time to a chronically infected heifer as a source of parasites. d Experiment 4: experimental transmissions with short exposure time to a chronically infected heifer as a source of parasites

Fig. 1

Diagrams of the experimental design. a Experiment 1: control group. b Experiment 2: experimental transmission with tachyzoite-enriched blood as a source of parasites. c Experiment 3: experimental transmissions with long exposure time to a chronically infected heifer as a source of parasites. d Experiment 4: experimental transmissions with short exposure time to a chronically infected heifer as a source of parasites

Fig. 2

Positive dFAT for tachyzoite culture (a) and for abdominal contents of S. calcitrans (b) after 1-h exposure on blood glass feeder preceded by 5 min of exposure to the heifer's skin (experiment 4). White rows indicate B. besnoiti parasites