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Ability of the Vector Tick Boophilus microplus To Acquire and Transmit Babesia equi following Feeding on Chronically Infected Horses with Low-Level Parasitemia

Ability of the Vector Tick Boophilus microplus To Acquire and Transmit Babesia equi following Feeding on Chronically Infected Horses with Low-Level Pa

Ability of the Vector Tick Boophilus microplus To Acquire and Transmit Babesia equi following Feeding on Chronically Infected Horses with Low-Level Parasitemia   (Citations: 11)
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The protozoan parasite Babesia equi replicates within erythrocytes. During the acute phase of infection, B. equi can reach high levels of parasitemia, resulting in a hemolytic crisis. Horses that recover from the acute phase of the disease remain chronically infected. Subsequent transmission is dependent upon the ability of vector ticks to acquire B. equi and, following development and replication, establishment of B. equi in the salivary glands. Although restriction of the movement of chronically infected horses with B. equi is based on the presumption that ticks can acquire and transmit the parasite at low levels of long-term infection, para- sitemia levels during the chronic phase of infection have never been quantified, nor has transmission been demonstrated. To address these epidemiologically significant questions, we established long-term B. equi infections (>1 year), measured parasitemia levels over time, and tested whether nymphal Boophilus microplus ticks could acquire and, after molting to the adult stage, transmit B. equi to naive horses. B. equi levels during the chronic phase of infection ranged from 10 3.3 to 10 6.0 /ml of blood, with fluctuation over time within individual horses. B. microplus ticks fed on chronically infected horses with mean parasite levels of 10 5.5 10 0.48 /ml of blood acquired B. equi, with detection of B. equi in the salivary glands of 7 to 50% of fed ticks, a range encompassing the percentage of positive ticks that had been identically fed on a horse in the acute phase of infection with high parasitemia levels. Ticks that acquired B. equi from chronically infected horses, as well as those fed during the acute phase of infection, successfully transmitted the parasite to naive horses. The results unequivocally demonstrated that chronically infected horses with low-level parasitemia are competent mammalian reservoirs for tick transmission of B. equi.
Published in 2005.
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    • ...The maintenance of tick-borne infections in natural reservoir hosts is dependent upon the efficiency of acquisition and transmission events at the tick-host and tick-pathogen interfaces (7, 20)...
    • ...The first mode is transstadial transmission that occurs when a tick stage (e.g., larval or nymphal) acquires the pathogen from a mammalian reservoir host and a subsequent life cycle stage within the same tick generation transmits the pathogen to an uninfected host (11, 18, 20)...
    • ...Transstadial transmission of B. equi parasites has been confirmed; R. microplus nymphs acquire B. equi infections during acquisition feeding on either acutely or chronically infected horses and, following molting and movement to a new host, can successfully transmit B. equi parasites to naõ ¨ve horses (20)...
    • ...Subsequent to incubation, for transmission feeding, approximately 100 adult male ticks were applied under a cloth patch and allowed to feed on four naõ ¨ve horses (H085, H090, H098, and H112) to determine their ability to transmit B. equi parasites (18, 20)...
    • ...Following 8 days of transmission feeding, all male ticks were forcibly removed, and their individual salivary glands were dissected (20)...
    • ...Systems, Inc., Minneapolis, MN) and tested by duplex nested PCR, targeting the B. equi ema-1 and R. microplus -tubulin genes (19, 20)...
    • ...Tick infection rates were calculated as previously described (7, 20) by dividing the total number of PCRpositive ticks by the total number of ticks tested...
    • ...The levels of B. equi organisms in the peripheral blood of horses exposed to acquisition feeding and in the salivary glands of R. microplus ticks were quantified by real-time PCR, targeting B. equi ema-1 as previously described (19, 20)...
    • ...The infection status of horses exposed to transmission feeding by adult male ticks was determined by Giemsastained blood smear and confirmed by nested PCR, targeting B. equi ema-1 (20)...
    • ...Genomic DNA samples were extracted as previously described (7), and nested PCR targeting ema-1 was performed to determine the B. equi infection status (20)...
    • ...The infection status of the splenectomized horses was determined by daily microscopic examination of Giemsa-stained blood smears and nested PCR targeting B. equi ema-1 (20)...
    • ...In contrast to the intrastadial transmission mode demonstrated with adult male R. microplus ticks and the previously documented transstadial transmission (20), the hypothesis that vertical passage of B. equi parasites would allow transmission by the subsequent R. microplus generation was rejected...
    • ...In summary, these studies establish that, in addition to the previously documented transstadial transmission (20), intrastadial transmission by adult male R. microplus ticks is a mechanism of transmission for B. equi parasites and should be targeted for control...

    Massaro W. Uetiet al. Persistently Infected Horses Are Reservoirs for Intrastadial Tick-Born...

    • ...Arthropod vectors transmit a wide diversity of microbial pathogens, including viruses, bacteria, and protozoa, to humans and animals (2, 12, 20, 25, 28)...
    • ...Immediately after removal, a cohort of ticks was dissected and the total midgut, including the luminal blood meal, was collected and DNA extracted, as previously described (13, 28), to confirm the ingestion of A. marginale by using quantitative PCR (see below)...

    Massaro W. Uetiet al. Identification of Midgut and Salivary Glands as Specific and Distinct ...

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