A comparative investigation of experimental prophylactic methods for tick-borne diseases transmitted by Ixodes ricinus

Transmission of Babesia spp by the cattle tick (Boophilus microplus) to cattle treated with injectable or pour-on formulations of ivermectin and moxidectin

OBJECTIVE

To assess the efficacy of ivermectin and moxidectin to prevent transmission of Babesia bovis and Babesia bigemina by Boophilus microplus to cattle under conditions of relatively intense experimental challenge.

DESIGN

Naive Bos taurus calves were treated with either pour-on or injectable formulations of either ivermectin or moxidectin and then exposed to larvae of B microplus infected with B bovis or larvae or adults of B microplus infected with B bigemina. One calf was used for each combination of haemoparasite, B microplus life stage, drug and application route.

PROCEDURE

Groups of calves were treated with the test drugs in either pour-on or injectable formulation and then infested with B microplus larvae infected with B bovis or B bigemina. B bigemina infected adult male ticks grown on an untreated calf were later transferred to a fourth group of animals. Infections were monitored via peripheral blood smears to determine haemoparasite transmission.

RESULTS

Cattle treated with either pour-on or injectable formulations of ivermectin and moxidectin became infected with B bovis after infestation with infected larvae. Similarly, larvae infected with B bigemina survived to the nymphal stage to transmit the haemoparasite to animals treated with each drug preparation. Cattle treated with pour-on formulations of ivermectin and moxidectin then infested with adult male ticks infected with B bigemina did not become infected with B bigemina whereas those treated with the injectable formulations of ivermectin and moxidectin did show a parasitaemia.

CONCLUSIONS

Injectable or pour-on formulations of ivermectin and moxidectin do not prevent transmission of Babesia to cattle by B microplus. Use of these drugs can therefore not be recommended as a primary means of protecting susceptible cattle from the risk of Babesia infection.

Ivermectin as a systemic insecticide

Like many broad-spectrum drugs, the antiparasitic agent ivermectin is not equally effective in the treatment of all parasitic infestations. Predicting arthropod susceptibility relies not only on an understanding of insect and acarine biology, but also on an appreciation of the pharmacokinetic properties of the drug which can be profoundly influenced by host differences and pharmaceutical formulation. In this review, Helen Jackson attempts to explain the diverse number of ivermectin-induced effects observed among parasitic arthropods feeding on treated animals and aims to provide an overview of the current and future use of ivermectin in the systemic treatment and control of arthropod pests of livestock.