A prospective clinical evaluation of the comparative efficacy of three trypanocides in the treatment of equine Trypanosomiasis in The Gambia

Abstract

Equine trypanosomiasis is endemic in many areas of the world incurring significant morbidity and mortality to affected populations. Trypanocides form an essential part of treatment strategies but evidence regarding efficacy in equids is scarce. This project was established to carry out a large scale evaluation and trypanocidal treatment of field cases of equine trypanosomiasis and to perform follow up examinations to assess treatment efficacy and record adverse reactions. A prospective randomised clinical efficacy study was performed in ten villages in The Gambia with recruitment of horses and donkeys that fulfilled 2/5 clinical inclusion criteria. Following randomised trypanocidal treatment (isometamidium, diminazene or Cymelarsan®) animals were observed for adverse reactions. Follow up was performed at 1 and 2 weeks. Blood samples underwent PCR analysis with specific Trypanosoma sp. primers. Morbidity was high in the Gambian equine population and less than half of equines had received previous veterinary care (43 %). Within the study population Trypanosoma sp. infection detected by PCR was common (66%); speciated as T. brucei sp. (15 %), T. congolense (45 %) and T. vivax (32 %). More than half were also positive for piroplasmosis (55 %). Haemoparasite co-infections were common (45 %). There was marked variation in disease phenotype; data analysis supported horse species, male gender and increasing co-infection status as contributory factors for more severe disease. There was a significant positive effect upon the Trypanosoma sp. PCR positive population following trypanocidal treatment for all groups; clinical evaluation, clinicopathological results and PCR status supported a superior treatment effect for isometamidium. Cymelarsan® was inferior to diminazene and isometamidium. Immediate side effects were only documented for isometamidium in donkeys (26 %). Diminazene had the longest duration of action. The data support the continuation of treatment with isometamidium (with careful titration of dosing in donkeys) and diminazene. Short and long term control strategies are recommended for this region. Future work is required to optimise control strategies with current therapeutics and evaluate the long term importance of identified host factors on disease phenotype