Treatment efficacy in equine trypanosomosis: a prospective comparative study of three trypanocides in over 250 clinical cases in working equidae

Trypanocides are essential in trypanosomosis management, but evidence regarding treatment efficacy in equids is scarce. The objective of this study was to establish the relative efficacy of three trypanocides (Diminasan® 3.5 mg/kg IM, Cymelarsan® 0.25 mg/kg IV and Samorin® 0.5 mg/kg IV) with respect to improvement of clinical parameters and parasitic burden and to evaluate adverse drug reactions. A prospective randomised clinical efficacy study was performed in ten villages in The Gambia. Owners were invited to present horses and donkeys for free examination (history, clinical examination and jugular blood sample for packed cell volume (PCV) and total serum protein). Horses and donkeys were enrolled if they fulfilled at least 2/5 inclusion criteria for trypanosomosis (anaemia (PCV<24%), poor body condition (≤1.5), limb or ventral oedema, abortion or pyrexia). Randomised trypanocide treatment was administered and the animals were observed for adverse reactions. Follow up evaluation was performed at one and two weeks to assess treatment effect. Blood samples for each animal collected at weeks 1, 2 and 3 underwent PCR analysis with validated specific primers1 for T. vivax west (TVW), T. congolense savannah (TCS) and T. brucei (TBR). 254/710 animals examined fulfilled study inclusion criteria with follow up data obtained for 243. Age, gender, species, median PCV (22%; range 8-26) and body condition score (median 1.5/5; range 0.5-2.5) were comparable between treatment groups (p>0.1). No immediate adverse reactions occurred following Cymelarsan® or Diminasan®. Immediate reactions occurred in 12/45 (27%) of donkeys treated with Samorin® ranging from neck scratching, lip smacking to tachycardia, cold extremities, sweating and hypothermia. Demeanour classifications improved following treatment with Samorin® or Diminasan® (p=0.002). PCV increased at 1 and 2 weeks post treatment for all treatment groups (p<0.001). On preliminary analysis of PCR results (n=65), animals representing four villages were positive before treatment (week 1) for TVW (55/65; 85%), TCS (44/65; 67%) and TBR (17/65; 26%) with mixed infection common (45/65; 69%). Trypanosome species profile varied between villages (p<0.05). Post treatment positives occurred in all groups for all Trypanosoma sp but with a marked decrease in prevalence (Fig 1). Positives were most common in the Cymelarsan® group, particularly for TCS (7/13; 54%). Two weeks post treatment Diminasan® (15/19; 79%) and Samorin® (19/23; 83%) had reduced parasitaemia below the threshold of detection in most cases. The data support the continuation of treatment with Diminasan® and Samorin® (with careful titration of dosing in donkeys). Further investigation to quantify parasitaemia in post treatment positives will aid differentiation between treatment failure, reduced parasitaemia, new infections and residual non-viable parasite DNA.


This work was funded by The Donkey Sanctuary.

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Safety and efficacy of three trypanocides in confirmed field cases of trypanosomiasis in working equines in The Gambia: a prospective, randomised, non-inferiority trial

Globally, working equines have a continued and growing socioeconomic role in supporting the livelihoods of between 300–600 million people in low income countries which is rarely recognised at a national or international level. Infectious diseases have significant impact on welfare and productivity in this population and equine trypanosomiasis is a priority disease due to its severity and prevalence. Strategies are required to improve the prevention, diagnosis, management and treatment of trypanosomiasis in equines and more data are required on the efficacy and safety of current trypanocidal drugs.

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Semi-longitudinal study of trypanosomiasis and its vectors in donkeys (equus africanus asinus, fitzinger) in the Lamu archipelago

Phoebe Mukiria
Raymond Mdachi
J. Thuita
James Mutuku
Kennedy Wanjala
J. Omolo
Mulugeta Getachew
Andrew F. Trawford
Johnson Ouma
Grace Murilla
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Kenya is home to some 600,000 donkeys that are found virtually in all ecological zones where they provide transport and draught power. In the Lamu archipelago where there is no motorised transport, donkeys are virtually the only available means of transport helping to transport farm produce, building materials and for getting from one place to the next. This study was conducted in April (dry season) and November 2009 (wet season) in four villages in Pate Island to investigate the prevalence and species of trypanosomes infecting donkeys and to identify the fly vectors playing a role in the transmission of trypanosomosis. Blood samples were collected from 288 and 319 donkeys and examined by buffy coat technique (BCT) and Giemsa stained blood smears. Trypanosomes were encountered in 3.1 and 7.5% of the examined donkeys in the dry and wet season respectively and there was no difference in the prevalence between villages during both seasons (p=0.159 and 0.709) but there was a significant difference (p=0.006) between seasons. Three species of trypanosomes detected were, in order of predominance were Trypanosoma congolense Broden (68.7%), Trypanosoma vivax Ziemann (21.8%) and Trypanosoma brucei Plimmer and Bradford (6.2%). Another 6.2% were mixed infections. There difference in mean PCVs between trypanosome infected and non-infected donkeys dry and wet seasons ranging significant to highly significant (p<0.05 and p<0.001) respectively. Trypanosome infection had a significant effect on mean body condition score of the donkeys during both seasons (p<0.05 and p<0.001). Prevalence of trypanosome infection was found to be independent of sex and age. However, mean PCV was significantly associated with age, sex and body condition scores. The entomological surveys revealed the presence of Glossina pallidipes Austen and other biting flies namely Stomoxys spp Linnaeus, Tabanus spp. Linnaeus, and Haematopota spp Linnaeus. Though the use of BCT for detection of trypanosomes in the field is almost universal, it has limited application especially in chronic infections and the field samples are in the process of being analysed using PCR to give a more accurate picture of the prevalence and as it relates to health and productivity of donkeys.

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