Sensitivity of Nigerian field isolates of Trypanosoma vivax and Trypanosoma congolense to commonly available trypanocides

Drug resistance in animal trypanosomiases: Epidemiology, mechanisms and control strategies

Animal trypanosomiasis (AT) is a complex of veterinary diseases known under various names such as nagana, surra, dourine and mal de caderas, depending on the country, the infecting trypanosome species and the host. AT is caused by parasites of the genus Trypanosoma, and the main species infecting domesticated animals are T. brucei brucei, T. b. rhodesiense, T. congolense, T. simiae, T. vivax, T. evansi and T. equiperdum. AT transmission, again depending on species, is through tsetse flies or common Stomoxys and tabanid flies or through copulation. Therefore, the geographical spread of all forms of AT together is not restricted to the habitat of a single vector like the tsetse fly and currently includes almost all of Africa, and most of South America and Asia. The disease is a threat to millions of companion and farm animals in these regions, creating a financial burden in the billions of dollars to developing economies as well as serious impacts on livestock rearing and food production. Despite the scale of these impacts, control of AT is neglected and under-resourced, with diagnosis and treatments being woefully inadequate and not improving for decades. As a result, neither the incidence of the disease, nor the effectiveness of treatment is documented in most endemic countries, although it is clear that there are serious issues of resistance to the few old drugs that are available. In this review we particularly look at the drugs, their application to the various forms of AT, and their mechanisms of action and resistance. We also discuss the spread of veterinary trypanocide resistance and its drivers, and highlight current and future strategies to combat it.

Drug-resistant trypanosome isolates populations in dogs in Enugu North Senatorial Zone, Southeastern Nigeria

African animal trypanosomosis is an important wasting and endemic protozoan disease causing morbidities and mortalities in animals in the sub-Saharan Africa. Currently, chemotherapy is the widely used method of African animal trypanosomosis control, especially in dogs in the sub-Saharan Africa. However, their efficacy is threatened by the emergence of drug-resistant trypanosomes owing to their extensive use and misuse over several decades amongst other factors. Thus, this study focused on the trypanocidal sensitivity and characterization of Trypanosoma species isolated from dogs in Enugu North Senatorial Zone (ENSZ), Southeastern Nigeria. Trypanosoma brucei (n = 44) and T. congolense (n = 4) isolated from naturally infected dogs in ENSZ, Southeastern Nigeria, between January and August 2016 were subjected to single dose test to assess their sensitivity to diminazene aceturate (DA) and isometamidium chloride (ISM). Subsequently, DA and multidrug-resistant isolates were further subjected to DA multi-dose test and CD₅₀ was determined and was used to characterize the drug-resistant trypanosomes. Clones were derived from a randomly selected multidrug-resistant isolate and their sensitivity also assessed. 100% and 83.3% of T. congolense and T. brucei respectively were resistant to the trypanocides. Amongst the drug-resistant isolates, 50%, 16.7%, and 33.3% were resistant to DA, ISM, and both trypanocides respectively with CD₅₀ ranging between 11 and 32.34 mg/kg. Drug-resistant trypanosomes were characterized into highly resistant (CD₅₀ = 11-24.99 mg/kg) and very highly resistant (CD₅₀ =  > 25 mg/kg) trypanosome isolates. Clones also expressed high levels of resistance to both DA and ISM with CD₅₀ values between 35.58 and 38.85 mg/kg. Trypanocidal resistance was, thus, confirmed and appears to be widespread in dogs in ENSZ, Southeastern Nigeria. The adoption of an integrated trypanosomosis control strategy in ENSZ is most desirous.