SUMMARYPathogenic animal trypanosomes affecting livestock have represented a major constraint to agricultural development in Africa for centuries, and their negative economic impact is increasing in South America and Asia. Chemotherapy and chemoprophylaxis represent the main means of control. However, research into new trypanocides has remained inadequate for decades, leading to a situation where the few compounds available are losing efficacy due to the emergence of drug-resistant parasites. In this review, we provide a comprehensive overview of the current options available for the treatment and prophylaxis of the animal trypanosomiases, with a special focus on the problem of resistance. The key issues surrounding the main economically important animal trypanosome species and the diseases they cause are also presented. As new investment becomes available to develop improved tools to control the animal trypanosomiases, we stress that efforts should be directed towards a better understanding of the biology of the relevant parasite species and strains, to identify new drug targets and interrogate resistance mechanisms.

Antimicrobial resistance among enteric organisms in food animals varied among countries, particularly for older antimicrobials, but resistance to newer compounds used to treat disease in humans was generally low.

The absolute bioavailability and lung tissue distribution of the triamilide antimicrobial, tulathromycin, were investigated in swine. Fifty-six pigs received 2.5 mg/kg of tulathromycin 10% formulation by either intramuscular (i.m.) or intravenous (i.v.) route in two studies: study A (10 pigs, i.m. and 10 pigs, i.v.) and study B (36 pigs, i.m.). After i.m. administration the mean maximum plasma concentration (C(max)) was 616 ng/mL, which was reached by 0.25 h postinjection (t(max)). The mean apparent elimination half-life (t(1/2)) in plasma was 75.6 h. After i.v. injection plasma clearance (Cl) was 181 mL/kg.h, the volume of distribution at steady-state (V(ss)) was 13.2 L/kg and the elimination t(1/2) was 67.5 h. The systemic bioavailability following i.m. administration was >87% and the ratio of lung drug concentration for i.m. vs. i.v. injection was > or =0.96. Following i.m. administration, a mean tulathromycin concentration of 2840 ng/g was detected in lung tissue at 12 h postdosing. The mean lung C(max) of 3470 ng/g was reached by 24 h postdose (t(max)). Mean lung drug concentrations after 6 and 10 days were 1700 and 1240 ng/g, respectively. The AUC(inf) was 61.4 times greater for the lung than for plasma. The apparent elimination t(1/2) for tulathromycin in the lung was 142 h (6 days). Following i.m. administration to pigs at 2.5 mg/kg body weight, tulathromycin was rapidly absorbed and highly bioavailable. The high distribution to lung and slow elimination following a single dose of tulathromycin, are desirable pharmacokinetic attributes for an antimicrobial drug indicated for the treatment of respiratory disease in swine.

16 Animal African trypanosomiasis (AAT), caused by Trypanosoma congolense and 17Trypanosoma vivax, remains one of the most important livestock diseases in sub-18 Saharan Africa, particularly affecting cattle. Despite this, our detailed knowledge 19 largely stems from the human pathogen T. brucei and mouse experimental 20 models. In the post-genomic era the genotypic and phenotypic differences 21 between the AAT-relevant species of parasite or host and their 'model organism' 22 counterparts are increasingly apparent. We aim to outline the timeliness and 23 advantages of increasing the research focus on both the clinically relevant 24 parasite and host species -improved tools and resources for both have been 25 developed in recent years. We propose that this shift of emphasis will improve 26 our ability to efficiently develop tools to combat AAT. 27 congolense and Trypanosoma vivax, our specific knowledge of the biology of 36 these pathogens is dramatically outweighed by that for Trypanosoma brucei, 37 variants of which cause HAT. Additionally, information on the host response, 38 particularly immunological processes, to these two AAT pathogens in the 39 economically and clinically relevant host -cattle -is scanty compared to the data 40 generated using mouse models (there is a lack of data overall relating to T. vivax 41 as most T. vivax strains do not grow in mice). 42In this article we outline the timeliness and benefits of increasing the research 43 emphasis on both the clinically relevant parasites and host species -recent 44 research developments have resulted in significantly improved tools and 45 resources. We contend that an increased emphasis on furthering our 46 understanding through the use of experimental models that incorporate both T. 47 congolense, T. vivax and the bovine host will result in more efficient development 48 of useful tools to combat AAT. 49 50 AAT -one disease, multiple causative agents 51 AAT is often treated as a single 'disease' but one of several factors in the 52 variation in clinical presentation is that AAT is caused by multiple species and 53 strains of trypanosomes, and often mixed infections. While the most 54 economically important are T. congolense and T. vivax, T. b. evansi is a significant 55 pathogen in cattle, and T. brucei s.l. is found in cattle, although it probably has a 56 minor role in pathogenesis. Additionally, within the parasite species, genetic 57 variation results in different clinical outcomes and relevance to disease in cattle, 58exemplified by greater pathogenicity of T. b. evansi compared with T. b. brucei, 59 and of T. congolense Savannah compared with T. congolense Forest or Kilifi 60 (reviewed in [3, 4] where comparative analyses between these species and T. brucei [8, 9] has 79 indicated some stark, and perhaps unexpected, differences. 80 81 Antigenic variation 82African trypanosomes are a paradigmal organism for antigenic variation [10, 11]. 83Trypanosomes express this phenotype through the variant surface glycoprotein 84 (VSG), which...

Graphical abstractHighlights► Diminazene transporter in Trypanosoma congolense has been proposed to be TcoAT1. ► Here, TcoAT1 was cloned and functionally expressed in Trypanosoma brucei. ► TcoAT1 did not mediate the uptake of diminazene, only of purine nucleosides. ► Expression of TcoAT1 did not alter drug sensitivity in trypanosomes. ► We conclude that TcoAT1 is a transporter for purine nucleosides, not for diminazene.