Leishmania Animal Models Used in Drug Discovery: A Systematic Review

SIMPLE SUMMARY: Animals are frequently used to determine whether new compounds have the potential to be used as drugs against the parasitic disease leishmaniasis. There is, however, no consensus on the best animal model, and many different ones are used. This review explored the many different models and identified their strengths and weaknesses. The work showed that many papers on animal models for leishmaniasis lack a thorough description of the experimental procedures used, are deficient in appropriate ethical review (to safeguard the welfare of the animals), and measures to reduce, refine or replace animal studies are hardly addressed. Mice and hamsters are most frequently used, but there are many differences in how the animal experiment is set up. We propose a more generalized animal model, in particular to ensure that different experiments can be better compared. Furthermore, we make a plea to report all animal experiments in the same way, and all experiments must be scrutinized by appropriate ethical review committees. ABSTRACT: Many different animal models are in use for drug development for leishmaniasis, but a universal model does not exist. There is a plethora of models, and this review assesses their design, quality, and limitations, including the attention paid to animal welfare in the study design and execution. A systematic review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines of available literature after the year 2000 describing animal models for leishmaniasis. The risk of bias was determined using the SYstematic Review Centre for Laboratory animal Experimentation (SYRCLE) risk of bias assessment tool. A total of 10,980 records were initially identified after searching the databases PubMed, EMBASE, LILACS, and SciELO. Based on the application of predetermined exclusion and inclusion criteria, a total of 203 papers describing 216 animal experiments were available for full analysis. Major reasons for exclusion were a lack of essential study information or appropriate ethical review and approval. Mice (82.8%; an average of 35.9 animals per study) and hamsters (17.1%; an average of 7.4 animals per study) were the most frequently used animals, mostly commercially sourced, in the included studies. All studies lacked a formal sample size analysis. The promastigote stages of L. amazonensis or L. major were most frequently used to establish experimental infections (single inoculum). Animal welfare was poorly addressed in all included studies, as the definition of a human end-point or consideration of the 3Rs (Replacement, Reduction, Refinement) was hardly addressed. Most animals were euthanized at the termination of the experiment. The majority of the studies had an unknown or high risk of bias. Animal experiments for drug development for leishmaniasis mainly poorly designed and of low quality, lack appropriate ethical review, and are deficient in essential information needed to replicate and interpret the study. Importantly, aspects of animal welfare are hardly considered. This underpins the need to better consider and record the details of the study design and animal welfare.