Equine trypanosomiasis, a systematic review and meta‐analyses: Prevalence, morbidity and mortality

BACKGROUND: Equine trypanosomiasis is a neglected protozoal disease. OBJECTIVES: To perform a systematic search of literature to explore: (1) In equines what is the global geographical distribution and prevalence of trypanosomiasis? In low and middle-income countries (LMICs) is trypanosomiasis more prevalent than in higher-income countries (HICs)? (2) Is trypanosomiasis infection a significant contributor to global morbidity and mortality? STUDY DESIGN: Systematic review and meta-analyses. METHODS: Studies were identified that described naturally occurring equine trypanosomiasis worldwide following 'Preferred Reporting Items for Systematic Reviews and Meta-Analyses' using eight international databases (1980-2022). Equine population data for each country were extracted. Meta-analyses were used to estimate point prevalence and disease characteristics. Country exposure risk to equines (negligible/low/medium/high) and clinical data (Trypanosoma sp.; outbreak (O) vs. endemic (E) disease) were categorised. RESULTS: Study quality was assessed (Question 1 prevalence: n = 147 manuscripts, median grade 'medium' (4/8 (range 2-6)); Question 2 morbidity and mortality: n = 46 'moderate' (n = 1), 'low' (n = 20) or 'very low' (n = 25)). Heterogeneity was high. LMICs were more likely to report disease (41/125; 33% vs. 7/80, 9%; (p < 0.001; OR 5.1 (2.1-14.2))). Fifty-six percent of the world's equines reside in a 'medium'/'high' risk country (61,507,601). Disease characteristics were summated. For Trypanosoma evansi: (O) Infection rate (IR) (42%; 95% CI 14-76), morbidity (47%; (13-85)), mortality (23%; 7-54) and death to case ratio (DCR) (45%; 20-73). Trypanosoma equiperdum: (O) IR 12% (7-18), morbidity 25% (9-49). Tsetse transmitted trypanosomiasis (O): IR 46% (29-63), morbidity 46% (29%-63%), mortality 6% (1-19), DCR 12% (2-38). (E) IR 50% (20-60), morbidity (no data), mortality 11% (7-14), DCR 9% (5-16). Trypanosoma vivax (O) IR 43% (10-83), morbidity 43% (10-83), mortality 15% (0-100), DCR 32% (0-100). MAIN LIMITATIONS: Publication bias, heterogeneity, descriptive data, missing data. CONCLUSIONS: Equine trypanosomiasis predominates in LMICs. Conservatively, globally more than eight million equines are estimated to be affected, with substantial morbidity and mortality.