Variation in disease phenotype is marked in equine trypanosomiasis

Pathogenicity and virulence of African trypanosomes: From laboratory models to clinically relevant hosts

African trypanosomes are vector-borne protozoa, which cause significant human and animal disease across sub-Saharan Africa, and animal disease across Asia and South America. In humans, infection is caused by variants of Trypanosoma brucei, and is characterized by varying rate of progression to neurological disease, caused by parasites exiting the vasculature and entering the brain. Animal disease is caused by multiple species of trypanosome, primarily T. congolense, T. vivax, and T. brucei. These trypanosomes also infect multiple species of mammalian host, and this complexity of trypanosome and host diversity is reflected in the spectrum of severity of disease in animal trypanosomiasis, ranging from hyperacute infections associated with mortality to long-term chronic infections, and is also a main reason why designing interventions for animal trypanosomiasis is so challenging. In this review, we will provide an overview of the current understanding of trypanosome determinants of infection progression and severity, covering laboratory models of disease, as well as human and livestock disease. We will also highlight gaps in knowledge and capabilities, which represent opportunities to both further our fundamental understanding of how trypanosomes cause disease, as well as facilitating the development of the novel interventions that are so badly needed to reduce the burden of disease caused by these important pathogens.

Risk factors for equine trypanosomosis and hematological analysis of horses in Paraguay

Animal trypanosomosis, caused by Trypanozoon trypanosomes (Trypanosoma evansi and T. equiperdum), and Trypanosoma vivax, is endemic to South American countries and has a negative impact on the livestock industry. However, the risk factors for trypanosomosis in Paraguay remain unknown. This study aimed to determine the risk factors for equine trypanosomosis in Paraguay based on a PCR-based molecular survey and individual horse sampling data. In this study, 739 blood samples were collected from horses in 16 departments of Paraguay between August 2019 and November 2020. To elucidate the risk factors for trypanosome infection, the relationship between trypanosome infection status detected by PCR and the location, sex, age, breed of horses, and season of sample collection was analyzed. There were no significant differences in trypanosome prevalence in horses between the eastern and western regions, ages, or breeds of horses in Paraguay. Sex and season were identified as risk factors for trypanosome infection in horses in Paraguay in the current study. These results suggest that the rainy-summer season, when vectors increase in number and their blood-sucking activity, could be the most important risk factor for trypanosome infection in Paraguay horses. Preventive measures and treatments should be developed to address these factors.

Co-infection with Trypanosoma congolense and Trypanosoma brucei is a significant risk factor for cerebral trypanosomosis in the equid population of the Gambia

Trypanosomosis is a major cause of morbidity and mortality in working equids in The Gambia. Recently, a progressive, severe neurological syndrome characterised by a diffuse lymphoplasmacytic meningoencephalitis has been identified and associated with Trypanosoma brucei infection of the central nervous system. The pathogenesis of cerebral trypanosomosis is unclear and the clinical syndrome not well described. This observational cross-sectional study aimed to identify host and parasite related risk factors associated with the development of cerebral trypanosomosis and to describe the neurological syndrome associated with cerebral trypanosomosis. History, signalment, clinical and laboratory parameters were collected from 326 horses and donkeys presented to The Gambia Horse and Donkey Trust. Neurological derangements in affected animals were described. Species-specific polymerase chain reaction (PCR) for Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei was performed. The associations between signalment, clinical and laboratory parameters and PCR results were assessed using multivariable logistic regression. The overall prevalence of trypanosomosis was 50 %, with infections dominated by T. congolense (44.1 %) and a lower intensity of T. brucei (7.4 %) and T. vivax (6.5 %). Overall, 54.8 % of neurological cases were PCR positive for trypanosomosis. Within the neurological sub-population prevalence remained similar to the whole population for T. congolense (48.4 %) and T. vivax (6.5 %); whilst the prevalence increased markedly for T. brucei (32.3 %). Co-infections were identified in 32.3 % of neurological cases. Donkeys typically presented with progressive cerebral dysfunction and cranial nerve deficits, whereas in horses a progressive spinal ataxia was predominant. Mortality in affected animals was high (82.4 %). The final multivariable model identified a significant association between body condition score ≤2 (OR 11.4; 95 % CI 4.6-27.9; P = <0.001), and T. congolense and T. brucei. coinfection (OR 20.6; 95 % CI 1.71-244.1; P = 0.016) with the presence of neurological deficits. This study has provided clinically relevant information confirming the link between T. brucei and neurological disease outbreak in the equid population of The Gambia, and crucially identified co-infection with T. brucei and T. congolense as a major risk factor for the development of neurological trypanosomosis. Further research is required to identify the epidemiology of co-infection in equidae of The Gambia, so that cerebral trypanosomosis can be better prevented in this vulnerable population.