Infectivity and virulence of Trypanosoma evansi and Trypanosoma equiperdum Venezuelan strains from three different host species.

This study compares the infectivity and virulence of seven strains of pathogenic protozoans, Trypanosoma evansi and Trypanosoma equiperdum, isolated from horses, donkeys, and capybaras, in a mouse model. It reveals significant differences in the pathogenic traits such as survival rates, animal weight, and various hematological parameters, within and between these species, which could contribute to the understanding of their pathogenicity.

Methodology and Results

• The research studied seven Venezuelan strains of Trypanosoma evansi and Trypanosoma equiperdum, which were isolated from horses, donkeys, and capybaras.
• These strains were analyzed in a mouse model for up to 41 days, with observed parameters including parasitemia (presence of parasites in the blood), animal weight, survival rates, packed cell volume (volume percentage of red blood cells in blood), hemoglobin levels, and erythrocyte (red blood cell) count.
• Results indicate two T. equiperdum strains and three T. evansi strains resulted in 100% mice mortality. However, the two T. evansi strains that were isolated from donkeys exhibited lower infectivity and mortality rates.
• T. equiperdum strains had shorter pre-patent periods (4 days) than the T. evansi strains (4-12 days). Pre-patent period is the time between infection and when the parasite can be detected in the blood.
• Regarding pathogenicity, the T. evansi horse strain and the two capybara strains caused a significant drop in the packed cell volume, hemoglobin concentration, and red blood cell count. In contrast, the T. evansi donkey strains did not show any changes in these hematological parameters.
• From the seven variables studied, only pre-patent period, the day of maximum parasitemia, the day of the first parasitemia peak, and the number of parasitemia peaks showed statistical significance.
• A decrease in weight was only observed in mice infected with the T. evansi horse strain.
• T. equiperdum strains demonstrated the highest mice lethality with a 7% survival rate by day 8 post-infection, with no significant change in hematological parameters.

Significance and Conclusions

• The three T. evansi horse and capybara strains showed 80%, 87%, and 97% survival rates respectively by day 12 post-infection. However, by day 20 post-infection, all the mice infected with the T. evansi horse strain had died while 53% and 27% of those infected by capybara strains survived.
• By day 40 post-infection, 53 and 73% of mice infected with T. evansi donkey strains had survived, indicating lower virulence compared to horse-derived strains.
• These findings demonstrate considerable differences in infectivity and virulence between Venezuelan T. evansi and T. equiperdum strains in NMRI mice.
• This research unveils potential avenues to understand intra- and interspecies variations contributing to the pathogenicity of these two Trypanosoma species.