Morphological and Genetic Comparisons between Babesia bovis and Trypanosoma spp. Found in Cattle and White-tailed Deer

Abstract

Babesia bovis has been an important disease agent in the U.S. cattle industry for over a century. Recently, B. bovis-like parasites have been identified in white-tailed deer (WTD; Odocoileus virginianus) in Texas. If the parasites found in the WTD are B. bovis that are able to infect cattle, the disease could re-emerge. Susceptible adult cattle often die from this disease, which would result in severe production losses, as well as a decrease in carcass weights of disease survivors. The B. bovis-like parasite found in WTD was compared to B. bovis from cattle, by ribosomal DNA sequence analysis. Babesia isolated from WTD were found to have 99% identity to B. bovis from GenBank cattle sequences. No cattle samples in this study were found to be positive for B. bovis. On culture of WTD samples, a Babesia parasite could not be visualized based on common morphological features.

Trypanosoma cervi has been studied for decades, but all the previous research identified this parasite solely by morphology. Trypanosoma species obtained from different host species was compared by ribosomal DNA sequence analyses. In this study, the Trypanosoma cultured from WTD had the morphological appearance of T. cervi. On sequence analysis, the cattle sequences aligned together with cattle isolates and the WTD sequences aligned closely with elk (Cervus canadensis) sequences, indicating that wild ungulates (WTD and elk) and cattle most likely have separate trypanosome species. On distribution analysis there was a trend in three South Texas counties, where the county with the highest occurrence of Trypanosoma had the lowest occurrence of Babesia; and vice versa. It is possible that Trypanosoma and Babesia blood parasites compete within the mammalian host, but the chi-squared test did not show a significant association between the two parasites in the different counties. On seasonal analysis, the correlation between positive samples and season could not be statistically confirmed, but it appears that Babesia infected animals are found in lowest numbers during hot, dry seasons. It also appears that there is another vector for Trypanosoma in South Texas besides the ked (Lipoptena mazamae) and tabanid fly (Tabanus spp.).