Molecular Detection of Hemotropic Parasites in a Sheep Flock in Tabasco, Mexico: A Retrospective Study

The objective of this study was to identify the possible presence of tick-borne pathogens in blood samples and tick specimens that were obtained from some infested animals in a sheep production unit in Tabasco, Mexico. To identify the presence of pathogens transmitted by ticks in sheep, a convenience study was carried out in which blood samples and tick specimens were obtained, in 3 different periods, from 77 tick-infested sheep located in the Central region of the State of Tabasco, Mexico. Blood samples were processed for microscopic and molecular identification of Babesia spp, Anaplasma spp, and Mycoplasma spp. Morphological analysis of the collected ticks (including male and female larvae, nymphs, and adults) allowed the identification of Amblyomma maculatum, the Gulf Coast tick. Microscopic examination of blood smears demonstrated the absence of classic intraerythrocytic forms compatible with Babesia spp. However, the presence of round intraerythrocytic inclusion bodies of approximately 1
m in diameter, with a marginal arrangement and morphologically compatible with Anaplasma sp, were observed in some samples analyzed, in addition to small round bodies attached to or adjacent to ovine erythrocytes, suggesting the presence of Mycoplasma sp (formerly, Eperythrozoon sp). The use of genus-specific PCR molecular tests confirmed the absence of Babesia sp in the herd and allowed the identification of 7 samples (9%) positive for Anaplasma sp. The results obtained by PCR for Mycoplasma sp detection showed that 62 (80.5%) of the samples tested were positive. DNA sequencing of amplicons obtained in the PCR test could shed light in this regard and define if the pathogen most probable involved is Anaplasma marginale rather than A. ovis as the sequence identity of the MSP-5 gene is 99%. Similarly, DNA sequencing and BLASTn homology analysis would show that the possible hemoplasma organism is either Mycoplasma wenyonii or Mycoplasma ovis as the sequence identity of the rDNA gene is >95%, without being able to demonstrate the presence of a co-infection in the sampled sheep. On the other hand, the role that A. maculatum may play in the transmission of pathogens in this flock cannot be elucidated, as it is necessary to carry out transmission experiments with the different stages of A. maculatum to determine if this is done mechanically or biologically.