“…In some situations, enzootic instability may be related to unsatisfactory passive immunity, stress, nutritional status, time of year, management, type of pasture or high infestation rates of pastures and cattle by a vector (BARROS et al, 2005;AMORIM et al, 2014). The primo-infection usually occurs between four and six months of life, with the peak of the parasitemia coinciding with the fall of the packed cell volume; in old age, primo-infection is usually severe and can be fatal (CARRIQUE MAS et al, 2000;SMITH et al, 2000).…”