RESUMEN
The Atlantic Forest biome is considered an area in which tick fever is endemic, while the Caatinga biome is considered an area in which tick fever is non-endemic. A survey on cattle tick fever was carried out in 448 cattle farms located in an area of the Atlantic Forest biome which borders the Caatinga biome. A retrospective study of five years, conducted from January 2018 to October 2022, allowed for the identification of the occurrence of tick fever in 44 out of the 448 herds visited. In 70.5% (31/44) of the herds involved, the disease was caused by Anaplasma marginale; in 6.8% (3/44), the disease was caused by Babesia spp.; and in 22.7% (10/44), the disease was caused by a coinfection of Babesia spp. and A. marginale. The disease mainly occurred from August to November (23/44). Bos taurus or B. taurus crossbreed animals were most affected (29/44) in an area in which 94% of the cattle were Bos indicus and 6% were B. taurus and B. taurus crossbreeds. In 24 herds (with adults affected in 17 and calves in 7), the implicated animals had recently been moved to the Atlantic Forest. In the other 20 herds (calves with heavy tick infestations were affected in 17 and adults in 3), tick fever occurred in non-moved cattle. Even though it is an endemic zone, tick fever is common and mainly affects B. taurus cattle, including adults moved from areas with enzootic instability and calves under nine months old with high tick loads.
RESUMEN
The present work reviews the epidemiologic situation of Anaplasma marginale and Babesia spp. infections and the occurrence of cattle tick fever outbreaks in Brazil. In areas of tick fever enzootic instability, environmental conditions interfere with the development of Rhipicephalus (Boophilus) microplus: chilly winter in the southern region, floods in the Pantanal, and low humidity in the Caatinga. In contrast, the climatic conditions of stable zones (Cerrado, Amazon and Atlantic Forest biomes) favor tick development. In enzootic areas, tick fever is uncommon because the animals are in frequent contact with the parasite, acquiring immunity naturally during the period of innate resistance; however, outbreaks may occur when calves become infested by considerable numbers of infected ticks during this period or in adults raised in tick-free environments that become infested for the first time when transporting to stable areas. It is necessary to better understand the disease's risk factors under stable conditions and the implications of the mechanical and other vector transmission of A. marginale. To prevent tick fever outbreaks in Brazil, it is important to develop and use anaplasmosis and babesiosis vaccines in cattle from enzootic unstable regions, especially when animals are moved to stable areas.
