Infection and seroconversion of susceptible animals introduced into a babesiosis endemic area

Abstract

The study aimed to determine the incubation period of Babesia sp. infection in naive cattle and to monitor the serological response once exposed to natural Boophilus microplus (Rhipicephalus microplus)-infested paddocks. The study was carried out on a farm located in Veracruz, Mexico. Five groups of five steers were relocated every 3 months from a tick-free area to a tick-infested paddock. Animals were introduced in October, January, April, July, and October. Blood samples were taken daily until day 21 to determine packed cell volume (PCV), percentage of parasitized erythrocytes (PPE), and antibody titers to Babesia bigemina and B. bovis by the indirect fluorescent antibody procedure. Detection of Babesia in blood was also performed by species-specific PCR. The estimated incubation period was 6-14 days post introduction to paddocks (PIP), with fever (41°C) for at least 3 days. PCV decreased by >25% and Babesia parasites were observed during the clinical phase of the disease. The highest individual PPEs (0.44% and 0.22% for B. bovis and B. bigemina, respectively) were observed from animals introduced in October. The four other groups showed a mean PPE ranging from 0.002-0.146% at day 14 PIP. All animals were detected as PCR positive between 8-14 days PIP. The highest antibody titers were 1:3328. The environmental conditions were favorable throughout the year for tick reproduction as the farm showed enzootic stability and hyperendemic conditions for bovine babesiosis. In this type of farm, strategic tick control could be accompanied by babesiosis vaccination, particularly for cattle relocated from tick-free areas. © 2008 New York Academy of Sciences.