Epidemiology of bovine anaplasmosis with special reference to an area of southern Brazil

Abstract

The literature on the epidemiology of bovine anaplasmosis is reviewed on a worldwide basis. An investigation into the epidemiology of the disease in an area of the Rio Grande do Sul state of Brazil is described.

Thin blood smears submitted to the laboratory from clinical cases were examined microscopically after staining with giemsa. A serological survey was carried out. 892 bovine sera from 26 properties were examined for antibodies to Anaplasma marginale using the complement fixation test (CFT). 102 of these sera were further subjected to the rapid card agglutination test (CT). A questionnaire was used to collect relevant data from the survey farms.

Laboratory - confirmed clinical cases showed a seasonal variation in incidence with three times as many confirmed outbreaks occurring during the autumn and winter (18) as during the spring and summer (6).

161 (18.1%) sera were negative to the CFT, 91 (10.2%) gave a suspicious reaction and 640 (71.7%) were positive. Mean herd prevalence of positive reactions was 76.4% but considerable variation occurred from farm to farm. The results of the CT and CFT were in agreement on 90% of 30 sera negative to the CFT while 76% of 72 sera giving a positive or suspicious CFT result were positive to the CT. Overall agreement was 80%. Questionnaire returns indicated a relationship between serological results and managmental practices controlling tick numbers.

It was concluded that the area is enzootically unstable for anaplasmosis and recommendations are made for control measures based on the use of A. centrale for immunoprophylaxis.