Anaplasmamarginale (A. marginale) is an obligate intra-erythrocytic rickettsia;it is the cause of anaplasmosis, an important tick-borne disease of cattle. Recovered and vaccinated cattle in endemic areas are apparently normal but remain persistently infected and serve as reservoirs for the parasite.This study intended to detect A. marginale in infected and apparently healthy subclinically infected cattle in North Western Libya. During the period extended from March-2006 till September-2007, blood samples and blood smears were collected from totally 119 adult cow (group – I). These cows were raised at some governmental and private farms in Tripoli, Al-Zawiya and Imssallata districts. Blood smears were stained with May-Grunewald- Giemsa stain and examined under Light microscope to detect the presence of intraerythrocytic bacteria. Indirect- ELISA (IELISA) using a 19 KD A. marginale recombinant antigen was used to detect serologically positive reactors.During the study period, 20 cases of acute anaplasmosis were diagnosed in these farms (Group-II); where, three cows died and two aborted. The Seroprevalence for A. marginale by IELISAwas 64% and 100% in group I and II, respectively. Stained thin blood smears failed to detect infective RBCs in group I, however, variable degrees of parasitaemia were detected in group II.
In conclusion, this study approved that serological test (IELISA) was more reliable than direct microscopic examination of stained blood smear in detection of chronic persistent anaplasma-infected cows in endemic areas.