Objective: The north part of Croatia, especially the Koprivnica-Krizevci County is a well known endemic area of several tick-transmitted diseases including tick-borne encephalitis, Lyme borreliosis and tularemia. Each summer numerous patients develop a nonspecific febrile illness after tick bite, etiology of which is sometimes never established.
Purpose of work: The aim of this prospective study was to determine whether the infection with Anaplasma phagocytophilum was associated with febrile illnesses occurring after tick bite. The epidemiological, clinical and laboratory characteristics, and diagnostic procedures in patients suffering from confirmed and probable anaplasmosis are presented.
Patients and methods: A prospective study to assess the potential ehrlichial etiology of febrile illnesses after tick bite was conducted at the Department of Infectious Disease, General Hospital, Koprivnica, Croatia, during the period from January 1998 to August 2004. The study included patients of all age groups with acute febrile illness (temperature higher than 38 degrees C) manifesting within 30 days of a tick bite, in whom a recent infection with Anaplasma phagocytophilum was established serologically by seroconversion or at least 4-fold increase in antibody titer to anaplasma antigen (defined as confirmed cases of anaplasmosis), or by the presence of positive IFA titer > or = 1: 256 in acute and convalescent phase serum samples without demonstrating a 4-fold titer change (defined as probable cases of anaplasmosis), and with no alternative explanation for the acute febrile illness. Thorough medical histories were collected, physical examinations performed, and several laboratory tests carried out. Giemsa-stained peripheral blood smears were examined by high microscopy for the presence of ehrlichial morulae within leukocytes. Acute and convalescent phase serum samples were tested by use of an indirect immunofluorescence assay (IFA) for the presence of specific IgG antibodies to Anaplasma phagocytophilum antigen. At the same time all serum samples were tested for other tick borne agents including tick-borne encephalitis virus, Borrelia burgdorferi sensu lato and Ehrlichia chaffeensis. Serological tests were performed at the Institute of Microbiology and Immunology, School of Medicine, University of Ljubljana, Ljubljana, Slovenia. Oral consent was obtained from all patients enrolled in the study.
Results: Of 132 patients included in the study during the 7-year period, eight (6%) patients were diagnosed with anaplasmosis, without any additional diagnosis, and were included in the analysis. Three patients fulfilled the case definition criteria for confirmed anaplasmosis, while five had probable anaplasmosis (three men and five women aged 17-43). Clinically, the disease presented as a nonspecific, flu-like febrile illness with leukopenia, thrombocytopenia and moderately elevated aminotransferases. Intracytoplasmic morulae were not seen in leukocytes in blood smears. Specific antimicrobial therapy was administered in four patients. All patients recovered rapidly and no long-term consequences were found during the one-year follow-up.
Conclusion: We report on the first patients meeting the case definition criteria for confirmed and probable anaplasmosis. The frequency and new concepts in the disease were analyzed.