Abstract
The aim of this study was to indicate the presence of tick-borne encephalitis (TBE) in an endemic area for Crimean-Congo haemorrhagic fever (CCHF) in Turkey. Of 39 CCHF suspected cases, one was found to be TBE virus Immunoglobulin M positive and seven were TBE virus immunoglobulin G positive. It is important to report this first appearance of the TBE virus in Turkey since 1967.
Introduction
Tick-borne encephalitis virus (TBEV) is classified within the Flavivirus (family: Flaviviridae) genus, and is pathogenic to humans. The Ixodes ticks play an essential role in the transmission of the virus. The incidence of TBE has been increasing during the past two decades. 1
TBE typically takes a biphasic course. After 7–14 days of incubation period, influenza-like prodromal symptoms are followed by neurological signs. TBEV can be isolated or detected by reverse-transcriptase-polymerase chain reaction during the viraemic phase of the disease, but admission to hospital is usually in the second phase, when the virus has already disappeared from blood and cerebrospinal fluid, and the newly formed TBEV specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies can be detected.1,2
In the Black-Sea and northern part of central Anatolian regions of Turkey, the first cases of Crimean-Congo haemorrhagic fever (CCHF) were reported in 2002, and the number of cases increased sharply in 2003. 3 After this important finding, we conducted a study to investigate the presence of the TBE virus.
Methods
Tokat is a province in the Black Sea region of Turkey, from which several acute haemorrhagic fever cases were reported to the Ministry of Health (MoH) in May 2002. MoH, the General Directorate of Primary Health Care and the Refik Saydam National Hygiene Center carried out three visits to the infected area between May 2002 and October 2003. Case information sheets were used to collect information from hospital records and retrospective interviews were done for those cases whose addresses could be found. The study was sponsored by Provincial Health Directorate. During the survey, 39 sera were collected and tested for laboratory confirmation of CCHF, and the remaining samples were stored and tested for the TBE virus in 2005.
The detection of antibodies was performed using ELISA tests (Euroimmun, Medizinische Labordiagnostika AG, Lubeck, Germany). The results were quantitative for IgG and semiquantitative for IgM. The tests were done according to manufacturers’ instructions. The titers were calculated by using the calibrator's extinction which was provided by manufacturer for calculation of the antibody titers of the serum samples. IgG titers were expressed in Relative Units (RU)/mL and the cut-off was 20 RU/mL. IgM results were accepted as positive when the extinction of the patient sample over calibrator and was ≥1.0. The odds ratio was calculated by EPI Info 6.0 statistic package program.
Results
Of the 39 serum samples, one had positive IgM antibody, and seven had solely positive IgG antibodies; they were accepted as previously exposed to the virus. Five patients among the IgG positives had been confirmed as having the acute CCHF infection by World Health Organization Collaborating Center for Arboviruses and Viral Haemorrhagic Fevers in Lyon, France. The characteristics of the study group are shown in Table 1.
Characteristics of the study group
Case report forms could not be completed for all patients TBE, tick-borne encephalitis
The TBE virus-IgM positive patient was a 74-year-old male farmer, with no tick bite history. A serum sample was taken two weeks after the onset of symptoms – he died in the third week. He had fever, weakness, headache, constipation and was unconscious. Laboratory findings were thrombocytopenia (25,000/mm3), leukocytosis (12,000/mm3). However, the liver enzymes were in the normal range. Magnetic resonance imaging was normal. He was classified as a possible case for TBE infection under the TBE case definition of the Working Group for Communicable Diseases Surveillance Case Definitions, Warshaw, Poland.
Discussion
No case of TBE had been reported in Turkey until 1967 when Serter diagnosed three human cases of TBE using the haemagglutination inhibition (HI) test; of the 81 healthy individuals tested in the Eagen region, 7.4% were seropositive. 4 The TBE virus was demonstrated among sheep by using HI method; there was, however, no virus isolation from ticks in the same area. 5
We demonstrated the presence of the TBE virus in the regions suspected to be endemic for tick-borne disease using the ELISA method. Although, the neutralization techniques have been recommended for confirmation of positive ELISA results, recently developed ELISA techniques have high sensitivity and specificity. 4 Moreover, as there is no flavivirus vaccination, the ELISA results clearly show TBE is prevalent in the study area.