Optimization of ELISA and immunoblot methods for the detection of IgG antibodies against old world hantaviruses in wild rodents

Abstract

Hantaviruses infect humans via inhalation of viral particles in infected rodents' secretions such as saliva, urine and faeces or via direct contact with infected rodents. The rodent species that are known as the carriers of Dobrava (DOBV), Puumala (PUUV), Saaremaa (SAAV), Tula (TULV) and Seoul (SEOV) viruses are found in our country. The presence of specific antibodies against hantaviruses have been demonstrated in rodents collected from Black Sea and Aegean Regions of Turkey in 2004 for the first time. The first hantavirus-related hemorrhagic fever with renal syndrome (HFRS) cases were reported in Black Sea region in 2009. The determination of the hantavirus prevalence in wild life and rodent populations in the field is crucial for the information about hantavirus-related cases and to clarify the state of risk. There is no commercial product optimized for the screening of rodent serum samples in terms of HFRS agents like DOBV and PUUV that are widely seen in Eurasia as well as Turkey. In this study, the antigens belonging to the commercial enzyme-linked immunoassay (ELISA) and immunoblot tests that are produced for the screening of human sera were used for the development of antibody screening tests against hantavirus in rodent sera and were optimized. The most appropriate serum and conjugate dilutions were determined for the optimization of ELISA (Anti-Hantavirus Pool ELISA; Euroimmun, Germany) and immunoblot (Euroline Anti-Hanta Profile 1 strips; Euroimmun, Germany) methods. Optimized ELISA method was used for the screening and optimized immunoblot method was used for the confirmation. A total of 84 wild rodent sera that belonged to Apodemus and Microtus species were evaluated with this procedure and the cut-off value, sensitivity and specificity of optimized ELISA method were determined. For the optimization of ELISA 1/50, 1/100 and 1/200 serum dilutions and 1/10.000, 1/20.000 and 1/40.000 conjugate dilutions were tested. For the optimization of immunoblot, 1/50 and 1/100 serum dilutions and 1/5.000 and 1/10.000 conjugate dilutions were tested. The horseradish peroxidase conjugated goat anti-mouse IgG for ELISA and the alkaline phosphatase conjugated goat anti-mouse IgG for immunoblot were used. We followed the manufacturer's recommendations for the incubation parameters, substrate and the number of washes. 1/50 serum dilution and 1/10.000 conjugate dilution for ELISA and 1/100 serum dilution and 1/5.000 conjugate dilution for immunoblot were determined as optimal concentrations. By using the optimized ELISA, 26.2% (22/84) of rodents were found positive for hantavirus antibodies according the determined cut-off value (OD(450/620): 0.325). By using immunoblot as a confirmatory test, 20 out of 22 ELISA positive samples could be studied because of the insufficient amount of sera and 17 of them was found positive in terms of DOBV antibodies. Of these rodents 11 were Apodemus flavicollis, three were Apodemus agrarius, two were Microtus guentheri and one was Apodemus sylvaticus. When the results of ELISA were compared to immunoblot results, the optimized ELISA's sensitivity and specificity were found as 100% and 95%, respectively. In this study, a method that can be used in the screening of rodent sera was constituted which uses commercial antigens that can be provided easily, gives fast and reliable results. Similar serological methods optimized for different types of rodents are of great importance for the realization of active follow-up and monitoring of the studies in the field.