The genetic heterogeneity of equine infectious anaemia virus field strains in Croatia
Equine infectious anaemia (EIA) is an infectious disease of equids caused by lentivirus. Equine infectious anaemia virus (EIAV) causes lifelong infection after integration of the proviral DNA into the host cell genome. Due to the obligatory slaughter of infected animals in most countries of the world, EIA is one of the most significant infectious diseases of horses. Control of EIA is based on antibody detection, but today the focus in diagnostics is aimed at PCR based methods. In this study, 98 AGID (agar gel immunodiffusion) positive sera samples, three spleen samples and cell cultures infected with EIA were tested for the presence of viral RNA or proviral DNA, using two nested PCR protocols. Out of all the samples 27 partial gag sequences of viral RNA were amplified. The Croatian isolates showed high diversity within the group of other available European sequences. Phylogenetic analysis showed that at least three gag gene subtypes are presently circulating in Croatia. The results of this study showed the limited efficiency of two PCR methods in terms of diagnostics, although the primers used for amplification targeted part of the viral RNA that was regarded as one of the most preserved. The high variability of the Croatian isolates obtained highlighted the necessity for determining more EIAV sequences to allow detection of less variable areas of the viral genome, to be used for amplification with universal primers.