However, the likelihood of simultaneous detection and differentiation of various types of EHV and rapid diagnosis offered by PCR is considered substantial over virus isolation technique under certain circumstances.
Serology-Based Assay: Serological testing for EHV antibodies in serum or plasma has been the key tool to gain retrospective diagnosis and forms a valuable part of longitudinal surveillance.
The IgG ELISA has been used in the epidemiological studies of EHV infection (Gilkerson et al., 1999; Yasunaga et al., 1998) as well as in the management of outbreaks of EHV-1 myeloencephalitis and abortion (Drummer et al., 1995; Studdert et al., 2003).
Immunofluorescence: Immunofluorescence (IF) is a technique to detect specific target antigens in nasal or nasopharyngeal swab samples or in frozen (cryostat) sections from aborted fetal tissues (lung, liver, thymus and spleen) and placental tissue in the detection of EHV using the fluorescent-labelled antibodies.
Direct immunofluorescence detection of EHV-1 or EHV-4 antigens in cryostat sections of tissues freshly dissected from aborted foetuses offers a rapid technique for the diagnostic laboratory to conduct an early diagnosis of EHV abortion (Allen et al., 2004).
Histopathology: Histopathology is a crucial method for confirming EHV infection in aborted foetuses and post-mortem samples collected from neurologically affected horses.
This features of EHV renders the conventional methods of detecting the virus in the latent form.
Molecular-based approaches are evidently more sensitive and specific, which have provided a rapid and accurate detection and characterization of EHV. By targeting these LATs, latency can be detected by using reverse transcriptase-polymerase chain reaction (RT-PCR) or by real-time PCR.
Nested, semi-nested PCR (Borchers and Slater, 1993; Pusterla et al., 2005; Varrasso et al., 2001) and multiplex nested PCR (Ataseven et al., 2009; Carvalho et al., 2000; Wang et al., 2007) for detection of EHV have been described.
Several PCR assays target different target genes of EHV; glycoprotein gene B (gB), C (gC), D (gD), H (gH) and thymidine kinase (TK) gene have been developed (Borchers and Slater, 1993; Carvalho et al., 2000; Lawrence et al., 1994; Varrasso et al., 2001).
The EHV could shed intermittently in the body without showing any clinical signs and thus, collecting the samples from asymptomatic horses outside the outbreak for PCR testing is not recommended (Lunn et al., 2009).
The drawback of the non-quantitative PCR is the incapability to measure the viral load in the clinical sample has led to a newer molecular platform of quantitative PCR assay with promising advantages for EHV detection.