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EQUINE VETERINARY EDUCATION / AE / july 2022
TABLE 1: A summary of commonly used serological techniques
Serological technique
ELISA
Infectious disease
EVA S. equi Additional information
Positive ELISA samples undergo a confirmatory VN test. EVA is notifiable in stallions in the UK and positive results if unexpected and not otherwise explained by vaccination are required to be notified to Defra.
There are two different ELISA tests commercially available. Each ELISA tests for antibodies produced to specific bacterial proteins. Cross reaction can occur if the target S. equi bacterial protein chosen for the test is similar to S. zooepidemicus proteins (resulting in false positives). The A/C ELISA tests for antibodies to two different S. equi surface proteins, with detection of antibodies against either or both proteins interpreted as a positive result (Robinson et al. 2013). The SeM ELISA tests for SeM-specific antibody.
EIA Piroplasmosis AGID HI SRH CFT EIA EIV
Screening test and if positive, AGID performed as a confirmatory test. EIA is notifiable in the UK and positive results are required to be notified to Defra.
Babesia caballi and Theileria equi tested for, with cross-reactivity of antibodies between the two. IFAT is often performed as a confirmatory test.
Also known as Coggins test. A more specific test compared to the EIA ELISA. The required test for some importing countries.
Equine influenza serotypes tested commonly include H7N7 Prague 056, H3N8 Miami 063 and H3N8 Newmarket 2 093. Cross-reactivity between antibodies to different H3N8 strains occurs.
Adenovirus None. EIV
EHV-1/-4
A more quantitative way for testing serological samples for an immune response to equine influenza, mainly utilised in research but can help in epidemiological investigations of EI outbreaks (Barquero et al. 2007).
EHV-1 and EHV-4 are commonly both tested for, with cross-reactivity of antibodies between the two; therefore, no distinction can be made regarding the infective strain from CFT results. Recent vaccination against EHV-1/-4 using inactivated vaccine will stimulate CFT antibodies, although antibodies after infection or vaccination are short-lived, declining after several weeks and will rise again if the animal is re-infected.
ERV-A/-B
IFAT VN
Piroplasmosis EHV-3 EVA
ERV-A and ERV-B are tested for, with cross-reactivity of antibodies between the two; therefore, no distinction can be made regarding the infective strain from CFT results. Recent vaccination against EHV-1/-4 using inactivated vaccine rather than EHV-1/-4 infection will stimulate CFT antibodies. Babesia caballi and Theileria equi tested for and may be used to confirm positive ELISA results For diagnosis of coital exanthema
A more specific test when compared to the EVA ELISA and is used to confirm positive ELISA results
ELISA, Enzyme-linked immunosorbent assay; AGID, Agar gel immunodiffusion; HI, Haemagglutination inhibition; SRH, Single radial haemolysis; CFT, Compliment fixation test; IFAT, Indirect fluorescence antibody test; VN, Virus neutralisation; EVA, Equine viral arteritis; S. equi, Streptococcus equi; EIA, Equine infectious anaemia; EIV, Equine influenza virus; EHV-1/-4, Equine herpes virus-1/-4; ERV-A/-B, Equine rhinitis virus-A/-B; EHV-3, Equine herpes virus-3. Clotted blood/serum required for all tests.
Substrate Substrate
Secondary antibody conjugate
Substrate Inhibitor antigen
Primary antibody conjugate
Antigen Direct ELISA Indirect ELISA Capture antibody Sandwich/Capture ELISA Competitive ELISA
Fig 1: ELISA method detailing the direct ELISA, indirect ELISA, sandwich ELISA and competitive ELISA. ELISA, enzyme-linked immunosorbent assay.
© 2021 EVJ Ltd Substrate
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