What question did this study set out to answer?

Assess the vaccine-mediated protection of ILTV via eye drop and vent brush methods in layer chicks.

January 10, 2026Avian Pathology0 citations

Insights into infectious laryngotracheitis virus vaccine-mediated protection: A comparative assessment of eye drop and vent brush vaccination methods

TMTanjin Tamanna MumuBangladesh Agricultural University TTToan TranNong Lam University Ho Chi Minh City SWStephen W. Walkden-BrownUniversity of New England

Key Result

Vent brush vaccination provided 99% protection against clinical signs, while eye drop vaccination conferred 90% protection in layer chicks challenged with virulent ILTV.

Key Points

Assess the vaccine-mediated protection of ILTV via eye drop and vent brush methods in layer chicks.
Vaccinated 4-week-old layer chicks with SA2 ILTV vaccine strain via eye drop or vent brush.
Conducted a virulent ILTV challenge two weeks post-vaccination.
Measured ILTV DNA levels and immune response markers post-challenge.
Both vaccination methods prevented increases in viral load after challenge.
Protection indices: VB 99%, ED 90% against clinical signs post-challenge.
VB showed lesions in conjunctiva and trachea of 83% and 78%, respectively; ED showed 74% and 69%.
Non-vaccinated challenged group had significant over-expression of immune markers, while vaccinated groups displayed similar profiles.

Structured PICO

Does SA2 ILTV vaccine administered via vent brush or eye drop provide protection against virulent challenge in 4-week-old layer chicks?

Population

4-week-old layer chicks

Intervention

SA2 infectious laryngotracheitis virus (ILTV) vaccine strain administered via vent brush (VB) or eye drop (ED)

Comparator

Non-vaccinated challenged group and vaccinated non-challenged group

Outcome

Vaccine-mediated protection against a virulent (Class 9) challenge, assessed by viral load, clinical signs, pathological lesion scores, and gene expression

Vent brush and eye drop vaccination methods confer equivalent clinical and immunological protection against infectious laryngotracheitis virus in chickens.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

Live attenuated chicken embryo origin (CEO) vaccines against infectious laryngotracheitis virus (ILTV) are commonly used in long-lived chickens in Australia and generally provide good protection when administered by eye drop (ED). Although vent brush (VB) vaccination provides excellent protection, the associated immune responses are not well characterised. This study compared vaccine-mediated protection conferred by SA2 ILTV vaccine strain administered via ED or VB to 4-week-old layer chicks against a virulent (Class 9) challenge two weeks after vaccination. No significant differences in ILTV DNA in choanal swabs were observed between vaccinated-challenged and non-challenged groups from 4 to 11 days post-challenge (DPC), indicating that both VB and ED vaccination prevented increases in viral load after challenge, although neither prevented infection. Both vaccination routes resulted in high protection indices against clinical signs after challenge (VB, 99%; ED, 90%) and pathological lesion scores in conjunctiva (VB, 83%; ED, 74%) and trachea (VB, 78%; ED, 69%). The non-vaccinated challenged group exhibited significant over-expression of complement component 5a receptor 1, interleukin 1 beta, interleukin 6, myxovirus resistance 1 (MX1), and signal transducer and activator of transcription 1 (STAT1) in both conjunctiva and trachea at DPC 4, whereas ED- and VB-vaccinated challenged groups displayed similar gene expression profiles, resembling those of vaccinated non-challenged group except for elevated MX1 expression at DPC 4 and 7, and STAT1 expression at DPC 4 in the trachea. In conclusion, VB and ED vaccination conferred equivalent clinical protection with gene expression profiles similar to vaccinated, non-challenged chickens, indicating comparable immunological efficacy.

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