Attenuated infectious laryngotracheitis virus vaccines differ in their capacity to establish latency in the trigeminal ganglia of specific pathogen free chickens following eye drop inoculation

Abstract

Infectious laryngotracheitis (ILT) is a respiratory disease that affects chickens. It is caused by the alphaherpesvirus, infectious laryngotracheitis virus (ILTV). This virus undergoes lytic replication in the epithelial cells of the trachea and upper respiratory tract (URT) and establishes latent infection in the trigeminal ganglia (TG) and trachea. Live attenuated vaccines are widely used to control ILT. At least one of these vaccines can establish latent infections in chickens, but this has not been demonstrated for all vaccines. The aim of the current study was to determine the capacity of three commercially available vaccines (SA2, A20 and Serva) and a glycoprotein G deletion mutant vaccine candidate (ΔgG ILTV) to establish latent infection in the TG of specific pathogen free (SPF) chickens. Five groups of 7-day-old SPF chickens were eye-drop vaccinated with either one of the vaccine strains or mock-vaccinated with sterile media and followed until 20 or 21 days post-vaccination (dpv). ILTV DNA was detected at 20–21 dpv in the TG of 23/40 (57.5%) vaccinated SPF chickens (SA2 = 10/10; A20 = 6/10; Serva = 3/10; ΔgG = 4/10) by PCR, but virus could not be reactivated from TG co-cultivated with primary chicken embryo kidney cells. In the birds from which ILTV DNA was detected in the TG, ILTV DNA could not be detected in the URT or trachea of 3 birds in each of the SA2, A20 and Serva vaccinated groups, and in 4 birds in the ΔgG vaccinated group, indicating that these birds were latently infected in the absence of active lytic replication and virus shedding. Results from this study demonstrate the capacity of commercial ILTV vaccines to establish latent infections and underline their importance in the epidemiology of this disease.

A five-year surveillance study of vaccination schedules using viral-vectored vaccines against infectious laryngotracheitis in a high-density layer region

“…As detected here by the PCR, a high frequency of positive chickens in an endemic area, usually without clinical disease and histologic lesions, may indicate latency and persistence of wild strains of GaHV-1 (Bagust et al 2000, Williams et al 1992). GaHV-1 can be reactivated from TG spontaneously or under stressful conditions (Bagust et al 2000, Hughes et al 1991, Thilakarathne et al 2019). In the present study, GaHV-1 DNA was also detected in the TG and trachea of healthy chickens from flocks without clinical or pathological evidence of ILT.…”

“…The major control measures for this disease include the combination of biosecurity measures and vaccination (Chin et al 2009). Both virulent field and live attenuated vaccine strains of GaHV-1 can establish latent infections within the trigeminal ganglia of chickens (Bagust 1986, Hughes et al 1991, Williams et al 1992, Thilakarathne et al 2019. Latency is a distinct characteristic of herpesviruses, which makes ILT difficult to control in layers and breeder type chickens (Bagust 1986, Guy & García 2008.…”

“…Compounding this is the fact that live ILTV vaccine strains can also establish a life long latent infection (Hughes et al 1991). Both virulent field and live attenuated vaccine strains of GaHV-1 can establish latent infections within the trigeminal ganglia of chickens (Bagust 1986, Hughes et al 1991, Williams et al 1992, Thilakarathne et al 2019. Consequently, the latent vaccine-derived virus can reactivate so that a flock can become a source of infection with continuous outbreaks of disease.…”

P53 maintains gallid alpha herpesvirus 1 replication by direct regulation of nucleotide metabolism and ATP synthesis through its target genes

“…Despite widespread immunization, ILTV infection still result in avian infectious laryngotracheitis (AILT), which leads to significant financial losses for the global chicken industry ( Ou and Giambrone, 2012 ). The major method for preventing and controlling AILT at current stage is vaccination with ILTV-attenuated vaccines ( Rodríguez-Avila et al, 2007 ; García and Zavala, 2019 ; Thilakarathne et al, 2019 ). However, with successive passage in the host, the attenuated viruses may regain virulence through the recombination of viral genome between different ILTV strains, including vaccine strains, which would cause new epidemic of AILT ( Lee et al, 2012 ; Fakhri et al, 2020 ).…”

“…However, with successive passage in the host, the attenuated viruses may regain virulence through the recombination of viral genome between different ILTV strains, including vaccine strains, which would cause new epidemic of AILT ( Lee et al, 2012 ; Fakhri et al, 2020 ). Additionally, similar to human alphaherpesviruses, ILTV is hard to be eliminated from the host and there is presently no viable therapeutic cure due to the formation of latent infection in the trigeminal ganglia following acute infection ( Thilakarathne et al, 2019 ). As a result, ILTV may reactivate from a latent infection once host immunity is impaired ( Coppo et al, 2013 ; Adler et al, 2017 ).…”