Infectious laryngotracheitis virus and pathogenicity and dose

It is also feared that present live virus vaccines may mutate and become responsible for continued disease outbreaks. This research project has three specific objectives. Objective 1 compares the complete genome sequences of field viruses collected in various regions of the United States over a 20 year period and compare those sequences with the complete genome sequences of chicken-embryo-origin CEO and tissue culture origin TCO vaccine strains of ILTV.

We have successfully developed methods for sequencing ILTV genomes using high-throughput NextGen sequencing technologies. Objective 2 evaluates changes in ILTV pathogenicity and sequence following bird-to-bird passage. Since the early s there has been a concern that ILTV increases in virulence following bird-to-bird passage. However, it is known that most commercial ILTV vaccines actually contain multiple viral genotypes.

It is possible that more invasive and pathogenic sub-populations of virus are selected during bird-to-bird passage. Using this "limit dilution, pock-purification" method, virus generated from one clone UDCEOA was used to inoculate 10 broiler birds via the intrachoanal route. On day 4 after infection, tracheal swabs were collected and used to inoculate an additional group of birds.

This procedure was repeated 20 times. Ultimately, control of ILT will depend on the development of safer and more effective vaccines. This virus stock will be serially diluted and then used to infect the chorioallantoic membranes CAM of 10 day embryonated chicken eggs.

After one week of incubation the infected CAMs will be evaluated. When CAMs containing single "pocks" are identified, these infected regions will be excised and used to create virus stocks. This sequenced will be assembled into a full length viral genome sequence using a bioinformatics pipeline developed in our laboratory manuscript in preparation. Experiment 3: The five CEO vaccine derivatives will also be evaluated for their pathogenicity and immunogenicity in week-old broiler chickens maintained in isolation units.

Birds 10 will be inoculated via the choanal cleft with Virulence and immunogenicity will be determined as previously described Poulsen et al.

Briefly, pathogenicity will be evaluated on a scale from day2 through day 10 after inoculation. In addition, birds will be swabbed by the oral-pharyngeal route 5 days after inoculation to determine the presence of virus. Two weeks after inoculation, the birds will be evaluated for resistance to challenge by administering Birds will again be evaluated for clinical signs of ILT on a scale from day2 through day 10 after challenge.

Objective 2: Evaluate changes in pathogenicity and sequence following bird, chicken embryo, and tissue culture passage of ILTV. Experiment 1: Using a defined plaque-purified CEO vaccine strain, a bird-to-bird passage study will be performed.

Birds 10 will be inoculated intratracheally with On day 5 after infection, tracheal swabs will be collected and used to inoculate an additional group of birds. This procedure will be repeated 20 times. The virulence of the initial virus and of virus isolated after passages 1, 10 and 20 will be determined as previously described Poulsen et al. These latent carriers are a source for spread of virus to non-vaccinated flocks.

Therefore, it is recommended that ILT vaccines be used only in endemic areas. Compared with protection afforded by TCO and CEO vaccines, there was no significant difference in the immunity of chickens at 10 wk post vaccination.

However, when chickens over 20 wk of age were vaccinated, the CEO vaccines induced better protection than TCO vaccines[ 66 ]. Methods for live vaccine administration are eye drop, drinking water, and aerosol spray. The drinking water route poses some problems in that chickens might not receive enough viruses at the target organ nasal epithelial cells and drinking water quality varies between poultry houses.

Thus, these birds may fail to develop protective immunity and may have rolling continual reactions[ 67 ]. On the other hand, with spray route, some chickens may develop severe reactions, because excess dosage of small droplets can penetrate deep into the respiratory tract[ 68 ].

Reports have shown that modified-live vaccines increase their virulence by bird-to-bird passage. Serially passaged modified-live ILT vaccines in vivo for 35 generations. After the 6th passage, this vaccine strain produced severe clinical signs in challenged chickens.

Furthermore, restriction endonuclease analysis of the viral genomes between original and final passage showed no differences between isolates. CEO vaccines have the tendency to increase in virulence more than TCO vaccines, when passed in chickens[ 69 , 70 ]. They revealed that some current field virulent isolates were closely related to vaccine strains. This implies that field isolates originated from vaccine strains after back passage in chickens[ 43 , 52 , 57 - 60 ].

Recently recombinant vaccines have been commercialized. A recombinant fowlpox vaccine, which contained ILTV glycoprotein B gB gene, was shown to induce protection against virulent strains[ 71 ]. Another recombinant fowlpox virus, which contains ILTV gB and UL 32 genes, showed some efficacy to provide protection against virulent strain challenge via wing web administration[ 72 ]. The other is produced by Intervet Intervet, Inc.

When these licensed commercial recombinant ILT vaccines were vaccinated by d-old embryos in ovo injection, they reduced the clinical signs, but not virus replication after challenge[ 73 ]. These recombinant ILTV vaccines did not cause latent infections and virulent reversion. Although these recombinant vaccines are safer than previously developed live vaccines, their increased cost and the fact that they must be injected has limited their use.

Several studies tried to develop new ILT vaccine candidates by gene deletion. Some ILTVs, with deleted virulent viral genes, retained their ability to induce immune responses without producing clinical signs and latency. Recombinant virus with deleted gJ, TK, and, UL0 genes readily showed attenuation, and could be used for vaccine production[ 74 - 76 ]. The gG-deficient ILTV, administered by either eye drop or drinking water routes for 3-wk-old specific-pathogen-free birds, induce adequate immunity against challenge.

Therefore, it may be able to a use for large-scale vaccination. However, further studies need to be done to determine the protection of this gG-deficient vaccine on commercial chicken farms[ 77 ].

There were also ILTV non-essential genes, which were deleted to test their ability as vaccines. These recombinant and gene-deleted ILTVs could be used as candidates to differentiate vaccinated from field-infected birds. This recombinant virus protected birds from homologous and heterologous H5N1 and H5N2 viruses challenge[ 83 , 84 ]. The gB gene combined with chicken IL as bicistronic vector induced better protection in chicken from ILTV challenge than the gB gene monocistronic vector alone[ 85 ].

It is important to avoid contact between vaccinated or recovered field virus infected birds with non-vaccinated chickens. It is also critical to remove contaminated fomites for prevention and control of ILTV infection. To control ILTV outbreaks, improved biosecurity and management practices are necessary. Biosecurity includes protocols and procedures to prevent pathogens from infecting and transmitting disease by humans, insects, wild birds, or other animals[ 87 ].

Rapid diagnosis, a suitable vaccination procedure, and co-operation between government and industry are critical for ILT control. Although the companies improved the biosecurity and vaccination in these farms, they did not stop the chickens from being infected with ILT. Therefore, a strategy of depopulation, extended downtime, and strict biosecurity eliminated ILT in these farms was performed[ 90 ].

Recently, for controlling the outbreaks, geographic information systems were used to provide the information of the regions for biosecurity, quarantine, vaccination, and the route to processing plants. Government agents, industry companies, growers, and veterinarians need to work together and design a program for outbreak control[ 91 ]. ILT continues as an economical important poultry disease.

House management and biosecurity measures should be performed for disease control. For eradication ILT, the modified-live vaccines need to be replaced by improved recombinant vaccines for the prevention of latent infection and virulent reversion. National Center for Biotechnology Information , U. Journal List World J Virol v. World J Virol. Published online Oct Author information Article notes Copyright and License information Disclaimer.

All rights reserved. This article has been cited by other articles in PMC. Abstract Infectious laryngotracheitis ILT is an important respiratory disease of chickens and annually causes significant economic losses in the poultry industry world-wide. Keywords: Infectious laryngotracheitis virus, Infectious laryngotracheitis, Gallid herpesvirus-1 , Polymerase chain reaction combined with restriction fragment length polymorphism, Recombinant laryngotracheitis vaccines. Table 1 Viral isolation from swabs in specific-pathogen-free embryonating eggs after sanitizer treatments.

Open in a separate window. Table 2 Infectious laryngotracheitis virus isolation from beetles in specific-pathogen-free embryos. Detection and identification of ILTV Laboratory diagnosis is required for ILT, because other diseases cause similar clinical signs and lesions, such as infectious bronchitis, Newcastle disease, avian influenza, infectious coryza, and mycoplasmosis.

Prevention and control of ILTV infection using chicken house management It is important to avoid contact between vaccinated or recovered field virus infected birds with non-vaccinated chickens. References 1. Toward a comprehensive phylogeny for mammalian and avian herpesviruses. J Virol. San Diego: Elsevier Academic Press; Topics in herpesvirus genomics and evolution. Virus Res. Tracheo-laryngotracheotis in poultry. J Am Vet Med Assoc. Psittacid herpesvirus 1 and infectious laryngotracheitis virus: Comparative genome sequence analysis of two avian alphaherpesviruses.

First complete genome sequence of infectious laryngotracheitis virus. BMC Genomics. Comparative analysis of the complete genome sequences of two Australian origin live attenuated vaccines of infectious laryngotracheitis virus. An increase in mortality and pathogenicity has been attributed to these vaccine revertant viruses. However, information is scarce on the pathogenicity and transmission potential of these Canadian isolates.

To this end, 3-week-old specific pathogen-free chickens were experimentally infected with each of the ILTV isolates and compared to uninfected controls.