Characterization of Infectious Laryngotracheitis Virus (ILTV) Isolates from Commercial Poultry by Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP)

Abstract

Infectious laryngotracheitis (ILT) is a highly contagious, acute respiratory disease of chickens, of worldwide distribution, that affects growth and egg production and leads to significant economic losses during periodic outbreaks of the disease. Live attenuated vaccines (chicken embryo origin [CEO] and tissue-culture origin [TCO]) have been widely used to control the disease in the United States. It is believed that most of the outbreaks in the United States are caused by vaccine-related isolates that persist in the field and spill over into naïve poultry populations. The objective of this study was to utilize the previously developed polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis to genotype recent ILT virus (ILTV) isolates from commercial poultry. Forty-six samples were collected during January 2006 to April 2007 from five poultry production regions of the United States and were characterized within PCR-RFLP groups III-VI. Sixty-three percent of the samples analyzed were categorized as closely related to the vaccine strains (groups III-V), whereas 33% were categorized as group VI viruses that differed in six and nine PCR-RFLP patterns from the CEO and TCO vaccines; a mixture of group IV and V viruses was detected in two samples (4%). In general, groups V and VI were the most prevalent viruses, found in 52% and 33% of the samples tested respectively. Both types of viruses were detected in vaccinated and nonvaccinated flocks. Although genetically different, both viruses produced severe disease in the field.

Molecular detection and characterization of infectious laryngotracheitis virus (Gallid herpesvirus-1) from clinical samples of commercial poultry flocks in India

“…A number of previous studies demonstrated that many ILTV strains circulating in the fields were genetically related to the vaccine strains [3,21]. In USA, [23,24] investigated ILTV isolates from commercial poultry that were collected between 1988 and 2007 and observed that most of the ILT outbreaks have caused milder clinical signs and have been associated with the vaccine-like strain virus. In Europe, 104 field isolates were collected during 35 years from eight different countries and it was shown that 98 of these field isolates had the same RFLP patterns as vaccine strains [21].…”

Molecular epidemiology of infectious laryngotracheitis: a review

“…Polymerase chain reaction (PCR) amplification of selected genome areas followed by restriction fragment length polymorphism (RFLP), or sequencing of PCR products are widely used. Initially, both PCR-RFLP and sequencing were critical in strain differentiation of GaHV-1 strains from the USA Oldoni et al, 2008), while complete genome comparisons of outbreak-related isolates and vaccine strains allowed further insight into the origin of GaHV-1 US isolates (Garcia et al, 2013). In the USA, the majority of commercial poultry outbreak-related strains are either indistinguishable from or closely related to vaccine strains, while outbreaks caused by wild-type strains occur to a much lesser extent than those attributed to live attenuated vaccine strains (Oldoni et al, 2008).…”

“…Initially, both PCR-RFLP and sequencing were critical in strain differentiation of GaHV-1 strains from the USA Oldoni et al, 2008), while complete genome comparisons of outbreak-related isolates and vaccine strains allowed further insight into the origin of GaHV-1 US isolates (Garcia et al, 2013). In the USA, the majority of commercial poultry outbreak-related strains are either indistinguishable from or closely related to vaccine strains, while outbreaks caused by wild-type strains occur to a much lesser extent than those attributed to live attenuated vaccine strains (Oldoni et al, 2008). In Australia, the introduction of the European-origin Serva CEO vaccine to a population of birds previously vaccinated with native vaccines SA2 and A20 resulted in the devastating emergence of novel virulent strains responsible for numerous outbreaks of ILT.…”

“…The use of multi-locus PCR-RFLP and sequencing of more than two genes produced the discriminatory power necessary to identify CEO-related isolates and differentiate these from non-vaccine-related isolates, particularly in North America, Europe, South America and East Asia (Chang et al, 1997;Han & Kim, 2001;Kirkpatrick et al, 2006b;Ojkic et al, 2006;Oldoni et al, 2008;Neff et al, 2008;Chacon et al, 2010;Moreno et al, 2010). In some cases a combination of PCR-RFLP and sequencing was necessary to achieve a greater degree of discrimination.…”

Comparison of the replication and transmissibility of two infectious laryngotracheitis virus chicken embryo origin vaccines delivered via drinking water

“…Genetic characterization of ILTV strains using molecular methods has allowed the differentiation of vaccine and field strains of ILTV (Creelan et al, 2006;Kirkpatrick et al, 2006b;Ojkic et al, 2006;Oldoni & García, 2007;Neff et al, 2008;Oldoni et al, 2008;Callison et al, 2009;Chacó n & Ferreira, 2009;Moreno et al, 2010). Using these techniques, studies from several geographic areas of the world have established that most outbreaks have been caused by vaccine-related ILTV strains (Creelan et al, 2006;Ojkic et al, 2006;Oldoni & García, 2007;Neff et al, 2008;Oldoni et al, 2008;Blacker et al, 2011). This phenomenon has led to the term ''vaccinal laryngotracheitis'' being coined in the USA (DufourZavala, 2008).…”