A pinboard by
Omid Fakhri

PhD candidate, The University of Melbourne


Natural recombination events in live attenuated ILT vaccines and formation of virulent strains

Recently, two very successful vaccines that were used to control a respiratory disease in chickens have stopped working. Previously, this disease was not a major problem in poultry industry but now it causes mortalities up to 30% and the current vaccines are not able to control it. Our team has done in-depth research to describe the reason for the failure of these vaccines. With the current knowledge, we're able to suggest optimised vaccination protocols and contribute to the vaccine research in order to avoid to have the similar situations with other viruses from the same family.


Growth kinetics and transmission potential of existing and emerging field strains of infectious laryngotracheitis virus.

Abstract: Attenuated live infectious laryngotracheitis virus (ILTV) vaccines are widely used in the poultry industry to control outbreaks of disease. Natural recombination between commercial ILTV vaccines has resulted in virulent recombinant viruses that cause severe disease, and that have now emerged as the dominant field strains in important poultry producing regions in Australia. Genotype analysis using PCR-restriction fragment length polymorphism has shown one recombinant virus (class 9) has largely replaced the previously dominant class 2 field strain. To examine potential reasons for this displacement we compared the growth kinetics and transmission potential of class 2 and class 9 viruses. The class 9 ILTV grew to higher titres in cell culture and embryonated eggs, but no differences were observed in entry kinetics or egress into the allantoic fluid from the chorioallantoic membrane. In vivo studies showed that birds inoculated with class 9 ILTV had more severe tracheal pathology and greater weight loss than those inoculated with the class 2 virus. Consistent with the predominance of class 9 field strains, birds inoculated with 10(2) or 10(3) plaque forming units of class 9 ILTV consistently transmitted virus to in-contact birds, whereas this could only be seen in birds inoculated with 10(4) PFU of the class 2 virus. Taken together, the improved growth kinetics and transmission potential of the class 9 virus is consistent with improved fitness of the recombinant virus over the previously dominant field strain.

Pub.: 19 Mar '15, Pinned: 30 Jun '17