Comparison of the replication and transmissibility of an infectious laryngotracheitis virus vaccine delivered via eye-drop or drinking-water

Abstract

Live attenuated vaccines have been extensively used to control infectious laryngotracheitis (ILT). Most vaccines are registered/recommended for use via eye-drop although vaccination via drinking-water is commonly used in the field. Drinking-water vaccination has been associated with non-uniform protection. Bird-to-bird passage of chick-embryo-origin (CEO) ILT vaccines has been shown to result in reversion to virulence. The purpose of the present study was to examine the replication and transmission of a commercial CEO infectious laryngotracheitis virus (ILTV) vaccine strain following drinking-water or eye-drop inoculation. Two groups of 10 specific-pathogen-free chickens were each vaccinated with Serva ILTV vaccine strain either via eye-drop or drinking-water. Groups of four or five unvaccinated birds were placed in contact with vaccinated birds at regular intervals. Tracheal swabs were collected every 4 days from vaccinated and in-contact birds to assess viral replication and transmission using quantitative polymerase chain reaction. Compared with eye-drop-vaccinated birds, drinking-water-vaccinated birds showed delayed viral replication but had detectable viral DNA for a longer period of time. Transmission to chickens exposed by contact on day 0 of the experiments was similar in both groups. Birds exposed to ILTV by contact with eye-drop vaccinated birds on days 4, 8, 12 and 16 of the experiment had detectable ILTV for up to 8 days post exposure. ILTV was not detected in chickens that were exposed by contact with drinking-water vaccinated birds on day 12 of the experiment or later. Results from this study provide valuable practical information for the use of ILT vaccine.

Protection Induced in Broiler Chickens following Drinking-Water Delivery of Live Infectious Laryngotracheitis Vaccines against Subsequent Challenge with Recombinant Field Virus

“…However, under field conditions, some birds may not consume drinking water containing the vaccine, or may receive a suboptimal dose of the vaccine because of reduced consumption. These birds, therefore, remain either unvaccinated or incompletely vaccinated [ 10 , 11 , 20 ]. Other factors may also limit the effectiveness of vaccines delivered via drinking water in poultry, including equipment limitations, poor water quality and sub-optimal preparation and handling of the vaccine [ 21 ].…”

“…Attenuated ILTV vaccines have been widely used to control the disease. However, these vaccines have several limitations, including insufficient attenuation [ 6 ], transmission of vaccine virus to unvaccinated birds [ 7 , 8 ], increased virulence after bird-to-bird transmission [ 9 ] and also incomplete protection in vaccinated birds [ 10 , 11 ].…”

Cytokine gene transcription in the trachea, Harderian gland, and trigeminal ganglia of chickens inoculated with virulent infectious laryngotracheitis virus (ILTV) strain

“…ILTV primarily infects the upper respiratory tract of chickens, the conjunctiva and tracheal mucosa being the main sites of viral lytic replication. Under experimental conditions, the peak of viral replication, for either vaccine strains or field isolates, is usually between 3 and 5 days postinfection (dpi) (Rodriguez-Avila et al, 2007;Oldoni et al, 2009;Coppo et al, 2012;Lee et al, 2015;Vagnozzi et al, 2015;Beltrán et al, 2017). In the trachea, the severity of lesions changes during the course of infection; at 2 dpi microscopic changes in tracheal mucosa include loss of goblet cells and infiltration of inflammatory cells.…”

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

“…(Coppo et al, 2012). This would create favourable conditions in the field for in vivo passage of the virus with the potential for reversion to virulence or possibly in vivo selection of viral subpopulations within the vaccine preparation.…”