Evaluation of the protection elicited by direct and indirect exposure to live attenuated infectious laryngotracheitis virus vaccines against a recent challenge strain from the United States

Figures & data

Figure 1.  ILT viral genome copy number (log₁₀) detected in the eye conjunctiva and trachea by Re-Ti-PCR from sentinel chickens (SE-NVx-Ch) of the non-vaccinated challenged group.

Figure 2.  Total clinical sign scores recorded per day in 8-week-old chickens from day 2 to 12 d.p.c. with ILT virus. Contact-exposed to tissue culture origin vaccinated challenge (CT-TCOVx-Ch), contact-exposed to chicken embryo origin (CT-CEOVx-Ch), and non-vaccinated challenge (NVx-Ch) groups were significantly different (P < 0.05) from the non-vaccinated-non-challenged (NVx-NCh) group, while the tissue culture origin vaccinated challenged (TCOVx-Ch) and chicken embryo origin vaccinated challenged (CEOVx-Ch) groups were not significantly different from the non-vaccinated-non-challenged (NVx-NCh) group.

Table 1.  Percentage mortality 12 d.p.c. with a group VI ILT virus

Group^a	Number dead/number per group	Mortality (%)^b
CEOVx-Ch	0/20	0^A
SE-CEOVx-Ch	0/20	0^A
CT-CEOVx-Ch	5/20	25^B
TCOVx-Ch	0/20	0^A
SE-TCOVx-Ch	0/20	0^A
CT-TCOVx-Ch	6/20	30^B
NVx-Ch	3/10	30^B
SE-NVx-Ch	4/10	40^B
NVx-NCh	0/20	0^A
^aCEOVx-Ch, chicken embryo origin vaccinated challenged; SE-CEOVx-Ch, sentinels chicken embryo origin vaccinated challenged; CT-CEOVx-Ch, contact-exposed chicken embryo origin vaccinated challenged; TCOVx-Ch, tissue culture origin vaccinated challenged; SE-TCOVx-Ch, sentinels tissue culture vaccinated challenged; CT-TCOVx-Ch, contact-exposed tissue culture vaccinated challenged; NVx-Ch, non-vaccinated challenged; SE-NVx-Ch, sentinels non-vaccinated challenged; NVx-NCh, non-vaccinated-non-challenged. ^bSignificantly different% mortality (P<0.05) shown by different superscript uppercase letters.

Table 2.  Mean (standard error) percentage change in body weight for groups of 20 chickens at 4 to 8 weeks of age (pre ILT challenge) and 12 days post ILT challenge

Group^a	Pre-challenge	Post-challenge
NVx-Ch	68.9 (1.9)	6.6^b (3.3)
SE-NVX-Ch	69.0 (1.4)	7.2^b (2.5)
CEOVx-Ch	67.6 (1.5)	17.1 (2.7)
CT-CEOVx-Ch	67.1 (1.4)	5.0^b (3.8)
SE-CEOVx-Ch	62.9 (1.7)	17.9 (3.1)
TCOVx-Ch	68.4 (2.0)	19.4 (3.0)
CT-TCOVx-Ch	65.7 (1.9)	6.6^b (3.5)
SE-TCOVx-Ch	66.5 (1.6)	18.0 (2.9)
NVx-NCh	68.6 (1.8)	20.7 (3.2)
^aSee key to Table 1. ^bMeans are significantly different from the negative control group using the Bonferroni procedure to control the overall type I error rate at 5%.

Table 3.  ILT ELISA results for sera samples collected before vaccination (4 weeks of age), pre-challenge (8 weeks of age), and 12 d.p.c.

	Pre-challenge		Post-challenge
Group^a	Positive^b	Titre range	Positive	Titre range
CEOVx-Ch	7	460 to 3427	7	922 to 7312
SE-CEOVx-Ch	0	0	0	0
CT-CEOVx-Ch	9	758 to 4332	9	551 to 3558
TCOVx-Ch	6	517 to 2054	6	449 to 3591
SE-TCOVx-Ch	0	0	0	0
CT-TCOVx-Ch	4	443 to 2628	4	293 to 598
NVx-Ch	0	0	3	270 to 821
SE-NVx-Ch	0	0	3	291 to 653
NVx-NCh	0	0	0	0
^aSee key to Table 1. ^bNumber positive of 10 samples tested.