The route of inoculation dictates the replication patterns of the infectious laryngotracheitis virus (ILTV) pathogenic strain and chicken embryo origin (CEO) vaccine

Figures & data

Figure 1. Haematoxylin and eosin (H&E) staining of conjunctiva and trachea sections of chickens inoculated with ILTV pathogenic strain 63140 (Figure 1(a,c,e,g)) or CEO vaccine strain (Figure 1(b,d,f,h)) and collected at five days post-inoculation. Presence of syncytial cell formation and intranuclear inclusion bodies in the conjunctiva (Figure 1(a)) and trachea (Figure 1(c)) of chickens inoculated with strain 63140 via the OC route, and in the conjunctiva of chickens inoculated with the CEO strain via the OC (Figure 1(b)) and IN (Figure 1(f)) routes. Absence of lesions in the conjunctiva (Figure 1(e)) and trachea (Figure 1(g)) of 63140-inoculated chickens and in the trachea (Figure 1(h)) and conjunctiva (Figure 1(d)) of chickens inoculated with the CEO strain via the IN and OC routes, respectively.

Table 1. Percentage of ILTV-positive samples as determined by histopathology examination and IHC.

		Route of inoculation
Virus	Tissues	OC^c		OR		IN		IT
Pathogenic 63140^a		D3^d	D5	D3	D5	D3	D5	D3	D5
	Conjunctiva	0	100	0	0	0	0	0	0
	Nasal cavity	100	100	25	100	50	75	0	100
	Trachea	0	100	0	0	0	0	100	100
CEO^b
	Conjunctiva	64	21	15	14	0	25	0	0
	Nasal cavity	14	57	100	86	67	100	33	50
	Trachea	0	0	0	0	0	0	100	100

^an = 4.

^bn = 6.

^cOcular (OC), Oral (OR), Intranasal (IN) or Intratracheal (IT).

^d3 and 5 days (D) post-inoculation.

Figure 2. Haematoxylin and eosin (H&E) and immunohistochemistry (IHC) staining of the Harderian gland sections collected at five days post-inoculation of chickens that received ILTV pathogenic strain 63140 or the CEO vaccine strain via the OC route. Absence of syncytial cell formation, intranuclear inclusion bodies and lymphocyte infiltration in the Harderian gland sections (Figure 2(a,b)). Viral antigen detection in the Harderian gland sections (Figure 2(c,d)).

Table 2. Mean number of ILTV antigen-positive cells per Harderian gland.

	Virus strain
Route	Pathogenic strain 63140	CEO vaccine
Ocular	20.89 (±5.18)^a	12.53 (±3.66)
Oral	8.75 (±1.90)	26 (±11.42)
Intranasal	6.2 (±2.88)	6.3 (±2.58)
Intratracheal	5.6 (±1.85)	5.2 (±0.96)

^aIn parenthesis the standard error of the mean.

Figure 3. Individual genome load of the pathogenic ILTV strain 63140 and CEO vaccine. Genome loads (Log₁₀ 2^−ΔΔCt) of 63140 (Figure 3(a–d)) and CEO vaccine (Figure 3(e–h)) at 3 and 5 days post-inoculation. Genome loads of 63140 and CEO vaccine for each tissue were compared among groups of birds inoculated via the ocular (OC), oral (OR), intranasal (IN) or intratracheal (IT) route by the one-way analysis of variance Kruskal–Wallis test. A significant genome load decrease (P < 0.05) is indicated by a lambda symbol (λ) and a significant genome load increase (P < 0.05) is indicated by an asterisk (*). The horizontal line depicts the mean genome load per tissue and the vertical line depicts the standard deviation in the group.