Abstract
Newcastle disease virus strains are velogenic, mesogenic, and lentogenic. This study aims to design a scoring system for lesions induced by different strains of Newcastle disease virus in chicken. Three experiments were conducted. In experiments 1 and 2, chickens were divided into infected and control groups. Infected groups of experiments 1 and 2 consisted of 6 and 24 specific pathogen-free (SPF) chickens, respectively. Control groups in experiments 1 and 2 consisted of 6 and 15 SPF chickens, respectively. In infected groups, infection was induced by intranasal administration of 105 50% EID50/0.1 mL of velogenic Newcastle disease virus strain (vNDV). Infected chickens in experiment 1 were euthanised by cervical dislocation on days 3, 6, and 7 postinoculation (pi). Infected chickens in experiment 2 were euthanised at hours (hrs) 2, 4, 6, 12 and days 1, 2, 4, and 6 pi. Chickens of the control group in experiment 1 were euthanised on days 3 and 7 pi, whereas control group chickens in experiment 2 were euthanised on days 0, 1, 2, 4, and 6 pi. Then in experiment 3, 15 SPF chickens were divided into three groups; in the first group, 5 SPF chickens were infected with vNDV, in the second group, 5 SPF chickens were infected with lentogenic NDV (lNDV) (103.0 EID50/0.1 mL), and the third group was kept without infection as a control group. Chickens were euthanised on day 5 pi. In all previous experiments, tissues of brain, trachea, lung, caecal tonsil, liver, kidney, spleen, heart, proventriculus, intestine, and thymus were collected, fixed in 10% buffered formalin, embedded in paraffin, and sectioned. HS staining was applied. Tissues were examined under light microscope and changes were recorded. A scoring system was designed for lesions induced by different strains of NDV and, accordingly, lesions were scored. The scoring system was found helpful in the evaluation of disease severity.
Highlights
Newcastle disease virus (NDV) can be grouped into five pathotypes with respect to tissue tropism and clinical signs, that is to say, (a) viscerotropic velogenic pathotype and (b) neurotropic velogenic pathotype
In the infected group of trachea, bursa of Fabricius, and spleen tissues which had scoring system of 6 grade (0-5), the lesions scoring in the trachea, on days 3, 6, and 7 pi, was 5.00 ± 0.00, 5.00 and 5.00 ± 0.00, respectively (Figure 1; Table 1)
In the tissue of proventriculus, which had a scoring system of 5 grades (0-4), the lesions scoring on days 3, 6, and 7 were 1.47 ± 0.24, 2.20, and 2.50 ± 0.00, respectively (Table 2)
Summary
Newcastle disease virus (NDV) can be grouped into five pathotypes with respect to tissue tropism and clinical signs, that is to say, (a) viscerotropic velogenic pathotype and (b) neurotropic velogenic pathotype. Both viscerotropic and neurotropic pathotypes cause high mortality rate accompanied by intestinal lesions or nervous signs; (c) mesogenic pathotype causes a low mortality rate and respiratory and nervous signs; (d) lentogenic pathotype is the causative agent of clinically mild or unapparent infections of respiratory tract; and eventually (e) asymptomatic pathotype and its reflection on chicks are unapparent intestinal infections [1]. There are velogenic, mesogenic, and lentogenic strains of ND virus (NDV). The isolates which do not manifest clinical picture are considered as lentogenic, the isolates of intermediate virulence are called mesogenic, and virulent isolates of high mortality rate are termed velogenic [2,3,4].
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