Pathogenicity evaluation of GVI-1 lineage infectious bronchitis virus and its long-term effects on reproductive system development in SPF hens

Abstract

Infectious bronchitis virus (IBV) has gained increasing attention in the poultry industry due to its ability to cause tissue injuries not only in the respiratory system and kidney but also in the reproductive system of layers. Recently, the GVI-1 lineage IBVs have spread widely in China, whereas their pathogenicity in egg-laying chickens has rarely been studied, especially its long-term influence in egg production upon the early infection in chicks. In this study, 10-day-old SPF chicks were infected with the GVI-1 lineage JX181 strain and monitored over a 170-day period after infection. The pathogenicity evaluation of the JX181 strain included clinical observations, immunohistochemical assay, viral load, viral shedding, gross autopsy, and laying rate. The results showed that JX181 has a high pathogenicity, causing severe system lesions, and the decrease in egg production. In summary, this study describes the long-term damages caused by the early infection with the IBV GVI-1 lineage on the reproductive system of hens, providing a comprehensive understanding of the pathogenicity of the IBV GVI-1 lineage and emphasizing the importance of its early prevention.

Keywords: GVI-1 lineage; early infection; egg production; infectious bronchitis virus; pathogenicity; reproductive system.

Figure 1

Gross lesions in the different organs of chicks inoculated with strain JX181. 10-day-old chicks were challenged with 10^6.5 EID₅₀ of JX181 via the ocular–nasal route. The representative gross lesions of the chicks sacrificed at 6 dpi were shown in (A,B) Larynx and trachea, (C,D) Pulmonary congestion, (E,F) Bursa of Fabricius, (G,H) Oviduct.

Figure 2

Histopathologic changes were observed in different tissues of chicks inoculated with strain JX181 at 6 dpi. (A,B) Trachea: the black arrow indicates the extensive loss and necrosis of ciliated epithelial cells, and the hollow arrow indicates the thickening of the lamina propria of the tracheal mucosa and lymphocyte infiltration. (C,D) Lung: the black arrow indicates erythrocyte infiltration in the bronchial lumen. (E,F) Spleen: black arrows indicate macrophages in the splenic sinus. (G,H) Kidney: black arrows indicate swelling and degeneration of tubular epithelial cells. (I,J) Bursa of Fabricius: the hollow arrow indicates the interstitial dilation of the lymphoid follicles, and black arrows indicate the lymphocyte loss.

Figure 3

Viral load in different tissues of chickens at 3, 6, 9, and 12 days post infection. The trachea, lung, spleen, kidney, and bursa of Fabricius samples were collected at 3, 6, 9, and 12 dpi, total RNA was extracted and reverse transcribed into cDNA, and RT–qPCR was used to measure the viral load in different tissues. LOD: limit of detection.

Figure 4

Viral shedding was detected in both oral and cloacal swab samples. Oral and cloacal swab samples were collected at 3, 6, 9, and 12 dpi, and RT-qPCR was used to measure the level of viral shedding in these samples. Statistical differences between two groups were assessed by the Student’s t-test Statistical significance was defined as follows: **p < 0.01.

Figure 5

Decreased egg production was observed in the challenge group. The number of eggs in each group was counted from 21 to 25 weeks. Statistical differences between two groups were assessed by the Student’s t-test Statistical significance was defined as follows: *p < 0.05, ***p < 0.001.

Figure 6

Gross lesions were observed in the ovary and oviduct of the hens at 170 dpi. (A) Well-developed organs from the control group. (B) Flaccid ovary. (C,D) The fluid yolk material and fibrin clots in the coelome. (E) Cystic dilation in the oviduct. (F) Oviduct and ovary with retarded development.

Figure 7

The lengths of the oviducts and the number of hierarchal ovarian follicles were impaired upon challenge with JX181 at 170 dpi. (A,B) The lengths of the oviducts were measured after the euthanasia of the chickens. (C) Statistical representation of the mean lengths of the oviducts. (D,E) The hierarchal ovarian follicles in mock and JX181 infected groups. (F) Statistical representation of the number of hierarchal ovarian follicles with diameters larger than 10 mm.