Epidemiological investigation of porcine pseudorabies virus and its coinfection rate in Shandong Province in China from 2015 to 2018

Abstract

Background: Pseudorabies, also known as Aujeszky's disease, is caused by the pseudorabies virus (PRV) and has been recognized as a critical disease affecting the pig industry and a wide range of animals around the world, resulting in great economic losses each year. Shandong province, one of the most vital food animal-breeding regions in China, has a very dense pig population, within which pseudorabies infections were detected in recent years. The data, however, on PRV epidemiology and coinfection rates of PRV with other major swine diseases is sparse.

Objectives: This study aimed to investigate the PRV epidemiology in Shandong and analyze the current control measures.

Methods: In this study, a total number of 16,457 serum samples and 1,638 tissue samples, which were collected from 362 intensive pig farms (≥ 300 sows/farm) covered all cities in Shandong, were tested by performing enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).

Results: Overall, 52.7% and 91.5% of the serum samples were positive for PRV-gE and -gB, respectively, based on ELISA results. In addition, 15.7% of the tissue samples were PCR positive for PRV. The coinfection rates of PRV with porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus, and classical swine fever virus were measured; coinfection with PCV2 was 35.0%, higher than those of the other two viruses. Macroscopic and microscopic lesions were observed in various tissues during histopathological examination.

Conclusions: The results demonstrate the PRV prevalence and its coinfection rates in Shandong province and indicate that pseudorabies is endemic in pig farms in this region. This study provides epidemiological data that can be useful in the prevention and control of pseudorabies in Shandong, China.

Keywords: Pseudorabies virus; coinfection; porcine circovirus; veterinary epidemiology.

Fig. 1. Clinical signs and gross lesions observed in PRV-infected pigs. (A) Typical neurological symptom: infected pigs paddled their limbs; (B, C) Stillbirth: pregnant sow had a miscarriage; (D) Brain: meningeal congestion and bleeding; (E) Tonsil: ulcerative necrosis around crypts; (F) Spleen: dense grayish-white necrotic foci on the surface; (G) Liver: grayish-white necrotic foci of varying sizes on the surface; (H) Lung: interstitial pneumonia with grayish-white necrotic foci; (I) Kidney: needle-shaped hemorrhage and grayish-white necrotic foci on the surface.

Fig. 2. Histopathological lesions in the tissues of pseudorabies virus-infected pigs. (A) Liver: hepatic sinusoids congestion, hepatocyte degeneration, and necrosis, red-stained inclusion bodies in cell nucleus (H & E stain. Original magnification: ×1,000); (B) Liver (control) (H & E stain. Original magnification: × 200); (C) Tonsillar crypts: intranuclear red-stained inclusion bodies in epithelia (H & E stain. Original magnification: ×400); (D) Tonsillar crypts (control) (H & E stain. Original magnification: ×400); (E) Brain: cerebral vascular congestion, perivascular cuffs of lymphocytes (H & E stain. Original magnification: ×400); (F) Brain (control) (H & E stain. Original magnification: ×400); (G) Lung: necrotic inflammation of the pulmonary interstitium, necrosis, and disintegration of infiltrating lymphocytes in necrotic foci (H & E stain. Original magnification: ×400); (H) Lung (control) (H & E stain. Original magnification: ×400); (I) Kidney: necrotic inflammation of renal interstitium, necrosis, and disintegration of infiltrating lymphocytes in necrotic foci (H & E stain. Original magnification: ×400); (J) Kidney (control) (H & E stain. Original magnification: ×400); (K) Spleen: intranuclear red-stained inclusion bodies in epithelia, nuclear disintegration, and necrosis (H & E stain. Original magnification: ×400); (L) Spleen (control) (H & E stain. Original magnification: ×400).

H & E, hematoxylin and eosin.