Pathogenesis and transmissibility of highly (H7N1) and low (H7N9) pathogenic avian influenza virus infection in red-legged partridge (Alectoris rufa)

Abstract

An experimental infection with highly pathogenic avian influenza virus (HPAIV) and low pathogenic avian influenza virus (LPAIV) was carried out in red-legged partridges (Alectoris rufa) in order to study clinical signs, gross and microscopic lesions, and viral distribution in tissues and viral shedding. Birds were infected with a HPAIV subtype H7N1 (A/Chicken/Italy/5093/1999) and a LPAIV subtype H7N9 (A/Anas crecca/Spain/1460/2008). Uninoculated birds were included as contacts in both groups. In HPAIV infected birds, the first clinical signs were observed at 3 dpi, and mortality started at 4 dpi, reaching 100% at 8 dpi. The presence of viral antigen in tissues and viral shedding were confirmed by immunohistochemistry and quantitative real time RT-PCR (qRRT-PCR), respectively, in all birds infected with HPAIV. However, neither clinical signs nor histopathological findings were observed in LPAIV infected partridges. In addition, only short-term viral shedding together with seroconversion was detected in some LPAIV inoculated animals. The present study demonstrates that the red-legged partridge is highly susceptible to the H7N1 HPAIV strain, causing severe disease, mortality and abundant viral shedding and thus contributing to the spread of a potential local outbreak of this virus. In contrast, our results concerning H7N9 LPAIV suggest that the red-legged partridge is not a reservoir species for this virus.

Figure 1

Kidney lesions of a H7N1 HPAIV (A/Chicken/Italy/5093/1999) infected partridge consisting in parenchymal pallor, lobular surface architecture and urate deposits in the urethers, 6 dpi.

Figure 2

Nasal turbinates, 6 dpi; (A) Necrosis of single cells of the olfactory epithelium, H/E. (B) Positive staining in olfactory epithelial cells, IHC.

Figure 3

Brain, 5 dpi; (A) Focal areas of malacia, H/E. (B) Positive staining in neurons, ependymal cells and glial cells, IHC.

Figure 4

Viral shedding (expressed as log₁₀ viral RNA copies/sample) detected by qRRT-PCR over 8 days in cloacal and oropharyngeal swabs and feather pulp samples of red-legged partridges (Alectoris rufa) infected with A/Chicken/Italy/5093/1999 H7N1 HPAIV and A/Anas crecca/Spain/1460/2008 H7N9 LPAIV. In A and B, rates above the bars indicate the relation between positive birds and the total number of animals examined. Limit of detection is indicated by the dashed line (1.46 log₁₀ viral RNA copies/sample). (A) H7N1 HPAIV intranasally inoculated partridges, (B) H7N1 HPAIV contact partridges, (C) H7N9 LPAIV intranasally inoculated partridges.