Comparison of influenza A virus infection in high- and low-birth-weight pigs using morphometric analysis

Epigenetic studies have shown that low-birth-weight (LBW) and growth restriction has been associated with reduced immune function in humans and reduced passive immunity in pigs. To examine the immune responses of high-birth-weight (HBW) and LBW groups of pigs, influenza A virus infection was used as an exemplifier of neonatal respiratory disease.

The objectives of this study were (i) to compare clinical, immunological, and pathological outcome of influenza infection in HBW to LBW pigs and (ii) to establish standardized sampling sites, score each site independently with set criteria, and compare scores between sites.

Sixty-eight 4-week-old pigs originating from either HBW or LBW litters were intratracheally inoculated with 10(6.3) TCID50 /ml of A/swine/Texas/4199-2/1998 H3N2 and euthanized 48 hours later. Samples were collected 2.5 cm from the tip of both cranial and middle lung lobes. The formalin-fixed paraffin-embedded tissue sections were scored in a blinded manner by a single pathologist using established scoring criteria for routine and immunohistochemical stains. Clinical parameters, lung and nasal swab virus titers, and cytokine levels for interferon-alpha and interleukin-1-beta, IL-6, and IL-8 were measured.

Lung lesion severity and influenza staining intensity were significantly lower in LBW compared with HBW pigs (P < 0.05). Additionally, examining just the LBW group, the significant difference between lobes (P = 0.009) showed that the mean score for the right cranial lung lobe was higher compared with the other three lobes.