Systemic distribution of different low pathogenic avian influenza (LPAI) viruses in chicken

Abstract

Background: Since we were able to isolate viable virus from brain and lung of H7N1 low pathogenic avian influenza virus (LPAIV) infected chickens, we here examined the distribution of different LPAIV strains in chickens by measuring the viral AI RNA load in multiple organs. Subtypes of H5 (H5N1, H5N2), H7 (H7N1, H7N7) and H9 (H9N2), of chicken (H5N2, H7N1, H7N7, H9N2), or mallard (H5N1) origin were tested. The actual presence of viable virus was evaluated with virus isolation in organs of H7N7 inoculated chickens.

Findings: Viral RNA was found by PCR in lung, brain, intestine, peripheral blood mononuclear cells, heart, liver, kidney and spleen from chickens infected with chicken isolated LPAIV H5N2, H7N1, H7N7 or H9N2. H7N7 virus could be isolated from lung, ileum, heart, liver, kidney and spleen, but not from brain, which was in agreement with the data from the PCR. Infection with mallard isolated H5N1 LPAIV resulted in viral RNA detection in lung and peripheral blood mononuclear cells only.

Conclusion: We speculate that chicken isolated LPAI viruses are spreading systemically in chicken, independently of the strain.

Figure 1

Scatter plot of 45-Ct values of viral RNA from organs of individual birds at 2 days post inoculation (d.p.i.). Chickens were inoculated with different LPAIV strains and the presence of viral RNA in organs was examined at 2 d.p.i. by qPCR. The horizontal line represents the mean of 5 or 6 individual birds with SD. Triangles represent the 45-Ct value of individual birds. The data were expressed as Ct-45 values, which means that increased values in the figures indicate increased amount of viral RNA and when Ct-45 is equal to zero no viral RNA was detected. No viral RNA was detected in controls (Ct = 45). M-LPAIV H5N1, C-LPAIV H7N1 and H7N7: n=6. C-LPAIV H5N2 and H9N2: n=5.

Figure 2

Scatter plot of 45-Ct values of viral RNA from organs of individual birds at 4 days post inoculation (d.p.i.). Chickens were inoculated with different LPAIV strains and the presence of viral RNA in organs was examined at 4 d.p.i. by qPCR. The horizontal line represents the mean of 5 or 6 individual birds with SD. Triangles represent the 45-Ct value of individual birds. The data were expressed as Ct-45 values, which means that increased values in the figures indicate increased amount of viral RNA and when Ct-45 is equal to zero no viral RNA was detected. No viral RNA was detected in controls (Ct = 45). M-LPAIV H5N1, C-LPAIV H7N1 and H7N7: n=6. C-LPAIV H5N2 and H9N2: n=5.

Figure 3

Weight gain during the experimental period. The bodyweight of the chickens was established pre- and post-infection. Symbols represent the mean of individual chickens. PBS control, M-LPAIV H5N1, C-LPAIV H7N1 and H7N7: n=6. C-LPAIV H5N2 and H9N2: n=5. **: P ≤ 0.01.