Experimental design.

<p>Thirty 2-week old SPF-chickens were randomly distributed into three groups. Animals received the first inoculum (day 0) and 2 weeks later (day 15), birds were challenged with the respective inoculum 2. Six birds from G1 and G2 were consecutively infected 2 weeks later (day 30) with the third inoculum.</p><p>Abbreviations: LPAIV = low pathogenic avian influenza virus; HPAIV = highly pathogenic avian influenza virus.</p>a<p>Chickens from G1 were inoculated intranasally with LPAIV A/<i>Anas plathyrhynchos</i>/Spain/1877/2009 (H7N2) (10^5.5 ELD₅₀). Birds from G2 and G3 received saline solution.</p>b<p>Chickens from G1 and G2 were intranasally challenged with HPAIV A/FPV/Rostock/34 (H7N1) (10^5.5 ELD₅₀) 15 days after the pre-exposure to H7N2 LPAIV. Birds from G3 received saline solution.</p>c<p>Chickens from G1 and G3 were inoculated intranasally with 10^4.5 ELD₅₀ of A/Great crested grebe/Basque Country/06.03249/2006 (H5N1) 15 days after the challenge with H7N1 HPAIV.