Figure 1. Clinical and laboratory findings from experimental highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus infection in alpacas, 2026. Stable 1 alpacas were sampled before euthanasia at 4 dpi; stable 2 alpacas were sampled for 20 dpi before euthanasia. A, B) Clinical signs; C–H) laboratory findings. A) Body temperature; shading indicates physiologic range; dotted vertical line indicates dpi that stable 1 alpacas were euthanized. B) Percentage of typical feed intake. C) Quantitative reverse transcription PCR (qRT-PCR) results on nasal swab samples showing H5N1 viral genome was detected until 7 dpi. Shading indicates LOD. D) Nasal swab sample infectious titers. E) qRT-PCR results on rectal swab samples. Shading indicates LOD. F) qRT-PCR results on tissue samples. Of note, only nose and trachea samples were qRT-PCR–positive as evaluated by endpoint dilution assays for quantification of infectious virus. Asterisks indicate samples that tested positive for infectivity by endpoint dilution at 10^1.88, 10^1.82, and 10^1.62 TCID₅₀/mL. G) ELISA specific for H5 antibodies, confirming positivity of samples collected at 20 dpi. H) Neutralization titers determined by using a live virus neutralization test against 100 TCID₅₀, with the endpoint defined as complete protection from cytopathic effect. Titers are expressed as reciprocal serum dilution, confirming measurable neutralizing capacity for 2 of the samples that tested positive by ELISA. dpi, days postinfection; L, left; LOD, limit of detection; LU, light unit; NanoLuc, nanoluciferase; R, right; TCID₅₀, 50% tissue infective dose.