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. 2023 Nov 8;13(1):2281356. doi: 10.1080/22221751.2023.2281356

Figure 1.

Figure 1.

Experimental design. Eight male Holstein calves, approximately 4 months old, were administered a 50/50 mixture of SARS-CoV-2 Delta (B.1.617.2, clade GK) and Omicron BA.2 (lineage B.1.1.529; clade GRA) intranasally (IN) using a MAD Nasal™ atomization device (Teleflex, Morrisville, NC, USA), and orally (PO) by a micropipette, with a total dose of 1 × 106 TCID50 in 4 mL (2.5 × 105 TCID50/mL). Two sentinel calves were isolated in a separate pen, physically distant and up-current of directional airflow from the challenged animals. The sentinel calves were co-mingled with the eight principal-infected calves after sampling at 1 DPC, 24 h post-challenge. Whole blood (EDTA) was collected on −1, 3, 7, 10, 14, 18, and 20 days post-challenge (DPC). Serum was collected on −1, 3 (calves HT1, HT8, 678 only), 7, 10, 14, 18, and 20 DPC. Nasal, oral, and rectal swabs were collected on −1, 1 through 5, 7, 10, 14, 18, and 20 DPC. Calves were humanely euthanized and postmortem examinations were performed at 3 (n = 3 principal-infected), 7 (n = 2 principal-infected), and 20 DPC (n = 5; 3 principal-infected, and 2 sentinels).