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Volume 31, Number 6—June 2025
Research Letter
Avian Influenza A(H5N1) Isolated from Dairy Farm Worker, Michigan
Table
Clinical signs and virus titers in ferrets infected with avian influenza A(H5N1) isolated from dairy farm worker in Michigan, 2024*
| Clinical signs and tissues sampled | Inoculated ferrets |
Transmission models |
||||
|---|---|---|---|---|---|---|
| Euthanized at 3 dpi | Euthanized at 5 dpi | Inoculated | DCT | RDT | ||
| Weight loss, %† | 4.5 (3/3) | 11.8 (3/3) | 9.8 (12/12) | 5.5 (6/6) | 6.6 (3/6) | |
| Fever, °C above baseline‡ |
0.9 (3/3) |
1.3 (2/3) |
1.8 (11/12) |
1.8 (6/6) |
2.0 (3/6) |
|
| Nasal wash | 6.1 (3/3) | 5.4 (3/3) | 5.1 (1–5 d) | 4.6 (5–7 d) | 4.5 (9–11 d) | |
| Conjunctival wash§ |
1.4 (3/3) |
NT |
3.2 (3 d) |
ND |
ND |
|
| Rectal swab¶ | 1.4 (3/3) | NT | 2.6 (3–5 d) | 1.0 (3 d) | 1.4 (3 d) | |
| Nasal turbinate | 6.6 (3/3) | 5.3 (3/3) | NT | NT | NT | |
| Ethmoid turbinate | 7.4 (3/3) | 6.5 (3/3) | NT | NT | NT | |
| Soft palate |
3.5 (1/3) |
NT |
NT |
NT |
NT |
|
| Tissues | ||||||
| Lung# | 3.5 (2/3) | 4.3 (3/3) | NT | NT | NT | |
| Trachea# | 5.9 (3/3) | 5.8 (2/3) | NT | NT | NT | |
| Intestine# | 1.8 (1/3) | ND (0/3) | NT | NT | NT | |
| Brain# | 2.4 (3/3) | 2.4 (2/3) | NT | NT | NT | |
| Olfactory bulb | 3.1 (2/3) | 4.2 (3/3) | NT | NT | NT | |
*Values are log10 PFU/mL (no. ferrets affected/total no. in group) except as indicated. DCT, direct contact transmission model; ND, not detected; NT, not tested; RDT, respiratory droplet transmission model. †Mean maximum weight loss after inoculation with 6.0 log10 PFU A/Michigan/90/2024 A(H5N1) virus in a 1 mL volume. ‡Mean maximum rise in body temperature from baseline (37.4°C–39.0°C). §Conjunctival washes collected from 6 of 12 inoculated animals and 3 each of DCT and RDT contact ferrets in the transmission experiment; number of ferrets with detectable virus or day of mean peak shown parenthetically. ¶Virus in rectal swab samples detected in 8 of 12 inoculated and 1 each of DCT and RDT contact ferrets in the transmission experiment; number of ferrets with detectable virus or day of mean peak shown parenthetically. #Values are log10 PFU/g