Orogastric Exposure of Cynomolgus Macaques to Bovine HPAI H5N1 Virus Results in Subclinical Infection

Since early 2022 highly pathogenic avian influenza (HPAI) H5N1 virus infections have been reported in wild aquatic birds and poultry throughout the United States (US) with spillover into several mammalian species1-6. In March 2024, HPAIV H5N1 clade 2.3.4.4b was first detected in dairy cows in Texas, US currently affecting more than 190 dairy farms in 14 states7,8. Milk production and quality are diminished in infected dairy cows, with high virus titers in milk raising concerns of exposure through consumption9-12. Here we investigated routes of infection with HPAIV H5N1 clade 2.3.4.4b in cynomolgus macaques, a surrogate model for human infection13. We show that intranasal or intratracheal inoculation of macaques caused systemic infection resulting in mild and severe respiratory disease, respectively. In contrast, infection by the orogastric route resulted in limited infection and seroconversion of macaques which remained subclinical. The study shows that consumption of contaminated products, such as milk, may lead to self-limiting, subclinical infection in primates.