Evaluation of In-Contact Transmission Potential of H5N1 Avian Influenza Virus in House Crows (Corvus splendens)

We evaluated the infection and transmission potential of the highly pathogenic avian influenza (HPAI) H5N1 virus from infected crows (Corvus splendens) to healthy in-contact crows. Six crows were inoculated with 10⁶ EID₅₀ of H5N1 virus (A/crow/India/01CA249/2021), and 24 hr later six in-contact crows were introduced with them. All the birds were observed for signs of illness, and swabs were collected up to 14 days postinfection (dpi). One of the infected birds showed dullness, ruffled feathers, shivering, and reluctance to move at 7 dpi, while the other five infected crows showed no significant clinical signs except ruffled feathers and some signs of mental confusion. All the in-contact crows remained asymptomatic throughout the experiment. Virus could be isolated in swabs of infected birds from 1 to 7 dpi, and viral quantification revealed viral shedding up to 8 dpi. Although virus was not isolated from the swabs collected from in-contact birds, low numbers of viral RNA copies were detected in some samples. Virus was isolated from the brain and trachea of most of the infected birds along with other tissues. Virus was also isolated from different tissues collected from three of the in-contact birds, albeit with low numbers of viral copies. All six infected and five in-contact crows were found to be seroconverted against H5N1 virus when analyzed on 14 dpi. These findings suggest that the H5N1 virus was transmitted to in-contact birds, but the infectious doses were low, resulting in only a limited infection. Our study highlights that H5N1 viruses may be transmitted by direct contact within the house crow population, a feature that might play an important role in the epidemiology of avian influenza.