This study aimed to investigate the potential of H9N2 avian influenza virus to cause disease and intra-species transmission in house crows (Corvus splendens). A group of six crows were intranasally inoculated with 10^6.0 EID₅₀ of H9N2 virus (A/chicken/India/07OR17/2021), and 24 h post-inoculation six naïve crows were co-housed with infected crows. Crows were observed for 14 days for any overt signs of illness. Oropharyngeal and cloacal swabs were collected up to 14 days to assess virus excretion. No apparent clinical signs were observed in either infected or in-contact crows. Virus excretion was observed only in infected birds up to 9 days post-infection (dpi) through both oropharyngeal and cloacal routes. All six infected crows seroconverted to H9N2 virus at 14 dpi, whereas all in-contact crows remained negative to H9N2 virus antibodies. No virus could be isolated from tissues viz., lung, liver, kidney, pancreas, small intestine and large intestine. Although crows became infected with the H9N2 virus, transmission of the virus was inefficient to the in-contact group. However, virus excretion through oral and cloacal swabs from infected crows suggests a potential threat for inter-species transmission, including humans. Crows, being a common synanthrope species, might have some role in influenza virus transmission to poultry and humans, which needs to be explored further.

We investigated the experimental infection of two highly pathogenic avian influenza H5N1 viruses isolated from crow (A/crow/Assam/142119/2008) and chicken (A/chicken/Sikkim/151466/2009) in house crows (Corvus splendens). Both viruses caused infection in crows, where four out of six and three out of six crows succumbed to H5N1 infection within 11 days post challenge by crow and chicken viruses, respectively. The major clinical signs in crows were wing paralysis, circling and torticollis. The virus shedding detected from swabs was not persistent in both crow nor chicken viruses. Both viruses were isolated more frequently from oral swabs than from cloacal swabs. Both virus strains were isolated from brain, lungs, heart, liver, pancreas, spleen, large intestines of crows that succumbed to H5N1 infection. The surviving birds seroconverted in response to H5N1 virus infection. Microscopically, both viruses caused coagulative necrosis in pancreas and kidneys. Brain showed gliosis and neuronal degeneration. This experimental study highlights that crows could be infected with H5N1 viruses from different hosts with minor differences in pathogenicity. Therefore, it is imperative to carry out surveillance of highly pathogenic avian influenza H5N1 virus in synanthropic birds along with biosecurity measures to mitigate the H5N1 spread in poultry population.

The H9N2 viruses can cause asymptomatic to clinical diseases in chickens under field conditions. Therefore, the present study was designed to assess the pathogenicity of Indian H9N2 avian influenza virus in experimentally infected specific pathogen free (SPF) chickens. The intravenous pathogenicity index of H9N2 virus isolated from Bareilly, Uttar Pradesh was found to be 0.00/3.00 suggesting its low pathogenicity in chickens. For infectivity study, six SPF chickens were inoculated intranasally with 100 μl of 10⁶ EID ₅₀ of A/Chicken/India/04TI05/2012 (H9N2) avian influenza virus. The sham phosphate buffered saline inoculated SPF chickens served as negative control. All the six H9N2 virus inoculated chickens got infected and virus could be isolated from oropharyngeal and cloacal swabs. More viral isolations were obtained from oropharyngeal swabs (38) as compared to cloacal swabs (16). Viral RNA was detected through 1 to 9 days post infection (dpi) by RT-qPCR. High viral RNA copy number (1.56x 10³-1.2x 10⁵) was detected in oropharyngeal swabs than cloacal swabs (1.15x10³4.81x10³). Clinically, all the H9N2 virus and sham inoculated birds did not show any overt signs of illness. All the experimental chickens seroconverted and the geometric mean haemagglutination inhibition titers at 6 and 12 and 30 dpi were 2^7.5, 2^8.33 and 2^7.66, respectively. This study indicates that the H9N2 virus isolated from a natural outbreak was of low pathogenicity under experimental conditions. Continuous shedding by the infected birds by oral and cloacal routes without any clinical signs might cause undetected spread of the virus under field conditions.