Pathogenicity and Transmission of Thai HPAI-H5N1 in Japanese Quails

Abstract

Pathogenicity and transmission of Highly Pathogenic Avian Influenza subtype H5N1 viruses (HPAI-H5N1) depend on the strains and infection doses of the viruses. In this study, experimental infection was performed to determine pathogenicity and transmission of the Thai HPAI-H5N1 in Japanese quails. One hundred and seven quails were divided into 4 groups, experimental groups 1-3 (n = 32 per group) and negative control group (n = 11). At the age of 9 weeks, 16 quails each from groups 1-3 were inoculated with 107, 105 and 103 EID50 of Thai HPAI-H5N1, A/chicken/Thailand/CUK2/04(CU-K2) virus. Twenty-four hours later, 16 quails were added as contact quails to each group. Group 4 served as negative control. The quails were observed for clinical presentation, morbidity and mortality. Histopathology and immunohistochemistry were evaluated to confirm viral infection. Oropharyngeal and cloacal swabs were collected and analyzed for virus shedding. Results showed that Thai HPAI-H5N1 (CU-K2) was highly pathogenic for quails similar to other HPAI-H5N1 strains but different in histopathology and tissue tropism. A negative correlation was observed between inoculated doses and mean death time, while a positive correlation was observed between inoculated doses and virus shedding. In addition, the virus can be detected earlier and at a higher titer in oropharyngeal swab than in cloacal swab. This result suggests that oropharyngeal virus excretion exceeds cloacal excretion in quails. Thus, oropharyngeal sampling is superior to cloacal sampling for HPAI-H5N1 surveillance in quails.