Abstract
Background:
Newcastle disease (ND) is a highly infectious disease of multiple avian species worldwide. In Pakistan, repeated ND outbreaks have presented substantial challenges to the poultry sector.

Aim:
Extensive surveillance in Pakistan over a decade has revealed a high prevalence of avian orthoavulavirus 1 (AOAV-1), highlighting the need for tailored vaccination approaches and continuous monitoring.

Methods:
This study presented a 10 years biosurveillance (2011-2020) of AOAV-1 across 1083 locations (including commercial farms, backyard poultry, live bird retail stalls, household birds, National zoos and wild migratory birds), with a total of 5145 samples (trachea and oropharyngeal swabs), and additionally 822 blood samples collected from 18 avian species. Tracheal and swab samples were inoculated in embryonated chicken eggs, and the positive allantoic fluids were assessed for AOAV-1 prevalence using reverse-transcriptase real-time PCR (rRT-PCR) targeting the fusion (F) gene. Serum samples were evaluated using a hemagglutination inhibition (HI) test to detect antibodies against AOAV-1.

Results:
rRT-PCR analysis showed a prevalence of 37.41%, while seroprevalence assessed through the HI assay was 48%. Moreover, over a decade following repeated outbreaks of virulent AOAV-1 that resulted in high morbidity and mortality in Pakistan, the responsible strain was detected in vaccinated chickens across multiple commercial poultry farms, despite the existence of elevated AOAV-1-specific antibody titers (>4.6 log2).

Conclusion:
The observations suggest a possible role for vaccinated poultry as a reservoir of virulent AOAV-1. These findings develop our understanding of the high prevalence of AOAV-1 in Pakistan, emphasizing the necessity for customized vaccination approaches and continuous monitoring to enable effective management of AOAV-1 in avian species.

Key words: Newcastle disease; AOAV-1; Biosurveillance; rRT-PCR; Hemagglutination inhibition.