In July 2017, the highly pathogenic H5N6 avian influenza was reported in the Philippines, leading to the culling of over 400,000 poultry in Central Luzon. Officials suspected the source to be either contact with migratory waterfowl in the Candaba swamp or smuggled ducks from China, though neither was confirmed [1,2]
To investigate potential virus transmission between wild and domestic birds, a collaborative surveillance study was conducted across Central Luzon by local and international institutions, including the UTMB One Health laboratory, Duke Global Health Institute, College of Pharmacy & Health Sciences, and CSIRO Australian Centre for Disease Preparedness. The goal of this study was to investigate which respiratory viruses are present in domestic ducks from Central Luzon and identify if these viruses are being passed between wild birds and domestic ducks.
From March 2019 to January 2020, researchers collected 1,740 swab samples from duck in the farm from Cabiao municipality in Nueva Ecija province and Candaba and San Luis municipalities in Pampanga province, Central Luzon, an area recognized as a key migratory route for wild birds. Samples were collected from native ducks raised on 54 farms for a total of 30 ducks per farm. To find out if migratory birds caused the first bird flu outbreak in the Philippines in 2017, a group of 30 ducks were placed in the Candaba Swamp—a known hotspot for wild birds—and tested for various respiratory viruses such as influenza, adenovirus, coronavirus, and enterovirus.
The study detected high pathogenic avian influenza (HPAI) H5N6 and low pathogenic avian influenza H5N8 on two duck farms in Candaba, with an overall prevalence rate of 2.3%. Candaba is known for its traditional farming methods, where young ducks are allowed to graze freely in rice fields, often coming into contact with migratory wild birds. No positive results were found for influenza C, adenoviruses, coronaviruses, or enteroviruses. The results point to an ongoing and potentially dangerous interaction between domestic and wild avian populations. The presence of highly pathogenic avian influenza strains in seemingly healthy domestic ducks raises alarms over possible spillover events, which could have devastating effects on poultry production and even pose risks to human health. This report showed the result of surveillance for respiratory viruses among mallard ducks in the same region where AIV has been previously detected [3].
This study emphasizes the urgent need for improved biosecurity measures in poultry farms, especially in high-risk regions like Candaba. Recommendations include physical barriers, controlled grazing, and regular veterinary monitoring to reduce interactions between domestic and wild birds.
While the study had certain limitations — including pooled testing and geographic concentration — it provides important evidence that domestic ducks are acquiring AIV from wild birds. Given the relatively low prevalence detected, the situation may still be manageable. However, proactive steps are crucial.
The study’s authors recommend that duck farmers implement measures to minimize or prevent the mixing of domestic ducks with wild bird populations, especially in high-risk areas like Candaba. This includes physical barriers, controlled grazing practices, and more frequent veterinary health checks.
Surveillance and early detection remain critical tools in mitigating the spread of avian diseases. As the poultry industry in the Philippines continues to grow, integrating science-based policies into traditional farming will be key to protecting both livestock and livelihoods.
References:
- Salvador R, Tanquilut N, Macmac R, Na Lampang K, Chaisowwong W, Pfeiffer D, et al. Evaluation of strategies using simulation model to control a potential outbreak of highly pathogenic avian influenza among poultry farms in Central Luzon, Philippines. PLoS One. 2020;15(9):e0238815. doi:10.1371/journal.pone.0238815 pmid:32913363
- Lee H, Lao A. Transmission dynamics and control strategies assessment of avian influenza A (H5N6) in the Philippines. Infect Dis Model. 2018;3:35–59. doi:10.1016/j.idm.2018.03.004 pmid:30839942
- Mananggit, M. R. et al. Detection and characterization of novel respiratory viruses among native ducks (Anas luzonica) in Central Luzon, the Philippines. Western Pacific Surveillance and Response, 16 (2025). [https://doi.org:10.5365/wpsar.2025.16.2.1124]https://doi.org:10.5365/wpsar.2025.16.2.1124 View
Image Credits:
- Photo of Candaba Swamp – Alchetron.com: https://alchetron.com/Candaba-Swamp#candaba-swamp-ab347481-f975-4980-8e77-26b641bc7ac-resize-750.jpeg
- Mallard duck farming – DOST-PCAARRD: https://ispweb.pcaarrd.dost.gov.ph/development-of-sustainable-philippine-mallard-duck-production-system/
- Rare birds in Candaba – GMA News: https://www.gmanetwork.com/news/scitech/science/551976/various-rare-birds-spotted-in-candaba/story/#goog_rewarded