Cross-species transmission of poultry pathogens in backyard farms: ducks as carriers of chicken viruses

ABSTRACT

In backyard farms of Lao People’s Democratic Republic, mixed-species rearing of poultry is a breeding-ground for cross-species transmission. Here, the epidemiology of viruses circulating among backyard poultry in Vientiane Province was assessed to guide future control strategies. Oral/tracheal and cloacal swabs, collected from 605 poultry (308 ducks, 297 chickens) between 2011 and 2015, were screened by PCR for Newcastle disease virus (NDV), coronavirus (CoV) and chicken anaemia virus (CAV). Chicken sera were screened for anti-NDV antibodies by ELISA. Statistical and phylogenetic analyses revealed transmission patterns and relationships.

Closely related strains co-circulated in chickens and ducks. While CoV RNA was detected in oral/tracheal swabs of 9.3% of the chickens and 2.4% of the ducks, rates were higher in faecal swabs of both species (27.3% and 48.2%). RNA of infectious bronchitis virus (IBV) and duck CoV was found in faecal swabs of chickens (19.7% and 7.1%) and ducks (4.1% and 44.1%). Moreover, DNA of the generally chicken-specific CAV was detected in oral/tracheal swabs of chickens (18.1%) and, sporadically, of ducks (2.4%). Despite serological evidence of NDV circulation or vaccination (86.9%), NDV RNA was not detected. We found a high prevalence and indication for cross-species transmission of different CoV strains in backyard poultry. Interestingly, ducks served as biological, or at least mechanical, carriers of viral strains closely related not only to IBV, but also to CAV. Bird containment and poultry species separation could be first steps to avoid cross-species transmission and emergence of novel strains with broad host range and enhanced pathogenicity.

RESEARCH HIGHLIGHTS

• High rates of avian viruses were detected by PCR in backyard poultry from Lao PDR.

• Diverse coronavirus and chicken anemia virus strains co-circulated.

• Phylogenetic analyses suggested virus transmission between chickens and ducks.

• Serological evidence of Newcastle disease was found, but viral RNA was not detected.

KEYWORDS:

• Poultry diseases
• Laos
• chicken
• duck
• bird health
• smallholders

Acknowledgements

We are grateful for the commitment of the students and staff from the Faculty of Agriculture in collecting the bird samples. We thank the village chiefs and the primary health workers of the villages for their support and the smallholders for their participation. We would also like to express our gratitude towards the Ministry of Agriculture and Forestry of Lao PDR for approving the study. A special thanks goes to Dr Bounlom and Dr Bounmy from the National Animal Health Laboratory who supported the sample collection in 2011. Solène Cordel and Claire Dording performed part of the laboratory analyses. The authors wish to thank Ulla Muller and Carole Weis, as well as the Institut Pasteur du Laos, for providing valuable logistic support.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Chantal J. Snoeck http://orcid.org/0000-0002-0000-1850

Additional information

Funding

This work was supported by the Ministère des Affaires étrangères et européennes, Luxembourg [project “Lao Luxembourg Partnership for Research and Capacity Building in Infectious Disease Surveillance I and II”]. The funder was not involved in the study.