A team of US-based scientists recently identified antibodies against H5 and N1 subtype influenza A virus in hunting dogs from Washington, USA.
The study is published in the journal Centers for Disease Control and Prevention (CDC). Emerging infectious diseases.
Letter: Antibodies to influenza A(H5N1) virus in hunting dogs retrieving wild birds, Washington, USA.. Image source: Anna Pozzi – Zoophotos / Shutterstock
Record
The H5 A/Goose/Guangdong/1/1996 (gs/GD) lineage of highly pathogenic influenza A viruses (HPIAV) emerged in China in 1996. The lineage has caused an unprecedented panzootic. The subtype 2.3.4.4b HPIAV H5N1 emerged in 2020 and was transmitted to several continents, causing substantial death in poultry and wild birds.
A fatal canine infection caused by a dog eating a duck carcass was reported in Thailand during an outbreak of HPIAV H5N1 in 2004. Subsequently, a subsequent serological survey in Thailand detected HPIAV H5N1 antibodies in 25% of outwardly healthy stray dogs.
Another fatal HPIAV H5N1 infection was identified in 2023 in Ontario, Canada, in a dog that ate a dead wild goose and developed severe respiratory and systemic symptoms. In this context, experimental evidence shows that greyhounds are highly susceptible to HPIAV H5N1 infections, as evidenced by high-level shedding of the virus and the development of severe symptoms.
Existing real-world and experimental data indicate that dogs are susceptible to HPIAV H5N1 infections with varying intensities of clinical signs. Dogs with high exposure to the virus are more likely to develop this infection.
In this study, scientists measured antibodies against the influenza A (H5N1) virus in dogs that hunt birds. These dogs are at high risk of contact with wild birds infected with HPIAV H5N1.
Study design
The scientists collected blood samples from 194 dogs during March – June 2023 in Washington, USA. This corresponded to a time frame of 1 – 4 months after the close of the waterfowl hunting season in Washington. The dogs have been involved in bird hunting or bird hunting programs and training programs over the past year.
Blood samples were analyzed using various techniques to detect serum antibody levels to influenza A (H5N1) virus.
Flowchart of participation in a serosurvey for antibodies to IAV in hunters and their hunting dogs, Washington, USA. CIV, canine influenza virus. ELLA, enzyme-linked lectin assay. HI, hemagglutination inhibition; IAV, influenza A virus; NP, nucleoprotein; VN, virus neutralization
Important observations
The wild birds most commonly encountered by dogs were ducks, which are notable reservoirs for HPIAV H5N1. This was followed by geese and diving ducks, also particularly vulnerable to HPIAV H5N1 infections.
About 38% of the dogs tested participated in more than 15 hunts and 78% were trained with dead or live birds more than 15 times. About 11% of the dogs retrieved dead or clinically ill waterfowl that showed no evidence of being shot or hunted.
| Dog breed | H5 and N1 seroprevalence (seropositive/tested samples) |
|---|---|
| Labrador retriever | 2/78 |
| Golden Retriever | 0/40 |
| German Shorthaired Pointer | 0/33 |
| Pudelpointer | 0/11 |
| Chesapeake bay retriever | 0/9 |
| German wire pointer | 1/5 |
| Brittany spaniel | 0/4 |
| long haired pointer Germain | 0/3 |
| English Setter | 0/2 |
| Weimaraner | 0/2 |
| Flat Coated Retriever | 0/2 |
| Boykin Spaniel | 0/1 |
| Epagneul pont-audemer | 0/1 |
| Irish Water Spaniel | 0/1 |
| Small munsterlander | 0/1 |
| Standard poodle | 1/1 |
| Total | 4/194 |
Antibody detection
Antibodies to the influenza A virus were detected in 9.3% of the dogs and no obvious symptoms of infection were observed. Of these infected dogs, 78% were seropositive for H3N2 and 72% were seropositive for H3N8 canine influenza virus. Cross-reactivity between H3N2 and H3N8 canine influenza viruses may be responsible for the observed closeness of results.
According to dog owners, about 67% of infected dogs were vaccinated against canine influenza. Anti-H5 and anti-N1 antibodies were detected in four of 18 (22%) infected dogs.
Among four H5- and N1-seropositive dogs, three were not vaccinated against canine influenza virus and were negative for H3N2 and H3N8 antibodies. An H5- and N1-seropositive dog vaccinated in 2021 had a low antibody titer against H3N2 canine influenza virus.
Eleven seronegative blood samples were analyzed separately in the study as negative field controls. All these samples were negative for anti-H5 antibodies. However, three of these samples tested positive for anti-N1 antibodies. The reason behind N1 seropositivity remained unknown.
According to dog owner reports, all four H5 and N1 seropositive dogs hunted waterfowl extensively during the past year in areas affected by HPIAV H5N1 outbreaks in wild waterfowl.
Three H5- and N1-seropositive dogs retrieved either dead waterfowl or waterfowl showing neurological symptoms. In addition, two H5- and two N1-seropositive dogs were from households that had multiple hunting dogs tested in this study. None of the other dogs from these households tested positive for antibodies to influenza A virus.
Importance of study
The study finds H5 and N1 seropositivity only in hunting dogs with high-level exposure to waterfowl. The findings suggest that transmission of HPIAV H5N1 from waterfowl to dogs is possible.
However, the low seroprevalence, the lack of overt symptoms in seropositive dogs, and the lack of evidence for dog-to-dog transmission observed in this study suggest that H5N1 HPIAV subtype 2.3.4.4b strains released in North America during the 2022-2023 is not well adapted to dogs.
Overall, the study findings highlight that monitoring the seropositivity of hunting dogs for influenza A virus and promoting the awareness of dog owners about the risk of infection could be an inexpensive and practical approach to reduce the risk of transmission of infection. in dogs.
