#18,006
While we await further developments surrounding the spread of HPAI H5N1 in American livestock, we have a follow up report from last summer's outbreak of H5N1 in Poland, which affected dozens of cats across multiple provinces (see Eurosurveillance: Two Papers On HPAI H5N1 clade 2.3.4.4b virus in cats, Poland, June to July 2023).
Although some cats were reportedly fed raw poultry, and others were allowed to roam outdoors, the source of the infection was never fully explained. Many cats suffered severe neurological manifestations and organ damage, and genomic analysis of the virus revealed several mammalian mutations.
While cats appear to be particularly susceptible to avian influenza viruses (see here, here, and here), dogs have occasionally been infected as well.
Unlike with cats, dogs are thought more likely to carry the virus asymptomatically (see J. Virulence: HPAI H5N1 Virus Infection In Companion Animals).
There have been a few notable exceptions, including the following report from Canada's Food Inspection Agency last year:
Domestic dog tests positive for avian influenza in Canada
From: Canadian Food Inspection Agency
Statement
April 4, 2023 – Ottawa, Ontario
Today, the Canadian Food Inspection Agency and the Public Health Agency of Canada issued the following joint statement:
The Canadian Food Inspection Agency's (CFIA) National Centre for Foreign Animal Disease, confirmed on April 1, 2023, that a domestic dog in Oshawa, Ontario has tested positive for highly pathogenic avian influenza (HPAI).
The domestic dog was found to have been infected with avian influenza after chewing on a wild goose, and died after developing clinical signs. The necropsy was completed on April 3, 2023, and showed respiratory system involvement. Further testing is underway. It is the only case of its kind in Canada.
Symptomatic H5 infection in dogs may be under-reported, however, since today's report points out ` . . . in most European countries, dogs presenting with respiratory symptoms are not routinely tested for influenza'.
As we've seen recently with HPAI in cattle, testing biases based on preconceived notions may be preventing us from seeing the bigger picture. It is axiomatic that the less diligently we look, the less evidence we'll find.
First some excerpts from the case report, after which I'll return with a postscript. Follow the link to read the report in its entirety.
Upper Respiratory Tract Disease in a Dog Infected by a Highly Pathogenic Avian A/H5N1 Virus
by
Olga Szaluś-Jordanow 1,*, Anna Golke 2, Tomasz Dzieciątkowski 3, Michał Czopowicz 4, Michał Kardas 5, Marcin Mickiewicz 4, Agata Moroz-Fik 4, Andrzej Łobaczewski 5, Iwona Markowska-Daniel 4 and Tadeusz Frymus 1
Abstract
In summer 2023, during an outbreak of highly pathogenic avian influenza (HPAI) in cats in Poland, a 16-year-old dog was presented to the veterinary clinic with persistent, debilitating, dry cough, submandibular lymphadenomegaly, mild serous nasal discharge, and left apical heart murmur. A preliminary diagnosis of kennel cough was made and the treatment with amoxicillin/clavulanic acid and dexamethasone was initiated.
Due to the lack of improvement within 2 days, a blood check-up, thoracic radiography and ultrasonography, and echocardiography were performed. Moreover, a rapid test for orthomyxovirus type A antigen in a throat swab was carried out and proved positive. The result was verified using RT-qPCR, which yielded a positive result for A/H5N1 influenza virus and negative results for A/H1N1, A/H3N2, type B influenza, and SARS-CoV-2.
This case indicates that HPAI should be considered as a differential diagnosis not only in cats, but also in dogs with upper respiratory tract disease, particularly in regions experiencing A/H5N1 avian influenza outbreaks.
(SNIP)
4. Discussion
Recent epizootics of HPAI in birds have also led to an increase in reported carnivore A/H5N1 infections over the last few years in Europe. Some examples are cases in cats in Poland and France [23,24,29], in foxes [30,31], in American minks, raccoon dogs on several fur farms in Finland [32], and in minks in Spain [33]. Generally, this infection has been much better characterized in domestic cats and wild felines than in other carnivores.
However, in the literature, there is a growing body of evidence indicating that both domestic dogs and wild canids can also harbor this agent, with the potential for both asymptomatic shedding and clinical disease. The few experimental infections of dogs with A/H5N1 virus performed so far resulted only in subclinical replication of the agent or a transient fever and respiratory symptoms, which were rather mild [34,35].
However, it should be emphasized that the outcomes of natural infections can significantly differ from experimental infections, as evidenced by studies on foxes. A natural A/H5N1 infection has been recently confirmed in two deceased foxes in Italy [31]. The animals were found in an area experiencing mass HPAI mortalities among farmed pheasants, pointing toward a possible link between avian canid infections. Post-mortem examinations revealed in these foxes lung alterations and the presence of bloody fluid in the pleural cavity.
Further insight into the virus’s impact on foxes was provided by an experimental study conducted by Reperant et al. [36]. The animals were divided into two groups: one received the A/H5N1 virus intratracheally, while the other was exposed through the consumption of infected bird carcasses. Foxes from the first group developed severe respiratory and systemic disease, including pneumonia, myocarditis, and encephalitis. In contrast, the group that consumed infected carcasses excreted the virus without manifesting severe illness, suggesting a potential asymptomatic shedding by foxes. The geographical scope of wild canid HPAI infections extends beyond Europe. In Asia, the A/H5N1 virus was confirmed in an Ezo red fox (Vulpes vulpes schrencki) and a tanuki (Nyctereutes procyonoides albus). The Ezo red fox was presented with viral meningoencephalitis and moderate virus replication in the upper respiratory tract [21].
In contrast to wild canids, reports about natural HPAI virus infections in domestic dogs have been scarce, thus far. There is only one published report of a natural A/H5N1 infection in a one-year-old dog from Thailand. This dog, which presented with severe respiratory symptoms, died in 2004 after ingesting a duck infected with the A/H5N1 virus. The virus was detected in multiple organs [2]. Controlled infection studies confirmed that dogs are susceptible to the A/H5N1 virus and can develop respiratory symptoms [34,35,37].
Our patient was a sick domestic dog, positive both in the influenza type A antigen test and in PCR for A/H5N1 sequences, presented to the clinic during a cluster of highly deadly cases in domestic cats caused by the A/H5N1 virus [23,24,25]. The dog showed symptoms that were initially suggestive of severe kennel cough, characterized by enlarged submandibular lymph nodes and a dry cough that persisted despite conventional treatment for an 18-day course. Unfortunately, information about the diet of this dog before the onset of the symptoms was not available.
The case described in our report confirms that on rare occasions the A/H5N1 virus can also induce a natural severe respiratory disease in dogs. While in some of them the infection remains asymptomatic, capable of shedding the virus [35], others exhibit mild symptoms such as transient fever [34], or even fatal disease [20].
Recently, five seropositive healthy dogs were found on a farm in Italy during an outbreak of clade 2.3.4.4b HPAI A/H5N1 infection in poultry. The virus isolated from birds had in the PB2 gene the T271A mutation, which is a marker of virus adaptation to mammals [38]. Studies by Maas et al. [35] using labeled A/H5N1 virus highlighted the agents’ ability to adhere to tissues in both the upper and lower respiratory tracts of dogs. This suggests a potential role of dogs as intermediate hosts in transmitting HPAI from birds to humans, as discussed by Chen et al. [37].
In Poland, as in most European countries, dogs presenting with respiratory symptoms are not routinely tested for influenza. The presented case confirms that in Europe dogs can develop a natural disease induced by the A/H5N1 virus, since HPAI outbreaks have become common in Europe during the last several years. Thus, in areas with endemic HPAI in birds, this infection should be considered in the differential diagnostics not only in cats but also in dogs, especially in patients with respiratory disease.
While the risk that your pet will be infected with H5N1 is still believed quite low, given what we've seen over the past couple of years, it does appear to be increasing over time.
Things that were once considered highly unlikely - like HPAI in cattle, or mass mortality events in marine mammals - are increasingly common, and we need to learn how to adjust to this `new normal'.
To that end the CDC has offered some advice to pet owners, to help keep their pets (and by extension, themselves) safe from HPAI.
Pet Owners
If your domestic animals (e.g., cats or dogs) go outside and could potentially eat or be exposed to sick or dead birds infected with bird flu viruses, or an environment contaminated with bird flu virus, they could become infected with bird flu. While it’s unlikely that you would get sick with bird flu through direct contact with your infected pet, it is possible. For example, in 2016, the spread of bird flu from a cat to a person was reported in NYC. The person who was infected [2.29 MB, 4 pages] was a veterinarian who had mild flu symptoms after prolonged exposure to sick cats without using personal protective equipment.
If your pet is showing signs of illness compatible with bird flu virus infection and has been exposed to infected (sick or dead) wild birds/poultry, you should monitor your health for signs of fever or infection.
Take precautions to prevent the spread of bird flu.
As a general precaution, people should avoid direct contact with wild birds and observe wild birds only from a distance, whenever possible. People should also avoid contact between their pets (e.g., pet birds, dogs and cats) with wild birds. Don’t touch sick or dead birds, their feces or litter, or any surface or water source (e.g., ponds, waterers, buckets, pans, troughs) that might be contaminated with their saliva, feces, or any other bodily fluids without wearing personal protective equipment (PPE).
More information about specific precautions to take for preventing the spread of bird flu viruses between animals and people is available at Prevention and Antiviral Treatment of Bird Flu Viruses in People. Additional information about the appropriate PPE to wear is available at Backyard Flock Owners: Take Steps to Protect Yourself from Avian Influenza.
Whether people will actually heed this advice - and for how long - is another matter.
