Could pet cats or dogs trigger an avian influenza pandemic?

Could pet cats or dogs trigger an avian influenza pandemic? by Michael Broad

In answering the question in the title, the first box to tick is on the issue as to whether avian flu is a zoonosis by which I mean can it be transferred from animals to people and between species of animal?

And the answer is yes because there are numerous but isolated instances of this happening. There have been avian flu (H5N1) outbreaks in cat shelters in South Korea. And the World Health Organisation received 882 reports of human infection with H5N1 bird flu in 23 countries of which 461 were fatal.

During the Covid-19 pandemic there was quite a lot of talk of pet cats and dogs becoming a possible reservoir for the disease but I saw no reports substantiating this possibility.

That’s an important point because the question is could pet cats or dogs trigger an avian influenza pandemic. If they can be a reservoir for the disease then there is obviously a greater possibility that they could trigger a pandemic. What I mean is the disease is transferred from birds and other animals to cats and dogs and then they harbour the disease and transfer it as an intermediary to people, normally their caregivers.

But pet cats and dogs are not the primary drivers of avian influenza transmission. They could theoretically play a role in spreading it under certain conditions and potentially contribute to a broader outbreak.

However, the chances of them triggering a pandemic are very low.

Cats and dogs can be infected by avian influenza as mentioned above with respect to the South Korea cat shelters. My research indicates that an infection is particularly likely to be with the H5N1 strain. They can become infected when coming into contact with infected birds. And some cats can spread the virus to other cats through close contact, though sustained cat-to-cat transmission hasn’t been confirmed as I understand it as a major route.

My research also indicates that dogs are generally less susceptible to avian influenza than cats. Dogs have been infected with the H3N2 strain. But similar to cats, infected dogs have not been identified as a key transmitter of the virus in large outbreaks.

And further, my research indicates that for a pet cat or dog to contribute to a pandemic the virus would need to mutate to a form that could more easily infect and transmit between humans. The likelihood of this happening on a large scale is low based upon current information. There have been fears among some experts that the disease could be harboured in pet cats and dogs where it mutates and then it is transferred to people.

Transmission from animals to people generally occurs in isolated in rare cases.

Pets might act as an intermediary or bridge host in rare circumstances. This means that they might facilitate the transmission of the virus between birds and people by coming into contact with both species.

But it requires several factors to align such as the pets contracting the virus plus viral mutations increasing its ability to infect mammals and then and then efficient transmission to and between humans.

There have been isolated cases of avian influenza in dogs and cats. None have led to large-scale transmissions to humans are animals. The World Health Organisation and the Centres for Disease Control and Prevention monitor the situation closely. Pets are not considered a major concern for starting a pandemic.

The conclusion is that while there is a possibility that domestic cats or dogs could be infected with avian flu and pass it onto people the chances of this leading to a full-blown pandemic is extremely low.

The main risk factors for the creation of an avian influenza pandemic would be close contact between humans and infected birds particularly in farming or market settings.

For this reason, there is continuous surveillance of both avian flu and its potential transmission directly from birds to people and from pets to people in order to ensure that the authorities are able to address evolving risks.

More: Avian flu killed 12 Texas farm cats in four days after getting the disease from cattle

How does avian flu kill people?

The first point is that the H5N1 strain of avian flu has a particularly high fatality in humans at around 60% of reported cases. Other strains like H7N9 also have high mortality rates but the severity of infection varies by strain.

Why is it so deadly? Unlike ordinary seasonal flu, which tends to result in upper respiratory infections, avian flu often infects the deep lung tissue causing a more severe disease and making treatment more difficult. Also, avian flu viruses are different from regular seasonal flu meaning that most humans have little or no pre-existing immunity to it.

Avian flu can kill humans by causing severe pneumonia and respiratory failure. Avian influenza primarily targets the lungs. On infection, the virus replicates in the cells lining the respiratory tract causing severe inflammation and damage to lung tissue. This can lead to viral pneumonia which is an overwhelming infection of the lungs.

There is an impact on breathing quite obviously as fluid and immune cells accumulate in the lungs in response to the infection. This fills the air sacs and prevents effective gas exchange leading to respiratory failure.

In severe cases inflammation in the lungs is so intense that it triggers acute respiratory distress syndrome which is a life-threatening condition where the lung stiffen which further limits oxygen exchange. A patient with this disease requires mechanical ventilation and is likely to die.

Further, in some cases avian influenza triggers an excessive immune response known as a cytokine storm. Cytokines are signalling molecules that coordinate the immune response. In a cytokine storm the immune system releases too many cytokines leading to uncontrolled inflammation.

Further, the resulting information doesn’t just attack the virus but also damages healthy tissue particularly organs such as the liver, lungs, kidneys and the heart. This results in multiple organ failure.

Cytokine storms contribute to the severity of symptoms like high fever and shock and difficulty in breathing. These are often seen in fatal cases of avian influenza.

Further, in severe cases the disease can cause sepsis which is a life-threatening condition where the body’s response to infection causes widespread inflammation leading to tissue damage and organ failure.

The weakened immune system can result in secondary bacterial infections especially bacterial pneumonia. The combination of viral and bacterial pneumonia can overwhelm the lungs leading to faster progression to respiratory failure.

If the infection spreads throughout the body it can lead to septic shock. This is when the body’s response to infection causes dangerously low blood pressure and poor blood circulation, which deprives organs of oxygen and nutrients leading to organ failure.

And severe avian flu can also stress the heart leading to cardiac complications including myocarditis which is inflammation of the heart muscle which can lead to heart failure.

In some rare cases, the disease can affect the nervous system causing conditions such as encephalopathy (brain dysfunction), seizures and possible coma.

As you can see, this is an incredibly serious disease and there is a high possibility of mortality.

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