The differences (and similarities) between bacterial and viral infections in dogs

The differences (and similarities) between bacterial and viral infections in dogs

Health & Safety

When it comes to contagious canine health conditions, the vast majority of them fall into either the bacterial or the viral category, each of which are distinct organisms that work in different ways and so, need to be tackled in the appropriate manner.

Just to confuse things, some conditions (or conditions that are very similar to each other) can potentially be caused by either bacteria or a virus and you may not be able to tell the difference without laboratory tests. All of this means that many dog owners do not really understand the differences between bacteria and viruses, nor really why they might need to know-but developing a very basic understanding of how bacteria and viruses compare to each other can be really helpful.

Understanding how a virus and a bacteria differ and the things that they have in common is essential information when it comes to the prevention, diagnosis and treatment of contagious illnesses, and taking the wrong approach or a broad approach to a respective bacterial or viral infection is unlikely to be effective, and may even prove harmful.

In this article we will look at bacteria and viruses in more detail, including the ways in which they differ and the areas in which they are similar in terms of their behaviour, transmission and treatment. Read on to learn more.

Bacteria versus virus

Huge tomes have been written about bacteria and viruses and how they work as well as their shared traits and minute differences, but for the average dog owner, a basic explanation of their core traits is more than sufficient!

The first thing you need to know in terms of major differences is that bacteria is classed as a living organism, and while many viruses can reproduce (which is usually one of the key identifiers of a living organism) viruses are not classed as a living entity.

In practice, the distinction is made in this way because bacteria can survive, thrive and reproduce outside of a host or carrier, on or in an inert object, while for a virus to remain viable, it requires a host to support it. Bacteria is made of a collection of cells that grow in the manner of any other life form and reproduce independently, while a virus is not constructed out of cells and in fact, needs to use the cells of their particular host in order to remain viable and able to spread and reproduce.

In terms of their action in the body, viruses invade the living cells of their host and ultimately turn the cells against the body by changing the genetic makeup of the host cells, while bacteria can live between the dog’s cells without needing to invade them.

Finally, viruses are universally harmful and invasive in terms of their actions-there are no “good” viruses that bring positive effects to their host-while bacteria can be either harmful, helpful or neutral. “Good” gut bacteria is one example of this!

Mode of transmission

In terms of how viruses and bacteria spread between dogs, the methods of transmission are often very similar. However, due to the differences between viruses and bacteria, different modes of transmission have different levels of effectiveness (in terms of its ability to enter the dog’s body and have an effect on it) and so tend to behave rather differently.

Because bacteria does not need a host in order to live, it is much more likely to remain viable in the environment when not inside of the body of a dog, making bacterial infections easier to transmit and catch due to the sheer range of environments that can support the,

Viruses, on the other hand, tend to be specific to a given host (or a small group of hosts in terms of zoonotic conditions-such as cats, dogs and humans but not plants or reptiles) and so they will not survive for very long outside of a host body, giving them less chance of being passed on in the environment. However, when a virus does successfully manage to spread from dog to dog, it tends to take hold with ease within the body, and so the chances of infection developing are higher, balancing out the easier availability of bacteria-friendly environments.

Viruses and bacteria may be airborne, transmitted via bodily fluids or by various other means, but the bacteria stands a better chance of remaining viable for longer when not transmitted directly from host to host.


While bacteria and viruses often cause very similar illnesses-for instance, colds can be due to either viral infections or less commonly, bacterial infections-their methods of treatment are completely different, and treatment for a bacterial illness is highly unlikely to work on a viral one (and vice versa).

When infected by either a virus or bacteria, the body deploys its own immune responses to eradicate the threat, and assuming that this is successful, the body builds up a level of immunity to that same strain of infection in the future.

Antibiotics can help the body to weed out and destroy bacterial infections, but these will not work for viral infections, much as antivirals do not work to kill viruses.

Ultimately, most dogs that are generally in good health and that have strong immune systems will be able to fight off the majority of transmissible infections on their own-but for serious, chronic or resistant problems, your vet will need to know what is causing the infection in order to know how to treat it.



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