Nocardiosis is an infection caused by Nocardia bacteria, which grow in long, thread-like strands. These bacteria live in the environment, in soil, rotting plants, water and dust [2], and they are found all over the world [1].
If your dog has a lump, abscess or draining sore under the skin after a wound, see your vet. If your dog has trouble breathing, see your vet now.
How dogs get it
The bacteria usually get in through a contaminated wound, such as a puncture or a bite, or are breathed in. Swallowing them is a less common route [1][2]. For why bite wounds need a vet, see bite wounds in dogs and cats.
Because the source is the environment, dogs mostly pick up the infection from their surroundings rather than from each other. One report did describe two puppies from the same litter who both became ill [2].
Which dogs get it
Animals with weak immune defences are more likely to get the infection [1]. In dogs, though, vets often cannot find any underlying cause, and young dogs seem to get the widespread form more often than adult dogs [2].
For the same infection in cats, see nocardiosis in cats.
Skin signs
In dogs and cats, the skin form shows up as swollen, inflamed tissue, lumps that break open into sores, and pockets of pus (abscesses). These often form channels that drain onto the skin [1]. The fluid that drains out is often a mix of blood and pus [1].
The sores tend to appear where the skin was hurt, most often on the legs and paws [1]. The lymph nodes near the area are often swollen [1]. The lymph nodes are small glands that help the body fight infection.
A lump like this can look like a growth. Only a vet can tell an infection from a growth.
Signs beyond the skin
Some dogs become ill all over. Signs can include fever, low energy, trouble breathing, pus around the lungs and changes in how the dog walks or behaves [1]. In the two puppies described above, the illness began with sudden lameness after skin wounds on the legs and then spread through the body [2].
How vets diagnose it
Your vet will look at the history and the sores. They may look at a sample of the fluid or tissue under a microscope, send a sample to a lab to grow the bacteria (a culture), or take a small piece of skin for testing (a biopsy) [1]. Lab tests can also identify the bacteria from their genetic material [1].
Treatment
Your vet will advise on treatment for your dog. Treatment is often long, and it may include cleaning out and draining the infected area [1].
At home, as directed by a vet:
- do not open, squeeze or drain a lump or abscess yourself;
- do not give your dog human or leftover medicines unless your vet says so;
- do not stop or change any medicine without talking to your vet;
- give any treatment exactly as your vet prescribes, for as long as your vet says;
- go back for any recheck your vet books.
Outlook
When the infection stays in the skin, the outlook is usually good. When it has spread through the body, the outlook is guarded to poor [1]. Guarded means the outcome is uncertain. Even when the cause is found, it can be hard to say how well treatment will work in the widespread form [2].
These are statements about groups of dogs. They cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- a lump, swelling or abscess in or under the skin, especially where a wound was [1];
- a sore that drains fluid [1];
- swollen lymph nodes [1];
- fever or low energy [1];
- sudden lameness after a wound on the leg [2];
- any wound or lump you are unsure about.
See your vet now if your dog has trouble breathing [1].
The bottom line
Nocardiosis is a bacterial infection from the environment that can follow a wound and cause lumps, abscesses and draining sores in a dog’s skin. Only a vet can find the cause with lab tests.
This article is for general information only and does not replace advice from your veterinarian. If your dog has a lump or abscess after a wound, see your vet.
Sources
- Torres SMF. 1.7 Actinomycetic Infections: Small and Large Animals. In: Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota Libraries Publishing, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/actinomycetic-infections-small-and-large-animals-2/
- Zendri F, et al. Disseminated Nocardiosis Caused by Nocardia farcinica in Two Puppy Siblings. Veterinary Sciences. 2023;10(1):28. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC9860694/