The connection between canine diabetes and infections

One of the lesser-known parts of canine diabetes is how it can affect a dog’s ability to fight infection. It’s something we’ve been learning about over the past couple of weeks.

Diabetes doesn’t just change how the body handles sugar — it also impacts the immune system. Elevated blood glucose levels can make it easier for bacteria to grow and harder for the body to respond effectively.

This means diabetic dogs can be:

• More prone to infections
• Slower to heal once an infection starts
• More likely to have infections that don’t respond right away to first-line antibiotics

Importantly, this isn’t a sign of poor care. It’s a physiological reality of diabetes. We are experiencing this with our 14-year old diabetic Border Terrier Parker.

Two weeks ago, Parker was in a good mood, playful and affectionate. The next day he was less interested in his treats and we thought, gee that’s odd as he’s very food motivated. 

The following morning he had a large lump on his back a few inches from his collar. It was swollen to the size of a coffee cup lid, pink and weeping clear liquid. 

He had recently been groomed so his fur was short. Parker has a lot of little skin tags and we wondered if one had been clipped accidentally and become infected.

Why infections in diabetic dogs can appear suddenly

We learned that infections in diabetic dogs often seem to come “out of nowhere.”

That’s because:

• Bacteria can already be present on the skin or in the body
• A small break in the skin, irritation, or stressor can tip the balance
• The immune response may not keep up as quickly as it would in a non-diabetic dog

What looks sudden is often something that has been quietly developing. 

We took him to our vet, who was surprised by the size and state of the lesion and prescribed antibiotics. They offered an injectable antibiotic, but we declined as we wanted to do a bit of research on it, so we went with an oral antibiotic (i.e., pills).

He immediately lost his appetite, so the next day we went back to the vet to get the injectable antibiotic. While at the clinic, they found more lesions, which you can see in the image above taken at the vet.

We saw no improvement over the next few days. The lesions continued to weep fluid and didn't reduce in size. We were concerned that there might be a serious, underlying condition.

Why infections may not respond to antibiotics right away

When an infection doesn’t improve after the first antibiotic, it’s understandably frightening. But in diabetic dogs, this is not uncommon.

Possible reasons include:

• The bacteria causing the infection isn’t sensitive to the initial antibiotic
• The infection is deeper than it appears on the surface
• Inflammation and poor circulation are limiting drug effectiveness
• Blood glucose instability is making healing harder

This is why vets may:

• Change or strengthen antibiotics
• Drain infected areas
• Take cultures or biopsies
• Treat more aggressively than they would in a non-diabetic dog

Back at our vet for a third visit about a week after things started, she recommended several tests to see if there was an underlying cause and prescribed a stronger antibiotic.

Over the next few days, the swelling subsided and the lesions were healing nicely. Phew!

But while on the new antibiotics (and pain meds) Parker had high blood glucose readings in the morning. 

He was consuming lots of water and had a reduced appetite, so we had to adjust his insulin accordingly based on how much he ate at breakfast.

I would check his urine for ketones every morning using a test strip. Thankfully he always had a neutral reading. 

Getting diabetic keto-acidosis would be a scary prospect at his advanced age and also very costly (about $5k - $7k for treatment we’ve been told by the emergency clinic).

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How infections can affect blood glucose control

Infections don’t just exist alongside diabetes — they can actively interfere with management.

When the body is fighting infection, it releases stress hormones like cortisol. These hormones can:

• Raise blood glucose levels
• Make insulin seem less effective
• Cause readings that don’t follow normal patterns

This can be incredibly frustrating for caregivers who feel like they’re “doing everything right.”

Often, once the infection is brought under control, blood glucose becomes more predictable again. 

Common types of infections seen in diabetic dogs

Diabetic dogs can experience many of the same infections as other dogs, but they may be:

• More frequent
• More persistent

Common examples include:

• Skin infections (including abscesses or lesions)
• Urinary tract infections
• Dental and gum infections
• Ear infections

Some are obvious. Others are subtle and only discovered through testing. 

Why follow-up and persistence matter

One of the hardest parts for caregivers is realizing that one vet visit may not be enough.

With diabetic dogs, it’s often appropriate — and responsible — to:

• Go back if things aren’t improving
• Ask for further testing
• Reassess when treatment doesn’t work as expected

This isn’t overreacting. It’s advocating.

Infections in diabetic dogs sometimes need:

• Time
• Adjustments
• A layered approach

We’re not in the clear quite yet. Parker has about five days left on the third antibiotic and we are going to be giving him Pentoxifylline, a drug recommended by the lab dermatologist that studied his tests and told our vet they’d seen good results using it with diabetic dogs.

What we learned

In Parker’s case, it took three different antibiotics and almost a week before we saw clear improvement. An antibiotic needs to be chosen based on the type of infection. 

It’s been a costly process as well. Three vet visits in one week and several different prescriptions including antibiotics, appetite stimulants, and pain management. 

It’s great to see Parker returning to his old self, playing with his toys and being insistent about certain things in a way that Terriers seem to know how to do.