Furunculosis in dogs

Health and Wellbeing

Skin conditions are one of the most common reasons for a vet visit, but noticing anything amiss under all that fur can be tricky.

Furunculosis in dogs

One condition that isn’t so difficult to spot is furunculosis, which causes nasty red boils to form on your dog’s skin. Although this condition isn’t nearly as common as other skin problems like folliculitis and pyoderma, these more commonplace conditions can progress into something serious like furunculosis.

There are other types of furunculosis too which can affect specific areas of your dog’s body, including their paws. Interdigital furunculosis which affects your pup’s paws is more common, and certain breeds are quite likely to encounter this uncomfortable condition at some point in their lives.

This guide is here to tell you everything you need to know about furunculosis in dogs, as well as the localised types of interdigital furunculosis and anal furunculosis. We’ll let you know how to spot and stop these painful conditions, as well as why it might have caused it and how to prevent it.

What is furunculosis in dogs?

Furunculosis in dogs is a deep infection inside the hair follicles which can cause pimples, abscesses or boils to develop on your dog’s skin. These lesions are known as furuncles and can appear anywhere on the body, but they often occur on the paws (interdigital) or on the dog’s back and neck.

Humans can develop furuncles too, but we usually just call them boils.

There are two other types of furunculosis that are more localised. These are interdigital furunculosis and anal furunculosis.

What is interdigital furunculosis in dogs?

Interdigital furunculoses are abscesses or boils that grow in between your dog’s toes, on the webbing of their paws. They are sometimes called “interdigital cysts” but the growths are not actually cystic.

These boils or furuncles can be filled with blood or pus which may leak out of the boil as discharge.

Just like furunculosis affecting other areas of your dog’s body, it’s caused by infection and inflammation in your dog’s hair follicles on their paws. Interdigital furunculosis is fairly common in dogs, especially those whose gait is affected by excess weight, orthopaedic problems, or abnormal foot formation of conformation.

What is anal furunculosis in dogs?

Anal furunculosis or “perineal fistula” is a condition where the skin around a dog’s anus becomes ulcerated and sore, sometimes developing boils. The presence of these boils is why the condition is referred to as a form of furunculosis.

However, anal furunculosis differs from other furuncle conditions because recent studies have indicated it may be an immune-mediated condition rather than an infection. It’s thought to be similar to Crohn’s disease in humans.

What causes furunculosis in dogs?

First and foremost, furunculosis in dogs is caused by some sort of infection. This could be bacterial, viral, fungal, or parasitic.

Sometimes a dog could have a typically superficial infection like pyoderma which moves into deeper layers of the skin such as the dermis. As the infection moves deeper, it can infect their hair follicles and cause furunculosis.

In many cases the infection is primary, meaning it came first and caused the initial irritation to your dog’s skin. However, some dogs will develop secondary infections after their skin becomes irritated and inflamed due to another skin condition or damage to the skin.

Causes of furunculosis in dogs include:

However, some causes of furunculosis may be idiopathic and have no identifiable cause. Similarly, interdigital furunculosis and anal furunculosis can also be idiopathic in nature.

What causes interdigital furunculosis?

Interdigital furunculosis can be caused by almost everything that can cause furunculosis in other areas of the body, including trauma to the skin or infection.

However, interdigital furunculosis can also be caused by a dog licking or chewing their paws excessively, which can damage the skin barrier and make them vulnerable to infection.

Walking on the hairy parts of the paws can also cause interdigital furunculosis as it can push the hairs on your pooch’s feet back into the skin of their paw, like an ingrown hair.

Foreign objects, like grass seeds, could also get lodged in the skin of your pup’s paw and cause inflammation and furuncles to develop.

Interdigital furunculosis can be caused by:

What causes anal furunculosis?

There are many potential causes for anal furunculosis in dogs, and recent studies have changed what many vets once viewed the cause to be.

It was previously thought that anal furunculosis was caused by an infection in the perineal area, usually from faeces and the bacteria it contains being spread around a dog’s anal and perineal skin by their tail. Impacted or infected anal glands were also considered to be a potential cause.

Because German Shepherds are particularly prone to the condition, it was thought that having a wide-based tail and more sweat glands around the anus than normal could also be a cause for anal furunculosis.

However, it’s now thought that it could also be an immune-mediated disease. This means it may be caused by a fault in your dog’s immune system, so their own immune system attacks part of their digestive tract and causes inflammation and ulceration.

Alternatively, their immune system might not be as effective as normal, and it can’t prevent bacteria and infection in the renal end of the digestive tract as well as it should, leading to anal furunculosis.

Is furunculosis in dogs contagious?

Furunculosis in dogs is not contagious itself, and most skin conditions and infections are not contagious either.

However, parasites such as fleas and mites can be contagious between dogs and other pets and they could cause the initial irritation which leads to secondary infection and conditions like furunculosis.

Are some dogs more at risk of furunculosis?

Certain dogs will also be at greater risk of furunculosis. Those with existing skin conditions or allergies will be at risk as these existing conditions can cause inflammation of the skin which can make it more vulnerable to infection.

Having short, thick fur can also make a dog more vulnerable to furunculosis, and short-haired breeds seem more predisposed to the condition compared to long-haired dogs. This is because it’s easier for short, thick hair to become ingrown or be forced back into the skin where it will cause inflammation.

Breeds with this kind of fur include Bulldogs, Staffordshire Bull Terriers, Shar Peis, Great Danes, Basset Hounds, Mastiffs, and Boxers.

Furunculosis in dogs

Wrinkly dog breeds  like Shar Peis, French Bulldogs, and Pugs are also more prone to skin infections, which can put them at greater risk of developing furunculosis.

Finally, some specific breeds of dog are simply more at risk of furunculosis compared to the rest of the doggy population, including German Shepherds and Labradors.

Increased risk of interdigital furunculosis

As well as being more at risk of furunculosis, the dog breeds named above with short, thick fur are also at greater risk of interdigital furunculosis.

Bulldogs, Shar Peis, and Labradors are also more likely to develop interdigital furunculosis because they have wide paws with prominent webbing in between their toes. They also have very short and thick hairs in between their paw pads which are more likely to be forced back into the skin and cause irritation and inflammation. Other breeds that seem more predisposed to interdigital furunculosis include Pitbulls, Mastiffs, and Bull Terriers.

Dogs with an irregular walk are also at greater risk of interdigital furunculosis. An irregular walk is often caused by orthopaedic problems such as hip dysplasia, elbow dysplasia, or arthritis. However, some dogs with exaggerated breed traits may walk in a peculiar way, such as a waddling wide-stanced Bulldog.

Increased weight-bearing also puts a dog at greater risk of developing interdigital furunculosis, meaning obese dogs and large breed dogs are predisposed to furuncles and cysts on their feet.

Increased risk of anal furunculosis

Meanwhile, German Shepherds are especially prone to anal furunculosis and almost all cases of the condition affect this breed. Due to how many cases of anal furunculosis affect German Shepherds it’s believed that genetics plays a part in causing the condition, so your dog might be more at risk if other dogs in their family have had the condition.

Intact male dogs (dogs who have not been neutered) and middle-aged dogs are also at greater risk of developing anal furunculosis. There also appears to be a potential link between colitis and anal furunculosis, but further study is needed to understand this.

How to prevent furunculosis

Because furunculosis in dogs is often caused by infection, maintaining good hygiene and grooming practises can help to prevent skin infections. Routine grooming also gives you the perfect opportunity to examine your dog for any lesions, wounds, parasitic infection, or other signs of illness.

Providing your dog with routine anti-parasitic medication will also help by preventing parasitic infection, which can cause irritation, inflammation, and secondary infection which can progress to furunculosis.

Feeding your dog a healthy diet will also help by providing them with the balance of nutrition they need to maintain a strong immune system that can fight off infection. Avoiding known allergens in your dog’s food could also help to prevent furunculosis or other skin conditions caused by dietary allergies.

Signs and symptoms of furunculosis in dogs

The symptoms of furunculosis in dogs can be hard to spot at first because your pooch’s thick fur might cover any pimples or boils they have. However, these lesions are the key sign of furunculosis in dogs.

The symptoms of furunculosis are:

  • Boils
  • Pus or bloody discharge from boils
  • Alopecia (hair loss)
  • Pain
  • Excessive licking, chewing, or scratching of the affected area
  • Lethargy

In the case of interdigital furunculosis, the boils are limited to your dog’s paws but are still the key symptom.

The symptoms of interdigital furunculosis are:

  • Lameness
  • Boils between the toes
  • Pus or bloody discharge from the boils
  • Excessive chewing and licking of paws

The symptoms of anal furunculosis are slightly different, although the skin around your dog’s anus will still be red, sore, and inflamed. They will also show signs of pain, especially when they’re trying to go to the toilet.

The symptoms of anal furunculosis are:

  • Pain (Particularly while toileting)
  • Straining to poo
  • Discharge from the anus
  • Matted fur around their rear
  • Foul smell coming from their rear
  • Sore, inflamed, or ulcerated skin around the anus and perineum
  • Holding their tail in an awkward or unusual position

Diagnosing the condition

The first step in getting a diagnosis is allowing your vet to give your dog a physical examination.  Your vet will assess your pup’s physical symptoms and general condition, and discuss their history and symptoms with you to build up a picture of what’s wrong.

In the case of furunculosis, examination is usually enough to come to a diagnosis. However, your vet might want to perform further tests to rule out other conditions such as secondary infections, or parasites like demodex mites[6] , which could have caused your dog’s initial infection which progressed into furunculosis.

They will often take a biopsy of the cysts so they can identify what is inside them and what is causing them. They may also pluck a few strands of your dog’s fur to examine under a microscope for signs of infection or parasites. Finally, they might take skin scrapings or tape samples to remove a small number of your dog’s skin particles to examine under a microscope to examine for other kinds of infection.

How to treat furunculosis in dogs

Firstly, the fur around the affected area will need to be trimmed to allow the skin to breathe and to enable your dog’s skin and boils to be cleaned effectively. The affected area will need to be bathed regularly to remove any discharge, dirt, or bacteria, and their skin must be kept clean and dry.

Because furunculosis is often caused by a deep infection in the hair follicles, treatment is usually provided in the form of oral antibiotics. Oral medications are often more effective as they work from the inside out, so they can sooner reach deep skin tissues such as the hair follicles compared to a topical ointment. However, antibiotic skin washes and lotions can also help to treat furunculosis in dogs, and in many cases may be enough to treat the condition and remove your dog’s furuncles.

The course of antibiotics used to treat furuncles will often be longer than average because the infection is in deep layers of the skin, so requires time to work its way out.

Your dog might also be given anti-inflammatories or steroids to help reduce their inflammation and decrease the size of their boils.

Your dog may receive a topical wash or ointment to be applied to their boils to help reduce inflammation. These often contain antimicrobials to clear any infection present and to help prevent any secondary infection in their skin.

Treatment for interdigital furunculosis

To treat interdigital furunculosis, you or your vet will need to trim the fur on your pet’s paws using scissors. (Not clippers, because this can aggravate the problem). This will make it easier to keep their paws clean and allow the skin to breathe.

You will have to bathe their affected paw every day in a medicated shampoo. Your pup will be prescribed topical ointments to apply to their skin which contains antimicrobial properties to protect against infection, and anti-inflammatories to reduce swelling.

In some cases, your vet might also prescribe oral antibiotics or anti-inflammatories for your dog if topical treatments don’t seem to be working as well as they should. However, topical ointments and regular bathing are often enough to treat interdigital furunculosis in dogs.

However, if your dog is suffering from interdigital furunculosis caused by a foreign object embedded in their skin, they may require surgery to remove the offending object.

Treatment for anal furunculosis in dogs

Treatment for anal furunculosis in dogs will usually involve a course of steroids or another immune-modulating drug like Ciclosporin. These medicines will reduce the swelling on your dog’s skin, reduce inflammation, and suppress their immune response. This will stop their immune system from attacking their own body, giving it time to heal.

Most dogs will improve rapidly on medication, but treatment can vary from 4 to 24 weeks.

In addition to immune-modulating medicines, your dog may need to take antibiotics to help treat and prevent any secondary infection they might have. They will also need to have the fur around their anus clipped to allow air to reach the skin and to make it easier for you or the vet to clean them. During your dog’s treatment, you will need to continue to keep the affected skin clean.

However, a handful of dogs might not see their lesions disappear while on medication and might require further surgical treatment. This may involve either cryotherapy or traditional surgery to remove any remaining lesions or scar tissue they have and to remove tracts that have developed within their skin. Some dogs may also have their anal glands removed.

Surgery is only used as a last resort though, as it carries a risk of possible complications and relapse. If a dog does require surgery, they will still need to take a course of drug therapy to reduce the lesions as much as possible before the operation takes place so they are less likely to need extensive skin closure techniques or plastic surgery.

However, it’s important to remember that anal furunculosis is often a recurring condition that has no outright cure. Medical treatment is the best way of managing the condition and will relieve your dog’s symptoms, but many dogs require long-term management or repeated treatment whenever a flare-up occurs.

Home treatments

There aren’t any curative home treatments for furunculosis in dogs, but there are a few things you can do at home to try and aid your dog’s recovery and prevent furunculosis from reoccurring.

One of the key parts of treating furunculosis is regularly washing the affected area with an antimicrobial shampoo. Once this has been prescribed by your vet, you can apply it at home. Keeping your dog’s lesions clean and the fur around it trimmed short is important to allow the skin to heal.

If your dog’s furunculosis was a result of allergies, you should consider following an elimination diet so you can identify and remove the offending allergen from your dog’s food that caused their initial skin irritation.

Under the advice of your vet, you may want to consider increasing the amount of omega-3 in your dog’s diet. Omega-3 can be found in meat and fish and offers natural anti-inflammatory and immune-modulating properties, making it an effective supplement to help reduce inflammation.

Remember, even natural supplements can be unsafe for dogs with underlying conditions and can react unpredictably with medication, so you should always seek your vet’s advice before giving your dog any new diets, supplements, or herbal remedies.

If your dog has interdigital furunculosis, you might consider putting protective booties on them to keep their paws clean and to prevent them from chewing at their skin. These booties can also prevent contact dermatitis, which might have caused your dog’s initial irritation.

You will also want to prevent your dog from chewing, licking, or scratching their boils and sores. You can use a preventative device such as an Elizabethan collar or an inflatable collar to prevent your dog from licking and chewing their skin and allowing it to heal.

Outlook

Furunculosis in dogs is not life-threatening and rarely requires hospitalisation, but it’s still a very painful and uncomfortable condition that will impact your dog’s wellbeing and quality of life. In the case of interdigital furunculosis, it can also affect your dog’s exercise needs, as they might avoid walking or playing because of their painful paws.

Treatment for furunculosis in dogs is generally very effective and it will reduce your dog’s inflammation, relieve their pain, and often remove their furuncles.

However, relapse is common in dogs who suffer from furunculosis, so you should continue providing regular grooming and physical examination of your dog so that you can spot any signs of recurring illness. Otherwise, you might choose for your dog to attend regular check-ups with your vet to assess their health and spot any signs of relapse early on.

Dr Andrew Miller BVSc MRCVS

Written by: Dr Andrew Miller MRCVS

Andy graduated from Bristol University in 2010 and sees nutrition as a foundation for our pet's wellbeing and takes a common-sense approach. We are what we eat, and it shouldn't be any different for our pets.

Sources
  1. Association between anal furunculosis and colitis in the dog: preliminary observations Journal of Small Animal Practice, 43, (3), March 2002, 109-114, doi.org/10.1111/j.1748-5827.2002.tb00039.x