Chronic treatment-resistant Demodicosis in dogs explained

Many dogs suffer from skin allergies that are triggered by mites, one of which is demodex spp. These microscopic mites are cigar-shaped, and they live in hair follicles on all dogs, no matter what the breed. Unfortunately, a dam transfers the mites to her offspring during the first days of their lives and the parasites remain in hair follicles throughout a dog’s life, but without causing any issues whatsoever because a puppy’s immune system keeps everything under control. The problems start when mite populations explode which results in irritation, inflammation and a skin disorder which is known as demodicosis and sometimes, it can turn into chronic treatment-resistant demodicosis.

The causes

Demodicosis can develop any stage of a dog’s life and as such the causes depend on when it flares up. Juvenile onset demodicosis as the name suggests develops when puppies are between the ages of 3 to 18 months old. The problem is typically either generalised of localised. With this said, why some puppies develop the disorder is not well understood, but there is some thought that it could be due a genetic defect in their immune systems which as a result sees a mite infestation developing.

Studies have shown that very often the problem resolves itself as a puppy matures because they are very healthy and therefore are not susceptible to suffering from other forms of infection. With this said, when the condition is “generalised” it is a severe disorder that needs veterinary attention sooner rather than later.

When an older dog has a “flare up”, which is known as adult onset demodicosis, the condition develops when dogs are around 4 years old and sometimes even older. The condition is generalised and therefore it is more severe than its juvenile counterpart. The mites would have remained in lower numbers throughout a dog’s life, but their population increases because of some form of systemic disorder that negatively impacts the immune systems. The most common causes being either cancer or hormonal disorders.

Signs to watch out for

Puppies and dogs suffering from the condition have bald patches in their coats and their skin is inflamed, irritated and red. The patches can occur around a dog’s face, on their heads, feet but these areas are not generally itchy.

The more serious form of the disease, namely “generalised demodicosis” is more of a problem with dogs developing lesions, bald patches combined with inflammation, sores and a thickening of skin in affected areas of the body. The result of the damage caused to hair follicles is typically a secondary infection and bleeding where lesions have developed. The problem generally starts around a dog’s face, head and feet before it spreads to other parts of the body causing pain and irritation which can include around a dog’s ears too.

Diagnosing the problem

A vet would want to know a dog’s full medical history before thoroughly examining them. The vet would pluck some hairs in an affected area and then examine them under a microscope to establish the presence of any mites. If a large number of mites are found, the vet would then recommend a treatment, bearing in mind that some cases are very difficult to clear up. Other tests a vet would want to carry would include the following:

• Blood tests
• CT scan
• Ultrasound

Treatment options

A dog would typically be treated by a vet as an outpatient, but regular visits are essential to prevent any overgrowth recurring and to monitor if there is a bacterial or yeast infection flaring up. The problem is when the condition is treatment-resistant in which case a vet would want to carry out a skin culture with an end goal being to rule out the following:

• Methicillin-resistant Staphylococcus intermedius group (SIG) infection
• To establish if there is an underlying health issues causing the problem

It is worth noting that treatments tend to be prolonged and not always successful when the disorder is treatment-resistant with many dogs not showing any signs of improvement for several months. Very often a vet would recommend using non-licenced treatments if all other licensed ones have failed.

Prognosis

The prognosis is generally good for puppies and dogs suffering from either localised or generalised demodicosis, but where the condition is treatment-resistant, it would mean a dog’s condition would need to be regularly monitored and various treatments tried out as a way of resolving the problem which means long-term treatments are generally necessary.