Derm Month: Bacterial & Fungal Infections of the Skin

Hot and humid environments are perfect for bacterial and fungi to thrive in.

While it is normal for our pets and us to have some level of commensal bacteria (commensal refers to the relationship between two different organisms that “eat from the same dish”. In this kind of relationship, neither benefits from the other or provokes any harm.) and fungi living on our skin surfaces, an upset in the population balance can trigger skin ailments.

Typical signs associated with bacterial and/or fungal overgrowth would include:

• foul odour
• greasy coat, sweaty skin
• excessive ear wax
• areas of hair loss
• scaly skin, dandruff
• red, inflamed skin patches
• excessive head shaking
• excessive feet chewing
• excessive scratching

Figure 1. Red, inflamed skin patch with some scaling

Common bacteria and fungi that can affect our pets are Staphylococcus, yeasts and ringworm. 

Staphylococcus and Bacterial Skin Issues

These are present normally on our skin and our pet's skin surfaces. But an overgrowth or sensitivity to the bacteria can trigger skin infection and inflammation in our pets. This can develop into bacterial dermatitis (skin inflammation) and bacterial pyoderma (skin pustules - pimples). Affected skin areas may exhibit moist, reddened appearances with pimple-like protrusions, hair loss, crusting or scaling of the skin.

Diagnosis is done by a veterinarian to identify the bacterial organisms involved via a skin cytology/culture test. Cytology is typically done very quickly by obtaining a surface sample of the skin using sticky tape or an impression smear on a glass slide, processing the sample and examining it under a microscope to identify the causative bacterium. Culture requires more time to grow the bacteria in the sample and antibiotic sensitivity tests can then be done to determine the appropriate antibiotic treatment against the causative bacterium. 

Treatment is typically a course of antibiotics, perhaps in combination with an anti-inflammatory drug to manage your pet if the itchiness is excessive and leading to skin damage.

Yeasts and Fungi

Yeasts love moist, dark areas so it's no surprise that the common areas they tend to manifest in are the ears and between footpads. 

Yeasts can lead to excessive earwax buildup and trigger excessive headshaking and ear scratching. Your pet may also be licking and chewing its feet more if yeasts have overgrown in the footpad areas. A foul odour may also be present.

Upon presentation to a veterinarian, samples will be taken for cytology and upon confirmation, antifungal drugs will be prescribed.

Fungi such as ringworm exhibit unique, round patches of hair loss. It can affect both cats and dogs and are typically less itchy than yeasts or bacterial skin infections. 

Figure 2. Ringworm lesions on a cat

Diagnosis of ringworm involves a wood's lamp diagnosis where a fluorescent light is shone onto the animal to identify areas of infection, this is not accurate for all species of Ringworm fungi though, and confirmation is carried out with a fungal culture. 

Prevention Tips

Some helpful, practical tips that I exercise with my own itchy pets include:

• Establishing a baseline observation of my pet's odours, itching and scratching behaviour. This enables me to identify when the pet is excessively scratching or may have a skin imbalance that warrants veterinary attention.
• Weekly to fortnightly baths with an antibacterial/antifungal shampoo to reduce the bacteria and fungal load.
• Regular cleaning of my pet's bedding and areas of contact
• Maintaining a single protein diet and limiting carbs
• Supplementation to manage gut and skin microbiome balance

Try it out and let me know what you think!