Inflammatory causes of non-itchy hair loss in guinea pigs are limited to ringworm and some lice and mites.
Ringworm is caused by a fungus. In guinea pigs the most common ringworm causing fungus is called Trichophyton Mentagrophytes. Ringworm is most common in young guinea pigs with lesions predominantly occurring around the head and legs. There is often some scabbing of the skin with hair falling out easily on the edges of the lesions. Severe cases may become more widespread and itchy. Definitive diagnosis can only be achieved with fungal culture although treatment may be recommended on the basis of compatible clinical signs. Treatment is with topical creams and washes, or oral medication if the condition is severe.
Lice are usually associated with itchiness, however, in mild cases this may not be immediately evident. The eggs of lice (nits) are visual with the naked eye on the hair shaft. Treatment is often with topical antiparasitics.
The mite Chirodiscoides Caviae can be present without any itchiness, although most guinea pigs do not have hair loss either. If this mite is causing no clinical signs it can be left untreated.
Non-inflammatory causes of non-itchy hair loss in guinea pigs are usually hormonal. The hormonal diseases that can cause hair loss include cystic ovarian disease, hyperthyroidism and Cushing’s disease. There are also a small number of disorders of the hair cycle that are rare in guinea pigs but may cause hair loss in the absence of itchiness. Finally there is an hereditary alopecia as seen in ‘skinny pigs’.
Cystic ovarian disease occurs to some degree in approximately 80% of adult, female guinea pigs. Ovarian cysts can be functional i.e. they produce hormones (usually oestrogen) or non-functional i.e. they do not produce hormones. Only functional ovarian cysts will result in hair loss. If your guinea pig has functional ovarian cysts you may see signs that include symmetrical non-itchy alopecia on the flanks, enlarged and crusty nipples and more aggressive behaviour. Treatment can be with the use of hormone injection or surgery to remove the ovaries.
Hyperthyroidism is an over-production of thyroid hormone by the thyroid gland in the underside of the neck. Reports suggest it may occur in as much as 30% of guinea pigs over the age of 3 years. Clinical signs often include a guinea pig that eats very well but is loosing weight, more skittish behaviour than previously normal and non-itchy hair loss. Your vet may be able to feel a swelling in the neck and detect a higher than normal heart rate. Definitive diagnosis is based on blood tests. However, response to treatment can be used in guinea pigs that have compatible clinical signs. Treatment often involves lifelong medication or surgery to remove the affected gland.
Cushing’s disease is also known as hyperadrenocorticism. It is an overproduction of steroid hormone (cortisol) by the adrenal glands. It currently considered to be a rare condition of guinea pigs. The signs you may see if your guinea pig has Cushing’s disease include drinking a lot, urinating a lot, increased appetite, symmetrical non-itchy hair loss, slowed behaviour, weight loss (becoming thin along the back but having a pot-bellied appearance), and bulging eyes. Diagnosis can be achieved by measuring cortisol levels in saliva. Vitamin C deficiency can cause high levels of cortisol in saliva, this should therefore be corrected or taken into account when your vet analyses the results. Cushing’s disease can be controlled with lifelong medication.