Itching in mice is often down to skin problems. Parasites, bacteria, yeasts, ringworm, viruses, diet, environment — a great many skin factors can lie behind the itching. Depending on how the itch shows itself, metabolic disorders can also be suspected.

External parasites

  • Mange mites. In small numbers they cause no visible signs. Heavy infestations quickly lead to self-inflicted damage from the severe itching. Hair loss, crusts, itching and sometimes a dull, ruffled coat are among the signs. Depending on the exact mite, the trouble may show up in different places. Some inbred lines suffer particularly from an allergy to a certain mite species, which can make the trouble worse. Immunocompromised or pregnant mice are also at risk. Treatments are available from the vet.
  • Lice. Rare — beware the risk of zoonosis.
  • Fleas. Only in mice living alongside cats or dogs.

Internal parasites

Some internal parasites can cause itching around the anus and the base of the tail.

Bacterial infections

They cause dermatitis that is often ulcerative and sometimes necrotising, and can bring on itching of varying intensity. Purulent abscesses are mainly caused by bacteria, sometimes linked to initial wounds from fighting. Bacterial dermatitis is often secondary to another, primary skin disease.
It is diagnosed after examining the clinical signs, taking samples and culturing them. Treatment is the usual one: curetting the abscesses, disinfecting and antibiotics.

Viral infections

These rarely cause itching, yet they carry a high death rate. Changes in the coat, a badly lowered general state, and skin signs (ranging from swelling to tissue loss) are warning signals.

Fungal infections

Dermatophytes are common in mice — some 60% of mice are said to be infected. Even so, they rarely cause any signs, which are usually localised bald patches (hair loss), sometimes with a reddish, crusty ring. Diagnosis and treatment are carried out by the vet.

Miscellaneous

  • Nutritional deficiencies cause hair loss but little itching.
  • Behavioural factors, such as fur-pulling in bullied mice, and fighting.
  • “Ringtail”, a condition encouraged by a damp environment and seen in the young. A constriction of the tail that leads to its loss. No itching.
  • Immune-mediated vasculitis. In laboratory mice, it leads to ulcerative dermatitis.
  • Tumours. These can prompt scratching out of discomfort or pain.
  • Idiopathic dry gangrene of the ear flaps. In young mice, a cold environment, too much grooming and lice can bring on this syndrome, which causes the ears to die back (necrosis). It is unclear whether the frequently seen condition of self-mutilation of the face with necrosis of the ears — which resists all treatment over the long term — is directly linked to this syndrome, or instead to a nephritis that might give rise to intense itching sensations. As yet, no treatment is known.