Crusted scabies

Crusted scabies (also sometimes referred to as Norwegian scabies) is a more severe form of scabies where thousands, or even millions, of scabies mites are present.

Crusted scabies can begin as scabies before developing into the more severe form following a skin reaction. Crusted scabies affects all parts of the body, including the head, neck and nails. Unlike normal scabies, the rash of crusted scabies does not itch and it can affect the scalp.

In crusted scabies, the increase in the number of mites causes the appearances of thick, warty crusts to appear on the skin. The condition is often misdiagnosed as psoriasis (a skin condition that causes red, flaky, crusty patches of skin that are covered with silvery scales).

Crusted scabies affects people who have a weakened immune system (the body’s natural defence against infection). People who may have a weakened immune system include:

• the very young
• people with brain disorders (neurological disorders, such as Parkinson’s disease)
• people with Down’s syndrome, a genetic disorder caused by an abnormality in one of the chromosomes (genetic material) that occurs when a baby is still in the womb (uterus)
• pregnant women
• elderly people
• people with a condition that affects their immune system, such as HIV or AIDs
• people who are taking steroids to treat other medical conditions
• people who are undergoing chemotherapy

Research has found that a healthy immune system seems to interrupt the reproductive cycle of the scabies mite. For example, most people who are affected by the condition will only have 5–15 mites on their body at any one time.

However, if your immune system is weakened, the number of scabies mites can increase significantly. People with crusted scabies can have thousands or millions of scabies mites in their body at any one time.

Due to the high number of scabies mites, crusted scabies is highly contagious. Even minimal physical contact with a person with crusted scabies, or with their bed linen or clothes, can lead to infection. However, transmission from someone with crusted mites will only lead to the normal type of scabies in people with a healthy immune system.

Crusted scabies can be treated by using insecticide creams, or a medicine called ivermectin, which is taken orally (by swallowing a tablet). Ivermectin kills the mites by stopping their nervous system from working.

Secondary infection

Excessive itching of the skin can break the surface of your skin, making it more vulnerable to a bacterial infection such as impetigo (a highly contagious bacterial skin infection). Antibiotics may be recommended to control a secondary infection.

See the Health A-Z topic about Impetigo for more information about this skin infection.

Scabies has been known to make other pre-existing skin conditions worse, such as eczema. However, if you have another skin condition, it should settle down once the scabies infection has been successfully treated.