Tick bites

Background

Ticks are blood-sucking parasites. When they take a blood meal, they can cause dermatologic disease directly by their bite, or indirectly as vectors of other diseases. Tick-borne diseases include:

• bacterial infections including Lyme disease, relapsing fever, tularaemia, and babesiosis
• rickettsial infections including Rocky Mountain spotted fever, other spotted fevers, ehrlichiosis and anaplasmosis, and Q fever
• viral diseases including tick-borne encephalitis, Crimean-Congo haemorrhagic fever, Colorado tick fever, Powassan encephalitis, and others

This page will focus on skin diseases that occur as a direct result of tick bites. Risk factors for tick exposure include outdoor activities such as camping, hiking, walking in long grass, or contact with animals. In endemic areas, infections can also be acquired during routine activities. Many cases of tick-borne disease occur in the summer months when ticks are most active.

Ticks

Tick bites

While tick bites can be painful, in many cases they can go unnoticed.

Ticks can be categorised as either hard or soft ticks and this distinction determines some of the clinical features of the tick bite. Hard ticks feed for a few days to several weeks, while soft ticks feed quickly and leave their host rapidly.

Ticks cause acute and chronic skin diseases through physical trauma, salivary secretions, toxins, excretions, body parts, or by causing a host to scratch. Skin disease may occur away from the site of the bite, and tick bites can also cause disease in other parts of the body such as 'flu-like symptoms, vomiting, paralysis and even anaphylaxis.

Tick bites

Acute or early skin manifestations of tick bites

For both hard and soft tick bites, 0.5 to 2 cm red areas, papules (small bumps), or thin plaques may form at the site of attachment within 1 to 3 days. The lesions may feel hard and may be surrounded by redness. Mild swelling or blister formation can occur. The bites can be mildly to severely itchy.

Necrotic (dead tissue) ulcers can form in severe cases; usually due to bites from soft ticks. Bites from soft ticks may be painful.

Specific tick species can also cause characteristic lesions such as bruising (purpura), urticaria, and ulceration.

Chronic or late skin manifestations of tick bites

Acute skin lesions can persist and become papules, nodules (larger solid lumps), or plaques. Over days to months, these lesions can form a tick bite granuloma; a 0.5 to 2 cm nodule made up of mixed inflammatory cells.

Tick bites can also rarely result in hair loss (alopecia), which may resolve within 1 to 3 months, or be permanent.

Tick bites can develop wound infection due to secondary infection by bacteria such as Staphylococcus aureus and Group A Streptococcus. Retained tick material and host scratching may increase the likelihood of this complication.

Diagnosis and treatment

Diagnosis can be difficult, especially if the bite has gone unnoticed. Microscopic examination of skin biopsy specimens may assist diagnosis.

Tick removal may improve symptoms (see below). Itch may be relieved with topical steroids and oral antihistamines. Tick bite granulomas can be surgically removed.

Prevention

• Avoid areas such as forests or fields where ticks are found.
• Use insect repellent containing DEET on the skin, and Permethrin on the clothes.
• Wear long-sleeved clothing that fits tightly around the wrists, waist, and ankles.
• Check twice daily for attached ticks and remove immediately. While wearing protective gloves, gently grasp the tick with tweezers as close as possible to the skin and slowly, gently pull it away.