The rainy season is here; watch out for the Nairobi fly

Paederus dermatitis is a skin irritation resulting from contact with the paederus beetle, commonly known in Kenya as the Nairobi fly.

The paederus beetle is commonly found in humid areas, hence its high prevalence during the rainy season.

It is attracted to light, especially fluorescent, and is therefore a common visitor in our homes around this time.

The Nairobi fly is approximately 1 centimetre long, about twice the size of a mosquito.

These beetles have a black head and lower abdomen, while the thorax and upper abdomen are red.

They rarely fly, but move fast. When threatened or disturbed, they curl up their abdomen and look like a scorpion ready to strike, even though they do not sting or bite.

Clinical Features of Paederus Dermatitis;

The areas commonly affected are the neck, arms, and face. You may not experience any symptoms for the first 12 to 24 hours, but thereafter, you may experience severe burning and itching around the affected area.

Two to three days after contact with the beetle, the area may redden and swell, and small blisters may appear, which may progress to look like boils.

For areas around the joints, where the Nairobi fly may have been crushed, lesions, referred to as “kissing” lesions, may appear.

The blisters will later burst and coalesce to appear like a burn. In fact, many patients only notice the lesions when the affected area begins to look like a burn. Further crusting and scaling may occur, but most symptoms resolve in two to three weeks.

Occasionally, areas affected by the Nairobi fly may develop secondary bacterial infection, and this may seem like a skin infection. In addition, the affected area may develop dark patches.

A condition known as Nairobi eye will occur when you come into contact with the beetle’s haemolymph (body fluid or blood), when you crush it against your skin. Their body fluid contains a toxin known as paederin, which is purported to be more toxic than a cobra’s venom.

Touching your eye with hands that have come into contact with the Nairobi fly’s toxins may lead to swelling of the eye, redness, or further complications.

Paederus dermatitis may be confused with herpes zoster, liquid burns, acute allergic reactions, millipede dermatitis, and contact dermatitis. The season, presence of the Nairobi fly, or spotting the fly on your skin may assist in diagnosis.

Treatment

• Once contact has been made with the fly, or if you crush the fly against your skin, wash your hands and the affected area immediately with soap and water.
• Apply a mild topical steroid ointment and where there is likelihood of bacterial super infection, apply an antibiotic ointment.
• Oral antihistamines will reduce the itchiness that results in scratching.
  

Prevention

It is important to avoid contact with the Nairobi fly in the first place since the resulting dermatitis can cause undue discomfort and, in a few cases, scarring. This can be achieved by;

• During the rainy season when the Nairobi fly is prevalent, close all doors and windows before it gets dark.
• Sleep under a mosquito net.
• If you see one crawling on your skin, blow it off rather than brush it away. This reduces the risk of crushing it. You can also use a piece of paper to remove it from your skin.
• Should you crush one, avoid touching your eyes. Wash your hands and the affected area with water and soap immediately.
• Check areas for the beetle around beds and ceilings before going to bed.
• Clear excess vegetation from and around houses.

The writer is a medical doctor and a public health specialist. Do you have any health-related questions? Write to doctormugambi@gmail.com