How to prevent and treat symptoms caused by oak processionary moth caterpillars

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    Last year, processionary caterpillar plagues spread across Europe, resulting in a record-breaking number of people visiting GPs with symptoms caused by the caterpillars’ stinging hairs. Despite the efforts of pest control specialists, not all nests have been removed from infested trees. This means that this year, many moths will again emerge from eggs as caterpillars to feed on the first leaves of spring. What can you do to prevent exposure to these stinging hairs? And what should you do if you develop symptoms anyway? We have some tips for you!

    Why are oak processionary caterpillars making their way up north?

    Infestations of oak processionary moth caterpillars have only been an annual problem in the northern half of the continent in recent years. The oak processionary caterpillar is originally a southern European species but has been spreading northwards due to climate change. The caterpillars are larvae of night-flying moths that lay eggs in clusters of 250 or more. Over the last few years, our climate had become increasingly warm and dry, causing most larvae to hatch from their eggs.

    Why do oak processionary caterpillars cause health problems?

    Once hatched, a thick line of grey furry caterpillars snake up the trunks of oak trees. They travel in nose-to-tail processions, hence their name, to search for leaves which they devour in large quantities. Infested oak trees can be recognised by white silken nests around branches and trunks, consisting of scales (caterpillars shed their skin often), hairs and droppings.

    Oak processionary moth caterpillars are covered in thousands of tiny hairs. These fine, barbed hairs are called bristles or setae. The bristles break off readily, become airborne and land on the skin, clothes or hair. They are so small (between 0.2 and 0.3 millimetres) that they can easily penetrate the skin. And because the hairs are barbed, they stick into your skin.

    The toxins on the bristles contain a protein that the body does not recognise. This generates a response in the body’s immune system: it releases histamine in an effort to expel the protein or ‘foreign invader’. This can cause various symptoms, depending on which part of the body is affected.

    What sort of symptoms do they cause?

    If the hairs or toxins come into contact with the skin, most people get allergic skin reactions. The symptoms generally appear four to eight hours after exposure. The most common skin reactions include:

    • Itchy rash.
    • Red patches, bumps and blisters on the skin.
    • Burning sensation.

    If the stinging hairs of oak procession caterpillars come in contact with the eyes, they can cause eye problems within one to four hours, such as:

    • Itchy eyes.
    • Red, irritable eyes.
    • Swollen eyelids.
    • Watery eyes.
    • Eye inflammation, which in rare cases can result in blindness.

    Some people get respiratory problems within four to eight hours of exposure. If you have asthma or another respiratory condition, you have a greater chance of developing respiratory problems, such as:

    • Itching in the mouth or throat.
    • Difficulty swallowing.
    • Sneezing or coughing.
    • Runny nose.
    • Chest tightness or shortness of breath.

    Although less common, gastrointestinal symptoms can occur when the hairs are ingested. This can result in the following symptoms:

    Complaints can be more severe when you repeatedly come in contact with oak processionary caterpillars. For some people, the toxic hairs can cause severe allergic reactions. Symptoms of severe allergic reactions include:

    • Severe breathing problems.
    • Swelling of the eyes, lips, tongue or other areas.
    • Vomiting.
    • Fever.

    Symptoms often become the most serious within 30 minutes of exposure. Get immediate medical attention if you develop any of these symptoms!

    What is the best way to avoid exposure to the hairs of oak processionary caterpillars?

    Oak processionary caterpillars can be found from April to July. Try to avoid the caterpillar and its stinging hairs as much as possible during this period. Here are some tips:

    • Keep away from streets, parks or woods with oak trees.
    • Cover your arms and legs when outside. Wear long-sleeved clothing.
    • Wear sunglasses, even if it’s cloudy.
    • Keep windows and doors closed.
    • Do not hang your laundry out to dry.

    Very important: don’t touch caterpillars or nests. The removal and incineration of nests should be carried out by experts only!

    What should you do if you develop these symptoms?

    Have you been exposed to the caterpillar’s hairs? Here are some tips that will minimise the complaints:

    • Try to avoid scratching as much as possible, as this only makes it worse.
    • Strip your skin with sticky tape. Stick it onto the skin and then pull it off again. If you’re lucky, you can remove the poisonous caterpillar hairs this way.
    • Then rinse the skin well with warm water. Wash your hair too, if necessary.
    • Treat irritated skin with a calming lotion or special processionary caterpillar gel to reduce irritation.
    • Drying the affected area with a hair dryer can also be effective. By heating up the bumps, the protein in the barbed hairs solidifies and, as a result, complaints disappear more quickly. A sauna is said to produce the same effect.
    • Irritated eyes? Rinse your eyes with lukewarm water. Try not to rub your eyes. If necessary, a doctor can prescribe soothing eye drops.
    • Wash worn clothing (apart from other clothing) at at least 60 degrees Celsius. Shaking out your clothing does not remove the bristles.

    Most complaints will disappear in a week or two. Consult a doctor if the side effects are persistent or severe. It may be necessary for your symptoms to be treated with Fagron, a topical corticosteroid ointment, or antihistamine tablets or cream.

    Let’s get through the summer itch free!

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