By: Dr. Thomas Kaiser
dr.kaiser@portugalresident.com
AFTER RECEIVING several calls from readers who had seen signs warning them against Processionary Caterpillars in some areas of the Algarve, The Resident asked Dr. Kaiser, who contributes a regular column, to provide readers with information and advice.
Dear Reader,
Every year I see quite a few victims of the Processionary Caterpillar in my practice.
There are a lot of rumours and myths about these tiny animals and the illnesses they can cause. The facts are the following:
The Processionary Caterpillar is the larva (prestage) of a type of silk producing moth called Thaumetopoeiae. The grubs live in large communal nests, known as bag nests, which hang from tree branches, most commonly in pine trees feeding from the tree’s needles.
When they have exhausted one tree, they move on to another, forming a line of caterpillars. This can lead to a “procession” of up to 50 caterpillars, hence the name.
In their evolution, they have developed a poison that covers their outer fine hair. This poison acts as protection against enemies that try to eat the little animals. It is very acidy and you can see the effect it can sometimes have on the tongues of dogs or cats – maybe you have seen a local dog or cat who has been a little too nosy and paid the price by losing a part of their tongue or lip? For this reason, it is important to keep a close eye on your pet at this time of year if you live close to pine trees.
I very rarely see dogs with tongue problems in my practice. Very commonly, though, between January and April, I see golfers, tennis players and holidaymakers who are suffering from desperately itchy rashes.
The medical profession calls this illness an “irritative dermatitis”. The rash is composed of red spots and sometimes even blisters that can form everywhere on the body. The most commonly affected areas are neck and legs and the spots are very itchy. They are caused by skin contact with the fine hair of the caterpillars which are coated with a poison that releases histamine in our skin.
Histamine is a mediator that typically causes dermatitis called nettle rash and is also responsible for several allergic reactions. It can, in a worst case scenario, trigger asthma attacks and even anaphylactic reactions.
Golfers and tennis players typically become “infected” by picking up a ball with fine hair on it and afterwards scratching their necks. A holidaymaker staying in a villa under pine trees however, cannot avoid contact with the hairs, as they are in the air.
Reactions
It surprises me every year how severe the reactions can be. While the moth that develops from the larva only lives one day, the dermatitis can itch for many weeks and effective treatment is often only possible with the use of Cortisone medication.
I was surprised that this problem is not only keeping doctors in Mediterranean countries busy, but those of Northern France and Germany too. Caterpillars living in oak trees in these areas are also causing skin problems. Global warming may be partially responsible for the northwards spread of the caterpillars.
How can you protect yourself?
Teach your children not to touch the caterpillars.
Cover head and neck during golf, tennis or walks in pine tree territory.
Use lots of moisturiser all over your body.
Take a shower and change clothes after your walk or golf game. The hairs stick best to your hair.
If you are suffering every year, consider taking an antihistamine when the season starts.
If you have a bad rash, see your doctor sooner rather than later. The treatment is then more effective.
Should you have lots of pine trees you could have them treated against the caterpillars. Please use a responsible pest treatment agent. Sometimes the pesticides used cause worse skin reactions than the caterpillars themselves.
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