Health and Safety | PPC96 August 2019

Insect stings by Hymenoptera species are very common, with more than half of the population being stung at some stage in their lives.

Pest management professionals are obviously more at risk than most when it comes to stinging insects.

Dr Andrew Whyte, a Consultant Allergist and Immunologist from Derriford Hospital, Plymouth gives us a lesson in insect venom and allergies designed to help us better advise our clients and protect ourselves.

The majority of Hymenoptera stings cause transient redness, pain, and localised swelling which can last up to a few days but generally resolves with simple symptomatic treatment.

However, some people get larger localised reactions or anaphylaxis which, in rare cases, can be fatal.

In adults, insect stings cause up to a quarter of cases of anaphylaxis, making it a very important public health issue particularly in those occupationally exposed to stings.

Identification of the insect is important

Identification of the insect responsible for an allergic reaction can be useful in diagnosis, testing, and management.

There are hundreds of species of Hymenoptera in the UK, but of these the groups Vespidae (wasps) and Apidae (bees) are the most common causes of allergic reactions.

Some important insects are:

• Vespula vulgaris (common wasp)
• Vespa germanica (German wasp)
• Vespa crabro (hornet)
• Dolichovespula species (median wasp)
• Apis mellifera (honey bee)
• Bombus species (bumblebee).

There are hundreds of species of Hymenoptera in the UK, but of these the groups Vespidae (wasps) and Apidae (bees) are the most common causes of allergic reactions.

When stung, features that can be useful in identification include:

• Colour, size and pattern of the insect
• If a stinger is left behind (which often happens with bees but rarely with wasps)
• The time of year given the lifecycle of the insects may be different
• Activity at the time of being stung (for example food attracts wasps)
• The geographical distribution of the insects, since some are only present in some parts of the country.

Identification of the insect is important because the venom from each is slightly different.

Honey bee venom is somewhat similar to bumblebee venom, but not identical. Wasp venom is quite different to bee venom, and within the wasp group Vespula, Vespa and Dolichovespula are all similar.

Polistes venom (a type of wasp occasionally seen in the UK but much more common elsewhere in Europe) is different again.

This means that a test for one type of venom may not detect allergy to other venoms, and optimising treatment depends on treating for the right insect.

Allergic reactions

It is normal to get some irritation and redness at the sting site, which can persist for a few hours to a couple of days.

In about 10% of the population stings can cause a ‘large local reaction’ in which the sting site swells markedly (10-15cm or more).

This swelling typically increases over one or two days and then resolves over a week or so.

Anaphylaxis is defined as involving more than one body system, and in venom allergy a rash is not always present.

The symptoms can occur very quickly (within minutes), and rarely longer than 30-45 minutes after the sting. Some of the symptoms are:

• Airway
• Swelling of tongue
• Swelling/tightening in throat
• Difficult talking/hoarse voice
• Breathing
• Difficult/noisy breathing
• Wheeze or persistent cough
• Circulation
• Persistent dizziness or collapse
• Loss of consciousness
• Other
• Abdominal pain
• Vomiting.

The risk of anaphylaxis following a large local reaction is about 10% or, in other words, of 10 people who have a large local reaction, one of them would have anaphylaxis if stung again.

On the other hand, if someone who has had anaphylaxis gets stung again the risk of anaphylaxis is about 50%.

Beekeepers are frequently stung, and anaphylaxis is more common in the first few years of beekeeping and in those who have fewer than 20 stings per year.

Interestingly beekeepers stung more than 200 times per year seem to be protected against anaphylaxis, although the reason for this is unclear.

There are no good studies on the risk of reactions with repeated wasp stings, and this is a vital piece of work that needs to be done.

Investigation of allergic reactions

The most important part of investigation is a detailed description of the symptoms and time course of the reaction, with as much information to identify the insect as possible.

There are blood tests for allergic antibodies that can be done for some insects, although they aren’t perfect.

There are skin tests that can be done as well, although again they aren’t perfect and the interpretation of both blood and skin tests depend on the clinical history.

Prevention of stings

Not all stings will be avoidable, although some strategies can be used to minimise the risk.

These include avoiding brightly coloured clothing, strongly scented materials, wearing appropriate clothing to cover exposed skin, being wary of locations where wasps and bees are likely to have nests, and avoiding eating or drinking outdoors particularly from cans or opaque containers.

Venom immunotherapy (desensitisation)

Venom immunotherapy is a way of preventing anaphylaxis in people who have had anaphylaxis in the past.

It involves injections of gradually increasing doses of venom over several days/weeks/months (depending on the method), followed by three to five years of injections every few weeks with the aim of training the body not to react.

The process is successful 95% of the time for wasp venom allergy and 85% of the time for bee venom, making it a very effective treatment.

If you have had anaphylaxis it is important to see your GP and be referred to a specialist allergy department with a view to discussing this treatment.

Venom immunotherapy is a way of preventing anaphylaxis in people who have had anaphylaxis in the past.

More information needed

There has been some research undertaken with beekeepers looking at the risk of reactions with repeated stings, and this is useful to increase our understanding of how and why some people have allergic reactions to stings and others don’t.

There is much less information on people exposed and stung repeatedly by other insects such as wasps.

Pest professionals are regularly exposed, and in the near future, I will be distributing a survey to find out how often pest controllers are stung, by what types of insects, and what sort of reactions they have.

This will hopefully increase our knowledge of allergy to insect stings and may help guide investigations and management in the future.

Treatment of allergic reactions

• To reduce pain and swelling you can apply a cold pack and elevate the area
• If a stinger is left in the skin, flick or scrape it out (to avoid compressing the venom sac and injecting more venom)
• Non-drowsy antihistamines (for example cetirizine or loratadine) can help with itching
• Paracetamol and/or ibuprofen can help with pain
• Occasionally infection and blistering can develop; this is not an allergic reaction but may need dressings and antibiotics if severe
• Contact your GP or call NHS 111 if you haven’t had symptoms of anaphylaxis but are worried about the sting, the symptoms don’t improve, you’ve been stung in the mouth or throat, or you feel unwell hours or days after the sting.

Anaphylaxis

• Sit or lie down on the ground
• Call 999 for an ambulance and say you are having anaphylaxis
• Use an adrenaline pen if available. If there is no improvement after five minutes use another if available.

Severity increases with:

• Older age
• Heart disease
• High blood pressure (and some medications used to treat it)
• Lung diseases such as asthma or COPD
• A very rare underlying condition called mastocytosis.

Want to help?

If you’d like to help us protect pest management professionals and learn more about stings and allergic reactions, register your interest now.

hello@bpca.org.uk