Author: Mika Verheul
Tramping in New Zealand can be challenging. One of the risks perhaps underestimated by many trampers is a severe reaction to wasp venom. There are various opinions about how to deal with possibly allergic people when they get stung by a wasp, often resulting in uncertainty and anxiety. Emergency response might get alarmed unnecessary or fatalities might occur when activated too late. What should be the initial treatment after a wasp sting?
For my study ‘Wilderness medicine’ I wrote an assignment on the treatment of wasp stings in the New Zealand outdoors. As we are entering the wasp season again, I’d like to share some bits of information about this subject.
Fortunately wasp stings are rare and the average person might experience the occasional sting once every 10-15 years. However, trampers can easily be exposed to wasps more frequently due to their activity.
The Vespula Vulgaris or Common wasp became established in New Zealand in 1978, whereas the Vespula Germanica or German wasp had already become established in 1945. Both species are considered pests due to their aggressive nature, their competition for resources with other species and their painful stings. The presence of honeydew (responsible for the black bark in beech forest) and the mild New Zealand climate are responsible for a very high density of wasps on the South Island with up to 30 nests per hectare, and the average nest size being amongst the biggest in the world. Common wasps forage on honeydew more efficiently than the German wasps hence it is the common wasp that dominates in the New Zealand beech forest.
Wasp activity depends on the weather and shows a seasonal variation with wasps being most active in summer time, from October to April. In New Zealand more than 85% of the wasp nests are built below ground, mostly in soil, on sunny river banks. The wasps can easily be disturbed by accidentally stepping on the nest, in particular when bush bashing.
People allergic for wasp venom are not likely to be allergic for bee venom and the other way round, as the venom is different. Often the severity of the reaction weans off over time when not exposed again.
The reaction to the wasp sting can occur as a normal local reaction, a large local reaction or a generalised reaction:
- The normal reaction is characterised by local pain, redness, and swelling at the site of the sting with a diameter up to 10cm. Pain medication (paracetamol or ibuprofen) can be taken to ease the discomfort.
- A large local reaction has a diameter larger than 10cm and symptoms persist longer than 24 hours, up to 5 days. Additional signs of fever, malaise and swollen glands might be present. Again pain mediation can be taken and, although researchers don’t agree, it can be beneficial to take oral antihistamine (2-4 times the normal daily ‘hayfever’ dose, continue for 4 days).
Severe local reactions are quite common and fortunately in most cases not life threatening. The risk of anaphylaxis in people with a history of severe local reactions is only 5-10%. A generalised reaction in allergic people seems to recur as often as not, and there is no linear relationship between those with severe local reactions and those developing generalised symptoms.
- Generalised reactions are not restricted to the site of the sting and can manifest in many different ways. Signs consist of low blood pressure, difficulty to breath, generalised swelling, sometimes a rash or hives, abdominal pain and loss of consciousness or collapse. The most severe is anaphylaxis. Generalised sting reactions occur in an estimated 0.4-5% of individuals. No clear characteristics are known to predict the risk of an individual to develop anaphylaxis. It is however more likely to occur after multiple stings, or when repeated stings occur over a short period of time. If someone has had a generalised reaction, a referral to an allergy specialist is recommended to perform blood tests and to discuss serious long term treatment by venom sensitization.
Fatalities due to anaphylaxis occur in an estimated 0.5 per one million people only and often without a past history of sting reactions. Anaphylaxis has a rapid onset and people feel very ill within minutes after being stung, often referred to as a ‘sense of impending doom’. All fatalities due to venom anaphylaxis happened within 5 minutes to 4 hours after being stung.
Adrenaline injections reduce symptoms in anaphylaxis, but only when injected in an early stage. For that reason an “epipen” (prefab adrenaline injection) can be taken along by people at risk. However, the epipen is quite expensive and in practice the injection method requires familiarisation and regular updating of skills.
In summary: prevention can make the largest difference!
During summer months you can reduce the risk of wasp stings by:
- Wearing protective clothes
- Staying on the tracks and avoid bush bashing, especially in beech forest with honeydew (Nelson Lakes area)
- Avoiding sunny river banks
- If a nest gets disturbed, run away for at least 30m, most preferably away from the water. As long as you are within the nest territory the wasps will attack you.
In addition to this the general recommendation is to let people with an allergic history go first when travelling as part of a tramping group in an area where there are many wasps, because the ones in front of the group are less likely to be stung.
Hopefully none of the above keeps you from tramping and appreciating nature!