Taumarunui farmer Janet Kelland thought she was "a gonner" after being attacked by swarms of wasps.

A single sting from a German or common wasp – New Zealand's most aggressive wasp species – sends a signal for others to attack.

Nelson Marlborough Health chief medical officer Dr Nick Baker said a wasp's venom could trigger a serious allergic reaction known as anaphylaxis.

It was a whole body, life-threatening, overreaction by the immune system which could be reversed by administering adrenaline.

MARION VAN DIJK An adrenaline kit of adrenaline and antihistamine tablets.

Baker said the blood vessels became leaky and body tissues became swollen which could cause difficulty breathing. The lack of blood circulation meant the body went into shock which lead to death.

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"Once it starts, the speed at which is comes on gives you a bit of a clue as to severity. If it is happening within seconds that is going to be a devastatingly bad reaction."

Baker said he was aware there had been deaths in the region from people who suffered an anaphylactic reaction from wasp stings.

"It is sort of OK to have pain, OK to have a little bit of local swelling or tenderness – and that can be quite big at times – but for some people it doesn't stop there."

Information from Nelson Marlborough Health showed between January 2012 and December 2016 there were 207 visits to Nelson and Wairau Hospitals for injuries related to wasp stings.

Wasp stings can cause allergic reactions in some people.

Of that number, 21 people were admitted to hospital for further treatment, an average of about four people a year.

Baker said while the numbers weren't overly dramatic, for someone to be admitted to hospital after a wasp sting they had to be quite unwell.

A 2015 Department of Conservation report into the cost of pest wasps in New Zealand estimated health costs of wasps each year to be $1.1 million, based on doctor visits, hospital stays, deaths and ACC claims.

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Allergy NZ estimates between two and three people die each year due to insect stings which could be an underestimate as fatal stings might not be properly documented.

Victoria University insect ecologist Professor Phil Lester said Nelson was the "wasp capital of New Zealand".

"The frequency of people being hospitalised or even dying … puts wasps as one of the most dangerous insects in the country."

MARION VAN DIJK/Stuff.co.nz Bryan Heslop was first at the scene to administer adrenaline to a forestry worker in 2004 who had multiple wasps stings leaving him with a severe allergic reaction.

Baker said people with a history of anaphylaxis needed to have worked out an action plan with their doctor which would involve having access to adrenaline or an EpiPen.

It was important people were aware of where they might encounter wasps to avoid being stung if possible.

Baker said he had an encounter with wasps and was stung several times but he did not have an allergic reaction.

"A few years ago I walked into a wasps' nest with a lawnmower and it was very unpleasant, for both the wasps and me," Baker said.

"I got about 10 on my legs, I was in shorts, it was memorable."

Desensitisation to wasp stings, also called venom immunotherapy, was available for people with severe allergies. It involved regular doses of venom to build up a tolerance.

Baker said he knew children locally that were receiving desensitisation for bee allergies but not for wasp allergies.

Nelson GP spokesman Dr Graham Loveridge said it was relatively common to see people with wasp stings over the summer months.

"Most people just get the local toxic reaction, they will get pain and swelling and redness and a bit of an itch that takes a few days to go away."

"Sometimes people get alarmed by that and think they have got a severe allergy because they get a swelling the size of the palm of their hand."

He said the "worrying allergy" known as anaphylaxis, was quite rare, affecting between 0.3 to 3 per cent of the population which could also depend on the number of stings someone received.

"Every so often you hear about someone who trips over a wasp nest out in the bush and gets stung 50 times and that is a riskier situation than being stung just once."

Adrenaline was used to counter anaphylaxis and could be administered through an injection or by using an EpiPen.

EpiPens are not funded in New Zealand and cost between $120 and $200 a pen per year.

However they were reliable and easy to use which was a big advantage, said Loveridge.

Loveridge said in the practice there were several children who were at risk of anaphylaxis and they had taught some of the families to administer adrenaline using a syringe and needle as the cost was minimal.

St John intensive care paramedic Gary Tobin said he attended a number of callouts for wasp stings in the 16 years he had spent on the Nelson Marlborough Rescue Helicopter.

He said the reaction to a wasp sting could vary from mild to severe allergy then anaphylaxis.

Tobin said most people who were stung by wasps didn't have an anaphylactic reaction, but for those that did, the situation was life threatening and potentially fatal.

For someone suffering from anaphylaxis it was vital they had access to adrenaline as soon as possible.

"It is one of those rare things where time is critical."

Tobin said what differentiated a severe allergic reaction from anaphylaxis was the "multi-system response".

Difficulty breathing, wheezing and clutching the throat along with the development of a rash like hives and a dropping heart rate were signs of anaphylaxis.

Adrenaline supported the airway to help breathing and increased the cardiovascular tone to normalise the heart rate, Tobin said.

The wasp venom worked it's way out of a person's system naturally but it was important people were monitored as the adrenaline could wear off before the anaphylaxis did.

Wasp horror stories

April 2015: A Hastings woman was holidaying on Arapawa Island in the Marlborough Sounds when she felt something sting her foot so she headed to the sea to stand in the cold water. But by the time she got down to the beach she was semi-conscious, her tongue was swelling and she had a ringing noise in her head. The Nelson Marlborough Rescue Helicopter treated the woman for anaphylaxis and flew her to Wairau Hospital in Blenheim where she was kept in observation for several hours before being released.

March 2014: Taumaranui farmer Janet Kelland was stung by hundreds of wasps in a remote valley. She was alone checking her farm's electric fence line when she stepped on a wasp's nest.For almost an hour she battled hundreds of wasp stings, clambering down massive steep slopes to a creek to dislodge them. She then staggered back up the slope and walked a further 40 minutes through bush to her quad bike and drove for 15 minutes until she had cellphone reception to call St John Ambulance. She was flown to Taumaranui Hospital and discharged a week later.

February 2014: Nine children and a grandmother were hospitalised following a wasp attack during a school trip to Tahunanui Beach in Nelson. The pupils were taking part in a pirate treasure hunt when one of them disturbed a wasp nest.

February 2012: Morris Robert Stretch died after being stung by thousands of wasps in the Marlborough Sounds. He was collecting firewood with a family member when they accidentally disturbed a wasp's nest. Attempts to resuscitate Stretch were unsuccessful and he died before emergency services arrived.

March 2011: Distracted by a wasp in his car, Rupert Charles Howard crashed into a cyclist on the Tarras to Cromwell Road. The cyclist, a Japanese tourist, was paralysed from the chest down. A court heard that Howard's family had a history of wasp allergies.

What to do if you are stung by a wasp?

A wasp sting is a minor irritation for most people. However, some people are especially sensitive and may develop a severe allergic reaction called anaphylaxis.

Symptoms

Swelling around the lips and eyes

Rapid development of a rash

Shortness of breath or wheezing and chest tightness

Severe dizziness or faints

Persistent sneezing or coughing and a hoarse voice

Difficulty swallowing or throat tightness

Signs of shock (pale skin, rapid pulse and fainting)

Avoid getting stung

Take care when eating food outdoors, especially sugary drinks and fish sandwiches, which can attract wasps.

Wasps also like bright-coloured or dark clothing, and perfumes. If you're hiking in bush and forest areas wear hats, long-sleeved shirts and long pants, and light colours.

If you are allergic to stings

If you have ever had an anaphylactic reaction to a sting, you should always carry a kit containing adrenaline (or an EpiPen), ventolin and antihistamine tablets.

Desensitisation therapy (immunotherapy) where small amounts of venom are regularly administered to stop your body reacting so badly in the future.

Source: Ministry of Health