Insect stings and bites: How deadly are they and when to seek medical attention
Wasps building a nest on a tree branch.
SINGAPORE — A 60-year-old man was cycling along a park connector in Sembawang when he was attacked by hornets. He later died from the stings.
At a coroner’s inquiry into the incident that happened in 2022, the court heard that the cause of death was multi-organ failure following the insect stings, as well as ischaemic heart disease.
Similar cases of insect stings turning deadly have been reported in the past:
- In 2019, a 66-year-old retiree succumbed to organ failure after being stung by hornets while picking rambutans and durians in a forest near Bukit Timah
- In 2016, a migrant worker died after developing a severe allergic reaction from bee stings. He had been doing landscaping maintenance work at the time
Although such fatal incidents are rare, insect stings can be a hazard.
Data from the National University Hospital (NUH) showed that last year, a total of 265 patients were seen for insect bites or stings at its emergency medicine department and children’s emergency.
Three quarters of the cases were children.
Five patients — one child and four adults — required hospital admission for further treatment.
Over at Tan Tock Seng Hospital (TTSH), its allergy service has seen 21 patients with insect venom allergy of all severities in the past five years.
TODAY spoke to doctors and experts who study insects to find out why some insect stings lead to bad effects and how to stay safe.
WHY INSECTS ATTACK PEOPLE
1. THEY ARE THREATENED AND DEFENDING THEMSELVES
Insects such as hornets, wasps and bees usually sting in self-defence when they feel threatened or are provoked.
Biologist Carl Baptista has had some “close shaves” when he accidentally disturbed nests during fieldwork, but understanding insect behaviour helped mitigate risks.
“Quick withdrawal and avoiding sudden movements helped prevent stings,” he added.
Mr Baptista is the founder and chief technology officer of Cuprina Holdings, a biomedical and biotechnology firm where the flagship product is a bio-dressing made of live medical-grade maggots.
Insects might sting also if someone provokes them in some way.
Nests or hives are usually disturbed unintentionally, which causes the insects to go into an “alert” mode.
“Even if one of the alerted insects is disturbed, the rest of the hive can be called (to home in on the threat),” Mr Baptista said.
2. THEY ARE GUARDING TERRITORY
Entomologist Moo Chee Yuan from Cuprina said that walking close to a nest may increase the risk of being stung since these insects are protective of their territory.
Insects may also go into an “alert” mode if a branch falls on their nest or hive, when grass is cut or pruned, or when mosquito fogging is carried out.
However, unprovoked attacks are rare unless a nest is disturbed or the insects feel threatened by human presence.
INSECTS THAT CAUSE SERIOUS EFFECTS WITH THEIR STINGS
Dr Jonathan Tang, a clinical toxicologist who practises at NUH and Alexandra Hospital, has seen his share of patients who had suffered from insect stings.
The consultant at NUH’s emergency medicine department and a specialist emergency physician said:
- Serious effects from stings and bites mainly occur when they are by members of Hymenoptera, which is one of the largest orders of insects
- They include bees, wasps and hornets, as well as stinging ants such as needle ants and fire ants
- Honeybees are only capable of stinging once because its stinger is detached from its body after that
- Wasps and hornets have the ability to retract their stingers and inflict multiple stings
- Hymenoptera venom contains histamine, a chemical that triggers an allergic response, and melittin, a substance that is responsible for pain
- The venom also contains proteins such as phospholipase and hyaluronidase that can be toxic to cells in the human body
Among these stinging insects, hornets are particularly notorious for their aggressive behaviour and potent venom, Mr Moo the entomologist said. The man who died in 2022 was stung by hornets.
INSECT STINGS THAT CAN BECOME DEADLY
Insect stings can be fatal when they trigger:
- A severe, life-threatening allergic reaction known as anaphylaxis
- Toxic envenomation, which is when the person is poisoned by the venom that spreads throughout the body and multi-organ failure occurs
Dr Tan Sze-Chin, a senior consultant at TTSH’s department of rheumatology, allergy and immunology, said that when anaphylaxis happens, the person "experiences profound low blood pressure or circulatory collapse; or the airway swells up and results in suffocation”.
However, deaths due to stings by Hymenoptera insects are “exceedingly rare”, Dr Tang from NUH said.
WHO ARE AT RISK OF SEVERE REACTIONS FROM INSECT STINGS
1. PEOPLE WHO HAVE RECEIVED A TOXIC DOSE OF VENOM
A significant dose of toxic venom would involve multiple stings — more than 50 to 100.
It is not just one to two stings, Dr Tang from NUH said.
However, he pointed out that an allergic reaction can occur even at lower doses of venom since it is the human body’s immune response.
2. PEOPLE WHO HAVE BEEN BITTEN OR STUNG BEFORE, OR HAVE EXISTING ALLERGIES
Anaphylaxis more commonly occurs in patients who have been exposed to bee venom in the past and in those with a history of allergic conditions such as allergic rhinitis (nasal symptoms of runny or blocked nose triggered by allergens), eczema and asthma.
Their immune system is already sensitised, making them more prone to severe reactions when they are re-exposed to the allergen.
Dr Tan from TTSH said that the risk of a serious allergic reaction can increase by up to 58 per cent if there was already a sting within the last two months. The increased risk applies even if the first sting was well-tolerated.
Bee stings also result in more serious allergic reactions in people with insect venom allergy, compared to wasp stings.
3. ADULTS AND THOSE WITH HEALTH PROBLEMS
Allergic reactions tend to be more serious in adults than children, Dr Tan said.
Other risk factors include having certain medical conditions such as lung and heart diseases, and being on certain medications such as angiotensin-converting enzyme inhibitors, which are used to treat high blood pressure and heart problems.
“While the exact reason (why adults get more severe allergic reactions from insect stings) is not defined, it is postulated that older individuals frequently suffer from co-existing heart and lung problems that impair the body’s ability to recover from a reaction,” Dr Tan added.
HOW TO STAY SAFE AND AVOID INSECT STINGS
If a wasp nest or bee hive is found near or in the home, people should not try to remove it themselves. Contact a professional pest control service for assistance.
Avoid wearing strong fragrances, perfumes or highly scented cosmetics, Dr Tan said.
If you have left an opened drink can or bottle unattended while outdoors, check before drinking to prevent being stung inside the mouth because insects are drawn to sweet beverages.
As for people who have had an allergic reaction to insect stings, be prepared with an allergy action plan and have the necessary standby treatment on hand.
“They should carry an EpiPen (containing adrenaline) that can be administered immediately if necessary. Such patients should also be reviewed by an allergy specialist,” Dr Tang from NUH said.
During their fieldwork, Mr Baptista and Mr Moo from Cuprina use insect repellent and are generally cautious around insect nests and habitats — something that they also ask the general public to do when outdoors.
“My advice to readers is to be aware of your surroundings, especially in nature, and avoid disturbing insects and their nests.
“Knowing how to react to a sting and when to seek medical help is also essential,” Mr Baptista said.
What you can do:
1. Move to a safe location to prevent further stings.
2. Do not “suck the venom out” of a bite or sting site, be they from insects, snakes or spiders. This risks soft tissue injury. “Don’t believe what you see on TV,” Dr Tang said.
3. Try removing the stinger to reduce the venom load — but do this by scraping it away with a sideways movement using a card or fingernail.
“Avoid pinching or squeezing the stinger because this may force more venom to be injected into the wound,” Dr Tang added.
4. Wash the affected area with soap and water, and apply a cold pack to reduce swelling and pain, Mr Baptista advised. Take antihistamines for itching and swelling, if necessary.
BODILY REACTIONS TO INSECT STINGS
The human body's reactions to insect stings can vary widely.
Dr Tang said that the majority of people usually have a mild local reaction that is self-limiting, including pain, swelling and redness over the affected site, which usually resolves within 24 hours.
“Larger local reactions (swelling of more than 10cm) can take up to a week to fully subside.”
Dr Tan from TTSH said that most patients who suffer allergic reactions frequently have skin symptoms such as itch, flushing, wheals, eye or lip swelling.
However, if there is toxic envenomation, it usually results in damage to the internal organs and requires blood investigations to diagnose and monitor.
“It is difficult to predict if an insect sting will be uneventful (apart from pain and minor swelling at the sting site) or whether a reaction will develop.
“Therefore, individuals who have been stung should be vigilant for any evolving signs or symptoms that might suggest a reaction.
“It is advisable they stop what they are doing immediately and move to an area where help is readily available, should any reaction develop,” Dr Tan added.
WHEN TO GET MEDICAL AID OR CALL FOR AN AMBULANCE
- Seek medical attention early when one has been stung multiple times
- Consult a general practitioner if there are signs of infection over the affected site, for example, increasing pain, swelling, redness and fever
- People who have been stung should also be aware that serious symptoms might not show up straight away
- Get medical attention when there are signs of anaphylaxis — swelling of the tongue or throat leading to hoarse voice or difficulty swallowing, difficulty breathing, vomiting, diarrhoea or abdominal pain, rapid heart rate, confusion or collapse
- Anaphylaxis symptoms occur early within minutes to a few hours after being stung, while toxic envenomation can have a delayed onset after 24 to 48 hours
Dr Tang said that there is no antidote to reverse the effects of venom.
People who get emergency help at hospitals will be assessed for how severe the reaction is and whether there is any immediate threat to life, the doctors said.
Treatment ranges from removing stingers to getting patients to take anti-histamines and corticosteroids (anti-inflammatory medication).
Patients will be observed for six hours and discharged if they have no symptoms, Dr Tang added.
For cases of toxic envenomation, supportive care is the main treatment.
“(These patients) will be managed in the intensive care unit for organ support till recovery. For example, dialysis for kidney failure, medications to support blood pressure.”
