Patients with bites and stings from arthropods are not uncommon encounters at outpatient and emergency departments globally. Patients often come with severe pain and body swelling, with or without difficulty breathing following multiple bee stings. However, bites and stings usually cause local pain, swelling, and reddening. Treatment is no more than applying an ice pack. If the sting or bite is associated with itching, an antihistamine often suffices. Some people are allergic to the saliva of some of the arthropods. So, they may need epinephrine injections to prevent severe hypersensitivity reactions (anaphylactic shock).
Arthropods represent about 80% of all animals on earth. In the group are two classes that are of biological importance to humans – insects and arachnids. What distinguishes the two classes is beyond the scope of today’s article. Insects that bite are mosquitoes, kissing bugs, lice, flies, fleas, and midges. Those that sting include wasps, hornets, and bees. Arachnids that pose a threat to humans are spiders, ticks, scorpions, and mites.
Most insect and arachnid bites and stings only cause self-limiting local pain and swelling. However, a few of them can cause severe allergic reactions. A few others act as vectors for some of the most notorious human diseases.
Ticks carry microorganisms that cause Lyme disease; Rocky Mountain spotted fever: relapsing fever, anaplasmosis, babesiosis, and tularaemia.
Mosquitoes carry organisms responsible for malaria, yellow fever, dengue fever: West Nile virus, equine encephalitis, chikungunya, and Zika virus.
The trypanosomes residing in kissing bugs cause Chagas disease, while those in tsetse flies cause African sleeping sickness. Flies are also responsible for tularaemia, bartonellosis, loiasis, and leishmaniasis.
Fleas spread germs for plague, tularaemia, and murine typhus. Body lice cause epidemic typhus and relapsing fever.
Besides local pain and swelling, several bites and stings may lead to weakness, confusion, difficulty breathing, fainting, vomiting and diarrhoea. Some people may develop kidney failure and cardiac arrest, and death due to severe hypersensitivity reactions.
A few spider bites lead to headaches and myalgia (muscle pains). Black widow spider bites typically cause intense burning with muscle spasms on the abdomen, back, and limbs followed by sweating, vomiting, and high blood pressure.
The clues to a diagnosis lie in the history and physical examination. We only conduct laboratory tests if we suspect any of the above diseases.
It is prudent to avoid bites and stings. In endemic regions, use repellents, wear long sleeves and trousers. Put the screen in the windows and doors. Sleep in insecticide-treated mosquito nets.
After a bite or sting, apply ice or cold packs. Treat any localised swelling or pain and itching with steroid creams or antihistamines. We reserve oral steroids and antibiotics for selected scenarios.
If you develop a hive or severe hypersensitivity reaction, immediately call your doctor for urgent help.
Do not scratch the bite or stung areas – you risk spreading the insect or spider saliva and increasing the pain, swelling, or any local reaction.
It’s noteworthy that spiders only bite when trapped. Their bites heal without any intervention. However, in a few cases, you may need a tetanus toxoid vaccine, analgesics, muscle relaxants, or antivenom in case of a black widow spider bite.