Insect sting reactions can be classified as immediate or delayed based upon their timing. Reactions can also be toxic, or allergic. A toxic reaction is due to compounds in the venom itself acting on cells and tissues of the body. A true allergic response is a result of the immune system making specific allergic antibodies (IgE) to components of the insect venom, leading - with exposure - to the generation and release of a variety of chemicals such as histamine that act on surrounding tissue to cause the symptoms associated with allergic reaction.
Immediate reactions are those reactions occurring within minutes to hours of a sting and can be further divided into local, large local, anaphylactic and toxic reactions. Immediate local reactions are often considered the "normal reaction." Signs and symptoms of immediate localized reactions are limited to the area of the sting site. Local reactions can occur in individuals who are not insect allergic.
Signs and symptoms may consist of:
- mild itching that may last for several hours
Reactions occurring more than four hours after a sting are classified as delayed reactions. There have been isolated reports of serum sickness-like syndromes occurring about a week after a sting. Other unusual reactions that have been reported in association with insect stings include Guillain-Barre syndrome, glomerulonephritis, myocarditis, vasculitis and encephalitis. Signs and symptoms may include:
- general discomfort
- joint pain
- pain or partial paralysis of extremities (hands, arms, feet, and legs)
- kidney pain
- chest pain (angina)
- headache, dizziness, loss of consciousness
Large Local Reactions
Large local reactions are characterized by redness and swelling that extends from the sting site over a large surrounding area. These reactions often peak within 48 to 72 hours and last up to 10 days. They may be accompanied by fatigue, low-grade fever, mild nausea, and discomfort and are often misdiagnosed as cellulitis.
Anaphylaxis is the most severe insect sting reaction. This reaction, involving multiple organ systems at the same time, most often begins within minutes of the sting although it can occasionally begin an hour or so later. If an anaphylactic reaction is suspected, give injectable epinephrine and an antihistamine (if available) and call 911 immediately. Signs and symptoms may consist of:
- flushing, itching
- sneezing, runny nose
- nausea, vomiting, diarrhea
- abdominal cramping
- heart irregularities
- swelling in the throat
- severe trouble breathing
- drop in blood pressure (hypotension)
- loss of consciousness
In the event of a sting from a poisonous spider or insect; or multiple, simultaneous stings from otherwise non-poisonous insects (as might be the case when a nest is disturbed, or when Africanized honeybees are involved); a toxic reaction may result. Toxic reactions are not caused by an allergic response, but rather by the effects of venom that acts as a poison. Local and toxic reactions can be seen in individuals who are not insect sting allergic, although some patients who experience toxic reactions can become allergic to insect venom later.Symptoms of a toxic reaction vary depending on the toxicity of the venom of the insect or spider, the amount of venom injected, and the individual's tolerance for that particular venom. Signs and symptoms may consist of:
- rapid swelling at the site of the sting
- muscle spasms
- fainting (syncope)
Usually, symptoms lessen or go away within 48 hours. Hives and shortness of breath may occur in an allergic reaction, but not in a toxic reaction. Though it is possible to have both a toxic reaction and an allergic reaction at the same time, this rarely occurs. A toxic reaction can be life-threatening and may lead to heart problems, shock and death.
If a toxic reaction is suspected, call 911, or seek professional medical attention immediately.