Spider bites can cause one or several rashes or lesions with fluid-filled blisters called bullae. However, other insect bites can too. And although MRSA looks very similar, it typically causes multiple rashes with small, pus-filled bumps called pustules.
This article explains the key differences between MRSA and spider bites, as well as other common bug bites. It also describes treatments and complications of MRSA and when it is time to see a healthcare provider.
Signs and Symptoms
Spider bites and MRSA are sometimes particularly difficult to tell apart, especially in the early stages when symptoms are just starting to emerge.
This is why it is important to monitor any suspected spider bite for changes in its appearance or numbers. It may not end up being a spider bite at all. And if it’s MRSA, fast treatment is needed.
Number of Bumps
While spider bites tend to be solitary, it is possible to get a few separate bites at once.
MRSA may start with one or several bumps, but the rash almost invariably grows in size and amount, causing a cluster of pustules that can merge into a larger pus-filled mass.
Appearance of Blisters
Spider bite symptoms can vary from person to person as well as by species. Typically, spider bites result in fluid-filled blisters (bullae) that can burst and form open ulcers.
If you get several in the same spot, you may experience a purplish discoloration of the skin with swelling, pain, warmth, and hardening.
In contrast, MRSA causes pustules. These bumps form when the immune system sends white blood cells to fight the infection.
This causes inflammation (swelling) at the site of infection and death to nearby tissues. Pus, the collection of the dead bacteria, white blood cells, and tissues, then fills the bumps.
These complications, some of which are life-threatening, further underscore the importance of telling the two conditions apart and getting treated quickly, if needed.
Complications of Spider Bites
In North America, four of the most venomous spiders are the black widow, brown recluse, hobo spider, and armed spider. The venoms of these four spiders are neurotoxic, meaning that they attack the nervous system.
Most cases cause headaches, lethargy, irritability, muscle pain, tremors, and impaired coordination.
But, in severe cases, potentially life-threatening complications can rapidly develop, including:
Tachycardia (abnormally rapid heartbeats) Bradycardia (abnormally slowed heartbeats) Acute renal failure (sudden kidney failure) Rhabdomyolysis (the potentially deadly breakdown of muscles) Stroke (typically caused by a severe spike in blood pressure and a spontaneous brain bleed) Anaphylaxis (a potentially life-threatening, whole-body allergy)
Complications of MRSA
In most cases, MRSA causes a mild skin infection. If left untreated, however, MRSA can cause complications affecting multiple organ systems.
This occurs when the bacteria disseminate beyond the skin through blood and lymph vessels, causing a systemic (whole-body) infection. Some of the possibly life-threatening complications include:
Pneumonia (an infection of the lung) Endocarditis (an infection of the heart) Meningitis (an infection of the lining of the brain and spinal cord) Osteomyelitis (a bone infection) Septic arthritis (joint pain inflammation caused by a bacterial infection) Sepsis (the body’s extreme overreaction to an infection)
When to Call a Healthcare Provider
Knowing the difference between a spider bite and MRSA can help you respond appropriately, particularly in emergency situations. As a rule of thumb, if you’re not sure what your blister or rash is but are worried, have it checked out.
Call 911 or seek emergency medical treatment if you experience any of the following after getting or finding what you think might be a bite of any kind:
Severe pain, swelling, or redness at the bite siteLightheadedness, dizziness, or faintingSevere muscle or abdominal crampsNausea or vomitingDifficulty breathingTrouble swallowingHigh feverDisorientationLoss of coordinationRapid, slowed, or irregular heartbeatsExtreme muscle stiffness or spasticitySeizures
Treatment
Spider bites often require no treatment unless you have a severe reaction. The same cannot be said for MRSA because it can be so easily spread.
If you have a small skin eruption caused by MRSA, your healthcare provider may make an incision to drain it.
Until the wound is fully healed, you need to keep it covered and take standard precautions to avoid infecting others. Wash your hands frequently and avoid the shared use of clothing, towels, and personal care items.
Not all MRSA infections need to be treated with antibiotics. And by definition, MRSA is resistant to some of these drugs. Still, there are several that can be used alone or in combination to treat the infection.
Antibiotics with demonstrated activity against MRSA include:
Bactrim (trimethoprim-sulfamethoxazole) Doxycycline Minocin (minocycline) Clindamycin Vancocin (vancomycin) Teicoplanin Zyvox (linezolid) Synercid (quinupristin/dalfopristin) Cubicin (daptomycin) Teflaro (ceftaroline) Tygacil (tigecycline)
The drugs may be given in orally in pill form (to be taken by mouth). Severe cases may need to be treated intravenously (by delivering the drugs into a vein).
If placed on the appropriate antibiotics, the symptoms of MRSA will usually resolve within seven to 14 days.
Signs MRSA Treatment Is Not Working
With that said, certain MRSA strains are harder to treat and may not respond as quickly or as well. In such cases, you would need to see a healthcare provider if:
The infection does not improve after three or four days of antibiotic therapy. The rash begins to spread or worsen. You develop a fever, or your fever get worse. The symptoms return soon after antibiotic therapy is completed.
Summary
It can be hard to tell the difference between a spider bite and MRSA. The most important clue may be the kind of blister that forms. MRSA blisters contain pus and spider bites contain fluid. Eventually, MRSA boils often expand and spread.
MRSA is an antibiotic-resistant bacteria that can be found in lots of community settings. If it’s not treated, it can enter the bloodstream and cause life-threatening infections.
If you’re not sure whether you have been bitten by a bug or you have a MRSA infection, the best thing to do is visit your healthcare provider for tests.
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