181: Arthropod Bites and Stings Flashcards
What are the medically significant classes of nonaquatic arthropods?
- Arachnida
- Chilopoda
- Diplopoda
- Insecta
What are the key histopathological features observed in the acute phase of arthropod bites?
- Superficial and deep, perivascular, and interstitial inflammatory infiltrate: characteristically wedge shaped
- Mixed infiltrates with an abundance of lymphocytes and eosinophils
- Neutrophils predominate in fleas, mosquitoes, fire ants, and brown recluse spiders
- Spongiosis may be present
- Possible progression to vesicle formation or epidermal necrosis
What are the treatment principles for managing arthropod bites?
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Local wound care:
- Cleanse the wound
- Remove any remaining arthropod parts
-
Patient discomfort management:
- Ice packs
- Topical corticosteroids and antipruritics
- Injection of local anesthetics
- Systemic analgesics (less frequently)
-
Supportive measures:
- Address systemic toxic and allergic reactions, including anaphylaxis
- Antibiotics for secondary infection
- Tetanus prophylaxis for bites from several terrestrial arthropod species
- Antivenom for severe envenomation (e.g., black widow spider)
- Desensitization immunotherapy for documented hypersensitivity
What distinguishes the class Arachnida from other arthropods?
- Lack of wings or antennae
- Presence of 4 pairs of legs and 2 body segments
- Note: Larval ticks, which only have 3 pairs of legs, are an exception to this rule.
What are the clinical findings associated with bites from the Latrodectus genus (widow spiders)?
- Often painful
- Usually result in mild dermatologic manifestations
- First 30 minutes: localized erythema, piloerection, and sweating
- Possible numbness or aching pain shortly after
- Urticaria and cyanosis may occur at the bite site
- Black widow venom contains the neurotoxin α-latrotoxin, which causes an irreversible release of acetylcholine at motor nerve endings.
A patient presents with a painful bite and localized erythema, piloerection, and sweating within 30 minutes. What is the likely culprit, and what is the mechanism of the venom?
The likely culprit is a black widow spider (Latrodectus genus). The venom contains α-latrotoxin, which opens ion channels at presynaptic nerve terminals, causing an irreversible release of acetylcholine at motor nerve endings and catecholamines at adrenergic nerve endings.
What are the three genera of spiders in the US whose bites are toxic to humans?
- Latrodectus
- Loxosceles
- Tegenaria
What is the significance of the black widow spider in terms of envenomation treatment?
- Antivenom is required for severe envenomation from the black widow spider.
- Awareness of potential arthropod-borne illnesses spread by each species is crucial.
What are the common sites where widow spider webs are typically found?
- Corners of doors and windows.
- Underneath woodpiles.
- In garages and sheds.
- On the undersides of eaves.
- Around outdoor toilet seats, leading to bites on or near the genitalia.
What are the characteristics of the Southern black widow spider?
- Most common and notorious widow spider in the US.
- Found in all but the most northern parts of the US.
- Often black in color with a red hourglass-shaped marking on its abdomen.
What is the role of desensitization immunotherapy in the management of arthropod bites?
- It is used for individuals with documented hypersensitivity to specific arthropod bites, helping to reduce allergic reactions upon subsequent exposures.
What are the common clinical findings associated with a brown recluse spider bite?
- Vary from mild local reactions to severe ulcerative necrosis (necrotic arachnidism).
- Transient erythema with central vesicle or papule.
- Hallmark: “red, white, and blue” sign, characterized by:
- Central violaceous area surrounded by a rim of blanched skin.
- Further surrounded by a large asymmetric erythematous area.
- Initial wound may progress to necrosis, usually beginning 2 to 3 days after the bite, with eschar formation occurring between the fifth and seventh days.
- May mimic pyoderma gangrenosum or erythema migrans of Lyme disease.
What management strategies are recommended for brown recluse spider bites?
- General treatment measures include:
- Cleansing the wound.
- Cold compresses.
- Analgesics for pain relief.
- Antibiotics to reduce secondary bacterial infection.
- Avoid warm compresses and strenuous exercise.
- Surgical excision and reconstruction may be necessary for necrotic wounds that heal slowly, sometimes over many months.
What are the clinical findings associated with a Tegenaria agrestis (hobo spider) bite?
- Local cutaneous effects can range from mild to serious, similar to those caused by the brown recluse.
- Initial bite is often painless.
- Induration and paresthesia occur within 30 minutes.
- A large erythematous area may form around the site.
- Vesicles can appear, often during the first 36 hours.
- Eschar may follow in severe cases, with necrosis and sloughing of the underlying tissue.
What are the common symptoms and management for tarantula bites?
- Common symptoms include mild local reactions, but more serious reactions can occur due to urticating hairs on the spider’s abdomen.
- When threatened, tarantulas may rub their back legs together, flicking hairs that can embed in skin or eyes, causing:
- Mild local pruritus to granulomatous reactions.
- Ocular sequelae such as conjunctivitis and keratouveitis.
- Management includes:
- Treating cutaneous reactions with topical corticosteroids.
- Ocular involvement requires ophthalmologic evaluation.
A patient in the Midwest presents with a necrotic ulcer and a ‘red, white, and blue’ sign. What spider is responsible, and what is the primary toxin involved?
The spider responsible is the brown recluse spider (Loxosceles reclusa). The primary toxin is sphingomyelinase D, which triggers a proinflammatory response and causes tissue destruction.
A patient develops necrotic arachnidism after a spider bite. What spider is most likely responsible, and what are the hallmark clinical findings?
The spider is likely the brown recluse spider (Loxosceles reclusa). Hallmark findings include the ‘red, white, and blue’ sign with central violaceous area, blanched skin, and surrounding erythema.
A patient develops severe systemic symptoms, including seizures and acute renal failure, after a spider bite. What spider is responsible, and what is the treatment?
The spider is likely a black widow spider (Latrodectus genus). Treatment includes intravenous calcium gluconate, narcotic analgesics, and antivenom if necessary.
A patient presents with a painful bite and a gray herringbone pattern on the spider’s abdomen. What spider is responsible, and what are the clinical findings?
The spider is the hobo spider (Tegenaria agrestis). Clinical findings include induration, paresthesia, and erythema, with possible necrosis and sloughing of tissue.
A patient develops a granulomatous reaction after handling a tarantula. What is the cause, and how should it be managed?
The cause is urticating hairs from the tarantula’s abdomen. Management includes topical corticosteroids and ophthalmologic evaluation if ocular involvement occurs.
A patient develops a necrotic lesion after a spider bite in the Pacific Northwest. What spider is responsible, and how does it differ from the brown recluse?
The spider is the hobo spider (Tegenaria agrestis). Unlike the brown recluse, it has a gray herringbone pattern on its abdomen and is more common in the Pacific Northwest.
A patient develops a necrotic lesion after a spider bite in the Midwest. What spider is responsible, and what is the primary toxin involved?
The spider is the brown recluse spider (Loxosceles reclusa). The primary toxin is sphingomyelinase D.
What are the common symptoms associated with a brown recluse spider bite?
Common symptoms include:
- Agonizing crampy abdominal pain
- Muscle spasms
- Headache
- Paresthesias
- Nausea and vomiting
- Hypertension
- Lacrimation and salivation
- Seizures and tremors
- Acute renal failure
- Paralysis (rare)
- Death (uncommon)
What is the hallmark sign of a Loxosceles spider bite?
The hallmark sign is the “red, white, and blue” sign:
- Central violaceous area surrounded by a rim of blanched skin
- Further surrounded by a large asymmetric erythematous area
What are the management strategies for a brown recluse spider bite?
Management strategies include:
1. General treatment measures:
- Cleansing the wound
- Cold compresses
2. Analgesics for pain relief
3. Antibiotics to prevent secondary bacterial infection
4. Avoid warm compresses and strenuous exercise
5. Surgical excision and reconstruction for necrotic wounds that heal slowly
What are the clinical findings associated with a Tegenaria agrestis bite?
Clinical findings include:
- Local cutaneous effects ranging from mild to serious
- Initial bite is often painless
- Induration and paresthesia within 30 minutes
- Large erythematous area may form around the site
- Vesicle formation often occurs during the first 36 hours
- Eschar may follow in severe cases, with necrosis and sloughing of underlying tissue
What systemic symptoms may arise from a Tegenaria agrestis bite?
Systemic symptoms may include:
- Severe headache (can persist for up to 1 week)
- Fatigue
- Nausea and vomiting
- Diarrhea
- Paresthesias
- Memory impairment
- Rarely, death due to severe systemic effects, including aplastic anemia
What is the primary cause of necrotic arachnidism in the Pacific Northwest of the US?
The primary cause of necrotic arachnidism in the Pacific Northwest is the Tegenaria agrestis, commonly known as the hobo spider or aggressive house spider.
What are the potential complications of a brown recluse spider bite?
Potential complications include:
- Severe ulcerative necrosis (necrotic arachnidism)
- Renal failure
- Hemolytic anemia
- Hypotension
- Disseminated intravascular coagulation (rare but serious)
What are the characteristics of tarantulas that may cause reactions in humans?
Tarantulas can cause reactions due to their urticating hairs, which may become embedded in the skin or eyes, leading to:
- Mild local pruritus
- Granulomatous reactions
- Ocular sequelae such as conjunctivitis and keratouveitis
What is the recommended management for ocular involvement due to tarantula hairs?
Ocular involvement due to tarantula hairs requires an ophthalmologic evaluation for appropriate treatment.
What is the significance of the L. mactans antivenom in the treatment of widow spider bites?
L. mactans antivenom (equine serum) appears to be effective for treating widow spider bites, but benefits should be weighed against the potential for allergic reactions to the antivenom.
What are the clinical findings associated with scorpion stings?
- Immediate, sharp, burning pain
- Numbness extending beyond the sting site
- Regional lymph node swelling
- Ecchymosis and lymphangitis (less common)
- Symptoms of neurotoxin exposure: muscle spasticity, nystagmus, blurred vision, slurred speech, excessive salivation, respiratory distress, pulmonary edema, and myocarditis
- Infants and young children are at greatest risk for serious complications.
What is the management protocol for mild scorpion envenomations?
- Symptomatic treatment is required, including:
- Analgesics
- Local ice compresses
- Hospitalization for close monitoring of respiratory, cardiac, and neurologic status is necessary for children.
What are the symptoms of neurotoxin exposure?
Symptoms include muscle spasticity, nystagmus, blurred vision, slurred speech, excessive salivation, respiratory distress, pulmonary edema, and myocarditis.
Who is at greatest risk for serious complications from neurotoxin exposure?
Infants and young children are at greatest risk for serious complications.
What is the management protocol for mild scorpion envenomations?
Symptomatic treatment is required, including analgesics and local ice compresses. Hospitalization for close monitoring of respiratory, cardiac, and neurologic status is necessary for children.
What is the treatment of choice for severe scorpion envenomations?
The treatment of choice is specific antivenom.
What are the two families of ticks and their significance?
Ixodidae (hard ticks) are responsible for the majority of tick-related diseases, while Argasidae (soft ticks) are less common but still significant.
What diseases are transmitted by ticks?
Diseases include Lyme disease, Ehrlichiosis, Babesiosis, Rocky Mountain spotted fever, Colorado tick fever, Q fever, and Tularemia.
What are the clinical findings associated with tick bites?
Findings include painless bites, possible granuloma formation, hypersensitivity reactions, localized swelling and erythema, and tick paralysis.
What is tick paralysis?
Tick paralysis is a potentially lethal complication caused by a neurotoxin in tick salivary secretions, leading to acute ascending lower motor neuron paralysis.
What is the recommended management for tick bites?
Inspect skin for ticks and remove them before they begin feeding. If a tick has inserted its hypostome, it must be forcibly removed.
What are the risks associated with antibiotic prophylaxis for tick bites?
The risks of antibiotic therapy must be weighed against the risks of vector-borne illnesses in the region.
What are the primary clinical findings associated with a scorpion sting?
Immediate, sharp, burning pain, numbness, regional lymph node swelling, and symptoms of neurotoxin exposure.
What are the characteristics of the scorpion species Centruroides exilicauda?
It is potentially fatal and has a small spine at the base of the stinger.
What are the key characteristics of centipedes?
Centipedes have one pair of legs per body segment, are nocturnal carnivores, and possess poisonous claws.
What distinguishes millipedes from centipedes?
Millipedes have two pairs of legs per body segment, feed on plant matter, and do not bite or sting.
What are the main families within the order Diptera?
Families include Culicidae (mosquitoes), Simuliidae (black flies), Ceratopogonidae (biting midges), Tabanidae (horse flies), and Psychodidae (sandflies).
What are the clinical implications of mosquito bites?
Mosquito bites can lead to pruritic wheals and lesions, and they are vectors for diseases like malaria and dengue.
What is cutaneous myiasis?
Cutaneous myiasis is caused by fly larvae deposited into skin or wounds, treated by local surgical excision and cleansing.
What is the primary treatment for pruritus caused by insect bites?
A short course of topical steroids and systemic antihistamines is recommended.
What are the characteristics of the Coleoptera order?
Coleoptera is the largest order with over 300,000 species of beetles, many of which can cause blistering.
What is the prophylactic use of ebastine?
Ebastine can be used prophylactically as a single 10-mg dose to reduce wheal formation and subsequent pruritus.
What are the characteristics of the Coleoptera order?
The Coleoptera order is the largest in the animal kingdom with over 300,000 species of beetles. They generally do not bite or sting humans, but many contain chemicals that can cause blistering.
What is the most well-known beetle causing blister beetle dermatosis?
The most well-known beetle causing blister beetle dermatosis is Lytta vesicatoria (Spanish fly), which contains the chemical cantharidin that causes vesiculation of the skin.
What are the clinical implications of the Reduviidae family?
The Reduviidae family, also known as kissing bugs or assassin bugs, has a triangular shape on their back formed by the meeting of the membranous wings. They possess piercing mouthparts used to feed on blood and are significant vectors for Trypanosoma cruzi, the causative agent of Chagas disease.
What are the common reactions to Cimex lectularius (bedbugs) bites?
Reactions to bedbug bites typically include wheals and papules, often with a small hemorrhagic punctum at the center.
What is the significance of the Tungidae family in relation to human health?
The Tungidae family includes the tropical flea species Tunga penetrans (sand flea), which is the etiologic agent of tungiasis.
What is the likely diagnosis for multiple erythematous papules on the feet after traveling to a tropical region?
The likely diagnosis is tungiasis, caused by the penetration of the adult female flea Tunga penetrans into the skin.
How should tungiasis be treated?
Treatment includes surgical excision, cryotherapy, or topical agents, along with tetanus prophylaxis.
What is the likely cause of a row of three bites (‘breakfast, lunch, and dinner’)?
The likely cause is bedbug bites (Cimex lectularius).
How should bedbug bites be managed?
Management includes symptomatic treatment with topical corticosteroids and oral antihistamines.
What insect is responsible for Chagas disease?
The insect is the kissing bug (Triatoma species).
How is Chagas disease transmitted?
Chagas disease is transmitted when the victim scratches infected feces into the wound.
What is the likely cause of a vesicular lesion after crushing a beetle against the skin?
The likely cause is blister beetle dermatosis, caused by the chemical cantharidin.
What is the management for blister beetle dermatosis?
Management includes local wound care.
What is the primary treatment for pruritus caused by insect bites?
A short course of topical steroids and systemic antihistamines is recommended to control pruritus.
What are the clinical implications of bites from the kissing bug?
Kissing bugs can act as vectors for Trypanosoma cruzi, the causative agent of Chagas disease.
How can one prevent vesiculation after exposure to beetles like Paederus species?
Washing of affected areas immediately after exposure may help prevent vesiculation.
What is the typical feeding behavior of bedbugs?
Bedbugs are nocturnal feeders that usually complete their blood meal in a matter of minutes.
What are the common sites of attachment for the sand flea (Tunga penetrans)?
The common sites of attachment include the feet, particularly the plantar surface.
What is the recommended treatment for hypersensitivity reactions to insect bites?
Treatment typically includes topical corticosteroids and oral antihistamines.
What is the role of the rat flea in public health?
The rat flea, particularly Xenopsylla cheopis, transmits bubonic plague and is a vector for endemic typhus.
What are the clinical manifestations of Hymenoptera stings?
Immediate burning and pain, followed by intense local erythematous reaction with swelling and urticaria.
What management strategies are recommended for mild local cutaneous reactions to Hymenoptera stings?
Local cleansing, application of ice, and oral diphenhydramine.
What are the treatment options for imported fire ant stings?
Systemic antihistamines, topical preparations containing menthol, and systemic steroids for severe reactions.
What is the significance of the Lymantria dispar caterpillar in relation to lepidopterism?
Lymantria dispar is a well-known cause of erucism, producing pruritic dermatitis characterized by multiple erythematous papules.
What are the potential symptoms caused by the Megalopyge opercularis caterpillar?
Intensely painful sting and a characteristic train-track pattern of purpura.
What is the species responsible for a painful sting and a ring-shaped lesion?
The species is the imported fire ant (Solenopsis invicta).
What immediate treatment should be administered for severe anaphylaxis after a bee sting?
Immediate treatment includes subcutaneous or intramuscular epinephrine.
What is the likely cause of pruritic dermatitis after contact with a caterpillar?
The likely cause is erucism, caused by contact with caterpillar hairs.
What is the management for a painful sting and train-track pattern of purpura?
Management includes systemic antihistamines and topical corticosteroids.
What is the mechanism of the lesion caused by fire ant stings?
The lesion is caused by solenopsin D in the fire ant venom.
What immediate steps should be taken after a Hymenoptera sting with systemic symptoms?
Immediate steps include removing the stinger and administering epinephrine.
What is the cause of pruritic dermatitis after contact with a gypsy moth caterpillar?
The cause is erucism from the caterpillar’s hairs.
What is the mechanism of the lesion caused by wasp stings?
The lesion is caused by venom injected through the wasp’s ovipositor.
What are the symptoms associated with Lymantria dispar exposure?
Cutaneous contact with hairs produces a pruritic dermatitis characterized by multiple erythematous papules.
What are the treatment options for reactions caused by lepidopterism?
Systemic antihistamines, topical preparations containing menthol, and systemic steroids for severe reactions.
What is the significance of carrying a preloaded epinephrine-filled syringe for individuals with Hymenoptera hypersensitivity?
It is crucial for emergency self-administration in case of anaphylactic reactions.
What are the potential consequences of not removing a honeybee stinger promptly?
If not removed swiftly, the stinger can continue to pump venom into the skin.
What are the common reactions associated with the sting of the Megalopyge opercularis?
Intense pain from the sting and a characteristic train-track pattern of purpura.
What preventive measures can be taken to avoid Hymenoptera stings?
Avoid walking barefoot or in sandals along beaches.
What neurotoxin is contained in black widow venom?
Black widow venom contains the neurotoxin latrotoxin.
What is the hallmark finding of a brown recluse spider bite?
The hallmark finding is a necrotic ulcer that may develop at the site of the bite.
What type of bite presents with immediate, sharp, burning pain followed by numbness?
A bite from a scorpion presents with immediate, sharp, burning pain.
What is the treatment of choice for severe envenomation from scorpions?
The treatment of choice is antivenom.
How can hard ticks be distinguished from other mites?
Hard ticks can be distinguished by the presence of a barbed hypostome.
What unique behavior do hard ticks exhibit when searching for a suitable host?
Hard ticks exhibit a behavior called questing.
What are some diseases transmitted by ticks?
Diseases transmitted by ticks include Lyme disease, Rocky Mountain spotted fever, and others.
What are the common names and species that act as vectors for onchocerciasis and tularemia?
Vectors for onchocerciasis are blackflies (Simulium spp.) and for tularemia are ticks.
What is the most effective repellent for all biting flies?
The most effective repellent is DEET (N,N-diethyl-3-methylbenzamide).
What is the recommended prevention strategy for tick bites?
The recommended prevention strategy includes wearing appropriate clothing.
What is the mechanism of action of certain toxins?
They act by opening ion channels at presynaptic nerve terminals, causing an irreversible release of acetylcholine at motor nerve endings and norepinephrine at adrenergic nerve endings.
What is the hallmark finding of a brown recluse spider bite?
The hallmark finding is a necrotic ulcer with a characteristic fiddle-shaped marking on the skin.
What type of bite presents with immediate, sharp burning pain followed by numbness and regional lymph node swelling?
A bite from a scorpion presents with immediate, sharp, burning pain followed by numbness extending beyond the sting site with regional lymph node swelling.
What is the treatment of choice for severe envenomation from scorpions?
The treatment of choice is antivenom administration.
How can hard ticks be distinguished from other mites?
Hard ticks can be distinguished by the presence of a barbed hypostome, which is inserted into the skin for feeding.
What unique behavior do hard ticks exhibit when searching for a suitable host?
They exhibit a unique behavior called questing.
List some diseases transmitted by ticks.
Diseases transmitted by ticks include:
1. Lyme disease
2. Rocky Mountain spotted fever
3. Anaplasmosis
4. Ehrlichiosis
5. Babesiosis
6. Tick-borne encephalitis
7. Tularemia
What are the distinguishing features of Insecta compared to other arthropods?
Insecta can be differentiated by the presence of:
1. Three body segments (head, thorax, abdomen)
2. Three pairs of legs
3. One pair of antennae
4. Wings (in many species)
What are the vectors for onchocerciasis and tularemia?
Black flies (Simulium species) are vectors for onchocerciasis and ticks (various species) are vectors for tularemia.
What is the common name for the species that transmits Old World leishmaniasis?
The common name is Phlebotomus (sand flies).
What is the common name for the species that transmits New World leishmaniasis and Carrión disease?
The common name is Lutzomyia (sand flies).
What is the common name for the species that transmits Loa loa filariasis and tularemia?
The common name is Chrysops (tabanid flies).
What condition may be caused by the deposition of fly larvae into intact skin or open wounds?
The condition is called myiasis, and it is best treated by removal of the larvae.
What are the reactions to mosquito bites?
Reactions are typically wheals and papules, often with a small hemorrhagic punctum at the center.
What is the common name for the species that acts as vectors for Trypanosoma cruzi?
The common name is kissing bugs (Triatominae).
What insect has a triangular shape on its back formed by the meeting of the membranous wings?
The insect is the wasp.
What happens to a honeybee after it stings?
A honeybee dies after stinging because it eviscerates itself to expel its paired venom sacs.
What is a well-known cause of erucism or caterpillar dermatitis?
A well-known cause is the Lonomia obliqua caterpillar, which presents with multiple erythematous papules often arranged in linear streaks.
What preventive measures can be taken to avoid spider bites?
Preventive measures include:
1. Wearing gloves while working in crawl spaces, garages, or basements.
2. Shaking out clothing and footwear before putting them on.
3. Wearing appropriate clothing with good coverage and avoiding rubbing against high brush and grass.
What is the most effective repellent for all biting flies, including mosquitoes?
The most effective repellent is DEET (N,N-diethyl-3-methylbenzamide), with concentrations of 10% to 30% providing adequate protection.
What is the recommended use of permethrin for tick prevention?
Permethrin can be sprayed on or impregnated into clothing and fabrics, including tents, bed nets, and sleeping bags, and remains effective through several wash cycles.
What should be done to maximize protection against ticks?
To maximize protection, a combined use of permethrin-treated clothing and DEET applied to the skin is recommended.
