Ectoparasite Infestations and Arthropod Bites and Stings

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Ectoparasite Infestations and Arthropod Bites and Stings:

Ectoparasite Infestations and Arthropod Bites and Stings


Introduction Ectoparasites are arthropods or helminths that infest the skin or hair of other animals, from which they derive sustenance and shelter. They may penetrate beneath the surface of the host or attach superficially by their mouthparts and specialized claws. These organisms damage their hosts by inflicting direct injury, eliciting a hypersensitivity reaction, inoculating toxins or pathogens, and inciting fear. The main medically important ectoparasites are arachnids (including mites and ticks), insects (including lice, fleas, bedbugs, and flies), pentastomes (tongue worms), and leeches.


Scabies The human itch mite, Sarcoptes scabiei , is a common cause of itching dermatosis , infesting 300 million persons worldwide. Gravid female mites that measure 0.3 mm in length burrow superficially beneath the stratum corneum , depositing three or fewer eggs per day. Nymphs mature in 2 weeks and then emerge as adults to the surface of the skin, where they mate and (re)invade the skin of the same or another host. Transfer of newly fertilized female mites from person to person occurs mainly by intimate contact and is facilitated by crowding, poor hygiene, and multiple sexual partners.


Scabies The itching and rash associated with scabies derive from a sensitization reaction directed against the excreta that the mite deposits in its burrow. An initial infestation remains asymptomatic for up to 6 weeks, and a reinfestation produces a hypersensitivity reaction without delay. Burrows become surrounded by infiltrates of eosinophils , lymphocytes, and histiocytes , and a generalized hypersensitivity rash later develops in remote sites. Immunity and associated scratching limit most infestations to <15 mites per person. Hyperinfestation with thousands of mites, a condition known as crusted scabies or Norwegian scabies , may result from glucocorticoid use, immunodeficiency, and neurologic and psychiatric illnesses that limit itching and scratching.

Treatment: Scabies:

Treatment: Scabies Permethrin cream (5%) is less toxic than 1% lindane preparations and is effective against lindane -tolerant infestations. Scabicides are applied thinly but thoroughly behind the ears and from the neck down after bathing and are removed 8 h later with soap and water. Successful treatment of crusted scabies requires preapplication of a keratolytic agent such as 6% salicylic acid and then of scabicides to the scalp, face, and ears. Repeated treatments or the sequential use of several agents may be necessary. Ivermectin has not been approved by the U.S. Food and Drug Administration (FDA) for use against any form of scabies, but a single oral dose (200 g/kg) effectively treats scabies in otherwise healthy persons; patients with crusted scabies may require two doses separated by an interval of 1–2 weeks.

Hymenoptera (WASPS, BEES, AND ANTS):

Hymenoptera (WASPS, BEES, AND ANTS) Hymenoptera: Most important venomous insect known to humans More fatalities result from stings by these insects. Three major subgroups: Apidae  includes honeybee and bumblebee Vespidae  includes yellow jackets, hornets and wasps Formicidae  ants Most of all allergic reaction reported yearly occur from vespid stings . Apids are usually docile, stinging only when provoked. Female bee is capable of stinging only once. (Male bees have no stinger). Vespid have ability to perform multiple stings.

Africanized honeybees :

Africanized honeybees Known as killer bees Now found in Texas, Arizona, California, and most of the temperate southeastern and southwestern states. Attack from these bees  massive stinging resulting in multisystem damage and death from severe venom toxicity.

Hymenoptera Venom:

Hymenoptera Venom Contain several components. Histamine is only a minor component within the venom. 50% of the venom consist of Melittin. Melittin is a known membrane-active polpeptide that can cause degranulation of basophils and mast cells. Yellow jackets venom is perhaps the most potent sensitizer.

Hymenoptera Venom: Local Reaction Toxic Reaction :

Hymenoptera Venom: Local Reaction Toxic Reaction Urticarial lesion contiguous with the sting site. Severe local reaction may involve one or more neighboring joints. If the sting involve the mouth or throat, it can produce airway obstruction. Multiple stings (Africanized bees) can lead to systemic toxic reaction. Symptoms may resemble anaphylaxis, but these pts can also develop N/V/D. They may also have HA, fever, drowsiness, involuntary muscle spasms, edema without urticaria, and convulsions. Complication  Renal / Hepatic failure, DIC, and Death

Hymenoptera Venom: Anaphylactic Reaction:

Hymenoptera Venom: Anaphylactic Reaction Can occur from a single sting or multiple stings. May range from mild to fatal and death within minutes. There is no correlation between the systemic reaction and the number of stings.

Hymenoptera Venom: Delayed Reaction:

Hymenoptera Venom: Delayed Reaction Delayed reaction appearing 5 – 14 days after the sting consists of serum sickness-like signs and symptoms. Pts can develop fever, malaise, HA, urticaria, lymphadenopathy, and polyarthritis. This reaction is believed to be immune complex-mediated.

Hymenoptera Venom: Treatment:

Hymenoptera Venom: Treatment Immediate removal of the bee stinger from the wound, is the important principle rather than the method of removal. Wash the sting site with soap and water to decrease risk of infection. Intermittently apply ice to the site to limit local reaction and delay absorption of venom. Oral antihistamines and analgesic may limit discomfort, pruritis, and decrease local reaction. If pts develop symptoms of anaphylaxis then most important agent to give is Epinepherine . Epinepherine 0.3 to 0.5mg (0.3 to 0.5 mL of 1:1000 conc.) in adults and 0.01 mg/kg in children (never more than 0.3 mg) given IM

Hymenoptera Venom: Treatment:

Hymenoptera Venom: Treatment Other treatment should include: Diphenhydramine 25 to 50 mg IV, IM or PO H2-receptor antagonists (ranitidine 50 mg IV) Methylprednisolone 125 mg Use Beta agonist nebulization if pt has evidence of bronchospasm IVF, oxygen, cardiac monitor, pulse ox. Persistent hypotension after multiple IVF bolus may require Dopamine or Epinepherine drip

Hymenoptera Venom: Disposition:

Hymenoptera Venom: Disposition Pts who develop severe systemic reactions should be admitted monitored for potential cardiac, bleeding, renal or neurologic complications. Skin tests and RASTs (radioallergosorbent test) are not reliable in determining which patients are at risk in developing future systemic reactions.

Hymenoptera Venom: Disposition:

Hymenoptera Venom: Disposition Every patient who has had a systemic reaction should be provided with an insect sting kit containing premeasured epinepherine and be carefully instructed in its use. The physician should stress that the patient must inject the epinepherine at the first sign of a systemic reaction.

Ants (Formicidae) :

Ants (Formicidae) 5 known species of fire ants (Solenopsis) ( S. aurea, S. geminata, S. xyloni, S. invicta, and S. richteri ) Fire ants swarm when provoked and they may attack in numbers. Fire ants sting simultaneously in response to an alarm pheromone released A Solenopsis xyloni major worker surrounded by minor workers

Ants (Formicidae):

Ants (Formicidae) Fire ants sting result in a papule that becomes a sterile pustule in 6 to 24 hrs. Pustule can lead to localized necrosis  scarring  secondary infection. Systemic reaction (urticaria / angioedema) can also occur. Treatment includes : local wound care. Usual treatment for anaphylaxis should be initiated if there is evidence of systemic reaction.

Spiders (Araneae):

Spiders (Araneae) More than 34000 species of spiders worldwide Only few dozen produce medically significant envenomations in humans Refer to Table 194 – 3 for medically important spiders by geographic location.

Necrotic Arachnidism (Loxosceles):

Necrotic Arachnidism ( Loxosceles ) Three species : L. reclusa ( true brown recluse ) L. laeta (corner spider) L. arizonica (Arizona brown spider) – produce majority of Loxosceles bites in the US. Prefers warm and dry areas (abandon buildings / woodpiles, and cellars) L. reclusa ( true brown recluse ) One of the most common species found in the US. Definitively diagnosing a brown recluse bite is difficult. The necrotic wound that develop can resemble other unrelated arthropod species and medical disorder (i.e. Necrotizing Fascitis).

L. reclusa (true brown recluse) :

L. reclusa (true brown recluse) Brown recluse has a dark brown violin shape on the cephalothorax (the portion of the body to which the legs attach).  The neck of the violin points backward toward the abdomen.  However, what you should look at instead is the eye pattern of 6 eyes in pairs with a space separating the pairs.  Most spiders have 8 eyes in 2 rows of 4.

L. Reclusa (brown recluse):

L. Reclusa ( brown recluse) Venom includes multiple enzymes such as Hyaluronidase Alkaline phosphate 5’ –ribonucleotide phosphohydrolase Sphingomyelinase D (major enzyme responsible for necrosis.) Necrotic wounds occur by way of neutrophil activation, platelet aggregation, and intravascular thrombosis. Clinical Features: Initially pts develop mild to severe pain several hrs after the bite  Erythema and blister formation  Bluish discoloration within the first 24 hrs  Lesion may become necrotic with eschar formation in 3 to 4 days.

L. Reclusa (brown recluse): Systemic reaction :

L. Reclusa ( brown recluse): Systemic reaction Are rare in adults, however more common in children Occur in 24 – 72 hrs after the bite. Can lead to N/V, Fever/chills, arthralgias, hemolysis, thrombocytopenia, hemoglobinuria, and renal failure. DIC and Death are rare

L. Reclusa (brown recluse):

L. Reclusa ( brown recluse) If a brown recluse bite is suspected, the following labs test should be perform: CBC Basic Chemistry tests BUN / Creatinine Coagulation Profile Treatment: Supportive measure should be the initial goal (Analgesic / clean wound site). Consider using antibiotics if any s/sx of infection develop. Must have close follow – up with physician for serial evaluations of the wound.

Hobo Spider (Tegenaria agrestis) :

Hobo Spider (Tegenaria agrestis) Found in the Pacific northwest of the US They are aggressive because it bite with minor provocation. Live in moist dark areas (woodpiles/basements). They are brown with grey markings, have 7 – 14mm body length and 27 – 45mm leg span

Hobo Spider (Tegenaria agrestis) Clinical Features::

Hobo Spider (Tegenaria agrestis) Clinical Features: Present similar to that of brown recluse spider. Initial bite is painless  delay presentation Induration may occur with surrounding erythema, followed by blistering, rupture, and necrosis. HA is the most common systemic symptom, but N/V and fatigue can occur. Aplastic anemia and death are rare complications.

Hobo Spider (Tegenaria agrestis) Clinical Features::

Hobo Spider (Tegenaria agrestis) Clinical Features:

Hobo Spider (Tegenaria agrestis) Treatment::

Hobo Spider (Tegenaria agrestis) Treatment: No diagnostic test for hobo spider envenomation. No proven treatment for local or systemic complications. Surgical resection with skin grafting may be necessary after the necrotizing process is completed.

Widow Spiders (Latrodectus):

Widow Spiders (Latrodectus) Has a worldwide distribution In the US, the black widow is the most well known of the 5 Latrodectus species L. mactans, L. various, and L. hesperus are black L. geometricus are brown and L. bishopi are red. Found most often in woodpiles, basements, garages, and sheds.

Widow Spiders (Latrodectus):

Widow Spiders (Latrodectus) L. mactans are the only species that have the classic hour glass-shaped (orange/red) marking.

Widow Spiders (Latrodectus):

Widow Spiders (Latrodectus) Female spiders Large in size Body size = 1.5 cm Leg spans 4 -5 cm Bites can penetrate human skin. Become aggressive when protecting her web and eggs. Male spiders Smaller in size 1/3 the size of female Liter in color Bites cannot penetrate human skin.

Widow Spiders (Latrodectus):

Widow Spiders (Latrodectus) Most bites occur between April and October and are usually seen on the hands and forearm. Inject a highly potent venom – most active component is latrotoxin. Through a calcium – mediated mechanism, latrotoxin cause the release of acetylcholine and norepinephrine from nerve terminals.

Widow Spiders (Latrodectus) Clinical Features::

Widow Spiders (Latrodectus) Clinical Features: Most bite site, initially feels like a pinprick then quickly cause increasing local pain that then involve the entire extremity. In 1/3 of cases the initial erythema evolves into a larger “target lesion”. The presence of the target lesion , severe pain and muscle spasm is pathognomonic for widow spider bites. Pts most commonly c/o muscle cramp like spasms in large muscle groups.

Widow Spiders (Latrodectus) Clinical Features::

Widow Spiders (Latrodectus) Clinical Features: Other s/sx: HA, nausea, diarrhea, diaphoresis, photophobia and dyspnea. May experience intermittent severe pain for 24+ hours Laboratory test to confirm Latrodectus bite is not available.

Widow Spiders (Latrodectus) Treatment::

Widow Spiders (Latrodectus) Treatment: Initial Tx: Support ABC. Clean the bite site. Use Opioids and benzodiazepines to control pain and muscle spasms. The most effective tx for severe envenomation are parental opioids and Latrodectus antivenom .

Widow Spiders (Latrodectus) Treatment::

Widow Spiders (Latrodectus) Treatment: Latrodectus antivenom: Cause rapid resolution of symptoms and significantly shorten the course of illness. When given properly, pt can often be d/c form ED after a short period of observation Produced in three countries: Anti Latrodectus antivenom available in Argentina Red-backed spider antivenom available in Australia Antivenin ( Latrodectus mactans ) available in U.S.A. (1-800-396-6250) Indications, amount, and route of administration vary according to product.


Tarantulas Large hairy spiders Popular as pets Family Theraphosidae Hairs found on the abdomen and legs are use defensively


Tarantulas When threaten, they may flick some of their hair. The hair cannot penetrate human skin however can cause conjunctiva and cornea injury. Pts who are handling tarantula and present with red eye must be evaluated via Slit-Lamp to identify hairs Hairs that are identify must be surgically removed. Initiate topical steroid tx to help control inflammation. Initial bite are painful  local erythema edema  Local joint stiffness following nearby bites. (systemic sx are rare).

Scorpions (Scorpionidae):

Scorpions (Scorpionidae) World-wide distribution Highly toxic species are found in Middle East, India, North Africa, South America, Mexico, and Trinidad. In the US, only the Centruroides exilicauda (bark scorpion) possesses venom potent enough to cause systemic toxicity.

Scorpions - Centruroides exilicauda Clinical features::

Scorpions - Centruroides exilicauda Clinical features: Venom can open neuronal sodium channels and cause prolonged and excessive depolarization. Immediate onset of pain and parathesias in the stung extremity is noted and may become generalized.

Scorpions - Centruroides exilicauda Clinical features::

Scorpions - Centruroides exilicauda Clinical features: Severe Systemic cases after bite can lead to: Abnormal roving eye movements, blurred vision, pharyngeal muscle incoordination and drooling. Other s/sx: Restlessness, seizure – like activity, N/V, tachycardia, and severe agitation. Symptoms can last 24 – 48hrs without anitvenom treatment. Cardiac dysfunction, pulmonary edema, pancreatitis , bleeding d/o, skin necrosis, and occasionally death can be seen with stings from Asian and African scorpions.

Scorpions - Centruroides exilicauda Treatment::

Scorpions - Centruroides exilicauda Treatment: Initial treatment is supportive / analgesics . Centruroides-specific antivenom is only available in Arizona and is produce from goat serum. (production has been stop, only used in severe systemic toxicity cases). Scorpion antivenom directed against different species is now used and available in 10 other countries.

Reptile Bites:

Reptile Bites Approx 3 million bites and 150,000 deaths occur each year from venomous snakes in the world. Most bites occur in the warm summer months (snakes and victims are most active). In the US, mortality has improve from 25% to only <0.5% (5 – 10 deaths /year). Major venomous snakes can be divided into 3 groups : Viperidae (vipers) Elapidae Hydrophiinae (sea snakes)

Crotalinae (Pit Viper) Bites::

Crotalinae (Pit Viper) Bites: Referred to as pit vipers because of bilateral depressions or pits located midway between and below the level of the eye and the nostril With in the pit vipers, the rattle distinguishes the rattlesnake from other crotaline snakes. Pit is a heat sensor that guides strikes at warm-blooded prey or predators.

Crotalinae (Pit Viper) Bites: Venom:

Crotalinae (Pit Viper) Bites: Venom Causes the following: Local tissue injury, systemic vascular damage, hemolysis, fibrinolysis, and neuromuscular dysfunction (CN weakness / resp. failure / MS∆. Quickly alters blood vessels permeability leading to loss of plasma and blood into the surrounding tissue  hypovolemia. Activates and consumes fibrinogen and platelets, causing a coagulopathy

Crotalinae (Pit Viper) Bites: Clinical features:

Crotalinae (Pit Viper) Bites: Clinical features The severity of poisoning following a crotaline bite depend on these factor: The species and size of the snake The age and size of the victim The time elapsed since the bite Characteristics of the bite (location, depth, and number, the amount of venom injected 25% of crotaline snakebites are termed dry :venom effects do not develop.

Crotalinae (Pit Viper) Bites: Clinical features:

Crotalinae (Pit Viper) Bites: Clinical features S/Sx of a bite: One or more fang mark on the body Localized pain with progressive edema. N/V, weakness, oral numbness, tachycardia, dizziness, and muscle fasciculation. Systemic reaction will lead to tachypnea, tachycardia, hypotension, and MS∆

Crotalinae (Pit Viper) Bites: Clinical features:

Crotalinae (Pit Viper) Bites: Clinical features Diagnosis is determined on the presence of fang marks and a history consistent with exposure to a snake

Crotalinae (Pit Viper) Bites: Clinical features:

Crotalinae (Pit Viper) Bites: Clinical features Snake bite injury maybe manifested in three ways: Local injury (swelling, pain, ecchymosis) Coagulopathy (Thrombocytopenia, elevated PT, hypofibrinogenemia) Systemic effects (oral swelling / parathesias, metallic or rubbery taste in the mouth, hypotension, tachycardia)

Crotalinae (Pit Viper) Bites: Treatment – Do’s and Don’t:

Crotalinae (Pit Viper) Bites: Treatment – Do’s and Don’t First aid treatment such as suction and incision are dangerous and should not be used. Tourniquets are contraindicated because they obstruct arterial flow and cause ischemia Constriction bands ** may be of some use especially when immediate medical care is not available. ** An elastic bandage / Penrose drain, rope, or piece of clothing wrapped above the bite. It’s applied with enough tension to restrict superficial venous / lymphatic flow while maintaining distal pulses and cap. refill. It retard venom absorption, increase local tissue injury but reduce the severity of systemic effects.

Crotalinae (Pit Viper) Bites: Treatment – Do’s and Don’t:

Crotalinae (Pit Viper) Bites: Treatment – Do’s and Don’t The Coghlan’s Snake Bite Kit should not be used (the blade in the kit can injure digital nerves, arteries and tendons). The use of the Sawyer Extractor suction pump to remove venom without incision is controversial. Electric shock to the bite site should be condemned. Ice water immersion worsens the venom injury

Crotalinae (Pit Viper) Bites: Treatment:

Crotalinae (Pit Viper) Bites: Treatment Initial treatment involves: Immobilize the limb IV access in the contralateral limb Establish ABC, oxygen, monitor, IVF Previously placed tourniquets and constriction bands should not be removed until IV access is established Clean bite site and update tetanus booster . Contact Poison control ASAP

Crotalinae (Pit Viper) Bites: Treatment:

Crotalinae (Pit Viper) Bites: Treatment Antivenom (FabAV / CroFab): Mainstay of treatment for poisonous snakebites Composed of heterologous antibodies derived from the serum of animal immunized with the appropriate snake venoms. Bind and neutralize the venom molecules Indication for antivenom tx: All crotaline bites that show evidence of progressive signs and symptoms. Pts with worsening of local injury (pain, ecchymosis, swelling) Pts with lab errors (decr platelet count, incr coagulation time, decr fibrinogen) Pts with systemic sx (unstable vitals / MS∆)

Crotalinae (Pit Viper) Bites: Treatment:

Crotalinae (Pit Viper) Bites: Treatment Observation for progression of edema and systemic signs of envenomation be continued during and after antivenom infusion. Limb circumference serve as an index of progression as well as a guide for antivenom tx. Lab results should be repeated every 4h or after every antivenom tx.

Crotalinae (Pit Viper) Bites: Other medical Treatment::

Crotalinae (Pit Viper) Bites: Other medical Treatment: IVF (must be continued) Vasopressor (maybe needed for ongoing hypot) PRBC / FFP / Platelet may be needed if antivenom is not effective in stopping the bleeding that can occur. Fasciotomy maybe needed if compartment syndrome occur secondary to venom spreading into the compartment. Cultures / Antibiotics only needed if signs of infection develop. Steroids should only be used for signs of allergic rxn or serum sickness (occur in 5% of pts after FabAV- fever / rash / arthralgias. Tx with prednisone 60mg/d for 1-2wk)

Crotalinae (Pit Viper) Bites: Disposition:

Crotalinae (Pit Viper) Bites: Disposition Indication for discharge: Swelling begins to resolve Coagulopathy is reversed Pt is ambulatory. Pt need close f/u for wound check Pt should be observed for at least 8hrs. Pts with severe sx or getting antivenom should be admitted to the ICU

Cobra Bite :

Cobra Bite Large snakes (1 – 1.5m in length) Found in most of Africa and southern Asia. 45% of cobra bites are dry bites.

Cobra Bite - Venom:

Cobra Bite - Venom Contain multiple toxin that produce different effect: 1. Neurotoxins in the venom bind to postsynaptic acetylcholine receptors and produce depolarizing neuromuscular blockade. 2. Some toxins from the venom poison cell membrane. Chief effect is on the heart producing arrhythmias and impaired contractility. 3. Third type of toxins contain enzyme that break down protein and connective tissue.

Cobra Bite – Clinical Features::

Cobra Bite – Clinical Features: Develop immediate pain at the bite site Reaction around the bite site may develop over 48hr (local hemorrage, bullae, and necrosis) Proceed to develop local and progressive soft tissue swelling, CN dysfunction (ptosis, diplopia, dysphagia)

Cobra Bite – Clinical Features::

Cobra Bite – Clinical Features: Generalized muscle weakness  Flaccid paralysis Parasympathetic stimulation (salivation, bronchorrhea, N/V) Venom spit into the eye (spitting cobra) will produce inflammation, edema, and d/c, but no systemic s/sx. Coagulopathy is rare following a cobra bite (except bites from spitting cobra bites).

Cobra Bite – Diagnosis::

Cobra Bite – Diagnosis: Diagnosing and distinguishing cobra bite from other snakes is difficult. If possible, the snake should be caught, killed, and brought in for identification. Snake venom assays have been developed to detect the type of snake from wound aspirate or urine.

Cobra Bite – Diagnosis::

Cobra Bite – Diagnosis: Standard labs should be obtained: CBC Serum Electrolytes Creatinine Coagulation tests

Cobra Bite - Treatment:

Cobra Bite - Treatment Bite wound incisions, vacuum extractors, cooling, or ice are not beneficial Proximal lymphatic and venous constricting elastic band approach used in crotalines bites is controversial. One important first aid that is proven to help is to use prompt and copious irrigation of the eyes that sustained a venom exposure (spitting cobra)

Cobra Bite - Antivenom Treatment:

Cobra Bite - Antivenom Treatment The only proven and specific tx for cobra envenomation. Some are monovalent, specific for a single species, but most are polyvalent, containing antibodies against several important or common cobra species in that country or region. Should be considered experimental and can have high incidence of allergic rxn. Should be started before the constricting band is loosened. Should be initiated in pts with s/sx of systemic toxicity. Reduces systemic toxicity but does not reduce local tissue damage and necrosis.

Cobra Bite – Treatment Disposition::

Cobra Bite – Treatment Disposition: Pts without signs of envenomation should be admitted for at least 24 h obs Death from cobra bite typically occurs within 2 – 6 h after the bite. Survival is possible without antivenom in pts with good cardio-pulmonary support.

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