Diagnosing And Treating Insect Bites And Stings On The Lower Extremity

Bites and stings from spiders, scorpions and ticks can lead to conditions ranging from irritating dermatological issues to more serious systemic consequences.This author discusses the diagnosis and treatment of allergic reactions, Lyme disease, scabies and other conditions that can result from insect bites and stings.

Many insect bites and stings occur on the foot and ankle due to skin exposure from wearing shorts and sandals in warm weather, and close proximity of the lower extremity to insect habitat. The effects of insect bites and stings can range from benign, barely noticeable symptoms to life-threatening systemic injury. Additionally, many insect bites are capable of disease transmission.

The phylum Arthropoda includes insects and arachnids. Arthropoda is an extremely diverse group that is present in the environment in very high numbers, making human contact unavoidable.
Insects include flies, fleas, bees, wasps, ants, lice and true bugs. Arachnids include ticks, mites, spiders and scorpions.

What You Should Know About Widow Spiders
There are several species of widow spiders, the most well known being the black widow spider, which has a characteristic red hourglass marking on its ventral abdomen.  Widow spiders inhabit the western and southern United States. They are commonly located in undisturbed, cluttered indoor and outdoor areas, including wood and debris piles.

Widow spider venom contains alpha-latrotoxin, which causes a massive presynaptic release of acetylcholine and resultant neurologic and autonomic dysfunction.^1,2 Symptoms of a widow spider bite typically begin within one hour of the bite and include muscle cramping, muscle spasms of the abdomen that can cause acute abdominal pain, nausea, weakness, diaphoresis and facial edema.³ The majority of widow spider bites are rarely life-threatening and typically resolve in 48 to 72 hours.³

The treatment of widow spider bites is supportive and includes narcotics for pain and benzodiazepines for muscle spasms. Antivenom treatments are available for use in children, the elderly and in cases with severe systemic symptoms.⁴

Treating Brown Recluse Spider Bites
Brown recluse spiders inhabit the south central and Midwestern United States. They are identifiable by a characteristic violin shaped marking on their dorsal thorax. Brown recluse spiders live in dark, dry, undisturbed areas including garages, attics, basements and linen closets. Given their habitat, recluse spider bites most commonly occur indoors.

The venom of brown recluse spiders contains sphingomyelinase D, alkaline phosphatase, lipase, hyaluronidase, deoxyribonuclease and ribonuclease, which lead to both local and systemic cytotoxic and hemolytic reactions.^1,2 The recluse spider bite initially causes minimal pain. However, several hours later, an intense inflammatory response occurs at the site, causing intense pain, a surrounding erythematous halo, central vasospasm and ischemia. In approximately 40 percent of cases, ischemia leads to central necrosis at the bite site.⁵ Recluse spider bites can cause several systemic symptoms including rash, fever, chills, nausea, vomiting, arthralgias, hemolysis and coagulopathy.

Despite being one of the most clinically significant spider bites, recluse spider bites have no established treatment protocols. The initial recommended treatment for recluse spider bites includes cleaning the bite site, cold compresses, elevation, immobilization, analgesics, antihistamines and tetanus prophylaxis.^6,7 Other treatment modalities include: antibiotics, glucocorticoids, hyperbaric oxygen and nitroglycerin, but none of these modalities have supporting randomized control studies to show clinical benefit.^8-11

Surgical intervention is contraindicated in the early management of recluse spider bites with studies showing no clinical benefit and possible worse clinical outcomes with extended dermonecrosis, delayed wound healing, secondary infection and scarring.^7,8,12 Late management of brown recluse spider bites with large areas of dermonecrosis may require delayed surgical intervention including debridement, excision of eschars and split thickness skin grafting.^7,8

When Scorpions Strike
Out of over 1,000 scorpion species, only 50 are known to be dangerous to humans. The only scorpion found in the United States with venom potent enough to cause systemic effects is Centruroides sculpturatus, which is located throughout the southwestern United States including New Mexico, Arizona, southern California and Texas.¹³

Scorpion stings are common on the feet as scorpions frequently hide in shoe gear to avoid sunlight. Scorpion stings can result in a wide range of symptoms from local skin irritation to systemic neurologic, cardiovascular and respiratory symptoms. Specific local symptoms include pain, swelling, redness, blister formation and paresthesias.¹⁴ C. sculpturatus venom can cause a systemic reaction by opening neuronal sodium channels, which causes excessive depolarization and membrane hyperexcitability. These neuronal changes can result in excessive neuromuscular activity and autonomic dysfunction.¹⁴
Systemic symptoms include cranial nerve abnormalities, excessive motor activity and autonomic dysfunction.¹⁴ Cranial nerve abnormalities can cause abnormal eye movements, blurry vision, excessive salivation, tongue fasciculations and slurred speech.^13,14 Excessive motor activity can cause fasciculations, ataxia, restlessness and seizure-like movements.^13,14 Autonomic dysfunction can result in agitation, tachycardia, nausea and vomiting.^13,14 Systemic reactions to scorpion venom are rare but can be severe and life-threatening, especially in children.

One can treat painful local skin reactions secondary to scorpion stings with symptomatic care including local wound care, analgesics and antihistamines.¹⁴ Young children and patients with significant systemic symptoms frequently require hospitalization and monitoring. Scorpion antivenom is available and administration depends on the severity of symptoms. Systemic treatment involves supportive care of the organ system specifically affected by the venom and may include benzodiazepines for excessive motor activity and IV fluids for autonomic dysfunction and hypovolemic cardiovascular changes.¹⁴  

Pertinent Pointers On Treating Stings By Bees, Wasps And Ants
Bees, wasps and ants belong to the Hymenoptera order. The majority of Hymenoptera stings cause only a transient local reaction but stings from these insects do account for the largest number of envenomation deaths in the United States.¹⁵ The majority of deaths from bee and wasp stings are due to immune mediated reactions, but death can also result from direct toxicity. Most bee and wasp stings result in immediate pain, wheal-and-flare reaction and edema. Numerous stings can result in toxicity with possible symptoms including nausea, vomiting, headache, fever, syncope, seizure, rhabdomyolysis and renal failure.¹⁴ Bee and wasp stings can result in immunoglobulin E–mediated allergic reactions and anaphylaxis.¹⁶

Treatment of local reaction secondary to bee and wasp stings depends on symptoms and can include ice, analgesics and antihistamines.¹⁴ Manage severe systemic reactions and anaphylaxis in the same manner by monitoring airway and ventilation status, subcutaneous or intramuscular epinephrine, intravenous antihistamines, intravenous fluids and corticosteroids.¹⁶

One of the most clinically significant types of ant is the fire ant, genus Solenopsis, which is named after the burning pain that results from its bite. Fire ants live primarily in the southeastern United States but their distribution is gradually extending west due to the urbanization that disturbs the sunny dirt habitats that the fire ants prefer. Fire ants build dirt mounds and aggressively attack in great numbers when disturbed. The severity of reaction to fire ant stings varies depending on the number of stings and the allergic response of the patient. Fire ants attack in number and inflict several stings within seconds, resulting in clusters of skin lesions most commonly on the lower extremities.

Local reaction to fire ant bites typically starts with a wheal followed by development of a sterile pustule. Pain, burning, edema and anaphylaxis can accompany the local skin reaction.¹⁷ Systemic reaction can include generalized urticaria, angioedema, bronchospasm, laryngeal edema and hypotension.¹⁷ Anaphylaxis can occur similar to stings from other insects in the Hymenoptera order.¹⁸

One can treat local skin reactions of fire ant bites with cold compresses, oral antihistamines, topical or intralesional corticosteroids and topical or injected local anesthetics. Patients with multiple stings and/or systemic reaction can use oral corticosteroids, oral antihistamines and analgesics. One should treat severe systemic reaction and anaphylaxis with intramuscular epinephrine.¹⁴

How To Treat Scabies From Mite Bites
Mites are one of the most diverse groups of arthropods with more than 48,000 of species, only a few of which are clinically significant to humans.¹⁹ Mites can cause direct parasitic infections, act as vectors to transmit disease and cause allergic reactions. The most clinically significant mites are Sarcoptes scabiei, which causes scabies in humans.

S. scabiei, the itch mite, is a parasitic arthropod that burrows into the skin. The life cycle of the mite occurs within the epidermis with eggs hatching in the superficial skin and larvae remaining there for 30 days while they mature into adult mites.^19,20 As the larvae develop, they feed on the stratum corneum and produce characteristic burrows as they leave behind fecal matter.^19,20 S. scabiei is found in all parts of the world. Transmission occurs by direct contact and infestations are common in areas of overcrowding. Primary skin lesions from scabies are small papules, vesicles and burrows. Secondary lesions are excoriations due to scratching, which can be complicated by secondary bacterial infections. Skin lesions are commonly visible on the flexor side of the wrists, interdigital webspaces of the hands, dorsal feet, axillae, elbows, waist, buttocks and genitalia.^21,22

Treatment of scabies includes the use of scabicidal agents (Permethrin cream), oral ivermectin, Lindane cream and antipruritic agents.^21,22 Since mites can survive on bedding and clothing, and spread easily by contact, treatment of all family members and laundering of clothing, linens, and towels in hot water is recommended.^21,22

When Lyme Disease And Rocky Mountain Spotted Fever Arise From Ticks
Ticks are vectors for numerous diseases including Q fever, Rocky Mountain spotted fever, tick paralysis, tularemia, babesiosis, human granulocytic anaplasmosis and Lyme disease.²³ Rocky Mountain spotted fever and Lyme disease are two of the most common tick-borne diseases in the United States.

Ixodes scapularis, the deer tick, transmits Borrelia burgdorferi, the bacteria that causes Lyme disease. While cases of Lyme disease have been reported in the entire country, the majority of cases are localized to the geographic regions of New England, the Mid-Atlantic, east-north central, south Atlantic and west north-central United States.²⁴ The deer ticks feed during spring and summer and attach to hosts, commonly on the lower extremity, as they walk through their habitat of tall grasses and bushes. The tick must typically remain attached for 36 to 48 hours in order to transmit B. burgdorferi. Immature ticks, known as nymphs, most commonly transmit disease as their small size allows them to avoid detection and remain attached longer to their host. Adult deer ticks can transmit disease as well but their size makes them more likely to be noticed and removed before bacteria can transmit.²³

Lyme disease affects multiple body systems and produces a wide range of symptoms. There is an incubation phase, lasting days to years (typically one to three weeks), from the time of transmission to the presentation of symptoms.²⁴ Lyme disease has three phases: early localized infection, early disseminated infection and late disseminated infection. The early localized infection most often presents with erythema migrans, a characteristic red, expanding rash. Erythema migrans can progress to have a bull’s-eye appearance with red inner and outer portions, and a central ring of clearing. Other common symptoms in the early localized stage include fever, headache and fatigue.²⁵

Early disseminated infection occurs as B. burgdorferi bacteria spread in the bloodstream. As this occurs, erythema migrans lesions may develop at distant sites and patients may experience migrating muscle and joint pain. Neuroborreliosis, neurologic symptoms secondary to disseminated B. burgdorferi, occurs in 10 to 15 percent of patients.25,26 Symptoms of neuroborreliosis include facial palsy, meningitis, radiculoneuritis and encephalitis.^25,26 Lack of or inadequate treatment of Lyme disease can result in late disseminated infection several months after the initial tick bite. Late disseminated infection affects many parts of the body including nerves, joints, eyes, the brain and the heart.

Approximately 5 percent of untreated/undertreated patients develop neurologic symptoms including polyneuropathy, Lyme encephalopathy and chronic encephalomyelitis.²⁷ Polyneuropathy causes burning and shooting pain in both the upper and lower extremity. Lyme encephalopathy is characterized by subtle cognitive problems and fatigue.²⁷ Chronic encephalomyelitis can cause cognitive impairment, lower extremity weakness, gait disturbance, facial palsy, vertigo and back pain.²⁷ Late disseminated Lyme disease can affect the joints causing Lyme arthritis. Lyme arthritis most commonly affects the knees and its characteristics are joint pain, swelling and occasional joint erosions.²⁸

Chemical repellents with DEET, Picaridin or Permethrin can prevent tick bites and subsequent Lyme disease.²⁹ If tick bites occur and are highly likely to carry B. burgdorferi, administering a single dose of doxycycline within 24 hours of the tick bite may reduce the risk of developing Lyme disease.³⁰ Antibiotics are the primary treatment for Lyme disease. For patients with early localized infection, oral doxycycline (Vibramycin, Pfizer) is the first choice antibiotic.³⁰ Doxycycline is contraindicated in children under 8 years of age and pregnant women. Oral amoxicillin or cefuroxime axetil (Ceftin, GlaxoSmithKline) are alternative treatment options for these patients.³⁰ Ceftriaxone is recommended in cases that do not respond to oral antibiotics or in cases of disseminated disease.

Rocky Mountain spotted fever is another common tick borne disease that results from the bite of Dermacentor variabilis, the American dog tick, which transmits the bacteria Rickettsia rickettsii. Rocky Mountain spotted fever is a misnomer as this disease occurs across the entire United States with the majority of cases occurring in North Carolina, Oklahoma, Arkansas, Tennessee and Missouri.³¹
Rocky Mountain spotted fever can be very difficult to diagnose, especially in its early stages.³² Symptoms of Rocky Mountain spotted fever typically begin one to two weeks following a tick bite. After transmission, Rickettsiae infect and multiply in cells that line small and medium blood vessels, resulting in damage and leakage of blood into surrounding tissues, which causes the characteristic rash of the disease.³¹ The classic triad of findings for Rocky Mountain spotted fever is rash, fever and a history of tick bite. The initial rash is usually maculopapular and subsequently takes on a petechial appearance with an inward spreading pattern starting in the extremities and moving toward the trunk.³² In addition to rash, blood leakage can lead to damage of numerous other tissues including those of the renal system, the gastrointestinal system, the central nervous system and respiratory system. Due to this extensive tissue damage, Rocky Mountain spotted fever has a high mortality rate. Risk factors for severe or fatal Rocky Mountain spotted fever include advanced age, male sex, chronic alcohol use and G6PD deficiency.³²

Given the high mortality rate of Rocky Mountain spotted fever, immediate treatment, even in suspected cases, is recommended. Doxycycline is the drug of choice for treatment and therapy should continue for three days after the resolution of fever and when there is significant clinical improvement.³¹ Possible sequelae of this infection include partial paralysis of the lower extremity, gangrene of the digits requiring amputation, hearing loss, bowel/bladder incontinence, movement disorders and speech disorders.³²

What You Should Know About Mosquito Bites
Diptera are two-winged insects that include mosquitoes, midges, gnats and flies. Mosquitos are the most clinically significant insects of this group. Their bite can cause local irritation and itching but more importantly can serve as a vector for disease transmission. Typical mosquito bites appear as a pruritic pink papule with a pointed center. It is common to see these bites on the feet and ankles due to a lack of protective clothing in summer months. Most mosquito bites cause transient itching but sensitivity varies and some people can show a prolonged reaction to the bite. Skeeter syndrome is an intense hypersensitivity reaction with fever due to allergens in the mosquito saliva.³³ Recommended treatment for this syndrome are oral antihistamines and corticosteroids.³³  

Worldwide, there are over 700 million cases of mosquito-transmitted disease per year, resulting in millions of deaths.³⁴ Some of the most common mosquito-transmitted diseases include West Nile virus, dengue fever, malaria and yellow fever. Dengue fever results from the transmission of the dengue virus by mosquitoes of the Aedes genus, which are mainly found in tropical areas although recent cases have been reported in Florida, Hawaii and Texas.³⁵ Dengue fever is also known as “breakbone fever” due to the significant joint and muscle pain that accompanies the fever. Symptoms of dengue fever include fever, headache, muscle and joint pain, and a measles-like rash consisting of 2 to 10 mm red macules that become confluent with central areas of spared tissue.³⁶ A small number of patients with dengue fever develop dengue hemorrhagic fever, which causes bleeding and low platelets.36 There is no antiviral medication for dengue fever. Treatment is supportive with analgesics, fluid replacement and rest.³⁶

West Nile virus is a mosquito-transmitted virus that first arose in Africa but rapidly spread worldwide. The virus occurs throughout the entire United States and is carried by 65 different mosquito species.³⁷ An estimated 80 percent of West Nile virus infections are subclinical or asymptomatic. Symptomatic individuals typically present with fever, headache, weakness, myalgia, arthralgia, nausea, vomiting and a transient maculopapular rash. Rarely, infected individuals develop neurologic disease, which can present as meningitis, encephalitis or paralysis. Treatment of West Nile virus is supportive involving monitoring, fluid replacement, analgesics and rest.

Essential Insights On Flea-Borne Diseases
Fleas are wingless insects that jump on to their hosts as they walk through flea habitats and live as parasites feeding off their host’s blood. In the United States, dog or cat fleas (Ctenocephalides) are the most common source of flea bites.³⁸ Fleas can affect their host both directly through their bite and also by serving as a vector for transmission of other diseases. The direct effect of a flea bite is due to allergic reaction to the saliva of the flea. Bites most commonly present as pruritic papules on the feet and ankles. Fleas serve as vectors for the transmission of numerous diseases including the plague, tularemia, cat scratch disease and cat flea typhus.³⁸

Treatment for fleas involves eradication and symptomatic treatment. Flea bites cause itching, which one can manage with antihistamines, topical corticosteroids and calamine lotion. Fleas on dogs and cats can persist for months and rapidly spread to the surrounding environment.³⁹ Pet treatment involves use of both an adulticide, which kills adult fleas, and an insect growth regulator, which kills immature fleas.³⁹ Similarly, home treatment is recommended with insecticide spray and insect growth regulator as well to target both life stages of the flea.³⁹  

In Conclusion
A wide array of insects and arachnids are present ubiquitously throughout our environment, making contact unavoidable. Insects and arachnids cause pathological changes through direct bites, allergic reactions and as vectors for the transmission of other diseases. The severity of insect bites and stings can range from minor annoyance to life threatening.

Dr. Hoffman is in private practice in Boulder, Colo.

References

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