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When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016
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Images courtesy of Wikimedia Commons | Oliver Arend (top left), Wikimedia Commons | SOA-AIDS Amsterdam (center), Wikimedia Commons | Michael Geary (top right), and Medscape (bottom left and right).
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Bites from insects and other arthropods provoke a variety of human skin reactions, depending on the feeding apparatus and the pharmacologic activity of substances injected with the bite. Allergic reactions and secondary bacterial infections can also affect presentation. Bites from bedbugs (top left) and other parasites can lead to a cutaneous hypersensitivity reaction termed papular urticaria.[1] Individual papules may surround a wheal and display a central punctum. Infestations of lice commonly cause pruritus, resulting in skin excoriation. Itching is especially intense at night, when lice are feeding. The pubic louse, Phthirus (also Pthirus) pubis, infests the groin and body hair (center). A pruritic rash and characteristic linear burrows under the skin's surface can be used to diagnose infestation with the scabies mite, Sarcoptes scabiei (top right). In adults, skin reactions to scabies mites appear as 1- to 3-mm, erythematous papules and vesicles filled with clear fluid. The fluid may appear cloudy if the vesicle is more than a few days old.
Rocky Mountain spotted fever has two principal North American tick vectors, Dermacentor variabilis (the dog tick) and D andersoni (the Rocky Mountain wood tick), with the former found in the eastern United States and the latter, in the Rocky Mountain region and Canada. Potentially deadly but curable, Rocky Mountain spotted fever is characterized by a maculopapular rash (bottom left) that spreads from the wrists and ankles to the trunk and extremities, eventually reaching the palms and soles.
Tungiasis, a subcutaneous infestation by Tunga penetrans (the chigoe flea) or a related species, is manifested by lesions that are in some cases asymptomatic but in others are pruritic or even extremely painful. The simplest infestations are marked by a white patch with a black dot (bottom right), but more advanced infestations are characterized by crusted, erythematous papules; painful, pruritic nodules; and crateriform lesions. The plantar surface of the foot is often involved, as are the intertriginous areas of the toes and the periungual regions. Secondary infections, such as lymphangitis or septicemia, can also occur.
Images courtesy of the Centers for Disease Control and Prevention (CDC) | Piotr Naskrecki (bedbug), CDC | James Gathany (louse), and CDC (mite).
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Blood feeding by bedbugs, lice, fleas, ticks and mites commonly cause dermatologic symptoms. Many of these parasites thrive in the conditions of overcrowding and decreased sanitation associated with poverty, but individuals of all socioeconomic backgrounds may be at risk. Clinicians should maintain a high level of suspicion regarding the appropriate set of clinical circumstances for identifying and treating infestations, as such infestations can cause substantial dermatologic and psychological discomfort for patients.
Images courtesy of Science Source | AJE Terzi (left and right) and Science Source | Stephen Dalton (center).
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Bedbugs
Bedbugs, which belong to the order Hemiptera, are parasitic insects related to stinkbugs, water striders, and assassin bugs. The common bedbug (Cimex lectularius, shown left and center) has an extendable beak tipped with paired, sawlike appendages for penetrating the host's integument. Typically less than 1 cm in length, it is reddish brown, oval, and dorsoventrally flattened. Its preferred habitats are crevices and margins in beds, walls, and floorboards, as well as behind peeling paint and in other small, narrow spaces associated with areas of clutter. C lectularius comes out at night in search of blood, with peak feeding times just before dawn. It is typically attracted to body heat, carbon dioxide in exhaled air, vibration, sweat, and odor[1] and can live up to a year without food.[2]
In September 2016, the presence of the tropical bedbug (C hemipterus, shown right), a species that spreads faster than C lectularius and that was known in Florida during the first half of the 20th century, was confirmed in the United States for the first time in decades in a published report. The insect, the only other bedbug species that commonly feeds on human hosts, was last documented in Florida in the 1940s, with the exception of an unpublished finding of the species in Orlando in 1989. In the 2016 study, however, the tropical bedbug was reported in Brevard County, Florida, based on a sample found the previous year.[3]
Image courtesy of the CDC | Piotr Naskrecki.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
After a bedbug finds a food source, it saws through the skin and injects anticoagulant and anesthetic compounds. The insect feeds by inserting its tubelike rostrum directly into superficial capillaries.[1] During feeding, the bedbug's color may change as it swells with host blood, as shown in this picture of a juvenile bedbug feeding on a volunteer host.
Image courtesy of Wikimedia Commons | Oliver Arend.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Bedbug bites themselves are typically painless. However, the subsequent allergic reaction that may develop can cause intense pruritus. While feeding, bedbugs may inject the host with one of several pharmacologically active substances, including hyaluronidase, proteases, and kinins.[1] These compounds may induce different skin reactions, such as erythema, wheals, vesicles, or hemorrhagic nodules. Repeated bites may sensitize individuals, leading to more pronounced cutaneous manifestations or systemic hypersensitivity reactions. The local trauma from bedbug bites can lead to secondary bacterial infection, causing ecthyma, cellulitis, or lymphangitis. There is little evidence that bedbugs transmit disease, but they have been investigated as possible vectors for hepatitis B virus[2,4,5] and Chagas disease.[2,6,7] Histologic findings from bite-site biopsy specimens typically show eosinophilic infiltrates, which are indicative of the allergic nature of the reaction. The image shows papular urticaria, which may develop from bedbug bites.
Image courtesy of Arlo Pelegrin.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Treatment for bedbug bites is typically supportive. If secondary infection occurs, apply a local antiseptic lotion or antibiotic cream/ointment. If an allergic reaction occurs, corticosteroid creams and oral antihistamines may be advised. Bedbugs can be eliminated with permethrin insecticides, baited traps, special bedbug-free beds, and bed nets. Homemade methods to eliminate these parasites, such as wrapping duct tape around bed legs, may be effective, but bedbugs have been known to climb other objects and then fall onto a bed. The image shows the ventral view of a bedbug's head, with eyes, antennae, and piercing beak visible.
Image courtesy of the CDC | James Gathany.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Lice
Lice are parasitic insects from the order Phthiraptera; their eggs are called "nits." They are grouped taxonomically as either chewing lice or sucking lice, but only the sucking lice purposefully infest humans. The three types of lice that feed on humans are Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Phthirus pubis (pubic louse; pubic lice are also called "crabs").[8] All three types periodically feed on human hosts by latching on with sickle-shaped tarsi and chewing through the epidermis with eversible teeth, after which they insert a hollow stylet into a capillary. Disease is known to be spread only by body lice.[8] Louse infestation (pediculosis) is a major problem in the United States. The image shows a female body louse.
Image courtesy of the CDC | James Gathany.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Body lice infest clothing, laying their eggs on fibers in fabric seams. In the United States, they typically affect homeless persons, who often are unable to frequently wash or change their clothes. Body lice are known vectors for three major bacterial diseases: typhus, trench fever, and relapsing fever. Rickettsia prowazekii causes typhus; typhus epidemics occur during periods of overcrowded conditions and infestations of body lice. Bartonella quintana causes trench fever (which was a major problem during World War I)[9,10] and bacillary angiomatosis.[10]Borrelia recurrentis causes louse-borne relapsing fever, which is highly fatal in malnourished individuals.[11] The image shows the three nymphal instars (N1-N3) and the adult forms of body lice.
Image of a female head louse (left) courtesy of the CDC | Reed & Carnrick Pharmaceuticals; image of a pubic louse (right) courtesy of the CDC | World Health Organization.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Head lice and pubic lice infest hair and lay their eggs on the base of hair fibers. Mature specimens can be distinguished by visual inspection; notably, the head louse (left) has an elongated body, while the pubic louse (right) has a wide, crablike body. Head lice are common in urban areas and spread easily. Concerned about the stigma associated with such infestations, affected individuals are often reluctant to confess their condition to people in their social circles.
Pubic lice are generally spread through sexual contact and may be used as a marker for other sexually transmitted diseases.[12] They can also be spread indirectly, if eggs are laid on hairs that are subsequently detached via host scratching and, as may occur in a restroom, end up in the vicinity of a new host.[13] Lice found on the eyelashes are typically pubic lice rather than head lice. P pubis can also reside in beards, armpits, and the perianal region.[13] DNA extracted from pubic lice in rape victims has been used to help identify perpetrators.[14]
Image courtesy of Wikimedia Commons | Kosta Y. Mumcuoglu.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Louse bites may reveal intradermal hemorrhage and eosinophilic infiltrates on histologic examination. The most common symptom of louse infestation is pruritus, but children may be asymptomatic. On examination, patients with head lice may have occipital lymphadenopathy and impetigo (shown). The scalp will show excoriations, dark specks of louse feces, nits, and adult lice. The heaviest infestation is typically in the retroauricular scalp.[12] All forms of pediculosis are diagnosed by direct visualization and identification of adult lice or nits. Body lice are found on the seams of clothing; hemosiderin-stained purpuric spots on the skin are a cutaneous sign of infestation. Pubic lice are typically visible throughout the pubic hair, clutching one or two strands with their hooked claws.
Image courtesy of Wikimedia Commons | Deutsche Pediculosis Gesellschaft e.V.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Treatment of louse infestation is typically approached via a community-wide effort; otherwise, reinfestation will occur. Control of objects that can harbor lice—by limiting the sharing of, or contact between, personal objects, such as combs, brushes, and clothing—is important. Pediculicides, such as permethrin and malathion, can be used to kill adult lice, but young nits are immune to neurotoxic agents because they do not have nervous systems.[12] Specialty combs (shown) can help to remove nits from hair follicles. Body lice can be treated by laundering infested clothing in hot water, ironing it them with a hot iron, or drying it in a hot dryer.[8,12,15] Topical agents may also be applied to clothing.
Image courtesy of Wikimedia Commons | Kalumet.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Mites
Mites are tiny arachnids related to spiders and scorpions. They have eight legs and a tubelike mouth and are one of the most diverse groups of animals, with over 48,000 known species.[16] Mites are found in every terrestrial environment; some are so small that they can live in close proximity to people without detection. Many species are agricultural pests, but only a few have clinical implications for humans.
S scabiei (shown) causes scabies in humans and can also parasitize dogs, cats, apes, boars, and some marsupials.[17] Scabies is a global health problem that flourishes in overcrowded populations. Poor public education often results in delayed diagnosis and treatment. Transmission occurs via direct and prolonged contact with an infected individual (skin-to-skin and sexual contact), but these small arthropods can survive on fomites such as bedding and clothing for up to 3 days.[18,19]
Image courtesy of Wikimedia Commons | Michael Geary.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Scabies mites go through three developmental stages before reaching maturity, at around 2 weeks.[20] They can penetrate human skin during all of these life stages via a combination of chewing and side-to-side motion of their mouthparts. Mite eggs hatch in the superficial skin layers,[18,19] with the larvae and nymphs secreting proteases that degrade the stratum corneum and then feeding on dissolved tissue. Females burrow down to the stratum granulosum and stratum spinosum, where they feed on live cells or tissue fluid.[20] Migrating female mites produce the characteristic egg-and-feces-filled burrows. Fertilized females live 4-6 weeks and produce up to four eggs per day, which hatch in 2-3 days. The primary clinical symptom of scabies is intense pruritus secondary to a hypersensitivity reaction. The most severe complication is bacterial superinfection.[18,19]
The image shows a magnified view of a scabies burrow, with a mite in the upper right-hand corner (arrow). Most patients are infected with 10-100 mites, but immunocompromised individuals may harbor more than 1 million mites (a condition termed "crusted scabies," formerly known as "Norwegian scabies").
Image courtesy of the CDC | Reed & Carnrick Pharmaceuticals.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
In adults, scabies infection usually occurs on the wrists, interdigital web spaces of the hands (shown), dorsal feet, axillae, elbows, waist, buttocks, and genitalia.[19,21] Pruritic papules and vesicles on the scrotum and penis in men or on the areolae in women are characteristic.[21] Infants and children may have diffuse lesions on the face, scalp, neck, palms, and soles.[21-23] Primary scabies is typically evident as small papules, vesicles, and burrows; secondary lesions are caused by rubbing and scratching. Scabies can be diagnosed through identification of mites, larvae, ova, or fecal pellets, using a light microscope.[18,19,21]
Image courtesy of Medscape.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Histologic examination of a skin biopsy specimen may reveal the presence of mites (arrows) within a hyperkeratotic stratum corneum, but a dermal infiltrate composed of lymphocytes, histiocytes, mast cells, and eosinophils is characteristic. Treatment of scabies consists of the use of a scabicidal agent (eg, permethrin cream, oral ivermectin, lindane cream/lotion), antipruritic agents, and, if the patient is secondarily infected, antimicrobials.[18,19,21] All household members and close personal contacts should be treated, and clothing, linens, and towels should be laundered in hot water. Typically, patients should be reevaluated 2-4 weeks after treatment to ensure adherence to the treatment regimen and eradication of the mites.
Image courtesy of Medscape.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Demodicosis is an infection of the eyelid caused by the mite Demodex folliculorum. The 0.1- to 0.4-mm mites (arrow) infest the eyelash hair follicles, where they feed on sebaceous gland cells and the follicular epithelium.[24,25] Accumulation of mite waste material may cause follicular plugging, leading to dry eyes and chalazion formation. D folliculorum has also been implicated in pityriasis folliculorum, signs of which include rosacealike papules and diffuse erythema.[24] On examination, patients with demodicosis may have thickened or scaled lids, loss of eyelashes, conjunctival inflammation, or decreased vision. Treatment involves a combination of brushing, washing with diluted baby shampoo, and applications of antibiotic ointment. The prognosis is typically very hopeful.
There has been a proposal to reclassify human demodicosis into a primary form (ie, spinulate demodicosis [pityriasis folliculorum], papulopustular/nodulocystic or conglobate demodicosis, ocular demodicosis, auricular demodicosis) and a secondary form (mainly associated with immunosuppression).[26]
Image courtesy of Wikimedia Commons | Denys Williams.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Ticks
Ticks are large parasitic mites that readily feed on humans, pets, livestock, and wildlife. They are more common in warm, humid regions. Ticks use a cement secreted by their salivary glands to attach themselves to their host and then use a tubular mouth covered in overlapping blades to bore a hole into their host and begin feeding. All ticks feed on blood, but only a few species attack humans. The above image shows a tick burrowed into the leg of its human host
Image courtesy of Medscape.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Ticks can transmit many pathogens, including Lyme disease (identifiable by its bulls-eye rash, shown). Rash accompanied by fever or flulike symptoms may indicate that a tick-borne disease is present.[27] In the United States, ticks also carry Rocky Mountain spotted fever, tularemia, ehrlichiosis, babesiosis, Colorado tick fever, and relapsing fever.[27] Most of the infectious agents spread by ticks are bacterial, so antibiotic treatment is usually indicated. (Normal precautions regarding antibiotics apply in the case of children younger than 8 years and pregnant women.) In some cases, antibiotic therapy can be complicated by a secondary condition, the Jarisch-Herxheimer reaction, which is characterized by fever and headache.[28]
Image courtesy of Arlo Pelegrin.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Most ticks that attack humans are tough to kill, because of their resilient anatomy. They have hard plates on the top and bottom, with an extremely flexible membrane in between. The membrane can stretch to accommodate vast amounts of host blood. Engorged ticks can simply be compressed until they pop, but empty ticks can resist being squeezed or crushed. Moreover, many ticks feed on humans when in the immature stage (so-called "seed ticks"), making them very difficult to spot. The lone star tick (Amblyomma americanum) is shown.
Tick removal
Use clean tweezers for tick removal, grasping the tick as close to the surface of the skin as possible but being sure not to squeeze the tick's body. Employing steady, even pressure, pull upward until the cement cone attaching the tick to its host breaks and the tick is dislodged. Twisting or jerking the tick can cause the mouth to break off and remain in the skin. If this occurs, remove the mouth with tweezers; however, if the mouth cannot be easily tweezed out, leave it in place and allow the skin to heal. Following tick removal, use soap and water or alcohol to clean the area.
Image courtesy of Medscape | CDC.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
Fleas
Fleas are wingless, parasitic insects in the order Siphonaptera. Their historical contribution to human misery cannot be overstated, for they transmit a wide variety of pathogens. Among the organisms vectored by fleas are bubonic plague, murine typhus, cat scratch fever, tungiasis, and tapeworms.[29-31] In North America, three species of flea commonly attack people: Pulex irritans (the human flea), Ctenocephalides felis (the cat flea), and C canis (the dog flea). The human flea actually feeds on a wide variety of mammals, and the cat and dog fleas readily trade hosts. Flea larvae are vermiform, eyeless, and limbless, burrowing deep into carpets and furniture to feed on decaying organic matter as they mature. Adult fleas are equipped with sharp, hooklike claws on their feet and piercing-sucking mouthparts. Their hind legs contain compressible elastomeric protein that, when released, catapults the flea up to 150 times its own body length,[29] the equivalent of a human jumping further than a football field. Xenopsylla cheopis (the Oriental rat flea), the primary vector for plague, is shown engorged with blood.
Image courtesy of Wikimedia Commons | Yerpo.
When Bugs Feast: What’s Causing That Itch?
Lars Grimm, MD, MHS; Arlo Pelegrin, MSc | November 15, 2016 | Contributor Information
A flea bite (shown) initially presents as a punctate, hemorrhagic area where the insect has probed to find an acceptable feeding site. A wheal usually develops around the bite, accompanied by pruritus. After 12-24 hours, a hardened, papillar lesion appears.[29] Secondary infection brought on by scratching is a possible further complication. The symptoms of the bites themselves are minor and can be relieved with over-the-counter salves and lotions. Fleas inhabit the nesting sites of wild and feral animal populations and often come into the home on domestic pets. Many insecticidal remedies are available.
Skin cancer is the most common form of cancer in the United States. Although many skin cancers are highly curable if detected early and treated, certain types are highly aggressive, with a tendency to invade and spread. Can you identify and differentiate between these malignancies?Slideshows, November 2016
Arthropod assaults on humans can have many manifestations clinically, histologically, and immunologically. Hemiptera is an order of insect species of "true bugs" that has piercing-sucking mouthparts and includes the family Cimicidae (bedbugs), which are blood-sucking ectoparasites of mammals or birds.Diseases/Conditions, February 2017
Lyme disease is a multisystem illness caused by infection with the spirochete Borrelia burgdorferi and the body's immune response to the infection. The disease is transmitted to humans via tick bites, from infected ticks of the genus Ixodes.Diseases/Conditions, March 2016
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Contributor Information
Authors
Lars Grimm, MD, MHS
Assistant Professor
Department of Diagnostic Radiology
Duke University Medical Center
Durham, NC
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Arlo Pelegrin, MSc
Entomologist
Littleton, CO
Disclosure: Arlo Pelegrin, MSc, has disclosed no relevant financial relationships.
Editor
Robert A. Schwartz, MD, MPH
Professor and Head, Dermatology
Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health
Rutgers New Jersey Medical School
Newark, New Jersey
Disclosure: Robert A. Schwartz, MD, MPH, has disclosed no relevant financial relationships.
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