Arthropod bites and stings | |
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Other names | Bug bite |
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Tick bite | |
Symptoms | Swelling, itching, pain |
Complications | Anaphylaxis,envenomation,disease transmission |
Many species ofarthropods (insects, arachnids, millipedes and centipedes) can bite or sting human beings. These bites and stings generally occur as a defense mechanism or during normal arthropod feeding. While most cases cause self-limited irritation, medically relevant complications includeenvenomation,allergic reactions, and transmission ofvector-borne diseases.[1]
Most arthropod bites and stings causeself-limited redness,itchiness and/or pain around the site. Less commonly (around 10% ofHymenoptera sting reactions), a large local reaction occurs when the area of swelling is greater than 10 centimetres (4 in). Rarely (1-3% of Hymenoptera sting reactions),systemic reactions can affect multiple organs and pose a medical emergency, as in the case ofanaphylactic shock.[2][3]
Many arthropods bite or sting in order to immobilize their prey or deter potential predators as adefense mechanism. Stings containing venom are more likely to be painful. Less frequently, venomous spider bites are also associated withmorbidity andmortality in humans.
Most arthropod stings involveHymenoptera (ants, wasps, and bees). While the majority of Hymenoptera stings are locally painful, their associated venom rarely cause toxic reactions unless victims receive many stings at once. The low mortality (around 60 deaths per year in the US out of unreported millions of stings nationwide) associated with Hymenoptera is mostly due to anaphylaxis from venomhypersensitivity.[4]
Mostscorpion stings also cause self-limited pain orparesthesias. Only certain species (from familyButhidae) injectneurotoxic venom, responsible for most morbidity and mortality. Severe toxic reactions can occur resulting in progressivehemodynamic instability, neuromuscular dysfunction,cardiogenic shock,pulmonary edema, multi-organ failure, and death. Although robust epidemiological data is unavailable, global estimates of scorpion stings exceed 1.2 million resulting in more than 3000 deaths annually.[5]
Spider bites most often cause minor symptoms and resolve without intervention. Medically significant spider bites involve substantialenvenomation from only certain species such aswidow spiders andrecluse spiders. Symptoms oflatrodectism (from widow spiders) may include pain at the bite or involve the chest and abdomen, sweating, muscle cramps and vomiting among others. By comparison,loxoscelism (from recluse spiders) can present with localnecrosis of the surrounding skin and widespreadbreakdown of red blood cells. Headaches, vomiting and a mild fever may also occur.[6]
Feeding bites have characteristic patterns and symptoms that reflect feeding habits of the offending pest and the chemistry of its saliva. Feeding bites are less likely to be felt at the time of the bite, although there are some exceptions. Since feeding requires longer attachment to prey than envenomation, feeding bites are more often associated with vector transmission of disease.[7]
Pest | Preferred body part | Felt at time of bite | Reaction |
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Mosquitoes | exposed appendages | usually not | Low raised welt, itches for several hours. |
Midges and no-see-ums | exposed appendages | usually | Itches for several hours. |
Fleas | prefer ankles and bare feet | usually | May make red itchy welt; several days. Later bites are less severe. |
Biting flies | any exposed skin | painful and immediate | Painful welt, several hours. |
Bed bugs | appendages, neck, exposed skin | usually not | Low red itchy welts, usually several together resembling rash, slow to develop and can last weeks. |
Hair Lice | pubic area or scalp | usually not | Infested area intensely itchy, with red welts at bite sites. Seepediculosis. |
Larval ticks | Anywhere on body, but prefer covered skin, crevices. | Usually not; may be scratched off before they are seen. | Intensely itchy red welts lasting over a week. |
Adult ticks | covered skin, crevices, entire body | usually not | Itchy welt, several days. |
Mites | mainly on the trunk and extremities | usually not | Intensely itchy welts and papules that may last for days. Seeacariasis. |
In addition to stings and bites causing discomfort in of themselves, bites can also spread secondary infections if the arthropod is carrying a virus, bacteria, or parasite.[8] The World Health Organization (WHO) estimates that 17% of all infectious diseases worldwide were transmitted by arthropod vectors, resulting in over 700,000 deaths annually.[9] The table below lists common arthropod vectors and their associated diseases. The figure below representsendemic areas of commonvector-borne diseases.
Vector | Pathogen class | Disease | Annual disease burden* |
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Mosquitoes (Culicidae) | Arboviruses (Togavirus, Flavivirus, Bunyavirus)
Nematode (Wuchereriabancrofti) | Chikugunya,Zika,Yellow fever,Dengue,West Nile, California encephalitis,Japanese encephalitis, Equine encephalitis,Rift Valley fever | >300 million |
Black flies (Simuliidae) | Nematode (Onchocercavolvulus) | River blindness | >10 million |
Assassin bug (Reduviidae) | Protozoa (Trypanosomacruzi) | Chagas disease | >6 million |
Sand fly (Phlebotominae) | Protozoa (Leishmania) | Cutaneous andvisceral leishmaniasis | >3 million |
Ticks (Ixodidae) | Arboviruses (Bunyavirus, Flavirus)
Protozoa (Babesia) | Heartland virus,Tick-borne encephalitis,Crimean-Congo hemorrhagic fever
| >500,000 |
Tsetse flies (Glossinidae) | Protozoa (Trypanosomagambiense, T.rhodesesiense) | African sleeping sickness | >10,000 |
Biting flies (Tabanidae) | Nematode (Loa Loa) | African eyeworm | NA |
Fleas (Siphonaptera,Pulicidae) | Bacteria (Yersinia pestis, Bartonella henselae) | Plague,Cat scratch fever | NA |
Lice (Phthiraptera,Pediculidae) | Bacteria (Borrelia recurrentis, Rickettsia prowazekii, Bartonella quintana) | Lice-borne relapsing fever,endemic typhus,Trench fever | NA |
*Estimated global number of cases annually according to WHO in 2017.[9] If a vector transmits multiple diseases, aggregate case numbers are listed. Rough estimates are only meant to provide a sense of scale. Unknown disease burden is listed as NA for not available.
Most arthropod bites and stings do not require a specific diagnosis since they typically improve with supportive management alone. Certain bites and stings present with characteristic appearances and distributions. In general, however,dermoscopic findings of bitten or stung skin rarely aid in diagnosis.[11] Rather, patient history (recent travel to endemic areas, outdoor activities, and other risk factors) primarily guides the diagnostic approach, which can raise clinical suspicion for more serious complications like vector-borne diseases.
Skinbiopsies are not indicated for bites or stings, since thehistomorphologic appearance isnon-specific. Bites and stings as well as other conditions (e.g. drug reactions,urticarial reactions, and earlybullous pemphigoid) can cause microscopic changes such as awedge-shaped superficialdermal perivascular infiltrate consisting of abundantlymphocytes and scatteredeosinophils, as shown in the adjacent figure:[12]
Prevention strategies against arthropod bites and stings comprise measures for personal protection, travel advisories, public health and environmental concerns.
Travelers should seek to minimize outdoor activity during peak activity times and avoid high risk areas such as regions with known outbreaks orepidemics. Standing water and dense vegetation also commonly attract arthropods. Clothes covering most exposed skin can also provide a measure of physical protection, which may be augmented when the fabric is treated with pesticides such asPermethrin. Topicalrepellants such as N,N-diethyl-m-toluamide (DEET) is supported by a large body of evidence.[7]
Vaccines may also help prevent vector-borne diseases for eligible patients. For example,Japanese encephalitis,Yellow fever, andDengue fever have FDA-approved vaccines available. Since they are relatively new vaccines, however, they are not standard of care as of 2023. Additionally, patients traveling toMalaria endemic regions are routinely prescribedMalaria chemoprophylaxis.[13]
Patients with a history of venomhypersensitivity may benefit from venomimmunotherapy (VIT). Patients eligibile for VIT include those with a prior anaphylactic reaction to a venomous sting and who haveIgE to venom allergens. VIT can help prevent future severe systemic reactions in select patients.[2]
International organizations such as WHO aim to reducedisease burdens of neglected tropical diseases, many of which are vector borne.[14] Such campaigns must incorporate multipronged approaches to consider global inequality, access to resources, andclimate change.[citation needed]
Most arthropod bites and stings require only supportive care. However, complications such as envenomation and severe allergic reactions can present as medical emergencies.
Local reactions to bites and stings are treated symptomatically. If a stinger is still embedded, manual removal can reduce further irritation. Washing the affected area with soap and water can help reduce risk of contamination. Oralantihistamines,calamine lotion, topicalcorticosteroids and cold compresses are common over the counter remedies to reduce itchiness and local inflammation. In more severe cases, such as large local reactions, systemicglucocorticoids are sometimes prescribed, although limited evidence supports their effectiveness. There are limited data to support one treatment over another.[15]
Systemic reactions from venom hypersensitivity can rapidly progress to a medical emergency. The mainstay of anaphylactic shock management is intramuscularly injectedepinephrine. The patient should be stabilized and transferred to an intensive care unit.[2]
Toxic reactions to envenomation are similarly managed with medical stabilization and symptomatic treatment.Tetanus prophylaxis should be up to date but antibiotics are typically unnecessary unless a bacterialsuperinfection is suspected. Antivenom drugs have been created for certain species such asCentruroides scorpion stings, but these drugs are not yet widely available and so typically reserved for severe systemic toxicity.[15]
Several vector-borne diseases can present emergently.
After confirmation of diagnosis, antimicrobials are prescribed according to standard of care.
A bite is defined as coming from themouthparts of the arthropod. The bite consists of both the bite wound and thesaliva. The saliva of the arthropod may containanticoagulants, as in insects and arachnids which feed from blood. Feeding bites may also containanaesthetic, to prevent the bite from being felt. Feeding bites may also containdigestive enzymes, as inspiders; spider bites have primarily evolved to paralyse and then digest prey. A sting comes from the abdomen; in most insects (which are all largelyhymenopterans), the stinger is a modifiedovipositor,[16] which protrudes from the abdomen. The sting consists of an insertion wound, and venom. The venom is evolved to cause pain to a predator, paralyse a prey item, or both. Because insect stingers evolved from ovipositors, in most hymenopterans only the female can sting. However, there are a few orders of wasp where the male has evolved a "pseudo sting" - the male genitalia has evolved two sharp protrusions which can deliver an insertion wound. However, they do not contain venom, so they are not considered a true sting.[17] Inants that bite instead of sting, such as theFormicinae, the bite causes the wound, but during the bite the abdomen bends forward to sprayformic acid into the wound, causing additional pain. In arachnids that sting (all largelyscorpions), the stinger is not a modified ovipositor, but instead ametasoma that bears a telson.[18] (Scorpions lack an ovipositor entirely and give birth tolive young.)