Bites and Stings

Latrodectus antivenin is very effective, often resolving symptoms rapidly and reducing the duration of illness—even when administered up to 90 hours postenvenomation.³² This antivenin is derived from horse serum, and hypersensitivity reactions are possible. One death from anaphylaxis has been reported in the United States after antivenin was given undiluted via IV push; however, slow administration of diluted antivenin is considered safe.³³

Diptera

The order Diptera of the phylum Arthropoda includes over 240,000 species. Among those, the mosquitoes and flies are the most medically relevant.

Mosquitoes
An actual mosquito bite itself causes minimal trauma and is not usually felt by the victim. However, the local anesthetic that is injected into the wound at the time of the attack causes local tissue damage. Mosquito bites can lead to both immediate and delayed reactions. Typical immediate reactions are of short duration and include edema, erythema, and pruritus. More severe reactions are extremely rare and consist of skin necrosis. Delayed skin reactions are fairly common, but tend to last longer, persisting for days or even weeks. Treatment is symptomatic, usually with antihistamines and NSAIDS.

Patients can acquire an allergy to mosquito saliva over time and develop increasingly pronounced edematous and pruritic lesions with subsequent bites. They can also experience fever, malaise, generalized edema, as well as severe nausea and vomiting.

Systemic or anaphylactic reactions are not known to occur. Instead, the greatest danger occurs with the transmission of life-threatening diseases. Malaria, yellow fever, dengue hemorrhagic fever, and different types of equine encephalitis are all transmitted by mosquito bites. One interesting newcomer to the United States is the West Nile virus (WNV), which has spread rapidly since its introduction in 2003. Over 1,850 cases were reported in 22 different states over the initial 8 months. Acute symptoms are mild in the majority of patients, but a small minority can experience fatal disease. Neurological symptoms include tumor, myoclonus, and Parkinsonism. An irreversible poliomyelitis-like syndrome may also develop. In addition to WNV, St Louis encephalitis and equine encephalitis also remain important pathogens in the United States.³⁴ Prevention of bites is crucial and includes the use of pyrethroid-impregnated mosquito netting, repellents, and oral malaria prophylaxis. N,N-diethyl-3-methylbenzamide (DEET) remains the most effective mosquito repellent.³⁵ Although toxic reactions are rare, they do occur and anaphylaxis has been reported. ^36,37

Flies
Flies are blood-sucking insects that feed by stabbing and piercing their victim’s skin. Their bites always cause some degree of pain and pruritus. Allergic reactions are possible, though not as severe as those produced by Hymenoptera venom. Treatment is largely symptomatic with ice, oral antihistamine, analgesics. and topical or oral steroids as needed. Secondary bite infection is a concern and antibiotics are sometimes necessary.

Shiponaptera

The order Shinoptera includes fleas and lice. All produce very similar lesions, making diagnosis difficult. One concern with these bites is the development of secondary infections, especially in children. The skin should be washed with soap and water. Calamine, cool soaks, and oral or topical antihistamine may all be helpful to reduce symptoms.

Fleas
With fleas, as with mosquitoes, there is additionally a concern for transmission of life-threatening diseases. Fleas transmit bubonic plague, endemic typhus, brucellosis, melioidosis, and erysipeloid. Fortunately, effective oral and injectable formulations for both dogs and cats are now available to control fleas on most family pets.

Lice

Head (Figure 4) and pubic lice have not been proven to transmit life-threatening diseases, though body lice remains an important disease vector. Body lice thrive in conditions of poverty. Studies among the homeless in industrialized countries have shown that Bartonella organisms can be transmitted by body lice and can cause endocarditis.^38,39 Furthermore, body lice remain important vectors for relapsing fever, trench fever, and epidemic typhus in refugee and war camps. In those settings, surveillance of lice for the presence of diseases has correctly predicted outbreaks of disease.⁴⁰

Hemiptera

The order Hemiptera includes two families that are medically relevant: the Reduviidae (“kissing bugs”) and Cimicidae (bed bugs; Figure 5). Found worldwide, both are blood-sucking arthropods and primarily nocturnal feeders that tend to hide in cracks and crevices near beds. Bites are typically painless and may result in erythematous papules, bullae, or wheals. Bed bug bites appear as erythematous papules, generally clustered and often linear. Kissing bug bites are not linear and are generally not accompanied by brown or black patterns of excrements on the bed linen—a distinctive characteristic of bed bugs.⁴¹ Treatment is largely supportive with patients often benefiting from local wound care and the use of topical corticosteroids.⁴²

Lepidoptera