Excerpt from Insect Bites

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Vectors

 

Excerpt from Insect Bites

 

Synonyms, Key Words, and Related Terms: bites, repellents, arthropod

bites, malaria, leishmaniasis, onchocerciasis, filariasis, rickettsial

diseases, Rocky Mountain spotted fever, RMSF, West Nile fever, dengue

fever, endemic typhus, lyme disease, babesiosis, ehrlichiosis,

tularemia, cat-scratch disease, viral encephalitis, pruritic

erythematous papule, mosquitoes, biting flies, ticks, Dermacentor

variabilis, D variabilis, Dermacentor andersoni, D andersoni, cat

fleas, Ixodes species, Ixodes scapularis, I scapularis, fire ants,

Dermacentor tick, Amblyomma tick, Amblyomma americanum, Chrysops deer

fly, Liponyssoides mouse mite, rickettsial pox, viral encephalitis,

plague, rat flea, Anopheles mosquito, sandfly, bartonellosis,

Leishmania braziliensis, Leishmania tropica, Leishmania infantum,

visceral leishmaniasis, bacillary angiomatosis, lice, trench fever,

typhus, rickettsial fever, Rhipicephalus tick, Rhipicephalus

sanguineus, Ixodes tick, scrub typhus, Trombidiidae chigger mite,

yellow fever, Aedes mosquito, Onchocerca volvulus, elephantiasis,

Culex mosquito, mansonian mosquito, mosquito-borne encephalitis,

diethyltoluamide, DEET, pruritic papules, bedbug bites, fleabites,

Cimex species, brown recluse spider bite, black widow spider bite,

Centruroides exilicauda, C exilicauda, Centruroides sculpturatus, C

sculpturatus, scorpion sting, boutonneuse fever, Ornithodoros,

borrelial relapsing fever

 

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Background: Insect bites are an unpleasant fact of life in most parts

of the world. Bite reactions typically present as intensely pruritic

erythematous papules that commonly are excoriated. Vesicular and

bullous reactions are not uncommon, and large pseudolymphomatous

nodules may occur. Systemic reactions to the insect order Hymenoptera

(bees, hornets, wasps, yellow jackets, ants) include fatal anaphylaxis.

 

Bites are not merely a nuisance; arthropods commonly serve as disease

vectors. Malaria, leishmaniasis, onchocerciasis, filariasis, and

rickettsial diseases remain primary public health problems in many

parts of the world. Control of arthropod vectors and personal

protection with repellents are important steps in controlling the

spread of arthropod-borne disease.

 

Pathophysiology: The physical insult of an arthropod bite or sting

causes little injury. Instead, lesions occur as a result of the body's

immune response to antigens introduced by the bite or sting. The time

course of insect bite reactions reflects the immune mechanism

involved. Immediate hivelike skin lesions reflect hypersensitivity to

the bite, mediated by immunoglobulin E (IgE). Delayed pruritic

papules, nodules, and vesicles usually become symptomatic within 48

hours following the bite. They are manifestations of a delayed

hypersensitivity (type IV cell-mediated immunity) to antigens

introduced during the bite.

 

Less commonly, lesions occur as a result of toxins introduced by the

bite or sting (eg, brown recluse spider bites). The extensive tissue

necrosis that can follow a brown recluse bite is the result of

endothelial injury mediated by neutrophils. Sphingomyelinase D is the

toxin responsible for initiating the neutrophilic reaction.

Hyaluronidase contained within the venom dissolves dermal ground

substance and allows the toxin to spread. After envenomation, necrosis

usually spreads in a dependent fashion as hyaluronidase dissolves the

gelatinous barrier of mucopolysaccharides within the skin and the

force of gravity causes the toxin to spread.

 

Frequency:

 

* In the US: Bites and stings are a problem throughout the United

States. In the Midwest and along parts of the East Coast, mosquitoes

and biting flies as well as ticks account for most bites. In arid

areas, including much of the southwest and parts of California, flying

insects are less common, and crawling arthropods are the primary cause

of bites and stings. Arthropod vectors commonly spread disease.

 

Rocky Mountain spotted fever (RMSF) is carried by a variety of

ticks. The highest incidence of disease transmission is noted on the

East Coast of the United States, especially North Carolina.

Dermacentor variabilis, a hard tick with a highly ornate scutum, is

the primary vector of the disease in the United States.

 

Formerly exotic diseases, such as West Nile fever and Dengue

fever, are now found in parts of the United States and are carried by

mosquito vectors.

 

In parts of south Texas, endemic typhus is carried by opossums

and is spread by cat fleas that feed on the opossums and then bite humans.

 

Lyme disease, babesiosis, and human anaplasmosis (human

granulocytic ehrlichiosis) are carried by the Ixodes species of hard

ticks. In parts of the northeastern United States, 90% of Ixodes

scapularis ticks carry the Lyme disease spirochete.

 

Fire ants are ferocious stingers that swarm and sting in great

numbers when their mounds are disturbed. They occur throughout the

warmer areas of the southern United States and are predicted to spread

as far north as the lower Mid-Atlantic states. One positive aspect

concerning the spread of fire ants is the observation that tick

populations decline dramatically when fire ants are present. Ticks lay

their eggs directly on the ground where fire ants forage in great

numbers, consuming most tick eggs.

 

Other arth .....

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