Pathogenic Organisms: Can You Identify?

August 2, 2002

Match each picture with the phrase below that best describes it. The organisms in these pictures might be microscopicor macroscopic, and they can be recovered from skin lesions or clothing by the patient and/or clinician.

Match each picture with the phrase below that best describes it. The organisms in these pictures might be microscopicor macroscopic, and they can be recovered from skin lesions or clothing by the patient and/or clinician.

1. This insect is a member of the Hymenoptera order.
2. This insect is also known as the "asp."
3. Itchy scalp would be associated with this organism.
4. Lesions produced by this organism resemble boils.

Photo A depicts the common paper wasp, Polistes annularis.Wasps, bees, hornets, yellow jackets, and fire antsare grouped together as Hymenoptera, or stinging insects.With the exception of the fire ant, these insects are all airborneand geographically quite widespread. Althoughmost Hymenoptera stings are painful but harmless, the major concern is withanaphylactic reactions among those persons who are extremely sensitive tovenom. Such individuals may require emergent medical attention following asting and should be taught how to self-administer epinephrine using one ofseveral commercially available kits.

Photo B shows the larval stage of the botfly, Dermatobiahominis. The gravid female fly glues fertilized eggs ontothe body of another insect (mosquito or stablefly mostoften). When the carrier insect, or vector, bites a humanvictim to secure a blood meal, the botfly larva emergesfrom the egg and enters the skin through the puncture wound. Subsequent inflammationcreates a tender, furuncle-like lesion.

The embedded larva can be removed, and the furuncle resolved, by injectinglocal anesthetic into the lesion, creating a small incision, and applyingpressure to the base. Occlusion of the central opening (as with pork fat orpetrolatum) may force the larva to migrate out onto the skin surface to avoidasphyxiation.

Photo C portrays the human head louse, Pediculushumanus var capitis. These organisms live on the skin ofthe scalp. Itching is the result of human sensitivity toeither louse salivary or fecal antigens. Suspicion of headlice should prompt examination of the hair above the earsand at the nape of the neck for eggs (nits). Finding the louse itself is difficult,because these small organisms can move up to 9 inches a minute. Excoriationand pyoderma may result from incessant scratching or rubbing the pruriticlouse bites.

Topical application of synergized pyrethroids or permethrin is standardtreatment. Application of malathion lotion or occlusive application of petrolatummay be required in stubborn cases.

Photo D shows the "asp" (puss) caterpillar, Megalopygeopercularis. This organism is found along the Easternseaboard and around the Gulf of Mexico. The caterpillar isquite distinctive, being covered with thick yellow- to graycoloredhairs. Stings from this insect are intensely painfuland may be accompanied by cardiovascular collapse (in up to 5% of victims)and/or convulsions (in up to 0.25%). Following a sting from the asp, affectedskin often demonstrates a grid-like pattern of hemorrhagic papulovesicles.