Medical Conditions Caused by Arthropod Stings or Bites

  • Jerome Goddard
Chapter
Part of the Infectious Disease book series (ID)

Abstract

Arthropods may cause a variety of negative health effects by their stings and bites. Non-allergic reactions to stings and bites include erythematous and edematous lesions which resolve in a couple of hours, while allergic reactions may be characterized by much more serious large local phenomena and even systemic symptoms such as anaphylaxis. This chapter focuses on the medical conditions associated with arthropod bites and stings, such as those mentioned above, as well as secondary infections resulting from skin puncture. Lastly, clues to recognizing insect sting or bite reactions are presented and discussed.

Keywords

Arthropods Morphology of mouthpart types Insects Stings Bites Allergic reactions Anaphylaxis Secondary infection Diagnosis Laboratory findings 

10.1 Introduction and Medical Significance

Arthropods cause a wide variety of clinical conditions in humans, but especially skin lesions, because people are inevitably exposed to biting and stinging organisms in the urban and suburban environment [1, 2, 3, 4, 5]. Skin lesions resulting from arthropod exposure may arise via various pathologic pathways, such as direct damage to tissue, hypersensitivity reactions to venom or saliva, or infectious disease. Direct injury can occur from mouthparts or stingers piercing human skin [6] and/or blisters or stains resulting from exposure to arthropods [7, 8]. In some cases, proteins in venom or saliva may cause direct mast cell degranulation, leading to urticaria [9]. In addition, secondary infections may result from bacteria entering the skin via the bite/sting punctum. This is especially likely if the bite/sting site is scratched extensively. As discussed in Part II, many vector-borne infectious diseases can also produce skin lesions such as rash, ulcers, or eschar.

10.2 Pathogenesis

10.2.1 Mouthpart Types

Insect mouthparts, at least in the medically important species, can be generally divided into three broad categories:
  1. 1.

    Biting and chewing

     
  2. 2.

    Sponging

     
  3. 3.

    Piercing–sucking (Fig. 10.1)

     
Fig. 10.1

Various insect mouthpart types: (a) chewing, (b) sponging, and (c) piercing–sucking mouthparts. (Adapted from: US DHHS, CDC, Publication No. 83: 8297 and other sources)

Within these categories, there are numerous adaptations and/or specializations among the various insect orders. Biting and chewing mouthpart types, such as those in food pest insects, and sponging mouthpart types (Fig. 10.2d), found in the filth fly groups, are of little significance regarding human bites, but piercing–sucking mouthparts, and especially the bloodsucking types, are of considerable importance. Insect piercing–sucking mouthparts vary in the number and arrangement of needlelike blades (stylets) and the shape and position of the lower lip of insect mouthparts, the labium (Fig. 10.2). Often, what is termed the proboscis of an insect with piercing–sucking mouthparts is an ensheathment of the labrum, stylets, and labium. These mouthparts are arranged in such a way that they form two tubes. One tube is usually narrow, being a hollow pathway along the hypopharynx, and the other is wider, formed from the relative positions of the mandibles or maxillae. On biting, saliva enters the wound via the narrow tube, and blood returns through the wider tube by action of the cibarial or pharyngeal pump.
Fig. 10.2

Typical mouthparts of medically important Diptera. (From: U.S. Navy Laboratory Guide to Medical Entomology, 1943)

10.2.2 Sting Apparatus

In all stinging wasps, bees, and ants (insect order Hymenoptera), the stinger is a modified ovipositor, or egg-laying device, that usually no longer functions in egg laying. Accordingly, in the highly social Hymenoptera, only a queen or other reproductive caste member lays eggs; the workers gather food, conduct other tasks, and can sting intruders. They build paper nests under or above ground (Figs. 10.3 and 10.4) which they will aggressively defend. A typical ovipositor (nonstinging) consists of three pairs of elongate structures, called valves, which can insert the eggs into plant tissues, soil, and so forth. One pair of the valves makes up a sheath and is not a piercing structure, whereas the other two pairs form a hollow shaft that can pierce substrate in order for the eggs to pass down through. Two accessory glands within the body of the female inject secretions through the ovipositor to coat the eggs with a glue-like substance.
Fig. 10.3

Paper wasp nests. (Photo copyright 2010 by Jerome Goddard, Ph.D.)

Fig. 10.4

Hornet’s nest, cut away to show inside. (Photo copyright 2010 by Jerome Goddard, Ph.D.)

For the stinging configuration, the ovipositor is modified to enable stinging (Fig. 10.5). The genital opening from which the eggs pass is anterior to the sting apparatus, which is flexed up out of the way during egg laying. Also, the accessory glands have been modified. One now functions as a venom gland, and the other, called the Dufour’s gland, is important in the production of pheromones. The venom gland is connected to a venom reservoir or poison sac, which may contain up to 0.1 mL of venom in some of the larger hymenopterans.
Fig. 10.5

Cut away view of yellowjacket stinger. (USDA Agri. Handbk)

The stinger itself is well adapted for piercing vertebrate skin. In the case of yellowjackets (Fig. 10.6), there are two lancets and a median stylet that can be extended and thrust into a victim’s skin. Penetration is not a matter of a single stroke but, instead, alternate forward strokes of the lancets, sliding along the shaft of the stylet. The tips of the lancets are slightly barbed (and actually recurved like a fishhook in the case of honeybees) so that they are essentially sawing their way through the victim’s skin. Contraction of venom sac muscles injects venom through the channel formed by the lancets and shaft. The greatly barbed tip of the lancets in honeybees prevents the stinger from being withdrawn from vertebrate skin. Thus, the sting apparatus is torn out as the bee flies away. Other hymenopterans, on the other hand, can sting repeatedly.
Fig. 10.6

Yellowjacket showing stinger. (Photo copyright 2008 by Jerome Goddard, Ph.D.)

10.2.3 Direct Damage to Tissue

Some lesions are the result of direct tissue damage from stings or bites. Arthropod mouthparts puncture skin by various mechanisms (siphoning tube, scissorlike blades, and so on) leading to skin damage. In this case, damage may be a small punctum, dual puncta (from fangs), or lacerations. By far, most lesions on the human skin are produced by host immune reactions to the offending arthropod salivary secretions or venom. Arthropod saliva is injected while feeding to lubricate the mouthparts on insertion, increase blood flow to the bite site, inhibit coagulation of host blood, anesthetize the bite site, suppress the host’s immune and inflammatory responses, and/or aid in digestion. Stingers are needlelike structures that may puncture and damage human skin as well. Venom from certain spiders may directly affect the human skin, causing tissue death (necrosis). In the United States, violin spiders are primarily responsible for necrotic skin lesions, although sac spiders (Cheiracanthium spp. ) and hobo spiders may also cause necrotic arachnidism [10, 11]. Brown recluse spider venom contains a lipase enzyme, sphingomyelinase D, which is significantly different from phospholipase A in bee and wasp venoms. This specific lipase is the primary necrotic agent involved in the formation of the typical lesions. It is possible that neutrophil chemotaxis is induced by sphingomyelinase D. The subsequent influx of neutrophils into the area is critical in the formation of the necrotic lesion (see Chap.  12).

10.2.4 Infectious Complications

Secondary infection with common bacterial pathogens can occur in any lesion in which the integrity of the dermis is disrupted, whether by necrosis or excoriation [12]. Infection may result in cellulitis, impetigo, ecthyma, folliculitis, furunculosis, and other manifestations. Three findings may be helpful in making the diagnosis of secondary bacterial infection [12]:
  1. 1.

    Increasing erythema, edema, or tenderness beyond the anticipated pattern of response of an individual lesion suggests infection.

     
  2. 2.

    Regional lymphadenopathy can be a useful sign of infection, but it may also be present in response to the primary lesion without infection.

     
  3. 3.

    Lymphangitis is the most reliable sign and suggests streptococcal involvement.

     

10.3 Clues to Recognizing Insect Bites or Stings

10.3.1 Diagnosis

If a patient recalls no insect or arachnid exposure, arthropod bites or stings may pose difficulty in diagnosis. No physician or entomologist can accurately determine what insect caused a particular bite or sting lesion; however, there might be helpful clues. Alexander [1] described a typical hymenopteran sting (excluding ants) as a central white spot marking the actual sting site surrounded by an erythematous halo. Generally, the entire lesion is a few square centimeters in area. Of course, allergic reactions may result in much larger lesions. He also described an initial rapid dermal edema with neutrophil and lymphocyte infiltration . Plasma cells, eosinophils, and histiocytes appear later.

Arthropod bites should be considered in the differential diagnosis of any patient complaining of itching. Bites are characterized by urticarial wheals, papules, vesicles, and less commonly, blisters. After a few days or even weeks, secondary infection , discoloration, scarring, papules, or nodules may persist at the bite site. Complicating the picture further is the development of late cutaneous allergic responses in some atopic individuals. Diagnosis may be especially difficult in the case of biopsies of papules or nodules. Biopsies may reveal a dense infiltrate of a mixture of inflammatory cells, such as lymphocytes, plasma cells, histiocytes, giant cells, neutrophils, and eosinophils. Lesions containing a majority of lymphocytes could be mistaken for a lymphomatous infiltrate. If the infiltrate is predominantly perivascular and extending throughout the depths of the dermis, the lesion might be confused with a lupus erythematosus. Eosinophils are commonly seen in papules or nodules from arthropod bites. There may be a dense infiltration of neutrophils, resembling an abscess. Occasionally arthropod mouthparts may still be present within the lesion, and there may be a granulomatous inflammation in and around these mouthparts. Scabies mites occur in the stratum corneum and can usually be seen on microscopic examination. New lesions from scabies, such as papules or vesicles are covered by normal keratin, whereas older lesions have a heaped-up parakeratotic surface. There may also be a perivascular infiltrate of lymphocytes, histiocytes, and eosinophils. Histopathologic studies of late cutaneous allergic responses have revealed mixed cellular infiltrates, including lymphocytes, polymorphonuclear leukocytes, and some partially degranulated basophils. A prominent feature of late cutaneous allergic reactions has been fibrin deposition interspersed between collagen bundles in the dermis and subcutaneous tissues.

Diagnosis of insect bites or stings depends on:
  1. 1.

    Maintaining a proper index of suspicion in this direction (especially during the summer months)

     
  2. 2.

    A familiarity of the insect fauna in one’s area

     
  3. 3.

    Obtaining a good history

     

It is very important to find out what the patient has been doing lately, e.g., hiking, fishing, gardening, cleaning out a shed, and so forth. However, even history can be misleading in that patients may present with a lesion that they think is a bite or sting, when in reality the correct diagnosis is something like urticaria, folliculitis, or delusions of parasitosis (see Chap.  14). Physicians need to be careful not to diagnose “insect bites” based on lesions alone and should call on entomologists to examine samples.

10.4 Summary and Conclusions

A human’s first line of defense against invasion or external stimuli is the skin. It may react in a variety of ways against all kinds of stimuli—physical or chemical—including arthropods and their emanations. Lesions may result from arthropod exposure, although not all lesions have the same pathological origin—some are owing to mechanical trauma, some owing to infectious disease processes, and some result from sensitization processes. Physicians and other healthcare providers are frequently confronted with patients having skin lesions attributed to a mysterious arthropod bite or sting. Diagnosis is difficult but may be aided by asking the patient numerous questions about the event and any recent activity that might have led to arthropod exposure. The following questions might provide useful information: “Did you see the offending arthropod?” “Was it wormlike?” “Did it fly?” “Where were you when these lesions occurred?” Most treatments (except in cases of infectious diseases) involve counteracting immune responses to venoms, salivary secretions, or body parts using various combinations of antihistamines and corticosteroids. Infectious diseases often require antibiotic/supportive care.

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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Jerome Goddard
    • 1
  1. 1.Extension Professor of Medical EntomologyMississippi State UniversityMississippi StateUSA

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