Arthropod Bites

 

Arthropod Bites

Primary Care Visit Report   

A 26-year-old male with no past medical history presented with a rash on bilateral arms and wrists. The patient had woken up with the skin lesions 1 day prior. They were very itchy. They had gotten progressively worse since they appeared and seemed to become more symptomatic after he showered. The patient applied topical Benadryl cream which did not help. 
 Vitals were normal. On exam, there were multiple scattered  erythematous pap-ules      with some excoriations on bilateral arms. There were no lesions in the web spaces of his fi ngers and no burrows. His right arm had an area of linear lesions, otherwise the lesions were diffusely scattered. 
 The lesions seemed to be bites; however, Primary Care was unsure of the source. The patient was treated for scabies with permethrin cream, and referred to dermatol-ogy in case the lesions did not clear up.  

Discussion from Dermatology Clinic 



Differential Dx   


  Arthropod bites  
  Scabies  
  Urticaria  
  Folliculitis     

Favored Dx   
On physical examination, the lesions appear to be arthropod bites. The phylum arthropods includes centipedes, millipedes,  spiders  , scorpions, and insects. The offending biter is diffi cult to identify without more details from the history, such as whether the individual has any pets (could suggest  fl ea   bites), if anyone else in the house has bites (scabies, fl eas, or bed bugs), or whether he spent time outdoors with his arms exposed ( mosquitoes     , outdoor bugs). The distribution of the bites would not be typical of scabies, which tend to appear around the wrists and interdigital spaces. Furthermore, scabies lesions typically feature more extensive excoriation.  

Overview   


 Arthropod bites are a signifi cant cause of morbidity worldwide [ 1 ]. Arthropod bites and  stings   cause a range of symptoms in humans, ranging from mildly uncomfortable to life threatening. The majority of arthropod bites cause local reactions; however, some bites can cause toxic and anaphylactic reactions [ 2 ]. Many arthropods serve as vectors for diseases such as malaria, dengue, West Nile virus, Rocky Mountain spotted fever, Southern tick-associated rash illness (STARI), and Lyme disease. 
 The species of concern in the USA include the black widow and brown recluse  spiders  , the lone star, black-legged ( Ixodes scapularis ) and dog ticks, bed bugs,  fl eas  , biting  flies, and  mosquitoes  . Their signifi cance is due to prevalence, severity of bite symptoms, or potential to transmit disease [ 1 ,  2 ]. Specifi cally, black widow spider bites cause severe muscle spasms and brown recluse spider bites can cause skin necrosis.  Tick   and mosquito bites are common, and the species are vectors for a number of diseases named above. 
 It is diffi cult to estimate the overall prevalence of bug  bites  , as many of them do not require any treatment. Systemic reactions from  hymenoptera   (insects such as  bees  ,  wasps  , and hornets)  stings   have a lifetime prevalence ranging from 0.3 % in children to 7.5 % in adults [ 3 ,  4 ]. Fatalities associated with insect bites are very rare; however, some bites may require emergency management.  
     Presentation   
 Arthropod bites present in a variety of ways. Multiple bites will present as dis-tinct pruritic lesions, often with a central  punctum   and surrounding erythema.  Hymenoptera   (e.g.,  wasps  ,  bees  ) bites may be accompanied by pain, burning or stinging sensations, as well as local edema.  Bed bug bites   typically manifest in groups of three lesions (referred to as breakfast, lunch, and dinner lesions); however, such a pattern is not specifi c to bed bugs and cannot preclude other insects, as  fl eas   are also known to cause a similar bite pattern (see Chap.   40     for more on bed bugs). 
  Scabies   lesions usually involve papules with burrows containing a serpiginous line with a tiny black speck at the end, and present on the wrists, elbows, interdigital web spaces, and lower abdomen (see Chap.   41    ).  Spider   bites are more likely to pres-ent with extreme pain, although this again is not a symptom specifi c to spider bites. Any insect bite can cause vesicle formation. Although it is not necessarily the case, patients with bites from infesting, indoor bugs may report family members also experiencing bites. Bites from outdoor bugs are more likely to occur on parts of the body that are exposed to the environment, such as the neck and extremities.  
     Workup   
 Patient history is helpful in diagnosing bug  bites  , as they may recall a biting incident. Additionally, patients should be asked about outdoor activities, clothes worn and areas exposed during time outdoors, pets, and whether family members or room-mates have also experienced bites. 
 If scabies are suspected, a scraping can be done and viewed under a microscope. Mineral oil is applied to a burrow or lesion, which is then scraped laterally with a number 15 blade. The scrapings are placed on a glass slide and viewed under a microscope. Microscopy may reveal eggs, mites, or fecal matter. Applying  KOH   to the slide may help visualize mite debris by dissolving keratin. Suspected cases of lice should include inspection of the hair shaft for any nits.  
     Treatment   
 Treatment of bites depends on the insulting arthropod and the accompanying symp-toms. All bite wounds should be cleaned and remaining stingers, if any, should be removed using the edge of a bank card or butter knife to push them out. Tweezers are not recommended as squeezing the stinger may cause further venom release, although the amount of venom might be very small. Symptomatic relief should be provided either in the way of  antihistamines   to control itch,  topical steroids   to con-trol infl ammation, and ice packs or analgesics for pain [ 1 ,  2 ]. 
 Bites such as the ones in this case are usually best treated with topical  steroids     . A medium potency steroid can be used on the limbs and trunk (excluding intertriginous areas), such as betamethasone valerate ointment 0.1% (Class III) applied to individ-ual lesions twice daily for up to 2 weeks. Sedating antihistamines such as hydroxy-zine may be taken by patients experiencing pruritus that interrupts their sleep. 
 Bites causing  anaphylaxis   should be treated with epinephrine or other vasoactive medications.  Tick   bites in geographical areas with high incidence of Lyme may be treated with a prophylactic 200 mg single dose of doxycycline if the tick species has been identifi ed and was attached for more than 36 h [ 2 ]. Severe  spider   bites may require treatment with an antivenom. Secondary infection on bite sites should be treated with an appropriate antibiotic, as determined by a wound culture. Treatment for  bed bug bites   (which are also treated with  topical steroids  ) and scabies are dis-cussed in more detail in their respective chapters.  
     Follow-Up   
 Patient follow up is somewhat dependent on the offending insect. Although many  mosquito  -born diseases are concentrated in tropical and subtropical areas, they still occur in North  America  . Patients with recent travel history and  mosquito   bites should be aware of common symptoms of malaria and dengue. Uncomplicated bug  bites   should resolve within 1–2 weeks of treatment with corticosteroid, although post infl ammatory hyperpigmentation may persist for several months.   
reactions; however, some bites can cause toxic and anaphylactic reactions [ 2 ]. Many arthropods serve as vectors for diseases such as malaria, dengue, West Nile virus, Rocky Mountain spotted fever, Southern tick-associated rash illness (STARI), and Lyme disease. 
 The species of concern in the USA include the black widow and brown recluse  spiders  , the lone star, black-legged ( Ixodes scapularis ) and dog ticks, bed bugs,  fl eas  , biting  flies, and  mosquitoes  . Their signifi cance is due to prevalence, severity of bite symptoms, or potential to transmit disease [ 1 ,  2 ]. Specifi cally, black widow spider bites cause severe muscle spasms and brown recluse spider bites can cause skin necrosis.  Tick   and mosquito bites are common, and the species are vectors for a number of diseases named above. 
 It is diffi cult to estimate the overall prevalence of bug  bites  , as many of them do not require any treatment. Systemic reactions from  hymenoptera   (insects such as  bees  ,  wasps  , and hornets)  stings   have a lifetime prevalence ranging from 0.3 % in children to 7.5 % in adults [ 3 ,  4 ]. Fatalities associated with insect bites are very rare; however, some bites may require emergency management.  
     Presentation   
 Arthropod bites present in a variety of ways. Multiple bites will present as dis-tinct pruritic lesions, often with a central  punctum   and surrounding erythema.  Hymenoptera   (e.g.,  wasps  ,  bees  ) bites may be accompanied by pain, burning or stinging sensations, as well as local edema.  Bed bug bites   typically manifest in groups of three lesions (referred to as breakfast, lunch, and dinner lesions); however, such a pattern is not specifi c to bed bugs and cannot preclude other insects, as  fl eas   are also known to cause a similar bite pattern (see Chap.   40     for more on bed bugs). 
  Scabies   lesions usually involve papules with burrows containing a serpiginous line with a tiny black speck at the end, and present on the wrists, elbows, interdigital web spaces, and lower abdomen (see Chap.   41    ).  Spider   bites are more likely to pres-ent with extreme pain, although this again is not a symptom specifi c to spider bites. Any insect bite can cause vesicle formation. Although it is not necessarily the case, patients with bites from infesting, indoor bugs may report family members also experiencing bites. Bites from outdoor bugs are more likely to occur on parts of the body that are exposed to the environment, such as the neck and extremities.  
     Workup   
 Patient history is helpful in diagnosing bug  bites  , as they may recall a biting incident. Additionally, patients should be asked about outdoor activities, clothes worn and areas exposed during time outdoors, pets, and whether family members or room-mates have also experienced bites. 
 If scabies are suspected, a scraping can be done and viewed under a microscope. Mineral oil is applied to a burrow or lesion, which is then scraped laterally with a number 15 blade. The scrapings are placed on a glass slide and viewed under a microscope. Microscopy may reveal eggs, mites, or fecal matter. Applying  KOH   to the slide may help visualize mite debris by dissolving keratin. Suspected cases of lice should include inspection of the hair shaft for any nits.  
     Treatment   
 Treatment of bites depends on the insulting arthropod and the accompanying symp-toms. All bite wounds should be cleaned and remaining stingers, if any, should be removed using the edge of a bank card or butter knife to push them out. Tweezers are not recommended as squeezing the stinger may cause further venom release, although the amount of venom might be very small. Symptomatic relief should be provided either in the way of  antihistamines   to control itch,  topical steroids   to con-trol infl ammation, and ice packs or analgesics for pain [ 1 ,  2 ]. 
 Bites such as the ones in this case are usually best treated with topical  steroids     . A medium potency steroid can be used on the limbs and trunk (excluding intertriginous areas), such as betamethasone valerate ointment 0.1% (Class III) applied to individ-ual lesions twice daily for up to 2 weeks. Sedating antihistamines such as hydroxy-zine may be taken by patients experiencing pruritus that interrupts their sleep. 
 Bites causing  anaphylaxis   should be treated with epinephrine or other vasoactive medications.  Tick   bites in geographical areas with high incidence of Lyme may be treated with a prophylactic 200 mg single dose of doxycycline if the tick species has been identifi ed and was attached for more than 36 h [ 2 ]. Severe  spider   bites may require treatment with an antivenom. Secondary infection on bite sites should be treated with an appropriate antibiotic, as determined by a wound culture. Treatment for  bed bug bites   (which are also treated with  topical steroids  ) and scabies are dis-cussed in more detail in their respective chapters.  
     Follow-Up   
 Patient follow up is somewhat dependent on the offending insect. Although many  mosquito  -born diseases are concentrated in tropical and subtropical areas, they still occur in North  America  . Patients with recent travel history and  mosquito   bites should be aware of common symptoms of malaria and dengue. Uncomplicated bug  bites   should resolve within 1–2 weeks of treatment with corticosteroid, although post infl ammatory hyperpigmentation may persist for several months.   
    Questions for the Dermatologist 
–  Is there a way to tell which insect is doing the biting?  
 No, unfortunately there is not. All bites are infl ammatory reactions to saliva or an antigen present in the bite. There are some diagnostic clues.  Flea   bites tend to be smaller than  bed bug bites  , but this is not always true. History is most helpful in determining which bug is doing the biting. If bites are found following an out-door activity like a picnic, they are probably outdoor bugs. Presence of blood on the sheets and new bites when the patient wakes up are suggestive of bed bugs. Bites in the dead of winter are more likely to be bed bugs. In that case patients should look for engorged bugs between 4 and 5 am, along the seams of their mattress. 
–  How can insect bites be distinguished from other rashes?  
  Rashes   tend to spread out and extend to different parts of the body. Eczematous rashes may have indiscreet edges. They do not appear as discrete lesions the way bites do. Bites have clear demarcations and appear as individual lesions in groups. 
–  Is there a way to tell whether the bites are caused by bed bugs? Scabies? Is therea lab test for any of the above?  
 There is no lab test for different types of bug  bites  . Suspected scabies lesions can be scraped and viewed under a microscope to look for eggs and droppings. Scrapings are placed in mineral oil on a glass slide and viewed under a microscope on low power. Otherwise defer to history. 
–  What is the best treatment for insect bites that are not scabies?  
 The best treatment is topical  steroids     . Medium potency steroids can be used on the arms and legs twice daily for a short period of time, i.e., 2 weeks.     
   References 
1.   Schwartz RA, Steen CJ. Chapter 210. Arthropod bites and stings [Internet]. In: Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K, editors. Fitzpatrick’s dermatology in general medicine. 8th ed. New York: McGraw-Hill; 2012. [cited 2015 Jan 21]. Available from:   http://accessmedicine.mhmedical.com.ezproxy.cul.columbia.edu/content.aspx?bookid=392& Sectionid=41138941    .  
2.    Juckett G. Arthropod bites. Am Fam Physician. 2013;88(12):841–7.  
 3.    Baker TW, Forester JP, Johnson ML, Stolfi  A, Stahl MC. The HIT study: Hymenoptera identi-fi cation test—how accurate are people at identifying stinging insects? Ann Allergy Asthma Immunol. 2014;113(3):267–70.
4.    Ruëff F, Przybilla B, Biló MB, Müller U, Scheipl F, Aberer W, Birnbaum J, Bodzenta-Lukaszyk 
A, Bonifazi F, Bucher C, Campi P, Darsow U, Egger C, Haeberli G, Hawranek T, Körner M, Kucharewicz I, Küchenhoff H, Lang R, Quercia O, Reider N, Severino M, Sticherling M, Sturm GJ, Wüthrich B. Predictors of severe systemic anaphylactic reactions in patients with Hymenoptera venom allergy: importance of baseline serum tryptase-a study of the European Academy of Allergology and Clinical Immunology Interest Group on Insect Venom Hypersensitivity. J Allergy Clin Immunol. 2009;124(5):1047–54.   

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