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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=Kalsang Dolma
|QuestionAuthor=Kalsang Dolma (Reviewed by Rim Halaby, Will Gibson, and Yazan Daaboul)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=General Principles
|MainCategory=Microbiology
|SubCategory=Microbiology
|SubCategory=General Principles
|MainCategory=General Principles
|MainCategory=Microbiology
|SubCategory=Microbiology
|SubCategory=General Principles
|MainCategory=General Principles
|MainCategory=Microbiology
|SubCategory=Microbiology
|SubCategory=General Principles
|MainCategory=General Principles
|MainCategory=Microbiology
|Prompt=A 28 year old female immigrant from Africa presents with complaints of an itchy swelling over her entire body. She is also concerned about body aches. On physical examination, non-tender swelling is noted over her the limbs on the right side of her body. Laboratory findings show eosinophilia. Microscopic examination of the blood shows the microfilaria of loa loa, and a diagnosis of loa loa filiariasis is made. The vector for this condition is:
|MainCategory=Microbiology
|Explanation=The correct answer is D. The vectors for loa loa filiaris are flies from the genus Chrysops. Loa loa filariasis is a skin and eye disease caused by the nematode worms called loa loa filaria. The diagnosis of loa loa filiarisis should be considered in any patient with a history of travel in an endemic area who presents with worms in their eyes, swollen lumps of tissue, itching, swelling, and unexplained peripheral eosinophilia.
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|Prompt=A 28-year-old female immigrant presents to the emergency department (ED) for diffuse pruritus and a foreign body sensation in her right eye for the past 2 hours. The patient states that she returned from a rainforest trip in western Africa 8 months ago. The patient has no significant past medical history. She takes no medications and has no known allergies. Physical examination is remarkable for a mild eyelid swelling and non-tender localized angioedema in the right forearm. Dim slit-lamp examination of the the right eye shows a thread-like worm in the subconjunctival space. Initial laboratory work-up in the ED reveals eosinophilia. Peripheral smear and PCR confirm the diagnosis. Which of the following vectors is most likely associated with the infectious agent responsible for this patient's condition?
|Explanation=''[[Loa loa]]'' is a human filarial nematode (roundworm) whose adult form migrates in the subcutaneous and deep connective tissues. [[Microfilariae]], ingested by [[mango flies]], [[horse flies]], or [[deer flies]] (''Chrysops'' spp.), may be transmitted to humans following a bite by the infected flies. The time for the ''[[Loa Loa]]'' to mature requires approximately 6-12 months, but a prolonged latency (several years) is not uncommon.  
 
''Loa loa'' is called the "eye worm" because it can cross the conjunctivae, creating an uncomfortable "foreign sensation in the eyes" among infected patients. Additionally, diffuse [[pruritus]] and a [[Calabar swelling]], a non-tender [[angioedema]] that is often observed in the forearms, may be seen in approximately half of the cases. The diagnosis is suspected when patients report a history of travel to endemic African regions, consistent clinical symptoms, and the presence of [[eosinophilia]]. The diagnosis is then confirmed by high Loa-specific antibody titer and a peripheral blood smear that often shows the microfilariae. PCR is the gold standard for diagnosis. Administration of oral ivermectin or diethylcarbamazine (DEC) is the optimal pharmacologic therapy for ''Loa loa''. However, surgical removal of the parasite as it passes through the corneal conjunctiva or the nasal bridge may be necessary.
|AnswerA=Black fly
|AnswerA=Black fly
|AnswerAExp=The black fly is the vector for Onchocerciasis.
|AnswerAExp=The black fly is the vector for [[onchocerciasis]] (fever blindness) caused by ''[[Onchocerca volvulus]]''.
|AnswerB=Soft tick
|AnswerB=Soft tick
|AnswerBExp=The soft tick is a vector for relapsing fever.
|AnswerBExp=The soft tick is a vector for [[relapsing fever]].
|AnswerC=Hard tick
|AnswerC=Ixodes tick
|AnswerCExp=The hard tick is a vector for lyme diseae, rocky mountain spotted fever, babesiosis, ehrlichiosis, tick-borne meningoencephalitis, colorado tick fever, Crimean-Congo hemorrhagic fever, and tick paralysis.
|AnswerCExp=Ixodes tick is the vector for [[lyme diseae]] and [[babesiosis]].
|AnswerD=The genus Chrysops
|AnswerD=Deer fly
|AnswerDExp=This is the correct answer. The vector for loa loa filariasis are flies from two species of the genus Chrysops; C. silacea and C. dimidiata.
|AnswerDExp=[[Deer fly]] (or Deerfly) is the vector for ''[[Loa loa]]''.
|AnswerE=Sandfly
|AnswerEExp=Sandfly is the vector for [[leishmaniasis]].
|EducationalObjectives=Deer flies transmit the infectious human filarial nematode ''Loa loa'' (eye worm) that causes [[loiasis]], a disease characterized by  Calabar swellings, pruritus, and worm migration in the conjunctiva causing a "foreign body sensation".
|References=Antinori S, Schifanella L, Million M, et al. Imported ''Loa loa'' filariasis: three cases and a review of cases reported in non-endemic countries in the past 25 years. Int J Infect Dis. 2012; 16(9):e649-62
 
Cho H, Lee Y, Shin S, et al. Sunconjunctival ''Loa loa'' with Calabar swelling. J Korean Med Sci. 2008;23(4):731-3.
 
 
First Aid 2014 page 154
|RightAnswer=D
|RightAnswer=D
|WBRKeyword=Loa Loa, Infectious disease, Deerfly, Deerflies, eye worm, Worm, Zoonotic, Microbiology, Vector
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 23:17, 27 October 2020

 
Author PageAuthor::Kalsang Dolma (Reviewed by Rim Halaby, Will Gibson, and Yazan Daaboul)
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles
Prompt [[Prompt::A 28-year-old female immigrant presents to the emergency department (ED) for diffuse pruritus and a foreign body sensation in her right eye for the past 2 hours. The patient states that she returned from a rainforest trip in western Africa 8 months ago. The patient has no significant past medical history. She takes no medications and has no known allergies. Physical examination is remarkable for a mild eyelid swelling and non-tender localized angioedema in the right forearm. Dim slit-lamp examination of the the right eye shows a thread-like worm in the subconjunctival space. Initial laboratory work-up in the ED reveals eosinophilia. Peripheral smear and PCR confirm the diagnosis. Which of the following vectors is most likely associated with the infectious agent responsible for this patient's condition?]]
Answer A AnswerA::Black fly
Answer A Explanation [[AnswerAExp::The black fly is the vector for onchocerciasis (fever blindness) caused by Onchocerca volvulus.]]
Answer B AnswerB::Soft tick
Answer B Explanation [[AnswerBExp::The soft tick is a vector for relapsing fever.]]
Answer C AnswerC::Ixodes tick
Answer C Explanation [[AnswerCExp::Ixodes tick is the vector for lyme diseae and babesiosis.]]
Answer D AnswerD::Deer fly
Answer D Explanation [[AnswerDExp::Deer fly (or Deerfly) is the vector for Loa loa.]]
Answer E AnswerE::Sandfly
Answer E Explanation [[AnswerEExp::Sandfly is the vector for leishmaniasis.]]
Right Answer RightAnswer::D
Explanation [[Explanation::Loa loa is a human filarial nematode (roundworm) whose adult form migrates in the subcutaneous and deep connective tissues. Microfilariae, ingested by mango flies, horse flies, or deer flies (Chrysops spp.), may be transmitted to humans following a bite by the infected flies. The time for the Loa Loa to mature requires approximately 6-12 months, but a prolonged latency (several years) is not uncommon.

Loa loa is called the "eye worm" because it can cross the conjunctivae, creating an uncomfortable "foreign sensation in the eyes" among infected patients. Additionally, diffuse pruritus and a Calabar swelling, a non-tender angioedema that is often observed in the forearms, may be seen in approximately half of the cases. The diagnosis is suspected when patients report a history of travel to endemic African regions, consistent clinical symptoms, and the presence of eosinophilia. The diagnosis is then confirmed by high Loa-specific antibody titer and a peripheral blood smear that often shows the microfilariae. PCR is the gold standard for diagnosis. Administration of oral ivermectin or diethylcarbamazine (DEC) is the optimal pharmacologic therapy for Loa loa. However, surgical removal of the parasite as it passes through the corneal conjunctiva or the nasal bridge may be necessary.
Educational Objective: Deer flies transmit the infectious human filarial nematode Loa loa (eye worm) that causes loiasis, a disease characterized by Calabar swellings, pruritus, and worm migration in the conjunctiva causing a "foreign body sensation".
References: Antinori S, Schifanella L, Million M, et al. Imported Loa loa filariasis: three cases and a review of cases reported in non-endemic countries in the past 25 years. Int J Infect Dis. 2012; 16(9):e649-62

Cho H, Lee Y, Shin S, et al. Sunconjunctival Loa loa with Calabar swelling. J Korean Med Sci. 2008;23(4):731-3.


First Aid 2014 page 154]]

Approved Approved::Yes
Keyword WBRKeyword::Loa Loa, WBRKeyword::Infectious disease, WBRKeyword::Deerfly, WBRKeyword::Deerflies, WBRKeyword::eye worm, WBRKeyword::Worm, WBRKeyword::Zoonotic, WBRKeyword::Microbiology, WBRKeyword::Vector
Linked Question Linked::
Order in Linked Questions LinkedOrder::