WBR0084

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::