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NBME 16 Answers

nbme16/Block 2/Question#38 (reveal difficulty score)
A 3-year-old boy is brought to the physician ...
Feces-contaminated soil ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–

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submitted by โˆ—cassdawg(1779)

I think this is Strongyloides stercoralis (threadworm) is a roundworm whose larvae live in soil and who can cause pulmonary disease. It has the ability to penetrate skin from the soil but can also be obtained by ingesting feces contaminates soil (FA2020 p159)

Most intestinal roundworms are fecal-oral route except strongyloides which can also penetrate skin, hookworm (necator americanus) which only penetrates skin, and trichinella which can come from undercooked meats (especially pork) but whose symptoms do not match that of the patient. Trichinella larvae enter the blood stream and infect muscle and can also cause trichinosis with fever, nausea, vomiting, periorbital edema, and myalgia.

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shervinbd  I think it is Ascaris, not Stringlyloides. The symptoms could be explained by Loeffler syndrome, caused by Ascaris larva migration. Ascaris is transmitted through fecal oral route, so ingestion of feces contaminated soil could cause the problem. Per FA, Strongylides is transmitted by larva penetrating skin. +23
drmifta  Its Ascaris. Fecal oral transmission -> Larvae penitrate GIT -> Blood Stream -> Lung {Maturation, Respiratory Symptom} -> Coughed up and swallowing -> Adult Warm in GIT -> Egg release -> Egg in stool. +1
i_hate_it_here  Didn't the stem mention that roundwarm larvae were found? I thought Ascaris is diagnosed by bile coated eggs in feces? +1
sexymexican888  I actually think @cassdawg is right. Its strongyloides. They found larvae in the feces (you find eggs in feces with ascaris) you can get pulmonary sx in both. Ascaris is also usually fecal oral transmission so its more likely to come from someone making food with contaminated hands. Strongyloides is transmitted through soil or sand and the larvae penetrate your feet so this makes more sense. +2
sexymexican888  You can find this is FA 2020 Pg 159. Also if you look at the table strongyloides is assoc. with pulmonary sx. However I think its both cause according to sketchy micro ascaris presents with respiratory sx +
coco  Although Strongyloides nematode worm infections are not overly common in the United States, the Appalachian area of the Southeast have reported cases. Ascaris lumbricoides is a common parasitic infection in Asia, Africa, and South America. Most cases in the United States arise in travelers to these regions. Loeffler syndrome can be caused by Strongyloides and Ascaris. Ascar:Stool microscopy reveals an oval egg with a thick outer shell and a single interior ovum Strongyloides:rhabditiform larvae seen in feces under microscope so.I think this is Strongyloides.If I make a mistake,please correct me. +2
melanoma  I think is ascaris lumbricoides also due to the size of the larva. UW Q 15549 +

 +1  upvote downvote
submitted by โˆ—victor_abdullatif(10)

Going against the grain here, I think this is Toxocariasis (organism: Toxocara canis)

Reasoning: (from UTD): Toxocariasis (also called visceral larva migrans [VLM]) refers to human infection caused by helminths that are not natural human parasites. Toxocariasis occurs as a result of human infection with the larvae of the dog ascarid, Toxocara canis, or, less commonly, the cat ascarid, Toxocara cati. VLM is principally a disease of young children, especially those with exposure to playgrounds and sandboxes contaminated by dog or cat feces.

Transpulmonary migration of Strongyloides larvae can produce dry cough, throat irritation, dyspnea, wheezing, and hemoptysis. Similarly, pulmonary involvement of toxocariasis may cause dyspnea, wheezing, and a chronic, nonproductive cough. Strongyloides larvae may be detected in stool, sputum, bronchoalveolar lavage fluid, or pleural fluid

Considering that it's a 3-year-old boy and that ingestion is the primary mode of transmission, I think Toxocariasis is the better diagnosis here

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chaosawaits  Definitive diagnosis of toxocariasis is larvae in stool. It definitely makes more sense than Strongyloides, which is found in the soil but PE found no abnormalities. So skin puncture is unlikely. Ascaris is fecal-oral but is more likely to be in contaminated food and is largely asymptomatic. Also, Ascaris would show eggs in feces, not larvae. +

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