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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Neurology, Infectious Disease
|SubCategory=Neurology, Infectious Disease
|Prompt=A 38-year old male was brought to the emergency department by his mother with complaints of hydrophobia and disorientation. History revealed that he has had three episodes of seizures in the past 2 weeks. Some days later, he was said to have had hallucinations, lapsed into a coma and died. The causative organism involved acts through which of the following?
|Prompt=A 38-year old male is brought to the emergency department by his mother with complaints of hydrophobia and disorientation. She reports that he has had three episodes of seizures in the past 2 weeks. Three days later, the patient experiences vivid visual hallucinations, lapses into a coma and dies. The most likely causal organism binds to which of the following cell surface molecules?
|Explanation=The patient in this vignette has Rabies Encephalitis, transmitted from dog, bat, raccoon and skunk bites. The disease progresses from fever, malaise to agitation, photophobia, hydrophobia, seizures, hallucination and then to paralysis, coma and death. After the bite from an infected animal, the virus binds to peripheral nerves by binding to nicotinic acetylcholine receptors or indirectly into the muscle at the site of inoculation. The virus moves by retrograde axoplasmic transport to dorsal root ganglia and the spinal cord.  The brain becomes rapidly infected when the virus gets to the spinal cord.
|Explanation=The patient in this vignette has [[rabies]] encephalitis, a viral infection that is transmitted from dog, bat, raccoon and skunk bites. The disease progresses from fever, malaise to agitation, photophobia, hydrophobia, seizures, hallucination and then to paralysis, coma and death. After the bite from an infected animal, the virus infiltrates peripheral nerves by binding to nicotinic acetylcholine receptors at the site of inoculation. The virus moves by retrograde axoplasmic transport to dorsal root ganglia and the spinal cord.  The brain becomes rapidly infected when the virus gets to the spinal cord.  The incubation period during which patients do not display symptoms is typically months.  However, death usually occurs within days of symptom onset.
|AnswerA=FGF3 receptors
|AnswerA=SNARE proteins
|AnswerAExp=Cell-signaling defect of FGF (Fibroblast growth factor) receptor 3 is seen in achondroplasia, which results in dwarfism.
|AnswerAExp=SNARE proteins are responsible for neurotransmitter release at synaptic junctions.  Clostridium tetani and clostridium botulinum produce toxins that cleave SNARE proteins and thereby cause paralysis.
|AnswerB=CD4 receptors
|AnswerB=CD4 receptors
|AnswerBExp=CD4 is the receptor for HIV, which is used as a marker of disease progression and when to commence therapy for HIV infection.
|AnswerBExp=HIV-1 binds to CD4 through its viral envelope protein gp120 to gain entry into host T-cells.  The number of CD4-positive T cells in the blood is a marker of disease progression in HIV infected patients.
|AnswerC=LDL receptors
|AnswerC=LDL receptors
|AnswerCExp=LDL receptor is associated with familial hypercholesterolemia, an autosomal dominant disorder with absent or decreased LDL receptors. It causes an accelerated atherosclerosis, tendon (Achilles) xanthomas and corneal arcus.
|AnswerCExp=LDL receptor is associated with familial hypercholesterolemia, an autosomal dominant disorder with absent or decreased LDL receptors. Familial hypercholesterolemia is associated with accelerated atherosclerosis, tendon (Achilles) xanthomas and corneal arcus.
|AnswerD=CCR5 receptors
|AnswerD=CCR5 receptors
|AnswerDExp=CCR5 receptor is a co-receptor for HIV virus found on macrophages and TH cells.
|AnswerDExp=CCR5 receptor is a co-receptor for HIV virus found on macrophages and Th cells.  Individuals with CCR5 mutations are protected from HIV infection.
|AnswerE=Ach receptors
|AnswerE=Acetylcholine receptors
|AnswerEExp=The rabies virus binds to nicotinic Ach receptors to cause the disease.
|AnswerEExp=The rabies virus binds to nicotinic acetylcholine receptors to travel from peripheral nerves to the brain.
|EducationalObjectives=The rabies virus binds to nicotinic acetylcholine receptors to travel from peripheral nerves to the brain.
|References=First Aid 2014 page 165, Lentz TL. Rabies virus binding to an acetylcholine receptor alpha-subunit peptide. J Mol Recognit. 1990;3(2):82-8.
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=Rabies, Virus, Viruses, Microbiology, Neurodegenerative, Hallucination, Seizure
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 00:19, 21 March 2014
Author [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::Neurology, SubCategory::Infectious Disease
Prompt [[Prompt::A 38-year old male is brought to the emergency department by his mother with complaints of hydrophobia and disorientation. She reports that he has had three episodes of seizures in the past 2 weeks. Three days later, the patient experiences vivid visual hallucinations, lapses into a coma and dies. The most likely causal organism binds to which of the following cell surface molecules?]]
Answer A AnswerA::SNARE proteins
Answer A Explanation AnswerAExp::SNARE proteins are responsible for neurotransmitter release at synaptic junctions. Clostridium tetani and clostridium botulinum produce toxins that cleave SNARE proteins and thereby cause paralysis.
Answer B AnswerB::CD4 receptors
Answer B Explanation AnswerBExp::HIV-1 binds to CD4 through its viral envelope protein gp120 to gain entry into host T-cells. The number of CD4-positive T cells in the blood is a marker of disease progression in HIV infected patients.
Answer C AnswerC::LDL receptors
Answer C Explanation [[AnswerCExp::LDL receptor is associated with familial hypercholesterolemia, an autosomal dominant disorder with absent or decreased LDL receptors. Familial hypercholesterolemia is associated with accelerated atherosclerosis, tendon (Achilles) xanthomas and corneal arcus.]]
Answer D AnswerD::CCR5 receptors
Answer D Explanation AnswerDExp::CCR5 receptor is a co-receptor for HIV virus found on macrophages and Th cells. Individuals with CCR5 mutations are protected from HIV infection.
Answer E AnswerE::Acetylcholine receptors
Answer E Explanation AnswerEExp::The rabies virus binds to nicotinic acetylcholine receptors to travel from peripheral nerves to the brain.
Right Answer RightAnswer::E
Explanation [[Explanation::The patient in this vignette has rabies encephalitis, a viral infection that is transmitted from dog, bat, raccoon and skunk bites. The disease progresses from fever, malaise to agitation, photophobia, hydrophobia, seizures, hallucination and then to paralysis, coma and death. After the bite from an infected animal, the virus infiltrates peripheral nerves by binding to nicotinic acetylcholine receptors at the site of inoculation. The virus moves by retrograde axoplasmic transport to dorsal root ganglia and the spinal cord. The brain becomes rapidly infected when the virus gets to the spinal cord. The incubation period during which patients do not display symptoms is typically months. However, death usually occurs within days of symptom onset.

Educational Objective: The rabies virus binds to nicotinic acetylcholine receptors to travel from peripheral nerves to the brain.
References: First Aid 2014 page 165, Lentz TL. Rabies virus binding to an acetylcholine receptor alpha-subunit peptide. J Mol Recognit. 1990;3(2):82-8.]]

Approved Approved::Yes
Keyword WBRKeyword::Rabies, WBRKeyword::Virus, WBRKeyword::Viruses, WBRKeyword::Microbiology, WBRKeyword::Neurodegenerative, WBRKeyword::Hallucination, WBRKeyword::Seizure
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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