A 32-year-old man is brought to the emergency department due to fever, agitation, and disorientation. According to his family, the patient has been acting strangely and seeing and hearing things that do not exist. He also drools excessively and has severe, painful throat spasms when he attempts to eat or drink. The patient returned 4 weeks ago from a camping trip in New Mexico. Physical examination shows a confused and combative patient with mydriasis and neck rigidity. Which of the following acts as an entry receptor for the causative agent of this patient's condition?

Question

A 32-year-old man is brought to the emergency department due to fever, agitation, and disorientation.  According to his family, the patient has been acting strangely and seeing and hearing things that do not exist.  He also drools excessively and has severe, painful throat spasms when he attempts to eat or drink.  The patient returned 4 weeks ago from a camping trip in New Mexico.  Physical examination shows a confused and combative patient with mydriasis and neck rigidity.  Which of the following acts as an entry receptor for the causative agent of this patient's condition?

Quizplus · Accepted Answer

11ec160b_3885_647d_9249_2d3d85ebc811_MD0001_00 This patient's progressive agitation, disorientation, and pharyngospasm raises strong suspicion for rabies, a fatal infection caused by a neurotrophic virus from the Rhabdoviridae family. Exposure usually occurs when patients come into contact with contaminated saliva from an infected animal (eg, dog, bat), which likely occurred during this patient's camping trip in New Mexico. The virus contains a bullet-shaped envelope with knob-like glycoproteins that allow it to attach to the nicotinic acetylcholine receptor at the neuromuscular junction. The virus replicates locally within the muscle tissue of the bite wound for several days or weeks and then travels in a retrograde fashion through peripheral nerve axons to the dorsal root ganglia. From there, it rapidly ascends the spinal cord and infects the diencephalon, hippocampus, and brain stem. Patients initially develop a nonspecific flu-like prodrome (fever, malaise, myalgias); paresthesias radiating proximally from a known wound site can be an important clue. When the virus enters the CNS, the infection typically evolves into rabies encephalitis, which is characterized by painful pharyngeal spasms leading to avoidance of water (hydrophobia), mental status changes, muscular rigidity, and autonomic dysfunction (pupil dilation, hypersalivation). Once symptoms of rabies encephalitis appear, postexposure prophylaxis is no longer effective and nearly all patients die. (Choice A) Epstein-Barr virus binds to CD21 on inactive B-lymphocytes and results in infectious mononucleosis, which is usually characterized by sore throat, swollen lymph nodes, malaise, and atypical lymphocytosis. Because this virus is a member of the Herpesviridae family, initial infection is followed by a long-standing (usually asymptomatic) latent infection. (Choice C) Rhinovirus binds intracellular adhesion molecule-1, which is found on nasopharyngeal and adenoid epithelial cells. It is associated with the common cold, not agitation, pharyngeal spasm, and hallucinations. (Choice D) The influenza virus has hemagglutinin glycoproteins that allow it to attach to sialic acids on the surface of the respiratory epithelium. Influenza is usually characterized by fever, myalgias, cough, headache, and respiratory symptoms; agitation and pharyngeal spasm are not typical features. (Choice E) Cytomegalovirus binds to vascular endothelial integrins, leading to replication within endothelial cells. Initial cytomegalovirus infections are often asymptomatic, but patients can develop a mononucleosis-type syndrome (eg, lethargy, fever, atypical lymphocytosis). Psychosis and disorientation would be atypical. Educational objective: Rabies virus has a bullet-shaped envelope with knob-like glycoproteins that bind to nicotinic acetylcholine receptors. Once transmission occurs (usually due to a bite wound from an infected animal), the virus replicates locally in muscle tissue for several days or weeks before spreading in a retrograde fashion through the peripheral nerve axons to the central nervous system. __________ References: The acetylcholine receptor as a cellular receptor for rabies virus. (http://www.ncbi.nlm.nih.gov/pubmed/6367238) Rabies virus binding to the nicotinic acetylcholine receptor alpha subunit demonstrated by virus overlay protein binding assay. (http://www.ncbi.nlm.nih.gov/pubmed/8887475)

A 32-Year-Old Man Is Brought to the Emergency Department Due