Podcast
Questions and Answers
Why is rabies post-exposure prophylaxis (PEP) ineffective once symptoms manifest?
Why is rabies post-exposure prophylaxis (PEP) ineffective once symptoms manifest?
- The virus transitions to a dormant stage, making it undetectable by the immune system.
- The virus has already caused irreversible damage to the central nervous system by the time symptoms appear. (correct)
- The patient develops an immunity to the HRIG and vaccine, rendering them useless.
- The antibodies produced by PEP exacerbate the inflammation, worsening the patient's condition.
What is the most likely mechanism by which rabies virus spreads from the initial site of infection to the central nervous system (CNS)?
What is the most likely mechanism by which rabies virus spreads from the initial site of infection to the central nervous system (CNS)?
- Via axonal transport within peripheral nerves, utilizing motor proteins for retrograde movement. (correct)
- Through the lymphatic system, facilitating rapid dissemination throughout the body.
- Directly through the bloodstream, infecting endothelial cells and crossing the blood-brain barrier.
- Through airborne transmission, directly infecting cells within the upper respiratory tract and accessing the brain via the olfactory nerve.
In a patient displaying flaccid paralysis, ascending from the site of a suspected animal bite, which diagnostic consideration would be MOST crucial in differentiating paralytic rabies from Guillain-Barré syndrome?
In a patient displaying flaccid paralysis, ascending from the site of a suspected animal bite, which diagnostic consideration would be MOST crucial in differentiating paralytic rabies from Guillain-Barré syndrome?
- Assessing the patient's deep tendon reflexes to look for areflexia, common in both conditions.
- Testing for hydrophobia and aerophobia, which would strongly suggest Guillain-Barré syndrome.
- Performing a lumbar puncture to analyze cerebrospinal fluid for elevated protein levels.
- Obtaining a skin biopsy from the nape of the neck for immunofluorescent staining of viral antigens. (correct)
A researcher is developing a novel antiviral therapy targeting the rabies virus. Which of the following targets would be most likely to prevent the virus from entering the central nervous system (CNS)?
A researcher is developing a novel antiviral therapy targeting the rabies virus. Which of the following targets would be most likely to prevent the virus from entering the central nervous system (CNS)?
Why is antemortem diagnosis of the rabies virus so difficult?
Why is antemortem diagnosis of the rabies virus so difficult?
In furious rabies, autonomic nervous system overactivity causes dilated pupils, excessive sweating, and increased salivation. Which of the following mechanisms is most directly responsible for these manifestations?
In furious rabies, autonomic nervous system overactivity causes dilated pupils, excessive sweating, and increased salivation. Which of the following mechanisms is most directly responsible for these manifestations?
Following a bite from a stray animal, a patient receives both human rabies immunoglobulin (HRIG) and a killed rabies vaccine as part of PEP. What is the primary immunological rationale for administering these treatments in conjunction?
Following a bite from a stray animal, a patient receives both human rabies immunoglobulin (HRIG) and a killed rabies vaccine as part of PEP. What is the primary immunological rationale for administering these treatments in conjunction?
How do Negri bodies form in rabies-infected cells, and what is their diagnostic significance?
How do Negri bodies form in rabies-infected cells, and what is their diagnostic significance?
A researcher discovers a new variant of the rabies virus that exhibits a significantly shorter incubation period. Which of the following mechanisms would most likely explain this accelerated disease progression?
A researcher discovers a new variant of the rabies virus that exhibits a significantly shorter incubation period. Which of the following mechanisms would most likely explain this accelerated disease progression?
If a new rabies virus strain were discovered that did not form Negri bodies, how would this affect postmortem diagnosis?
If a new rabies virus strain were discovered that did not form Negri bodies, how would this affect postmortem diagnosis?
Flashcards
Rabies virus
Rabies virus
A helical, enveloped, negative-sense, single-stranded RNA virus belonging to the Rhabdoviridae family.
Early Phase (Prodromal Phase) of Rabies
Early Phase (Prodromal Phase) of Rabies
Malaise, headache, fever, and paresthesia (tingling, itching, or burning) at the infection site.
Encephalitic (Furious) Rabies
Encephalitic (Furious) Rabies
Fever, hydrophobia, foaming at the mouth, agitation, and aggression due to autonomic nervous system overactivity.
Paralytic (Dumb) Rabies
Paralytic (Dumb) Rabies
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Rabies virus binding site
Rabies virus binding site
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Negri bodies
Negri bodies
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Post-Exposure Prophylaxis (PEP) for Rabies
Post-Exposure Prophylaxis (PEP) for Rabies
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RT-PCR for Rabies
RT-PCR for Rabies
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Rabies Spread
Rabies Spread
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High-Risk Groups for Rabies
High-Risk Groups for Rabies
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Study Notes
- Rabies is caused by a helical, enveloped, negative-sense, single-stranded RNA virus belonging to the Rhabdoviridae family.
- Transmission primarily occurs through the saliva of infected animals, such as dogs, skunks, raccoons, foxes, and bats, usually via a bite.
- In rare instances, rabies can spread through airborne droplets, such as in bat caves.
Early Phase (Prodromal Phase)
- Symptoms include malaise, headache, fever, and paresthesia (tingling, itching, or burning) at the infection site.
Encephalitic (Furious) Rabies
- This is the most common presentation.
- Symptoms include fever and hydrophobia (fear of water).
- There is foaming at the mouth caused by uncontrollable pharyngeal spasms when trying to drink.
- Other signs include saliva production, sweating, and dilated pupils due to autonomic nervous system overactivity, as well as agitation and aggression.
Paralytic (Dumb) Rabies
- This presentation is less common, accounting for about 20% of cases.
- Symptoms include flaccid paralysis starting at the bite site and ascending gradually.
- It leads to respiratory failure, coma, and death.
- There is no hydrophobia or agitation.
- Paralytic rabies is often misdiagnosed as Guillain-Barré syndrome.
- Both types of rabies are usually fatal, with death resulting from respiratory failure due to spasms or paralysis.
- Glycoprotein spikes on the virus envelope bind to nicotinic acetylcholine receptors on muscle cells, allowing entry.
- Rabies prefers neurons and crosses the neuromuscular junction to enter motor neurons for replication.
- The virus travels retrograde along peripheral nerves toward the CNS, using dynein, at a rate of a few millimeters per day.
- Once in the CNS, it invades the brain and spreads to other structures, including the salivary glands.
Diagnosis
- Antemortem (before death) diagnosis requires multiple tests due to insufficient sensitivity of single tests.
- RT-PCR detects viral RNA in saliva.
- Immunofluorescent staining on a skin biopsy detects viral antigen in cutaneous nerves of hair follicles.
- Antibody detection is done in blood or cerebrospinal fluid (CSF).
- Postmortem (after death) diagnosis involves detecting:
- Negri bodies in brain cells: intracellular sacs full of viral proteins, found in Purkinje cells (cerebellum) and pyramidal cells of the hippocampus.
- These inclusions are eosinophilic, staining dark pink with eosin dye.
- Viral antigens in brain tissue are also detected.
Incubation Period
- The virus has an incubation period of 1–3 months.
- The time depends on the entry location, with longer distances from the CNS leading to delayed symptoms.
Treatment and Prevention
- Post-Exposure Prophylaxis (PEP): must be given before symptoms appear, including wound cleaning, passive immunization with human rabies immunoglobulin (HRIG), and active immunization with a killed rabies vaccine.
- Once symptoms develop, only palliative care is given.
- The rabies vaccine is given preemptively to high-risk groups, such as veterinarians and lab workers handling rabies virus.
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