West Nile Virus: Symptoms and Diagnosis

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Questions and Answers

Which of the following statements accurately describes the transmission dynamics that differentiate Zika virus from other flaviviruses like West Nile virus and Japanese encephalitis virus?

  • Zika virus can replicate efficiently in human hosts, allowing human-to-mosquito transmission, whereas West Nile virus and Japanese encephalitis virus primarily cycle between animals and mosquitoes. (correct)
  • Zika virus transmission is primarily vector-independent, relying on direct human-to-human contact, unlike the strict vector-borne transmission of West Nile virus and Japanese encephalitis virus.
  • Zika virus has a limited capacity to replicate in human hosts, which requires multiple mosquito bites for sustained transmission, unlike other flaviviruses.
  • Zika virus, unlike West Nile virus and Japanese encephalitis virus, relies exclusively on avian hosts for amplification, limiting its transmission range.

A 68-year-old patient presents with acute onset of altered mental status, high fever, and neck stiffness. A lumbar puncture reveals evidence of viral meningitis. Given the patient's age and symptoms, which of the following diagnostic considerations should be prioritized to differentiate between West Nile virus and Japanese encephalitis virus?

  • Evaluate the presence of tremors in the upper extremities, a unique feature associated with West Nile meningitis.
  • Assess the patient's recent travel history and potential exposure to mosquito vectors in Asia.
  • Perform serological tests to detect IgM antibodies specific to each virus to confirm the diagnosis. (correct)
  • Conduct a thorough examination to identify any skin rashes, which are more commonly associated with Japanese encephalitis virus.

In the context of flavivirus infections, how does the role of the Culex mosquito species differ in the transmission cycles of West Nile virus (WNV) and Japanese encephalitis virus (JEV)?

  • Culex mosquitoes equally mediate the transmission of both WNV and JEV, serving as the main vectors in both disease cycles without any difference in their roles.
  • Culex mosquitoes facilitate the enzootic cycle of WNV among birds, while in JEV they primarily transmit the virus between pigs and humans.
  • Culex mosquitoes are primary vectors for WNV but play no significant role in JEV transmission, which relies on Aedes species.
  • Culex species are the primary vectors for both WNV, maintaining the disease in bird populations, and JEV, transmitting it between wading birds, pigs, and occasionally humans. (correct)

Given that there is no specific antiviral treatment for Zika virus, what is the rationale for advising patients to avoid NSAIDs like ibuprofen until dengue is ruled out?

<p>NSAIDs increase the risk of hemorrhagic complications in dengue fever, a possibility that must be excluded before their use. (A)</p> Signup and view all the answers

How does the ability of Zika virus to infect and affect keratinocytes, fibroblasts, and dendritic cells contribute to its unique pathogenesis compared to West Nile virus and Japanese encephalitis virus?

<p>It contributes to specific clinical manifestations such as skin rash, muscle and joint pain, and conjunctivitis, which are less commonly observed in West Nile virus and Japanese encephalitis virus infections. (B)</p> Signup and view all the answers

Which statement accurately contrasts the long-term neurological sequelae associated with Japanese encephalitis virus (JEV) and the potential congenital effects linked to Zika virus (ZIKV)?

<p>JEV can lead to significant motor and cognitive impairments in survivors, whereas ZIKV is linked to microcephaly and other severe fetal abnormalities. (A)</p> Signup and view all the answers

Considering the infection process of West Nile virus, what is the functional significance of the E2 lipid membrane protein in the viral lifecycle?

<p>It mediates the entry of the virus into host cells through clathrin-mediated endocytosis. (D)</p> Signup and view all the answers

How does the neurotropism of Japanese encephalitis virus (JEV) contribute to the severity and specific neurological manifestations of the disease?

<p>JEV's ability to cross the blood-brain barrier and infect the basal ganglia, thalamus, midbrain, and pons results in encephalitis, seizures, and potential death. (B)</p> Signup and view all the answers

Which of the following statements accurately distinguishes the diagnostic approach for Zika virus infection from that of West Nile virus and Japanese encephalitis virus?

<p>Zika virus is diagnosed by detecting IgM antibodies in serum or cerebrospinal fluid (CSF) using an immunoassay test, while West Nile virus and Japanese encephalitis virus diagnosis may involve MRI imaging to reveal characteristic brain lesions. (C)</p> Signup and view all the answers

What is the most critical implication of Zika virus's ability to be transmitted through blood transfusions and sexual contact, compared to the exclusive vector-borne transmission of West Nile virus?

<p>It increases the risk of Zika virus outbreaks in regions with limited mosquito vector populations. (D)</p> Signup and view all the answers

Flashcards

West Nile Virus

A single-stranded, positive-sense, enveloped RNA virus transmitted by mosquitoes.

West Nile Virus Infection Process

Enters cells via E2 protein, replicates, and exits via budding.

West Nile Virus Symptoms

Fever, headache, rash (moderate); meningitis/encephalitis, tremors (severe).

West Nile Virus Treatment and Prevention

Supportive care; prevention (repellent, protective clothing).

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Japanese Encephalitis Virus (JEV)

Arbovirus transmitted by Culex mosquitoes, primarily between pigs/birds.

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Japanese Encephalitis Virus (JEV) Symptoms

Asymptomatic/flu-like (mild); encephalitis, seizures (severe).

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Japanese Encephalitis Virus (JEV) Treatment

Supportive care and prevention via mosquito control and vaccination.

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Zika Virus

An arbovirus transmitted by Aedes mosquitoes.

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Zika Virus Infection Process

Infects keratinocytes, hijacks cell machinery, and can transmit via blood/sex.

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Zika Virus Symptoms

Low-grade fever, rash, joint pain; can cause microcephaly in newborns.

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Study Notes

  • Japanese Encephalitis Virus, Zika Virus, and West Nile Virus are single-stranded, positive-sense, enveloped RNA-containing flaviviruses.

West Nile Virus

  • West Nile Virus (WNV) is an arbovirus transmitted by insects.
  • The primary vector is the mosquito, especially female Culex species.
  • WNV was first discovered in Uganda, west of the Nile, and has since been reported worldwide.
  • WNV comprises positive single-stranded RNA surrounded by an icosahedral capsid and a lipid membrane envelope.

West Nile Virus Infection Process

  • WNV enters host cells via clathrin-mediated endocytosis through the E2 lipid membrane protein.
  • The virus membrane fuses with the host cell membrane, releasing RNA into the cytoplasm.
  • The virus replicates and exits the host cell through outward budding of the host plasma membrane.

West Nile Virus Symptoms and Diagnosis

  • Symptoms develop 2 to 14 days post-infection.
  • Approximately 80% of those infected are asymptomatic; 20% develop moderate to severe symptoms.
  • Moderate symptoms include fever, chills, headache, vomiting, or rash.
  • Severe symptoms include meningitis or encephalitis, seizures, altered mental status, weakness, vision changes, severe headaches, neck pain or stiffness, and tremors.
  • Tremors in the upper extremities is a unique feature of West Nile meningitis.

West Nile Virus Treatment

  • Treatment is supportive, with steroids or antiviral agents like ribavirin considered for meningitis or encephalitis.
  • Prevention includes using mosquito repellent and wearing long-sleeve shirts and pants.

Japanese Encephalitis Virus

  • Japanese Encephalitis Virus (JEV) can cause encephalitis.
  • Less than 1% of infected individuals develop neuroinvasive disease.
  • JEV is the leading cause of viral encephalitis in Asia, with 68,000 new cases annually.

Japanese Encephalitis Virus Infection Process

  • JEV primarily cycles between pigs and wading birds, transmitted by Culex mosquitoes.
  • Humans are incidental hosts when bitten by infected mosquitoes.
  • The virus enters the bloodstream (viremia) and can infect macrophages.
  • In some cases, JEV crosses the blood-brain barrier, leading to brain infection and damage in the basal ganglia, thalamus, midbrain, and pons.

Japanese Encephalitis Virus Symptoms and Diagnosis

  • The incubation period is 5 to 15 days, with varying symptoms.
  • Mild cases present as asymptomatic or mild flu-like illness.
  • Severe cases involve encephalitis, seizures (more common in children), and potential death.

Japanese Encephalitis Virus Treatment and Prevention

  • Treatment is supportive, and there is no specific antiviral therapy.
  • Prevention includes mosquito control and vaccination.

Zika Virus

  • Zika virus is an arbovirus transmitted by mosquitoes.
  • The virus multiplies after an infected mosquito bites a human.
  • It is well-adapted to humans, allowing replication to levels that can reinfect mosquitoes, continuing the transmission cycle.
  • Zika virus can be found in the blood during the first week of infection.
  • Primarily transmitted by Aedes mosquitoes, which are most active during the daytime.

Zika Virus Infection Process

  • Zika virus infects keratinocytes, fibroblasts, and dendritic cells.
  • The virus injects single-stranded positive RNA into host cells, using the cellular machinery to replicate.
  • Infected cells die and release more viruses to spread the infection.
  • Also transmitted through blood transfusions and sexual contact.

Zika Virus Symptoms

  • Most infected people are asymptomatic (80%).
  • When present, symptoms are usually mild, including low-grade fever, skin rash, muscle and joint pain, headaches, and conjunctivitis (red eyes).
  • The incubation period is estimated to be a few days to a week.
  • Zika virus can be transmitted from mother to baby, leading to microcephaly (abnormally small head and brain).

Complications of Zika Virus

  • Microcephaly leads to severe neurological and intellectual deficits, seizures, and vision/hearing impairments.

Zika Virus- Treatment and Prevention

  • There is no vaccine.
  • Treatment is symptomatic: rest and hydration, acetaminophen for pain and fever (avoid NSAIDs until dengue is ruled out).
  • Prevention includes avoiding areas with outbreaks, using mosquito repellent, and taking precautions against mosquito bites.

Zika Virus Diagnosis

  • Diagnosis involves detecting IgM antibodies in serum or CSF using an immunoassay test.
  • CT or MRI scans may help rule out other neurological diseases.
  • MRI imaging may reveal characteristic brain lesions.

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