Public Health Quiz: Rabies and West Nile Virus

Viral Pathogens of the CNS/Encephalitis

• This presentation covers viral causes of CNS infections, including meningitis and encephalitis
• Meningitis: inflammation of the meninges
• Encephalitis: inflammation of the brain parenchyma
• Viral meningitis is typically caused by enteroviruses, often self-limiting
• Viral encephalitis: HSV, WNV, Tick-borne, Japanese, Polio, Rabies, and other viruses can cause CNS manifestations
• Other important viruses with CNS manifestations include polio, Zika, measles, JC virus, and HIV.
• Transmissible spongiform encephalopathies (TSEs) are also discussed, including their aetiology and the differences between sporadic and variant CJD.

Key Differences Between Meningitis and Encephalitis

• Meningitis is inflammation of the meninges (membranes surrounding the brain and spinal cord)
• Encephalitis is inflammation of the brain tissue itself.
• Meningoencephalitis occurs when both the meninges and brain tissue are inflamed.

Viral Infections of the CNS

• Viral infections of the CNS can be part of a generalized infection (e.g., polio) or can solely affect the CNS.
• They can present some time after the initial infection (e.g., measles- associated Subacute sclerosing panencephalitis (SSPE))

Viruses Causing CNS Infection

• Meningitis: Enteroviruses, Herpes viruses (HSV, VZV, HHV6), Mumps
• Encephalitis: Herpes viruses (HSV, VZV, HHV6), Enteroviruses, Mosquito-borne viruses (WNV, JE), Tick-borne flaviviruses, Rabies
• Paralysis: Enteroviruses (esp. poliovirus), WNV, JE, Zika
• Post-infectious complications: Measles (post-infectious encephalitis-including SSPE), VZV (vasculitis, arteritis, stroke).

Viral Meningitis in Ireland

• Provides a visual representation through a graph of the frequency of cases from 1988-2019 in Ireland.
• The data shows which virus subtype was the most frequent cause of viral meningitis in Ireland.

Viral Encephalitis in Ireland

• Provides a visual representation through a graph of the frequency of cases by type from 1992-2019 in Ireland.

Infectious Disease Notifications in Ireland, 2019-2023

• Presents data on the number of reported cases of viral encephalitis, viral hemorrhagic fevers, and viral meningitis in Ireland from 2019-2023
• Categorized by year.

Congenital Infection and CNS Damage

• Rubella, Cytomegalovirus, and Zika virus are associated with congenital damage to the CNS.

Viral Meningitis

• More common than bacterial meningitis
• Viral causes include Enteroviruses (Echoviruses, Coxsackie B, Enterovirus 71), Herpes viruses (Herpes simplex, VZV), Mumps, and Arboviruses (e.g., West Nile virus, Japanese encephalitis virus)
• Route of infection: After primary multiplication in other sites (e.g., GI tract for enteroviruses), the virus can reach the CNS via the bloodstream, along nerve pathways, or through the olfactory mucosa.

How Do Viruses Cause Damage in the CNS?

• The pathology of viral infection in the CNS is multifactorial, including virus multiplication and resultant cellular damage and host immune response (cellular response + cytokines)
• Symptoms typically include fever, headache, stiff neck, vomiting and photophobia

Non-Polio Enteroviruses

• Common pathogens causing viral meningitis, particularly in infants and young children
• Subtypes include Echoviruses, Coxsackie B, and Enterovirus 71.
• Often self-limiting, but can be severe in neonates
• Peak activity is in late spring to autumn.
• Transmission usually through the faecal-oral route, multiplying in the GI tract and occasionally causing GI symptoms leading to the bloodstream and seeding multiple organs including the CNS. .
• Other CNS manifestations like encephalitis (esp. in the East & SE Asia) and acute flaccid paralysis are also listed

CSF Findings in Viral Meningitis

• Provides a schematic table of CSF findings in bacterial, viral, and TB meningitis, including protein levels, glucose levels, and cell types.

CJD- Creutzfeldt-Jakob Disease

• A fatal degenerative brain disease
• Acquired through BSE, contaminated products, and contaminated blood.
• Genetic mutation of a prion protein, or contamination through medical procedures

Herpes Simplex Encephalitis

• HSV-1 is the most frequent cause in Northern Europe
• Commonly affects the temporal lobe in adults and children older than 3 months
• It has a high mortality rate without treatment.
• Diagnosis: MRI, EEG, and CSF with HSV PCR
• Treatment if suspected: IV aciclovir (acyclovir).
• Neonatal HSV encephalitis: typically acquired during delivery via maternal secretions, significantly high mortality rate and diagnosed by IgM presence, treated with IV aciclovir.

Varicella-Zoster Encephalitis (VZV)

• Can be a complication of chicken pox or shingles reactivation
• Presents similarly to HSV encephalitis
• Diagnosis: Detection of VZV DNA by PCR in CSF
• Treatment: high dose aciclovir IV

Rabies

• Viral, zoonotic disease causing acute encephalitis.
• A high number of human deaths annually
• 95% of cases in Africa and Asia.
• Main reservoir: wild and domestic dogs, wolves, foxes, coyotes, dingoes, bats.
• Incubation period: depends on distance virus has to travel to reach CNS (3- >1=2 weeks)
• Diagnosis: clinical, PCR, immunofluorescence, serology and CSF testing (if no prior rabies vaccination)
• Treatment: immediate wound washing, post-exposure prophylaxis (within 10 days of exposure), rabies immunoglobulin, and rabies vaccine.

West Nile Virus

• Arbovirus transmitted via mosquito bites
• Common in temperate countries (late summer/early autumn) and tropical climates.
• Often asymptomatic or has mild flu-like symptoms
• More serious cases can include encephalitis or meningoencephalitis (risk increased with age and immunosuppression)
• Diagnosis: West Nile Virus IgM (blood or CSF), presence of viral RNA early, serology.
• Treatment: supportive, including hydration, fever reduction.

Japanese Encephalitis

• Major cause of encephalitis in Asia; related to WNV
• Transmitted by infected Culex mosquitoes; human= incidental host
• Reservoir: primarily pigs and wading birds
• Endemic in rural agricultural areas (rice paddy fields, flood irrigation)
• Primarily affects children; adults build immunity.
• Symptoms range from asymptomatic to severe neurological disease, including encephalitis and meningoencephalitis.
• Diagnosis: JE virus specific IgM detection on blood & CSF
• Treatment: No antiviral; supportive care

Tick-Borne Encephalitis Virus

• RNA flavivirus, member of arboviruses
• Transmitted by infected Ixodes ticks, occasionally from unpasteurized milk.
• 10-12,000 cases per year
• Incubation period: 6-28 days
• Clinical features: 60-70% asymptomatic; biphasic illness with initial febrile phase, followed by interval and then second phase when CNS involvement occurs, mortality 0.5-1%
• Diagnosis: Travel/exposure hx, viral RNA PCR in blood, TBE IgM and IgG in blood & CSF, convalescent serology
• Prevention: Minimize exposure (avoid tick areas, use repellents), Immunization (part of childhood immunization schedules in some endemic countries).

Other Causes of Viral Encephalitis

• Other enteroviruses (including polio), and various arboviruses can also lead to encephalitis

Poliovirus

• Important cause of paralysis prior to vaccination
• Human-only reservoir; transmitted faecal-orally
• High success with global eradication program, with extremely low incidence in 2020.
• Prevention: live oral or inactivated IM or intradermal vaccines.
• Clinical presentation: most cases are asymptomatic or mild; some cases include meningitis, bulbar or bulbospinal polio.

Paralysis Syndrome

• Different types, including spinal polio (80%), and bulbar/bulbospinal conditions
• Typically causes asymmetric paralysis of muscles innervated by infected anterior horn cells

Polio Re-Emergence

• Waning vaccine uptake and disruptions to vaccine programs have led to re-emergence in areas where polio was previously considered eradicated.
• Critical for public health campaigns.

Zika Virus

• RNA virus of the Flaviviridae family; mainly transmitted via Aedes mosquitos
• Infection of the CNS and peripheral nervous system
• Congenital Zika Syndrome, including severe microcephaly and decreased brain tissue.
• Associated with Guillain-Barre Syndrome, a post-infectious paralysis.

Chronic CNS Viral Infections

• Subacute sclerosing panencephalitis (SSPE) : persistent measles infection in CNS, years after the initial infection, rare, behavioral/intellectual deterioration, seizures.
• HIV Encephalopathy : HIV associated; convulsion, dementia, and progressive multifocal leukoencephalopathy (PML)- opportunistic infections.

Additional notes:

• The slides also include diagrams and graphs illustrating the various aspects of these diseases. The presentation format for these topics is a slide presentation, hence the information is presented in a condensed and detailed way.
• This document summarizes the main points from the slides and is intended for study notes.

Test your knowledge on the recommended protocols for rabies post-exposure prophylaxis and the transmission dynamics of West Nile Virus. This quiz covers key preventive measures and statistics related to these infectious diseases. Challenge yourself and enhance your understanding of public health measures.