Clinical Virology Study Notes on Rabies and Ebola Virus

Incidence
- Fewer than 10 cases in the United States annually (mostly imported).
- Hundreds of cases occur in developing countries, primarily due to rabid dogs.
- Worldwide, approximately 50,000 people die from rabies each year.
Immunization Status
- In 2007, the United States was declared 'canine-rabies free' due to widespread dog immunizations.
Identification of Virus Strain
- The origin and reservoir host of rabies virus strains can often be identified through genome RNA sequencing.
- Example: A person developed clinical rabies in the U.S. from a strain identified as Mexican after being bitten by a dog in Mexico months earlier.

Initial Infection and Spread
- The virus multiplies at the bite site and infects sensory neurons.
- It uses axonal transport to move to the central nervous system (CNS), evading the immune system.
- Multiplication occurs in the CNS, followed by travel to peripheral nerves, salivary glands, and other organs.
- The virus enters the saliva and is transmitted through bites.
- There is no viremic stage in rabies infection.
CNS Effects
- Encephalitis develops, leading to neuron death and demyelination.
- Infected neurons show eosinophilic cytoplasmic inclusions known as Negri bodies—important for laboratory diagnosis.
- Survivors of rabies provide limited information on immunity.

Incubation Period
- Varies based on the bite's location; ranges from 2 weeks to 16 weeks or longer.
- Shorter incubation for bites on the head (closer to CNS).
Prodrome Symptoms
- Nonspecific: fever, anorexia, paresthesias at the bite site.
Rabies Encephalitis
Two Forms of Encephalitis:
1. Furious (Encephalitic)
  - Occurs in approx. 80% of cases.
  - Symptoms: agitation, delirium, seizures, hydrophobia (painful pharyngeal spasm leading to water aversion).
2. Dumb (Paralytic)
  - Symptoms: primarily paralysis without agitation or hydrophobia.
  - Typically involves ascending paralysis.
Mortality: Death occurs almost invariably for both forms, although some individuals survive with life support.

Animal Diagnosis
- Rapid diagnosis via brain tissue examination using:
- PCR assay
- Fluorescent antibody staining
- Histologic staining for Negri bodies
- Virus isolation takes too long for immediate decision-making about vaccination.
Human Diagnosis
- Techniques include PCR assay, fluorescent antibody staining from biopsy samples, saliva or spinal fluid testing, and titer rises in antibodies.
- Samples can be taken from the neck skin or corneal scrapings.

Treatment
- Supportive care available, NO antiviral therapy for rabies patients.
Vaccination
- In the U.S., rabies vaccination is critical and involves inactivated virus grown in human diploid cells.
- Other countries use duck embryo vaccines and nerve tissue vaccines (less preferred).
- HDCV (human diploid cell vaccine) is favored due to lower risk of allergic reactions.
Immunization Strategies
- Preexposure Immunization:
  - Recommended for high-risk individuals (vets, zookeepers, travelers to endemic areas).
  - Consists of three doses on days 0, 7, and 21 or 28.
  - Booster doses as necessary (maintaining an antibody titer of 1:5).
- Postexposure Immunization:
  - Administered after viral exposure (animal bite).
  - Involves rabies vaccine + human rabies immune globulin (RIG).
  - Immediate wound cleaning is essential.
  - Example of passive-active immunization.
  - Consideration for tetanus immunization also recommended.

Disease
- Causes Ebola hemorrhagic fever (EHF).
- Named after the Ebola River in Zaire, the site of the first outbreak in 1976.
- Significant outbreak occurred in West Africa in 2014-2015.
Epidemiology
- Post-1976 outbreaks sporadically occurred in sub-Saharan Africa.
- 2014-2015 outbreak killed over 10,000 people, with a 60% fatality rate.

Classification
- Member of the filovirus family; filamentous enveloped viruses.
- Contains a single-stranded, nonsegmented, negative-polarity RNA genome.
- Strains:
- Ebola-Zaire (most pathogenic)
- Ebola-Sudan
- Ebola-Ivory Coast (Tai Forest)
- Ebola-Bundibugyo
- Ebola-Reston (pathogenic for monkeys but not humans).
Physical Characteristics
- Virus is elongated and can measure thousands of nanometers.
- Viruses can be inactivated by lipid solvents and bleach.
Containment
- Cultured in BSL-4 facilities due to high virulence.

Pathogenesis
- High mortality linked to viral glycoprotein causing endothelial cell death and hemorrhage.
- Viral proteins inhibit interferon response, leading to ineffective antibody response.
- Massive lymphocyte and macrophage death.
Incubation Period
- Typically 5-7 days, but can extend to 21 days.
Initial Symptoms
- Fever, headache, sore throat, myalgia, arthralgia, epigastric pain, vomiting, and diarrhea.
Progression
- Subsequent bleeding, shock, disseminated intravascular coagulation, multi-organ failure, and very high mortality rates up to 90%.
Post-Ebola Syndrome
- Survivors may experience blurred vision, cataracts, hearing loss, fatigue, and insomnia due to lingering effects of the disease.

Diagnostic Methods
- Primarily through PCR assays to detect viral RNA.
- Other tests include ELISA for viral antigens or serological tests for IgM antibodies.
- Risk warrants extreme care when handling samples.

Treatment
- Supportive treatment (fluids, electrolytes).
- Experimental therapies (monoclonal antibodies, antiviral drugs) have variable effectiveness.
Prevention
1. Focus on preventing secondary transmission through use of personal protective equipment (PPE) and proper handling of patient fluids.
2. Quarantine individuals exposed for up to 21 days.
3. Available vaccines:
  - Live recombinant vaccine (rZEBOV) for pre- and post-exposure.
  - Other vaccines include recombinant adenovirus and recombinant vaccinia virus vaccines.