Ebola virus transmission
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I now have comprehensive information from multiple authoritative textbooks. Here is a thorough overview of Ebola virus transmission:
Ebola Virus Transmission
The Pathogen
Ebola virus (EBOV) belongs to the family Filoviridae - named for the Latin filo ("thread"), reflecting its filamentous shape. It is a single-stranded, lipid-enveloped RNA virus with a genome of roughly 10-19 kilobases. Four species cause disease in humans. The virus can be relatively easily inactivated in the environment (e.g., by heat).
1. Zoonotic (Animal-to-Human) Transmission
Reservoir: Fruit bats are the primary suspected reservoir of Ebola virus, though definitive evidence is still being sought. Transmission to humans likely occurs via:
- Exposure to infected bat excreta or saliva
- Direct contact with the blood or body fluids of infected nonhuman primates (gorillas, chimpanzees) or other wild animals - typically during hunting or butchering
Since hemorrhagic fever viruses are rapidly inactivated by heating, infection occurs during butchering and preparation of "bushmeat," not from eating well-cooked meat. Sick nonhuman primates may be especially easy prey for hunters, which ironically increases exposure risk.
Goldman-Cecil Medicine
2. Human-to-Human Transmission
Direct Contact with Body Fluids (PRIMARY ROUTE)
Human-to-human transmission requires direct contact with contaminated blood or body fluids. The attack rate for Ebola Zaire virus is generally low (< 15%) under ordinary circumstances, reflecting how contact-dependent transmission is.
Ebola virus has been isolated from:
- Blood
- Saliva
- Urine
- Aqueous humor
- Semen (persists in semen of survivors - sexual transmission documented)
- Breast milk (live virus cultured; at least one fatal case associated with breastfeeding)
- Sweat, vomit, and stool
When is a Person Most Infectious?
Infectivity parallels clinical severity - patients are most infectious late in severe disease, when viral loads are highest and they are shedding virus via vomiting, diarrhea, and bleeding. The risk from asymptomatic persons or during the incubation period is negligible.
Goldman-Cecil Medicine; Red Book 2021
Common Transmission Settings
- Household caregiving - close contact while nursing a sick family member
- Healthcare settings (nosocomial) - inadequate PPE, unsafe injection practices, contaminated needles/syringes
- Funeral/burial practices - rituals requiring touching or washing of the corpse have been a major amplifier in multiple outbreaks
- Sexual transmission - via semen from male survivors (virus can persist for months post-recovery)
3. Aerosol / Airborne Transmission
There is no evidence for natural aerosol transmission between humans. While experimental aerosolized virus can infect nonhuman primates under artificial conditions (raising bioweapon concerns), this route does not occur in natural outbreak settings.
However, in healthcare settings, aerosol-generating procedures (e.g., endotracheal intubation, airway suctioning) require additional precautions (N95/particulate respirator, negative-pressure room) out of prudence.
Goldman-Cecil Medicine; Red Book 2021
4. Fomites
Infection through contaminated objects (fomites such as clothing, bedding, needles, and medical equipment) cannot be excluded and is considered a likely secondary route in outbreak settings.
5. Persistence in Survivors
A clinically important aspect unique to Ebola: viral persistence in immune-privileged sites (eyes, CNS, testes) can occur in survivors. Sexual transmission from convalescent males is documented, and semen should be tested after recovery before resuming sexual activity without barrier protection.
Summary Table
| Route | Evidence | Notes |
|---|---|---|
| Direct contact with blood/body fluids | Strong | Primary route; requires broken skin or mucous membrane exposure |
| Needlestick / contaminated sharps | Strong | Major nosocomial risk |
| Funeral/burial contact with corpse | Strong | Amplifier in many outbreaks |
| Fomites (bedding, equipment) | Probable | Cannot be excluded |
| Sexual transmission (semen) | Documented | Virus persists post-recovery in males |
| Breastfeeding | Documented | Live virus in milk; fatal case reported |
| Zoonotic (bats, primates) | Documented | Triggers index cases / new outbreaks |
| Airborne / aerosol (natural) | None | No evidence in natural settings |
Infection Control Implications
Standard, contact, and droplet precautions are recommended for hospitalized patients. A negative-pressure room is advised as an extra measure and is required during aerosol-generating procedures. Full PPE includes:
- At least 2 pairs of gloves
- Fit-tested N95 or particulate respirator (face shield if using N95)
- Impermeable/fluid-resistant gown
- Protective apron
- Shoe covers or rubber boots
- No skin exposed; buddy system for donning/doffing
Red Book 2021
Sources: Goldman-Cecil Medicine (26th ed.), Harrison's Principles of Internal Medicine (22e), Red Book 2021 (AAP), Tintinalli's Emergency Medicine, The Washington Manual of Medical Therapeutics, Creasy & Resnik's Maternal-Fetal Medicine.
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