EBOLA OVERVIEW: Ebola is an elongated filamentous virus, which can vary between 800 – 1000 nm in length, and can reach up to 14000 nm long (due to concatamerization) with a uniform diameter of 80 nm. It contains a helical nucleocapsid (with a central axis), 20 – 30 nm in diameter, and is enveloped by a helical capsid, 40 – 50 nm in diameter, with 5 nm cross-striations. The pleomorphic viral fragment may take on several distinct shapes (e.g., in the shape of a “6”, a “U”, or a circle), and are contained within a lipid membrane. Each virion contains a single-strand of non-segmented, negative-sense viral genomic RNA.
Ebola virions enter host cells through endocytosis and replication occurs in the cytoplasm. Upon infection, the virus affects the host blood coagulative and immune defense system and leads to severe immunosuppression. Early signs of infection are non-specific and flu-like, and may include sudden onset of fever, asthenia, diarrhea, headache, myalgia, arthralgia, vomiting, and abdominal pains. Less common early symptoms include conjunctival injection, sore throat, rashes, and bleeding. Shock, cerebral edema, coagulation disorders, and secondary bacterial infection may co-occur later in infection.
Ebola occurs mainly in areas surrounding rain forests in equatorial Africa with the exception of Reston, which has been documented to originate in the Philippines. No predispositions to infection have been identified among infected persons.
The largest recorded ebolavirus outbreak to date began in March 2014, with initial cases reported in Guinea and then additional cases identified in the surrounding regions (Liberia, Sierra Leone, Nigeria). A new strain of the ZEBOV species was identified as the causative agent of the outbreak.
INFECTIOUS DOSE: Viral hemorrhagic fevers have an infectious dose of 1 – 10 organisms by aerosol in non-human primates.
COMMUNICABILITY: Communicable as long as blood, body fluids or organs, contain the virus. Ebolavirus has been isolated from semen 61 to 82 days after the onset of illness, and transmission through semen has occurred 7 weeks after clinical recovery.
SUSCEPTIBILITY TO DISINFECTANTS: Ebolavirus is susceptible to 3% acetic acid, 1% glutaraldehyde, Triton X-100, alcohol-based products, and dilutions (1:10-1:100 for ≥10 minutes) of 5.25% household bleach (sodium hypochlorite), and calcium hypochlorite (bleach powder). The WHO recommendations for cleaning up spills of blood or body fluids suggest flooding the area with a 1:10 dilutions of 5.25% household bleach for 10 minutes for surfaces that can tolerate stronger bleach solutions (e.g., cement, metal) Footnote 62. For surfaces that may corrode or discolor, they recommend careful cleaning to remove visible stains followed by contact with a 1:100 dilution of 5.25% household bleach for more than 10 minutes.
PHYSICAL INACTIVATION: Ebola are moderately thermolabile (denatured by heat) and can be inactivated by heating for 30 minutes to 60 minutes at 60°C, boiling for 5 minutes, or gamma irradiation (1.2 x106 rads to 1.27 x106 rads) combined with 1% glutaraldehyde Footnote 10 Footnote 48 Footnote 50. Ebolavirus has also been determined to be moderately sensitive to UVC radiation.
SURVIVAL OUTSIDE HOST: Filoviruses have been reported capable to survive for weeks in blood and can also survive on contaminated surfaces, particularly at low temperatures (4°C). One study could not recover any Ebolavirus from experimentally contaminated surfaces (plastic, metal or glass) at room temperature. In another study, Ebolavirus dried onto glass, polymeric silicone rubber, or painted aluminum alloy is able to survive in the dark for several hours under ambient conditions (between 20°C and 25°C and 30–40% relative humidity) (amount of virus reduced to 37% after 15.4 hours), but is less stable than some other viral hemorrhagic fevers (Lassa). When dried in tissue culture media onto glass and stored at 4 °C, Zaire ebolavirus survived for over 50 days. This information is based on experimental findings only and not based on observations in nature. This information is intended to be used to support local risk assessments in a laboratory setting. A study on transmission of ebolavirus from fomites in an isolation ward concludes that the risk of transmission is low when recommended infection control guidelines for viral hemorrhagic fevers are followed. Infection control protocols included decontamination of floors with 0.5% bleach daily and decontamination of visibly contaminated surfaces with 0.05% bleach as necessary.
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