Ebola 101: A Primer On What You Need To Know

Ebola Virus

Amid continued confusion over how Ebola spreads, the World Health Organization issued new guidance aimed at public education.

First, the agency says, the virus is not airborne. Catching it through the air would depend on getting an infectious dose of the virus from a suspended cloud of tiny particles.

That’s how diseases like the flu and measles are spread.

Those viruses become airborne because specific cells that line the lungs and nose release a fine spray of viral particles into the air, says Elke Muhlberger, PhD. She’s a microbiologist at the Boston University School of Medicine who specializes in the study of Ebola.

People don’t even need to have symptoms to spread those diseases, she says. Ebola, on the other hand, is contagious only when someone has symptoms.

Scientists have been studying Ebola for decades, and they’ve never seen the disease passed through the air, according to the WHO. What’s more, it’s highly unlikely that the virus could change to become airborne.

The only way Ebola gets into the air is in large droplets of vomit or saliva. These droplets are heavy and wouldn’t be able to travel very far.

In theory, people might be able to catch it if someone coughed or sneezed directly onto them, but people who get Ebola generally don’t cough or sneeze.

What’s more, the WHO says it’s not aware of any studies that have ever shown the virus spreading this way.

Catching Ebola from someone else requires “close and direct” contact with infected body fluids, the WHO says. The most infectious body fluids are blood, stool, and vomit.

The virus has also been found in breast milk and urine — and in semen for up to 70 days, though those fluids are considered to be less infectious.

Finally, the WHO says saliva and tears may also carry some risk, but it says more research is needed.

In studies of saliva, the virus was only found in people who were in advanced stages of the disease. The live Ebola virus has never been found in sweat, the WHO says.

The CDC says that in a single study, done under ideal conditions, the virus has been found to remain active on solid surfaces for up to 6 days.

In theory, then, a person might be able to touch a contaminated surface, rub their nose or eyes, and become infected.

But the WHO believes the risk of getting the disease this way is probably low. You can cut that risk even further by properly cleaning and disinfecting surfaces.

Ebola virus is one of at least 30 known viruses capable of causing viral hemorrhagic fever syndrome. The genus Ebolavirus is currently classified into 5 separate species: Sudan ebolavirus, Zaire ebolavirus, Tai Forest (Ivory Coast) ebolavirus, Reston ebolavirus, and Bundibugyo ebolavirus.

Signs and symptoms

The following 2 types of exposure history are recognized:

  • Primary exposure – This typically involves travel to or work in an Ebola-endemic area
  • Secondary exposure – This refers to refers to human-to-human exposure (eg, medical caregivers, family caregivers, or persons who prepared deceased patients for burial), primate-to-human exposure (eg, animal care workers who provide care for primates), or persons who collect or prepare bush meat for human consumption

Physical findings depend on the stage of disease at the time of presentation. With African-derived Ebolavirus infection, there is an incubation period (typically 3-8 days in primary cases and slightly longer in secondary cases).

Early findings may include the following:

  • Fever
  • Pharyngitis
  • Severe constitutional signs and symptoms
  • Maculopapular rash (best seen in white patients)
  • Bilateral conjunctival injection

Later findings may include the following:

  • Expressionless facies
  • Bleeding from intravenous (IV) puncture sites and mucous membranes
  • Myocarditis and pulmonary edema
  • In terminally ill patients, tachypnea, hypotension, anuria, and coma

Survivors of Ebola virus disease have developed the following late manifestations:

  • Myalgias
  • Asymmetric and migratory arthralgias
  • Headache
  • Fatigue
  • Bulimia
  • Amenorrhea
  • Hearing loss
  • Tinnitus
  • Unilateral orchitis
  • Suppurative parotitis

See Clinical Presentation for more detail.

Diagnosis

Diagnostic studies that may be helpful include the following:

  • Basic blood tests – Complete blood count (CBC) with differential, bilirubin, liver enzymes, blood urea nitrogen (BUN), creatinine, pH
  • Studies for isolating the virus – Tissue culture (only to be performed in one of a few high-containment laboratories throughout the world), reverse-transcription polymerase chain reaction (RT-PCR) assay
  • Serologic testing – Enzyme-linked immunosorbent assay (ELISA) for antigens or for immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies
  • Other studies – Immunochemical testing of postmortem skin, electron microscopy

See Workup for more detail.

Management

General principles of care are as follows:

  • Supportive therapy with attention to intravascular volume, electrolytes, nutrition, and comfort care is of benefit to the patient
  • Such therapy must be administered with strict attention to barrier isolation; all body fluids contain infectious virions and should be handled with great care
  • No specific therapy is available that has demonstrated efficacy in the treatment of Ebola hemorrhagic fever
  • There are no commercially available Ebola vaccines; however, neutralizing antibodies have been studied that may be useful in vaccine development or as passive prophylactic agents

At present, no specific anti-Ebolavirus agents are available. Agents that have been studied for the treatment or prevention of Ebola virus disease include the following:

  • Ribavirin (possesses no demonstrable anti-Ebolavirus activity in vitro and has failed to protect Ebolavirus -infected primates)
  • Nucleoside analogue inhibitors of S-adenosylhomocysteine hydrolase (SAH)
  • Interferon beta
  • Horse- or goat-derived immune globulins
  • Human-derived convalescent immune globulin preparations
  • Recombinant human interferon alfa-2
  • Recombinant human monoclonal antibody against the envelope glycoprotein (GP) of Ebola virus
  • DNA vaccines expressing either envelope GP or nucleocapsid protein (NP) genes of Ebola virus
  • Activated protein C[1]
  • Recombinant inhibitor of factor VIIa/tissue factor[2]

In those patients who do recover, recovery often requires months, and delays may be expected before full resumption of normal activities. Weight gain and return of strength are slow. Ebola virus continues to be present for many weeks after resolution of the clinical illness.

See Treatment and Medication for more detail.

Image library

Ebola virus. Courtesy of the US Centers for DiseasEbola virus. Courtesy of the US Centers for Disease Control and Prevention.

Although some of the hemorrhagic fever viruses are normally spread by ticks or mosquitoes, all but one (ie, dengue hemorrhagic fever) are capable of being spread by aerosols, and this capability makes these viruses potential bioterrorism agents.

The family Filoviridae resides in the order Mononegavirales and contains the largest genome within the order. This family contains 2 genera: Ebolavirus (containing 5 species) and the antigenically distinct Marburgvirus (containing a single species).

In patients who have Ebola virus infection, exposure to the virus may be either primary (involving presence in an Ebolavirus -endemic area) or secondary (involving human-to-human or primate-to-human transmission). Physical findings depend on the stage of disease at the time of presentation. (See Presentation.)

Studies have demonstrated that patients who die of Ebola viral infection do not develop a humoral immune response. However, in survivors neutralizing antibody can be detected. It is likely that a broad humoral immune response can increase the likelihood of an infected patient surviving Ebola.

Currently, no specific therapy is available that has demonstrated efficacy in the treatment of Ebola hemorrhagic fever, and there are no commercially available Ebola virus vaccines. (See Treatment.) General medical support is critical. Care must be administered with strict attention to barrier isolation. Because the source of Ebola virus is unknown, education and prevention of primary cases is problematic. Education of communities at risk, especially healthcare workers, can greatly reduce the number of secondary person-to-person transmissions.

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