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Ebola Virus

Ebola virus causes viral hemorrhagic fever in humans and nonhuman primates such as monkeys, gorillas, and chimpanzees. Five subspecies of Ebolavirus have been identified. Four of the five have caused disease in humans: Ebola virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus); and Bundibugyo virus (Bundibugyo ebolavirus). The fifth, Reston virus (Reston ebolavirus), has caused disease in nonhuman primates, but not in humans.

The first 49 cases of the current West African epidemic of Ebola virus disease were reported on March 22, 2014 in Guinea. By October, 2014, a total of 9178 cases and 4546 deaths had been reported in West Africa. Cases have been reported in Guinea, Liberia, Sierra Leone and Nigeria.  On October 20, WHO officially declared that Nigeria was free of Ebola virus transmission.  Three travel associated cases have been reported in the United States, Spain and Senegal.  Two health care workers in Texas have become infected.

Comparison of the genomes of the current Ebola virus in West Africa with a strain that caused an outbreak in Central Africa in 2004 demonstrated that more than 400 mutations have occurred over this 10 year interval.

Sophisticated genomic analyses of 99 Ebola virus samples obtained from 78 patients in Sierra Leone demonstrated that the current Ebola Virus Disease outbreak most likely originated less than a year ago with a single person attending a funeral of a traditional healer in Guinea. It then spread to Sierra Leone and other nations.

Previous Ebola virus outbreaks appear to have been caused by direct human exposure to infected fruit bats or other animals. Bats are believed to be the natural reservoir.  It is then spread person-to-person through direct contact with bodily fluids. Incubation period is usually 8 to10 days, but can range from 2 to 21 days. Patients can transmit the virus while febrile and through later stages of disease, as well as postmortem, when persons contact the body during funeral preparations.

Blood, feces and vomit appear to be the most infectious. Ebola virus has also been detected in breast milk, urine and semen. In a convalescent male, the virus can persist in semen for at least 70 days. Saliva and tears may also carry some risk of transmission, especially in severely ill patients. Live virus has not been isolated from sweat. There is no evidence that Ebola virus has mutated into a form that could cause airborne transmission.

Ebola virus can also be transmitted indirectly by contact with previously contaminated surfaces and objects. During outbreaks of Ebola virus, disease can spread quickly within health care settings when hospital staff is not wearing appropriate protective equipment such as masks, gowns, and gloves. Risk of indirect transmission is low and can be reduced even further by appropriate cleaning and disinfection procedures.

Ebola virus disease is characterized by sudden onset of fever and malaise, accompanied by other nonspecific signs and symptoms, such as myalgia, headache, vomiting, and diarrhea. Patients with severe forms of the disease may develop multi-organ dysfunction, including hepatic damage, renal failure, and central nervous system involvement, leading to shock and death.

Health care workers should take a detailed travel and exposure history with patients who exhibit fever, severe headache, muscle pain, weakness, diarrhea, vomiting, stomach pain, unexplained hemorrhage. If the patient is under investigation for Ebola, health care workers should activate the hospital preparedness plan for Ebola, isolate the patient in a separate room with a private bathroom, and ensure standardized protocols are in place for PPE use and disposal. Health care workers should not have physical contact with the patient without putting on appropriate PPE.     

Current screening criteria for Ebola virus disease include clinical and epidemiologic risk factors. Clinical criteria include fever and additional symptoms such as severe headache, muscle pain, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage.  Epidemiologic risk factors within the past 21 days before the onset of symptoms include:

Residence in, or travel to, an area where EVD transmission is active (see AND

  • Contact with blood , other body fluids or human remains of a patient known to have or suspected to have EVD
  • Direct handling of bats, non-human primates, and other animals from disease-endemic areas or
  • Direct handling of unpreserved tissues from any of these animals.

If both clinical and epidemiologic criteria are met, the patient should be moved to a private room with a bathroom, and STANDARD, CONTACT, and DROPLET precautions followed during further assessment. They should be immediately reported to hospital leadership and the state health department.

State and local health departments must be contacted before samples are collected  for Ebola virus testing. CDC and the U.S. Army Research Institute of Infectious Disease (USAMRIID) have developed a PCR test for Ebola virus and distributed this assay to a network of public health laboratories. The test gives a presumptive positive or negative result, which must then be confirmed by parallel testing at the CDC.

When CDC determines testing is necessary, an identification number will be provided by CDC or state officials to track the suspected Ebola patient.  Ebola testing requires collection of two 4 mL plastic tubes of whole blood, collected in EDTA and shipped at 2 to 8? C. One specimen is shipped to the designated network laboratory for preliminary testing, and the other specimen will be sent to the CDC for confirmatory testing.  While in the patient room, the treatment team member should wipe the outside of tubes with approved disinfectant and label tubes with a printed patient chart label, adding date/time of collection to the label. These samples are considered Category A infectious materials and should be packaged accordingly.

Commercial carriers may or may not accept the shipment, depending on CDC classification of risk level for individual patients. Decisions are made on a case by case basis. State public health departments or CDC may assist in arranging for specimen transportation to their facility for testing.

CDC Health Alert Network, July 28, 2014, CDCHAN-00363

Genomic surveillance elucidates Ebola virus origin and transmission during the 2014 outbreak. Gire SK, Sabeti PC, et al. Science (published online August 28, 2014)

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