Welcome back. In this lecture, I will be discussing some of the etiological and epidemiological characteristics of Ebola infection. Ebola virus disease is a type of viral hemorrhagic fever, which are types of illnesses that cause fever and hemorrhage or bleeding. Ebola is a very serious illness as it evades the immune system to disseminate through the body, and is highly contagious and deadly. The first identified outbreaks of Ebola were in Sudan and Zaire, now known as the Democratic Republic of Congo in 1976, with a disease taking its name from the Ebola River, a tributary of the Congo River. There are now six known species of Ebola virus. The Zaire Ebola Virus is the most common and deadly form. This one has caused most of the human outbreaks and deaths due to Ebola virus disease, including the 2013-2016 West African epidemic. There's also the Sudan Ebola Virus which has been responsible for a number of smaller outbreaks and was also discovered the same year as the Ebola virus in 1976. The Bundibugyo Ebola virus was more recently discovered after an outbreak in Uganda in 2007. Reston Ebola Virus, Tai Forest Ebola virus, and Bombali Ebola viruses have been found in primates and other animals. The Tai Forest Ebola Virus, was contracted by a single scientist, While the Reston and Bombali Ebola viruses have not been contracted by any humans. All Ebola virus disease in humans can be typified by the following symptoms: fever, lethargy, and joint pain, which are non-specific symptoms, and features of hemorrhage, bleeding, including disseminated intravascular coagulation. When blood clots form throughout the body leading to extended bleeding. There's a high case fatality ratio for Ebola virus about 60 percent in the West African epidemic. But it varies by patient characteristics with young children and the elderly most at risk, with a case fatality ratio of up to 80 percent. There's no known cure and the only treatment available is supportive care. The best tools against Ebola outbreaks are preventive measures to halt the spread of the virus. These include isolation or quarantine, contact tracing, infection control procedures, such as the use of personal protective equipment and disinfection, the safe and dignified burial bodies, we'll learn why in a moment, and the careful disposal of waste through incineration. Vaccination is currently only experimental, but has been used in recent outbreaks by the World Health Organization, the WHO. Ebola transmits easily from person to person, Ebola Virus Disease is not transmitted through the inhalation of airborne particles as with influenza. Transmission happens through close contact with infected body fluids including: blood, feces, vomit, and semen. Body fluids can be infectious even after someone has died of Ebola virus disease. Family members have been infected with Ebola through religious rights in which the bodies of deceased Ebola patients were touched or washed. To avoid this form of transmission, WHO has developed a protocol for this safe and dignified burial of deceased Ebola patients. One of the ways to understand how an infectious disease will spread, is to estimate its basic reproduction number or R_o. This is the average number of new infections that are caused by one infectious person in a population of susceptible people. A basic reproduction number of less than one, will mean that the infection will usually die out. While an R_o greater than one means that the infection can spread through a population. In general, the higher the R_o, the more difficult the epidemic can be to control. For Ebola virus, the reproduction number has varied across different outbreaks as the reproduction numbers affected by characteristics of the population and the environment. Estimates of R_o have varied from 1.4-4.7 depending on the sources used to estimate the reproduction number, and the location and timing of the outbreak. In summary, Ebola is a challenging emerging infection first identified in 1976, and is responsible for a number of deadly outbreaks. Most commonly caused by the main Ebola virus which is one of six identified species. Like many emerging infections, Ebola poses a number of challenges to identify and control outbreaks. Ebola has a high case fatality ratio and there is no cure for Ebola. An experimental vaccine is being tested with alternative vaccines under development.
