Ebola is considered an emerging infectious disease. It was first recognized in 1976 as the cause of twin outbreaks of disease near the Ebola River in the Democratic Republic of the Congo (then known as Zaire) and in a region of Sudan. Some 300 people in each country became infected. The mortality rate was 88 percent in Zaire and 53 percent in Sudan (the Zaire subtype is the most deadly). Although the circumstances of the original human infections are not known, the disease spread through close direct contact and as a result of unsafe and unsanitary hospital practices, such as the use of contaminated needles and the lack of sufficient containment measures.
Sporadic and smaller outbreaks have erupted over the succeeding years in the Democratic Republic of the Congo, Gabon, Uganda, and Sudan. An outbreak in the DRC in late August of 2014, that lasted several months, resulted in 66 cases and 49 deaths. As in prior outbreaks, the initial case was traced to the handling of infected bushmeat. This outbreak in the DRC was caused by a different variant of the Ebola virus that produced the much larger and wide-spread outbreak in the same year in West Africa.
The Reston Ebola Virus Outbreak
The Reston subtype of Ebola virus was first identified in 1989 in the United States in monkeys housed in a quarantine facility in Reston, Virginia. At least four humans became infected, but none became ill. Additional outbreaks of the Reston subtype occurred between 1989 and 1996 in Texas, Pennsylvania, and Italy. No humans suffered illness in any of these cases. The source of all the Reston subtype outbreaks was traced to a single facility in the Philippines that exported the monkeys. In July of 2009, the discovery of the Reston subtype in domestic pigs in the Philippines was reported. Genetic analysis suggests that the virus has been widely circulating in swine for many years, possibly even before the 1989 outbreak in the United States. The virus has been detected in farmers who have had contact with infected pigs, but they have not shown any signs of illness.
The 2014 Outbreak
In 2014, a large and rapidly spreading outbreak of EVD erupted, for the first time, in West Africa. Although it took several months for the disease to become recognized as Ebola, it appears that the first victim was a 2-year old boy in a small village in southeastern Guinea who died in December of 2013, followed by the deaths of several members of his family. Although these family members were not tested, their symptoms and the subsequent pattern of virus spread are consistent with the EVD outbreak. The child is thought to have played in a tree that housed Ebola-infected bats, so that he likely came in direct contact with the bats or their droppings. The virus transmitted by these bats is closely related to the Zaire Ebola virus.
In mid-March of 2014, cases of EVD in Guinea were recognized and reported to the World Health Organization and soon thereafter cases were reported in Liberia and then Sierra Leone. Reports came from multiple regions within these countries. Ebola arrived in Nigeria during July when a person who had had contact with an Ebola victim in Liberia traveled by plane to Nigeria and infected several contacts. In late August, Ebola reached a fifth country when Senegal confirmed its first and, to date, only case. Mali reported its first case in October after a symptomatic young girl traveled from Guinea to Mali and died shortly afterwards, and then an independent small cluster arose a short time later after an elderly man with undiagnosed disease traveled from Guinea to Mali. The outbreak was quickly contained in Mali, Senegal and Nigeria, but widespread transmission occurred in Liberia, Guinea, and Sierra Leone.
The initial transmission of Ebola virus outside of West Africa came to light in early October 2014 when a nursing assistant at a hospital in Spain contracted EVD after she had helped care for a missionary who had become infected in Sierra Leone and then flown to Spain. She recovered from EVD, and tests were negative for the presence of the virus following her illness. Several other people who contracted Ebola in West Africa were treated in hospitals in the United States and in Spain, Germany, the United Kingdom, France, and Norway, but to date no further transmission has occurred.
The first diagnosis of Ebola virus infection in the United States was announced on Sept. 30, 2014. Prior to traveling to Dallas, Texas, a man had had direct contact with a woman in Liberia who was dying of Ebola. His symptoms appeared only after he arrived in the United States. While seeking medical attention at a hospital in Dallas, his illness was not immediately recognized as Ebola and he was sent home. He was admitted to the same hospital three days later when his condition worsened, and he died ten days after he was admitted.
A nurse who had contact with this patient during his second hospital stay was confirmed to have EVD on Oct. 12. This was the first known case of transmission within the United States. A second nurse at the same hospital tested positive for Ebola three days later. Both nurses recovered and have been declared free of the virus. Other contacts of the Liberian patient, including family members who shared an apartment with the patient, did not become infected. A fourth diagnosis of Ebola infection in the United States occurred later in October when a doctor who had returned to New York from treating patients in Guinea tested positive for Ebola virus. He was hospitalized and has recovered and is free of the virus. His contacts completed the 21-day follow-up period without becoming infected.
At the end of 2014, the toll of reported cases stood at approximately 20,200, of whom more than 7,900 died. Actual numbers are thought to be higher. Nearly all of the deaths occurred in Liberia, Sierra Leone, and Guinea. There was one death in the United States, six in Mali, and eight in Nigeria. Until December, the highest numbers of cases and deaths had occurred in Liberia, but towards the end of 2014 the number of new cases surged in Sierra Leone surpassing the count in Liberia. Sierra Leone remains the country with the most confirmed cases of EVD, although the death toll is highest in Liberia.
Progress became apparent during the early months of 2015 when overall numbers of new cases declined. Towards the end of the year, the outbreak was declared over in Liberia in September, in Sierra Leone in November, and in Guinea in December after each of these countries completed a period of 42 days, double the maximum incubation time, in which no new confirmed cases were reported.
The WHO declared an end to the international public health emergency in West Africa at the end of March 2016. By this time, an overall total of more than 28,600 cases and 11,300 deaths had occurred as a result of this Ebola virus outbreak.
The 2018 Outbreaks in the Democratic Republic of the Congo
The first outbreak of Ebola virus in the Democratic Republic of the Congo of 2018 was reported in early May after two cases caused by the Ebola Zaire virus were confirmed in laboratory tests. This was the ninth EVD outbreak in the DRC in the last four decades (the prior one occurred in May 2017). The outbreak was declared ended by the WHO in July after contacts of confirmed cases who had been vaccinated did not display Ebola virus symptoms within 42 days (double the maximum incubation period for infection). In total, there were 54 confirmed or probable cases, including 32 deaths, as a result of this outbreak, which was confined to regions within the northwestern part of the country. The four cases in the large urban center of Mbandaka, a major transportation hub, had caused the greatest concern.
The short duration of the first 2018 outbreak appeared to be due to benefits from the scientific knowledge gained during the 2014 outbreak in West Africa and the results of a vaccination trial conducted in Guinea during 2015. Once the 2018 outbreak was reported, a wide partnership of governmental and health agencies worked quickly to curtail it. Using the rVSV-ZEBOV vaccine (developed by Merck) - which is not yet licensed nor formally approved - but was shown to be safe and effective during the vaccine trial in Guinea, a ring vaccination campaign was undertaken in which the contacts of confirmed cases, and their contacts, as well as healthcare workers and others with potential exposure to the virus were given the experimental vaccine. More than 3000 people were vaccinated.
The respite was short-lived, however, as on August 1, a little more than a week later, another outbreak - the tenth in the DRC - was declared. The new cluster of cases was reported in the North Kivu Province in the northeastern part of the country, a remote, conflict-plagued region that shares porous borders with Uganda and Rwanda and which hosts over a million displaced persons. These conditions have made it much more difficult to curtail the spread of the virus.
As of June 1 2019, a total of 1994 EVD cases in two neighboring northeastern provinces (North Kivu and Ituri) have been reported in this ongoing outbreak according to the World Health Organization. Of these cases, 1339 people have died (although the true number of cases and deaths is thought to be higher). This now ranks as the second largest Ebola epidemic ever (the 2014 outbreak in West Africa was the largest).
In spite of the use of proven control measures, such as ring vaccination (over 120,000 people have been vaccinated so far), and the availability of preventive and therapeutic tools, containment of the virus has been hindered by the geographical challenges, security hazards, distrust of authorities, and a lack of understanding about the disease. Efforts to control the outbreak were further challenged by attacks on two Ebola treatment centers in late February. The risk of continued national and regional transmission remains very high.