Ebola is a viral hemorrhagic fever, with sudden onset, high fever, prostration and often severe internal and membrane bleeding. It was confused with yellow fever for many years and later with Lassa fever. Ebola was distinguished from related diseases by severity, sudden onset and high mortality–reaching 90 percent in some outbreaks. Victims die after an average of about a week. Those who survive two weeks are likely to recover.
Working in 1976 at the Antwerp Institute of Tropical Medicine in Belgium, Peter Piot, Rene Delgadillo and Guido van der Groen cultured the virus from samples brought from Zaire and obtained electron photomicrographs. The shape and size appeared different from other viruses known at the time.
Antibody tests developed in the 1970s provided the first biochemical diagnosis. Shortly afterward, molecular biology made it possible to distinguish viruses reliably, using genetic tags and sequences. Ebola and related viruses persist in wild animals–some capable of infecting people and others not–including bats, rats, monkeys and primates. These RNA viruses mutate rapidly. About 400 distinct Ebola mutations are now known.
New viral strain: The recent west African outbreaks of Ebola have been attributed to a new strain. As of mid-September, 2014, full gene sequences have been obtained for over 100 samples. Deep sequencing, up to 2,000 sequences per sample, showed that an infection is often a mosaic of multiple sub-strains. Adaptation to evade treatments has already been documented.
In Guinea, the first positively identified case from the recent outbreak occurred in December, 2013. By mid-April, 2014, about 200 cases and 120 deaths were known. The outbreak soon spread to Liberia and Sierra Leone and has rapidly grown worse. As of mid-September, about 5,000 cases and 2,500 deaths had been reported in the three countries combined. The worst prior outbreaks have been in Zaire–1976, 318 cases and 280 deaths–and in Uganda–2000, 425 cases and 224 deaths.
Data provided September 12 by the Columbia Predictions of Infectious Diseases for July and August showed a doubling time for mortality of about five weeks. If that rate were maintained, in a year the death count would grow to about 2-1/2 million. In another year, the entire human population of tropical Africa would be gone.
Very large outbreak: The number of Ebola cases reported in west Africa so far is more than ten times the number from any previous outbreak. The types of resources that halted previous outbreaks have been exhausted, so that large numbers of victims are not being isolated from the population and get no care.
Writing in the Washington Post, Lena Sun reported that so far this year the United States has contributed $100 million to efforts. The Obama administration has sent requests to Congress, she wrote, for about $650 million more. These amounts are comparable to $600 million in emergency aid requested by the World Health Organization.
– Beacon staff, Brookline, MA, September 15, 2014
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