Ciebov Rebov

Humans

Humans

Cynomolgus monkeys

Contact with blood or other body fluids

Contact with blood or other body fluids

Severe hemorrhagic disease Africa

Severe hemorrhagic disease Africa

Severe hemorrhagic Philippines disease in monkeys, attenuated in man

"Natural reservoirs unknown.

kidneys were being processed for cell culture production (for use in preparing poliovirus vaccine). Twenty-five laboratory workers were infected and six secondary cases resulted; of these 31 infected people, 7 died. The monkeys in the shipment, which originated in Uganda, also died. Subsequent studies with the virus isolated during the outbreak showed that it caused lethal illness in African green monkeys following experimental infection. The natural history of the virus remains a mystery. There were 3 cases of Marburg in South Africa in 1975 (the source of infection was probably Zimbabwe) with one death, 2 cases in Kenya in 1980 (infection probably in Uganda), one case in Kenya in 1987, and an outbreak of 99 cases in Zaire (now Congo) in 1998-2000. The locations of these outbreaks are shown on the map in Fig. 4.12. The fatality rate in these various outbreaks has averaged about 30%. There must be a reservoir of the virus somewhere in Africa from which it can spread to man or to monkeys, but the identity of this reservoir is unknown.

The second filovirus known is Ebola virus. Ebola virus was first isolated during a 1976 epidemic of severe hemor-rhagic fever in Zaire and Sudan and named for a river in the region. During this epidemic, the >600 cases resulted in 430 deaths. Asymptomatic infection appears to be rare. One case of Ebola occurred in 1977, and in 1979 there were 34 cases with 22 deaths in the Sudan. In this latter epidemic, an index case was brought to the hospital and the virus spread to four people there, who then spread it to their families. After this, Ebola disease in Africa disappeared until 1994. In late 1994, a Swiss ethologist working in the Ivory Coast performed necropsies on chimps. She contracted Ebola but survived, and a new strain of Ebola was isolated from her blood. Then, in May 1995, there was an epidemic in Kikwit, Zaire, that resulted in at least 315 cases with >75% mortality. This was followed by several deaths in western Africa that resulted from consumption of a monkey that had died of Ebola. Recently there has been a prolonged series of smaller outbreaks in Gabon from 1995 through 1997. In 2000, Ebola appeared in Uganda for the first time and caused an epidemic of more than 425 cases as of the latest tally. A map showing these various filoviral outbreaks is shown in Fig. 4.12.

The natural reservoir of Ebola virus in Africa also remains a mystery, despite extensive effort by the Centers for Disease Control (CDC) and other health care agencies to identify it. It is clear that monkeys can be infected by the virus and spread it to humans, but how the monkeys contract it or how human epidemics get started when monkeys are not implicated is not known.

Ebola virus has recently caused epidemics of hemor-rhagic fever in monkeys imported from the Philippines. The first epidemic occurred in Reston, Virginia, near Washington, D.C. in 1989. The deaths were at first attributed to simian hemorrhagic fever virus (SHFV), but investigation by the U.S. Army Medical Research Institute for Infectious Diseases and the CDC found that both SHFV and Ebola virus were present in the monkeys. Believing that the community was at risk for Ebola, the army team quickly decided to euthanize the monkeys and decontaminate the facility. Follow-up studies showed that four animal handlers at the facility had been infected by the virus but had suffered no illness. Thus the strain of Ebola present in the Reston monkeys, called Ebola-Reston to distinguish it from Ebola-Zaire, seems to be nonpathogenic for man although it remains pathogenic for monkeys. The story of the Reston incident was recounted in a book called The Hot Zone by Richard Preston. Since this first epidemic of Ebola-Reston, further outbreaks have happened in Reston and in an animal facility in Texas. Nucleotide sequencing has shown that Ebola-Reston is closely related to Ebola

1995 315 (77%) 1995/96 37 (57%) 1996/97 60 (75%) 2000 425 (53%)

Ebola

Year Cases/ Country %Mortality

Marburg

Year Cases/ Country %Mortality

1975 3 (33%) Zimbabwe

Ebola

Year Cases/ Country %Mortality

Sudan

Zaire*

Zaire *

Sudan

Gabon

Ivory Coast

Zaire *(Kikwit)

Gabon

Gabon

Uganda

Now called Democratic Republic of Congo

FIGURE 4.12 Map of Africa showing the different filovirus outbreaks. [Data from Porterfield (1995, p. 320) and later data from Georges-Courbot et al. (1997), Peters and Kahn (1999), and news bulletins from the World Health Organization (2000) at their web site: http://www.who.int/disease-outbreak-news/

from the Sudan epidemics. The reason it is attenuated in man is still unexplained, and high containment is used for studies of Ebola-Reston in the laboratory. The natural history of the virus is unknown, but it is thought that it might be a Philippine virus or an Asian virus, rather than an African virus.

Because of the dramatic symptoms caused by Ebola virus, as well as by other hemorrhagic fever viruses, and the high fatality rate following infection, it has been the subject of discussion in the popular press and has appeared in a number of works of nonfiction as well as fiction. To date, the virus has caused only a limited number of human cases, but there is always the fear that if the virus were to adapt to man in a way that allowed for easier transmission, it could become a very big problem.

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