1. Microbiology by Nestor, Roberts, Pearsall Anderson Nester (1998) ISBN 0-697-28602 p. 786 Ebola Hemmorrhagic Fever Typically, symptoms begin abrutply, with fever, chills, headache, and malaise, and progress to abdominal pain, diarrhea, shock a, and hemorrhage. Some infected persons develop a rash 5 to 7 days after the onset of fever. The mortality is 50% to 90%. The disease was first identified in 1976 in the former Zaire and Sudan. Recurrent outbreaks have occured in parts of Africa since then. Cause Ebola virus, in RNA virus of the filovirus family. Transmission occurs by close physical contact and exposure to blood, vomitus, and stool. Reservioir of the virus is unknown. Epidemics have arisen from contact with wild chimpanzees that have died of the disease. Incubation period: 2 to 21 days. Strains of the virus vary considerable in virulence. Inroductions into the United States have occurered with imported monkeys, and travelers could theoretically bring the virus in during the incubation period. However the virus is not highly contagious, and tests for rapid diagnosis have now been devised. No antiviral treatment is presently available. comment: The virus is the same from host to host and throughout the stages of its promulgation/incubation/spread within a host. During the asymptomatic period the virus is growing in number, but not itself progressing through any stages. In the earlier stages there is simply less of it in the host organism. But all it takes is one functioning virus to leave the host and make contact with an open wound in the skin, or the mucus membranes or the mouth for that solitary Ebola invader to colonize a new host. This is not a contradiction of the statement that the virus is not highly contagious. Yet given the fact that once it does reach a new host, death is 90 percent certain (for the Zaire strain) within two weeks of the initial fever symptom and the fact that asymptomatic carriers can infect others, even in 10 percent or 5 percent or even 3 percent of physical contact episodes is sufficient -- given the fact of up to three weeks of asymptomatic carrying -- to generate an unbounded pandemic under current customs of physical contact in our day to day lives. 2. Microbiology Jacquelyn G Black 6th edition (200% ISBN: 0-471-42084-0 p. 708 Filovirus Fevers. Filoviruses, or filamentous viruses, display unusual variability in shape. Some are branched, others are fishhook- or U shaped, and still others are circular. They contain negative-sense RNA in a helical capsid an vary in length from 130 to 4,000 nm. Two filoviruses have been associated with human disease. The Ebola virus caused outbreaks of homorrhagic fever, first in 1976, with a mortality of 88% in Zaire and 51 percent in Sudan. Nearly one-fifth of the popularion of rural areas of Central Afric have antibodies to Ebola. Transmission is person to person. A 1995 outbreak of Ebla virus in Zaire .. more than 200 cases were documented, with a mortality rate of about 75%. ... p. 273 Filoviridae. The filoviruses are enveloped, filamentous, single (-) sense RNA viruses. These viruses can be transmitted from person to person by close contact with blood, semen, or other secretions any by contaminated needles. The filoviruses include the viruses responsible for Marburg and Ebola diseases, which are hemorrhagic fevers. 3. Biology of Microrganisms Brock and Madigan (1991) ISBN 0-13-08381-79 Information about epidemics and about epidemiology in general 4. Virology Levy, Fraenkel-Conrat and Owens (1994) ISBN: 0-13-953753-8 Pp. 98-100 The single-stranded Marburn and Ebola RNA viruses were initially considered rhabdoviruses, but they have specific properties that warrant their placement in a separate family called Filoviridaw, a term that describes their morphology (Fig./ 4.18). They appear as long filamentous forms in a variey of shapes including U, 6-shaped, and circular. Thes viruses, with a diameter of 80 nm, have a helical nucleocapsid (50 nm) and are enveloped with surface projections. They contain an RNA of 4.6 X [ten raised to the sixth power] Da and five major and two minor protein components, similar in size and presumably function to the rhabdovirus proteins. They can cause infections in monkeys, guinea pigs, hamsters, and mice. The replication of filoviruses resembles that of other negative-sense RNA viruses. By genome analysis they have some replication signals similar to those of the rhabdo- and paramyxoviruses. Infection of cells in culture leads to extensive cytopathic effects with intracytoplasmic inclusion bodies containing ribonucleocapsides. Since virion RNA is not readily detected in the cells, a fast replication process most likely occurs with negative-sense RNA being released rapidly within virions. Marburg virus was first recognized in humans afflicted with severe and often fatal hamorrhagic fever in Marburg Germany, in 1967. It infected researchersgrowing poliovirus in African green monkey kidney cells originally obtained from animals in Uganda. The recent demonstration that Marburg virus can infect cultured human endothial cells could explain in part its pathogenic nature. Ebola virus, first recognized in 1976, represents a major problem in Africa, with a death rate from severe hemorrhagic fever of 50 percent to 90 percent in different countries due to at least two subtypes, Sudan and Zaire. The reservoire for these latter viruses is still unknown. These filoviruses commonly give rise to hemorrhagic disease with major pathologic findings in the lungs, liver, and gastrointestinal tract. The infection can be contained by standard quarantine procedures, particularly avoidance of close contact with infected individuals and exposure to contaminated needles and syringes. Comment: Notice it says avoidance of close contact with infected individuals and that it did not say avoidence of close contact with symptomatic individuals. The as yet asymptomatic individual carrier is an infected individual too. 5. Microbiology Tortora, Funke and Case 6th edition (1998) p. 617 Emerging Viral Hemorrhagic Fevers ... Certain other homorrhagic diseases are considered new or emerging hemorrhagic fevers. In 1967, 31 people became ill and 7 died when some African monkeys were imported into Europe. The virus was strangely shaped, in the form of a filament (filoviruses) and was named for the site of the outbreak, Marburg, Germany. Nine years later, outbreaks in Africa of another highly lethal hemorrhagic fever, caused by a similar filovirus, caused a disease with a mortality approaching 90%. Named Ebola, for a regional river, this is now a well-publicized disease ... The natural host is unknown, but most cases have been caused by contact with blood through unsterilized needles. Comment: Note that the Marburg outbreak of the filovirus resulted from contact with monkeys not exhibiting symptoms, or rather from livers of monkeys that were not exhibiting symptoms when the livers were taken. The symptoms are only evidence that the virus has multiplied sufficiently to bring itself to human attention, but it is contagious even before that point is reached, the virus can transfer to another, theoretically, within minutes after establishing residence with the prior host. p. 616 Most hemorrhagic fevers are zoonotic diseases; they appear in humans only from infectious contact with their normal animal hosts. Some of them have been medically familiar for so long that they are considered classic hemorrhagic fevers. First among these is yellow fever. They yellow feveor virus (an aborvirus) is injected into the skin by a mosquito, Aedes aegypti. ...Yellow fever is still endemic in many tropical areas, such as Central America, tropical South America, and Africa. At one time, the disease was endemic in the United States. The last U.S. case of yellow fever in the United States occurred in Lousiana in 1905. Mosquito eradication campaigns initated by the U.S Army surgeon Waler Reed were effective in eliminating yellow fever in the United States. Monekys are a natural reservoir for the virus, but human-to-human transmission can maintain the disease. .... 5. Microbiology Tortora, Funke and Case 6th edition (2002) ISBN 0-8053-7597 -X p.373 A viron is a complete, fully developed, infectious virual particle composed of nucleic acid and surrounded by a protein coat that protects it from the environment and is a vehicle of transmission from one host cell to another. Viruses are classified by differences in these coats. p. 372 The host range of a virus is the spectrum of host cells the virus can infect. ... The particular host range of a virus is determined by the viruss requirements for its specific attachment to the host cell and the availability within the potential host of cellular factors required for viral multiplication. For the virus to infect the host cell, the outer surface of the virus must chemically interact with the spedific receptor sites on the surface of the cell. The two complementary components are held together by weak bond, such as hydrogen bonds. ... For animal viruses the receptor sites are on the plasma membranes of the host cells. comment: The carrier of Ebola virus in the asymptomatic period of the course of the Ebola disease is indeed carrying Ebloa virons within the fluids of the hosts body and these can escape and reach the susceptible cells of another persons body. The Ebola virus is being transmitted from person to person at times when neither of them are exhibiting symptoms of the disease, not even the fever or rash which are usually the very first signs of Ebola hemmrrhagic fever.
Posted on: Thu, 09 Oct 2014 13:23:40 +0000
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