CHARACTERISTICS: Filoviridae; 800-100 nm elongated filamentous virion, single stranded, negative sense RNA
Virus is assigned to the genus 01.025.0.01. "Marburg–like viruses"; family 01.025. Filoviridae; order 01. Mononegavirales.
EPIDEMIOLOGY: 1967 - outbreak in Germany and Yugoslavia following exposure to African green monkeys imported from East Africa (31 cases with 7 deaths); 1975 and 1982-4 cases reported in South Africa (originated in Zimbabwe); 1980 - two cases in Kenya
Virions have a complex construction and consist of an envelope, a nucleocapsid, a polymerase complex, and a matrix. Virions are enveloped. Virions are filamentous, or pleomorphic with extensive branching, or U-shaped, 6-shaped, or circular forms occur (particularly after purification) flexible; about 80 nm in diameter; 790 nm long (after purification). The surface projections are distinctive knob-shaped peplomers evenly covering the surface. They are spaced widely apart; evenly dispersed and embedded in a lipid bilayer. The surface projections comprise surface glycoproteins (GP) and are composed of one type of protein. Surface projections are 10 nm long; spaced 10 nm apart. The nucleocapsid exhibits helical symmetry. The nucleocapsid is helical; is cross-striated; 50 nm in diameter. Axial canal is distinct; in 20 nm in diameter; basic helix is obvious; pitch of helix is 5 nm. Morphologically aberrant forms are observe (after centrifugation).
The incubation period for hemorrhagic fever Marburg virus is 2 to 21 days.
Intrahepatic Marburg
Transmission and Tissue Tropism
The mode of primary infection in any natural setting is unknown with Marburg and Ebola viruses. All secondary cases have been nosocomial or caused by intimate contact with a patient. Transmission occurs usually by contaminated blood samples. One Marburg case was acquired by sexual contact more than 60 days after the original infection. In addition, there is evidence to suggest respiratory spread of infection. Epidemiological data of the 1989 Reston outbreak suggest that droplet or vomit transmission was a major factor in virus spread within quarantine facilities. Virus is usually recovered from acute-phase sera and has also been found in throat washes, urine, soft tissue effusates, semen and anterior eye fluid, even when the specimens were obtained late in convalescence. It has also been regularly isolated from autoptic material, such as spleen, lymph nodes, liver and kidney but rarely from brain or other nervous tissues.
"The initial symptoms are a severe frontal & temporal headache, generalised aches & pains, malaise, by the second day the victim will have a fever. Later symptoms include watery diarrhoea, abdominal pain, nausea, vomiting, a dry sore throat, & anorexia. By day seven of the symptoms, the patient will have a maculopapular (small slightly raised spots) rash. At the same time the person will develop thrombocytopenia & haemorrhagic manifestations, particularly in the gastrointestinal tract, & the lungs, but it can occur from any orifice, mucous membrane or skin site. By day twelve the skin starts to peel away from the rash. Ebola causes lesions in almost every organ, although the liver & spleen are the most noticeably affected. Both are darkened & enlarged with signs of necrosis. The cause of death is normally shock, associated with fluid & blood loss into the tissues.
The haemorrhagic & connective tissue complications of the disease are not really understood, but may be related to the fact that the VP40 protein is antigenically related to human cell matrix proteins (abdominal aortic aneurism protein & MFAP-4), leading to autoimmune attack.
Why does the immune system not clear the infection?
This may be associated with the two forms of the virus glycoprotein. The glycoprotein gene has a translation stop codon in the middle of it, preventing the synthesis of the full length protein. Approximately twenty percent of the mRNA isolated from infected cells had been edited to contain an extra adenosine in a stretch of seven adenosine residues at positions 1019-1026. This causes a frame shift, allowing the synthesis of the full length protein . The larger protein (130Kd - GP) is membrane associated protein, & the truncated version (approximately 60 Kd - SGP) is secreted.
A possible role for SGP is to protect the virus from the immune system as a decoy antigen. However, SGP binds to neutrophils & interferes with their function. Moreover, GP also appears to be immunosuppressive, further interfering with the response to infection."