Marburgvirus
Marburgvirus, genus of viruses in family Filoviridae, known for causing severe disease in humans and other primates. One species has been described, Marburg marburgvirus (formerly Lake Victoria marburgvirus), which is represented by two viruses, Ravn virus (RAVV) and Marburg virus (MARV). In humans, marburgviruses are responsible for Marburg virus disease (MVD), a zoonotic disease that is characterized by high fever, malaise, nausea, vomiting, diarrhea, skin rash, and hemorrhage (bleeding). MVD case fatality rates have been as high as 80 to 90 percent.
MARV was first isolated in 1967, following an outbreak of hemorrhagic illness in laboratory workers in Marburg and Frankfurt, Germany, and in Belgrade, Yugoslavia (now in Serbia). The workers had been producing polio vaccine using kidney cell cultures derived from African monkeys known as grivets (Chlorocebus aethiops). The grivets had been imported from Uganda to laboratories in all three locations and were identified as the source of infection. The virus was named after the city of Marburg, where most of the more than 30 cases in the 1967 epidemic were documented. RAVV was discovered in 1987, in a 15-year-old Danish boy who suffered from viral hemorrhagic fever in Kenya; the strain was named for the patient. RAVV was later detected in the Democratic Republic of the Congo in 1998–2000, when MVD sickened more than 150 people, and in Uganda in 2007, when marburgviruses were isolated from four humans and a small number of Egyptian fruit bats (Rousettus aegyptiacus).
Marburgvirus was the first genus of Filoviridae to be described, and hence its members are prototypical filoviruses. Virion particles are cylindrical and filamentous, with occasional branching or rod-, ring-, or U-shaped forms. The virion is roughly 80 nm in diameter, and its length averages 790 nm but is highly variable. A helical nucleocapsid houses a negative-strand RNA genome, about 19 kilobases in length. The genome encodes seven structural proteins, one of which is glycoprotein, a surface protein that plays a fundamental role in mediating viral entry into host cells. Virions are covered with glycoprotein spikes, which project outward 5–10 nm from the particle surface.
Marburgviruses enter the body through lesions in the skin and contact with mucosal membranes. The liver, lymph nodes, and spleen are the primary targets of early infection, though the virus quickly disseminates to other tissues. Marburgviruses specifically infect cells of the immune system, including monocytes and dendritic cells, thereby suppressing immune activation and allowing for uncontrolled viral replication. Although lymphocytes are not directly infected, significant numbers of the cells undergo apoptosis, an effect that is considered to be a hallmark of MVD pathology. The death of bystander lymphocytes is also thought to be mediated by the release of cytokines (molecules involved in inflammation), such as tumour necrosis factor-alpha (TNF-α). The unregulated production of cytokines is a suspected source of vascular damage in MVD and likely contributes to hemorrhaging. Hemorrhaging also results from abnormalities in coagulation (blood clotting) that are associated with viral infection. In severe cases, those effects may be exacerbated by the depletion of clotting factors produced by the liver, which appears to trigger organ failure. The pathology of MVD is similar to that of Ebola virus disease, which is caused by filoviruses of genus Ebolavirus—a group of deadly infectious agents that are closely related to members of Marburgvirus.
Marburgviruses appear to be confined to central and eastern Africa, where outbreaks of MVD have been traced to humans who recently visited or worked in caves. The Egyptian fruit bat is a suspected reservoir of marburgviruses; in addition to the isolation of marburgviruses from the species, its geographical distribution overlaps with the distribution of MVD outbreaks.