Aetiology

The Marburg and Ravn viruses are members of the Filoviridae family (genus Marburgvirus; order: Mononegavirales). These viruses are elongated, filamentous RNA structures of variable length.

Marburgviruses are thought to be initially acquired from infected animals such as bats and non-human primates, but can also be spread by human-to-human transmission. Transmission occurs by close contact with body fluids of infected patients. The incubation period after infection is typically 5 to 10 days, although some estimates range from 2 to 26 days.[8][9][10]

The level of virus in the blood increases during the course of the illness and patients are most infectious in the later 'wet' stages of the disease (i.e., during diarrhoea, vomiting, and haemorrhage). Large amounts of virus can be found in the skin and, as sweat may also contain the virus, touching an infected patient may result in transmission. Burial practices where mourners have direct contact with the deceased have been associated with the spread of the virus.

The virus can still be detected in semen 7 weeks after recovery from infection, possibly due to testicular tissue being an immunologically protected site.[2] This means that sexual transmission may be possible long after the infection has resolved. [Figure caption and citation for the preceding image starts]: Transmission electron micrograph of Marburg virus virionsCDC Public Health Image Library (PHIL) [Citation ends].com.bmj.content.model.Caption@6a28a60e

Pathophysiology

Macrophages, monocytes, Kupffer cells, and dendritic cells are all primary target cells for filovirus infection. It is theorised that Marburg virus-induced ‘paralysis’ of innate immune responses contributes to systemic viral replication in vivo. At the organ level, liver and lymphoid tissues are the main viral targets, leading to deleterious changes in the lymphoid tissues and depletion of lymphocytes. Other targets include the reticulo-endothelial system, adrenal glands and pancreatic islets, fibroblast-like cells, and hepatocytes. Liver parenchyma necrosis is a common finding and probably contributes to coagulation defects, since multiple clotting factors are synthesised in the liver. Systemic viral replication likely triggers multi-organ failure observed in severe cases. Adrenal cortical necrosis probably leads or contributes to hypotension, hypovolaemia, and shock. Central nervous system involvement occurs late in disease and contributes to development of encephalopathy.[9]

Classification

Virus taxonomy

The virus is a member of the Filoviridae family (genus Marburgvirus). Two Marburgviruses, Marburg virus (MARV) and Ravn virus (RAVV), have been isolated to date and both can cause Marburg virus infection in humans.

Other filoviral infections

The Filoviridae family of viruses includes the genera Ebolavirus and Marburgvirus, among others.

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