Flaviviridae

Flaviviridae are viruses that are classified as RNA viruses on the basis of their single-stranded RNA. The genera Pestivirus, Flavivirus and Hepacivirus belong to the Flaviviridae family.

What are Flaviviridae?

Flaviviridae belong to the group of single-stranded RNA viruses. They are often referred to as flaviviruses, although the Flaviviridae also include the pestivirus and the hepacivirus in addition to the flaviviruses. All members of the Flaviviridae family are wrapped. They are between 40 and 60 nm in size. In general, the Flaviviridae show poor tenacity. The term tenacity comes from microbiology and describes the resistance of microorganisms to environmental influences. The viruses from the group of Flaviviridae can easily be inactivated by lipid solvents and disinfectants and thus rendered harmless.

The Flaviviridae reproduce in the cell fluid of the host cell. They remain stable in a pH range between 7 and 9. In humans, the viruses can cause yellow fever, hepatitis C or early summer meningoencephalitis (TBE), among other things.

Occurrence, Distribution & Properties

The flaviviruses from the Flaviviridae family are usually transmitted to birds or mammals by arthropods, known as arthropods. The TBE virus is transmitted by ticks, for example. Dengue virus, Usutu virus, West Nile virus, yellow fever virus, and Zika virus are all transmitted by mosquitoes. Some of the viruses can also be transmitted through sexual intercourse or through infected blood products. In some cases, the virus can be transmitted through the placenta from the infected mother to the unborn child.

Most of the viruses of the genus Flavivirus are native to the African continent. But there are also infections with flaviviruses in South America and Asia. The TBE virus is an exception. The virus is spread in endemic areas in Bavaria, Thuringia, Hesse, Rhineland-Palatinate and Baden-Württemberg.

The hepatitis C virus belongs to the genus Hepacviruses and thus to the family of Flaviviridae. Humans are the only natural hosts of the hepacivirus. Great apes can also be infected, but chronic infections like those in humans are rather rare. The virus is spread all over the world. It is transmitted parenterally. Blood and blood products are the most common sources of infection. The virus is rarely transmitted sexually. Intravenous drug abuse, dialysis (especially dialysis performed before 1991), tattoos, and piercings are considered risk factors for infection with the hepacivirus. In a third of the patients, however, the transmission route is unknown.

Illnesses & ailments

The viruses of the Flaviviridae family can cause a large number of viral infections in humans. Yellow fever is caused by an infection with the yellow fever virus (genus Flaviviridae). Yellow fever, together with dengue fever, is a virus-related hemorrhagic fever. The disease has two phases. The first symptoms of the disease appear after six days of incubation. These include fever, headache, chills, nausea, vomiting, muscle pain and yellowing of the skin. In some patients, symptoms resolve on their own after a few days. Others develop the second phase of the disease with a slow heartbeat, fever and a tendency to bleed. In this phase of the disease, the mortality rate is 50 percent. A causal treatment of yellow fever is currently not possible.

Dengue fever is also caused by a flavivirus. After an incubation period of about a week, people will show flu-like symptoms. The notifiable infectious disease starts suddenly with a high fever, chills, headache, body aches, joint pain and nausea. After four to five days of illness, swelling of the lymph nodes and a rash develop. Initial infections with dengue fever often show a rather uncomplicated course. 90% of the patients show only very mild symptoms or no symptoms at all. However, hemorrhagic dengue fever can develop through a second infection with the virus. This is far more dangerous and can be fatal.

One disease that is triggered by flaviviruses and can also be found in Germany is early summer meningoencephalitis. The TBE virus is transmitted by ticks. In the primary stage, those affected develop flu-like symptoms with aching limbs, headaches and a slightly elevated temperature. After the symptoms have subsided, a symptom-free phase follows. Around three weeks after infection, 10 percent of all infected people develop the secondary stage. Early summer meningoencephalitis can manifest as encephalitis, meningitis, or myelitis at this stage. The heart muscle, liver and joints can also be infected by the virus. TBE meningitis is associated with a high fever and severe headache. There may be meningism. When encephalitis is present in addition to meningitis, patients have impaired consciousness, hyperkinesis, and speech disorders. With additional involvement of the spinal cord, paralysis of the shoulders and upper extremities can occur. Bladder paralysis is also possible.

Hepatitis C, caused by the hepacivirus from the Flaviviridae family, is usually more chronic. Acute and symptomatic courses are expressed by exhaustion, flu-like symptoms and yellowing of the skin. However, more than 80 percent of all HCV infections are initially asymptomatic, but then tend to become chronic in the further course. Chronic hepatitis C leads to progressive destruction of the liver. 20 percent of all patients with chronic hepatitis C develop cirrhosis within 20 years. The risk of developing hepatocellular carcinoma is increased in cirrhotic patients. Over half of all liver cancers in Germany can be traced back to an infection with the hepacivirus.