Flaviviridae are viruses that are classified as RNA viruses because of their single-stranded RNA. The Flaviviridae family includes the genera Pestivirus, Flavivirus, and Hepacivirus.
What are flaviviridae?
Flaviviridae belong to the group of single-stranded RNA viruses. They are often referred to as flaviviruses, although in addition to flaviviruses, the Flaviviridae also include pestivirus and hepacivirus. All members of the Flaviviridae family are enveloped. They are between 40 and 60 nm in size. In general, the Flaviviridae show low tenacity. The term tenacity originates from microbiology and refers to the resistance of microorganisms to environmental influences. Viruses from the Flaviviridae group are easily inactivated by lipid solvents and disinfectants, rendering them harmless. The Flaviviridae replicate 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 diseases.
Occurrence, distribution, and characteristics
Flaviviruses of the Flaviviridae family are usually transmitted to birds or mammals by arthropods, or arthropods. For example, the TBE virus is transmitted by ticks. Dengue virus, Usutu virus, West Nile virus, yellow fever virus, and Zika virus are transmitted by mosquitoes. Some of the viruses can also be transmitted through sexual intercourse or through infected blood products. In some cases, diaplacental transmission of the virus from the infected mother to the unborn child is possible. Most viruses of the genus Flavivirus are native to the African continent. However, there are also frequent infections with flaviviruses in South America or Asia. An exception is the TBE virus. The virus is widespread 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 Flaviviridae. Humans are the only natural host of the hepacivirus. Great apes are equally infectable, but chronic infections as in humans are rather rare. The virus is distributed worldwide. It is transmitted parenterally. Blood and blood products are the most common sources of infection. Sexual transmission of the virus is rare. Risk factors for hepacivirus infection include intravenous drug abuse, dialysis (especially dialysis performed before 1991), tattoos, and piercings. However, in one-third of patients, the route of transmission is unknown.
Diseases and medical conditions
The viruses of the Flaviviridae family can cause a wide range of viral infections in humans. For example, yellow fever is caused by infection with the yellow fever virus (genus Flaviviridae). Yellow fever, together with dengue fever, belongs to the virus-related hemorrhagic fevers. The disease progresses in two phases. After six days of incubation, the first symptoms of the disease appear. These include fever, headache, chills, nausea, vomiting, muscle aches, and yellowing of the skin. In some patients, symptoms resolve on their own after a few days. In others, the second phase of the disease develops with a slowed heartbeat, fever and a tendency to bleed. In this phase of the disease, mortality is 50 percent. There is currently no causal treatment for yellow fever. Dengue fever is also caused by a flavivirus. After an incubation period of about one week, those affected show flu-like symptoms. The notifiable infectious disease begins suddenly with high fever, chills, headache, aching limbs, joint pain and nausea. After four to five days of illness, lymph node swelling and a skin rash develop. Initial infections with dengue fever often show a rather uncomplicated course. 90% of patients show only very mild symptoms or none at all. However, a second infection with the virus can lead to dengue hemorrhagic fever. This is far more dangerous and can be fatal. A 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, affected individuals develop flu-like symptoms with aching limbs, headache and a slightly elevated temperature. After the symptoms subside, a symptom-free phase follows. About three weeks after infection, the secondary stage develops in 10 percent of all infected persons. At this stage, early summer meningoencephalitis can manifest as encephalitis, meningitis or myelitis. The virus can also affect the heart muscle, liver and joints. TBE meningitis is accompanied by high fever and severe headache. There may be meningismus. If encephalitis is present in addition to meningitis, patients have impaired consciousness, hyperkinesis, and speech problems. If there is additional spinal cord involvement, paralysis of the shoulders and upper extremities may occur. Bladder paralysis is also possible. Hepatitis C, caused by the hepacivirus of the Flaviviridae family, tends to be chronic. Acute and symptomatic courses are manifested by fatigue, 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 as the disease progresses. Chronic hepatitis C leads to progressive destruction of the liver. Twenty percent of all patients with chronic hepatitis C develop cirrhosis within 20 years. Cirrhotic patients are at increased risk of developing hepatocellular carcinoma. More than half of all liver cancers in Germany are due to hepacivirus infection.
