Virology TEM micrograph showing<unk>  virus virions (the cluster of dark dots near the center)<unk>  virus (DENV) is an RNA virus of the family Flaviviridae; genus Flavivirus. Other members of the same genus include yellow fever virus, West Nile virus, Zika virus, St. Louis encephalitis virus, Japanese encephalitis virus, tick-borne encephalitis virus, Kyasanur forest disease virus, and Omsk hemorrhagic fever virus. Most are transmitted by arthropods (mosquitos or ticks), and are therefore also referred to as arboviruses (arthropod-borne viruses). The<unk>  virus genome (genetic material) contains about 11,000 nucleotide bases, which code for the three different types of protein molecules (C, prM and E) that form the virus particle and seven other non-structural protein molecules (NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5) that are found in infected host cells only and are required for replication of the virus. There are five strains of the virus, called serotypes, of which the first four are referred to as DENV-1, DENV-2, DENV-3 and DENV-4. The fifth type was announced in 2013. The distinctions between the serotypes are based on their antigenicity. Transmission The mosquito Aedes aegypti feeding on a human host<unk>  virus is primarily transmitted by Aedes mosquitos, particularly A. aegypti. These mosquitos usually live between the latitudes of 35° North and 35° South below an elevation of . They typically bite during the early morning and in the evening, but they may bite and thus spread infection at any time of day. Other Aedes species that transmit the disease include A. albopictus, A. polynesiensis and A. scutellaris. Humans are the primary host of the virus, but it also circulates in nonhuman primates. An infection can be acquired via a single bite. A female mosquito that takes a blood meal from a person infected with<unk> , during the initial 2- to 10-day febrile period, becomes itself infected with the virus in the cells lining its gut. About 8–10 days later, the virus spreads to other tissues including the mosquito's salivary glands and is subsequently released into its saliva. The virus seems to have no detrimental effect on the mosquito, which remains infected for life. Aedes aegypti is particularly involved, as it prefers to lay its eggs in artificial water containers, to live in close proximity to humans, and to feed on people rather than other vertebrates.<unk>  can also be transmitted via infected blood products and through organ donation. In countries such as Singapore, where<unk>  is endemic, the risk is estimated to be between 1.6 and 6 per 10,000 transfusions. Vertical transmission (from mother to child) during pregnancy or at birth has been reported. Other person-to-person modes of transmission, including sexual transmission, have also been reported, but are very unusual. The genetic variation in<unk>  viruses is region specific, suggestive that establishment into new territories is relatively infrequent, despite<unk>  emerging in new regions in recent decades. Predisposition Severe disease is more common in babies and young children, and in contrast to many other infections, it is more common in children who are relatively well nourished. Other risk factors for severe disease include female sex, high body mass index, and viral load. While each serotype can cause the full spectrum of disease, virus strain is a risk factor. Infection with one serotype is thought to produce lifelong immunity to that type, but only short-term protection against the other three. The risk of severe disease from secondary infection increases if someone previously exposed to serotype DENV-1 contracts serotype DENV-2 or DENV-3, or if someone previously exposed to DENV-3 acquires DENV-2.<unk>  can be life-threatening in people with chronic diseases such as diabetes and asthma. Polymorphisms (normal variations) in particular genes have been linked with an increased risk of severe<unk>  complications. Examples include the genes coding for the proteins TNFα, mannan-binding lectin, CTLA4, TGFβ, DC-SIGN, PLCE1, and particular forms of human leukocyte antigen from gene variations of HLA-B. A common genetic abnormality, especially in Africans, known as glucose-6-phosphate dehydrogenase deficiency, appears to increase the risk. Polymorphisms in the genes for the vitamin D receptor and FcγR seem to offer protection against severe disease in secondary<unk>  infection.
Dengue fever
Leptospirosis
Chikungunya
Malaria
Blackwater fever
Yellow fever
Ross River fever
Viral hepatitis