|Group:||Group IV ((+)ssRNA)|
Zika virus (ZIKV) is a member of the Flaviviridae virus family and the flavivirus genus. In humans, it causes a disease known as Zika fever. It is related to dengue, yellow fever, West Nile and Japanese encephalitis, viruses that are also members of the virus family Flaviviridae.
Along with other viruses in this family, Zika virus is enveloped and icosahedral with a non-segmented, single-stranded, positive sense RNA genome. It is most closely related to the Spondweni virus and is one of the two viruses in the Spondweni virus clade. The virus was first isolated in 1947 from a rhesus monkey in the Zika Forest of Uganda, Africa and was isolated for the first time from humans in 1968 in Nigeria. From 1951 through 1981, evidence of human infection was reported from other African countries such as Uganda, Tanzania, Egypt, Central African Republic, Sierra Leone and Gabon, as well as in parts of Asia including India, Malaysia, the Philippines, Thailand, Vietnam and Indonesia. It is transmitted by mosquitoes and has been isolated from a number of species in the genus Aedes - Aedes aegypti, Aedes africanus, Aedes apicoargenteus, Aedes furcifer, Aedes luteocephalus and Aedes vitattus. Studies show that the extrinsic incubation period in mosquitoes is about 10 days. The vertebrate hosts of the virus include monkeys and humans.
The pathogenesis of the virus is hypothesized to first infect dendritic cells near the site of inoculation, and then spread to lymph nodes and the bloodstream. In terms of replication, flaviviruses generally replicate in the cytoplasm, but Zika virus antigens have been found in infected cell nuclei.
Common symptoms of infection with the virus include mild headaches, maculopapular rash, fever, malaise, conjunctivitis, and arthralgia. The first well documented case of Zika virus was in 1964, beginning with a mild headache and progressing to a maculopapular rash, fever, and back pain. Within 2 days, the rash was fading, and within 3 days, the fever was gone and only the rash remained. There is no vaccine or preventive drug for Zika virus, and only treatment of symptoms is possible. Usually non-steroid anti-inflammatories and/or non-salicylic analgetics are used.
The first outbreak of the disease outside of Africa and Asia was in April 2007, on the island of Yap in the Federated States of Micronesia. The condition was characterized by rash, conjunctivitis, and arthralgia, and was initially thought to be dengue. The Chikungunya and Ross River viruses were also suspected. However, serum samples from patients in the acute phase of illness contained RNA of Zika virus. The Zika fever disease process was relatively mild: there were 49 confirmed cases, 59 unconfirmed cases, no deaths and no hospitalizations.
A recent larger outbreak of Zika virus outside Africa and Asia was confirmed in April 2015, in Brazil. In the district of Camaçari and the neighbor Salvador city, capital of the state of Bahia, healthcare authorities confirmed that a previously unknown disease affecting around 500 patients with flu-like symptoms followed by rash and arthralgia is indeed an ongoing outbreak of Zika fever, as proved by RT-PCR technique by researchers from UFBA. Local authorities link the outbreak to recent increased flow of foreign visitors prompted by the 2014 FIFA World Cup, coupled with the large population of insect vectors such as Aedes aegypt and Aedes albopictus mosquitoes that inhabit the region. The spread follow a similar pattern to the also recent outbreak of chikungunya virus in the same region, another disease previously unknown to local population.
Zika virus could be considered an emerging pathogen, as it spread outside Africa and Asia for the first time in 2007. Thus far, it has been a relatively mild disease with limited scope, but its true potential as a virus and as an agent of disease is currently unknown.
In 1947, scientists researching yellow fever placed a rhesus macaque in a cage in the Zika Forest (zika meaning “overgrown” in the Luganda language), near the East African Virus Research Institute in Entebbe, Uganda. A fever developed in the monkey, and researchers isolated from its serum a transmissible agent that was first described as Zika virus in 1952. It was subsequently isolated from a human in Nigeria in 1954. From its discovery until 2007, confirmed cases of Zika virus infection from Africa and Southeast Asia were rare. In 2007, however, a major epidemic occurred in Yap Island, Micronesia. More recently, epidemics have occurred in Polynesia, Easter Island, the Cook Islands and New Caledonia.
Human to human transmission
In 2009, it was proved that Zika virus can be sexually transmitted between humans. Brian Foy, a university biologist from the Colorado State University at the Arthropod Borne and Infectious Disease Laboratory, visited Senegal to study mosquitos and was bitten on a number of occasions during his research. A few days after returning to the USA he fell ill with Zika, but not before having vaginal intercourse with his wife. His wife subsequently showed symptoms of Zika infection, along with extreme sensitivity to light. Foy is the first person known to have passed on an insect-borne virus to another human by sexual contact.
This article contains public domain text from the CDC as cited
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