Zika virus
Encyclopedia
Zika virus 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, +ssRNA 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 mosquito
es, and has been isolated in Ae. africanus, Ae. apicoargenteus, Ae. luteocephalus, Ae. aegypti, Ae vitattus, and Ae. furcifer, all members of the Aedes mosquito family. 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 cell
s 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
. This virus 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 uncomfirmed cases, no deaths and no hospitalizations.
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.
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.
Flaviviridae
The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin...
virus family and the flavivirus
Flavivirus
Flavivirus is a genus of the family Flaviviridae. This genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, and several other viruses which may cause encephalitis....
genus. In humans, it causes a disease known as Zika fever
Zika fever
Zika fever is an illness caused by the Zika virus, a member of the family Flaviviridae. The fever and virus are named after the Ugandan forest where the virus was first isolated. The virus is commonly found in Africa but has also been found in Malaysia and Micronesia, including Yap Island. ...
. It is related to dengue
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...
, yellow fever
Yellow fever
Yellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....
, West Nile
West Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
and Japanese encephalitis
Japanese Encephalitis
Japanese encephalitis —previously known as Japanese B encephalitis to distinguish it from von Economo's A encephalitis—is a disease caused by the mosquito-borne Japanese encephalitis virus. The Japanese encephalitis virus is a virus from the family Flaviviridae. Domestic pigs and wild birds are...
, 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, +ssRNA 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
Uganda
Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...
, Africa, and was isolated for the first time from humans in 1968 in Nigeria
Nigeria
Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...
. From 1951 through 1981, evidence of human infection was reported from other African countries such as Uganda, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
, Central African Republic
Central African Republic
The Central African Republic , is a landlocked country in Central Africa. It borders Chad in the north, Sudan in the north east, South Sudan in the east, the Democratic Republic of the Congo and the Republic of the Congo in the south, and Cameroon in the west. The CAR covers a land area of about ,...
, Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, and Gabon
Gabon
Gabon , officially the Gabonese Republic is a state in west central Africa sharing borders with Equatorial Guinea to the northwest, Cameroon to the north, and with the Republic of the Congo curving around the east and south. The Gulf of Guinea, an arm of the Atlantic Ocean is to the west...
, as well as in parts of Asia including India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Malaysia, the Philippines, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
, and Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. It is transmitted by mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es, and has been isolated in Ae. africanus, Ae. apicoargenteus, Ae. luteocephalus, Ae. aegypti, Ae vitattus, and Ae. furcifer, all members of the Aedes mosquito family. 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 cell
Dendritic cell
Dendritic cells are immune cells forming part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system. That is, dendritic cells function as antigen-presenting cells...
s near the site of inoculation, and then spread to lymph nodes and the bloodstream. In terms of replication, flaviviruses generally replicate in the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within 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
Maculopapular rash
A maculopapular rash is a type of rash characterized by a flat, red area on the skin that is covered with small confluent bumps. The term "maculopapular" is a compound: macules are small, flat discolored spots on the surface of the skin; and papules are small, raised bumps...
, fever, malaise, conjunctivitis
Conjunctivitis
Conjunctivitis refers to inflammation of the conjunctiva...
, and arthralgia
Arthralgia
Arthralgia literally means joint pain; it is a symptom of injury, infection, illnesses or an allergic reaction to medication....
. 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
Yap
Yap, also known as Wa'ab by locals, is an island in the Caroline Islands of the western Pacific Ocean. It is a state of the Federated States of Micronesia. Yap's indigenous cultures and traditions are still strong compared to other neighboring islands. The island of Yap actually consists of four...
in the Federated States of Micronesia
Federated States of Micronesia
The Federated States of Micronesia or FSM is an independent, sovereign island nation, made up of four states from west to east: Yap, Chuuk, Pohnpei and Kosrae. It comprises approximately 607 islands with c...
. This virus 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
Zika fever
Zika fever is an illness caused by the Zika virus, a member of the family Flaviviridae. The fever and virus are named after the Ugandan forest where the virus was first isolated. The virus is commonly found in Africa but has also been found in Malaysia and Micronesia, including Yap Island. ...
disease process was relatively mild: there were 49 confirmed cases, 59 uncomfirmed cases, no deaths and no hospitalizations.
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.
Human to human transmission
In 2009, it was proved that Zika virus can be sexually transmitted between humans. Professor Brian Foy, a university biologist from the Colorado State University at the Arthropod Borne and Infectious Disease Laboratory, visited SenegalSenegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
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.
External links
- http://www.cdc.gov/eid/content/15/9/1347.htm
- http://www.nytimes.com/2007/07/03/health/03virus.html?_r=1
- http://content.nejm.org/cgi/content/short/360/24/2536