Zika Fever

 

 Zika fever is caused by Zika virus. Zika virus ( ZIKV ) is a member of the Flaviviridae virus family and the Flavivirus genus, transmitted by daytime- active Aedes mosquitoes, such as A. aegypti.

General

Zika virus is related to dengue, yellow fever, Japanese encephalitis, and West Nile viruses. The illness it causes is similar to a mild form of dengue fever, is treated by rest, and cannot yet be prevented by drugs or vaccines. There is a possible link between Zika fever and microcephaly in newborn babies by mother- to- child transmission, as well as a stronger one with neurological conditions in infected adults, including cases of the Gullain- Barre syndrome.

Along with other viruses in this family, Zika virus is enveloped and icosahedral and has 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.

Transmission

Zika virus is transmitted by daytime- active mosquitoes and has been isolated from a number of species in the genus Aedes, such as A. aegypti.Studies show that the extrinsic incubation period in mosquitoes is about 10 days. Zika virus can migrate between humans through sexual contact and it can also cross the placenta, affecting an unborn fetus. A mother already infected with Zika virus near the time of delivery can pass on the virus to her newborn around the time of birth, but this is rare. The vertebrate hosts of the virus are primarily monkeys and humans. Before the current pandemic, which began in 2007, Zika virus rarely caused recognized ” spillover ” infections in humans, even in highly enzootic areas.

The potential societal risk of Zika virus can be delimited by the distribution of the mosquito species that transmit it ( it’s vectors ). The global distribution of the most cited carrier of Zika virus, A. aegypti, is expanding due to global trade and travel. A. aegypti distribution is now the most extensive ever recorded – across all continents including North America and even the European Periphery. A mosquito population capable of carrying the Zika virus has been found in a Capitol Hill neighborhood of Washington D.C., and genetic evidence suggests they survived at least the last four winters in the region. The study authors conclude that mosquitoes are adapting for persistence in a northern climate.

In 2009, Brian Foy, a biologist from the Colorado State University, sexually transmitted Zika virus to his wife. He visited Senegal to study mosquitoes and was bitten on a number of occasions. A few days after returning to the United States he fell ill with Zika, but not before having had unprotected intercourse with his wife. She subsequently showed symptoms of Zika infection 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.

In 2015, Zika virus RNA was detected in the amniotic fluid of two fetuses, indicating that it had crossed the placenta and could cause a mother- to- child infection.

Clinical

Common symptoms of infection with the virus include mild headache, maculopapular rash, fever, malaise, conjunctivitis, and joint pains. The first well- documented case of Zika virus was described in 1964; it began with a mild headache, and progressed to a maculopapular rash, fever, and back pain. Within two days, the rash started fading, and within three days, the fever resolved and only the rash remained. Thus far, Zika virus has been a relatively mild disease of limited scope, with only one in five persons developing symptoms, with no fatalities, but it’s true potential as a viral agent of disease is unknown.

As of 2016, no vaccine or preventative drug is available. Symptoms can be treated with rest, fluids, and paracetamol ( acetaminophen ), while aspirin and other nonsteroidal anti- inflammatory drugs should be used only when dengue has been ruled out to reduce the risk of bleeding.

Link to microcephaly

In December 2015, it was suspected that a transplacental infection of the fetus may lead to microcephaly and brain damage. In December 2015, the European centre for Disease Prevention and Control issued a comprehensive update on the possible association of Zika virus with congenital microcephaly. The U.S. CDC states that, ” There have been reports of microcephaly in babies of mother who were infected with Zika virus while pregnant. Zika virus infections have been confirmed in several infants with microcephaly; it is not known how many of the microcephaly cases are associated with Zika virus infection.

Other neurological complications

In a French Polynesian epidemic, 73 cases of Guillain Barre Syndrome and other neurologic conditions occurred in a population of 270,000, which may be complications of Zika virus.

Vaccine development

Effective vaccines exist for several Flaviviruses vaccines for yellow fever virus, Japanese encephalitis, and tick- born encephalitis were introduced in the 1930s, while the vaccine for dengue fever has just recently become available for use.

Work has begun towards developing a vaccine for Zika virus, according to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. The researchers at the Vaccine Research Centre have extensive experience from working with vaccines for other viruses such as West Nile virus, chikungunya virus, and dengue fever. Ni kos Vasilakis of the center for Biodefense and Emerging Infectious Diseases predicted that it may take two years to develop a vaccine, but 10 to 12 years may be needed before an effective Zika virus vaccine is approved for regulators for public use.

 

Dr. A. K. M. Aminul Hoque

Formerly prof. of Medicine

Dhaka Medical College

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