The Zika virus causes fever, joint pain, headaches, a rash, conjunctivitis and muscle pain. As with other viruses, it is characterised by spreading via the cells of the body. Both men and women can contract the disease. It is a member of the Flavivirus genus which is a member of the Flaviviridae family.
Flavivirus genomes are between 40 and 60 nm in size. Viruses in this family are also responsible for infectious diseases such as dengue fever, Japanese encephalitis, yellow fever and West Nile virus.
Mosquitoes are believed to be mainly responsible for the transmission of the disease to humans. There are over 3000 types of mosquitoes but it is usually the Aedes mosquitoes that spread Zika from one infected person to another.
The virus tends to be found in the tropical locations that the mosquitoes inhabit. Risk areas are also places where stagnant water allows mosquito larvae to thrive. The mosquitoes that carry the virus are the Aedes aegypti which is found in tropical environments and the Aedes Albopictus which has the ability to cope in cooler locations.
Although the exact incubation period is unknown, the virus appears to be present for some days before full symptoms are developed.
The symptoms tend to be fairly mild and last for a few days and it is unusual for someone to die from the disease. There are however concerns about the long-term effects of the virus, as relatively little is known about them.
The virus was first discovered in 1947 in a rhesus monkey living in the Zika forest. The disease was then later detected in the Aedes mosquito that also lives in the Zika forest.
Around 20 years later, tests were run on Nigerian patients who were found to have the virus in their system. Prior to 2007, just 14 cases were documented in medical documents.
The Zika virus is believed to be endemic in patients in Asia, Africa. As well as these continents, the virus has also now been detected in the Pacific and Americas.
Sexual transmission of the Zika virus
Some cases also imply that the Zika virus can be transmitted through sexual intercourse. A malaria researcher, Brian Foy of Colorado contracted the Zika virus while working in Senegal. He returned home and his wife caught it from him while his children were unaffected.
Brain and his colleague wrote about this outcome in a study for the Journal of Emerging Infectious Diseases. Since then there has been another case in the USA.
Effects of the Zika virus
There is growing evidence to connect women who have contracted the Zika virus while pregnant, having a higher risk of giving birth to infants who have the birth defect microcephaly, a condition which results in the child being born with a smaller than usual head and an under-developed brain.
An increase in the number of cases of microcephaly have been found in new born babies in Brazil where there has been a recent outbreak of Zika.
In a previous outbreak in French Polynesia, health professionals noticed a rise in the cases of Guillain-Barré syndrome, a disease that affects the nervous system and results in symptoms such as muscle weakness, pain and numbness as well as co-ordination problems. Some patients become paralysed. People who develop the disease tend to recover but in rare cases they do die.