This is difficult to determine as the definition and use of the term is not consistent. Diagnosis of microcephaly can occur any time from second trimester to delivery. Also data collection on birth defects is collected in different ways. It is expected that, as the Zika virus outbreak evolves, countries other than Brazil will see microcephaly and other birth anomalies as pregnant women receive prenatal care and deliver.
It is known that the fetus can contract the Zika virus from the mother during pregnancy, although it is not known how often this occurs. The chance of the fetus developing birth defects if the mother contracts the virus during pregnancy is also not known. Whether an infection in a previous pregnancy will impact on a subsequent pregnancy is thought to be unlikely with no evidence to suggest this.
Unfortunately, it is currently unknown at what stage a pregnant woman is most susceptible to the virus. The infection can occur any time during the pregnancy and can be passed onto the fetus. It is thought that microcephaly is more likely to develop if infection occurs in the first trimester.
Check out the current status of Zika Virus.
Immunity post infection is likely, assuming that the Zika virus behaves in a similar way to other infections.
There have been no reported cases of this. It is thought that it behaves like other flaviviruses and is spread mainly by mosquito bite.
Although yet to be determined, it is thought to have an incubation period of 3 days to 2 weeks. This is similar to other flaviviruses.
It is considered that the virus is present in the blood of an infected person for about a week. Evidence suggests that it may remain in the semen of infected men for longer, but it is undetermined as to how long the semen remains infective. Therefore, the risk of sexual transmission exposure is yet to be determined.
Firstly, it is recommended that a thorough history is taken to determine the level of risk to the patient. This includes the potential for exposure to the Zika virus due to travel in high risk areas, whether the patient is pregnant, and the vaccination history (Dengue or Chikungunya viruses). A blood test will then be done. A screening test is done and if this is positive a more definitive test is then done.
Get more details at The Zika Virus Summarised.