Historically, adult human infection with Zika virus has presented with mild, non-life threatening symptoms in 20% of infected patients, with 80% being clinically asymptomatic during initial infection.
Typical acute symptoms persist from days to one week, and include fever (37.9°C or below), maculopapular rash (average duration 6 days), arthralgia (average duration 3.5d, range 1 to 14d) and/or conjunctivitis, myalgia, headache, retro-orbital pain and emesis.
Cases described in Africa over the following years have characterised the ZIKV infection as a sudden-onset febrile episode followed by a mild headache and a pruriginous maculopapular rash on the second day involving the face, trunk, limbs, hand palms and feet soles. Fever usually declines within one or two days upon rash onset, which may persist for 2-14 days (six days, on average).
Fever is usually low, although it was higher in some case reports in Brazil and reaching 39º C.5 Muscle and joint pains and low-grade back pain have been reported although, unlike chikungunya, these are less intense and usually affect hands, knees and ankle joints. These usually decline one week later (3-5 days, on average). Conjunctivitis has been frequently described and is usually non-purulent. Other nonspecific manifestations may occur, including anorexia, nausea, vomiting, dizziness and retroorbital pain.
Recent reports of unusually high rates of GBS (Guillain-Barrésyndrome) and primary microcephaly, which are temporally and spatially associated with the Zika virus outbreak in Brazil, have raised concerns that the virus variant circulating in these regions represents an altered public health threat, with neuropathic and teratogenic outcomes. Nevertheless, the association between ZIKV infection and GBS, microcephaly still needs to be confirmed by laboratory studies.
The incubation period is 3-12 days upon the bite of an infected mosquito, similar to what was described with other arboviruses.
Zika virus usually remains in the blood of an infected person for about a week but it can be found longer in some people.
1, Pinto Júnior VL, et al. Zika virus: a review to clinicians, Acta Med Port 2015 Nov-Dec;28(6):760-765
2, Marina Basarab specialty registrar. et al .Zika virus. BMJ 2016; 352:i1049 doi: 10.1136/bmj.i1049