Zika virus (ZV) was first discovered in 1947 and is named after the Zika Forest in Uganda. For sixty years after discovery, up to 20 confirmed human cases of ZV infection were reported. In 2016, ZV emerged as a major outbreak in Americas causing severe neurological complications and central nervous system congenital malformations.
The exact number of ZV infection cases during the recent outbreak is unknown. 712 000 cumulated cases were reported in 2015-2016 in Americas. The lack of laboratory capacity in endemic areas could underestimate the number. On the other hand, many patients, initially thought to have Zika disease, were infected with chikungunya virus. Incidence of ZV infection in the Americas peaked in 2016 and declined substantially throughout 2017 and 2018. The main suggested explanation for the decline is a protective level of herd immunity. No vector-borne locally acquired ZV disease had been reported in Europe.
ZV infection is transmitted by Aedes aegypti mosquito. It can also be transmitted from mother to foetus, through sexual contact, transfusion of blood and blood products, and organ transplantation.
Most people infected with ZV do not develop any symptoms or have a mild disease. However, since the 2015‒2017 epidemic, ZV has been associated with Guillain-Barré syndrome in adults and congenital malformations collectively characterized as congenital Zika syndrome, including microcephaly, abnormal brain development, limb contractures, eye abnormalities, etc.
There is no treatment or vaccine for ZV infection. ZV virus circulation has decreased but the possibility of its emergence or re-emergence should be considered in all areas with competent mosquito vectors.
Key points:
- The exact number of ZV infection cases during the recent outbreak is unknown.
- Many patients, initially thought to have Zika disease, were infected with chikungunya virus.
- No vector-borne locally acquired ZV disease has been reported in Europe.
- ZV virus circulation has decreased but the possibility of its emergence or re-emergence should be considered in all areas with competent mosquito vectors.
References:
Musso D; Cao-Lormeau V. Is the Zika threat over? Clin Microbiol Infect. 2018; 24: 566-567.
Paz-Bailey G, Rosenberg ES, Sharp TM. Persistence of Zika Virus in Body Fluids - Final Report. N Engl J Med. 2019 Jan 10;380(2):198-199.
WHO Zika Epidemiology update. July 2019: h