Zika virus infection

Zika virus disease
Zika virus infection is a vector borne disease, which recently has called the attention of the international community due to a large outbreak started in 2015 that affected more than 70 countries and territories1. 

The recent rapid spread of the Zika virus in previously unaffected regions has provided strong epidemiological evidence that infection with this virus might be associated with neurological complications in adults and with an increase in severe congenital brain and central nervous systems malformations of new-borns.  Consequently, in February 2016, the World Health Organization (WHO) has declared the recent outbreak of the Zika virus a Public Health Emergency of International Concern.  In November 2016, WHO indicated that Zika virus and associated consequences remain a significant public health challenge requiring intense action2 . 

Causes
The disease is caused by a virus of the Family Flaviviridae and it is transmitted mainly by an infected mosquito from the Aedes genus, mainly Aedes aegypti.  This mosquito has an imperceptible bite, is more active during day time hours and lives in close association with human habitation5.  It is thought to have high capacity to transmit pathogens and is also the carrier of other arboviruses including Dengue, Chikungunya and yellow fever virus.

Other modes of transmission of Zika virus are sexual, congenital and perinatal.

Consequences
Clinical manifestations of Zika virus infection are generally mild and a large proportion of infected persons remain asymptomatic3. Most frequent symptoms include macular or papular rash, fever, joint pain (arthralgia), conjunctivitis, headache and retro-orbital pain4,5.

Zika virus infection during pregnancy is associated with the congenital Zika syndrome responsible for microcephaly and ocular abnormalities.  In adults, it can increase the risk of Guillain-Barré Syndrome.  Associations with other possible neurological complications are under study4.

Global Burden
Since its first description in 1947 in monkeys of the Zika forest in Uganda5, few cases were reported in Asia and African countries, until 2007, when the first large outbreak of Zika infection was reported from the Island of Yap (Federated States of Micronesia)4.

Since then, outbreaks have been reported in different territories, being the most recent one in the Americas, which started in Brazil (2015) and spread to 48 countries of this region6. More than 540.000 suspected cases and >198.000 confirmed cases have been reported up to January 20177.

Vaccines
There is not specific treatment or vaccine available against Zika virus. Preventive measures are centred on avoiding mosquito bites, reducing other forms of transmission (e.g. sexual transmission) and controlling the vector (mosquitos)5.  These measures can, however, be challenging and have variable efficacy.

Although disease symptoms are generally mild, the possible complications to pregnancy, new-borns and neurologic complications in adults, highlight the need of effective measures to prevent this disease.  In this context, in March 2016, experts gathered at WHO agreed that the development of a preventive vaccine is a major priority to respond to Zika epidemics in the future8.  A first target product profile (TPP) for Zika vaccines was recently finalised and published jointly with UNICEF3,9.

References

  1. WHO. Situation report. Zika virus, Microcephaly, Guillain-Barré Syndrome. (2017, January 5). Retrieved from:   http://apps.who.int/iris/bitstream/10665/252762/1/zikasitrep5Jan17-eng…

  2. WHO. Fifth meeting of the Emergency Committee under the International Health Regulations (2005) regarding microcephaly, other neurological disorders and Zika virus. (2016, November 18). Retrieved from: http://www.who.int/mediacentre/news/statements/2016/zika-fifth-ec/en/

  3. Vannice KS, et al. Meeting Report: WHO consultation on considerations for regulatory expectations of Zika virus vaccines for use during an emergency. Vaccine. 2016 Dec 1. pii: S0264-410X(16)30969-0. doi: 10.1016/j.vaccine.2016.10.034. [Epub ahead of print]

  4. Zika virus: Fact sheets. (2016, September 6). Retrieved from:  http://www.who.int/mediacentre/factsheets/zika/en/

  5. Petersen LR, et al. Zika Virus. N Engl J Med. 2016 Apr 21;374(16):1552-63. doi: 10.1056/NEJMra1602113. Epub 2016 Mar 30.

  6. PAHO. Zika - Actualización Epidemiológica Regional de la OPS (Américas). (2017,  January 26). Retrieved from: http://www.paho.org/hq/index.php?option=com_content&view=article&id=115…

  7. PAHO. Zika cases and congenital syndrome associated with Zika virus reported by countries and territories in the Americas, 2015 – 2017. Cummulative Cases. (2017,  Januay 18). Retrieved from: http://www.paho.org/hq/index.php?option=com_docman&task=doc_view&Itemid…

  8. WHO and experts prioritize vaccines, diagnostics and innovative vector control tools for Zika R&D. (2016, March 9). Retrieved from: http://www.who.int/mediacentre/news/notes/2016/research-development-zik…

  9. WHO. Zika virus vaccine product development. (2016, November). Retrieved from: http://www.who.int/immunization/research/development/zika/en/index2.html