Zika Virus

Greetings

The best part of 2016 as of yet, is that the Ebola epidemic which is more than a year long, the worst among all previous Ebola spread looks like is over and currently not reporting any new cases. If the situation remains stable, WHO will declare the epidemic to be officially over in another couple of weeks. The sad part, blood-based Ebola therapy trial results is not promising. And the worst part is, there appears to be an increasing number of cases of a rare virus infection- Zika Virus.

Fig 1: Documented ZIKV outbreaks.
Source

Zika Virus (ZIKV) is a member of mosquito borne- Flavivirus group. Structurally it is similar to other Flavivirus members. The vision has an icosahedral-like symmetry, containing nucleocapsid surrounded by a host-membrane derived lipid bilayer studded with envelope proteins E and M. First discovered in an experimental rhesus monkey which was caged in Zika forest in 1947 for research on yellow fever. Subsequently the agent was isolated and characterised in 1952 and named as Zika virus. The first human case was described from a Nigerian patient in 1954. Interestingly, this virus has been reported in extremely rare numbers upto 2007.

Fig 2: States with laboratory-confirmed cases ZIKV

Brazil 2015. Data as on 23 November 2015.

Source

There has been a total of 3 outbreaks prior to the current suspected epidemic. The first documented outbreak was reported from Yap Island in 2007 (April to June 2007). There were a total of 185 cases of suspected Zika virus disease. Of these, 49 (26%) were confirmed and 59 (32%) were probable cases. The second was an outbreak in Tahiti. I have not been able to find the accurate number of cases, but literature published has estimated 8273 suspected cases. In 2014 two places, Cook Island and New Caledonia showed up in the map. The Cook island outbreak was over quickly with 932 suspected and 50 confirmed cases. New Caledonia had 1400 confirmed cases of which 35 was imported cases. Fig 1, shows a representation of documented ZIKV outbreaks. By May 2015 Brazil reported its first case of Zika and by December 2015 the virus had been demonstrated in several countries of Central and South America (See Fig 1). The outbreak continues to expand in terms of number of cases.

Photo 1: A child with Microcephaly,
mother diagnosed with ZIKV.
Source

Microcephaly is a congenital defect represented by abnormally small growth of head, with incomplete brain development. In African region 2013, 167 cases and in 2014 147 cases of microcephaly was recorded. In 2015 nearly 3000 cases has been reported. The headlines over the media is that Zika virus has a role in microcephaly. Of course, as of yet there is no formal proof yet. But it appears that ZIKV genetic tests were positive in at least a good number of cases with children who are born of microcephaly. Further a CNS disorder- Guillain-Barré syndrome (GBS) has been previously shown to have some association with ZIKV infection. Infant 74 patients who had Zika symptoms, later developed neurological or autoimmune syndromes - out of them, 42 were diagnosed as GBS.

There are a couple of things to note here. ZIKV is similar to dengue and antibodies are cross reactive thus making ELISA tests sometimes confusing. Currently, only genetic test is diagnostic. It should also be noted that currently ZIKV infection is in quite good number and hence it is statistically hard to tell the association. But the sudden 20 fold increase in cases is something that needs to be looked into. There is also a good chance that this virus is slowly migrating.

At this point many experts have commented that it is too early to suggest that ZIKV is behind the small brains. 

Duffy MR, Chen TH, Hancock WT, Powers AM, Kool JL, Lanciotti RS, Pretrick M, Marfel M, Holzbauer S, Dubray C, Guillaumot L, Griggs A, Bel M, Lambert AJ, Laven J, Kosoy O, Panella A, Biggerstaff BJ, Fischer M, & Hayes EB (2009). Zika virus outbreak on Yap Island, Federated States of Micronesia. The New England journal of medicine, 360 (24), 2536-43 PMID: 19516034

Roth A, Mercier A, Lepers C, Hoy D, Duituturaga S, Benyon E, Guillaumot L, & Souares Y (2014). Concurrent outbreaks of dengue, chikungunya and Zika virus infections - an unprecedented epidemic wave of mosquito-borne viruses in the Pacific 2012-2014. Euro surveillance, 19 (41) PMID: 25345518

Campos GS, Bandeira AC, & Sardi SI (2015). Zika Virus Outbreak, Bahia, Brazil. Emerging infectious diseases, 21 (10), 1885-6 PMID: 26401719