With the last confirmed death related to Ebola in January 2016, the disease looks tamed. Meanwhile however, the next adversary is emerging: The Zika virus started spreading in Brazil in April 2015 and quickly set out to other parts of Latin America and even as far as Europe. This article will give a quick recap on the virus itself, its latest history, known pattern of spreading and currently employed counter-measurements as well as research projects designed to fight it.
Latest History and spreading patterns and methods
Back in April 2015, when Zika started to spread in Brazil, officials first suspected a direct link to the 2014 FIFA World Cup a year prior. Analysis of Oxford University’s Department of Zoology and Brazilians Evandro Chagas Institute showed that America’s outbreak arose from a single contact and estimated occurrence between May and December 2013 – >12 months prior to first detection. According to Oliver Pybus, a professor at Oxford University, there was a 50% rise in the number of passengers travelling to Brazil from countries with Zika. Since the outbreak virus is closely related to a strain from French Polynesia (99.7 % match in genome), introduction during the Confederations Cup soccer tournament by French Polynesian visitors seems plausible.
Zika mainly spreads through mosquito bites of the Aedes species (A. aegypti and A. alnopictus), sexual intercourse and pregnancy. These mosquitoes breed near standing water like buckets, bowls, animal dishes and flower pots and bite both during the day and night time.
The Center for Disease Control and Prevention (CDC) states that sexual transmission is possible and that the virus is longer present in semen than blood .
On 25th March, the CDC published interim guidelines on ensuring healthy pregnancies and babies amid the outbreak. The CDC guidance of 6 months for prior-infected men was based on the longest-known risk period (62 days) multiplied by three.
The CDC further states that, by March 24th 2016, 258 people with residence in the Continental United States, including 18 pregnant women, have transmitted Zika since the beginning of this year. This appears to have happened through travel, not by mosquito-linked infection within the US. The CDC has not yet provided data on travellers returning in March, but for the prior months: 116 persons have conducted Zika between January 1 2016 and February 26, 2016. Of these, 1 was a congenital infection, 110 persons had recently travelled to active areas, and 5 had had sexual intercourse with such a traveller. All patients showed signs of clinical illness. The cases were verified by reverse transcription polymerase chain reaction (RT-PCR) (-> Since a normal PCR can only amplify DNA, the enzyme Reverse Transcriptase synthesises the complimentary copy DNA strang).
According to the European Centre for Disease Prevention and Control, there is currently no evidence of transmission of the Zika Virus in Europe.
On April 2, Austria Press Agency reported a case of a Catalonian pregnant woman who recently visited Columbia, therefore limiting the reported cases of Zika to travel-borne ones.
On Wednesday, April 6, the Obama Administration redirected $510 million of Ebola funds and $79 million of funds from other Department of Health and Human Services programs to mosquito control and surveillance programs, public information campaigns, laboratory structures and diagnostic tests.
Virus – Particle, Genome, Infection
The Zika virus, first described in 1947, belongs to the systematic group of Flaviviridae and is a relative to dengue, Yellow Fever, Hepatitis C and the West Nile virus. While its close relatives Yellow Fever and Dengue are far deadlier, taking up 50.000 lives per year each, Zika proved immensely contagious and infected as much as 1.5 m people during the recent outbreak alone.
An animated Zika virion can be viewed here.
The icosahedral virion of Zika is 50 nm in diameter and contains a single-stranded, positive-sense Ribunucleic Acid (RNA genome, ((+)ssRNA, 10.794 bp long), which also serves directly as viral messenger RNA, and three types of proteins ( E, M and C). The (+)ssRNA can directly be translated in viral proteins. This translated polyprotein ( 3417-3423 amino acids) is cleaved to all structural and non-structural proteins by host and viral proteases. Apart from the structural proteins, the genome encodes for various non-structural proteins, ones that are not packed into new assembled virions, which coordinate viral-replication and inhibit the immune response. An high resolution study using cryo-EM of ZIKV was recently published in Science .
The 3´terminus of the (+)ssRNA forms a loop structure, which is cleaved off by cellular RNAse XRN1. This results in a virulence factor, subgenomic flavivirus RNA (sfRNA) and is linked to inhibiting host RIG-I antiviral activity similar to the Dengue virus.
The surface proteins E and M form a regular spherical shell and allow the particle to enter the cell. While the surface-particle interaction is still not fully understood, a linkage to the AXL surface protein (among others) was suggested by researchers. In a recent (30th April 2016) published study in Cell Stem Cell researchers conducted that AXL is mainly found in so called radial glial cells, neural stem cells only found in the second trisemester of pregnancy. AXL aggregates toward areas where the neural progenitors come into contact with either cerebrospinal fluid or blood vessels. This unique position would give a virus such as Zika an easy way to reach a vulnerable population of host cells.
Infected suspects suffer from mild rashes, fever, head and joint pain or vomiting. These symptoms usually last a week at last and it is not known yet, if a recent infection makes the suspect (temporally) immune.
In a recent published article in the Cell Stem Magazine, Researchers confirmed that the Zika virus can directly infect human neural progenitor cells (hNPCs) in vitro with high efficiency and that infection of hNPCs leads to attenuated population growth through virally apoptosis and cell-cycle dysregulation. Infected hNPCs also release infectious viral particles, which presents a significant clinical challenge for developing effective therapeutics to arrest or block the impact of infection.
Brazilian Researchers from the D’Or Institute for Research and Education (IDOR) and Federal University of Rio de Janeiro (UFRJ) observed the degenerative effects of ZIKV by infecting human-derived induced pluripotent stem cells ( iPS). These neurospheres (clusters of free-floating stem cells) and brain organoids (artificially in-vitro grown three-dim structure in a bioreactor) represent excellent models to investigate developmental neuropathologies, as they can outline, in vitro, several characteristics of the fetal brain formation. The infection caused cell death, malformations and reducing growth by 40%. The researchers also compared these results with the ones generated with Dengue Virus (DENV2). Even though DENV2 infected the cells such as ZIKV, there were no damaging outcomes registered to the neural cells, neurospheres or organoids.
This underlines the assumption that Zika is the main driver of a stark increase in cases of microcephaly in Brazil in 2015.
True cases, however, are only just in the single digits: When first cases drew attention in 2015, the Brazil Health Ministry published a bulletin for doctors to look for microcephaly in new-borns. Unsurprisingly, the number of reported cases spiked instantly. This leads to a twofold assumption: either cases were not properly identified prior to 2015, raising doubts about the validity of that years´s 150 official reported cases, since a lot of the reportings where later discarded, microcephaly was simply overdiagnosed.
Speaking in numbers: as of 12 March, there were 6,398 suspected cases of microcephaly and/or central nervous system malfunctions reported by the Brazil´s health ministry since November 2015. Since then, of these 2,197 investigated cases, 854 have turned out to be microcephaly and just 97 of these 854 have turned out to be linked to Zika through lab tests.
As for this high difference in suspicions as opposed to actual diagnoses, a look at Brazils classification for microcephaly sheds light on the issue: the threshold for a positive diagnosis was changed from 33 cm (October 2015) which, according to an article in The Lancet would result in potential 600k reports of small, but healthy babies, to 32 cm in December (est. 200k suspect cases). Finally, in March 2016, Brazil adopted the WHO recommendation of <31.9 cm and 31.5 cm for full-term babies, which, in the future, will lower the number of new suspected cases even further.
Furthermore, relating microcephaly to Zika appears overly simplistic: according to Dr. Thomaz Gollop, a specialist in fetal medicine in Sao Paulo, microcephaly just means “small head”, whereas the abnormalities seen in recent cases are far more complicated. In his view, the term “Zika syndrome” would be correct: a series of symptoms caused by Zika. Connecting one symptom with Zika alone is unhelpful, but the public is almost exclusively talking about this one connection alone since the very beginning.
Additionally, Zika is linked to the Guillain-Barré Syndrome, an auto-immune disorder, causing muscle weakness and on rare occasions paralysis or death. This linkage is weakend by the fact that many common pathogens cause Guillain-Barré, e.q. Campylobacter infections from undercooked poultry.
Furthermore, Brazils northeast relies heavily on an agriculture marked by the heavy usage of pesticides, which are poorly regulated. Some have shown heavy neurotoxic capabilities. In presence of these environmental factors, calling Zika the main root of central nervous system malfunctions seems inplausible. To really test the link in a conclusive and comprehensive manner, case-control epidemiological studies will have to be completed.
Current counter-measurements and research
The World Health Organization promptly started to share information about Zika and released travel warnings. This cumulated in declaring Zika a Global Health emergency on February 1st 2016.
Since then, the WHO has convened seven international meetings and published documents covering latest research into interim practical guidance to support countries as they respond to this outbreak and its neurological complications.
The World Health Organisation’s Director-General, Margaret Chan, stated that in less than a year, the status of Zika has changed from “a mild medical curiosity” to a disease with severe public health implications, warning that “the more we know, the worse things look.”
While there are currently no specifically licensed medical countermeasures (vaccines, therapeutics or preventive drugs) available for the Zika virus infection and disease , several are in the making: 23 vaccine projects are currently worked on by 14 different countries, including the US, France, Brazil, India and Austria.
On March 28th 2016, scientists, government officials and representatives of the private sector met at the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland to speed up current development of vaccines, diagnostics and treatments. One auspicious experimental vaccine was developed by the Butantan Institute in Sao Paulo, Brazil: an inactivated vaccine made from purified Zika virus. Human trails could start by 2018 or 2019. These inactivated vaccines seem to be the best and safest inoculation for pregnant women and became a top research priority by the WHO back in March 2016.
According to Alexander Precisio, director of the clinical trials and pharmacovigilance division of the Butantan Institute, an attenuated vaccine (reduction of virulence) might be the most effective one, since it mimics the natural course of infection better and closer than inactive ones, but are far more complex to develop and won´t enter safety trials till 2017.
Another approach would not bother attacking the virus itself, but try to limit and possibly contain its spreading by eliminating the mosquito-borne transmission. Labs of the International Atomic Energy Agency (IAEA) participate in a new € 2.3m initiative in researching novel sterile insect techniques (SIT) in Seibersdorf, Austria. The Austrian researchers use ionising radiation to damage male gonads. These then-released mosquitoes will mate with wild females, prompting them to produce infertile eggs <fn>http://www.themalaymailonline.com/features/article/in-fight-against-zika-irradiated-mosquitoes-help-zap-virus-spread?utm_medium=twitter&utm_source=twitterfeed</fn>.
The IAEA aims at training local staff in affected countries on insect management and the strengthening of knowledge transfer and information exchange between countries.
Another possible solution lies in the world of genetics: British firm Oxitec established a transgenic mosquito using the Release of Insects Carrying a Dominant Lethal Gene System (RIDL).
Transgenic males, are homozygous for a dominant lethal gene, which is under control of expression of tTA, a fusion protein that combines sequence-specific tetracycline-repressible binding to tRe, a tetracycline-response element, to a eukaryotic transcriptional activator. In the absence of tetracycline, this protein will bind to the tRe sequence, activating transcription of the lethal gene, which leads to the death of the single insect.
Mating with indigenous insect population results in offspring that are heterozygous for the lethal gene. This results in the death of the developing embryo and hence eventual suppression of the mosquito population due to a critical decrease in its reproductive capacity.
As more and more research is finished Zika’s menace of becoming a huge neurological disease threat seems diminishing in regard to tightened definition of microcehpaly, research progress and strategies currently deployed fighting the mosquito-born transmission. The WHO is able to quickly contain biological threats easily, if they deploy action right from the beginning (as opposed what happened during the Ebola outbreak) and conflate, supervise and lead research and development of vaccines. Since Zikas relation to Dengue, knowledge of the virus and its airborne-spreading pattern will contribute in fighting other diseases like West-Nil and Dengue. Research in the neurological infection pathway may also contribute in a better understanding of fetal brain development in general and introduce novel research models for other neurological degenerative diseases.
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