Zika Virus Infection as a Cause of Congenital Brain Abnormalities and Guillain–Barré Syndrome: Systematic Review

Background The World Health Organization (WHO) stated in March 2016 that there was scientific consensus that the mosquito-borne Zika virus was a cause of the neurological disorder Guillain–Barré syndrome (GBS) and of microcephaly and other congenital brain abnormalities based on rapid evidence assessments. Decisions about causality require systematic assessment to guide public health actions. The objectives of this study were to update and reassess the evidence for causality through a rapid and systematic review about links between Zika virus infection and (a) congenital brain abnormalities, including microcephaly, in the foetuses and offspring of pregnant women and (b) GBS in any population, and to describe the process and outcomes of an expert assessment of the evidence about causality. Methods and Findings The study had three linked components. First, in February 2016, we developed a causality framework that defined questions about the relationship between Zika virus infection and each of the two clinical outcomes in ten dimensions: temporality, biological plausibility, strength of association, alternative explanations, cessation, dose–response relationship, animal experiments, analogy, specificity, and consistency. Second, we did a systematic review (protocol number CRD42016036693). We searched multiple online sources up to May 30, 2016 to find studies that directly addressed either outcome and any causality dimension, used methods to expedite study selection, data extraction, and quality assessment, and summarised evidence descriptively. Third, WHO convened a multidisciplinary panel of experts who assessed the review findings and reached consensus statements to update the WHO position on causality. We found 1,091 unique items up to May 30, 2016. For congenital brain abnormalities, including microcephaly, we included 72 items; for eight of ten causality dimensions (all except dose–response relationship and specificity), we found that more than half the relevant studies supported a causal association with Zika virus infection. For GBS, we included 36 items, of which more than half the relevant studies supported a causal association in seven of ten dimensions (all except dose–response relationship, specificity, and animal experimental evidence). Articles identified nonsystematically from May 30 to July 29, 2016 strengthened the review findings. The expert panel concluded that (a) the most likely explanation of available evidence from outbreaks of Zika virus infection and clusters of microcephaly is that Zika virus infection during pregnancy is a cause of congenital brain abnormalities including microcephaly, and (b) the most likely explanation of available evidence from outbreaks of Zika virus infection and GBS is that Zika virus infection is a trigger of GBS. The expert panel recognised that Zika virus alone may not be sufficient to cause either congenital brain abnormalities or GBS but agreed that the evidence was sufficient to recommend increased public health measures. Weaknesses are the limited assessment of the role of dengue virus and other possible cofactors, the small number of comparative epidemiological studies, and the difficulty in keeping the review up to date with the pace of publication of new research. Conclusions Rapid and systematic reviews with frequent updating and open dissemination are now needed both for appraisal of the evidence about Zika virus infection and for the next public health threats that will emerge. This systematic review found sufficient evidence to say that Zika virus is a cause of congenital abnormalities and is a trigger of GBS.


Biological plausibility
Summary: Total, 6 items in 4 groups reviewed. Reviewer assessments found sufficient evidence for 2 of 3 questions about biologically plausible mechanisms by which ZIKV could trigger the immune-mediated pathology of GBS. There is evidence that supports a role for molecular mimicry, a proposed mechanism of autoimmunity in the development of GBS, which has been reported in Campylobacter jejuni-associated GBS. Direct neurotropic effects of ZIKV might also occur.
Case-control study, 1 [112]; Sequence analysis and phylogenetics, 2 [54, 114] [102,116] linked to [112] French Polynesia 3 0 Evidence for molecular mimicry comes from 2 in silico approaches and 1 clinical study:  Analysis of peptide sharing between the ZIKV polyprotein and human proteins related to myelin (de-myelination or axonal neuropathy) and human autoantigens known to be involved in GBS identified 99 candidate proteins with epitope sharing, of which many have been shown to be involved in autoimmune disease [114];  The prediction of B-cell epitopes of ZIKV and the comparison to B-cell epitopes in the human proteome identified several candidate proteins for both a Brazilian (Asian lineage) and African ZIKV strain. The proteins with the highest probability were Optineurin, Synaptogyrin-1, von Willebrand factor A, Pro-neuropeptide Y, Neuron Navigator Y (Brazilian strain only). 3D modelling of the ZIKV Brazil polyprotein showed matches for Pro-neuropeptide Y, Synaptogyrin, Neurotrophin 4, neural cell adhesion molecule, and von Willebrand factor A for a ZIKV region adjacent to high affinity MHC II binding site suggesting B and T-cell co-presentation. These findings suggest that antibodies against ZIKV may also target host proteins involved in neurologic and haemostatic processes [54];  IgM/IgG containing serum samples from GBS patients in French Polynesia were evaluated for reactivity to glycolipids using ELISA and combination microarray screening. 13 (31%) of GBS patients showed positive reactivity to glycolipids at admission and 10 (24%) had equivocal results using ELISA. 17 showed reactivity (8 positive, 9 equivocal) towards GA1 either as a single glycolipid or complex. In the microarray most sera showed no or low level binding activity to glycolipid complexes except for antibody binding affinities to GA1-sulphatide complex (N=19, 46%). After three months, the proportion of reactive sera was increased compared to admission: GM11 (26%), GA1 (32%), GD1a (29%), GD1b (29%) or any (48%  linked to [112]  5 studies excluded acute dengue virus (DENV) infection [110,112,113,117,118] Table).

Strength of association
This question was intended to look for evidence about autoimmune mechanisms. Auto-antibodies have been found in Zika-related GBS cases (see dimension 2, biological plausibility).
We did not find any studies of animal models of autoimmunity and ZIKV.

Analogy
Summary: Selected studies reviewed for 2 of 3 questions. Analogous mosquito-borne neurotropic flavivirus infections have been reported in association with GBS (West Nile virus, WNV; DENV; Japanese encephalitis virus, JEV). WNV and JEV have also been reported to be associated with direct neurotropic effects and poliomyelitis-like acute flaccid paralysis. The time lag between ZIKV symptoms and GBS symptoms is analogous to intervals reported for other infectious triggers of GBS. There is some evidence that, as for C. jejuni-associated GBS, molecular mimicry could be involved. Evidence was not reviewed systematically. 8.1 Do other flaviviruses or arboviruses cause GBS and by which mechanism(s)?
Studies not found through systematic searches Evidence about GBS following mosquito-borne flavivirus infections (WNV, DENV, JEV).
 WNV: A population-based study identified cases of acute paralysis following an outbreak of WNV in Colorado, USA in 2003 in an area of 724,000 residents. Of 32 cases with acute paralysis and WNV infection confirmed by serum IgM, only 6 (19%) had paralysis alone whereas the others had concomitant encephalitis or meningitis. 27 cases (84%) had asymmetric weakness consistent with poliomyelitislike syndrome (19 with cranial nerve involvement), 4 (13%) had symmetric ascending weakness with sensory abnormalities consistent with GBS and 1 had thoracic nerve paralysis. 26 patients (81%) reported no underlying morbidity. In the cases with poliomyelitis-like paralysis, the median latency between WNV infection symptoms and onset of paralysis was 3 days (range 0-18 days) and electromyographic studies suggested involvement of the anterior horn cells. The electromyographic findings in the GBS patients were indicative of demyelinating sensorimotor neuropathy [129]. In an in vitro experiment the infection of rat Schwann cells with WNV led to an upregulation of MHC class I and II molecules suggesting that Schwann cells may act as antigen presenting cells and bind to immune cells leading to peripheral nerve cell damage [135].  A narrative review identified 247 studies about neurological complications of DENV infection, of which 57 studies were related to immune-mediated complications including 13 studies about GBS. The average latency between illness and onset of weakness was one week [128].  GBS [130,131] as well as poliomyelitis-type acute flaccid paralysis [133,134] have also been reported as sequelae of JEV. Mice experimentally infected with JEV showed hindlimb paralysis and demyelination as well as production of antibodies against myelin basic protein (MBP) and proliferation of MBP-specific T cells suggesting a pivotal role of autoimmunity in JEV pathogenesis [138].  A review of vaccine adverse events reports found 6 cases of GBS as suspected side effects 7-27 days after live attenuated 17D-204 yellow fever vaccination in combination with other vaccinations [132]. 8.2 Do other pathogens cause GBS and by which mechanism(s)?
Studies not found through systematic searches jejuni is one of the pathogens commonly associated with GBS. It is estimated that C. jejuni precedes GBS in 10-30% of all cases, but only one in every 2000-5000 cases of C. jejuni infection will develop GBS [124,126]. The median latency between symptoms of C. jejuni infection and onset of GBS symptoms is reported as 9 days (range 1-23 days) [123,124,126,127]. Several laboratory experiments have provided some evidence for molecular mimicry of human nervous system proteins and pathogen proteins. Potential human candidate proteins for sequence homology are gangliosides and heat shock proteins (HSP) (summarised in [136]).  M. pneumoniae has also been associated with GBS.
Antibodies against galactocerebroside isolated from GBS patients have been found to cross-react with multiple types of M. pneumoniae [137]

Consistency
Summary: For 3 of 4 questions, there was sufficient evidence of consistency. By geographical region, ZIKV transmission has been associated with the occurrence of GBS in 2 of 3 regions where ZIKV has circulated since 2007. By study design, the association between ZIKV infection and GBS has been found in studies at both individual and population level and with both retrospective and prospective designs. By population group, ZIKV infection has been linked to GBS in both residents of an affected country and travellers from non-affected countries whose only possible exposure to ZIKV was having travelled to an affected country. Is the association between ZIKV infection and cases with GBS consistently found across different ZIKV lineages/strains? None N/A N/A N/A The data on differential pathogenicity by ZIKV strain or lineage is inconsistent to date:  Several countries in Africa, where the African lineage ZIKV is presumably endemic have not reported GBS as a complication of ZIKV infection. Differences in the sensitivity of surveillance systems between countries that have and have not reported cases have not been examined.  An increase in reports of GBS has only been reported from countries in which Asian lineage ZIKV transmission has been found for the first time. These differences may be true or confounded by differential surveillance and/or population sizes. This hypothesis cannot be supported nor rejected to date. 10.4 Is the association between ZIKV infection and cases with GBS consistently found across different study designs? None N/A N/A N/A Evidence of an association between ZIKV infection and GBS has been shown in different epidemiological study designs:  11 case series or case reports provide evidence in favour of causality for at least one dimension of causality;  1 case-control study provides evidence in 3 dimensions of causality;  Ecological studies in 9 countries found evidence of an increase in GBS at the same time as ZIKV transmission but 7 did not.