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Does Zika Virus Cause Microcephaly - Applying the Bradford Hill Viewpoints
Asma Awadh1, Abrar Ahmad Chughtai2, Amalie Dyda3
1University Of New South Wales University Of New South Wales.
Introduction:
Zika virus has been documented since 1952, but been associated with mild, self-limiting disease. Zika virus is classified as an arbovirus from a family of Flaviviridae and primarily spread by Aedes Aegypti mosquitos. However, in a large outbreak in Brazil in 2015, Zika virus has been associated with microcephaly.
Methods:
In this review we applied the Bradford-Hill viewpoints to investigate the association between Zika virus and microcephaly. We examined historical studies, available data and also compared historical rates of microcephaly prior to the Zika virus outbreak. The available evidence was reviewed against the Bradford Hill viewpoints.
Results:
All the nine criteria were met to varying degrees: strength of association, consistency of the association, specificity, temporality, plausibility, coherence, experimental evidence, biological gradient and analogy. Conclusion: Using the Bradford Hill Viewpoints as an evaluation framework for causation is highly suggestive that the association between Zika virus and microcephaly is causal. Further studies using animal models on the viewpoints which were not as strongly fulfilled would be helpful.
Insights
The Zika virus, primarily spread by Aedes Aegypti mosquitoes, is strongly linked to microcephaly. Applying the Bradford-Hill criteria suggests a causal relationship between Zika virus infection and microcephaly development.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Zika virus, an arbovirus from the Flaviviridae family, has been known since 1952, typically causing mild illness.
- Historically, Zika virus transmission occurred primarily through Aedes Aegypti mosquitoes.
- A significant outbreak in Brazil in 2015 revealed a novel association between Zika virus and microcephaly.
Purpose of the Study:
- To investigate the potential causal association between Zika virus infection and microcephaly.
- To evaluate the evidence for Zika virus as a cause of microcephaly using established epidemiological criteria.
Main Methods:
- A comprehensive review of existing literature and data on Zika virus and microcephaly.
- Application of the nine Bradford-Hill viewpoints to assess causality.
- Comparison of microcephaly rates before and during the Zika virus outbreak.
Main Results:
- The review found that all nine Bradford-Hill criteria were met to varying degrees.
- Evidence demonstrated strength of association, consistency, specificity, temporality, biological plausibility, coherence, experimental evidence, biological gradient, and analogy.
- The findings strongly suggest a causal link between Zika virus and microcephaly.
Conclusions:
- The application of the Bradford-Hill criteria provides compelling evidence for a causal relationship between Zika virus and microcephaly.
- Further research, particularly using animal models, is recommended to strengthen evidence for criteria not fully met.
- This study underscores the significant public health implications of Zika virus during pregnancy.