Does Zika Virus Cause Microcephaly - Applying the Bradford Hill Viewpoints

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.