Zika virus (ZIKV), a mosquito-borne flavivirus, is a significant global health concern due to its association with neurodevelopmental disorders such as congenital Zika syndrome (CZS). This study aimed to compare the replication kinetics, viral persistence, cytopathogenic effects, and immune gene expression in human microglia cells (CHME-3) infected with an Asian lineage ZIKV (PRVABC59, referred to as ZIKV-PRV) and an African lineage ZIKV (IBH30656, referred to as ZIKV-IBH). We found that ZIKV-PRV replicated more efficiently and persisted longer while inducing lower levels of cell death and inflammatory gene activation compared with ZIKV-IBH. These findings suggest that the enhanced replication and persistence of ZIKV-PRV, along with its ability to evade innate immune responses, may underlie its increased neuropathogenic potential, especially in the context of CZS. In contrast, ZIKV-IBH, with its stronger immune gene activation and higher cytopathogenicity, may lead to more acute infections with faster viral clearance, thereby reducing the likelihood of chronic central nervous system (CNS) infection. This study provides crucial insights into the molecular and cellular mechanisms driving the differential pathogenicity of ZIKV lineages and highlights the need for further research to pinpoint the viral factors responsible for these distinct clinical outcomes.

Zika virus (ZIKV) remains a public health concern, with epidemics in endemic regions and sporadic outbreaks in new areas posing significant threats. Several mosquito-borne flaviviruses that can cause human illness, including West Nile, Usutu, and St. Louis encephalitis, have associations with birds. However, the susceptibility of chickens to ZIKV and their role in viral epidemiology is not currently known. We investigated the susceptibility of chickens to experimental ZIKV infection using chickens ranging from 1-day-old chicks to 6-week-old birds. ZIKV caused no clinical signs in chickens of all age groups tested. Viral RNA was detected in the blood and tissues during the first 5 days post-inoculation in 1-day and 4-day-old chicks inoculated with a high viral dose, but ZIKV was undetectable in 6-week-old birds at all timepoints. Minimal antibody responses were observed in 6-week-old birds, and while present in younger chicks, they waned by 28 days post-infection. Innate immune responses varied significantly between age groups. Robust type I interferon and inflammasome responses were measured in older chickens, while limited innate immune activation was observed in younger chicks. Signal transducer and activator of transcription 2 (STAT2) is a major driver of host restriction to ZIKV, and chicken STAT2 is distinct from human STAT2, potentially contributing to the observed resistance to ZIKV infection. The rapid clearance of the virus in older chickens coincided with an effective innate immune response, highlighting age-dependent susceptibility. Our study indicates that chickens are not susceptible to productive ZIKV infection and are unlikely to play a role in the ZIKV epidemiology.