The recent emergence of Zika virus (ZIKV) in Brazil was associated with an increased number of fetal brain infections that resulted in a spectrum of congenital neurological complications known as congenital Zika syndrome (CZS). Herein, we generated de novo from sequence data an early Asian lineage ZIKV isolate (ZIKV-MY; Malaysia, 1966) not associated with microcephaly and compared the in vitro replication kinetics and fetal brain infection in interferon α/β receptor 1 knockout (IFNAR1-/-) dams of this isolate and of a Brazilian isolate (ZIKV-Natal; Natal, 2015) unequivocally associated with microcephaly. The replication efficiencies of ZIKV-MY and ZIKV-Natal in A549 and Vero cells were similar, while ZIKV-MY replicated more efficiently in wild-type (WT) and IFNAR-/- mouse embryonic fibroblasts. Viremias in IFNAR1-/- dams were similar after infection with ZIKV-MY or ZIKV-Natal, and importantly, infection of fetal brains was also not significantly different. Thus, fetal brain infection does not appear to be a unique feature of Brazilian ZIKV isolates.
Getah virus (GETV) is a mosquito-transmitted alphavirus primarily associated with disease in horses and pigs in Asia. GETV was also reported to have been isolated from mosquitoes in Australia in 1961; however, retrieval and sequencing of the original isolates (N544 and N554), illustrated that these viruses were virtually identical to the 1955 GETVMM2021 isolate from Malaysia. K-mer mining of the >40,000 terabases of sequence data in the Sequence Read Archive followed by BLASTn confirmation identified multiple GETV sequences in biosamples from Asia (often as contaminants), but not in biosamples from Australia. In contrast, sequence reads aligning to the Australian Ross River virus (RRV) were readily identified in Australian biosamples. To explore the serological relationship between GETV and other alphaviruses, an adult wild-type mouse model of GETV was established. High levels of cross-reactivity and cross-protection were evident for convalescent sera from mice infected with GETV or RRV, highlighting the difficulties associated with the interpretation of early serosurveys reporting GETV antibodies in Australian cattle and pigs. The evidence that GETV circulates in Australia is thus not compelling.
In Australia, infection of horses with the West Nile virus (WNV) or Murray Valley encephalitis virus (MVEV) occasionally results in severe neurological disease that cannot be clinically differentiated. Confirmatory serological tests to detect antibody specific for MVEV or WNV in horses are often hampered by cross-reactive antibodies induced to conserved epitopes on the envelope (E) protein. This study utilized bacterially expressed recombinant antigens derived from domain III of the E protein (rE-DIII) of MVEV and WNV, respectively, to determine whether these subunit antigens provided specific diagnostic markers of infection with these two viruses. When a panel of 130 serum samples, from horses with known flavivirus infection status, was tested in enzyme-linked immunosorbent assay (ELISA) using rE-DIII antigens, a differential diagnosis of MVEV or WNV was achieved for most samples. Time-point samples from horses exposed to flavivirus infection during the 2011 outbreak of equine encephalitis in south-eastern Australia also indicated that the rE-DIII antigens were capable of detecting and differentiating MVEV and WNV infection in convalescent sera with similar sensitivity and specificity to virus neutralization tests and blocking ELISAs. Overall, these results indicate that the rE-DIII is a suitable antigen for use in rapid immunoassays for confirming MVEV and WNV infections in horses in the Australian context and warrant further assessment on sensitive, high-throughput serological platforms such as multiplex immune assays.