Sequencing of Historical Isolates, K-mer Mining and High Serological Cross-Reactivity with Ross River Virus Argue against the Presence of Getah Virus in Australia

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.

The use of an immunoelectron microscope-decoration technique to observe serological relationship of carlaviruses

An immunoelectron microscope-decoration technique was used to define serological relationships among carlaviruses (5 viruses and 9 antisera). The degree of relationship among these viruses was assessed on the basis of the intensity of antibody coating when the viruses were decorated with heterologous antibodies. A relationship was observed among PVM, PVS, CLV, CVB, LilMV, HoLV, HoMV and between WPSV and LilMV. PopMV was not related serologically to any of these viruses. The PVS particles were occasionally surrounded by an external spiral of an unidentified protein material.

The determination of the degree of serological relationship among four carlaviruses using an immunoelectron microscope-decoration technique and cross-absorption tests

A very close serological relationship was found between CVB and PVS, while only a distant relationship was shown between CVB and CLV. Each of these viruses had its own characteristic major "antigenic fraction", distinguishing it from the others, and small "antigenic fraction" common to all four. The antiserum to CLV was shown to be the richest in various antigenic fractions, antisera against PVM and PVS had the same number of fractions but of different specificity and CVB-antiserum had the relatively smallest number of fractions.