Improved detection of flaviviruses in Australian mosquito populations via replicative intermediates

Complete inactivation of orthoflavi- and alphaviruses by acetone for safe titering by ELISA

The tissue culture infectious dose 50 (TCID50) end-point dilution assay is the gold-standard assay to titer viruses with negligible or ambiguous cytopathic effects. The assay's specificity is improved when followed by an Enzyme-Linked Immunosorbent Assay (ELISA) to detect viral antigens. Cells infected with mosquito-borne orthoflavi- and alphaviruses are fixed after TCID50, prior to ELISA, using paraformaldehyde (PFA) or acetone. While 4 % PFA has been shown to effectively inactivate these viruses for safe handling in low biocontainment conditions, equivalent studies have not been reported for standard acetone fixation methods (20 % acetone for 24 hours at 4°C). This study evaluated the inactivation efficacy of acetone on orthoflavi- and alphaviruses using dengue virus (DENV) and Ross River virus (RRV), as exemplar viruses from each genus, respectively. We show that 50 % acetone and 4 % PFA fully inactivate DENV and RRV, but 20 % acetone does not reduce the infectivity of these viruses. Importantly, ELISA-based detection of DENV- and RRV-infected cells fixed with 50 % acetone was effective, with calculated titres comparable to cells treated with 20 % acetone. Together, our results inform a fixation method for titrating orthoflavi- and alphavirus samples by TCID50/ELISA, ensuring the safe handling and processing of these viruses under low biocontainment conditions.

The Troublesome Ticks Research Protocol: Developing a Comprehensive, Multidiscipline Research Plan for Investigating Human Tick-Associated Disease in Australia

In Australia, there is a paucity of data about the extent and impact of zoonotic tick-related illnesses. Even less is understood about a multifaceted illness referred to as Debilitating Symptom Complexes Attributed to Ticks (DSCATT). Here, we describe a research plan for investigating the aetiology, pathophysiology, and clinical outcomes of human tick-associated disease in Australia. Our approach focuses on the transmission of potential pathogens and the immunological responses of the patient after a tick bite. The protocol is strengthened by prospective data collection, the recruitment of two external matched control groups, and sophisticated integrative data analysis which, collectively, will allow the robust demonstration of associations between a tick bite and the development of clinical and pathological abnormalities. Various laboratory analyses are performed including metagenomics to investigate the potential transmission of bacteria, protozoa and/or viruses during tick bite. In addition, multi-omics technology is applied to investigate links between host immune responses and potential infectious and non-infectious disease causations. Psychometric profiling is also used to investigate whether psychological attributes influence symptom development. This research will fill important knowledge gaps about tick-borne diseases. Ultimately, we hope the results will promote improved diagnostic outcomes, and inform the safe management and treatment of patients bitten by ticks in Australia.

Arthropod-Borne Virus Surveillance as a Tool to Study the Australian Mosquito Virome

Mosquitoes (n = 4381 in 198 pools) were collected in March and April 2018 to survey the presence of West Nile virus Kunjin strain in mosquito populations around crocodile farms in the Darwin region of the Northern Territory (NT) of Australia. While no Kunjin virus was detected in these mosquitoes, we applied our viral replicative intermediates screening system termed monoclonal antibodies to viral RNA intermediates in cells or MAVRIC to this set of samples. This resulted in the detection of 28 pools with virus replicating in C6/36 mosquito cells and the identification of three insect viruses from three distinct virus classes. We demonstrate the persistence of the insect-specific flavivirus Palm Creek virus in Coquillettidia xanthogaster mosquitoes from Darwin over almost a decade, with limited genetic drift. We also detected a novel Hubei macula-like virus 3 strain in samples from two mosquito genera, suggesting the virus, for which the sequence was originally detected in spiders and soybean thrips, might be involved in a horizontal transmission cycle between arthropods and plants. Overall, these data demonstrate the strength of the optimized MAVRIC system and contribute to our general knowledge of the mosquito virome and insect viruses.