Pathogenic potential and growth kinetics of Muko virus in mice and human-derived cells

Abstract

Background: Ticks have been long known as vectors of various pathogens, some of which can cause high fatality rates among infected individuals. Our enhanced tick surveillance around Nagasaki, Japan, led to the isolation and identification of a new strain of a recently identified Orbivirus, Muko virus (MUV). The orbiviruses have a wide host range, including humans, and is related to a spectrum of clinical outcomes. However, the zoonotic potential of some members of the genus, although reported, were not clearly elucidated. Hence, it is imperative to characterize newly isolated orbiviruses and investigate its ability to endanger public health.

Methods: In this study, we explored the in vivo pathogenicity of a newly isolated MUV strain (MUV-Hay) using a mouse model and demonstrated its growth kinetics in human-derived cells.

Results: Our results showed the ability of MUV-Hay to propagate in human neuronal and renal cells with some cytopathic effect. Furthermore, intracerebral inoculation of our new isolate caused high mortality in adult A129 mice.

Conclusion: Our study provided a first step to experimentally test the hypothesis, that MUV can replicate and produce cytopathic effect in human cells and demonstrate virulence in adult mice.

Keywords: Human-derived cells; Mouse model; Muko virus; Tick-borne virus.

Fig. 1

Map showing the location of Nagasaki and Nishinomiya in Japan

Fig. 2

Phylogenetic tree of tick-borne Orbiviruses. The phylogenetic tree was constructed based on the VP1 region by LG + G substitution model. Colorado tick fever virus, of the genus Cortivirus, was selected as an outgroup. One thousand bootstrap replications were conducted. Bootstrap values (shown as percentage) are described at the nodes

Fig. 3

Survival curves of A129 mice in six different dosage groups (total n = 36) pertaining to inoculation dose ranging 10⁻² to 10³ pfu of MUV (n = 6 per group). Each mouse within the groups was inoculated subcutaneously and observed for 14 days. a Weight changes expressed as weight ratios. b Survival rate per group. c Mortality and morbidity rates. Morbidity of mice was estimated by degree of weight loss

Fig. 4

Viral RNA levels in tissues of MUV-infected A129 mice at 1 (a) and 3 (b) days pi. Asterisks show the pairs that exhibit significant differences by Tukey’s multiple comparison test that indicate P < 0.05 by the analysis of variance

Fig. 5

MUV propagation in SK-N-SH, T98-G, and HEK-293 cells. CFs were harvested every 24 h for 3 days pi. Growth curves in the CFs are indicated by plaque-forming unit per milliliter. Error bars represent the standard errors