Abstract
The presence of the giant virus of amoeba Marseillevirus has been identified at many different sites on the human body, including in the bloodstream of asymptomatic subjects, in the lymph nodes of a child with adenitis, in one adult with Hodgkin's disease, and in the pharynx of an adult. A high seroprevalence of the Marseillevirus has been recorded in the general population. Whether Marseillevirus can disseminate and persist within a mammal after entry remains unproven. We aimed to assess the ability of the virus to disseminate and persist into healthy organisms, especially in the lymphoid organs. Parenteral inoculations were performed by intraperitoneal injection (in rats and mice) or intravenous injection (in rats). Airway inoculation was performed by aerosolization (in mice). Dissemination and persistence were assessed by using PCR and amebal co-culture. Serologies were performed by immunofluorescent assay. Pathological examination was conducted after standard and immunohistochemistry staining. After intraperitoneal inoculation in mice and rats, Marseillevirus was detected in the bloodstream during the first 24 h. Persistence was noted until the end of the experiment, i.e., at 14 days in rats. After intravenous inoculation in rats, the virus was first detected in the blood until 48 h and then in deep organs with infectious virus detected until 14 and 21 days in the liver and the spleen, respectively. Its DNA was detected for up to 30 days in the liver and the spleen. After aerosolization in mice, infectious Marseillevirus was present in the lungs and nasal associated lymphoid tissue until 30 days post inoculation but less frequently and at a lower viral load in the lung than in the nasal associated lymphoid tissue. No other site of dissemination was found after aerosol exposure. Despite no evidence of disease being observed, the 30-day long persistence of Marseillevirus in rats and mice, regardless of the route of inoculation, supports the hypothesis of an infective potential of the virus in certain conditions. Its constant and long-term detection in nasal associated lymphoid tissue in mice after an aerosol exposure suggests the involvement of naso-pharyngeal associated lymphoid tissues in protecting the host against environmental Marseillevirus.
Highlights
Giant viruses of amoebas were discovered in 2003, with the isolation of Acanthamoeba polyphaga Mimivirus by coculturing on amoeba
We subsequently reported the presence of Marseillevirus in the blood and lymph nodes of a patient with Hodgkin’s disease (Aherfi et al, 2016a)
The study of viruses in non host organisms and their interaction remain an unexplored area of virology. These findings suggest that the particles or DNA markers of Marseillevirus may persist during a long period in humans in some cases
Summary
Giant viruses of amoebas were discovered in 2003, with the isolation of Acanthamoeba polyphaga Mimivirus by coculturing on amoeba. Marseilleviridae is a new family of amoebal giant viruses defined in 2012 (Colson et al, 2013b). Contact between giant viruses and humans were suggested. Concordant data argue for the pathogenicity of these viruses, such as mimiviruses-associated pneumonia (La Scola et al, 2005; Raoult et al, 2006; Bousbia et al, 2013; Saadi et al, 2013a,b) or the recently described association between phycodnaviruses and cognitive impairment (Yolken et al, 2014). The presence of giant viruses of amoeba, including those of marseilleviruses within human biological material, was more recently revealed by high throughput metagenomics, confirming contacts between these viruses and humans (Colson et al, 2013a; Rampelli et al, 2016; Verneau et al, 2016)
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