Giant Viruses of Amoebae as Potential Human Pathogens

Abstract

Giant viruses infecting phagocytic protists are composed of mimiviruses, the record holders of particle and genome size amongst viruses, and marseilleviruses. Since the discovery in 2003 at our laboratory of the first of these giant viruses, the Mimivirus, a growing body of data has revealed that they are common inhabitants of our biosphere. Moreover, from the outset, the story of Mimivirus has been linked to that of patients exhibiting pneumonia and it was shown that patients developed antibodies to this amoebal pathogen. Since then, there have been several proven cases of human infection or colonization with giant viruses of amoebae, which are known to host several bacteria that are human pathogens. Mimiviruses and marseilleviruses represent a major challenge in human pathology, as virological procedures implemented to date have not used appropriate media to allow their culture, and molecular techniques have used filtration steps that likely prevented their detection. Nevertheless, there is an increasing body of evidence that mimiviruses might cause pneumonia and that humans carry marseilleviruses, and re-analyses of metagenomic databases have provided evidence that these giant viruses can be common in human samples. The proportion of human infections related to these giant mimiviruses and marseilleviruses and the precise short- and long-term consequences of these infections have been scarcely investigated so far and should be the subject of future works.

Faustovirus, an Asfarvirus-Related New Lineage of Giant Viruses Infecting Amoebae

“…This proposition was validated experimentally by the isolation of mimivirus from atypical pneumonia patients and by the detection of marseilleviruses in blood donors and in human lymph nodes (7)(8)(9). Moreover, we and others identified sequences associated with giant viruses in metagenomes generated from human tissues, suggesting that giant viruses are a component of the human virome (10). Because the investigation of a virome typically starts with a filtration procedure that eliminates giant viruses (11), we developed a new culture approach that does not prevent the detection of these viruses.…”

“…In addition to the commonly studied species A. polyphaga, we also assessed five other protists that were never previously used to isolate giant viruses, including Vermamoeba vermiformis, the antibiotic mix at a concentration of approximately 10 6 amoebae/ml. Samples (100 l) were inoculated onto amoebae (500 l in a 24-well plate) and incubated at 32°C in a humid environment.…”

Detection and quantification of human adenovirus genomes in Acanthamoeba isolated from swimming pools

“…Lorenzo-Morales et al (2007) considered Acanthamoeba a potential reservoir of HAdVs in the aquatic environment, and Battistini et al (2013) demonstrated the resistance of HAdV for 105 days internalized in amoebae. These protozoa may also serve as a replication niche or training fi elds for resistance to the microbicidal effects of phagocytic cells, including human macrophages, which represent the first line of defense against invading pathogens (Thomas and Greub 2010, Colson et al 2013, Scheid 2014. Phagocytosis and macropinocytosis are the main internalization processes in amoebae, being similar to the mechanisms involved in mammalian cells (Ghigo 2010), and free-living amoebae can be simultaneously infected with viruses and other microorganisms, such as bacteria (Yutin and Koonin 2009).…”

“…This association should also be considered in cases of pneumonia given the growing body of evidence showing that mimiviruses might cause pneumonia in humans and because respiratory HAdV can reach the respiratory system using the same vectors as those reported by giant viruses (Colson et al 2013), being able to stand up to the micro bicidal effects of human macrophages as they have the ability to resist phagocytic cells (Thomas and Greub 2010). The present fi ndings reinforce the idea that Acanthamoeba may act as a reservoir and promote HAdV transmission through contaminated water.…”

A Need to Discover the World of Giant Viruses

“…New strategies for culture, purification [17] and isolation techniques [16] are reported in the present issue. Also, for the first time, these techniques have enabled the isolation of Mimivirus from a respiratory sample [18,19] and the stools of a patient with pneumonia [20]. However, it is likely that serology is more effective in the detection of specific antibodies against the Marseilleviridae family, as related in Gilbert Greub's work in this journal [21].…”