New viruses were discovered in Brazil in blood samples taken between 2013 and 2016 during the Dengue, Zika and Chikungunya epidemics.
Symptoms such as fever, fatigue, muscle pain and skin rashes often indicate infection. In epidemics, these clinical signs may lead to tests that directly detect the presence of an infectious micro-organism in a sample or use antibodies specifically produced by the immune system against the microbe to infer the identity of the pathogen causing the infection. If these tests are positive, the diagnosis is then relatively clear. On the contrary, if the results are negative, the etiology of the infection, if it is an actual infection, seems to be more uncertain. Sometimes new tests are performed. But often the diagnosis is not made: If symptomatic treatment (of the clinical symptoms themselves) is proposed to accompany recovery, the identity of the pathogenic micro-organism causing the clinical symptoms remains unknown.
For example, between 2013 and 2016, a period marked by several epidemics of dengue, Zika and Chikungunya in the north of Brazil, in hundreds of blood samples taken from patients with symptoms indicative of these three infectious diseases (high fever, headache, rashes, etc.), none of the pathogens responsible for any of these three diseases was detected in the blood of any of the patients. In 2020, a team of researchers re-examined these samples, not using tests routinely used by healthcare institutions, but using techniques used in research laboratories. These metagenomic methods, which allow the sequencing of all DNA molecules present in a sample, led these scientists to discover two new types of viruses.
Metagenomics allows the analysis of the DNA sequences of microorganisms (especially bacteria and viruses) present in a sample. They are often used to study complex environments, such as intestinal microbiota, where several types of microbes live together.
Discovery of two viruses of the Parvoviridae family in humans
In a study published online by Plos One, researchers showed that of the 781 samples that tested negative for dengue antibodies, particularly Zika and Chikungunya, two samples each contain a viral genome that has never been described before.
In fact, the first sample contained an unknown viral species that the researchers believe belongs to the genus chapparvovirus. Since it is known that this virus genus infects many mammals, this discovery seems to have been a small surprise for Brazilian virologists: Although chapparvoviruses have been described in birds (turkeys, cranes, chickens, peacocks) and fish (tilapia, Black-striped pipefish), several microorganisms of this genus were discovered in 2000, infecting rats, mice, dogs, but also pigs, bats and, above all, several monkeys. Since the species barrier between some of these mammals and humans is apparently not very difficult for viruses to overcome, the detection of a Chapparvovirus in humans, therefore, seems logical. However, are the infection symptoms of the patient to whom the sample belongs attributable to this new virus? In other words: is this unknown Chapparvovirus pathogenic? Once the ability of a chapparvovirus to cause clinical symptoms of disease in rats has been demonstrated in the laboratory, further studies will need to be carried out to clarify the consequences of infection with this virus in humans.
The second sample contained a virus belonging to the genus Ambidensovirus. “The detection of a genome [of the ambidensovirus] in human plasma was more surprising,” the researchers admit in their study. In fact, this type of virus is known to infect invertebrates such as insects, crustaceans, echinoderms such as starfish or sea urchins, or animals far from humans: The species barrier that separates these creatures from humans seems to be more difficult for viruses to overcome. If, according to the researchers, no contamination of the initial sample could have occurred during sample handling in the laboratory, the presence of this new ambidensovirus in a patient’s blood could be explained by an infection of the latter by invertebrate parasites, which in turn carry the unknown virus. Further studies should be carried out to validate this hypothesis and investigate the possible pathogenicity of this ambidensovirus.
Detection of other viruses
In the remaining 781 samples examined, virologists had found viruses that had been previously characterized and were known to infect humans. According to the researchers, 80% and 19% of the samples contained anelloviruses and pegiviruse 1. “These two viruses are widespread throughout the world and are generally considered to be commensal infections, inducing no significant pathology,” reassure the researchers in their study.
However, the HIV genome was detected in a sample. And analyses by virologists also revealed the presence of B19 parvovirus DNA in 17% of the available samples. “B19 viremia may, therefore, account for a significant proportion of unexplained fever in Brazilian adults,” the researchers said in their study. Indeed, the B19 parvovirus, which is more common in children than adults, is known to cause flu-like symptoms and possible rashes. In pregnant women, this infectious agent can also cause potentially serious damage to the fetus.
Continuation and completion of the tests
Although the work of these virologists is aimed at describing the viral diversity found in Brazil, their initial findings highlight important public health issues. Since two new species have indeed been described, additional studies should be carried out to evaluate not only the pathogenicity of these viruses, but also their transmission route: is the contamination of these new infectious agents in humans likely to trigger an epidemic?
Moreover, did the Dengue, Chikungunya and Zika epidemics in Brazil between 2013 and 2016 mask the spread of other known infectious agents? This was suggested, for example, by the virologist Paolo Zanotto in 2018 in a study published in the journal Clinical Infectious Diseases: In his opinion, the significant spread of the Zika virus in 2018 could have masked an epidemic of parvovirus B19. If researchers come to similar conclusions between 2013 and 2016, it could be important to more systematically question the masking of one infectious event by another. For example, could the focus on the COVID 19 pandemic in 2020 mask not only the emergence of other viruses, but also the recurrence or spread of other long identified infectious agents?