Thousands of unique arboviruses and flaviviruses identified from samples collected between 1954-2018

By Dr. Priyom Bose, Ph.D.Apr 12 2023Reviewed by Benedette Cuffari, M.Sc.

The Evandro Chagas Institute (IEC) has isolated (entirely or partially) and classified virological and serological data for over 80 years. Around 200 types of arboviruses (human pathogens) have been isolated and classified by the IEC, some of which have not been taxonomically classified.

The similarities in symptoms and antigenic resemblance caused by arboviruses pose difficulty in their diagnosis in laboratory settings. In addition, disorderly urbanization and garbage accumulation favor the increase in arbovirus vectors, which leads to the emergence and re-emergence of diseases, particularly by Flaviviruses and Alphaviruses.

A recent article published in the journal Viruses presents the encephalitogenic viruses registered at the Department of Arbovirology and Hemorrhagic Fevers (SAARB) of the IEC over the past six decades.

Study: Isolation of Flaviviruses and Alphaviruses with Encephalitogenic Potential Diagnosed by Evandro Chagas Institute (Pará, Brazil) in the Period of 1954–2022: Six Decades of Discoveries. Image Credit: angellodeco / Shutterstock.com

Background

A broad spectrum of infections has been associated with arbovirus infections, such as mild febrile illness, hemorrhagic fevers, and neurologic symptoms.

Arboviruses are viruses maintained in nature through biological transmission between susceptible vertebrate hosts and hematophagous arthropods, or between arthropod hosts by the transovarian and/or venereal route. They are able to reproduce in vertebrate hosts, multiply in arthropod tissues, and be passed on to new susceptible vertebrates by arthropod bites after an extrinsic incubation period”.

At present, seven viral families of arboviruses, including Asfaviridae, Rhabdoviridae, Flaviviridae, Phenuiviridae, Sedoreoviridae, Togaviridae, and Peribunyaviridae have been shown to be capable of infecting humans and animals. Among these, the West Nile virus (WNV), Chikungunya virus (CHIKV), Dengue virus (DENV), Rocio virus (ROCV), and Zika virus (ZIKV) are neuroinvasive viruses with high epidemiological interest in Brazil.

The genus Alphavirus of the Togaviridae family includes 32 viruses, including CHIKV, Eastern equine encephalitis virus (EEEV), and the Western equine encephalitis virus (WEEV), all of which are extremely important to public health.

Alphaviruses are positive-sense, single-stranded RNA viruses that contain an icosahedral capsid envelope. These viruses are transmitted through mosquitoes, ticks, bed bugs, and lice. These viruses are also transmitted through vertebrate hosts, such as non-human primates, humans, birds, rodents, and pigs.

The genus Flavivirus belongs to the family Flaviviridae and is composed of 53 viruses, including the Japanese encephalitis virus (JEV), WNV, ZIKV, and DENV. These viruses also contain a positive-sense RNA genome with an icosahedral symmetrical structure. Flaviviruses are transmitted through cycles between vectors and vertebrate hosts.

About the study

The Laboratory of Viral Isolation/SAARB/IEC has its own Vero and C6/36 cell lines that have been consistently studied between 1954 and 2009. Between 1999 and 2018, these cells were used to isolate Flaviviruses and Alphaviruses from human samples.

A large number of Flavivirus isolates were obtained from the Northern region of the country, whereas Alphavirus isolates were obtained from states in the Northeastern region.

In addition to isolating viruses from cell cultures, viruses with encephalitogenic potential were isolated from infected mice and mosquitoes. Taken together, 1,347 arbovirus samples with encephalitogenic potential were isolated from mice, 639 of which were Flaviviruses and 708 were Alphaviruses were isolated.

These viral samples were geographically distributed in the State of Pará and other states of the Brazilian federation, such as Aripuanã (Mato Grosso State), Serra do Navio-ICOMI (Amapá State), Boca do Acre (Acre State), Macapá (State of Amapá), Tocantins State, Macapá (State of Amapá). In the northern region of Brazil, particularly in the state of Pará, Flaviviruses were isolated from armadillos and sloths, while Alphaviruses were found in ticks and horses.

A total of seven Alphaviruses and four Flaviviruses were partially identified. Around 293 isolated viruses belonged to the family Picornaviridae, Arenaviridae, Flaviviridae, Togaviridae, Sedoreoviridae, Rhabdoviridae, and Peribuniviridae. Some viruses, such as Cajazeira virus, Cantá virus, Uruará virus, Iriri virus, Marajó virus, Galibi virus, Codajás virus, Tracambé virus, and Naranjal virus, were partially identified and have unknown pathogenesis.

The method by which Flaviviruses and Alphaviruses were isolated from mice by using mosquitoes as an animal model of origin was practiced by IEC from 1966 to 2012. This isolating method was reinstated in 2018, exclusively using C6/36 cell culture. 

Conclusions

The current study highlighted the urgent need to combat forest degradation, which influences the spread of diseases transmitted by arthropods. The adaptation of arthropods in domestic settings increases the risk of emerging or re-emerging zoonoses.

The general population must be encouraged to modify behaviors that could prevent disease manifestation. At present, no vaccines are available for the majority of arboviruses; therefore, strong preventive measures must be developed to prevent arbovirus infection.