The arboviruses are a heterogeneous group of arthropod - borne viruses to humans or other animals. Its name derives from this particularity and is a contraction of the first two syllables of English «Arthropod-Borne Viruses«. The group is made up of nine virus families that encompass more than 534 types of viruses.
They comprise a complicated life cycle, involving the primary vertebrate host and the secondary invertebrate vector. Arboviruses were discovered during the 1930s. In the 1950s and 1960s, thanks to the efforts of researchers and the advancement of virus isolation technologies, knowledge related to arboviruses increased exponentially.
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It is estimated that 150 arboviruses are responsible for causing disease in man, from infections without some symptoms to fatal diseases. Prominent examples are dengue and chikungunya, widely distributed and frequent conditions in Latin American countries.
Worldwide, these infectious agents cause a high mortality rate in humans and other domestic animals, such as rodents or birds.
The current increase in arboviruses is attributed to several causes, mainly environmental changes, urbanization, changes in water use policies, agricultural practices with a high environmental impact, deforestation, among others.
characteristics
The only characteristic that unites these viruses in a single group is their complex life cycle and the ability to be transmitted by some arthropod. Collectively, they are not a natural group that reflects evolutionary relationships and common ancestry.
These viruses are transmitted in nature in zoonotic cycles, which are not directly related to humans. Human infection only occurs by chance. In few cases, humans coincide with the main reservoir of the virus, as in the case of dengue and yellow fever.
These viruses are frequently found in regions with tropical and subtropical climates, since the vectors are usually abundant in these ecosystems. They are classified as zoonotic viruses since they are transmissible from animals to humans.
Historically, the definition of arbovirus was based on transmission of the virus from a blood-sucking arthropod vector, such as a mosquito. However, recent discoveries (thanks to the use of molecular biology) allowed the definition of arbovirus to be extended to other arthropod taxa.
There are certain species of arthropods where a series of arboviruses have been identified, where no type of disease has been recognized in humans or other animals.
Classification
The term "arbovirus" includes a wide range of viruses, among about 500, which are very heterogeneous. This term is not a valid taxonomic indicator. The entity in charge of establishing the classifications is the international committee for the taxonomy of viruses, abbreviated ICTV for its acronym in English.
Its taxonomy is based on the same principles used for different groups of viruses. The taxonomic scheme is not usually used based on an evolutionary principle, in contrast, diseases and pathologies that they cause in their hosts are used as a grouping characteristic.
Other characteristics are also usually taken into account, such as relationships between antigens and the morphology visualized with the electron microscope.
Arbovirus families
They are usually classified into three main families: Bunyaviridae, Flaviviridae, and Togaviridae.
The first family, Bunyaviridae, includes La Crosse encephalitis, Hantaviruses, and Orepuche fever. The Flaviviridae family includes the viruses that cause dengue, yellow fever and Zika virus, whose frequency of appearance has been remarkable in recent years. The third family, Togaviridae, is made up of the Chikungunya and Mayaro viruses.
The remaining families are Reoviridae, Rhabdoviridae, Orthorryxoviridae, Arenaviridae, and Poxviridae. Some members of the group have not been classified in any family.
However, arboviruses are also classified in terms of the diseases they cause in their host, such as encephalitis, fever and myalgia, arthritis, and rash and hemorrhagic fever.
Transmission
Arboviruses are transmitted by a great diversity of arthropods, call it mosquitoes, ticks, fleas, among others. It appears that each virus is associated with a specific species of invertebrate.
Mosquitoes appear to be the favorite vectors for arboviruses. Approximately 300 species of mosquitoes are capable of transmitting this huge viral group.
In Latin American regions, arbovirus transmissions are predominant through a mosquito of the genus Aedes, mainly responsible for the spread of dengue and chikungunya. Aedes has been found to be the vector for about 115 types of arboviruses.
Similarly, the genus Culex is an important vector associated with more than 100 types of arboviruses.
These viruses can remain alive for several months (or even years) in mosquito eggs, until the rainy season arrives and encourages the hatching of an infected arthropod.
This extensive diversity of arthropod species that they infect, which in turn implies a wide worldwide distribution, explains why arboviruses have been so successful.
Symptoms of contagion
Arboviruses include a wide spectrum of symptoms, ranging from harmless infections without noticeable symptoms to serious pathologies that can cause the death of the host.
In general, they can be classified into three large groups based on the clinical symptoms they produce in humans: those that cause fever, hemorrhagic fever and invasive neurological diseases.
It is striking that, although the viral agents are very diverse among themselves, the diseases share these three common characteristics.
Most arbovirus infections are characterized by a nonspecific febrile process in the acute phase of the disease, followed by full recovery of the patient.
On the other hand, in patients who develop severe conditions, the disease caused by the virus can be divided into two phases, with an acute febrile process followed by the appearance of arthritis, hemorrhagic fevers or diseases related to the nervous system.
In these cases, the pathologies usually leave sequelae related to permanent neurological damage and arthritis.
It is worth mentioning that the symptoms listed above can vary widely if the same virus occurs in different human individuals.
On the other hand, the arthropod is not affected. The vector, while possessing the virus, shows no detectable signs of disease.
References
- Arredondo-García, JL, Méndez-Herrera, A., & Medina-Cortina, H. (2016). Arbovirus in Latin America. Acta pediátrica de México, 37 (2), 111-131.
- Coffey, LL, Vasilakis, N., Brault, AC, Powers, AM, Tripet, F., & Weaver, SC (2008). Arbovirus evolution in vivo is constrained by host alternation. Proceedings of the National Academy of Sciences.
- Estébanez, P. (2005). Humanitarian medicine. Díaz de Santos editions.
- Lambrechts, L., & Scott, TW (2009). Mode of transmission and the evolution of arbovirus virulence in mosquito vectors. Proceedings of the Royal Society of London B: Biological Sciences, rspb-2008.
- Vasilakis, N & Gluber, D. (2016). Arboviruses: molecular biology, evolution and control. Caister Academic Press.