Bunyaviridae family comprises viruses that infect humans, animals and even plants. The main viral genera that make up the Bunyaviridae family are: Orthobunyavirus, Phlebovirus, Nairovirus, Tospovirus and Hantavirus genera. While Orthobunyavirus, Phlebovirus, Nairovirus and Hantavirus all infect animals, the genera Tospovirusonly infect plants. Majority of viruses in the Bunyaviridae family are arthropod-borne viruses because they are transmitted by arthropods especially blood-sucking insects such as mosquitoes, sand flies and ticks. Bunyaviruses (including Orthobunyavirus, Phlebovirus, Nairovirus, Tospovirus and Hantavirus) are found in arthropods and transmitted by arthropods as well as through rodents like mice. Viruses that are transmitted through arthropods or insects to humans are generally known as arboviruses (Table 1).
Viruses in this family have a helical nucleocapsid and they are enveloped viruses. They replicate in the cytoplasm and they are released from their host cell through cytoplasmic membrane by a budding process. The viruses in Bunyaviridae family measure between 80 to 120 nm in diameter. Bunyaviruses have a ss(-)RNA genome. The viruses in the Bunyaviridae family that cause infection in humans are found in the genera Orthobunyavirus (for example, La Crosse virus), Nairovirus (for example, Crimean-Congo haemorrhagic fever virus) and Phlebovirus (for example, Rift Valley fever virus, Sand fly Fever Sicilian virus). Generally, the viruses in the Bunyaviridae family that infect humans cause haemorrhagic fever; and they can also be referred to as “haemorrhagic fever viruses” as is applicable to Ebola and Lassa fever viruses. The infections caused by Bunyaviruses are usually benign, and they are characterized by febrile infections that include haemorrhagic fevers. In severe cases of the disease, the central nervous system (CNS) may also be affected. Bunyaviruses can produce mild to severe diseases in humans and animals.
Table 1 Viral diseases transmitted to humans through insects or arthropods
|DISEASE (CAUSATIVE AGENT)||INSECT VECTOR||CLINICAL FEATURES||GEOGRAPHICAL DISTRIBUTION|
|Dengue fever (caused by Dengue virus)||Aedes aegypti mosquitoes||Joint pains, fever, rashes on the chest and lower limbs, muscle pains and headache||Asia, South and Central America, Australia and the Caribbean|
|Chikungunya fever (caused by Chikungunya virus)||Aedes aegypti mosquitoes||Malaise, chronic fatigue, joint pains, maculopapular rash, debilitating fever and myalgia||Africa, Europe and Asia|
|West Nile fever (caused by West Nile virus)||Culex pipiens mosquitoes||Maculopapular rash, stiffness of the neck, fever, meningitis, encephalitis and myalgia||North America, Middle East. Asia, Africa and Europe|
|Yellow fever (caused by Yellow fever virus)||Aedes aegypti mosquitoes||Jaundice, vomiting, nausea, muscle pain, fever and liver dysfunctions||Worldwide, but mostly common in regions without active vaccination against the disease|
|Rift Valley fever (caused by Rift Valley fever virus)||Bite of infective blood-sucking mosquitoes||Febrile illness||Africa, Asia, Europe and India|
|Eastern equine encephalitis (caused by Alphavirus species)||Blood-sucking mosquitoes||Photophobia, vomiting, fever and myalgia||USA and the Caribbean|
|Western equine encephalitis (caused by Alphavirus species)||Blood-sucking mosquitoes of different species||Chills, sudden headache, fever, malaise, myalgia, and drowsiness||South America and USA|
Orthobunyaviruses causes benign forms of encephalitis; Nairoviruses causes haemorrhagic fevers; Phleboviruses causes sandfly fever or phlebotomous fever; and Hantaviruses causes Hantavirus pulmonary syndrome (HPS) in humans. All the genera of Bunyaviridae family that cause infections in humans with the exception of Hantavirus genera are transmitted to humans through arthropods. Hantaviruses are transmitted to humans through rodents such as mice and rats. Human infection with Hantaviruses (which is notorious in causing haemorrhagic fevers in humans) is usually through the inhalation of aerosols from the excreta or body secretions (for example, urine, saliva and faeces) of the animals or rodents that harbour the virus. Such transmission of viruses from rodents to humans is generally known as an aerogenical transmission. It is noteworthy that “Arbovirus” is not a viral family. Instead, the phrase ‘arbovirus’ is generally used to describe arthropod-borne viruses; and they include a wide array of viruses transmitted to humans through blood-sucking insects (Table 1).
Arbovirus is more an ‘ecological grouping of viruses’ based on their mode of transmission and it is not a viral family of its own. Most arbovirus infections (i.e., viral infections transmitted to humans through blood-sucking insects and mosquitoes) are endemic and common in the tropics especially in sub-Saharan Africa and other tropical part of the world. But the diseases caused by these pathogenic viruses also occur in the sub-tropics; and they can be conveyed from the tropics to places where they do not exist before, through travelers and globalization. Rodentssuch as rats and mice are the natural reservoirs of Hantavirus, and they remain apathogenic in these animals (i.e., they do not cause infections in them). However, they cause serious infections in humans when they are aerogenically transmitted to humans. Prevention of infections caused by Bunyaviruses is through avoidance of contact with rodents, rodent droppings and insect bites.
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