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Arbovirus: Definition, Classification & Diseases

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

Many of the viruses you hear about in the news are arboviruses. In this lesson, we are going to take a close look at arboviruses by discussing what they are, which classifications they fit into, and the diseases that they can cause.

Arbovirus

Doesn't it seem like there is always a new virus to worry about? Each year, we hear reports of one virus or another that wreaks havoc on people, causing massive sickness and even death. At one point, it was West Nile Virus, and more recently, it has been the Zika virus. The interesting thing is, that most of these viruses are all inter-related. They belong to a group known as an arbovirus, and are transmitted to humans through the bite of an arthropod. Arthropods that transmit these viruses include bugs such as mosquitoes, ticks, fleas and gnats.

Ticks and other arthropods transmit arboviruses CREDIT: NIAID https://www.flickr.com/photos/niaid/33224393243
Picture of a tick

The term ''arbovirus'' itself, tells you exactly what it is. The 'ar' refers to arthropod, and 'bo' refers to borne, meaning it is an arthropod-borne virus.

Classification

There are similarities between the viruses, but there are also many differences. Arboviruses are classified based on these differences. The three main classifications of arboviruses are flavivirus, alphavirus, and bunyavirus. Let's look at each of these in detail:

Flavivirus is the genera of single-stranded, enveloped RNA viruses. Members of this particular genera are the ones that you are probably most familiar with, as they have been very active recently. These viruses are all transmitted by either ticks or mosquitoes. Some examples of tick-borne flaviviruses are Tick-borne encephalitis, Omsk hemorrhagic fever, and Kyasanur Forest disease. Examples of mosquito-borne flaviviruses include West Nile virus, Zika virus, and Yellow Fever.

Alphavirus is a genera of enveloped, single-stranded RNA viruses that belong to the Togavirus family that have a coated virion, which is the infective component of the virus. All of the viruses belonging to alphavirus are transmitted through mosquito bites. These include chikungunya, Ross River virus, and both western and eastern equine encephalitis.

Bunyavirus is a family of segmented, enveloped RNA viruses. It is one of the largest families of viruses and can be transmitted by arthropods or rodents. We are going to focus on the ones that are transmitted by arthropods. There are a wider range of arthropods that transmit bunyaviruses to include ticks, mosquitoes and various types of flies. Some examples of the bunyavirus include Jamestown Canyon virus and California encephalitis.

Diseases

Let look at some of the diseases that were just discussed. We'll start with the mosquito-borne West Nile virus. For as much concern as it caused, it is amazing to know that only about 20 percent of people that contract West Nile virus, actually show any symptoms.

The full transmission cycle for West Nile virus. Notice the role of mosquitoes in the cycle.
Diagram of the transmission cycle of West Nile virus

Most of that 20 percent will have mild symptoms such as a fever with body aches, vomiting, diarrhea, and painful joints. This mild case of the disease is also characterized by fatigue, headaches, and weakness. Rarely, the virus will make its way into the central nervous system and infect the brain and/or spinal cord causing encephalitis and/or meningitis. At this point, the condition becomes a matter of life and death.

Chikungunya is a rare, mosquito-borne viral infection that causes body aches and joint pain. You will usually start to notice symptoms of this infection within a week or less of being bitten. Other symptoms that may go along with this infection include headache, weakness, fatigue, and a rash. Africa, the Caribbean, Asia or Europe are the most common areas for this virus to occur. The good news about chikungunya is that it isn't life-threatening, and people usually recover from it fairly quickly, only requiring over-the-counter pain medication.

California encephalitis is a viral infection that tends to infect the central nervous system of children. It is also fairly rare, but still of concern, since there are at least 100 or more new cases each year. It got its name because it was first discovered in California. Now, the viral infection seems to be tied to another arbovirus infection called La Crosse virus. Most children that contract this infection do not show any symptoms or the symptoms are mild and go away on their own. About 1 in 10 children that contract it will have severe symptoms such as recurring seizures, coma, encephalitis, and/or paralysis.

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