What is an Alphavirus and how do they cause disease?

Instances of alphavirus infection occur each year, yet the specific mechanisms by which these viruses cause disease are still not well understood.

The genus Alphavirus contains a large number of arthritogenic alphaviruses, meaning they are known to cause arthritis in humans and other animals, including O’nyong-nyong virus, Ross River virus, Sindbis virus, Semliki Forest virus, Chikungunya virus, Rubella virus and Venezuelan equine encephalitis virus. This article will help you understand what an alphavirus is and how it causes disease.

Arthritogenic alphaviruses

The family Togaviridae contains several important viruses that can infect humans, including bunyaviruses, flaviviruses, toroviruses and alphaviruses. Of these, arthritogenic alphaviruses have been most studied with regard to their possible roles in viral arthritis or acute arthralgia.

Arthritogenic alphaviruses include Semliki Forest virus (SFV), Ross River virus (RRV) and Venezuelan equine encephalitis virus (VEEV). These viruses replicate within endothelial cells of venules, leading to vascular damage, hemorrhage and edema formation.

Alphavirus causes

All four human alphaviruses are important causes of human disease. The three serious clinical manifestations of alphavirus infection are acute or severe febrile illness, hemorrhagic fever, and encephalitis. Primary alphaviruses (e.g., Venezuelan equine encephalitis virus) typically produce clinical symptoms after 10–15 days of exposure to infected mosquitoes.

Arboviral infections can be very serious in immunocompromised individuals who do not recover completely from the initial infection. Once a human has been infected with one serotype of a primary arbovirus, cross-reactivity among different serotypes often results in additional viremia; however, reinfection by another serotype rarely leads to more severe or prolonged illness.

Alphavirus treatment

There are currently no approved vaccines or specific drugs available for the treatment of human alphavirus infections. Currently, supportive care treats symptoms caused by alphaviruses. For example, it is recommended that patients avoid dehydration through proper hydration and the consumption of fluids.

Acetaminophen (Tylenol) may be used to manage fever and pain, though NSAIDs should be avoided due to their possible risk for increased bleeding. Ribavirin, which has been shown effective against related viruses in cell culture, has shown some potential as a therapeutic treatment for a number of alphaviruses including the Sindbis virus and Ross River virus. However, its efficacy in clinical trials on humans has not yet been proven.

Transmission of arthritogenic alphaviruses

You are probably asking, How does alphavirus get from one person to another? This can happen in two ways: direct contact or vector transmission. Direct contact transmission means that you get infected by direct contact with bodily fluids (like blood) of a person already infected with alphaviruses.

Vector transmission means that mosquitoes come into play. Mosquitoes are very good at carrying viruses between people and animals, not only alphaviruses but many other types of pathogenic agents as well.

Prevention methods against arthritogenic alphaviruses

These include insecticide spraying for mosquitos, which are a common vector of transmission; vaccination of at-risk populations with live attenuated vaccines that protect against Venezuelan equine encephalitis; and personal protective measures such as regular mosquito repellents.

Because there is no specific treatment for arthritogenic alphaviruses, medical attention should be sought as soon as possible for symptomatic patients to ensure early management.

Antibiotics are not effective against viral infections. Treatment may include pain relievers (analgesics) such as acetaminophen or aspirin in order to relieve joint aches or fever, bed rest, getting out of hot environments (as heat makes symptoms worse), and taking warm baths to relieve swelling or muscle spasms.


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