The PetriDish: Chikungunya a new viral threat from mosquitoes
August 23, 2014
I was sitting in my living room the other night when I happened to notice a mosquito on my arm. A quick swat left a mangled body and a rather large spot of blood; I gather the thing had been feeding for a while. This encounter prompts me to write about a newly emerging disease that is transmitted by mosquitoes — Chikungunya virus. You may not have heard of Chikungunya virus before, but chances are that it will be all over the news before long. The virus is spread through mosquito bites and causes an illness that is characterized by flu-like symptoms and can sometimes be followed by severe joint and muscle pain. In fact, the term "chikunguny" is a term used by an ethnic group in southeast Tanzania and northern Mozambique to describe the contorted posture of patients suffering from joint pains. While the infection is usually not fatal and cleared in a few days, the joint pain can sometimes persist for months or even years. There is no cure for the disease, so treatment is focused on relieving the symptoms.
Prior to 2006, Chikungunya was generally limited to Africa and parts of Asia. But in 2006, there was a severe outbreak on the French Island of La Reunion in the Indian Ocean that killed more than 250 people. Since then, the virus has spread to the western hemisphere with the first confirmed cases in the Caribbean in December 2013 (St. Martin). The virus then spread to other Caribbean islands and has subsequently reached Brazil, El Salvador, Mexico and the United States. Over the last couple of months, cases have been confirmed in Florida, North Carolina, Georgia and Arkansas. It looks like the virus is spreading all across the western hemisphere and is with us to stay. The virus has also been found as far afield as the Philippines, Taiwan and Australia.
The sudden spread of the virus has been of considerable interest to epidemiologists. The disease is not directly transmitted between people like the flu, but is dependent on the mosquito as a vector. Infected mosquitoes transmit the Chikungunya virus when they take a blood meal (i.e., bite), injecting the virus directly into the blood stream. Early studies had indicated that the virus was transmitted by Aedes aegypti mosquitoes that have limited geographical range. However, analysis of the virus that caused the La Reunion outbreak revealed that it had acquired the ability to be transmitted by the more widely distributed Aedes albopictus, otherwise known as the Asian tiger mosquito. This change was due to a single point mutation in one of the viral genes that increased virus infectivity and also enhanced the virus's ability to survive in the Tiger mosquito. Importantly, this increased the range of the virus by introducing it into areas where the Asian tiger mosquito is present. This change in mosquito preference explains a recent Chikungunya epidemic in Italy and is exacerbating the spread of the disease across the western hemisphere.
The rapid advance of Chikungunya illustrates how quickly new diseases can spread globally and become endemic in new regions. It also highlights the dangers of emerging diseases, since there may be no treatments or vaccines available to combat them. In the case of Chikungunya, there is no approved vaccine, and while several vaccines are under development, it will likely be some years before anything is generally available. Fortunately, Chikungunya can be readily contained by mosquito control (spraying) and the personal use of insect repellants, so it is possible to reduce transmission in highly populated areas.
It may interest you to know that there are several thousand different kinds of mosquitoes. But you will be relieved that relatively few of them are able to survive the dry climate and short summers here in Summit County. So I am not worried that my chance encounter with a mosquito will result in Chikungunya. My joint pains are more likely due to old age.
David L. "Woody" Woodland, Ph.D. is the chief scientific officer of Silverthorne-based Keystone Symposia on Molecular and Cellular Biology, a nonprofit dedicated to accelerating life science discovery by convening internationally renowned research conferences in Summit County and worldwide. Woody can be reached at 970-262-1230 ext. 131 or firstname.lastname@example.org.
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