Chikungunya Virus
Etiology/Virology
Baltimore Classification
Group IV: (+) ssRNA Virus
ICTV Classification
Family |=Togaviridae Genus |=Alphavirus Species |=Chikungunya Virus
Description
By classification using the Baltimore Classification, Chikungunya Virus (CHIKV) is a positive-sense single-stranded RNA virus. CHIKV can also be further classified as an Arbovirus or Arthropod Bourne Virus because of its transmission via mosquitoes. The alphavirus genus is known to be small, spherical viruses with envelopes and are 60-70 nanometers in diameter[3]. The genome of CHIKV encodes for four nonstructural proteins and three structural proteins. {NCBI} Also, alphaviruses viruses further classified into seven complexes varying by different antigenic properties;Barmah Forest (BF), Eastern equine encephalitis (EEE), Middelburg (MID), Ndumu (NDU), Semliki Forest (SF), Venezuelan equine encephalitis (VEE), and Western equine encephalitis (WEE)[4]. CHIKV is part of the Semliki Forest complex. In addition, it is known as an Old World Virus because of its pathogenicity and ways it interacts with the host. Chikungunya Virus can cause the disease Chikungunya Fever, which is very similar to Dengue Fever, Zika Virus, and other tropical arboviruses. When bitten by an infected mosquito, a patient will present symptoms within 3 to 7 days. The most prevalent and problematic symptoms consist of high-grade fever, severe arthralgia (joint pain), and a rash on the torso. Chikungunyna Fever is usually not fatal; no antiviral regimens or vaccines exist.
Pathogenesis
Transmission
There are two distinct transmission cycles that have been found for CHIKV. The endemic cycle is transmitted by the A. aegypti species of mosquitoes which is found in tropical areas.[5] However, A. albopictus species has been found to be a carrier also, which are located in temperate regions and contributing to CHIKV becoming a global dilemma.[6] Chikungunya Fever is contracted via a human-mosquito-human pathway where the mosquito obtains the virus from biting an infected human and transmits the virus by biting a non-infected human. Human to human transmission is currently not proven to be possible. Upon infection, the virus enters the subcutaneous capillaries, and can also enter macrophages, endothelial cells, and fibroblasts. [6] The virus quickly evades the immune system and enters the blood and lymph circulation. CHIKV then has access to multiple areas of the body and is able to produce systemic complications and symptoms.
Epidemiology
Chikungunya is endemic to Southern and Southeast Asia. The first Asian epidemic was in 1958 in Bangkok, Thailand with rises and falls until 1974. The most catastrophic outbreak occurred in 2006 on Reunion Island, and island in the Indian Ocean. This outbreak resulted in 237 deaths. Around the same time 1.4 million people were suffering from the disease on the Indian Subcontinent. Unfortunately through local transmission, this disease is not considered a tropical disease only. Cases have been seen in Europe and the United States. This is probably due to the fact that the A. albopictus species resides in temperate forests and can now carry the disease farther from the equator. In July 2014, a person in the United States caught the virus and had not traveled to a location where there had been outbreaks. This was the first reported case of local transmission in the U.S. and has been 11 more reported cases as of December 2014; all reported cases were in Florida. [7]
Diagnosis
Physical Examination
Physical examination is the primary method for diagnosing a patient with Chikungunya disease. Patients will present with high-grade fevers that can be as high as 105 ° F, shaking/chills, and headaches. Other common symptoms in severe cases include arthralgia and rash. Arthralgia is usually the most problematic symptom of Chikungunya disease. Small joints in the hands, wrists, and ankles are most commonly affected, with not much involvement of the larger joints. Arthralgia ceases within 1-2 weeks of pain onset in most patients, but 10-12% may have persistent arthralgia that lasts from months to years.[7] Manifestations of disease are also seen on the skin in the form of a erythematous maculopapular rash on the torso.[7]This rash appears red with flat, small bumps present also. In some patients, a tourniquet test may be performed to gauge the level of capillary fragility and hemorrhagic tendency; but it has proven to not be a reliable diagnostic tool.
Diagnostic Criteria
Patients who are suspected to have the virus present the symptoms mentioned previously during physical examination. However, because Chikungunya disease has many of the same symptoms as dengue fever, malaria, and more, the ability to omit infection by all other diseases aid in the diagnosis of CHIKV. A more straightforward diagnosis can be made if the patient has traveled to an area where recent outbreaks of CHIKV have occurred.
Treatment and Prevention
Treatment
Chikungunya virus is usually not fatal. Currently, there are no antiviral treatments for the disease either; this is probably because the immune system can eliminate the virus on its own. Treatments are usually centered around symptom management and include hydration, management of electrolyte balance, hemodynamic monitoring, rest, and pain management with medication. However, use of nonsteroidal anti-inflammatory drugs (NSAIDS) are not advised because of a possible missed dengue fever diagnosis, which could lead to increased hemorrhaging and death. Papaya leaf juice has also been used to combat inflammation and boost the immune system.
Prevention
There are no vaccines available for CHIKV currently. The only method of prevention is vector control on a personal and community level. People traveling to areas where there have been reported cases and/or traveling to areas that the A. Aegypti or A. albopictus species are located should be cautious. It is recommended that these people wear long-sleeved shirts and long pants, apply mosquito repellent, and have screens on windows. In the community, it is beneficial to remove mosquito breeding sites and have large scale spraying of mosquito repellent. The virus can only be spread when a mosquito bites an infected human and then transfers the virus to another human. Because of this, avoiding mosquito bites is the best prevention.
Damage Response Framework
The damage response framework is a way to measure the level of damage done to the host. This framework begins with commensalism then progresses to no effect, colonization, latency, disease, and finally death. In addition, the host immune response is another contributing factor to the amount of damage that will be done. Other damage response frameworks show host damage as a function of time. It is not known for sure, but similar to common viral diseases, the weaker the host's immune response, the more damage that the host will incur.
References
1 [[3]]
2 [[4]]
3 [[5]]
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Created by Amber Hubbard, student of Dr. Tyrrell Conway at the University of Oklahoma
