Chikungunya fever is a viral disease transmitted to humans by the bite of infected mosquitoes. Chikungunya virus was first isolated from the blood of a feverish patient in Tanzania in 1953. It has since been cited as the cause of numerous human epidemics in many areas of Africa and Asia, and most recently in a limited area of Europe.
Chikungunya is Makonde for "that which bends up." This refers to the stooped posture that develops in some infected people.
Signs and Symptoms
Chikungunya virus infection can cause a debilitating illness, most often characterized by the following:
“Silent” chikungunya virus infections (infections without illness) do occur; but how common they are is not yet known. Chikungunya virus infection (whether clinically apparent or silent) is thought to confer life-long immunity. Acute chikungunya fever typically lasts a few days to a couple of weeks, but as with Dengue, West Nile fever, o'nyong-nyong fever and other arboviral fevers (diseases that are caused by blood-sucking insects), some people have prolonged fatigue lasting several weeks. Additionally, some people have reported incapacitating joint pain, or arthritis, which may last for weeks or months.
The incubation period (time from infection to illness) can be 2–12 days, but is usually 3–7 days.
Chikungunya fever is caused by a virus which belongs to the genus Alphavirus, in the family Togaviridae.
Preliminary diagnosis is often based on clinical features, places and dates of travel (if the person is from a non-endemic country or area), activities, and epidemiologic history of the location where infection occurred.
Laboratory diagnosis of arboviral infections is generally accomplished by testing the blood or cerebrospinal fluid, or CSF (the fluid that surrounds the brain and spinal column) to detect virus-specific antibodies.
During an acute infection, certain viruses can be isolated through culture or detected by nucleic acid amplification, or PCR (a technique that makes multiple copies of the viral genetic material, making it easier to detect).
In fatal cases, nucleic acid amplification (PCR), histopathology using immunohistochemistry (a technique that uses antibodies to identify proteins in diseased cells), and virus culture of autopsy tissues can also be useful. Only a few state laboratories or other specialized laboratories, including those at the Centers for Disease Control and Prevention (CDC), are capable of doing this specialized testing.
There is no vaccine or specific antiviral treatment currently available for chikungunya fever. Treatment is symptomatic and can include rest, fluids, and medicines to relieve symptoms of fever and aching. Medicines such as ibuprofen, naproxen, acetaminophen, or paracetamol can help relieve pain and fever. Aspirin should be avoided. During the first few days of illness, infected persons need to be protected from further mosquito exposure by staying indoors in areas with screens and/or under a mosquito net. This is so that they do not contribute to the transmission cycle, which leads to further infection of other people.
The best way to prevent chikungunya virus infection is to avoid mosquito bites. There is no vaccine or preventive drug currently available. Prevention tips are similar to those for other viral diseases transmitted by mosquitoes, such as dengue or West Nile. The following can help avoid mosquito bites:
- Using insect repellent containing DEET, Picaridin, oil of lemon eucalyptus, or IR3535 on exposed skin.
- Wearing long sleeves and pants (ideally treat clothes with permethrin or another repellent)
- Having secure screens on windows and doors to keep mosquitoes out
- Getting rid of mosquito sources in the yard by emptying standing water from flower pots, buckets, and barrels
- Changing the water in pet dishes and replacing the water in bird baths weekly Drilling holes in tire swings so water drains out
- Keeping children's wading pools empty and turned on their sides when they aren't being used
Additionally, a person with chikungunya fever can reduce the risk of spreading the fever by limiting exposure to mosquito bites. Mosquito repellents help discourage mosquito bites, as does limiting exposure to mosquitoes (by staying indoors or using screens or mosquito nets).
How Chikungunya is Spread
Humans become infected with chikungunya virus by the bite of an infected mosquito. Aedes aegypti, a household container breeder and aggressive daytime biter is the primary vector of chikungunya virus to humans. The Asian tiger mosquito (Aedes albopictus) has also played a role in human transmission is Asia, Africa, and Europe. Various forest-dwelling mosquito species in Africa have been found to be infected with the virus.
Mosquitoes become infected with chikungunya virus when they feed on an infected person. The infection is spread when the mosquito bites another person. Monkeys, and possibly other wild animals, may also serve as reservoirs of the virus.
Fatalities related to chikungunya virus are rare and appear to be associated with increased age.
The virus primarily inhabits Africa and Asia. Given the current large chikungunya virus epidemics and the world wide distribution of Aedes aegypti and Aedes albopictus, the virus could be imported to new areas by infected travelers.
Below is a list of some chikungunya outbreaks:
- Tanzania in 1953-1954 (first recorded outbreak)
- Kolkata, India in 1963
- 27 people in Port Klang, Malaysia, in 1999
- 237 deaths and 33% of people infected in Réunion in 2006 and 2007
- 160 people in Italy in 2007
- 43,138 people in Kerala in 2007
- Melborne, Australia in 2008
Pregnancy and Chikungunya
Pregnant women can become infected with chikungunya virus during all stages of pregnancy and have symptoms similar to other individuals. Most infections will not result in the virus being transmitted to the fetus. The highest risk for infection of the fetus/child occurs when a woman has recently been infected and has the virus in her blood at the time of delivery. There are also rare reports of first trimester (0–14 weeks) abortions occurring after chikungunya infection. Mosquito repellants containing DEET can be used in pregnancy without adverse effects.
Breastfeeding and Chikungunya
Currently, there is no evidence that the virus is transmitted through breast milk.
The first animal model of Chikungunya infection was developed in 2008. The model allows researchers to study infection in greater detail, and thus guide future drug and vaccine treatments. For the model, mice are genetically engineered to have a deficiency in a gene that encodes a protein involved in the immune system response to viral infection. The model has already showed that the virus replicates in the liver before infecting skin, joints, and muscles. The central nervous system becomes involved in the most serious infections.
- ↑ EurekAlert Web site. Researchers create first chikungunya animal model.
- ↑ Couderc T, Chrétien F, Schilte C, et al. A mouse model for Chikungunya: young age and inefficient type-I interferon signaling are risk factors for severe disease. PLoS Pathog. 2008 Feb 8;4(2):e29. Abstract | Full Text | PDF