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Chikungunya refers to an infection caused by the Chikungunya virus, an alphavirus of the Togaviridae family. Like its close relative, the Semliki Forest virus, the Chikungunya virus is transmitted from human to human via mosquito bites.
Chikungunya is characterized by fever, joint and muscle pain, and rash. The disease was discovered in Tanzania in 1952, and since that time has been identified in over 60 countries around the world. The word “Chikungunya” means “that which bends up” in the Makonde language, spoken by a group indigenous to Tanzania and Mozambique. It is thought that this term was coined to describe the posture of patients affected with severe disease.
Mosquito species that carry Chikungunya include Aedes aegypti in the tropics, Aedes albopictus in the tropics and colder areas, and approximately one dozen Aedes species in Africa, including Aedes furcifer and Aedes taylori. Transmission occurs after a mosquito bites someone infected with Chikungunya and then subsequently bites someone else. Mosquitos pick up the virus from human blood, the chikungunya virus replication happens inside the mosquito and can be transmitted via their salvia. Once a mosquito acquires the virus, it will likely carry it for the rest of its life. There is evidence that some animals, including non-human primates, rodents, and birds, may act as reservoirs for an acute Chikungunya virus.
Signs and symptoms of Chikungunya develop after a 2-12 day incubation period. Cases vary in severity, and asymptomatic infection may occur. The rate of asymptomatic cases is estimated to be between 4% and 28%.
Cases often begin with an abrupt onset of fever. Polyarthralgia occurs in 70% of cases, usually involving small joints. Swelling of joints may also occur, typically without fluid accumulation. In greater than 50% of cases, a maculopapular rash on the palms, soles, limbs, torso, and/or face is present. This rash may progress to desquamation. Fever generally resolves within one week, but joint pain may persist for months. Sometimes, a “saddle-back fever curve” is seen, with fever resolving and then returning. Moderate to severe lymphopenia is often noted. Thrombocytopenia, leukopenia, elevated liver enzymes, anemia, and elevated creatinine may also be observed.
Facial and neck erythema and conjunctival suffusion may be noted as symptoms. Headache, photophobia, retro-orbital pain, pharyngitis, nausea, and vomiting can occur. Sometimes, pneumonia and dry cough are seen. Pruritus is common. Patients may complain of exhaustion and insomnia as symptoms as well. Symptoms of Chikungunya can persist from one week to several months. Residual chronic joint pain may continue in some cases. Chronic disease is more common in older patients and patients with prior rheumatological disease.
Chikungunya can also cause neurological and ophthalmologic complications. Eye involvement may include retinitis, retinal detachment, optic neuritis, uveitis, dendritic lesions, and Fuchs heterocyclic iridocyclitis. Neurological manifestations can include altered mental function, encephalitis, seizures, myelopathy, Guillain-Barré syndrome, bulbar palsy, acute flaccid paralysis, focal neurological deficit, and sudden sensorineural hearing loss.
Additional rare complications of Chikungunya include hemorrhagic syndrome, cardiovascular shock, arrhythmias, myopericarditis, renal failure, rhabdomyolysis, and thrombocytopenic purpura.
Children with Chikungunya are more likely to experience neurological and dermatological symptoms, and less likely to have arthralgia. Transplacental transmission of the virus can occur and may result in neonatal encephalopathy, neonatal respiratory distress, sepsis, necrotizing enterocolitis, and cardiologic complications. Infants who become infected during the perinatal period may experience fever, rash, peripheral edema, lymphopenia, and thrombocytopenia. Congenital and perinatal infections are associated with poor neurodevelopmental outcomes. Transmission of Chikungunya via breastfeeding has not been noted.
Fatalities from Chikungunya are rare, occurring in about 1 per 1,000 cases. Fatalities are more common in newborns and individuals with multiple medical comorbidities. The use of NSAIDs prior to hospitalization is associated with an increase in disease severity. Infection with Chikungunya is likely to protect against future disease.
A diagnosis of Chikungunya should be considered in individuals living in – or having traveled to – areas with known outbreaks presenting with acute onset of fever and joint pain. Dengue fever and Zika virus infection should be considered in a differential diagnosis of Chikungunya, as they are also carried by Aedes species mosquitoes and may present with similar signs and symptoms.
PCR, serology, and viral culture can be used for laboratory confirmation of Chikungunya. Chikungunya is classified as a biosafety level-3 pathogen, and samples should be handled accordingly. Blood-borne transmission from patients to healthcare workers and laboratory personnel has been documented.
Patients with Chikungunya are treated with supportive care, including hydration and pain management. It is important to prevent mosquito bites during the first week of illness, in order to prevent additional transmission.
Between 1952 and 2013, virus outbreaks were identified in Africa, Asia, Europe, and the Indian and Pacific Oceans. In 2013, cases were first identified in the Americas and nations of the Caribbean, and today the majority of cases occur in these locations – where populations have no preexisting immunity.
Over the past decade, the countries that reported most cases of Chikungunya have included Haiti, Dominican Republic, Guadeloupe, Martinique, El Salvador, Honduras, Nicaragua, Columbia, Bolivia, Brazil, Ethiopia, Chad, India, Laos, and French Polynesia. If you have a GIDEON account, click to explore Chikungunya Outbreak Map.
Between 2004 and 2006, an outbreak of Chikungunya that began in Kenya resulted in 500,000 cases in countries of the Indian Ocean, including one-third of the population of La Reunion Island. This outbreak spread to India, where almost 1.5 million people were infected. Ongoing outbreaks have been occurring in Brazil since 2014, with over 300,000 infections occurring in 2016. It is thought that a mutation occurred around 2005 that enabled the virus to survive in Aedes albopictus; and that having this additional species as a vector has fueled recent outbreaks.
Local transmission was reported for the first time in Europe in 2007, with 197 infected individuals occurring in north-eastern Italy. The source of this outbreak was traced to a single individual who had returned from India with the infection. A second outbreak occurred in Europe in 2014, centered mainly in France and the UK and resulting in about 1500 instances of infection.
In 2014, local transmission of the virus was identified in the territories of the United States for the first time, with 4,659 cases occurring between American Samoa, Puerto Rico, the U.S. Virgin Islands, and Florida. Since that time, the rate of local transmission in the United States has decreased each year, with 179 instances occurring in 2016, 8 instances in 2018, and no instances in 2020.
There is currently no vaccine to prevent Chikungunya. The CDC recommends the use of the Environmental Protection Agency (EPA)-registered insect repellents when traveling to areas with outbreaks in the prevention of this viral infection. Wearing long sleeves and pants can also reduce transmission, as can sleeping in places with air conditioning and window and door screens. The CDC also recommends using 0.5% permethrin to treat clothing and gear to repel mosquitos.
During outbreaks, measures should be taken to control mosquito populations by reducing both natural and artificial water-filled habitats where they may breed. Any items that may hold water, such as pools, buckets, planters, and trash containers, should be regularly emptied and cleaned.