Chikungunya

Introduction

Chikungunya is a mosquito-borne viral disease caused by the chikungunya virus (CHIKV), an RNA virus in the alphavirus genus of the family Togaviridae. The name “chikungunya” derives from a word in the Kimakonde language of Southern Tanzania, meaning “to become contorted” and describes the stooped appearance of sufferers with joint pain.

Transmission 

Vector and transmission

Chikungunya is transmitted to humans by infected female mosquitoes, primarily Aedes aegypti and Aedes albopictus. These two species can also transmit other mosquito-borne viruses, including dengue and zika viruses. They bite throughout daylight hours, although there may be peaks of activity in the early morning and late afternoon.

In addition to vector-borne transmission, other transmission routes of CHIKV have been documented: blood-borne transmission among laboratory personnel and healthcare providers and mother-to-child transmission, mainly intrapartum when the mother is viraemic around the time of delivery. Rare in utero transmission has been described, mostly during the second trimester. There have been no reports to date of infants acquiring CHIKV infection through breastfeeding.

Genetic Lineages of chikungunya virus

Phylogenetic analysis identified three lineages corresponding to their respective geographical origin: West Africa, East-Central-South Africa (ECSA), and Asian lineage. In 2004, an ECSA CHIKV strain emerged in Kenya and subsequently spread to the Indian Ocean Islands, where it caused outbreaks of an unprecedented magnitude, particularly in La Réunion. The extent of this outbreak has led to the emergence of a fourth phylogenetic lineage termed Indian Ocean lineage (IOL), which has subsequently dispersed to Asia and India and caused autochthonous transmission (local disease spread) in Mediterranean Europe (Italy and France).

Reservoirs

Humans are the major reservoir of chikungunya virus. However, in Africa natural hosts of chikungunya virus are wild primates bitten by forest-dwelling Aedes mosquitoes.

Life cycle

Two distinct CHIKV transmission cycles exist: transmission between non-human animal host and insects (sylvatic cycle) with occasional transmission to humans and urban transmission, between humans and mosquitoes. 
Sylvatic cycles still exist in Africa and likely also in parts of Asia, however, urban transmission is increasingly more important.

Risk for traveller

Travellers visiting regions where chikungunya is endemic or experiencing outbreaks are at risk of infection. The risk is highest in areas undergoing active chikungunya epidemics, which typically occur during the tropical rainy season and subside during the dry season. 

Incubation period  

3–7 days (range 1–12 days).

Symptoms

Approximately 3% to 28% of people infected with chikungunya virus will remain asymptomatic. In others it is characterized by an abrupt onset of fever, severe joint pain, muscle pain, headache, nausea, fatigue, and a maculopapular rash. Joint pains are typically severe, can be debilitating and may persist for months or even years. It usually involves multiple joints, typically bilateral and symmetric. It is most common in hands and feet but can affect more proximal joints. 
Acute symptoms of chikungunya typically resolve in 7 to 10 days. Fevers typically last for less than one week and can be biphasic.

Severe complications and death are rare but have been reported during chikungunya outbreaks. These occur more often among patients >65 years and patients with underlying chronic medical problems (e.g., diabetes and cardiovascular disease).

Chronic chikungunya

Chronic arthritis and arthralgia are common long-term effects of chikungunya infection, with a prevalence ranging from 25% to 75% of patients, depending on factors like geography, virus strain, and individual health conditions. Symptoms typically affect joints involved during acute illness and can be persistent, relapsing, or incapacitating. Some patients develop new chronic inflammatory polyarthritis, while others experience exacerbations of pre-existing arthritis. Risk factors include age over 45, severe acute arthritis and pre-existing osteoarthritis. 

Pregnancy 

Pregnant woman experience symptoms and outcomes similar to those of the general population, and most infections during pregnancy do not lead to foetal transmission of the virus. Intrapartum transmission, when the mother is viraemic around the time of delivery, can result in neonatal infection with severe complications (e.g., haemorrhagic symptoms, myocardial disease and neurologic disorders) with a poor neurocognitive outcome. 

Lifelong Immunity

It is considered that natural infection with CHIKV will induce life-long protective immunity against re-infection or disease caused by re-infection. 

Additional information

• Wikitropica: background information on chikungunya for medical professionals
• Chikungunya factsheet (WHO 2022)
• CDC Yellow book: Travel-related Infectious Diseases – Chikungunya (CDC 2024)

References

• Bartholomeeusen et al. Chikungunya fever. Nat Rev Dis Primers. 2023 Apr 6;9(1):17. Erratum in: Nat Rev Dis Primers. 2023 May 19;9(1):26.
• Ixchiq: EPAR - Medicine overview
• Advisory report of the Superior Health Council on vaccination against chikungunya (HGR 2025)