Chikungunya cycles

Chikungunya virus is a serious global threat for both the sheer number of individuals it infects, as well as the intensity and duration of the suffering it causes in each patient. The small virus is transmitted to humans by the simple bite of a mosquito, yet can cause months of debilitating joint pain. Since the 1950s, Chikungunya has spread throughout Africa and Asia, and in 2013 the virus was discovered in the Caribbean Islands and South America. Read more to find out about this widespread and pressing virus.

The Virus and Disease

“The fever lasted for four days …I sat down and couldn’t get up. My body and all of my bones hurt. The second day I was bedridden. I needed help to bathe.” – Marie Therese Lindor [1]

“I wouldn’t wish Chikungunya on my worst enemy.” – Naomi Hattaway [2]

What is Chikungunya?

The Chikungunya (chik-en-GOON-yuh) virus derives its name from the Kimandoke people of Tanzania. The phrase means “to be contorted” and describes the bent-over posture often exhibited by those suffering from the painful infection [3]. Chikungunya virus, carried by mosquitoes, infects humans, primates, rodents, and birds. With no vaccines to prevent its spread and few drugs to relieve suffering, Chikungunya has become a very real threat to citizens across much of the globe. Since it is transmitted by mosquitoes, our best defense is still to prevent bug bites with sprays and protective clothing [3].

Why is Chikungunya so painful?

The quotes above give us an idea of how debilitating the pain from a Chikungunya infection can be. After the mosquito bite, the Chikungunya virus replicates until it is released and circulates in the blood, and enters support cells in the muscles and joints [6]. The arthritis-like pain can last for months, but the virus can only be spread during the first week of illness. Like most mosquito-borne infections, the virus can only be transmitted by blood-to-blood contact, through a mosquito bite or transfusion with infected blood. There is no risk of contracting Chikungunya from an infected patient by touching or caring for them.

Sadly, there is little that doctors can do to relieve the pain or destroy Chikungunya virus. Anti-inflammatory drugs like ibuprofen can help, or the arthritis medication methotrexane can be effective [7]; however, both these drugs only treat the symptoms. Many academic labs and pharmaceutical companies are studying drugs to directly target the virus.

How does Chikungunya virus spread?

During infection, the virus replicates so aggressively that up to 1 million viruses can be found in a single drop of blood! [4] When a mosquito bites an infected individual, the bug gets a stomach full of virus that then replicates in the mosquito – without killing the mosquito. The next organism bitten by the mosquito, human or animal, will then be infected with Chikungunya virus as well. Of the many species of mosquitoes across the globe, two species play critical but distinct roles in the spread of Chikungunya virus: Aedes aegypti and Aedes albopictus (Figure 1) [7]. One species spreads the virus among wild animals, and the other spread the virus in urban areas among humans.

Figure 1 Two cycles of Chikungunya transmission from two species of mosquitoes [adapted from 7]. A) Sylvatic cycle: Aedes aegypti mosquitoes breed in the wild and prefer to feed on primates, rodents, and birds in the wild. Humans traveling in forested areas may be at risk for rare infections. B) Urban cycle: Aedes albopictus mosquitoes that breed in man-made containers in urban areas prefer to feed on humans and carry Chikungunya virus between humans.

Where did this virus come from?

Geographically, the Chikungunya virus originated in Africa and was passed to us via mosquitoes that also feed on our primate cousins. Scientists first isolated the virus from the 1952 and 1953 outbreaks in East Africa. Public health officials have noted subsequent outbreaks throughout West Africa, and South/Central Africa, and out to Madagascar and the nearby islands. Since 2005, Chikungunya also spread through the Asian continent, with epidemics in India, China, and many other countries, including “spillover” epidemics in France and Italy. This surge in epidemics corresponds to an evolutionary change in which Chikungunya virus acquired a small mutation that improves its ability to infect the human-biting Aedes albopictus mosquitoes [6]. In 2013, Chikungunya cases appeared in the Caribbean Islands, culminating in over 700,000 infections so far [1]. The virus is now spreading through North and South America.

The expansion of Chikungunya across the globe is attributed to several factors. First, climate changes over the last fifty years have allowed Aedes mosquitoes to breed across a broader geographic area. Second, Chikungunya-infected humans flying between countries have carried the virus long distances in rare cases. For example, a mini-outbreak Chikungunya occurred in Italy in 2007 when an Italian woman visited relatives in India and came home ill with the virus. Then local Aedes albopictus mosquitoes carried the virus to 197 other Italians [4].

How do we fight Chikungunya virus?

The best strategies we have to block mosquito-borne diseases is bug spray and vaccination. While many academic groups and companies are researching a Chikungunya vaccine, none have yet reached large scale clinical trials. The US government-sponsored National Institute of Allergy and Infectious Disease has developed a leading vaccine candidate, effective in monkeys and safe in small human trial [8].

To slow the geographic spread of the virus, we can slow the spread between humans. Many scientists are studying known and newly-designed drugs to shorten the duration of infection and relieve suffering. Caring for pain-stricken infected individuals in a shelter (clinic or private home) with air conditioning or at least enclosed by screens will keep a mosquito from biting the patient and passing the virus to someone else. However, many countries are unable to ensure sheltered care for the afflicted.

Figure 2 This November 2014 map from the Center for Disease Control (CDC) [2] displays countries in dark green that have confirmed cases of locally acquired Chikungunya. Countries with imported cases are not shown.

Important ethical and legal debates surround policy-level public health interventions for Chikungunya virus, and other “emerging” and endemic infectious diseases. Surveillance helps efficiently allocate resources, but if poorly implemented it can compromise personal privacy. Quarantine effectively limits virus spread, but sacrifices civil liberties. Travel bans may prevent viral spread yet carry an economic burden. Culling populations of infected or vulnerable “reservoir” animals halts the virus, but is ethically upsetting. Epidemiologists, legal ethicists, and government officials actively debate these issues with each new disease threat [9]. In each case, the biology of the virus (its route of transmission, incubation period, clinical symptoms, etc.) will dictate what public health measures will be most appropriate. With mosquito-borne viruses such as Chikungunya, a travel ban will do little to slow the spread, because infected individuals will appear healthy during the 4 to 10 day incubation period and spread the virus despite screening efforts. Our best hope is an effective vaccine and vigilant personal protection from mosquito-bites to reduce human infections.

Chikungunya virus is rapidly expanding across the globe and will continue to infect millions each year. Citizens, scientists and health officials should all work to limit the suffering it brings. People around the globe should be vigilant about controlling the mosquito population near their homes; for mosquito control information check out local resources [10]. With local efforts and scientists at work, we can minimize the cases of Chikungunya in our communities.

Ann Fiegen Durbin is a PhD student in the Virology program at Harvard Medical School and MIT.


[1] Bernard J. “Why Chikungunya – And the Mosquitoes – Are Overwhelming Haiti.” WLRN Miami/South Florida.

[2] Hattaway N. Blog July 2014.

[3] “Chikungunya virus.” Center for Disease Control and Prevention.

[4] Thiberville S. et al. “Chikungunya fever: Epidemiology, clinical syndrome, pathogenesis and therapy.” Antiviral Research, Issue 99, 2013.

[5] “Fact Sheet 327: Chikungunya.” World Health Organization.

[6] Hu D., et al. “Chikungunya Virus Glycoproteins Pseudotype with Lentiviral Vectors and Reveal a Broad Spectrum of Cellular Tropism.” PLoS One. 9(10). 2014.

[7] Petersen L. “Chikungunya virus: Possible Impact on Transfusion Medicine.” Transfusion Medicine Reviews. 24(1), 2010.

[8] Doucleff M. “Experimental Vaccine for Chikungunya Passes First Test.” National Public Radio, August 18, 2014.

[9] Lemon S. et al. “Ethical and Legal Considerations in Mitigating Pandemic Disease: Workshop Summary.” National Academies Press, 2007.

[10] “Mosquito Control Methods.” National Pesticide Information Center.

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