How Chikungunya has spread in the New World

Chikungunya is picking up a pretty rough reputation for its painful and debilitating effects. It's also picking up ground. Previously found in Asia and Africa, it spread to the Caribbean in 2013 and is now in North and South America. A mosquito bite in parts of Florida and Texas could spread Chikungunya.

What is Chikungunya?

Chikungunya (chik-en-gun-ye) is a viral infection causing fever and joint pain that spreads from person to person by mosquito bites. 

The name means "that which bends up" in the Makonde language In Tanzania where the disease was first identified in the 1950's. The name refers to how those infected appear: hobbled over by joint pain.

How does Chikungunya spread?

The infection is spread by a bite from a female Aedes aegypti or Aedes albopictus mosquito. The bite must occur after the mosquito had bitten someone infected with Chikungunya. Returning travelers will not spread disease if not bit by one of these mosquitoes.

The Aedes aegypti mosquito is found in southern areas of Florida, Texas, and Arizona as well as limited parts of California. The Aedes albopictus mosquito has spread further north in the last decade, reaching Chicago and New York City. However, the density of these mosquitoes is not as high as in parts of the Caribbean where the disease has spread rapidly. Central America as well as parts of South America, especially Venezuela, have had particularly high rates. 

Epidemics are often explosive in populations not previously infected - especially in urban areas with substantial mosquito populations. Over 1 in 3 were infected in an epidemic on Reunion Island, a French territory in the Indian Ocean in 2005.

These mosquitoes bite all day long, though more at dusk. They frequently bite indoors and they can bite all year round in warm climes. They breed in stagnant water, such as found in buckets, toilets, and tires.

An infected mother can pass the infection to her child at birth. However, pregnancies are normally healthy if infection occurs well before birth. Infections could also be spread by blood transfusion.

Do some types of Chikungunya spread faster than others?

Yes, fortunately, the strain now found in the Americas is not the strain that spreads quickly through the more commonly found mosquito in North America, Aedes albopictus. There are 3 strains - West African, East/Central/South African (ECSA), and Asian. Some ECSA strains have a mutation (referred to as A226V, within the E1 protein) which allows Aedes albopictus to rapidly spread Chikungunya.

Where has it spread?

Chikungunya was historically found in Africa and Asia. It spread to Reunion Island in 2005, to India in 2006, as well as to Italy and France through air travel. However, before 2013, it was only found in returning travelers in the Western Hemisphere. Chikungunya first spread within this hemisphere in 2013 when it was found in St Martin. It has subsequently spread throughout the Caribbean, including to Puerto Rico, Haiti, and the Dominican Republic. It has spread to Florida and has been found in mosquitoes in Texas and in patients in Mexico. It is now in almost all countries in Central and northern countries in South America, as well as in the South Pacific.

The strain that arrived in the Caribbean appears to have originated in Asia. This strain is closely related to a strain from the Philippines as well as ones found in China (Zhejiang) and Micronesia.

How do I protect myself?

The simple answer: avoid mosquito bites. Vacations to areas with mosquitoes with Chikungunya may put travelers at risk. If there are mosquitoes with Chikungunya, it is important to prevent bites and mosquito breeding. Mosquitoes can breed in any uncovered water containers. Don't let water sit in tires or buckets. Empty containers. Wear long sleeves and pants to avoid bites. Use insect repellant, such as DEET. Use screens in windows and doors, if possible.

Those who are febrile and in the first weeks of infection may wish to lie under a mosquito net during the day to prevent mosquito bites from spreading infection.

Will I spread it back home?

Probably not if you live in a colder climate. The infection is often "imported" by returning travelers who do not spread the infection to others. Most parts of the US and Canada do not have the mosquitoes needed to spread the disease. A mosquito needs to bite the infected person and then bite another person to spread infection (except with blood transfusion or birth). The bite would have to occur while the virus is still in the infected person's the blood. The virus usually incubates for 3 to 7 days and acute symptoms usually resolve within 7 to 10 days. Most people who return with joint aches are likely not infectious 2-3 weeks after symptoms began.