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Year two of chikungunya in the Americas

What is local transmission of chikungunya

Public health officials had been expecting the arrival of chikungunya in the Western Hemisphere for some time so they were not surprised when cases began appearing in Dec. 2013 on the French side of the island of St. Martin. As of April 17, 2015, chikungunya had been confirmed with autochthonous (local) transmission in virtually every country and territory in North and South America. Bermuda, Canada, Chile, Cuba and Peru deny any locally contracted illnesses.

Chikungunya is a viral illness similar to dengue which is transmitted from human to human by the bite of an infected mosquito. The prevalent genotype in the Americas is the Asian. In mid-2014, Brazilian authorities began to record illnesses due to the East/Central/South African genotype of the virus.

At this time, the illness is being transmitted almost exclusively by the Yellow Fever mosquito, Aedes aegypti. In other parts of the world, including Europe, one serotype of the illness has been transmitted by the Asian Tiger mosquito, Aedes albopictus. While it is possible that some chikungunya illnesses have resulted from the bite of an infected Asian Tiger mosquito, the overwhelming majority are believed to be from the Yellow Fever mosquito.

Chikungunya in the United States

In 2014, southeastern Florida saw 11 cases of locally acquired chikungunya. About 2,300 total cases were diagnosed in the United States where the patient had contracted the infection outside the country. Haiti, the Dominican Republic and Puerto Rico were the top sources for these imported illnesses.

The Yellow Fever mosquito makes its habitat near humans in tropical or sub-tropical climates. Outbreaks of yellow fever have been historically noted in cities as far north as Boston, Massachusetts, in summers that were hot and humid. The mosquito, absent the right weather conditions, can primarily be found along the Gulf of Mexico coast and across Florida.

Under the right climatic circumstances, the potential for a chikungunya outbreak exists anywhere that a yellow fever outbreak is recorded in the history books. With the same mosquito vectors as chikungunya, the four dengue viruses could also potentially cause illnesses in areas with historic yellow fever.

Symptoms and treatment of chikungunya

With the number of probable and confirmed chikungunya cases now totaling nearly 1.4 million, the symptoms of the illness and its after effects have become much clearer. The Pan American Health Organization has this to say about chikungunya’s symptoms:

It can cause high fever, join and muscle pain, and headache. Chikungunya does not often result in death, but the joint pain may last for months or years and may become a cause of chronic pain and disability.

There is no vaccine against chikungunya. There is no cure for chikungunya. Physicians will treat the symptoms as possible, with fever reducers and pain relievers. As with most illnesses, infants, the elderly and those with compromised immune systems may experience the most serious infections which can, very rarely, result in death.

Prevention and Control

Prevention efforts, on both a community and a personal level, can reduce the chances of contracting a mosquito borne illness.

Mosquito control programs in areas with Yellow Fever mosquito habitat need to adapt their treatments and techniques to affect the existing population and the growth of the population of Aedes aegypti. The mosquito vectors for chikungunya are day feeders, unlike those that transmit West Nile or many other mosquito species who feed at dusk or dawn, or after dark. Control measures must be applied when the mosquitoes are active and the usual routine of dusk spraying will not be effective.

The vectors breed in fresh water. Containers that can capture rainwater, areas that retain puddles and abandoned swimming pools should receive attention. Efforts should be focused on providing as little breeding space as possible. Old tires are a favorite as are cisterns. Cisterns can be covered with screen, and tires removed.

On a personal level, the routine use of mosquito repellants whenever going outside is necessary. Doors and windows should be fitted with screens with a small enough mesh to prevent mosquitoes from entering the building. The Yellow Fever mosquito is often found indoors and can breed in as little water as that around a houseplant. The use of air conditioning is encouraged because it slows the activity of any mosquitoes in the building.

Chikungunya and the summer of 2015

The United States can expect to see many more locally acquired cases of chikungunya in 2015. The disease had made its way into Mexico, including the Acapulco area, and will appear in the Rio Grande Valley, north through Houston and the Gulf Coast, within months. Just like 2014, Florida will also see cases as its mosquito population recovers from the winter. Both areas have seen locally acquired dengue outbreaks in the last several years.

The risk to the remainder of the United States is very dependent upon the weather. Several weeks of hot and humid weather in places such as New Orleans or Atlanta could result in the appearance of some chikungunya cases. While the number of locally acquired infections cannot be predicted, it is most likely going to be a low number rather than a high number.

Chikungunya is not contagious human to human. It is spread by the bite of an infected mosquito. That mosquito must bite someone with chikungunya, become infected and then bite someone new all in its limited lifespan of about six weeks. In much of the United States, the climate will not permit a Yellow Fever mosquito-friendly habitat for that long.

In those areas that can support Aedes aegypti, mosquito control programs, the use of screens and repellants and the use of air conditioning will reduce exposures. The living conditions seen in the Dominican Republic or Columbia do not exist for the most part in the United States. Large numbers of chikungunya illnesses are very unlikely for that reason.

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