In an April 28 story about chikungunya, the Sun Herald quotes Dr. Jerome Goddard, entomology professor at Mississippi State University, as saying “… everybody, including me, says that’s going to be the next West Nile.” He is talking about the mosquito borne illness chikungunya, expected to reach the United States within two years. The last such illness which swept across the country was West Nile.
There is little comparison between the two diseases other than mosquitoes transmit both to humans. They are unrelated viruses, carried by different mosquito species. They affect humans in very different ways.
The West Nile virus is carried by various Culex mosquito species as they feed on birds. It is an avian disease. While humans, horses and a few other animals can contract an illness, the Centers for Disease Control state that only birds become sick enough to pass the illness on to mosquitoes for re-transmission.
About 80 percent of people infected with West Nile fever will have no symptoms. In about 20 percent, the illness will produce “flu-like” symptoms. In less than one percent of illnesses, a serious neurologic illness may occur. As many as ten percent of those patients will die.
West Nile illnesses are seen in nearly every state. The Culex family of mosquitoes is well adapted to temperate climates and ranges throughout the Northern Hemisphere. Birds are their primary feeding choice and birds serve as a permanent reservoir for the West Nile virus.
Chikungunya is a human illness. It is carried by two mosquito species, Aedes aegypti and Aedes albopictus, which mainly inhabit regions with a tropical or sub-tropical climate. Aedes aegypti, the Yellow Fever mosquito, is the vector for the current chikungunya outbreak in the Caribbean. Aedes albopictus, the Asian Tiger mosquito, has been identified as transmitting the illness in some Asian outbreaks, but that chikungunya variant has not yet appeared in the Western Hemisphere.
Chikungunya has a rapid onset of symptoms. Fever, headache and joint pain are the most common. Deaths related to the illness are rare. Complications from a chikungunya illness are common, with many patients experiencing debilitating pain for weeks, months or years.
Primates, apes and monkeys, are believed to act as a reservoir species for chikungunya in some parts of Africa and Southeast Asia. In many chikungunya outbreaks, such as one in Italy in 2007, non-human primates play no role.
In the United States, the Yellow Fever mosquito has a limited habitat. In general, it may be found south of the Ohio River and east of the Mississippi. It is also found in eastern Texas and in southern California. The Asian Tiger mosquito shares that same habitat as well as ranging into more temperate climates. It has been found as far north as Chicago and Long Island.
Chikungunya illnesses in the United States will not result from persistent infections in a reservoir species. They will appear in clusters where the vector mosquitoes have been feeding on sick people and become infected. Those mosquitoes will then transmit the illness to other humans. Such disease behavior, however, does not preclude large numbers of patients if the mosquito vector is uncontrolled. Since Dec. 2012, the Caribbean outbreak has produced over 36,000 confirmed and suspected chikungunya cases.