This is part IV of a blog series that examines recent U.S. outbreaks of diseases that are not yet endemic to the U.S. and for which we usually do not see cases in the continental U.S. other than in international travelers.
In part I, I reviewed the history of some of these outbreaks. In part II, I discussed dengue fever and in part III, I wrote about Zika virus disease. The common denominator was that dengue and Zika are both flaviviruses; the diseases they cause are both vector-borne meaning that these viruses are transmitted to humans primarily through an insect – in the cases of these viruses, a specific species of mosquitoes – rather than human-to-human transmission or zoonotic transmission (animal à human) as are so many of the diseases that I have previously written about; the outbreaks have occurred in the southern U.S.; and given the fact that these viruses generally are endemic in tropical and subtropical areas of the world, these recent outbreaks may be, at least in part, related to climate change making previously less favorable environments in the northern hemisphere more hospitable for the mosquitoes that transmit these diseases.
In this part IV blog piece, I will discuss chikungunya. No doubt you are already wondering where this strange name came from and what it means. I’ll explain below.
The chikungunya virus is an alphavirus in the Togavirus family (this is a different group of viruses than that to which dengue virus and Zika virus belong). It was first identified in Tanzania in 1952, however, it received little attention, research interest or efforts at containment until it did two concerning things – (1) adapted to be able to be transmitted by an additional species of mosquito, allowing for greater spread of the disease and (2) relatedly, began causing disease in the northern hemisphere. [I know you are wondering, so here you go. There are about 3,000 different species of mosquitoes and approximately 200 species can be found in the U.S.]
Since its emergence in Tanzania, the virus has been detected in other countries of Africa and Asia. The first recorded outbreaks in urban areas were in Thailand in 1967 and in India in the 1970s.
Prior to 2006, we rarely identified chikungunya infection in U.S. travelers who travelled abroad.
Between 2006 and 2013, we would detect evidence of recent chikungunya in about 28 Americans on average per year who travelled to Africa, Asia or areas surrounded by the Indian Ocean.
In 2013, chikungunya virus was detected in Central and South America, the Caribbean islands and some U.S. territories.
Beginning in 2014, we began receiving reports of chikungunya virus disease among U.S. travelers returning from Central and South America, but more concerningly, we began seeing local transmission (this means the mosquitoes and virus were circulating in these areas) in Florida and Texas as well as Puerto Rico and the U.S. Virgin Islands.
Given the fact that we did not conduct much research into this virus and the disease it causes until relatively recently, unfortunately, it is now a public health threat for which we have many knowledge gaps, no known effective treatments and no vaccine available.
Chikungunya virus is transmitted by the same mosquitoes that transmit the dengue virus and the Zika virus.
Chikungunya infection causes high fever and disabling joint pains of varying duration. This is where the name of chikungunya comes from. Kimakonde is the language spoken by the Makonde, an ethnic group in the southeastern part of Tanzania. You will recall that Tanzania was where chikungunya was first identified. Also recall from part II of this blog series that people called dengue fever – breakbone fever – a reference to the intensity of bone, joint and muscle pains. The Makonde named this virus chikungunya – the Kimakonde word that means “to become contorted,” another reference to the intensity of the musculoskeletal pain associated with infection.
The onset of symptoms with chikungunya infection is usually 4 – 8 days, but can be as short as 2 or as long as 12 following the mosquito bite. Fortunately, not everyone develops severe symptoms. The most severe cases tend to be in the very young and the elderly. Most often, when patients are symptomatic, the first symptoms are fever and joint pain, usually with a rather abrupt onset. The joint pain is generally so disabling that people are largely bed-ridden in their homes or a hospital. These pains may last only a couple or few days, but unfortunately, in some, the pains may last weeks, months, or even years. Patients also often experience muscle pains and headache. Some will develop swelling of their joints. As with dengue fever, some will develop a rash.
Most patients fully recover, though eye, heart and neurological complications have been reported. Fortunately, at this time, the evidence supports lasting immunity against repeat infection.
Fortunately, and for not entirely clear reasons, cases of locally-contracted chikungunya have declined rapidly in the continental U.S. with no cases reported since 2015, but slower in the U.S. territories, with the last reported cases in 2019.
As with our discussion of these other vector-borne outbreaks, there are no specific precautions for Americans to undertake unless travel is planned to areas where these infections are endemic. My purpose in writing about these disease outbreaks is to raise the level of concern as I believe that these are warning signs that should promote more preparedness, testing capabilities, and research into treatments and vaccines for all of these vector-borne diseases.
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