Well, it's here. The mosquito-borne chikungunya virus finally trekked its way into the Western Hemisphere, arrived in the Americas, and has begun infecting Caribbean mosquitoes, confirming one of the worst fears of public health officials on this side of the prime meridian. This pathogen, notorious for its explosive outbreaks and debilitating joint pains, arrived on the Caribbean island of Saint Martin and has caused over 200 infections since December 5 of 2013. The outbreak marks the first time that chikungunya has been locally transmitted by native mosquitoes in the Americas. The multisyllabic chikungunya is the new kid on the arbovirus block, a promising member of a squad of up-and-coming arthropod-transmitted viruses that are gaining ever more attention thanks to climate change and globalization. Discovered in southern Tanzania in the early 1950s, it's tongue-twisting name derives from the Makonde of Tanzania and Mozambique, meaning "stooped walk," describing the hunched, protected stance of those suffering from the severely debilitating joint pain (1)(2). In Congo, the disease has earned the name “buka-buka,” meaning “broken-broken" (3). Infection with chikungunya virus via the bite of an infected mosquito results in an acute fever with throbbing, aching joint pain accompanied by a rash and muscle pains. Joints most commonly afflicted include the fingers, wrists, elbows, knees, ankles and toes (4). Chronic disabling joint pain following a bout of chikungunya is common and can last for months and even years.
Countries with reported cases of active or resolved infections of local transmitted chikungunya virus as of January 6, 2014. The map does not include countries where only imported cases of the virus have been documented. Its clinical presentation resembles dengue infection, a situation that lends itself to many false diagnoses. There is no treatment, and medical care can only alleviate the excruciating symptoms of the disease. Luckily, the virus is rarely fatal, with 1 death in every 1000 cases; deaths most commonly occur in neonates and immunocompromised adults (4). High morbidity and low mortality are the characteristics of chikungunya virus. The virus is the itinerant hippie backpacker of the arboviral group, having traipsed its way through nearly 40 countries and causing outbreaks throughout Africa, Asia, and Europe since a massive outbreak (1). For many years, chikungunya was localized to the African continent, but its recent history has been dramatic, characterized by geographic expansion ever eastwards. In early 2005, after years of sporadic outbreaks in Africa, chikungunya shifted to the Indian Ocean basin and south Asia. Over a period of two years, it caused massive outbreaks and infected nearly 2 million people, hitting large urban populations within India, Indonesia, Maldives, Myanmar and Thailand (1)(2). In some regions of India, over 45% of the population was infected with the virus (5). From there, this viral vagabond ventured to Italy and France via an infected traveler returning from India (6). It infected nearly 200 people, spooking European health officials operating under the assumption that tropical arboviruses would never infect mosquitoes of European ilk. This outbreak was unique in that it was largely accelerated by a single nucleotide mutation that enhanced the virus’s ability to replicate in the mosquito species Aedes albopictus, though it typically infects the species of Aedes aegypti (7). The Italian outbreak is a disturbing case study for public health practitioners eyeing the Saint Martin outbreak, as French researchers noted warily in their 2011 report on chikungunya entry to southeastern France (8):
The efficient [chikungunya] transmission in Italy and southeastern France sheds new light on its dissemination potential in Europe from one index case, regardless of the viral genetic background and mosquito species in the region of origin of the imported [chikungunya].
This is why the Caribbean outbreak is so troubling: one index case, one big outbreak. In the beginning days of the Saint Martin outbreak, the European Centre for Disease Prevention and Control (ECDC) warned that there is a high risk of chikungunya expanding into nearby Caribbean islands; already cases are being reported in the isles of Martinique and Saint Barthélemy. The ECDC notes that “the [immunologically] naïve population, the presence of an effective vector in the region and the movement of people in and between islands are factors that make it likely the outbreak will continue to spread geographically and increase in numbers" (9). The onset of the Christmas tourist season did not help matters.
What could be chikungunya's next destination? From a 2006 article, an approximation of the global distribution of the mosquito species Aedes albopictus (dotted lines) along with the distribution of variants of chikungunya virus (stars) from western Africa to southeastern Asia. The color of the stars reflects the major evolutionary lineages of the virus. Source: Parola P et al. (2006) Novel Chikungunya Virus Variant in Travelers Returning from Indian Ocean Islands. Emerg. Infect. Dis. 12(10): 1493-9. Chikungunya’s pattern of relentless outbreaks and adaptive evolution to novel mosquito species only underscores the difficulties of containing and controlling the geographical expansion of the virus. These factors, along with its known propensity for globe-trotting, do not bode well for arresting the spread of chikungunya to other Caribbean islands, let alone to the rest of the Americas. Its appearance in the Caribbean is a nasty “happy new year” to public health officials in the region. The outbreak in Saint Martin has largely glided the radar so far as our major news outlets have been concerned, but the appearance of chikungunya on this side of the globe no doubt warrants close attention and quick action to halt its spread throughout the Americas. This is a pattern that is occurring over and over again, one that has been repeatedly explored in this blog: novel pathogens are gaining a foothold in new territories assisted by changing climates, globalization, and international travel. As we’ve seen with the entry of both West Nile virus and dengue in the United States, this country is exquisitely vulnerable to arboviruses arriving from tropical locales. All signs point strongly to the possibility of chikungunya establishing an endemic presence in the Western hemisphere; it’s just a matter of when. Resources Pathogens are finding new homes in a world changed by globalization and climate. Previously on the Body Horrors blog: Imported Goods: Dengue’s Return to the United States,Valley Fever, The Archaeologist’s Scourge,Coming to America: Neglected Tropical Diseases Are Here (To Stay?). The CDC’s recent travel watch notice regarding chikungunya in the Caribbean. Read more here about the ECDC's report on chikungunya's appearance in Saint Martin rapid assessment. References 1) World Health Organization. (January 2014 ) Chikungunya Factsheet #327. Accessed on January 13, 2014 here. 2) Chevillon C et al. (2008) The Chikungunya threat: an ecological and evolutionary perspective. Trends Microbiol.16(2): 80-8 3) Simon F et al. Chikungunya: a paradigm of emergence and globalization of vector-borne diseases. Med Clin North Am.92(6): 1323-43 4) Weaver SC et al. (2012) Chikungunya virus and prospects for a vaccine. Expert Rev Vaccines.11(9): 1087-101 5) Panning M et al. (2008) Chikungunya fever in travelers returning to Europe from the Indian Ocean region, 2006. Emerg Infect Dis.14(3): 416-22 6) Pfeffer M & Dobler G. (2010) Emergence of zoonotic arboviruses by animal trade and migration. Parasit Vectors.3(1): 35 7) Rosenberg R & Beard CB. (2011) Vector-borne infections. Emerg Infect Dis.17(5): 769-70 8) Grandadam M et al. (2011) Chikungunya Virus, Southeastern France. Emerg Infect Dis.17(5): 910-3 9) European Centre for Disease Prevention and Control (ECDC). (December 11, 2013) Rapid risk assessment: Autochthonous cases of chikungunya fever on the Caribbean island, Saint Martin. Accessed on January 14 2014 here.