And Just When You Thought It Was Safe Out There, Along Comes Chikungunya
Emerging pathogens are always in the news--West Nile, SARS, Flu and more to come. The recent development of an Emerging Pathogens Initiative (EPI) at the University of Florida (UF) is Florida's effort to address emerging pathogens. Mosquito-borne pathogens and the resulting diseases they cause are one of the concerns of Florida Mosquito Control. Emerging pathogens are the priority issues to be addressed by the EPI and the reason why the Florida Mosquito Control Association played an important role in supporting UF to obtain the State funds to support the EPI.
Florida mosquito control, the FMEL, and PHEREC have a long history of addressing Florida's mosquito borne pathogens, all of which can be considered as emerging. Mosquito-borne pathogens emerge periodically to cause outbreaks in Florida. Our goal, reiterated often in previous Buzz Words, is to provide an ability to predict outbreaks in time and space well in advance of human cases so targeted effective control measures can be implemented. Our Florida sentinel surveillance system is set up with this objective as the primary goal. The topic on our plate the past few years has been West Nile virus. But of course we also have been aware of St. Louis encephalitis virus, Eastern equine encephalitis virus, dengue virus, malaria, yellow fever virus, and we have even heard papers at our Mosquito Control Association meetings on Rift Valley fever virus.
And then along comes chikungunya virus (CHIKV)!
Why the concern over CHIKV? Chickungunya is a disease that was first described in 1952 in Tanzania. The name is from the Makonde language (it is not Swahili as has been reported in the press and some articles) (see information at http://research.yale.edu/swahili/learn/?q=en/chikungunya_makonde). The name is derived from a word meaning to become contorted, and signifies the cause of a contortion or folding. Some say the word is from the phrase "to walk bent over." From these phrases alone readers should realize this is not something to be treated cavalierly--you do not want this disease. The disease has an incubation period of 4-7 days and then there is a sudden onset of the symptoms.
Patients often develop painful inflammation of the joints that result in a stooped posture. The other symptoms can include fever (>104°F), headache, vomiting, nausea and a skin rash (ca. 80% of cases have the rash). The symptoms here can easily be confused with dengue. Although rarely fatal, children can develop neurological problems. Symptoms usually subside within 3-5 days. However, the joint pain can persist for many months or even years after the other symptoms have subsided. Approximately 12% of cases develop chronic joint symptoms. There is no vaccine and no specific therapies for treatment. The vectors unfortunately, and this should send a chill through U. S. mosquito control and public health workers, are Aedes aegypti and Aedes albopictus.
Although there have been historic epidemics of chikungunya, particularly in Africa, it is the recent epidemics in Asia that certainly are cause for alarm. Since late 2004 there has been an enormous outbreak in the countries bordering the Indian Ocean. The numbers of cases have been staggering. The French Island of Reunion (pop. 770,000) has had 244,000 cases and 200 deaths. One of every three people infected with the virus! More recently the epidemic spread to several states in India. The Indian State of Karnataka Bangalore has reported 78,000 cases and Andhra Pradesh reported ca. 200,000 cases. Cases also occurred in the Indian State of Maharashtra, and on the Indian Ocean islands of Mayotte, Mauritius, Seychelles, Madagascar, and Comoros. Humans develop a high viremia and therefore the mosquito-man-mosquito cycle can spread the virus. Literally 100s of thousands of people have been infected in this region. It is certainly of concern that France has reported 307 imported chikungunya cases from travelers returning to France from these regions. Although the animal reservoirs for CHIKV are jungle primates (monkeys and baboons) that are unlikely to directly spread to the U. S., it would not be difficult for CHIKV to gain a foothold with the arrival of a human infected traveler wherever there are Ae. aegypti or Ae. albopictus; hence the reason why the U. S. is at real risk.
Why chikungunya, and why now? Some light on this may have been provided by a recent paper by Schuffenecker et al. (2006. Genome microevolution of chikungunya viruses causing the Indian Ocean outbreak. PLoS Med. 2006 July; 3) that can be accessed on line at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1463904. The authors provide the complete sequence for 6 viral isolates from the outbreak obtained from patients in different areas and times. They also sequenced the viral gene E1 from 121 other patients because this gene was useful in establishing relationships in several previous studies going back to 1982. The authors show that the Indian Ocean strains were derived from East Africa, and that the East African strain quickly diverged into distinct variants in the Indian Ocean epidemic. There are several regions of the genome that diverged but the authors point to one segment on the E1 protein that is common to all the epidemic isolates. This change is in a region of the virus genome known to be important in forming the virus outer shell. The authors speculate that this change may have made this variant more efficient in replicating itself in the mosquito vector and this is the reason for the rapid and widespread outbreak. Of course this is speculation and this hypothesis will need to be tested directly.
CHIKV has caused an enormous epidemic in Asia possibly the result of some genetic changes in the virus. The mosquito vectors responsible for this epidemic are already present in the U. S., and of course in Florida. Imported human cases have already appeared in Europe. This is not good. Stay tuned; be watchful for a chikungunya outbreak in the U. S.
And now there is CHIKV.
Walter J. Tabachnick, Ph.D. - Retired
Florida Medical Entomology Laboratory
Department of Entomology and Nematology
University of Florida/IFAS/Vero Beach, Florida
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