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Florida and Chikungunya: Lessons from Chikungunya Italian Style

The danger to the U. S. from the entry of exotic mosquito-borne pathogens is real. The spread of West Nile virus throughout the U. S. in only 8 years shows all too clearly the effects on public health from a new mosquito-borne pathogen, and the challenges and difficulties for the U. S. in mitigating these effects. It is clear that public health and mosquito control professionals must be vigilant against mosquito-borne diseases.

Those charged with mosquito control and protecting public health must be vigilant, while at the same time avoiding unnecessary scares to the public to promote the necessity of our professions. Florida Mosquito Control has professional responsibility to discuss and prepare in advance for the introduction of new mosquito borne pathogens, and to alert other government agencies as well on these potentials. Though many parts of the U. S. have experienced much higher incidences of West Nile in humans than Florida, Florida mosquito control must continue and improve its abilities to mitigate a Florida West Nile outbreak. Elsewhere in many columns in BuzzWords we have discussed West Nile in Florida, reasons for the low incidence, and why Florida is at risk for West Nile epidemics with 100's to even 1000's of human cases.

And then there is Chikungunya.

Is Chikungunya a real risk to Florida? Some may believe that a Florida Chikungunya epidemic is unlikely. I hope that they are right. On the other hand, with equal validity one could argue that the potential for a substantial outbreak of Chikungunya in Florida is real, and we must be prepared. It is only prudent to be vigilant and prepared. Why would one say Florida is at great risk?

Chikungunya Outbreak in Italy: The 2005-06 Indian Ocean outbreak of Chikungunya was unprecedented with over 1 million human cases. The mosquito culprits were Aedes albopictus in the southern region of the Indian Ocean, and Aedes aegypti in India. Subsequently, Chikungunya virus has spread to many different countries carried by infected travelers from the Indian Ocean region. U. S. CDC reported 38 confirmed Chikungunya cases in travelers to the U. S. during the past two years. Fortunately there has been no evidence of subsequent transmission from these travelers in the U. S.

We have been fortunate, but Italy was not. In June 2007 a traveler from Kerala India returned to his home to near the villages, Castiglione de Cervia and Castiglione di Ravenna, both about 6 Km from the Adriatic coast in the province of Ravenna, in the Emilia Romagna Region of Italy. He had two episodes of fever, on June 15 and June 23 and during the second episode he was visiting a cousin in Castiglione de Cervia for several hours. His cousin was the second reported case with onset of symptoms on July 4. The outbreak occurred quickly. The vector was Ae. albopictus, known to have been present in these villages since 2005. When human cases subsided with no new cases in October there were 334 suspected human cases of which 204 were confirmed by laboratory diagnosis with PCR. Cases were reported in some nearby villages in people with no travel history to the index villages, showing that mosquito transmission was indeed occurring elsewhere. Symptoms were similar to cases in the Indian Ocean Region with 95% experiencing arthralgia. An 83 year old patient with underlying conditions, died.

Italy mosquito control and public health are now facing questions that must be answered. Will they see Chikungunya again? Why this specific region and not other regions of Italy with Ae. albopictus where travelers with Chikungunya have visited? There have been over 30 reports of Chikungunya in visitors to Italy. Guidelines for controlling Ae. albopictus issued by the Italian Ministry of Health in 1994 are being implemented, and Ae. albopictus is being monitored now in the Emilia Romagna Region by 1800 ovitraps with 2500 ovitraps planned for 2008. For more information see the European Center for Disease Prevention and Control Report at http://www.ecdc.eu.int/pdf/071030CHK_mission_ITA.pdf.

So what of Florida? Consider the same sequence of events in Florida, where there are large numbers of visitors from throughout the world, including regions where there is Chikungunya transmission, and populations of Ae. albopictus and also Ae. aegypti waiting to become infected from such a traveler, and transmit the virus in Florida. The two Italian villages have a combined population of 3767 people and had around 150 Chikungunya cases within a 10 week period. A description of the housing in both villages is that typically houses are low (two floors) surrounded by small gardens with many flowers, plants, and flower pots. In the streets, drainage systems are visible, indicating open stagnant water underground. Sound familiar? The incidence in the two villages over 10 weeks was ~40 per 1000. That means about 4300 Chikungunya cases in Gainesville, 9120 cases in Orlando, and 1200 cases in Key West just in the residents alone. For illustration Key West could experience 4000 cases during the tourist season.

And then there was Chikungunya!

Walter J. Tabachnick, Ph.D, Professor
Florida Medical Entomology Laboratory
Department of Entomology and Nematology
University of Florida/IFAS