Thanks to Greg Folkers for sending the link to this NEJM article: Chikungunya Virus in the Americas — What a Vectorborne Pathogen Can Do. Excerpt:
Given their similarities, dengue might provide the best predictive model for the expected course of chikungunya in the United States. In 2013, 2.4 million cases of dengue were reported in the Americas, including 773 travel-related and 49 locally transmitted cases in the continental United States.
Several factors will probably help mitigate the spread of chikungunya in the continental United States, including the ability to avoid mosquito bites by using air conditioning in homes and businesses. During a dengue outbreak on the Texas–Mexico border in 1999, Ae. aegypti mosquitoes were three times as abundant on the American side as on the Mexican side, but the number of persons infected with dengue virus was twice as high on the Mexican side.4 Analysis revealed that the absence of air conditioning in one's home was the factor most closely associated with testing positive for dengue.
There is no population immunity to chikungunya virus in the Americas. The number of cases will therefore continue to increase in places where local transmission has occurred, and the virus will spread to new areas in the region. In the French territories initially affected by the outbreak, 12 to 15% of the population has already presented for medical care with symptoms compatible with chikungunya virus infection.1
On the basis of previous surveys, we can expect at least 30% of populations in areas with local circulation to become infected unless control measures or seasonal conditions intervene.3,5
In temperate areas, colder temperatures and autumn conditions will reduce the abundance of vectors and probably stop virus transmission, as occurred with a chikungunya outbreak in Italy in 2007.5
In tropical areas, the intensity of transmission will probably wane as drier conditions take hold. However, because the relevant mosquitoes often breed in water-holding containers (e.g., flowerpots, gutters, buckets, or birdbaths) in and around homes, drier conditions are unlikely to stop transmission completely. In fact, there was a chikungunya outbreak in Kenya at a time of drought, since people were keeping more water-storage containers in and around their homes.
The future course of the chikungunya virus outbreak is uncertain. It is not known what role Ae. albopictus may play in transmitting this virus in more temperate areas or whether an enzootic cycle will be established to maintain the virus in the region.
It's also unclear how the coexistence of chikungunya and dengue will affect the epidemiology of these diseases in the region or whether the long-term morbidity will be as pronounced as that seen after outbreaks around the Indian Ocean. Only time will tell how this emerging virus will behave in relatively new and uncharted territory.