Do we have heartworm in Colorado? Unfortunately, with a resounding yes, we do. Although we are still a dry state, and thus have less than areas such as Florida, we do have the mosquitoes that carry the larva, and thus adult infestation in dogs and cats. We usually cite the American Heartworm Society for the 1-2% incidence in Colorado, though that varies in imported pets from higher infection states.
How are you protecting your pets? We recommend testing for the infection yearly, and keeping your pet on preventative for 9-12 months of the year. Both dogs and cats are at risk for the infection, inside or outside, because mosquitoes are highly mobile. It requires an infected dog to pass the infection on to the mosquito creating a reservoir; and only 30% of our dogs are tested and on the medication.
Due to the safe and easy nature of most heartworm preventatives, we do strongly recommend this medication be added to your monthly regimen of care in both dogs and cats. In this case, the expense of the preventative monthly (usually between $15-20) is worth the expense of the cure (usually in the thousands due to hospitalization and testing).
There is much information out there about the life cycle and other issues surrounding heartworm, remember to go to trusted sites, such as the Cornell University, UC-Davis, and CSU Veterinary sites.