LA county appears to be an oddity when it comes to heart worm incidence. Our Northern California neighbors and counties to the east such as San Bernardino experience almost 6 times more cases than LA county. Similarly, states such as Texas, Louisiana, Florida and New Jersey have 100x more cases than LA county. The reason why we enjoy a relative low incidence of the disease is not very well known.
The LA County Department of Veterinary Public Health collects information on several animal diseases including heart worm disease through a self-reporting system. From this data, the number of reported heart worm disease cases reached a high in 2009 and has slightly decreased since then. However, it is highly likely that dogs with the disease were not reported to LA County Department of Veterinary Public Health.
Factors that contribute to the incidence of heart worm disease include mosquito density and the number of heart worm positive animals present in the area.
Mosquitos flourish in enjoy warm climates and Southern California’s sunny climate supports a robust mosquito population. Although, mosquitos require a water source to deposit their eggs- they are not picky about where they leave their children. Some mosquitos can lay their larvae in water that has accumulated in leaves whereas others prefer flowerpots or marshes. The eggs are tolerant to both extreme heat and cold and can be frozen or dessicated before achieving temperatures conducive to hatching.
LA county has several mosquito preventive programs in place to control the number of mosqutos. These programs include draining stagnant water that may serve as a mosquito breeding ground, use of mosquito fish to eat mosquito eggs and larvae and chemical methods to decrease mosquito populations.
Many pet owners are well educated about the dangers of heart worm disease and use heart worm preventives. However the importation of heart worm positive animals from heart worm endemic regions like the South-East can contribute to the prevalence of heart worm disease in Southern California. Rescue agencies working to alleviate the burden of shelter animals in other states may inadvertently transport infected animals to areas with low rates of infection.
Although programs are in place to mitigate the risk of pets becoming infective with heart worm it does not completely eliminate the risk of developing the disease. The use of heart worm preventives such as Revolution, Sentinel and Heartgard greatly reduce the risk of a dog or cat developing heart worm disease. In addition, many of these preventives also protect against heart worm but other internal and external parasites as well such as fleas, tapeworms and roundworms.