[...] warmer weather brings increased levels of parasites, including heartworms, the most dangerous parasite dogs can contract. "The disease can be contracted through mosquitoes that carry immature heartworms, and in Texas we have mosquitoes year-round," said veterinarian Laurel Douglass of the Sunset Boulevard Animal Clinic. "When that worm dies, some of the pieces of that worm go off to the lungs because the heart muscle pushes blood to the lungs, and that causes inflammation," Douglass said. According to the Companion Animal Parasite Council (CAPC), Harris County carries a high risk of heartworm infections in dogs - one in 27 dogs here will contract the disease, and 22 percent of all heartworm cases in the state are in Harris County. Heartworm disease is not the only major parasite pet owners should be cautious of - giardia is a single-cell organism that causes diarrhea in adult dogs and can be transferred to humans.