"Infective heartworm" refers to a stage in the life cycle of a parasite called heartworm. This stage is when the parasite is capable of infecting other animals, such as dogs or cats, and causing a disease. Full definition
Heartworm disease is spread through mosquitoes; so when a mosquito carrying infective heartworm larvae bites a dog (or other pet), it transmits the infection. (morenapethospital.com)
HEARTGARD Chewables should be given at monthly intervals during the period of the year when mosquitoes (vectors), potentially carrying infective heartworm larvae, are active. (medi-vet.com)
Heart Shield Plus ® flavored chewables should be given at monthly intervals during the period of the year when mosquitoes potentially carrying infective heartworm larvae are active. (vetiq.com)