Fleas as Acceptable Intermediate Hosts of the Do Heartworm, Dirofilaria immitis.

Abstract

The method of natural transmission of the dog heartworm, Dirofilaria immitis, is still incompletely elucidated. The larvae of this parasite have been shown to develop in many species of mosquitoes and, thus, mosquitoes have been believed to be incriminated in the natural transmission, but substantial proof of this is lacking. The possibility that other blood-sucking arthropods serve as transmitters was overlooked until 1921, when Breinl reported finding the micro-filarial embryos of Dirofilaria immitis in the fleas, Ctenocephalides canis and Ctenocephalides felis, collected from heartworm infected dogs in Australia. He also observed the advanced stages of development of this parasite in the Malpighian tubules of the fleas and the infective stage larvae in the hemocelic cavity. Recently, Brown has observed the microfilariae and partially developed larvae of this parasite in Ctenocephalides canis collected from heartworm-infected dogs in the eastern United States. In November of 1938, the writer, in examining dogs for heart-worm infection in New Orleans, observed the typical microfilariae of Dirofilaria immitis in Ctenocephalides canis. The early developmental stages and the infective larvae were also seen in the hemocelic cavity of fleas collected from a dog having a heavy infection. On other dogs harboring Dirofilaria immitis Ctenocephalides felis and Pulex irritans were found similarly infected. The female fleas of the 3 species were much more frequently infected and were more heavily infected with all the larval stages of the parasite than were the males. From some dogs infected with heartworm as many as 100% of the female fleas examined contained one or more infective-stage larvae and many of the earlier stages of development. The males harbored these stages only in small numbers and rarely contained the infective stage larvae.