Dirofilariasis: Current Status and Treatment Perspectives

Abstract

Companion animals are known to be the home of various endoparasites. A thread-like filarial nematode called Dirofilaria immitis is pathologically and economically critical for pet owners worldwide as it causes “Heartworm Disease” in Dogs. The parasite causes disease by residing in the pulmonary arteries where they provoke injury and inflammation. (Noack, Harrington, Carithers, Kaminsky, & Selzer, 2021) The maturation of these nematodes in the infected dog leads to a disease syndrome that includes respiratory complications, congestive heart failure and pulmonary heart disease. The mature parasite can reach lengths of 12 – 31 cm long depending on the sex. (Amy C. Dixon-Jimenez, et al., 2018) (Bowman & Atkins, 2009) Mosquitoes of several genera are responsible for the biological transmission of D. immitis and more than 60 species of mosquito can harbor parasite infection leading to transmission. While an infected female mosquito takes blood from a host, her labium ruptures and releases hemolymph containing the infective larvae, which are deposited onto the host’s skin. This infective larvae then proceed to invade the host through the mosquito puncture wound. The parasite then starts its journey towards the right heart and pulmonary arteries where they sexually mature. The cycle continues when a fertilized female parasite releases microfilariae in the bloodstream allowing another female mosquito to get infected during subsequent blood meal and spread the parasite. (Dantas-Torres, 2023) (Bowman & Atkins, 2009) Although canines are known to be the definitive hosts, dirofilariasis can also occur in cats. Heartworm infection in cats are more severe and fatal just being caused by few filariae. (Noack, Harrington, Carithers, Kaminsky, & Selzer, 2021) Other canine hosts include coyotes, gray wolf , red fox, gray fox and maned wolf. (Bowman & Atkins, 2009) dirofilariasis has wide distribution globally, nevertheless is more prevalent in the temperate and tropical regions. (Tahir, Davoust, & Parola, 2019) Treatment regimen in infected dogs usually include prolonged dose of adulticide eg; melarsomine, exercise restriction and in rare cases surgical removal of adult worms. With the limited availability of melarsomine in several regions around the world, a less effective and controversial “slow- kill” protocol has been proposed. (Noack, Harrington, Carithers, Kaminsky, & Selzer, 2021) (Dantas-Torres, 2023) With the discovery of the endosymbiont Wolbachia in D. immitis and the detrimental effects of tetracyclines against it. Several combination therapies and preventative protocols with macrocyclic lactones and melarsomine have been devised. (Bowman & Atkins, 2009)