Unlike Heartworm disease caused by Dirofilaria immitis and D. repens, a more rare filarial worm Dipetalonema reconditum differs in primarily infecting the subcutaneous regions of the cat rather than the heart. Historically, confusion arose in dogs when blood tests used to visualise the presence of larval stages (microfilaria) could not distinguish between these two filarid worm. D. reconditum is relatively harmless to cats and has only rarely been reported as an incidental finding on autopsy.
D. reconditum is a global parasite that is found wherever mosquito reside. This parasite differs dramatically to other filarids in that:
- it is usually transmitted by fleas, lice (Heterodoxus spiniger) and ticks (Ixodes spp) rather than mosquitoes.
- adult D. reconditum reside in connective tissue rather than the heart
The flea ingests a microfilaria when feeding on an infected dog. The microfilaria develops into an infective larva in 7 to 14 days. Microfilariae are 215 to 270 um in length, and are 4.7 to 5.8 um wide. When the flea again feeds on a dog the infective larva is injected into the skin. The larva develops to the adult stage in the connective tissue of the dog’s skin. The female worm lays microfilariae which find their way into the blood. The prepatent period is about 61 to 65 days.
Humans are dead-end hosts for this parasite, but the developing larvae can cause pathologic changes where they reside in connective tissue throughout the body. D. reconditum has been reported recently in a human eye. Control of zoonotic filariae in the canine and feline reservoirs would be of great veterinary interest and could contribute to a decrease in human cases.
It is difficult to distinguish D. immitis from D. reconditum in canine blood smears because of the similarity in their morphology and PCR tests are now available. Such tests are moot in cats since the likelihood of circulating larvae in feline blood is extremely unlikely. In dogs, routine diagnosis is carried out through microscopic examination of the morphology of and/or cellular distribution in microfilariae isolated from blood or skin snips, or use of ELISA assays now available as ‘in-house’ tests at most vet clinics. PCR identification of D. reconditum is also available for research purposes.
Successful preventative treatment occurs when routine monthly ivermectins are used. Anecdotal reports of adulticidal therapy using ivermectins to kill adult Dipetalonema spp is unavailable. Control of fleas, ticks and lice seems warranted.
- ↑ Lindemann BA, McCall JW. (1984) Experimental Dipetalonema reconditum infections in dogs. J Parasitol 70(1):167-168
- ↑ Holmes PR, Kelly JD. (1973) The incidence of Dirofilaria immitis and Dipetalonema reconditum in dogs and cats in Sydney. Aust Vet J 49(1):55
- ↑ Casiraghi M, Bazzocchi C, Mortarino M, Ottina E, Genchi C. (2006) A simple molecular method for discriminating common filarial nematodes of dogs (Canis familiaris). Vet Parasitol 141(3-4):368-372