MadSci Network: Zoology |
“Heartworm” is the common name given to the nematode _Dirofilaria immitis_ of the Class Filarioidea. All filarids are thin, long worms (“philum” in Latin means “thread”) and are transmitted by insect vectors. Dirofilaria infects mostly dogs, but other animals like cats, foxes or wolves can also become infected. Man is an occasional (accidental) host. The insect vectors are mosquitoes of the genus _Aedes_ or _Anopheles_, which transmit infective larvae when they obtain a blood meal. The larvae go into the conective tissues where they mature into young adults. These worms go into the bloodstream and via the venous circulation reach the pulmonary arteries. There they mature to sexually active males and females and copulate. Filarids, unlike other roundworms (nematodes) do not lay eggs. Instead, the female releases from the uterus embryos known as microfilariae. These microfilariae reach the bloodstream and when another mosquito obtains a boodmeal, they are sucked into the insect’s gut. Inside the mosquito, microfilariae undergo changes until they molt into infective larvae after several weeks. The presence of adult worms in the pulmonary arteries can cause inflammatory changes in the walls of these blood vessels, which can lead to partial occlusion of them. This in turn can produce pulmonary hypertension, which in turn can cause hypertrophy of the right ventricle of the heart and subsequent heart failure. The inflammatory changes can also disrupt the blood flow and thrombi can be produced. These can embolize to the lungs and other organs. Additionaly, very heavy infections produce large accumulations of adult worms in the pulmonary arteries and the right ventricle, leading to mechanical obstruction and failure.of these organs. In conclusion, heartworms will cause death because of the severe cardiovascular changes that they will induce in the host. http://math.smith.edu/~sawlab/fgn/pnb/diro.html http://cal.vet.upenn.edu/parasit/heartworm/hw_1.html http://www.biosci.ohio-state.edu/~parasite/dirofilaria.html
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