ANFS332 Lecture Notes - Lecture 26: Microfilaria, Filarioidea, Hematophagy
4 Feb 2020
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➢ Heartworm - Dirofilaria immitis
○ Heartworm
■ Heartworm is caused by a roundworm
● Dirofilaria immitis
○ Example of filaria or small thread like worm
■ Leading host is the dog but it can also infect cats, wolves, coyotes,
raccoons, and foxes
■
○ Life Cycle-I
■ Dirofilaria immitis is dependent on both the canine and the mosquito to
fulfill its lifecycle.
■ In an infected dog the adult worms live in the dog's heart and lungs.
■ The adult worms mainly live in the chambers of the right side of the heart
and pulmonary artery.
■ Individual eggs developing in the uterus (of the worm) are enclosed in a
thin membrane. As the embryo elongates, the surrounding membrane
stretches to form an enclosing sheath. At birth, the membrane is lost and
the embryo appears in the blood as a sheathless microfilariae.
○ Life Cycle-II
■ The young worms called microfilariae circulate in the bloodstream of the
dog. These worms must infect a mosquito in order to complete their life
cycle.
■ Mosquitoes become infected when they blood feed on the sick dog.
Once inside the mosquito, the microfilaria leave the gut of the mosquito
and live in the body of the insect.
■ First, they migrate from the intestine, within 24 to 36 hours, into the
insect version of kidneys, where further development and a molt from the
first to the second stage juvenile occurs.
■ After 9 days they enter the abdominal hemocoel, where the second molt
occurs.
■ Third stage larvae are about 900 um long and appear 10 to 20 days after
entering the mosquito.
■ After transforming twice in one mosquito the third stage infective larvae
move to the mosquito's mouth parts, where they will be able to infect an
animal.
■
■
○ Life Cycle- III
■ When the mosquito blood feeds, the infective larvae are deposited on the
surface of the skin.
■ The larvae enter the skin through the wound caused by a mosquito bite. If
the worms have infected an unsuitable host such as a human the worms
usually die at this point.
■ The worms burrow into the skin where they remain for 3-4 months and
continue to mature. The fourth stage juveniles attain lengths up to 25 mm.
■ They begin entering the right side of the heart shortly after the fourth molt
60 to 70 days after entering the dog.
■ Development to maturity with males 14 to 19 cm long and females 23 to
31 cm takes 174 to 223 days, at which time microfilariae appear in the
blood. The reproductive period exceeds 2 years and may extend to 5.
Document Summary
Example of filaria or small thread like worm. Leading host is the dog but it can also infect cats, wolves, coyotes, raccoons, and foxes. Dirofilaria immitis is dependent on both the canine and the mosquito to fulfill its lifecycle. In an infected dog the adult worms live in the dog"s heart and lungs. The adult worms mainly live in the chambers of the right side of the heart and pulmonary artery. Individual eggs developing in the uterus (of the worm) are enclosed in a thin membrane. As the embryo elongates, the surrounding membrane stretches to form an enclosing sheath. At birth, the membrane is lost and the embryo appears in the blood as a sheathless microfilariae. The young worms called microfilariae circulate in the bloodstream of the dog. These worms must infect a mosquito in order to complete their life cycle. Mosquitoes become infected when they blood feed on the sick dog.
