Párasitos del Corazón -
Dirofilaria immitis
Dirofilaria immitis, the dog párasitos del corazón, is a nematode classified as a member of the
superfamily Filarioidea and the family Onchocercidae. It is a large, whitish worm.
The females are approximately 30cm long,
while the males are 23cm long with a
spirally coiled tail. Adults are primarily found in the
right ventricle and pulmonary arteries of dogs. After reproduction, the females produce
small, vermiform embryos called microfilariae. They can
cross the capillary beds and so are found throughout the vascular circulation.
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The Life Cycle:
Circulating microfilariae are ingested by a female mosquito while taking a bloodmeal from an infected host (A). Over 60 species of mosquito are capable of functioning as intermediate hosts. These prelarval stages migrate to the Malpighian tubules of the mosquito vector where development, involving two molts after the microfilariae differentiate into first stage larvae, will continue to the third stage (L3) larva (B). These infective L3's migrate from the tubules to the lumen of the labial sheath in the vector's mouthparts.
Development in the mosquito is temperature dependent, requiring approximately two weeks of temperature at or above 27C (80F). Below a threshold temperature of 14c (57F), development cannot occur, and the cycle will be halted. As a result, transmission is limited to warm months, and duration of the transmission season varies geographically.
During a later bloodmeal on an appropriate host (C), the L3 will exit the labium, enter the bite wound, and penetrate local connective tissues. Molting to the L4 ensues within seven days of infection (D). L4 stages undertake extensive migration through the subcutis, which continues for some 60-90 days until the final molt to the immature adult (E). The juvenile worms migrate to the right heart within a few days of their final molt (F), presumably carried by the venous circulation.
Final maturation and mating occur in the pulmonary arteries, and the adult worms live
in the right heart and pulmonary arteries, where they
may survive for up to seven years. Production of microfilariae by inseminated female worms
begins approximately six and a half months (192 days) after infection. Microfilariae are
then released into the circulation, for a mosquito to ingest during a subsequent blood
meal.
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