"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

January 21, 2010

January 21 - Dirofilaria immitis

Heartworm, Dirofilaria immitis, is a filarial nematode parasite that usually infects dogs or other canines, but can also infect cats, foxes, ferrets, and sea lions. The adult worms live in the right ventricle of the heart, hence their common name. After the adults mate, they produce microscopic larvae known as microfilariae, which are ingested by mosquitos when they bite the mammalian host. The larvae complete their development in the mosquito and then are transmitted to a new host when she feeds again. Although most dogs do not show signs of infection, in some cases worms can cause issues and need to be treated. However the treatments are sometimes risky because the dead worms can get carried to the lungs and cause respiratory distress or failure. Preventative therapies, such as giving dogs the drug ivermectin, are effective and safe. Heartworm are also hosts to the endosymbiotic bacteria, Wolbachia (see January 12th).

Image from this website.


  1. Can immitis survive absent Wolbachia? What's the nature of the endosymbiosis? What beneficial effect (antiviral or otherwise) does Wolbachia exert that allows it to insinuate itself so readily in so many species?

  2. Yes, D. immitis can survive without Wolbachia. Some studies have shown that the bacteria may contribute to the pathology of the heartworm in dogs, however. Similar results are now known from some of the Wolbachia-infected human filarial worms as well. For lots more information, I suggest this recent review done by Jack Werren and colleagues.

  3. Thanks for the link, Sue! But I don't think the article's available to the public :-(

  4. No, it is not published in an open-access journal.

  5. Jack Werren's website has a lot of info and some links to publications, including one to his older review on Wolbachia.