Thursday, October 23, 2014

Shot Through The Heart

A nematode? Can shoot through a heart? Yes. And it will definitely give love a bad name. 


Heartworms are a parasitic nematode and their scientific name is  Dirofilaria immitis. Listed Below is their taxonomy (Nolan 2004):

Kingdom: Animalia
                 Phylum: Nemathelminthes
        Class: Nematoda
                Order: Spiruda
                          Family: Filariidae
                                Genus: Dirofilaria


Canine heartworms are long, white skinny worms. They have a cuticle that has 3 outer layers to help protect them when they invade their hosts (Nolan 2004, Encly of Life 2011). Adult males can be 12 to 16 cm in length and have a curly posterior. The adult females are much larger, having lengths up 25 to 30 cm and have a straight posterior (Encly of Life 2011). 



Heartworms are a special parasite that require two different hosts to survive. The first host they need is called an intermediate host, and it has to be a mosquito. One study from 1970 had already identified over 60 species that served as intermediate hosts, also called a carrier or vector. The second host they need is called the definitive host, also known as the primary hosts. This definitive host can be dogs, cats, foxes, wolves, seals, coyotes, horses, bears, raccoon, wolverines, muskrats, and red pandas (Encly of Life 2011).

Life Cycle

Mature heartworms in the primary hosts lay microfilaria in the blood stream of their hosts. These microfilaria are the embryonic stages of the larvae. When a mosquito bites and eats blood from the host, it ingests these microfilaria and becomes their first host. These larvae stay in the mosquito for the first 3 larval stages, which takes about 14 days, and then they start waiting for the mosquito to bite a primary host, where they will enter through the mosquitoes bite (Nolan 2004). These microfilaria have been known to stay in a mosquito for 2 years waiting for it to bite a compatible primary host (Encly of Life 2011). After entering the primary host, they work their way towards the heart area. Heartworms do not mature until they are in the pulmonary tissue of their host, including major arteries and heart tissue (Nolan 2004). Once in the pulmonary tissues, they stay here for mating and until death. 

Heartworms cause heartworm disease, Dirofilariasis, by clogging the arteries and damaging the heart tissue of their host. Once a host has contracted heartworms, it is nearly impossible to get rid of them. Major effects of heartworm disease include coughing, exhaustion, fainting, severe weight loss, and coughing up blood (CDC 2012).


Heartworms, especially canine heartworms are fairly common around the world. They are literally found every where in the world with the exclusion of places that are relatively cold year round. To be more specific, these worms like temperate, tropical, coastal areas, and terrestrial places for living. They can be found in deserts, rainforests, swamps, lakes, savannahs, woodlands. Known regions of existence are Southern Europe, India, China, Japan, Australia, North America and South America (Encly of Life 2011).


The larvae of these nematodes eat different components of the mosquito, such as the malipighian tubes, and things in the blood the mosquito eats. As adults, the worms then feed on the blood of their hosts. 

Scary Fact: These worms have NO KNOWN PREDATORS (Encly of Life 2011). 

Testing for Heartworms

There are a few different tests that can be used to detect heartworms in a definitive host. Some of the techniques include a blood smear, antigen and antibody tests, and an ultrasound (Nolan 2004). Many times heartworms can do undectected, because after the initial infection, it takes about 200 days for microfilariae to be detected in the blood stream (Nayor and Conelly).

Here is an example of a microfilarae in a blood smear:


Center for Disease Control and Prevention. (2012). Dirofilariasis FAQs. Received from:

Encylcopedia of Life. (2011). Dirofilaria immitis: Heartworm. Received from:

Ludlam K, Jachowski L & Otto G. (1970). Potential Vectors of Dirofilaria immitis. Journal of the American Veterinary Medical Association. Vol 157 p: 1354-1359.

Nayor J and Connelly C. Mosquito-Borne Dog Heartworm Disease. SP 134: Pests in and around the Florida Home. University of Florida. Received from:

Nolan. (2004). Dirofilaria immitis Homepage. Received from:

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