Dracunculus Infections in Animals

Dracunculus insignis, also known as the Guinea worm, is found mainly in subcutaneous connective tissues of the legs in raccoons, mink, and other animals, including dogs and cats, in North America and possibly other parts of the world. River otters have their own species of guinea worm, called Dracunculus lutrae, which appears to infect only otters.

D insignis females are much longer (≥ 275 mm; see adult female image) than males (approximately 20 mm). They produce ulcers in the skin of their host, through which they protrude on contact with water. Females produce characteristic long, thin-tailed larvae.

Dracunculus insignis, adult female

Image

Courtesy of Dr. Liandrie Swanepoel.

Copepods are the intermediate host in which infective D insignis larvae develop. Dogs become infected through ingestion of contaminated water, paratenic hosts (frogs), or, potentially, fish. The parasite has a 1-year prepatent period, and some evidence suggests that infection by D insignis can lead to a false-positive result on a heartworm (Dirofilaria immitis) antigen test, presumably because of cross-reaction between D insignis antigens and the ELISA. D insignis antigens may have a similar binding region as the female uterine antigen of D immitis, causing the heartworm ELISA to produce a false-positive result.

D insignis infection is characterized by subcutaneous, serpentine, inflammatory tracts and nonhealing, craterlike, edematous skin ulcers. Infections are rare but occasionally occur in animals that have spent time near small lakes and bodies of shallow, stagnant water.

D insignis infection is treated via careful, slow extraction of the parasite (see extraction image). Administration of benzimidazole compounds can be useful in that they can lessen inflammation and decrease the duration of disease.

Dracunculus insignis extraction

Image

Courtesy of Dr. Liandrie Swanepoel.

Antimicrobials are recommended for dogs infected with D insignis to decrease the chance of secondary bacterial infections. In addition, anti-inflammatories and antihistamines can be useful to prevent immune system reactions. The effectiveness of anthelmintics in decreasing worm burdens is incompletely known; further research is needed to determine the efficacy, if any, of these products.

Dracunculus medinensis, the Guinea worm of parts of Africa, Asia, and the Middle East, although primarily a parasite of humans, is also found in dogs and other animals.