Dracunculus insignisin a Texas cat
By Mindy Borst, LVT and Thomas Craig, DVM, PhD, DACVM
With over 800,000 tests run annually, TVMDL encounters many challenging cases. Our case study series will highlight these interesting cases to increase awareness among veterinary and diagnostic communities.
An 8-year-old spayed domestic short haired cat from east Texas presented to the veterinarian for a lesion on the right hip. When the lesion was shaved, a worm presented itself and was extracted. The worm was submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL), where it was identified as Dracunculus insignis.
Dracunculus insignis, more commonly known as the guinea worm, is a helminth most frequently transmitted through the ingestion of drinking water containing infected copepods i.e. small aquatic crustaceans or “water fleas”. Wild and domestic animals may also contract the parasite by eating other infected animals, such as frogs, snails, or snakes, which may act as paratenic hosts. After ingestion, Dracunculus larvae penetrate the gut and begin to invade the subcutaneous tissues, migrating mainly to the axillary regions. The prepatent period from ingestion of the parasite to the release of larvae from the adult female worm is 10 – 14 months, during which time she may reach between 30 and 120 cm in length. Males are much smaller, approximately 2 cm in length, are shorter-lived than females, and usually do not cause any clinical signs. Despite the mature female worm’s large size, there are typically no clinical signs of note until she protrudes her anterior end from the skin; this causes edematous, sometimes draining, ulcers which often fail to heal on their own. When completely submerged in cool water, the adult female worm’s uterus will prolapse, releasing hundreds to thousands of first stage larvae into the water for copepods to eventually ingest, thus perpetuating the cycle.
Infections with Dracunculus insignis are generally rare in domestic animals, and dogs appear to be represented most often in documented cases. According to the American Association of Veterinary Parasitologists (AAVP), feline cases are exceedingly rare, with only a handful of published cases available. If Dracunculus insignis is suspected, the adult female worm may be slowly and carefully extracted, placed in ethanol or formalin for preservation, and submitted to TVMDL for parasite identification. It is also possible to hold a small vial of cool water over the suspected lesion to stimulate the release of first stage larvae, which can be microscopically identified in the sediment after centrifugation.
To learn more about this case, contact Mindy Borst, licensed veterinary technician in the Clinical Pathology section at the College Station laboratory or Dr. Thomas Craig, TVMDL parasitologist. For more information on TVMDL’s test offerings, visit tvmdl.tamu.edu or call 1.888.646.5623.
Close-up of a female Dracunculus insignis worm; note the uterus filled with numerous first stage larvae.
References
Helminths of the Skin. (2016). In The Merck Veterinary Manual (11th ed., p. 904). Kenilworth, NJ: Merck & Co.
Nematodes That Infect Domestic Animals. (2012). In Diagnostic Parasitology for Veterinary Technicians (4th ed., pp. 48-49). St. Louis, MO: Elsevier.
Bowman, A. (2014, June 17). Dracunculus spp. Retrieved April 15, 2018, from http://www.aavp.org/wiki/nematodes/spirurida/dracunculoidea/dracunculus-spp/