Dracunculus spp.
(Figure 4-44)
The species of Dracunculus (Draco = snake or serpent) that has been reported from cats has often been identified asDracunculus medinensis (Linnaeus, 1758) Gallandat, 1773. This worm was known to the ancients of Medina in Arabia as being the cause of lesions in the feet and ankles of humans. One of the earliest cases recorded from the domestic cat is that of Sonsino (1889). Due to great strides in providing clean water and mass chemotherapy programs, the distribution of human infections with Dracunculusmedinensis is rapidly shrinking, bordering on extinction. Due to humans being the major host for this parasite, the areas of the world where infections in cats might be expected is also rapidly diminishing. Left around the world are only a few sites in Northern Africa, the Near East, and parts of India and Pakistan.
The females of these species are large white worms that are typically seen protruding from a blister on the leg or foot of the host (Fig. 4-44). Identification is readily made by putting a drop of the exudate on a glass slide with a little water and seeing the 600 μm long larvae with their long tails swimming about. For purposes of determining whether a cat is infected with Dracunculusmedinensis or Dracunculusinsignis, the easiest means of identification will be by the geographic range of these parasites. Dracunculusmedinensis being found in the Old World, and Dracunculusinsignis being found only in the America. Of course, if the cat has traveled, and hunted during its excursions, it will be very difficult to determine the identity of the worm causing the infection. Also, around the world, there are probably still to be described species of Dracunculus of wild animals that may also find their way into domestic cats, thus, it is highly likely that a specific specimen recovered from a cat will on most occasions not be capable of being assigned a certain specific name.
The female nematode lives under the skin, and gains access to the outside through a blister in the skin. The typical site of the blister is on the legs. From the blister, the female slowly protrudes and releases first-stage larvae from her degenerating body into the environment. If released into water, the first-stage larvae move actively and are eaten by copepods. Within the copepod, the larva develops to a third-stage larva which is infective to the final host. The final host becomes infected by drinking water containing infected copepods. Once ingested, the larvae penetrate the intestinal mucosa and make their way to the thoracic and abdominal muscles. By 43 days after infection, they have made their way to the subcutaneous tissues, and sometime soon thereafter undergo the final molt to the adult stage. The males only reach a size of 1 to 3 cm, but the females reach lengths of up to 80 cm. The males seem to die within 6 months after infection, but the females move to the extremities between 8 to 10 months after infection. After moving to the extremities, the females induce the blister from which the larvae are released. Thus, the entire cycle takes about one year to reach completion.
Using a species that commonly occurs in North America in the raccoon, Dracunculus insignis (Leidy, 1858) Chandler, 1942, Crichton and Beverley-Burton (1977) and Eberhard and Brandt (1995) have shown that this species is capable of using tadpoles as paratenic hosts. After the tadpoles are infected, it is possible to ultimately recover infective larvae from the adult frogs that develop. The larvae recovered from the adult frogs were shown capable of infecting ferrets. Thus, with this species and potentially other members of this genus, it is possible that cats might be infected by the ingestion of a paratenic host.
There have been almost no cases of Dracunculus described from naturally infected cats. Muller (1968) described cases in experimentally infected cats and found a single adult female emerging from the leg of one of seven cats that had been infected 3653 days previously, but no larvae were recovered from this worm. Young stages were found in three cats upon dissection. Chun-Siun (1966) reported on a case of dracunculosis in a cat in Kazahkstan. A second report of Dracunculus from cats in Kazakhstan was made by Genis in 1972. Hsu and Li (1981) reported on Dracunculus in a cat in Guandong, China.
Ivermectin has been very successful in the treatment of human cases of dracontiasis, and it is likely to prove just as efficacious in cats.
REFERENCES:
Chun-Siun F. 1966. Med Parazit Parazitar Bolezni 35:374-375 [Russian]
Crichton VFJ, Beverly-Burton M. 1977. Observations on the seasonal prevalence, pathology and transmission of Dracunculusinsignis (Nematoda: Dracunculoidea) in the raccoon (Procyonlotor (L.)) in Ontario. J Wildl Dis 13:273-280.
Eberhard ML, Brandt FH. 1995. The role of tadpoles and frogs as paratenic hosts in the life cycle of Dracunculus insignis (Nematoda: Dracunculoidea). J Parasitol 81:792-793.
Genis DE. 1972. New cases of Dracunculusmedinensis infection in domestic animals (cats and dogs) in Kazakhstan. Med Parazit Parazitar Bolezni 50:365.
Hsu & Li. 1981. Annals Bull Parasit Soc Guandong Province. 3:
Muller RL. 1968. Experimental dracontiasis in animals. Parasitology 58:7p-8p
Sonsino P. 1889. Studie e notizie elmintologiche. Atti Soc Tosc Sc Nat Proc Verb 6/7: 273-285.
FIGURES
Figure 4-44. Dracunculusinsignis emerging from the leg of a naturally infected dog.