Endoparasites - The Merck Veterinary Manual

Endoparasites

The stress of captivity coupled with a closed environment predisposes to a heavy internal parasite burden in reptiles. Many common endoparasites of reptiles have direct life cycles and can multiply to staggering numbers. Every effort must be taken to rid reptiles of parasite burdens, and the environment of intermediate hosts.

Pathogenic trematodes infect the vascular system of turtles, and the oral cavity, respiratory system, renal tubules, and ureters of snakes. Chemotherapeutic agents have not been effective in eliminating these parasites, although praziquantel administered at 5-8 mg/kg, IM or PO, has shown some promise.

Tapeworms are found in all orders of reptiles but are rare in crocodilians. Reptiles may act as the definitive, paratenic, or intermediate hosts for a large number of species. Although most species of tapeworms are generally nonpathogenic in wild reptiles, weight loss and death have been reported. The complex life cycle of cestodes and restricted geographic range of intermediate hosts limit the number of cases in captive reptiles. When present, proglottids may be found around the cloaca, or typical cestode ova may be isolated from feces. Treatment is with praziquantel at 5-8 mg/kg, IM or PO, repeated in 2 wk. Plerocercoids of the genus Spirometra may be found as soft swellings in the subcutis. These larval stages may be removed surgically.

Nematodes are found in all orders of reptiles, and several genera are important. Strongyloides spp frequently inhabit the intestinal tract of reptiles; larvae are seen in the respiratory tract and respiratory exudate. In snakes, the larvae have been seen within granulomas distributed throughout the body wall, suggesting that the larvae may be able to penetrate the skin. Overwhelming parasitism is common when poor hygiene results in highly contaminated environments. Rhabdias and related species have been found in the lungs of a variety of snakes; embryonated ova may be found in the oral cavity and in lung aspirates. Embryonated ova and free larval forms may be seen in the feces. Larvae resembling Rhabdias also have been seen in the gingiva of snakes with stomatitis. Infections often are subclinical but may be associated with secondary bacterial pneumonia. In severe cases, death may result.

Rhabdias/Strongyloides larva in fresh feces

Embryonated ova characteristic of Rhabdias and Strongyloides, python

Hookworm (Kalicephalus spp) ova, chondropython

Stomach worms of the genus Physaloptera are seen in lizards. Gastric ulceration may occur in severe infections. Ova are elliptical and may be embryonated. Numerous snakes are infected by Kalicephalus spp . This hookworm, capable of transcutaneous infestation, prefers the upper GI tract and causes erosive lesions at sites of attachment. Ova are similar to those of Physaloptera spp . Large granulomas caused by the above species have also caused GI obstruction in snakes.

Ascarids frequently infect reptiles. Ova are similar to those of ascarids from mammalian hosts. Severe lesions and death may be seen in infected snakes. Clinically infected snakes frequently regurgitate partially digested food or adult nematodes and are anorectic. The major lesions are large granulomatous masses in the GI tract; they may abscess and perforate the intestinal wall.

Many other nematode species may be found in reptiles. Capillarid, trichurid, and oxyurid ova may be found on fecal examination. The nonpathogenic larval and oval forms of parasites of prey items (eg, Syphacia obvelata , the mouse pinworm) may be found when infected prey is consumed. Treatment should be attempted when evidence of parasitism is present.

Some larval forms of nematodes are suspected or confirmed to penetrate the skin (eg, Strongyloides and Kalicephalus ), bypassing the oral reinfection route. The subtle nature of reinfection by this route often goes unnoticed until the reptile is overwhelmed by parasites. Close attention to the immediate removal of excreta and fastidious sanitation help to reduce parasite burdens in captivity.

The drug of choice for treating nematode infections is fenbendazole at 10-25 mg/kg, PO, for 3-5 days. Administration is stopped for 10 days, and then the 3- to 5-day regimen is repeated. Administering fenbendazole on consecutive days is more effective than giving doses once every 7-10 days. If protozoans are to be treated concurrently, dosage may be increased to 50 mg/kg fenbendazole with the aforementioned regimen. When parasites are resistant to fenbendazole or have not been eliminated after 2 oral courses, the reptile can be treated with ivermectin at 0.2 mg/kg, PO, once every 7-10 days for 3 treatments. Fenbendazole has a much broader margin of safety than ivermectin and should be used first. Complications, from mild ataxia to paralysis and death, have been associated with the use of ivermectin, although it has been used safely in snakes and lizards at 0.2-0.4 mg/kg. In turtles, ivermectin toxicity (paresis) has been seen at dosages as low as 0.025 mg/kg; therefore, ivermectin is not recommended for use in turtles. Levamisole at 10-50 mg/kg via intracoelomic, IM, or SC injection, and at 200 mg/kg, PO, has been reported to be effective for Rhabdias spp . The margin of safety for levamisole is very narrow, and it should be used with caution.

Dermal lesions caused by the spirurid worm Dracunculus spp may be seen. Numerous species of spirurids infect the mesentery, coelomic cavity, and blood vessels. These worms require a mechanical vector, so their incidence is reduced in captive-bred reptiles or in reptiles that have been in captivity longterm. Treatment consists of increasing the environmental temperature to 95-98°F (35-37°C) for 24-48 hr. However, some “cool-adapted” reptiles may not tolerate this treatment.

Pentastomes are found in a wide variety of reptiles, with variable pathogenicity. Pentastomid infections are occasionally associated with pneumonic signs, but these primitive arthropods can inhabit any tissue and symptoms will vary with their migration path and tissues responses. Pentastomes were initially found primarily in tropical poisonous snakes; however, as more necropsies on reptiles were performed, more were found. Necropsy results from 88 bearded dragons showed that 11 were infested with pentastomes. No truly effective treatment has been reported, but praziquantel at dosages >8 mg/kg and ivermectin at 5-10 times normal dosages have been shown to reduce ova numbers being shed, but have not eliminated the worms. The most novel approach has been to endoscopically locate and mechanically remove all the adult pentastomes. Recognization of pentastomal infestations is important because these parasites are thought to present a risk of zoonotic infection. Euthanasia is a valid consideration due to public health concerns.