Parasitic Diseases of Reptiles
A limited number of ectoparasites are seen, except on wild and newly acquired reptiles. Mites are distributed worldwide, and most reptilian species can be affected. Reduced vitality and, in heavy infestations, death due to anemia or bacterial or viral infection may occur. Skin of affected reptiles appears coarse, and dysecdysis is frequent. The common snake mite (Ophionyssus natricis) and lizard mite (Hirstiella spp) are generally <1.5 mm long and are often found around the eyes and skin folds, which should be examined carefully. Mites may also be associated with mechanical transmission of Aeromonas hydrophila, a variety of other bacteria, rickettsial agents, and viruses. Mites are visible to the naked eye but are hard to see in small numbers. If mites are suspected, gently rubbing the reptile while it is standing over a piece of white paper will allow the mites to be seen after they have fallen off. Affected reptiles often spend an inordinate amount of time soaking to drown the mites. Examination of the water dish can reveal the drowned remains of many mites.
There are many methods of treatment; however, a permethrin is specifically licensed for use in reptiles, whereas ivermectin is also frequently effective in squamates.
Ticks are common on free-ranging or imported reptiles or those kept outside, and heavy infestations may result in anemia. Argasid ticks may cause paralysis, with muscle degeneration at the site of the bite. The transmission of green-lizard papilloma–associated virus, several hemogregarines, and the filarid worm Macdonaldius oscheri have been associated with ticks. Ticks can transmit Ehrlichia ruminantium, the cause of heartwater, and consequently the importation of African reptiles has been controlled. Ticks can be removed manually or by using permethrin spray. Systemic antibiotics may be indicated because of systemic infections associated with multiple cutaneous bite wounds and, potentially, with transmission of pathogenic bacteria.
Leeches have been found on the legs, head, neck, and in the oral cavity of a variety of turtles and crocodilians.
Chelonians housed outside are at risk from cutaneous myiasis. Bot flies (including Cuterebra sp) create a cutaneous wound in which to lay their eggs, which hatch into bots that live in cyst-like structures until mature enough to leave the wound. These lesions are characterized as a lump under the skin; on closer inspection, they have an opening often lined by a black, crusted material. Treatment consists of slightly expanding the natural opening and manually removing the bot with a forceps. The wound is then flushed with povidone-iodine or chlorhexidine, and an antibiotic ointment is instilled. Systemic antibiotics are rarely indicated unless local or systemic infection is confirmed. Cutaneous myiasis also occurs secondary to existing wounds, and maggots must be manually removed and the underlying lesion treated with topical and, if indicated, systemic antibiotics. During heavy fly seasons, turtles are often housed indoors or with screens over their enclosures to offer some protection.
Ectoparasite infestations are best prevented by thorough screening and quarantine of all new animals entering a collection.
The stress of captivity coupled with a closed environment predisposes to potentially heavy burdens of parasites with direct life cycles. Every effort must be taken to appropriately screen and treat reptiles in quarantine before entering a collection. Parasites with complex life cycles are rarely an issue for reptiles kept indoors because of the lower incidence of intermediate hosts. It is important to differentiate between true parasites of reptiles and pseudoparasites (parasites of prey animals that are simply translocating through the reptile's GI tract).
Pathogenic trematodes (spirorchids) infect the vascular system of turtles and infect the oral cavity, respiratory system, renal tubules, and ureters of snakes. Chemotherapeutic agents have not effectively eliminated these parasites, although praziquantel 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, repeated in 2 weeks. 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 washes. Embryonated ova and free larval forms may also 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.
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 intestinal 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 intestinal tract; they may abscess and perforate the alimentary 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 are fed. 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 reduce parasite burdens in captivity.
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 hours. 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 venomous snakes; however, they have also been identified in various lizards. No truly effective treatment has been reported, but praziquantel and ivermectin have been shown to reduce ova numbers being shed but have not always eliminated the adults. As relatively large parasites, death of many worms may result in severe antigenic effects. The most novel approach has been to endoscopically locate and mechanically remove all the adult pentastomes. Recognition of pentastomal infestations is important, because these parasites are thought to present a zoonotic risk.
Numerous protozoans are found in reptiles; most are harmless commensals. The most serious protozoal pathogen of reptiles, especially snakes, is Entamoeba invadens. Clinical signs are anorexia, weight loss, vomiting, mucoidal or hemorrhagic diarrhea, and death. Entamoebiasis may be epidemic in large snake collections. Herbivores appear less susceptible than carnivores; a number of reptiles that seldom become affected or die can serve as carriers, including garter snakes, northern black racers, and box turtles. Although most turtles are more resistant, the giant tortoises are susceptible. Other resistant groups include eastern king snakes, crocodiles, and cobras (possibly as an adaptation that allows them to eat snakes). Most boas, colubrids, elapids, vipers, and crotalids are highly susceptible. Transmission is by direct contact with the cyst form. Hepatic abscesses containing numerous E invadens trophozoites are common in chronic cases. At necropsy, gross lesions may extend from the stomach to the cloaca. The intestines tend to show areas of ulceration, caseous necrosis, edema, and hemorrhage. Multifocal abscesses in a swollen, friable liver are seen in the hepatic form. Identification of trophozoites or cysts in a wet preparation of fresh feces or tissue impressions, or in histologic sections, is diagnostic. Turtles and snakes should not be housed together.
E invadens is best treated with metronidazole. Tetracycline and paromomycin have been used but are considered ineffective against the hepatic form. Strict sanitation and hygiene measures should be observed.
Flagellates, especially Hexamita spp, have been reported to cause urinary tract disease in chelonians and intestinal disease in snakes. The “Giardia” seen in some cases of enteritis in snakes may actually be Hexamita or one of the relatively nonpathogenic flagellates that inhabit the intestinal tract of snakes. Differentiation between the species requires expertise, and special preservatives and stains are required to identify most of these organisms. Metronidazole has been used to treat flagellates. Indigo snakes, king snakes, and uracoan rattlers have exhibited neurologic disease with high doses. Early studies with benzimidazoles are very encouraging and should also be considered as a viable therapy.
Several coccidial organisms have been reported: Klossiella from the kidney, Isospora from the gallbladder and intestine, and Eimeria from the gallbladder. Intranuclear coccidiosis is a major tortoise pathogen, especially in Old World tortoises. It tends to be multisystemic, infecting epithelial cells, and can be associated with lymphoplasmacytic or mixed inflammation and variable necrosis and epithelial hyperplasia. Clinical findings are nonspecific and may include anorexia, lethargy, weight loss, emaciation, weakness, diarrhea, ocular and nasal discharge, ulcers of the oral or GI mucosa, respiratory distress, swollen erythematous vent, and ascites. The course of disease is often rapid, and mortality rates are high.
The severity of disease varies with the coccidia and affected species. Because of their direct life cycle, these parasites can increase to tremendous numbers, especially in immunosuppressed reptiles. Oocysts are not fragile and can survive for weeks in a dessicated condition. Fastidious, daily cleanings are necessary to remove all feces and feces-contaminated food and water. Insects and other food items must be removed on a daily basis, because they are another source of contamination (eg, crickets may eat the oocysts while gathering fluid from the feces).
Persistent treatment using sulfadimethoxine is required until infection is resolved, often taking 2–4 weeks; success should be measured by serial fecal samples. Trimethoprim-sulfa is another useful drug to treat coccidia. Care should be taken when using sulfa in reptiles with dehydration or renal compromise. If in doubt, a balanced electrolyte solution should be administered PO at appropriate dosages. Even under the best conditions, treatment is seldom 100% effective. Treatment resulting in a reduction of coccidia is still important, and coccidial numbers should be periodically monitored.
Cryptosporidiosis is frequently reported in association with postprandial regurgitation (snakes, Cryptosporidium serpentes), diarrhea (lizards, Cryptosporidium saurophilum), marked weight loss, and chronic debilitation. The organism affects the GI mucosa, resulting in marked thickening of the gastric rugae and loss of segmented motility. A mass in the gastric region is often, but not always, palpable in snakes, and contrast radiographs or endoscopic examination reveals rugal thickening. Many lizards, including Old World chameleons, leopard geckos, and savannah monitors, are affected primarily in the intestine. Mucosal thickening develops as a result of invasion by numerous cryptosporidial organisms. Diagnosis can be made using acid-fast stains on fresh feces or on the coating from regurgitated items or endoscopic gastric biopsies, which will identify the tiny oocysts. Although several treatments have been suggested, none (except for hyperimmune bovine colostrum) have been especially effective. Intensive supportive care will often stabilize and help prolong the life of the affected reptile. Euthanasia is a valid option for diseased reptiles. Cryptosporidiosis was previously considered a zoonotic disease; however, it now appears that the species commonly found in reptiles do not affect mammals.