Haemogregarines in Reptiles and Amphibians

Chris Faggioni, DVM; Kenneth S. Latimer, DVM, PhD; Bruce E. LeRoy, DVM, PhD; Frederick S. Almy, DVM, MS, Dipl ACVP; Kung-Il Kang, DVM

Class of 2006 (Faggioni) and Department of Pathology (Latimer, LeRoy, Almy, Kang) College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7388

Introduction

Haemogregarines are apicomplexan intracellular parasites which infect reptiles and amphibians. They are the most common intracellular blood parasite in reptiles with over 300 species described.¹ These parasites typically infect erythrocytes (RBC) and, to a lesser extent, leukocytes of the intermediate host.² Currently, six genera of haemogregarines have been identified that infect the RBCs of the intermediate vertebrate host while having a hematophagus definitive invertebrate host.³ Of these six genera, four are known to infect reptiles and amphibians. The genera that infect reptiles and amphibians include Haemogregarina, Hemoliva, Karyolysus, and Hepatozoon (Table 1). The other two genera, Desseria and Cyrilia, are thought to infect fish and leeches exclusively. Each genus is distinguished in part by its life-cycle within the various host species. For example, the genus Karyolysus has only been shown to infect lizards of the genus Lacerta and possibly scincids (skinks).¹ In contrast, the genus Haemogregarina has an almost exclusively aquatic life-cycle, infecting turtles and leeches.

Transmission

Unlike mammalian transmission of intraerythocytic parasites which typically occurs via a blood-sucking vector, the transmission of haemogregarines can be due to a blood sucking vector as well as ingestion of an infected host. The transmission of haemogregarines typically varies by genera and has not been elucidated for all of these organisms. Several of the genera are known to be transmitted by mites. Hepatozoon appears to have the most numerous invertebrate hosts including sucking lice, fleas, triatomid bugs, flies, mosquitoes, sandflies, tsetse flies, and acarina species such as ixodid and asgasid ticks and mites.⁴ Leeches have been suggested as another possible vector of Hepatozoon spp.³ It has even been suggested that congenital transmission of Hepatozoon spp. can occur in some snakes.⁴ Hemoliva spp. typically are transmitted via infected ticks that have either infested or been consumed by the vertebrate host. The leech is the definitive host for Haemogregarina sp. In contrast, members of the genus Karyolysus can be transmitted by either arthropods or leeches.⁴ Hepatozoon and Hemoliva are unusual in that they can be transmitted to snakes and lizards by the ingestion of other infected hosts such as amphibians and lizards.⁴ This fact may account for the ability of Hepatozoon to be transmitted to abnormal intermediate hosts.⁴

Table 1. Genera of haemogregarines that infect reptiles and amphibians as either intermediate or definitive hosts.

Diagnosis

Diagnosis of haemogregarine infection is usually accomplished by examination of Romanowsky-stained blood films. All of the infectious haemogregarines have a similar morphologic appearance of the organism within the RBCs. These organisms are typically straight to slightly curved with a central, eccentric or saddle nucleus (Figure 1). ¹ Heavily infected animals may have two or more parasites within a single RBC.² The RBC may have mild morphologic changes associated with infection such as a hypertrophied or macrocytic appearance with a displaced nucleus due to the presence of the protistans.¹ Wright’s stain can be used to differentiate haemogregarines from other hemoparasites such as Plasmodium sp. and Haemoproteus sp. Both Plasmodium sp. and Haemoproteus sp. have refractile pigment granules associated with the gametocytes of these organisms.² Although examination of the stained blood smear is the easiest method to diagnose infection by haemogregarine parasites, this technique cannot differientiate the various genera of haemogregarines. However, this distinction usually is of little clinical significance to the clinical veterinarian.⁴

Figure 1. Elongate to crescent-shaped haemogregarine parasites within the cytoplasm erythrocytes in Romanowsky-stained blood smears of a snake (left) and turtle (right) (Diff-Quik stain).

Pathogenesis and Pathologic findings

Unlike mammalian hemoparasites, haemogregarines in reptiles and amphibians generally do not cause significant clinical disease. Changes associated with haemogregarine infections may include displacement of hemoglobin within infected RBCs and mild dysproteinemia (alterations in serum or plasma proteins).¹ The meronts of haemogregarines may form cysts in various organs of the body including liver, spleen, kidney, and brain. These cysts may contain deposits of pigment or may be surrounded by inflammatory cells.^1,4 Many of the recent studies on host population effects of haemogregarine infection have been done using Lacerta vivipara lizards. One of these studies has suggested that haemogregarine infection may be responsible for deaths of some older Lacerta vivipara lizards in wild populations and cause a significant reduction in tail regeneration rate in parasitized lizards.⁴ In addition, environmental stress also can increase the intensity of haemogregarine infections in these lizards.⁵ Despite these observations, the overall effect of hemogregarine infection in wild populations of lizards is considered negligible at this time.

Treatment and Prevention

Currently, an effective treatment for haemogregarines does not exist. However, it is unlikely that a treatment protocol will be necessary based on the limited ability of haemogregarines to cause clinical disease. Prevention of parasitic infection can be achieved by acquiring reptiles and amphibians that are free of the parasite on blood smear examination and by using an appropriate food supply that will not introduce the parasite into the collection. This is especially important for the genus Hepatozoon that can be transmitted to abnormal host species. Proper insect control and routine quarantine measures also should be instituted so animals that are haemogregarine test-negative are not exposed to any haemogregarine test-positive animals the collection. Reptiles and amphibians also should be maintained in enclosures that reduce environmental stress by preventing overcrowding. This, in turn, may reduce the overall parasite burden of captive reptiles and amphibians.

In summary, haemogregarines are a common parasites of reptiles and amphibians. Parasitic infection can be diagnosed easily by microscopic examination of a Romanowsky-stained blood smear observing the presence of organisms within RBCs and/or leukocytes. However, if parasites are observed, they generally are considered benign and do not warrant treatment.

References

1. Fudge AM: Laboratory Medicine Avian and Exotic Pets. Philadelphia, W.B. Saunders Co., pp. 247-249.

2. Mader D: Reptile Medicine and Surgery 1^st. Philadelphia, W.B. Saunders Co., 1996, pp. 192-193,380-381.

3. Smith TG: The Genus Hepatozoon (Apicomplexa: Adeleina). J Parasitol 1996; 82:565-585.

4. Davies AJ, Johnston MRL: The biology of some intraerythrocytic parasites of fishes, amphibia and reptiles. Adv Parasitol 2000; 45:1-107.

4. Oppliger A, et al: Environmental Stress Increases the Prevalence and Intensity of Blood Parasite Infection in the Common Lizard Lacerta vivipara. Ecology Letters 1998; 1, pp 129-138.

Acknowledgement

Snake IV watercolor, goauche/paper by B.F. Postelis from the Pyramid Studios Art Gallery website and is used with permission.

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