How pathogenic is this parasite?
A 4-month-old quarter horse colt was submitted for necropsy. Per submission history, the foal was behaving normally in the pasture the previous morning. Around 3pm, he was down and could not get up. His temperature was >108 °F, and although aggressive supportive care was initiated, the foal was found dead in his stall around 5pm.
No significant gross abnormalities were observed during the necropsy examination. The GI tract contents were watery and muddy, indicating diarrhea. A fecal sample was submitted for a diarrhea panel to determine if there were any viral, bacterial, or parasitic infections.
A centrifugal fecal flotation with Sheather’s sugar solution (specific gravity, 1.26) was performed, and a low number of strongyle type eggs were detected.
Histologic examination of the small intestine revealed a low number of intraepithelial protozoan gamonts (Figure 1).
Figure 1: Histologic examination of small intestine 200x magnification.
The pathologist on the case requested another fecal examination to confirm this protozoan infection. Another centrifugal fecal flotation was performed with saturated sodium nitrate solution (specific gravity, 1.39) and again showed a low number of strongyle eggs and additional protozoan oocysts (arrow) that were not evident on the first fecal flotation (Figures 2 & 3).
Figure 2: Centrifugal fecal flotation with saturated NaNO3 solution (specific gravity, 1.39) 100x magnification.
Figure 3: 200x magnification.
Eimeria leuckarti oocysts
Eimeria leuckarti is an intestinal coccidian parasite common in horses and donkeys. Oocysts are large and ovoid in shape (~ 80 x 60 microns) with a thick dark shell and distinct micropyle. Diagnosis can be challenging. Due to the heavy/dense oocysts, a sedimentation procedure has been recommended, or flotation with a higher specific gravity solution, as in the present case.
Infections appear to have minimal clinical significance in horses; however, it has been incriminated as a cause of intermittent diarrhea. In this case, rotavirus was detected by PCR, which was thought to be the primary cause of severe diarrhea, resulting in sudden death.
Special thanks to Dr. Rory Chia-Ching Chien, DVM, MSc, DACVP for sharing the case and a photo of the histologic examination.
Why did the snake cross the road?
A juvenile, rat snake was brought to a wildlife rescue in Oklahoma after being hit by a car. Due to poor prognosis, the snake was euthanized and sent to necropsy. Necropsy revealed a severe spinal fracture, which most likely occurred during the accident. Also, three partially digested mice were recovered from the gastrointestinal tract. A fecal sample from the snake was sent to the parasitology diagnostic lab, and a centrifugal fecal flotation was performed with Sheather’s sugar solution (specific gravity, 1.25). The following organisms were observed.
Figure 1: 200x magnification
Figure 2: 400x magnification
Psorobia (= Psorergates) simplex mites.
Psorobia simplex is also known as the “follicle mite of mice.” This is a small, round mite, and both adults and nymphs have four pairs of legs. Each tarsus terminates in a pair of simple claws and a pad-like empodium.
Natural hosts for this parasite are mice, although infestation of laboratory mice is now extremely rare. Infestation of mice with P. simplex is characterized by formation of small, distended, white-colored, nodules in the skin. These nodules are thought to form as a result of epidermal growth to accommodate internal pressure of space-occupying mites. All life stages of the mite are found inside these nodules.
In this case, these mites were found in the snake as a spurious parasite – The snake ate the mice, and the mites were just passing through the GI tract of the snake.
Baker. Flynn’s Parasites of Laboratory animals, 2nd ed. Pages 366-367.
Hop to it!
An approximately 6-year-old, intact female, mixed breed rabbit was euthanized after battling with the last stage of uterine adenocarcinoma and brought to necropsy. Besides confirming the adenocarcinoma, gross examination revealed some focal, irregular, depressed areas on the surface of the kidneys. On histologic examination, several spores were observed in the epithelial cells of the kidneys (Figures 1 & 2).
Figure 1: Spores indicated by arrow.
Figure 2: Spores indicated by arrows.
Encephalitozoon cuniculi is a spore-forming pathogen with worldwide distribution and has been isolated from various mammal species such as rabbits, shrews, mice, hamsters, muskrats, guinea pigs, goats, sheep, pigs, horses, domestic dogs, domestic cats, foxes, non-human primates, and man. Historically this pathogen was considered a protozoan parasite; however, due to its unique features, it is currently classified in the phylum Microsporidia. Infection occurs by ingestion or inhalation of spores shed in the feces, mucus, and urine of infected animals. Transplacental transmission has been also reported. Encephalitozoon cuniculi can cause granulomatous lesions in a wide range of tissues, but primarily affects the brain, kidney, or eyes. Most immunocompetent rabbits do not show any clinical signs; however, in some severe cases, granulomatous lesions associated with E. cuniculi can cause vestibular disease, chronic renal failure, lens rupture, pyogranulomatous uveitis, and cataracts.
Ante-mortem diagnosis of E. cuniculi infection is challenging, and the gold standard is post-mortem histologic examination with immunochemical staining. In this case, the E. cuniculi infection was an incidental finding.
Molly Varga, 2014. Textbook of Rabbit Medicine, 2nd ed.
Frank Kunzel, et al. 2018. Clinical signs, diagnosis, and treatment of Encephalitozoon cuniculi infection in rabbit. Veterinary Clinics of North America: Exotic Animal Practice. https://www.sciencedirect.com/science/article/pii/S1094919417302025?via%3Dihub#fig3
Incidental finding or cause of death?
An approximately 8-year-old miniature donkey mare had difficulty foaling. The referring veterinarian provided aggressive supportive therapy but unfortunately the foal and mare did not survive. To determine the cause of death both carcasses were submitted for necropsy.
Grossly, the mare was remarkably emaciated, and there were mild, chronic, multifocal ulcers in the stomach. Histologic examination of the stomach confirmed moderate, chronic-active, multifocal ulcerative gastritis with bacterial infection. Additionally, histologic examination of the mare’s kidney revealed multiple, variable sized parasites in the renal tubular epithelium (Figures 1-3). No abnormalities were detected grossly or microscopically in the foal.
Figure 1: Various parasite stages in the renal epithelial cells (indicated by arrows).
Figure 2: Multiple nuclei lie along the periphery – notice how they look like a flower, these are called “sporoblasts” (indicated by arrow).
Figure 3: Free/Mature sporoblasts (indicated by arrow) – each of these sporoblasts undergoes further divisions to form sporocysts.
Klossiella equi is a protozoan parasite observed in the kidney of equines. The life cycle has not been fully understood; however, it is thought to be a direct life cycle. Sporocysts are passed in the urine and infection takes place by ingestion of sporulated sporocysts. Klossiella equi infection is thought to be fairly common throughout the world but rarely seen.
Klossiella eqi is considered non-pathogenic and usually is not associated with clinical signs. In this case, K. equi infection was an incidental finding, and bacterial translocation from the gastric ulcers and subsequent septicemia was likely related to the death of the mare and foal.
Special thanks to Dr. Rory Chia-Ching Chien, DVM, MSc, Anatomic Pathology Resident at Oklahoma State University, Center for Veterinary Health Sciences for sharing his case and photos!
Taylor MA, Coop RL, Wall RL. Veterinary Parasitology (4thedition).
Gardiner CH, Fayer R. Dubey JP. An Atlas of protozoan parasites in animal tissues.
Ballweber LR, Dailey D, Landolt G. (2012). Klossiella equiInfection in an Immunosuppressed Horse: Evidence of Long-Term Infection. Case Reports in Veterinary Medicine. 2012, 4. doi:10.1155/2012/230398.
Reinemeyer CR, Jacobs RM, Spurlock GN. (1983). A coccidial sporocyst in equine urine. J Am Vet Med Assoc.182(11). 1250–1251.
A fluke finding: is it a fluke egg?!
An approximately 20-year-old, intact male African spurred tortoise was presented to an exotic animal practice with a history of bleeding from the cloaca. Centrifugal fecal flotation with Sheather’s sugar solution (specific gravity, 1.25) and a direct fecal smear with saline solution were performed. A moderate number of large (> 60 µm), brown and yellow/orange colored, oval shaped objects with a cap-like structure on one side (Figures 1 & 2) were observed on the direct fecal smear. Centrifugal fecal flotation revealed many similar looking objects but with a collapsed appearance (Figures 3 & 4).
Figure 1: Direct fecal smear with saline solution. 200X magnification.
Figure 2: Direct fecal smear with saline solution. 600X magnification.
Figure 3: Centrifugal fecal flotation with Sheather’s sugar solution. 400X magnification.
Figure 4: Centrifugal fecal flotation with Sheather’s sugar solution. 400X magnification.
Nyctotherus spp. cysts
Nyctotherus is a large ciliated protozoa commonly found in herbivorous reptiles such as tortoises and some species of lizards. Nyctotherus spp. cysts are often confused with trematode or oxyurid eggs due to the presence of a structure that resembles an operculum on one side. Although uniformly distributed cilia should be apparent on cysts, they are subtle and can be easily overlooked. Nyctotherus is usually harmless, and it was less likely that Nyctotherus caused the cloacal bleeding.
Nyctotherus cysts seem to be fragile, and centrifugal flotation tends to collapse the cysts making it difficult to observe the details of cyst morphology. Direct fecal smear seems to be the best diagnostic test to recover intact Nyctotherus spp. cysts.
A 2-year-old intact male Labrador Retriever dog was presented to a small animal emergency clinic in Sacramento, California, USA with a recent onset of lethargy and inappetence and a single episode of vomiting and bloody diarrhea. Physical examination revealed fever of 105.2°F, enlarged lymph nodes, and dehydration.
After providing supportive care, a centrifugal fecal flotation and fecal sedimentation were performed. Results are shown below.
Figure 1: Centrifugal fecal flotation. 100X magnification
Figure 2: Centrifugal fecal flotation. 400X magnification
Figure 3: Fecal sedimentation. 100X magnification
Figure 4: Fecal sedimentation. 400X magnification
Nanophyetus salmincola eggs
This is a case of “salmon poisoning” caused by Neorickettsia helminthoeca. The rickettsial agent responsible for disease is found within a fluke – Nanophyetus salmincola – that uses salmonid fish as an intermediate host. Dogs and other canids are extremely susceptible to this infection, and disease occurs by consumption of infected raw fish. Disease is most commonly associated with fish in coastal streams of the Pacific Northwest of the USA, including the states of Washington, Oregon, and northern California, and southern Vancouver Island in Canada. The prognosis with appropriate treatment for the N. helminthoeca infection (doxycycline) is good; however, dogs that do not receive appropriate antibiotics will deteriorate quickly and often die.
Note: Although a fecal sedimentation test is preferred to detect fluke eggs, it has been reported that N. salmincola eggs can often be found by a centrifugal fecal flotation test. However, eggs on flotation might be collapsed, folded, or deformed due to the high specific gravity solution (Figures 1 & 2).
Suggested reading: Sykes, J. E., et al. (2010). "Salmon poisoning disease in dogs: 29 cases." JVIM 24(3): 504-513.
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