Results
AFIP Wednesday Slide Conference - No. 14
December 14, 1998

Conference Moderator:
LTC Michael J. Topper
Walter Reed Army Institute of Research
Division of Pathology
Washington, D.C. 20307

 

Case I - 98-4779 (AFIP 2638822)

 

Signalment: Tissue from a two-day-old, male, quarter horse.

 

History: This horse presented to the veterinary teaching hospital with contracted flexor tendons in all limbs and prognathism. Radiographic examination of the metacarpal bones showed incomplete ossification. The foal was euthanized and necropsied.

 

Gross Pathology: The carpal joints had an angle of 140° at full extension. The thyroid gland was grossly normal.

 

Laboratory Results: No antemortem blood tests were performed. Liver selenium levels were deficient (0.11 mg/g wet weight). Adequate liver selenium range is between 0.200 - 0.600 mg/g wet weight.

 

Contributor's Diagnosis and Comments: Congenital thyroid hyperplasia with secondary flexural limb deformities and prognathism.

 

In sections of both lobes of the thyroid gland, follicles are small and lack colloid. Follicular epithelial cells are columnar to polygonal and occasionally bilayered. The cytoplasm is eosinophilic, abundant, and contains large, clear, poorly defined vacuoles. Basal to central nuclei are large (up to 15 mm in diameter), round and have coarsely stippled chromatin.

 

The histologic changes in the thyroid gland, including lack of colloid in follicles in conjunction with hypertrophy and hyperplasia of the follicular epithelial cells, and the clinically noted delayed ossification and contraction of the limbs are consistent with a syndrome described in newborn foals called thyroid hyperplasia with concurrent musculoskeletal deformities (TH-MSD).1,2 Similar lesions have also been described in aborted equine fetuses.3 The cause of TH-MSD is unknown. Males and females are affected equally, and the syndrome has been documented in eight different breeds making a genetic predisposition unlikely. Many cases originate from farms where the syndrome has been present in other foals during the same or other foaling seasons, suggesting that a dietary deficiency, toxic substance or infectious agent is responsible. Similar lesions have been reported in foals from mares consuming feeds contaminated with fungi (Acremonium coenophialum and Claviceps purpurea) or locoweed (Astragalus mollisimus).

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Case14-1. Thyroid. There is diffuse follicular epithelial hypertrophy and hyperplasia. Relatively few follicles have discernable lumens or colloid production.

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Case14-1. Thyroid. Follicular epithelium is hypertrophic and vacuolated. Follicle colloid is globular and sparce.

 

AFIP Diagnosis: Thyroid gland: Hyperplasia, follicular, diffuse, severe, quarter horse, equine.

 

Conference Note: Goiter, defined as non-neoplastic and noninfectious enlargement of the thyroid gland, is a common presentation of thyroid disease. Goiter may be diffuse or multinodular, and hyperplastic or colloidal. Development of goiter has been associated with iodine deficient diets, ingestion of goitrogens that interfere with thyroid hormone synthesis, excess dietary iodide, and genetic enzyme defects involved in thyroid hormone biosynthesis.

 

Impairment of thyroid hormone production leads to hypothyroidism and compensatory secretion of thyroid stimulating hormone (TSH) from the pituitary gland, increased serum TSH levels, and hypertrophy and hyperplasia of thyroid follicular cells with the resultant gross enlargement of the gland. The severity of glandular enlargement is related to the level and duration of deficiency of thyroid hormone.

 

In animals, congenital hypothyroidism is almost always associated with hyperplastic goiter and results when inadequate maternal thyroid hormone crosses the placental barrier during development in utero. The fetal pituitary gland responds by secretion of TSH, resulting in fetal hyperplastic goiter. The dam may not have signs of thyroid gland dysfunction. Dystocia, retained placenta, and prolonged gestation have also been associated with congenital hypothyroidism in newborn animals. In horses, affected foals are born extremely weak and die within a few days of birth. The thyroid gland may be only slightly enlarged in these cases. Calves, piglets, lambs, and kids are also susceptible to congenital hypothyroidism to varying degrees. Myxedema and a visibly enlarged thyroid gland are more common in these species compared to the horse. In carnivores, congenital hyperplastic goiter is not a common feature of hypothyroidism, though congenital thyroid enlargement in puppies has been reported and may result in fetal asphyxiation and dystocia.

 

In humans, hypothyroidism occurring during infancy or early childhood is termed cretinism. Cretinism results from the severe neurological deficits and central nervous system malformations that occur if the fetus is deprived of maternally derived thyroid hormones during critical periods of in utero brain development. Other clinical features of cretinism include impaired development of the skeletal system, protrusion of the tongue, and umbilical hernia.

 

Skeletal deformities in humans include severe dwarfism, delayed appearance of deciduous teeth, lack of closure of fontanels of the skull, and delayed closure of the epiphyses. These skeletal deformities are due to defects in cartilage maturation. The maturation of the zone of cartilage hypertrophy is delayed, and the zone of cartilage proliferation is narrowed, resulting in disorderly progression and failure of proper endochondral ossification. Disturbances and delays in endochondral ossification in the horse most often affect the carpal bones, and failure of proper ossification of the carpal and tarsal cuboidal bones may lead to angular limb deformities in foals. The angular limb deformities observed in this foal are the result of defects in endochondral ossification secondary to congenital hypothyroidism.

 

Contributor: Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040.

References:

1. Doige CE, McLaughlin BG: Hyperplastic goitre in newborn foals in western Canada. Can Vet J 22:42-45, 1981.

2. Allen AL, Doige CE, Fretz PB, Townsend HGG: Hyperplasia of the thyroid gland and concurrent musculoskeletal deformities in western Canadian foals: Reexamination of a previously described syndrome. Can Vet J 35:31-38, 1994.

3. Allen AL: Hyperplasia of the thyroid gland and musculoskeletal deformities in two equine abortuses. Can Vet J 36:234-236, 1995.

4. Capen CC: The endocrine glands. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., 4th ed., vol. 3, pp. 315-321, Academic Press, 1993.

5. Palmer N: Bones and joints. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., 4th ed., vol. 1, pp. 22-24, Academic Press, 1993.

6. Cotran RS, Kumar V, Collins T: The endocrine system. In: Robbins Pathologic Basis of Disease, 6th ed., pp. 1132-1140, WB Saunders, Philadelphia, PA, 1999.

7. Schiller AL: Bones and joints. In: Pathology, Rubin R, Farber JL, eds., page 1315, JB Lippincott Co., Philadelphia, PA, 1988.

 

 

Case II - 4435-98 (AFIP 2643729)

 

Signalment: Seven-month-old, female, Yorkshire Terrier.

 

History: The dog was slobbering and bewildered on presentation to the veterinarian.

 

Gross Pathology: A prominent vascular shunt was identified in the liver by the veterinarian at surgery.

Laboratory Results: Alkaline phosphate 184; SGPT 100; SGOT 108; Total Bilirubin 0.2; Pre-prandial bile acids: 3.9 mmol/L (normal is less than 5); Post-prandial bile acids: 329 (normal is less than 15).

 

Contributor's Diagnosis and Comments: Portosystemic vascular shunt, congenital.

 

The surgical biopsy of the liver shows essentially no portal vein branches, but there is mild reduplication of the arterioles in the portal areas. The lobules seem small as evidenced by a subjective decrease in distance between portal triads.

 

A prominent shunt was identified by the surgeon at the time of biopsy. Corrective surgery was performed several weeks later. A ring was installed that closed the shunt over a three week period, and the dog recovered completely and was normal one month post-surgery. In cats and small breed dogs, the shunts are usually extra-hepatic and occur between the portal vein and caudal vena cava or azygous vein. In large breed dogs, intra-hepatic shunts are more common and occur as a result of a patent ductus venosus. Congenital aplasia/hypoplasia of the portal vein with secondary collateral circulation development and subsequent portosystemic shunting has also been described in dogs.

Shunts cause the portal circulation to bypass the liver and enter the systemic circulation. The lack of portal circulation leads to a small liver with small hepatocytes because the stimulating factors such as insulin, glucagon, and amino acids are decreased. The portal vein branches in the liver are very small or absent.

 

The decreased functional liver mass is reflected in the increase in the post-prandial blood bile acids level. Bile acids are produced in the liver; the organ has a tremendous reserve capacity for bile acid production, but little reserve capacity for its conjugation and excretion. Pre-prandial bile acids are usually also increased with hepatic insufficiency, but can be normal after a prolonged fast. The hepatic lobules from the liver of this Yorkshire terrier were 40-50% smaller (decreased distance between portal triads) when compared to a liver from a normal three-month-old Yorkshire terrier. Acquired shunts may result from chronic hypertension and may be accompanied by ascites.

 

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Case14-2. Liver. Somewhat serpentine arrangements of arteriolar smooth muscle cells represent portal arteriolar hyperplasia. Portal veins are not discernable. Scattered hepatocytes contain brown pigment.

 

AFIP Diagnosis: Liver: Arteriolar hyperplasia, portal, diffuse, moderate, with portal vein hypoplasia and lobular atrophy, Yorkshire terrier, canine.

 

Conference Note: Portosystemic shunts are communications between the portal and systemic vasculature that allow passage of portal blood to the systemic circulation without first passing through the liver; shunts may be acquired or congenital. Congenital vascular shunts occur more often in dogs, less frequently in cats, and sporadically in other domestic animals including calves, foals, and pigs. Acquired shunts most often form as a result of compensatory development of collateral vessels in response to sustained portal hypertension caused by severe diffuse hepatic disease, such as chronic hepatitis and cirrhosis. Acquired shunts are usually multiple and occur as a tortuous plexus of vessels that communicate with the perirenal caudal vena cava. Rarely, young dogs may have arteriovenous (arterioportal) fistulae and develop portal hypertension, ascites, and acquired shunts.

 

Animals with portosystemic shunts are often small for their age and breed, and present in marginal or poor nutritional condition. The animal is frequently presented to the veterinarian for signs of hepatoencephalopathy (HE), including disorientation, hypersalivation, aggression, ataxia, blindness, and seizures. Central nervous system (CNS) signs typically wax and wane and are exacerbated by meals or high protein diets.

 

The pathogenesis of HE is probably multifactorial, and the condition results from inadequate clearance of enterically derived toxins in portal blood, including ammonia, mercaptans, short-chain fatty acids, and gamma aminobutyric acid. During periods of hyperammonemia, ammonia crosses the blood-brain barrier and is directly toxic to astrocytes. Furthermore, astrocytes metabolize ammonia to glutamine, which is also thought to be neurotoxic. Increased blood levels of amino acids, including tryptophan, phenylalanine, and tyrosine, readily reach the CNS due to changes in the blood-brain barrier in HE. Tryptophan in particular is toxic to the CNS, while tyrosine can give rise to octopamine which can act as a pseudotransmitter. Increased synthesis and absorption of gamma-aminobutyric acid (GABA) by bacteria occurs in the gut in animals with portosystemic shunts; this powerful inhibitory neurotransmitter may disrupt the balance of neuronal excitation and inhibition.

Gross neuropathological changes are not present in animals with HE. While not specific for HE, microscopic changes in the brain include spongiform change or polymicrocavitation of the white matter and the presence of Alzheimer type II cells. Alzheimer type II cells occur as small clusters of astrocytes with swollen, clear nuclei. In HE, spongiform changes occur diffusely in the white matter and are bilateral and symmetrical in distribution.

In addition to neurological signs, animals with shunts may suffer from renal, cystic, or urethral calculi due to increased urinary excretion of ammonia and uric acid with the resultant formation of ammonium biurate crystals, especially in alkaline urine. The urate calculi are usually green. In addition to the derangements in bile acids noted by the contributor, animals with portosystemic shunts often have hypoalbuminemia in the absence of proteinuria, low blood urea nitrogen, hypoglycemia, and hypocholesterolemia; the decrease in these serum chemistry values reflects reduced hepatic synthesis and metabolism of these compounds due to decreased functional hepatic mass. Erythrocytic microcytosis is a common finding in animals with portosystemic shunts; the cause is unknown, but it is not related to iron deficiency.

 

Contributor: Arkansas Livestock and Poultry Commission, #1 Natural Resources Drive, Little Rock, AR 72205.

 

References:

1. Center SA: Biochemical evaluation of hepatic function in the dog and cat. In: Current Veterinary Therapy IX, Kirk RW, ed., pp. 924-936, WB Saunders Co., Philadelphia, PA, 1986.

2. Center SA, Hornbuckle WE: Congenital portosystemic shunts in cats. In: Current Veterinary Therapy IX, Kirk RW, ed., pp. 825-836, WB Saunders Co., Philadelphia, PA, 1986.

3. Kelly, WR: The liver and biliary system. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., vol. 2, pp. 323-324, Academic Press, San Diego, CA, 1993.

4. Summers BA, Cummings JF, de Lahunta A: Degenerative diseases of the central nervous system: Metabolic and circulatory disorders. In: Veterinary Neuropathology, pp. 208-211, Mosby Yearbook, St. Louis, MO, 1995.
5. Johnson SE, Sherding RG: Diseases of the liver and biliary tract. In: Manual of Small Animal Practice, Birchard SJ, Sherding RG, eds., pp. 751-753, WB Saunders, Philadelphia, PA, 1994.

 

 

Case III - 97-1455 (AFIP 2643519)

 

Signalment: Four-year-old, castrated male, Cocker Spaniel.

 

History: The dog presented to the Veterinary Teaching Hospital at North Carolina State University with a two week history of diarrhea, melena and ascites. Clinical blood count (CBC) and chemistry data revealed a macrocytic anemia, thrombocytopenia, leukocytosis, neutrophilia with regenerative left shift, monocytosis, eosinopenia, hypoproteinemia, hypoalbuminemia, azotemia, hyperphosphatemia, hypernatremia, hyperkalemia and hypochloremia. Urinalysis was normal, and the specific gravity was 1.018. Ultrasonography of the abdomen revealed increased hepatic arterial blood flow and decreased portal blood flow of 0.06 m/s (normal 0.15-0.20) into the liver. The dog failed to respond to supportive therapy over the following two weeks and was euthanized.

Gross Pathology: The abdomen contained three liters of light yellow, clear, watery fluid. The liver was small, tan, firm, had a coarse, granular surface, and comprised 1.5% of the body weight. There were 5-10 white, firm nodules, ranging from 3-7 millimeters in diameter, on the liver surface. Engorged mesenteric veins drained from the duodenum into the caudal vena cava.

 

Laboratory Results:

 

Clinical Blood Count:

Test	Results (x1000/ml)	Normal Range
PCV	20%	(33-58)
MCV	72.9 fl	(63.6-70.1)
MCHC	37.6 g/dl	(33.9-36.7)
Platelet count	148	(181-350)
WBC	75.4	(6.4-15.8)
Mature neutrophils	67.9	(3.0-11.5)
Band neutrophils	2.3	(0.0-0.3)
Monocytes	3.8	(0.15-1.35)
Eosinophils	0	(0.1-0.75)
Aggregate reticulocytes	6.0%	(0.0-1.5)

Clinical Chemistry:

Test	Result	Normal Range
Albumin	1.4 g/dl	(2.8-3.8)
Alk. phos	50 IU/L	(16-71)
ALT	18 IU/L	(5-35)
Bilirubin	0.3 mg/dl	(0.0-0.5)
BUN	44 mg/dl	(6-23)
Ca++	7.7 mg/dl	(8.8-10.7)
Creatinine	1.3 mg/dl	(0.9-1.5)
Glucose	111mg/dl	(83-122)
Phosphorus	5.9 mg/dl	(2.3-5.1)
Total protein	3.6 g/dl	(5.5-6.8)
Na+	138 mmol/l	(144-150)
K+	5.1 mmol/l	(3.5-4.7)
Chloride	108 mmol/l	(109-118)
Bile acids preprandial	105.0 umol/l	(1.0-12.7)
Bile acids postprandial	321.4 umol/l	(0.0-15.1)

Abdominocentesis Results:
The abdominal fluid had a specific gravity of 1.006, protein 0.3 g/dl, and 700 nucleated cells/ml consisting of 84% mature nondegenerate neutrophils, 15% large mononuclear cells and 2% lymphocytes. It was characterized as a transudate.

 

Contributor's Diagnosis and Comments: Lobular dissecting hepatitis, chronic, diffuse, severe, with minimal nodular regeneration.

 

The liver is characterized by diffuse dissociation of hepatocytes including disruption of the limiting plate, thin bands of reticular and fibrous connective tissue dissecting through sinusoids, a marked absence of clearly discernible central veins, the presence of mildly distended portal lymphatics, a mixed inflammatory cell infiltrate, pigment-laden Kupffer cells, hepatocyte pseudorosettes and binucleate hepatocytes. The abnormal hepatic lobule morphology resulted in sinusoidal hypertension and ascites as well as functional liver deficits, as indicated by elevated serum bile acids. Hepatocyte injury, however, may not have been a significant component of this disease, as evidenced by normal serum ALT levels. Other indications of sinusoidal hypertension were the decreased portal blood flow and compensatory hepatic arterial blood flow identified at ultrasound, and engorged mesenteric shunt vessels noted at necropsy. No prehepatic portal vein nor post hepatic vein thrombi were found. Although mild endocardiosis was present on the mitral and tricuspid heart valves, cardiac insufficiency leading to passive congestion is not thought to play a significant role in the hepatic changes nor development of ascites in this animal due to the absence of other signs of right sided heart failure, such as hepatomegaly, centrilobular congestion, sinusoidal dilation or atrophy, and hepatocyte vacuolar degeneration or necrosis.

 

Lobular dissecting hepatitis is a distinct form of hepatitis seen only in the dog1. It differs in morphology from the syndromes of chronic active hepatitis, chronic persistent hepatitis, and chronic lobular hepatitis of man, as well as micro and macronodular cirrhosis of dogs. It is most similar to a form of human neonatal hepatitis complex, which is thought to arise from various etiologies including viruses, toxoplasmosis, Treponema pallidum, metabolic disturbances, toxins, and idiopathic causes. A specific etiology has not been identified in prior reports of the disease in dogs, nor was one found in this case. Lobular dissecting hepatitis affects young dogs from three months to five years of age, and has been reported in several breeds including the Rottweiler, Golden Retriever, Cocker Spaniel and mongrels. Reports of similarly affected dogs from the same litter and household suggest both genetic and/or common etiologic sources. The lobular dissecting reaction pattern appears restricted to the juvenile period, and it has been suggested that lobular dissecting hepatitis be regarded as a pattern unique to this age2.

 

Ancillary tests included rhodanine stain for copper or copper-associated protein, which was negative in the hepatocytes, trichrome and reticulin stains. The reticulin stain revealed an increase in sinusoidal reticulin fibers dissecting between hepatocytes. In liver cirrhosis, Ito cells have been shown to play an important role in the deposition of excess collagen and the progression of fibrosis. It is unknown whether a similar pathogenesis occurs in lobular dissecting hepatitis.

 

Interestingly, the cytoplasm of many hepatocytes stained positively when an immunohistochemical stain against alpha-1-antitrypsin was applied. Alpha-1-antitrypsin is a protease inhibitor synthesized by hepatocytes. In man, serum deficiency of this enzyme has been shown to result from a mutation in the gene encoding alpha-1-antitrypsin. The mutation causes misfolding of the protein product and its defective translocation from the endoplasmic reticulum. The mutated protein accumulates within hepatocytes and can result in pulmonary and hepatic damage from unregulated tissue proteases. Work by Sevelius et al. identified a cohort of dogs affected by several different types of hepatopathies with intrahepatocellular accumulations of alpha-1-antitrypsin3. Descriptions of liver histopathology in the affected dogs included several that resembled lobular dissecting hepatitis. The pathogenesis of alpha-1-antitrypsin accumulation in canine hepatocytes remains to be elucidated, but may be linked to unregulated tissue proteases causing hepatic parenchymal damage.

 

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Case14-3. Liver. There is diffuse dissociation of hepatocytes, increased numbers of cells in the sinusioids, and pale eosinophilic material (collagen) in centrilobular locations. Central veins are inconspicuous. Kupffer cells contain abundant pigment.

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Case14-3. Liver. Reticulin stain demonstrates increased sinusoidal reticulin extending from portal to centrilobular areas of the liver.

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Case14-3. Liver. This magnification shows abundant reticulin and individualization of hepatocytes.

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Case14-3. Liver. Blue staining areas localize collagen.

 

AFIP Diagnosis: Liver: Fibrosis, dissecting, diffuse, moderate, with hepatocellular degeneration and loss, lymphoplasmacytic, histiocytic, and neutrophilic hepatitis, canulicular cholestasis, and biliary hyperplasia, Cocker Spaniel, canine.

 

Conference Note: This case was reviewed by the Department of Hepatic Pathology. They identified features of subacute necro-inflammatory injury, delicate intra-acinar centrilobular fibrous strands, and focal nodular regeneration. They did not identify histologic features resembling human neonatal hepatitis, such as lobular disarray with focal hepatocyte necrosis, panlobular or portal giant cell transformation of hepatocytes, mild mononuclear cell infiltration of portal areas, and extramedullary hematopoiesis. As noted by the contributor, lobular dissecting hepatitis is not a recognized condition in humans. In humans, extreme subacute hepatic injury may be related to drug-induced hepatotoxicity, autoimmune hepatitis, and hepatitis of viral etiology. The Department of Hepatic Pathology found the lesions in this case suggestive of a toxic injury.

 

As in humans, most cases of hepatitis in animals are of infectious or toxic etiology. The specific inciting cause often remains undetermined, especially in the dog in which chronic progressive liver disease occurs with some frequency. Chronic hepatitis in dogs is not a single disease, and various histopathological classifications taken from human pathology have been applied, including chronic progressive hepatitis, chronic lobular hepatitis, and chronic active hepatitis. The etiologies, pathogenesis, and predisposing genetic factors in chronic canine hepatic disease are not well understood. Lobular dissecting hepatitis appears to be a distinctive histopathologic presentation of severe hepatic injury in some young dogs.

 

Contributor: North Carolina State University, College of Veterinary Medicine, 4700 Hillsborough Street, Raleigh, NC 27606.

 

References:

1. Van den Ingh TSGAM, Rothuizen J: Lobular dissecting hepatitis in juvenile and young adult dogs. J Vet Intern Med 8:217-220, 1994.

2. Bennett AM, Davies JD, Gaskell CJ, Lucke VM: Lobular dissecting hepatitis in the dog. Vet Pathol 20:179-188, 1983.

3. Sevelius E, Andersson M, Jönsson L: Hepatic accumulation of alpha-1-antitrypsin in chronic liver disease in the dog. J Comp Path 111:401-412, 1994.

4. Kelly, WR: The liver and biliary system. In: Pathology of Domestic Animals, Jubb K, Kennedy P, Palmer N, eds., vol. 2, pp. 361-362, Academic Press, 1993.

5. Cotran RS, Kumar V, Collins T: The liver and biliary tract. In: Robbins Pathologic Basis of Disease, 6th ed., pp. 866-877, WB Saunders, Philadelphia, PA, 1999.

6. Dill-Macky E: Chronic hepatitis in dogs. Vet Clin North Amer Small Anim Pract 25:387-397, 1995.

 

 

Case IV - 98 ND2 (AFIP 2642107)

 

Signalment: Thirteen-month-old, male, llama (Llama glama).

 

History: The animal was recently purchased and had initially done well. The animal then suffered a 2-3 week duration of respiratory disease that initially responded to antibiotic therapy. The animal subsequently became anorectic and continued to lose weight, however. Anthelminthic treatment resulted in no clinical improvement. Fecal flotation, bacterial culture for salmonellosis, and Johne's disease agar gel immunodiffusion tests were performed, but the animal died prior to additional diagnostic procedures.

 

Gross Pathology: On necropsy there was marked pulmonary edema, increased pericardial fluid, and a diffusely pale, mottled heart. There were multiple coalescing foci of ulceration in the third compartment (C-3) of the stomach. Scattered, small, 0.2-0.3 cm foci of pallor were present on both the capsular and cut surfaces of the liver.

 

Laboratory Results:

 

Feces:

Fecal flotation: No parasite eggs identified.
Salmonella sp. bacterial culture: No growth.
Mycobacterium paratuberculosis agar gel immunodiffusion: Negative.

 

C-3 mucosal ulcerations:
BHV-1 and BVD fluorescent antibody: Negative.
Clostridium perfringens isolated from lesions.

 

Additional laboratory findings:
Escherichia coli was isolated from the lungs and heart.
Hepatic selenium analysis was within normal limits for a yearling llama.

 

Contributor's Diagnosis and Comments: Multifocal, moderate, acute necrotizing myocarditis and myositis with intralesional protozoal zoites (Toxoplasma gondii).

 

Hallmarks of systemic toxoplasma infection include interstitial pneumonitis, focal hepatic necrosis, myocarditis, lymphadenitis, and nonsuppurative meningoencephalitis. Systemic toxoplasmosis has been reported in most species of domestic animals, but is most common in immunologically immature neonates and immunosuppressed hosts, such as dogs with canine distemper virus infection and human patients with acquired immunodeficiency syndrome. Serologic surveys indicate that up to one third of llamas have been exposed to this parasite, but with the exception of recent reports describing rising toxoplasma titers in llama abortions, there are few reports of disseminated disease in camelids.

Protozoal organisms consistent with Toxoplasma gondii were readily distinguishable among foci of necrosis and nonsuppurative inflammation in the heart and diaphragm of this young llama. Organisms were also identified in the gastric smooth muscle underlying the C-3 compartment ulcerations, and in association with multifocal necrotizing adrenalitis, thyroiditis, and encephalitis as well. Mild multifocal hepatic necrosis and hepatitis, mild nonsuppurative interstitial nephritis, and focal pulmonary interstitial necrosis were also observed in this animal, although organisms were not identified in these lesions. Concurrent evidence of lymphoid depletion suggested juvenile llama immunodeficiency syndrome as a probable factor underlying the development of disseminated infection in this animal.

 

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Case14-4. Heart. There are multiple coalescing foci of myocardial cell degeneration, necrosis, edema, and an inflammatory cell infiltrate.

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Case14-4. Heart. This focus of necrosis has loss of cross striations, hyalinization, and fragmentation of cardiomyocytes, edema, with karyorrhectic nuclei and scattered macrophages. There are two clusters of 2-3u diameter protozoa.

 

AFIP Diagnosis: Heart and diaphragm: Myositis, necrotizing, lymphohistiocytic, subacute, multifocal, moderate, with intracellular and extracellular protozoa, llama (Llama glama), camelid.

 

Conference Note: Conference participants identified moderate numbers of protozoal organisms associated with foci of necrosis and inflammation in the heart and diaphragm. Because the tachyzoites of Toxoplasma gondii and Neospora caninum are morphologically indistinguishable in routine hematoxylin and eosin stained sections, unstained tissue sections were submitted to Dr. J.P. Dubey of the Agricultural Research Center of the United States Department of Agriculture for immunohistochemical studies. The protozoal organisms in the heart and diaphragm are immunohistochemically positive for Toxoplasma gondii.

 

Toxoplasma gondii is a coccidian protozoal parasite of the phylum Apicomplexa and is characterized by small (4-6mm long), crescentic, tachyzoites. The protozoan may form tissue cysts in infected animals that are spherical to elongate, have a thin 0.5mm wall, measure between 10-100mm in diameter, and are found in various tissues including muscle, liver, retina, and brain. Toxoplasma gondii, unlike other protozoa with the exception of Neospora caninum, has the ability to infect a wide range of homeothermic hosts, and natural infection has been reported in birds, nonhuman primates, rodents, insectivores, herbivores, carnivores, and in humans. Domestic and wild felids are the only definitive hosts, while both felids and nonfelids serve as intermediate hosts. While documented reports of toxoplasmosis in llamas are scarce, it is not surprising that this species is susceptible to infection.

 

Transmission of toxoplasma protozoa can occur to intermediate hosts by ingestion of oocysts in feline feces, ingestion of cysts from the tissue of infected animals (meat), and transplacentally via tachyzoites, especially in sheep and goats in which the organism is an important cause of abortion. Upon ingestion of sporulated oocysts, sporozoites excyst and multiply as tachyzoites in the intestines and associated lymph nodes. The tachyzoites continue to multiply, and eventually parasitemia develops, disseminating the protozoa to various tissues where the organisms penetrate a variety of cell types, including macrophages, fibroblasts, and smooth muscle cells. Actively replicating tachyzoites are found within a parasitophorous vacuole in infected cells. Necrosis is a common feature of disseminated disease and is due to continued replication of the organisms, leading to cell death. Cell to cell transmission may occur within an infected organ, and the characteristic histologic findings are variably sized foci of necrosis, nonsuppurative inflammation, and the presence of intracellular tachyzoites in the vicinity of necrotic areas.

 

In most instances of disease, immunity to toxoplasmosis develops in a few days which reduces but does not terminate infection. Immune animals develop a dormant form of disease characterized by the formation of bradyzoite-filled cysts within 1-2 weeks of initial infection. Functional cell-mediated immunity is important for inducing cyst formation and eliminating tachyzoites from the circulation and visceral organs. Lymphoid depletion, immunodeficiency, and loss of cell-mediated immunity may be the underlying cause for the fulminant case of toxoplasmosis in this llama.

 

Differential diagnosis briefly discussed by conference participants included other protozoa, such as Neospora caninum, Leishmania sp., Trypanosoma, and Sarcocystis and the yeast forms of Histoplasma capsulatum. Thus far, the cysts of Neospora caninum have only been identified in tissues of the central nervous system of infected animals and are characterized by thick, 1-4mm, cyst walls; identification of protozoal cysts within tissues other than the central nervous system suggests infection with T. gondii. Leishmania and Trypanosoma are morphologically characterized by the presence of a kinetoplast perpendicular and parallel to the nucleus, respectively; tachyzoites of T. gondii lack kinetoplasts. Sarcocystis have merozoites that invade endothelial cysts, and the tissue cysts, primarily found in the heart and skeletal muscle of wild and domestic ruminants, may become so large as to be seen by the unaided eye. Histoplasma capsulatum was included in the differential diagnosis based on size and morphology of the yeasts in tissues. In histoplasmosis, the organisms incite histiocytic and/or granulomatous inflammation and stain with Grocott's methenamine silver (GMS) and other fungal stains.

 

Contributor: North Dakota State University, Veterinary Diagnostic Laboratory, Van Es Hall, Fargo, ND 58105.

 

References:

1. Cheney JM, Allen GT: Parasitism in llamas. Vet Clin N Amer Food Anim Pract 5:217-225, 1989.

2. Barker IK, Van Dreumel AA, Palmer N: The alimentary system. In: Pathology of Domestic Animals, Jubb, Kennedy, Palmer eds., 4th ed., vol. 1, pp. 308-310, Academic Press, San Diego, 1993.

3. Hutchinson JM, Garry F: Update on llama medicine: Ill thrift and juvenile llama immunodeficiency syndrome. Vet Clin N Amer Food Anim Pract 10:331-343, 1994.

4. Jones TC, Hunt RD, King NW: Diseases caused by protozoa. In: Veterinary Pathology, 6th ed., pp. 555-561, Williams and Wilkins, Baltimore, 1997.

5. Gardiner CH, Fayer R, Dubey JP: Apicomplexa. In: An Atlas of Protozoal Parasites in Animal Tissues, 2nd ed., pp. 53-60, Armed Forces Institute of Pathology, Washington DC, 1998.

 

Ed Stevens, DVM
Captain, United States Army
Registry of Veterinary Pathology*
Department of Veterinary Pathology
Armed Forces Institute of Pathology
(202)782-2615; DSN: 662-2615
Internet: STEVENSE@afip.osd.mil

 

* The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology. The C.L. Davis Foundation also provides substantial support for the Registry.

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