AFIP Wednesday Slide Conference - No. 10
4 November 1998

Conference Moderator:
Dr. Georgina Miller
NCRR LSS SSB, Bldg. 28A, Room 117
28 Library Drive, MSC 5210
Bethesda, MD 20892-5210

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Case I - RT97-1153 (AFIP 2639047)

Signalment: Adult, female, Spontaneous Hypertensive Rat (SHR).
History: This animal was submitted due to a history of anorexia and abnormal breathing. It was used in a hypertension study and was euthanized with CO2.

Gross Pathology: The rat was moderately dehydrated and thin with diffuse skeletal muscle atrophy and little abdominal body fat. Moderate dehydration was evident. The urinary bladder was devoid of urine; testing of residual urine on the mucosa revealed moderate to high ketonuria and trace glycosuria. The walls of mesenteric vessels throughout the gastrointestinal tract were thickened and formed 1-3 mm diameter reddish purple nodules. Other major organs appeared normal.
Case 10-1. Gross photos (see paragraph above)

Contributor's Diagnosis and Comments:
Morphologic Diagnosis: Mesenteric arteries/arterioles - arteriopathy with smooth muscle hypertrophy and thrombosis.
Etiologic diagnosis: Hypertensive arteriopathy/arteriolopathy.
The rat had multiple organ abnormalities secondary to vascular disease, consistent with hypertension. Arteriolar changes in the myocardium included medial hypertrophy and medial fibrinoid degeneration. Mesenteric and pancreatic arteries and arterioles were prominently dilated, tortuous, and had subintimal proliferation and medial hypertrophy, with mild to variable amounts of chronic perivascular inflammation. Many of the vessels were partially to completely occluded by thrombi. There were increased numbers of blood vessels of varying size within the mesentery. Pulmonary edema was present, along with increased numbers of alveolar macrophages and erthyrophagocytosis, consistent with chronic congestive heart failure. One adrenal gland and a section of small intestine were infarcted secondary to vascular compromise. Renal abnormalities included medial hypertrophy and intimal proliferation of arterioles, multifocal glomerulosclerosis, and associated tubular ectasia with proteinaceous fluid. The predominant findings in this case are consistent with vascular disease and related sequelae secondary to hypertension.
The enlarged and tortuous mesenteric arteries demonstrate a number of changes associated with hypertension. In some areas, the endothelial lining appears relatively normal whereas in other regions, the endothelium is necrotic with fibrin deposition and thrombi formation. Most of the thickening of the arteries is in the tunica media, and enlarged myocytes with enlarged nuclei are clearly seen in the smooth muscle indicating hypertrophy. In some areas, a discrete border is lacking between the muscle cells and adventitial fibroblasts. The adventitial layer is distended due to increased collagen deposition. Hemorrhage and hemosiderin deposits are present. There is an inflammatory reaction consisting predominately of neutrophils in both the media and the adventitia. Affected arterioles are evident in both the muscularis and submucosa of the intestine. Some arterioles have a narrowed lumen with characteristic "onion skinning". Based on gross morphology, the principal differential diagnosis is polyarteritis nodosa, a generalized immune-complex disease. In rats with polyarteritis, vascular lesions are commonly found in mesenteric arteries and their branches, but muscular arteries in any organ may be involved. Grossly, the arteries are tortuous and often exhibit thrombosis or occlusion.
The spontaneous hypertensive rat (SHR) was first developed in 1963 from outbred Wistar Kyoto rats by Okamoto and Aoki to develop an animal model for hypertension. The strain has been successful in that 100% of the rats develop spontaneous hypertension. Long term hypertension is known to cause severe arterial disease which can result in hemorrhage, infarction and nephrosclerosis. The arterioles in spontaneous hypertensive rats show a thickening of the tunica media consistent with periarteritis nodosa, and the structural adaptation of the vessels occurs in response to an increased pressure load.
In severe hypertensive animals, arteries progress through a number of phases based on the age of animal and the degree of blood pressure elevation. Arteries with a diameter of less than 300 mm determine pressure resistance. In hypertension, pressure resistance is elevated, implying a narrowing of vasculature. The mesenteric artery of SHR has a 16% smaller luminal diameter and a 49% thicker media than nonhypertensive rats. Blood pressure increases steadily after 6 weeks of age in SHR, rising from 170 mmHg to around 200 mmHg and finally reaching over 250 mmHg by death. The arteries go through phases beginning with a prehypertensive period to eventually irreversible damage. During the prehypertensive phase, the surface of the internal elastic lamina becomes irregular, then the elastic lamina is destroyed, and modified medial smooth muscle cells appear. Finally, the internal and medial elastic lamina are both completely destroyed and small fragments of the laminae are all that remain.
Before six weeks of age, mesenteric arterial smooth muscle cells appear morphologically normal with blood pressure around 170 mmHg. After 6 to 7 weeks, the innermost medial smooth muscle cells begin to show alterations of shape because of an increase of cell organelles. The prominent morphological changes include a marked increase and dilatation of rough endoplasmic reticulum containing electron-dense material. By around 13 weeks of age, blood pressure has increased to around 210 mmHg and the smooth muscle cells of the mesenteric arteries show greater change. The shape of the smooth muscle cell is irregular and few organelles are seen in the cytoplasm. The internal elastic lamina and the medial smooth muscle cells begin to interact via plasma membrane protrusions from the muscle cells. The shape of the smooth muscle cell is extremely irregular in the middle layer of the media. Once blood pressure has increased to over 240 mmHg, the rat has reached advanced stages of hypertension. This usually occurs by week 28 and there are marked degenerative and degradative changes in the smooth muscle cells, especially in the inner media. Prominent protrusions of the plasma membrane extend to the internal elastic lamina and elastic fiber becomes fragmented, indicating destruction of the internal elastic lamina by smooth muscle cells. Commonly, medial smooth muscle cells will migrate into the subintimal region. By the final stage of hypertension, the internal elastic lamina appears fragmented and the media is thickened.
Thickening of the arterial wall in chronic hypertension is thought to be the result of both hypertrophy and hyperplasia of the medial smooth muscle cell, although the degree of each differs based on the type of artery: elastic, muscular, or arteriolar. For example, both hypertrophy and hyperplasia contribute to wall thickening in muscular arteries, but arteriolar vessels show a greater amount of hyperplasia. It has been suggested that hyperplasia is a very early event which reaches its maximum even while blood pressure is submaximal. The degree and duration of hypertension determines which is predominant.
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Case 10-1. Mesentery. There is medial hypertrophy and inflammatory infiltrates around the affected vessels. Some arteries have fibrinoid degeneration and/or thrombi in arterial lumens. Perivascular mesenteric fat contains high numbers of inflammatory cells (steatitis).
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Case 10-1. Mesenteric artery. There is extensive fibrinoid degeneration of the vessel and moderate perivascular infiltrates of lymphocytes and macrophages.
AFIP Diagnoses:
1. Mesentery, arteries: Arteriopathy, characterized by fibrosis, medial hypertrophy, fibrinoid change, thrombosis and chronic-active arteritis, spontaneous hypertensive rat (SHR), rodent.
2. Mesenteric adipose tissue: Steatitis, chronic-active, diffuse, mild.
Conference Note: The pathogenesis of the vascular changes occurring in spontaneous hypertensive rats (SHR) has been well described by the contributor. Interestingly, the anatomical locations, gross appearance, and histomorphology of the lesions in SHR are very similar to those of polyarteritis (periarteritis) nodosa (PAN). As mentioned by the contributor, the vascular lesions attributed to hypertension in SHR develop early (6 to 7 weeks) and progress with age. The severity and distribution of affected arteries is greater in SHR males than in females. Clinically, polyarteritis nodosa tends to occur in aged rats (reports vary between 498 and 900 days), and the incidence is higher in males than females. The lesions of PAN are often found incidentally at necropsy. PAN is believed to be an immune-mediated disease.
In the absence of history and signalment, differentiating the histologic changes of PAN and those developing in SHR can be problematic. The microscopic vascular lesions that occur in SHR have been characterized and sequenced by the contributor. PAN is classically described as necrotizing vasculitis and fibrinoid necrosis affecting small and medium-sized vessels of multiple organ systems. In the acute phase, the vasculitis is characterized by transmural infiltration of the vascular wall by high numbers of neutrophils, eosinophils, and mononuclear cells with fibrinoid necrosis of the inner half of the vessel. At later stages, the acute inflammatory infiltrate disappears and is replaced by fibrous thickening of the vessel wall accompanied by a mononuclear cell infiltrate13. A characteristic finding in PAN is the presence of unaffected and severely affected blood vessels within the same tissues, as well as segmental lesions along individual blood vessels14. Subjectively, the vascular lesions in PAN seem to be characterized by higher numbers of inflammatory cells that are more disruptive to the vessel walls compared to the arterial changes in SHR.
In this case, in some sections of the small intestine, arterioles within the lamina propria and tunica muscularis are characterized by concentric, laminated thickening of the vessel wall, which narrows or occludes the lumen, consistent with "onion-skinning" as noted by the contributor. Though hypertension may be a complication in humans suffering from PAN, the microscopic feature of "onion skinning" with luminal obliteration in this rat is characteristic of hyperplastic arteriolosclerosis. Hyperplastic arteriolosclerosis is more consistent with hypertension than an immune-mediated etiology.
Contributor: Pathology Unit, Laboratory Sciences Section, Veterinary Resources Program, NCRR, National Institute of Health, 9000 Rockville Pike, Bethesda, MD 20892.
1. Black MJ, et al.: Vascular growth responses in SHR and WKY during development of renal hypertension. Amer J Hypertension 10:43-50, 1997.
2. Dominiczak AF, et al.: Vascular smooth muscle polyploidy and cardiac hypertrophy in genetic hypertension. Hypertension 27:752-759, 1996.
3. McGuffee LJ, Little SA: Tunica media remodeling in mesenteric arteries of hypertensive rats. Anatomical Record 246:279-292, 1996.
4. Dilley RJ, Kanellakis P, Oddie CJ, Bobik A: Vascular hypertrophy in renal hypertensive spontaneously hypertensive rats. Hypertension 24:8-15, 1994.
5. Ganten D, de Jong W: Experimental and genetic models of hypertension, In: Handbook of Hypertension, vol. 16, Elsevier Science B.V., Amsterdam, Holland, 1994.
6. Ito H: Pathophysiological changes of the membrane system of the arterial smooth muscle cells. In: Membrane Abnormalities in Hypertension, Kwan CY ed., vol. 2, pp. 2-21, CRC Press Inc., Boca-Raton, Florida, 1989.
7. Lee RMKW: In: Blood Vessel Changes in Hypertension: Structure and Function, vol. 1, pp. 2-17, CRC press Inc., Boca-Raton, Florida, 1989.
8. Lee RMKW, Forrest JB, Garfield RE, Daniel EE: Ultrastructural changes in mesenteric arteries from spontaneously hypertensive rats. Blood Vessels 20:72-91, 1983.
9. Cox, R: Basis for the altered arterial wall mechanics in the spontaneously hypertensive rat. Hypertension 3:485-495, 1981.
10. Andrews EJ, Ward BC, Altman NH: In: Spontaneous Animal Models of Human Disease, vol. 1, pp. 51-54, Academic Press, New York, 1979.
11. Baker HJ, Lindsey JR, Weisbroth S: In: The Laboratory Rat: Volume I Biology and Diseases, pp. 63-72, Academic Press, Inc., New York, 1979.
12. Benirschke K, Garner FM, Jones TC: In: Pathology of Laboratory Animals, vol. 2, pp. 2018-2055, Springer-Verlag New York, Inc., New York, 1978.
13. Cotran RS, Kumar V, Collins T: Blood vessels. In: Robbins Pathologic Basis of Disease, 6th ed., pp. 510-522, WB Saunders, Philadelphia, PA, 1999.
14. Snyder PW, et al.: Pathologic features of naturally occurring juvenile polyarteritis in beagle dogs. Vet Path 32:337-345, 1995.
15. Anver MR, Cohen BJ: Lesions associated with aging. In: The Laboratory Rat Volume I Biology and Disease, Baker HJ, Lindsey JR, Weisbroth SH eds., pp. 383-384, Academic Press Inc., New York, New York, 1979.
16. Wexler BC, McMurtry JP, Iams SG: Histopathologic changes in male vs female spontaneously hypertensive rats. J Gerontol 36:514-519, 1981.
17. Suzuki T, Oboshi S, Sato R: Periarteritis nodosa in spontaneously hypertensive rats - incidence and distribution. Acta Pathol Jpn 29:697-703, 1979.
Case II - Vn-72-98 (AFIP 2642410)
Signalment: One-year-old, male, guinea pig (Cavia porcellus).
History: This is one of five guinea-pigs which were raised as pets in a household. The owner brought the animal to the attention of a veterinary practitioner because of "growths" on its ears that had been present for almost five months. The animal was otherwise normal. A decision was made to euthanatize the guinea-pig, and it was submitted to our lab for necropsy.

Gross Pathology: The pinna of the right ear was irregularly swollen and alopecic, and the overlying skin of the dorsum of the pinna was bright red, ulcerated and covered by crusts (color transparency). At the base of the left ear there was a gray, firm, alopecic nodule measuring 1.5 cm in diameter. Other organs were unremarkable.
Case 10-2. Gross photo (see description above)
Laboratory Results: None.
Contributor's Diagnosis and Comments: Skin of the ear: Dermatitis and panniculitis, granulomatous, focally extensive, moderate to severe, with intracytoplasmic protozoal amastigotes within macrophages, etiology consistent with Leishmania sp. (cutaneous leishmaniasis), guinea-pig (Cavia porcellus).
Leishmaniasis is a zoonotic disease caused by many pathogenic species and variously named subspecies of the genus Leishmania (order Kinetoplastida, family Trypanosomatidae). Differentiation among species cannot be made based only on their morphological aspects in tissue sections. Differentiation is based on clinical signs and pathological changes, morphological aspects and behavior of the parasite, and on specific laboratory tests (e.g., serology, immunohistochemistry, indirect immunofluorescence).
Leishmania spp. occur in two parasite forms. The intracellular amastigotes (found in parasitophorous vacuoles within macrophages of the vertebrate host) and the promastigote (found predominantly in the sandfly vector). The amastigotes are spherical, 2.5 to 5 mm, have a prominent, eccentric nucleus, and a transversely oriented kinetoplast.
Diseases caused by Leishmania sp. are transmitted by hematophagous sandflies which include the genera Lutzomyia sp. (in the New World) and Phlebotomus (in the Old World). When the insect vector takes a blood meal, it becomes infected by ingestion of infected macrophages containing amastigotes. These are released from the macrophages in the midgut of the insect and transform into promastigotes (10-20 mm in length). The insect vectors then take another blood meal and, in doing so, infect the next mammalian host. There is usually a primary reservoir host for a given Leishmania species in a particular area where the parasite is maintained in a cycle between the insect and the vertebrate host.
Clinically and epidemiologically, the disease can be divided into three main forms caused by different species of Leishmania. Dermal cutaneous leishmaniasis (L. tropica, L. major), visceral leishmaniasis (L. donovani), and mucocutaneous leishmaniasis (L. braziliensis, L. mexicana). The lesions of the case described here are restricted to the dermis and subcutis and are characterized by marked proliferation of epithelioid macrophages and moderate amounts of fibrovascular tissue. Most of these macrophages contain phagocytized amastigotes with morphology consistent with Leishmania sp. The large numbers of parasites observed in these sections, although not a consistent finding in leishmaniasis, has been described previously.
Histoplasmosis, toxoplasmosis, blastomycosis, and trypanosomiasis should be considered in the differential diagnosis. A kinetoplast and a small nucleus can be identified in Leishmania organisms in tissue sections. These structures are absent in the causative organisms of the first three diseases. The tissue phase of Trypanosoma cruzi has a kinetoplast, but the distribution and type of lesions in trypanosomiasis (Chagas disease) differ from those found in leishmaniasis.
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Case 10-2. Ear. The dermis is expanded by large numbers of macrophages and lymphocytes.
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Case 10-2. Leishmanial amastigotes appear as oval 3-5u basophilic structures surrounded by clear halos.
AFIP Diagnosis: Haired skin, auricular: Dermatitis, histiocytic and lymphoplasmacytic, diffuse, severe, with ulceration, serocellular and hemorrhagic crust, and numerous intrahistiocytic protozoal amastigotes, guinea pig (Cavia porcellus), rodent.
Conference Note: Most conference participants preferred the morphologic diagnosis of histiocytic and lymphoplasmacytic dermatitis rather than granulomatous dermatitis because of the lack of multinucleate macrophages and activated epithelioid macrophages (macrophages with abundant eosinophilic cytoplasm and large, vesiculate nuclei containing prominent nucleoli), the histologic hallmarks of granulomatous inflammation.
Leishmania amastigotes are the only protozoa that survive and replicate in the macrophage phagolysosome. After phagocytosis of the promastigotes by macrophages, the acidity in the phagolysosome induces them to transform into amastigotes. The amastigotes are protected from lysosomal acid by a proton-transporting ATP-ase which maintains the intracellular pH of the parasite at 6.5. Additionally, leishmanial organisms have on their surface two glycoconjugates which appear to be important virulence factors. Lipophosphoglycans are glycolipids that form a dense glycocalyx and bind to C3b and iC3b. Organisms resist lysis by complement C5-C9, and are phagocytosed by macrophages through complement receptors CR1 (LFA-1) and CR3 (Mac-1)6. Lipophosphoglycans may also serve to protect amastigotes by inhibiting lysosomal enzymes and scavenging oxygen free radicals. The second glycoconjugate, gp63, is a zinc-dependent metalloproteinase that cleaves complement and some lysosomal enzymes.
Conference participants briefly discussed the predisposition for development of cutaneous lesions on the ears in several reports of leishmaniasis in various animals. The skin of the face and the ears are most exposed to the environment, and may predispose these areas on hosts to inoculation by the sandfly vector. Another explanation for the predilection of lesions at these anatomical sites may be related to temperature. Leishmania sp. that cause visceral disease grow at 37°C in vitro, while those that cause mucocutaneous disease, grow only at 34°C6. The tips of the ears are probably cooler than other areas of skin.
Like the contributor, participants considered a similar differential diagnosis for this cutaneous lesion based upon the character of the inflammation, the presence of intrahistiocytic organisms, and organism morphology. In tissue sections, leishmanial amastigotes are spherical to ovoid and measure 2 by 5mm. Each amastigote contains a round, eccentric nucleus and rod-shaped kinetoplast that lies perpendicular to the nucleus; both structures are basophilic in hematoxylin and eosin stained sections; in Giemsa-stained sections the nucleus is red.
In contrast, the kinetoplast of Trypanosoma cruzi amastigotes is found parallel to the nucleus, and is larger and more basophilic than that of Leishmania. Histoplasma organisms, also typically found within macrophages, are similar in size to Leishmania and may illicit an intense histiocytic to granulomatous response; however, the yeasts lack a kinetoplast and are stained by the PAS and GMS methods. Blastomyces dermatitidis, usually found as a spherical yeast measuring between 7-15mm with a double-contoured cell wall, is found both within macrophages and extracellularly; the organism is characterized by single, broad base budding and stains with GMS and PAS. Toxoplasma gondii and Neospora caninum tachyzoites may be round, oval, or crescent-shaped, measure between 4 to 6mm, contain a basophilic nucleus, and lack a kinetoplast. Tachyzoites may be found within a variety of host cells, including leukocytes, endothelial cells, stromal cells, and epithelial cells.
Contributor: Universidade Federal de Santa Maria, Departamento de Patologia, 97105-900, Santa Maria RS, Brazil.
1. Jones TC, Hunt RD, King NW: Diseases caused by protozoa. In: Veterinary Pathology, 6th ed., pp. 549-600, Williams and Wilkins, Baltimore, 1997.
2. Ramos-Vara JA, Ortiz-Santiago B, Segalès J, Dunstan RW: Cutaneous leishmaniasis in two horses. Vet Pathol 33:731-734, 1996.
3. van der Lugt JJ, Stewart CG: Leishmaniasis. In: Infectious Diseases of Livestock with Special Reference to Southern Africa, Coetzer JAW, Thomson GR, Tustin RC eds., vol.1, pp. 269-272, Oxford, Cape Town, South Africa, 1994.
4. Gardiner CH, Fayer R, Dubey JP: Sarcomastigophora. In: An Atlas of Protozoal Parasites in Animal Tissues, 2nd ed., pp. 3-10, Armed Forces Institute of Pathology, Washington DC, 1998.
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.
6. Cotran RS, Kumar V, Collins T: Infectious diseases. In: Robbins Pathologic Basis of Disease, 6th ed., pp. 391-392, WB Saunders, Philadelphia, PA, 1999.
7. Yager JA, Wilcock BP: Nodular and/or diffuse dermatitis. In: Color Atlas of Surgical Pathology of the Dog and Cat, pp. 119-130, Wolfe Publishing, London, England, 1994.
Case III - 97N0525 (AFIP 2642200)
Signalment: 2½-year-old, Walker hound, male, canine.
History: This dog was one of a litter of three puppies raised together as a hunting group. Animals were kept in an outdoor kennel year round and were current on vaccinations. Each animal developed ulcerated hind limb digital pads and was treated for bacterial infections with systemic antibiotics, local debridement, and hydrotherapy. This dog had a digit amputated due to the severity of the ulceration that had progressed to gangrene. One of the other littermates died and was not necropsied. This dog became severely dyspneic and anorexic and was presented in lateral recumbency. The dog died despite fluid therapy, intravenous broad-spectrum antibiotics, and steroids. The surviving dog seemed to improve with systemic gentamycin and topical therapy of the toes.
Gross Pathology: A 25 pound (11.3 kg), adult, male, black and tan Walker hound was presented for necropsy. The dog was in adequate nutritional status and had mild autolysis. The right rear footpad had sloughed, and the caudal tarsus had a two centimeter diameter ulcer of the plantar surface above the footpad. The toenail of the second digit was missing. The liver was enlarged and had an accentuated lobular pattern. Both kidneys had several wedge-shaped depressions characteristic of chronic infarcts. The right cranial and caudal lung lobe vessels each contained 15 or more nematodes typical of Dirofilaria immitis. The main pulmonary artery had more than 15 adult worms. The left and right cardiac ventricles were enlarged; the chambers were dilated and the free walls were thickened. The mitral and tricuspid valve leaflets were thickened and irregular. The femoral, saphenous, and tarsal veins and arteries contained adult nematodes. All lymph nodes seen were enlarged and dark red. Both testes were firm, small, and intraabdominal. The prostate gland was very small.
Case 10-3. Tarsal region. The metatarsal pad is necrotic and covered with a brown exudate which contains a pale tan nematode parasite.
Laboratory Results: A mixed population of bacteria grew from a culture of the right hind footpad.
Contributor's Diagnosis and Comments: Tarsal and carpal vessels: Inflammation, perivascular, focal, mild, chronic, with adult filarial nematodes in perivascular tissue and in arteries.
Etiology: Dirofilaria immitis.
It is unusual even in endemic areas to see Dirofilaria immitis adults in the systemic arteries and in tissues. This dog and its littermates had never received heartworm preventive treatment and had overwhelming infections. The adult heartworms in the arteries of the distal limbs led to inflammation and blockage of the vessels with impedance of blood flow. This created the appropriate environment for gangrene.
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Case 10-3. Fibroelastic artery. There are cross sections of two nematodes within a large artery. The 10x view shows two empty uteri and a smaller gut in the pseudocoelom. There is a coelomyarian musculature on either side of two large flattened lateral cords (top & bottom center). Portions of a fibrin thrombus and the arterial wall are in the lower right corner.
AFIP Diagnosis: Subcutis, fibroelastic arteries: Arteritis, chronic-active, focally extensive, moderate, with periarteritis, fibrin thrombus, and intraluminal adult nematode parasite, Walker hound, canine, etiology consistent with Dirofilaria immitis.
Conference Note: This case was studied in consultation with Dr. C.H. Gardiner, parasitology consultant to the Department of Veterinary Pathology. Morphologically, this adult nematode parasite is characterized by a cuticle with lateral internal ridges that project into hypodermal chords, coelomyarian, polymyarian musculature which is divided by the flattened hypodermal chords, and a pseudocoelom which contains an intestine with small lumen and two reproductive tubes (uteri). In some sections, the uteri contain sperm, indicating that copulation had occurred.
Aberrantly located adult heartworms have been infrequently reported in dogs since the middle of the 19th century. Reported sites include the eyes, subcutaneous interdigital cysts, intramuscular cysts and abscesses, peritoneal cavity, bronchioles, in a salivary gland mucocele, and the central nervous system including the lateral ventricles and the epidural space. Clinical signs observed in dogs with systemic arterial dirofilariasis include lameness, weakness, poor peripheral perfusion, paresthesia of the hindlimbs, and ischemic necrosis of tissues such as muscle and digits due to thromboembolic disease.
Systemic arterial dirofilariasis is an uncommon condition, and the pathogenesis is not completely understood. In some reported cases, migration of parasites was thought to have occurred from the right ventricle through an identified ventricular septal defect, patent ductus arterious, or a patent foramen ovale after development of high right heart pressures and pulmonary hypertension. In other cases, no congenital cardiovascular defect was identified during necropsy. In these cases, the condition may have occurred due to aberrant migration or development of L5 heartworms within the systemic arterial circulation. While the mechanism of systemic arterial dirofilariasis is not understood, the presence of adult worms in the abdominal aorta may manifest as thromboembolic disease with subsequent infarcts in the spleen, kidneys, liver, and stomach resulting in multiple acute organ failure and/or ischemic muscle or digital necrosis.
Based on morphology and location of a nematode within an artery, Angiostrongylus sp. was also considered in the differential diagnosis. The adults of Angiostrongylus vasorum reside in the pulmonary arteries and right ventricle of dogs and foxes and incite a proliferative endarteritis similar to that in dirofilariasis. Angiostrongylus spp. are metastrongylid parasites characterized by a large intestine with few multinucleate cells and a microvillar border, in contrast to the small, indistinct intestine of Dirofilaria. The presence of eggs in the uterus of adult angiostrongylidae is another distinguishing morphologic feature.
Conference participants also discussed several other intravascular metazoan parasites known to occur in animals. Schistosoma sp. (blood flukes) are trematodes that predominately affect portal and mesenteric vessels in various animal species. The fourth stage larvae of the nematode Strongylus vulgaris primarily affects the mesenteric arteries of horses. Elaeophora schneideri, the arterial worm of deer and sheep, is a nematode primarily affecting the carotid arteries and is the cause of the clinical entity known as sorehead.
Contributor: Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA 70803.
1. Frank J, et al.: Systemic arterial dirofilariasis in five dogs. J Vet Intern Med 11:189-194, 1997.
2. Goggin G, et al.: Ultrasonographic identification of Dirofilaria immitis in the aorta and liver of a dog. J Amer Vet Med Assoc 210:1635-1637, 1997.
3. Henry CJ: Salivary mucocele associated with dirofilariasis in a dog. J Amer Vet Med Assoc 200:1965-1966, 1992.
4. Slonka FS, Castleman W, Krum S: Adult heartworms in the arteries and veins of a dog. J Amer Vet Med Assoc 170:717-719, 1977.
5. Chitwood M, Lichtenfels JR: Identification of parasitic metazoa in tissue sections. In: Experimental Parasitology, 32:458-460 and 491-495, Academic Press, 1972.
6. Davidson WR, Nettles VF: White-tailed deer. In: Field Manual of Wildlife Diseases in the Southeastern United States, 2nd ed., Southeastern Cooperative Wildlife Disease Study, University of Georgia, GA, 1997.
Case IV - 38613 (AFIP 2643569)
Signalment: Nine-year-old, female, pygmy chimpanzee (Pan paniscus).
History: Several animals in the pygmy chimpanzee group exhibited signs of upper respiratory tract infection including nasal discharge, coughing, sneezing, tachypnea and open-mouth breathing. The animals were also lethargic and inappetent. Animals were treated symptomatically (expectorant, non-steroidal antiinflammatory drug). This adult female was found dead on the morning of the fourth day. She was three weeks post-parturient.
Gross Pathology: Abundant mucopurulent to sanguineous fluid flowed from the nostrils bilaterally. The nasal mucosa was reddened. Bilaterally, vocal sacs contained abundant mucopurulent to hemorrhagic exudate. A moderate amount of white froth partially filled the trachea and bronchi. Dorsal-caudal lung lobes were firm and discolored purple. Cranioventral lobes and the periphery of the dorsal lobes were slightly firm and discolored. The cut surfaces of the lungs were dry and dense. Sections of lung from all areas were observed to float in formalin. Tracheobronchial lymph nodes were mildly enlarged. The cervix was closed. The uterus was mildly enlarged, had a slightly reddened mucosa, and contained 3 to 5 milliliters of dark red/brown fluid, consistent with post-partum status. Milk was easily expressed from both teats.
Laboratory Results:
1. Bacterial cultures:
a. Aerobic culture of lung: 1+ Streptococcus viridans group, 1+ Staphylococcus aureus.
b. Aerobic culture of vocal sac: 3+ Staphylococcus aureus.
c. Aerobic culture of heart blood: Streptococcus viridans group, Enterobacter cloacae, non-hemolytic streptococcus, Staphylococcus aureus, Streptococcus viridans group II, beta-hemolytic streptococci group B.
d. Anaerobic culture of lung and vocal sac: No growth.
e. Fungal culture of lung and vocal sac: No growth.
f. Virus isolation lung and nasal exudate (Simian Diagnostic Lab, San Antonio, TX): No virus isolated.
2. Cytology:
a. Nasal exudate: Mucopurulent exudate with numerous extra- and intracellular gram-positive cocci.
b. Air sac: Purulent exudate, sloughed columnar epithelial cells and extra- and intracellular gram-positive cocci.
c. Lung: Abundant neutrophils and erythrocytes, with fewer macrophages and epithelial cells. Macrophages tend to have abundant foamy cytoplasm. Epithelial cells have enlarged nuclei, and there are occasional binucleated forms. Low numbers of intracellular gram-positive cocci and occasional large extracellular gram-positive rods are detected.
d. Uterus: Abundant erythrocytes with low to moderate numbers of foamy macrophages. Small amounts of pigment (hemosiderin) and degenerate neutrophils.
3. Immunofluorescence (direct or indirect IFA) of nasal epithelial scraping (Rhinoprobe, University of San Diego Medical Center):
a. Positive for respiratory syncytial virus.
b. Negative for parainfluenza 1, 2, 3; adenovirus; influenza A and B.
4. Immunohistochemistry of lung (R. C. Hackman, Fred Hutchinson Cancer Research Center): Positive for respiratory syncytial virus.
Contributor's Diagnoses and Comments:
1. Lungs: Severe, diffuse, subacute, suppurative bronchoalveolar pneumonia with type 2 pneumocyte hyperplasia, hypertrophy and syncytial cell formation.
2. Lung: Mild, multifocal, chronic acariasis (not present in all sections).
Etiology: Respiratory Syncytial Virus with secondary bacterial infection (gram-positive cocci).
Syncytial cell formation in alveolar epithelium with degeneration and necrosis of bronchiolar and, to a lesser extent, bronchial epithelium are characteristic of respiratory syncytial virus (RSV) infection. Positive immunofluorescence and immunohistochemistry confirmed the diagnosis of RSV infection. The marked suppurative nature of the lesion in this case may be due to secondary bacterial infection, though neutrophils may be a prominent component of RSV pneumonia.
RSV infection is a common cause of morbidity in human infants and children. Mortality is uncommon and generally occurs in children with underlying pulmonary, cardiac or immunosuppressive disease. Disease in adult humans is usually limited to mild cold symptoms. Adult fatality is rare unless complicated by immunosuppression or general debilitation (old age). Although it is common knowledge that chimpanzees and a few other primate species are susceptible to RSV infection, there are very few reports or descriptions of naturally acquired RSV pneumonia in the literature.
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Case 10-4. Lung. Bronchointerstitial pneumonia. A suppurative exudate fills many alveoli.
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Case 10-4. Higher magnification demonstrates type II pneumocyte hyperplasia, syncytial giant cells, and suppurative alveolar exudate.
AFIP Diagnosis: Lung: Pneumonia, broncho-interstitial, acute to subacute, diffuse, severe, with type II pneumocyte hyperplasia, edema, syncytial cells, and cocci, pygmy chimpanzee (Pan paniscus), nonhuman primate.
Note: Some sections contain lung mites.
Conference Note: Some conference participants identified rare arthropod parasites within bronchioles. The morphology of these lung mites is consistent with Pneumonyssus sp. Cocci are gram-positive by the Brown and Brenn staining method.
Respiratory syncytial viruses (RSV) are best known as causes of respiratory disease in humans, other primates, and cattle (bovine RSV). RSV is a single-stranded, encapsulated, RNA virus that matures by budding through the cytoplasmic membrane. It is classified as a pneumovirus (subfamily pneumovirinae) in the family Paramyxoviridae. The genus pneumovirus also contains a virus that causes pneumonia in mice, though it is antigenically unrelated to RSV in humans or cattle. The other subfamily of the Paramyxoviridae, paramyxovirinae, includes paramyxovirus (parainfluenza 1, 2 , and 3, equine paramyxovirus, snake paramyxovirus), morbillivirus (measles, canine distemper, rinderpest, phocine distemper, cetacean morbillivirus), and rubulavirus (velogenic viscerotropic Newcastle disease).
In nonhuman primates, RSV was first isolated from a chimpanzee with respiratory disease and called chimpanzee coryza agent (coryza meaning inflammation with discharge from the nasal mucosa). Viral pneumonias may predispose animals to secondary pulmonary bacterial infection by compromising host defense mechanisms, and RSV infection likely predisposed this animal to infection by the gram-positive cocci.
Other potential causes of viral respiratory disease in nonhuman primates include adenovirus, herpesvirus, orthomyxovirus (influenza), paramyxovirus (parainfluenza), picornavirus, and morbillivirus (measles). Conference participants particularly considered measles virus due to the similarity in microscopic findings to RSV. Both viral pneumonias may cause type II pneumocyte hyperplasia, syncytial cell formation, and eosinophilic intracytoplasmic and intranuclear inclusions. While RSV infection is almost always limited to the respiratory tract, measles virus often manifests with a concurrent maculopapular rash and erythema, especially on the face. Other systemic features of measles virus infection include white, necrotic foci on the gingiva and tongue, generalized lymphadenopathy, and syncytial cells and inclusions in various organs including the liver, lymph nodes, intestines, salivary glands, and lungs.
Contributor: Department of Pathology, Zoological Society of San Diego, P.O. Box 120551, San Diego, CA 92112-0551.
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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
* 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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