Ocular Lesions in Red-Tailed Hawks (Buteo jamaicensis) With Naturally Acquired West Nile Disease

Ocular lesions are common in red-tailed hawks with West Nile (WN) disease. These lesions consist of pectenitis, choroidal or retinal inflammation, or retinal necrosis, but detailed investigation of the ocular lesions is lacking. Postmortem examination of the eyes of 16 red-tailed hawks with naturally acquired WN disease and 3 red-tailed hawks without WN disease was performed using histopathology, immunohistochemistry for West Nile virus (WNV) antigen, glial fibrillary acid protein, cleaved caspase-3, and the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method. Retinal lesions were classified as type I or type II lesions. Type I lesions were characterized by lymphoplasmacytic infiltrates in the subjacent choroid with degeneration limited to the outer retina (type Ia lesion) or with degeneration and necrosis of the outer retina or outer and inner retina (type Ib lesion) while retinal collapse, atrophy, and scarring were hallmarks of type II lesions. Type II retinal lesions were associated with a more pronounced choroiditis. Although not statistically significant, WNV antigen tended to be present in larger quantity in type Ib lesions. Type I lesions are considered acute while type II lesions are chronic. The development of retinal lesions was associated with the presence of an inflammatory infiltrate in the choroid. A breakdown of the blood-retina barrier is suspected to be the main route of infection of the retina. Within the retina, virus appeared to spread via both neuronal and Müller cell processes.

Neuronal Storage Disease in a Group of Captive Humboldt Penguins (Spheniscus humboldti)

A neuronal storage disease affecting 5 captive Humboldt penguins is described. One bird died after 3 days of lethargy and anorexia. The 4 remaining birds died after a slowly progressing course of disease with signs that included lethargy, weakness, and neurologic dysfunction. Neurologic signs included dysphagia and ataxia. Gross lesions in the first animal to die consisted of hepatosplenomegaly indicative of avian malaria, which was confirmed histologically. The 4 remaining animals were mildly to moderately emaciated. Moderate to marked vacuolation of the neuronal perikarya was observed in Purkinje cells, neurons of the brainstem nuclei, and motorneurons of the spinal cord in all birds. By electron microscopy the vacuoles represented multilayered concentric lamellar structures. These findings were indicative of sphingolipidosis. All animals had been prophylactically treated for avian malaria, aspergillosis, and possible bacterial infections with chloroquine, itraconazole, and enrofloxacin. circumstantial evidence implicates chloroquine therapy as the possible cause of the storage disease.

Pulmonary atresia with intact ventricular septum and hypoplastic right ventricle in an Arabian foal

Pulmonary atresia with intact ventricular septum, rudimentary tricuspid valve, hypoplastic right ventricle, and right-to-left atrial shunting were identified in a four-day-old, male Arabian foal with clinical signs of cyanotic heart disease. Pulmonary blood flow was apparently derived from a ductus arteriosus. Echocardiographic evaluation revealed the majority of cardiac abnormalities and also findings compatible with right-sided congestive heart failure. Congenital cardiac defects have a high incidence in this breed, and this is the first description of this combination of congenital cardiac defects.

Clinical features, intestinal histopathology, and outcome in protein-losing enteropathy in Yorkshire Terrier dogs

Background

A poorly understood protein‐losing enteropathy (PLE) disorder has been reported in Yorkshire Terrier dogs.

Objectives

To describe clinical features, intestinal histopathology, and outcome in Yorkshire Terrier dogs with PLE, and to identify variables predictive of outcome.

Animals

Thirty client‐owned Yorkshire Terrier dogs with PLE.

Methods

Retrospective study. Records of dogs with a diagnosis of PLE were reviewed. Intestinal histopathology was interpreted using the World Small Animal Veterinary Association gastrointestinal histopathology classification system. Discriminate analysis techniques were used to identify variables predictive of outcome.

Results

Females outnumbered males (20/30). Median age was 7 years (range 1–12). Common clinical signs were diarrhea (20/30), vomiting (11), ascites and abdominal distension (11), and respiratory difficulty (8). Histopathologic abnormalities included villous lymphatic dilatation, crypt lesions, villous stunting, and variable increases in cellularity of the lamina propria. All dogs were treated with glucocorticoids. Of 23 dogs with long‐term follow‐up, 9 had complete, and 3 had partial, resolution of signs, and 11 failed to respond to treatment. Median survival of responders was 44 months and of nonresponders was 12 months, with 4 dogs experiencing peracute death. Vomiting, monocytosis, severity of hypoalbuminemia, low blood urea nitrogen concentration, and villous blunting were predictive of survival <4 months.

Conclusions

In addition to classic GI signs, Yorkshire Terriers with PLE often show clinical signs associated with hypoalbuminemia and low oncotic pressure. Lymphatic dilatation, crypt lesions, and villous stunting are consistent histopathologic findings. Clinical outcomes are variable, but many dogs experience remission of clinical signs and prolonged survival.

Characterization of Neuronal Ceroid-Lipofuscinosis in 3 Cats

Three young domestic shorthair cats were presented for necropsy with similar histories of slowly progressive visual dysfunction and neurologic deficits. Macroscopic examination of each cat revealed cerebral and cerebellar atrophy, dilated lateral ventricles, and slight brown discoloration of the gray matter. Histologically, there was bilateral loss of neurons within the limbic, motor, somatosensory, visual, and, to a lesser extent, vestibular systems with extensive astrogliosis in the affected regions of all 3 cases. Many remaining neurons and glial cells throughout the entire central nervous system were distended by pale yellow to eosinophilic, autofluorescent cytoplasmic inclusions with ultrastructural appearances typical of neuronal ceroid-lipofuscinoses (NCLs). Differences in clinical presentation and neurological lesions suggest that the 3 cats may have had different variants of NCL. Molecular genetic characterization in the 1 cat from which DNA was available did not reveal any plausible disease-causing mutations of the CLN1 ( PPT1), CLN3, CLN5, CLN8, and CLN10 ( CTSD) genes. Further investigations will be required to identify the mutations responsible for NCLs in cats.

Spinal Meningeal Oligodendrogliomatosis in Two Boxer Dogs

Two Boxer dogs developed progressive ataxia in association with a neoplastic infiltration of the spinal leptomeninges. In the first dog, the leptomeningeal neoplasm encompassed the entire cord and the ventral aspect of the brainstem and extended bilaterally into the piriform lobes. In the second, the neoplasm surrounded the C1–C3 segments of the spinal cord and the brainstem without involvement of the brain or spinal cord parenchyma. In both dogs, the neoplastic cells had variably distinct cell borders, clear to eosinophilic cytoplasm, and a round to ovoid hyperchromatic nucleus. Neoplastic cells were immunopositive for Olig2 and doublecortin in both dogs and for vimentin in one dog but were immunonegative for glial fibrillary acidic protein, S-100, CD34, E-cadherin, cytokeratin, CD3, and CD20. The morphological and immunohistochemical features of the neoplastic cells were consistent with an oligodendrocyte lineage. This hitherto poorly recognized neoplasm in dogs is analogous to human leptomeningeal oligodendrogliomatosis.

Purkinje Cell Heterotopy With Cerebellar Hypoplasia in Two Free-Living American Kestrels (Falco sparverius)

Two wild fledgling kestrels exhibited lack of motor coordination, postural reaction deficits, and abnormal propioception. At necropsy, the cerebellum and brainstem were markedly underdeveloped. Microscopically, there was Purkinje cells heterotopy, abnormal circuitry, and hypoplasia with defective foliation. Heterotopic neurons were identified as immature Purkinje cells by their size, location, immunoreactivity for calbindin D-28 K, and ultrastructural features. The authors suggest that this cerebellar abnormality was likely due to a disruption of molecular mechanisms that dictate Purkinje cell migration, placement, and maturation in early embryonic development. The etiology of this condition remains undetermined. Congenital central nervous system disorders have rarely been reported in birds.

Tularaemia in Minnesota: case report and brief epidemiology

The 2008 case presented here of tularaemia in a cat and its owner occurred in an urban setting and was associated with animal contact, a relatively rare mode of transmission in Minnesota in recent years. Response to this case exemplified a 'One Health' approach involving pre-existing relationships, cooperation between multiple disciplines and laboratory infrastructure that facilitated information sharing.

Genetic characterization of orf viruses isolated from various ruminant species of a zoo

In the present study, an outbreak of proliferative dermatitis in musk ox (Ovibos moschatus), Sichuan takin (Budorcas taxicolor tibetana) and domestic Shetland sheep (Ovis aries) in a zoo is described. Skin lesions consisted of severe, persistent, multifocal, proliferative dermatitis in musk ox, and mild, transient, focal, dermatitis in the Sichuan takin and Shetland sheep. Parapoxviruses were isolated from skin lesions, and characterized by restriction enzyme analysis and partial gene sequencing. The results of this investigation indicate that the outbreak of proliferative dermatitis was due to infection by a single parapoxvirus, which is genetically closely related to other orf virus (ORFV) strains but distant to bovine papular stomatitis virus (BPSV) and pseudocowpox virus (PCPV).

Immunohistological and serological investigations of morbillivirus infection in Black Sea harbour porpoises (Phocoena phocoena)

In the present study the occurrence of morbillivirus infection in harbour porpoises (Phocoena phocoena) from the Black Sea was investigated. Blood and tissue specimens of lung, brain and spleen from 73 stranded or by-caught harbour porpoises derived from the three Black Sea subregions such as Bulgaria, Georgia and Ukraine were collected between 1997 and 1999 and processed for histology, immunohistochemistry and serology. Age determination was performed according to dental growth layers and body length. The age of the investigated population ranged from neonates to a 12-year-old animal. Morbillivirus-specific neutralizing antibodies were detected in 53% of harbour porpoises. Generally, titres were very low and ranged from 20 to 270. There was no correlation between age, geographical origin and titre levels. The most common histological finding (97%) consisted of a mild to severe granulomatous bronchopneumonia due to lung worm infection. There were no changes indicative of a morbillivirus infection. Using immunohistology none of the animals were positive for morbillivirus antigen. However, the serological data are suggestive of a continuously circulating morbillivirus among harbour porpoises from the Black Sea indicating that harbour porpoises may serve as carriers for fatal diseases in susceptible cetacean species.

Immunohistochemical investigation of the cross-reactivity of selected cell markers from various species for characterization of lymphatic tissues in the harbour porpoise (Phocoena phocoena)

To facilitate a detailed investigation of cetacean lymphoid organs, 13 canine-, six bovine-, one equine-, one human- and four killer whale-specific monoclonal antibodies (mAbs) directed against cell surface antigens of the haematopoietic system (including CD2, CD4, CD8, CD45R, MHC class II, granulocyte, thrombocyte, pan-T cell and B-cell antigen), as well as a mAb and a polyclonal antibody (pAb) directed against the -peptide of the human CD3 complex, were tested for immunohistochemical cross-reactivity on frozen or formalin-fixed, paraffin wax-embedded lymphatic tissues of harbour porpoises. Eight of 26 mAbs and the pAb showed a specific reaction with harbour porpoise cells. Lymphocytes in T-cell compartments were labelled by the mAb and the pAb directed against the CD3 complex and by two killer whale mAbs specific for CD2 antigen. CD45R, labelled by a killer whale-specific mAb, was strongly expressed on B and weakly on T cells. MHC class II antigen, recognized by killer whale- and bovine-specific mAbs, was expressed on B and T cells. A canine MHC class II-specific mAb recognized an epitope on the surface of antigen-presenting cells and B lymphocytes. An anti-equine-pan-leucocyte marker labelled the majority of cells in B- and T-cell compartments. Thus, with leucocyte antigen markers from various species, it is now possible to determine the phenotype of lymphocytes in normal and diseased lymphoid organs of harbour porpoises.

Post-mortem findings in harbour porpoises (Phocoena phocoena) from the German North and Baltic Seas

Between 1991 and 1996, necropsies were performed on 445 harbour porpoises (Phocoena phocoena), in various states of preservation, stranded on German coasts or accidentally caught by German fishermen. The animals originated from the North and Baltic Seas, and 133 were considered suitable for histopathological, immunohistochemical and microbiological examination. Most of the lesions in these 133 porpoises were caused by parasites, in particular in the respiratory tract, two-thirds of the animals exhibiting pneumonia associated with the parasites. Pneumonia was considered to be the cause of death in 46% of the stranded subadult and adult animals. The findings gave no evidence of any epidemic due to bacterial or viral infection. Bacteriological examination suggested that pneumonia was mainly caused by secondary bacterial infection and not by parasitic infestation alone. Beta-haemolytic streptococci were considered to be the main infectious agents. Morbillivirus antigen was not detected immunohistochemically.

Periventricular changes associated with spontaneous canine hydrocephalus

Causes of canine juvenile hydrocephalus have been well documented. However, the effects of hydrocephalus on periventricular white matter have been only partially described. The present report shows that hydrocephalus-associated lesions of the periventricular white matter, i.e., formation of diverticula, clefts, and tears, are prevalent. Marked hydrocephalus was identified at necropsy in 20 juvenile dogs between 1990 and 1999. The severity grade was based upon a ratio of lateral ventricular dimensions to cortical thickness. All animals exhibited ependymal lesions consisting of attenuation, with or without abortive attempts of ependymal regeneration, and ulceration. In 10 dogs (50%), unilateral or bilateral periventricular diverticula and cleft formation in the region of the caudate nucleus were observed. The diverticula were formed at the caudal pole of the caudate nucleus, communicated with the ventricular lumen, and were associated with ependymal denudation. Loss of the ependymal lining probably contributes to a bulk shift of cerebrospinal fluid from the ventricular lumen to the periventricular white matter, leading to diverticulum formation. Clefts were observed within the parenchyma at the border of the internal capsule and putamen, consistent with an ischemic insult. Occasionally tearing with separation of the caudate nucleus from the subcortical white matter was found, representing unification of expanding clefts and diverticula. In one of the few clinically well-documented cases, tearing was correlated with a sudden decline in neurologic function, culminating in euthanasia. However, tears and clefts may exhibit a chronicity of several days, as indicated by the presence of astroglial scars along the lesion margins.

Immunohistological and serological investigation of morbillivirus infection in harbour porpoises (Phocoena phocoena) from the German Baltic and North Sea

The role of morbillivirus infection as a cause of disease or death in harbour porpoises (Phocoena phocoena) from the German North and Baltic Sea was investigated by serology, histology and immunohistochemistry. Blood and tissue samples of lung, brain and lymph nodes from 74 stranded or by-caught harbour porpoises from German waters were collected between 1991 and 1997. According to dentinal growth layers and body length, animals were grouped into four age classes (neonates, 0-1, 1-4, 4-16 years of age). Formalin-fixed, paraffin-embedded sections were stained by hematoxylin and eosin (HE). Immunohistology was done in all lung tissues using the avidin-biotin-peroxidase technique and a polyclonal canine distemper virus (CDV) nucleoprotein-specific antibody, which cross-reacts with porpoise morbillivirus (PMV) antigen. A virus neutralization assay for detection of (Onderstepoort-strain) CDV- and PMV-specific antibodies was performed. Due to the cytotoxicity of some sera, only titres of 1:20 or greater were considered positive. PMV or CDV-specific neutralizing antibody titres were found in 88 and 50% of the animals, respectively. Titres were always highest against PMV indicating infection with a homologous porpoise virus strain. There were no significant differences in neutralizing antibody titres between animals of the different age groups. No histological lesions specific for morbillivirus infection were detected and by immunohistology all cases were negative for morbillivirus antigen. The absence of morbillivirus antigen and the lack of characteristic morbillivirus-specific lesions showed that morbillivirus infection was not a cause of death or illness in the investigated population. However, the high incidence of PMV-specific antibodies in all age groups indicated a continuous spread of infection with a morbillivirus among harbour porpoises from the German Baltic and North Sea.

Calcium hydroxylapatite deposition disease in a Great Dane Puppy

A 10-week-old male Great Dane Puppy was presented for sudden onset tetraataxia and severe paresis of the front legs. Mineral deposits were detected radiographically, at gross postmortem examination, and light microscopically between the vertebral arches of multiple cervical and lumbar vertebrae. These deposits were associated with the interarchial ligaments (ligamentia interarcualia), along the interfaces of the synovium and articular cartilage of multiple cervical, thoracic, and lumbar facets, on the dorsal aspect of several thoracic intervertebral discs, and at the insertion of muscles at the lateral aspect of several cervical and thoracic vertebral bodies. The mineral deposits were associated with a granulomatous inflammation and synovial fibrocartilaginous metaplasia and proliferation, which was focally exuberant. X-ray diffraction analyses of the mineral deposits revealed calcium hydroxylapatite as the major component. The clinical signs in this puppy were due to focal compression of the spinal cord by marked extraarticular ligament-associated fibrocartilaginous proliferation.

Genital diseases in the peruvian dusky dolphin (Lagenorhynchus obscurus)

Ovarian cysts and one ovarian tumour, uterine tumours, vaginal calculi, abscesses of the broad ligament or undetermined testicular lesions were observed in 25 out of 502 female and male dusky dolphins (Lagenorhynchus obscurus) caught off Peru in 1985-1987 or 1993-1994. Tentative or definitive diagnoses included Graafian follicle cysts, luteinized cyst, ovarian parasitic granulomatous inflammation, dysgerminoma, leiomyoma, fibroleiomyoma and chronic fibrino-suppurative inflammation of the broad ligament. All lesions described represented first reports for L. obscurus, and the diagnosis of dysgerminoma was the first in a cetacean. It is also the first time that trematode eggs have been reported in the ovaries of cetaceans and that a vaginal calculus has been encountered in a sexually immature cetacean. The finding of struvite as a major component in two vaginal calculi suggested an infectious aetiology. Of 11 mature females with ovarian tumour or cysts or uterine tumours, only one (9.1%) was pregnant, i.esignificantly less than the expected pregnancy rate (53.3% in a random sample of Peruvian dusky dolphins). Several females with ovarian or uterine lesions and males with aberrant testes were large animals. It is possible that some of these lesions were associated with normal senescence of the reproductive system.

Phenotypical characterization of T and B cell areas in lymphoid tissues of dogs with spontaneous distemper

CD3, CD4, CD5, and CD8 antigen expression of T cells and IgG expression of B cells and canine distemper virus (CDV) antigen distribution were immunohistochemically examined in lymphoid tissues (lymph node, spleen, thymus, and tonsil) of control dogs and animals with spontaneous canine distemper. In addition, CNS tissue of all animals was studied for neuropathological changes and CDV antigen distribution. Based on the degree of depletion distemper dogs were classified into two groups. Group I represented animals with moderate to marked lymphoid depletion, while group II dogs displayed mild or no depletion. CDV antigen was mainly found in lymphocytes and macrophages of group I dogs, whereas CDV expression was most prominent in dendritic cells of group II animals. In group I dogs, a marked loss of CD3, CD4, CD5, CD8, and IgG expression was noticed, hereby loss of CD4+ cells was more prominent than depletion of CD8+ cells. In the lymphoid tissues of group II animals, a significant increase in the number of T and B cells was observed compared to group I dogs. The number of CD3+, CD4+, and CD8+ cells in group II dogs was similar to the findings in controls, however, CD5 and IgG expression was mildly reduced in T and B cell areas, respectively. Additionally, in groups I and II dogs, CD3+ and CD5- T cells were detected in T cell areas. Whether this cell population represents a cell type with autoimmune reactive potential remains to be determined. Surprisingly in group II animals, viral antigen was found predominantly in dendritic cells indicating a change in the cell tropism of CDV during chronic infection and a possible mechanism of viral persistence. The two patterns of lymphoid depletions correlated to two different types of canine distemper encephalitis (CDE). Group I dogs displayed acute non-inflammatory CDE, whereas group II dogs suffered from chronic inflammatory demyelinating CDE, indicating a pathogenic relationship between lymphocytic depletion and inflammatory brain lesions in distemper.

Thymic cysts in harbor porpoises (Phocoena phocoena) from the German North Sea, Baltic Sea, and waters of Greenland

Thymic cysts have not been previously reported in harbor porpoises (Phocoena phocoena). Two hundred forty stranded or "by-caught" harbor porpoises originating from the German North Sea and Baltic Sea and 14 animals from the waters of Greenland were necropsied. Thymuses of 78 porpoises of the North Sea and Baltic Sea were considered suitable for histopathologic examination based on the extent of postmortem autolysis. Immunohistochemistry using an anti-cytokeratin antibody was employed to demonstrate thymic epithelial structures in selected cases. Thymic macrocysts were rare and were only found in animals > or =7 years of age. Thymic microcysts, lined by a single cytokeratin-positive cell layer, were common in involuting thymuses, and the prevalence increased with advancing age. Thymic cysts might have arisen from degenerating Hassall's corpuscles or condensed epithelial reticulum. Thymuses were easily identified macroscopically in most adult healthy harbor porpoises, suggesting that physiological thymic involution proceeds slowly in this species.

Rhizopusmycosis in a harbor porpoise from the Baltic Sea

A case of systemic mycosis due to a Rhizopus sp. infection is described in a dead-stranded, 10-yr-old, male harbor porpoise (Phocoena phocoena) found on the beach of Neustadt, Schleswig-Holstein on the Baltic Sea (Germany). At necropsy, granulomatous mycotic lesions in brain, lung, kidneys, testis, and draining lymph nodes were found. In addition, a focal ulcerative gastritis of the first stomach, due to a nematode infection, was present and is suspected to be the portal of entry for the fungus.

Identification of CD4+ and CD8+ T cell subsets and B cells in the brain of dogs with spontaneous acute, subacute-, and chronic-demyelinating distemper encephalitis

CD4 and CD8 antigen expression of T cells as well as B cell and canine distemper virus (CDV) antigen distribution were immunohistologically examined in the cerebellum of dogs with spontaneous distemper encephalitis. Cellular and viral antigen expression were evaluated at intralesional and extralesional sites and in the perivascular space. Histologically, acute and subacute non-inflammatory encephalitis and subacute inflammatory and chronic plaques were distinguished. Demyelination was a feature of all subacute and chronic lesions, although the majority of plaques exhibited no or only a low level of active demyelination as demonstrated by single macrophages with luxol fast blue positive material in their cytoplasm. CDV antigen expression, observed in all distemper brains, was reduced in chronic plaques. CD4+, CD8+, and B cells were absent in controls and in some brains with acute encephalitis. A mild infiltration of CD8+ cells was noticed in the neuropil of the remaining brains with acute and all brains with subacute non-inflammatory encephalitis. Single CD4+ cells were found in two brains with acute and in all brains with subacute non-inflammatory encephalitis. Numerous CD8+ and CD4+ cells and few B cells, with a preponderance of CD8+ cells, were detected in subacute inflammatory and chronic lesions. In contrast, in perivascular infiltrates (PVI) of subacute and chronic lesions a dominance of CD4+ cells was detected. The dominating CD8+ cells in acute and subacute non-inflammatory encephalitis might be involved in viral clearance or contribute as antibody-independent cytotoxic T cells to early lesion development. In subacute inflammatory and chronic lesions CD8+ cells may function as cytotoxic effector cells and CD4+ cells by initiating a delayed-type hypersensitivity reaction. The simultaneous occurrence of perivascular B and CD4+ cells indicated that an antibody-mediated cytotoxicity could synergistically enhance demyelination. Summarized, temporal and spatial distribution of CD4+, CD8+ and B cells and virus antigen in early and late lesions support the hypothesis of a heterogeneous in part immune-mediated plaque pathogenesis in distemper demyelination.

Up-regulation of major histocompatibility complex class II antigen expression in the central nervous system of dogs with spontaneous canine distemper virus encephalitis

Major histocompatibility complex class II (MHC II) and canine distemper virus (CDV) antigen expression were compared by immunohistochemistry in the cerebellar white matter of ten dogs with naturally occurring canine distemper encephalitis. In addition, infiltrating mononuclear cells were characterized by employing poly- and monoclonal antibodies directed against human CD3, canine MHC II, CD5, B cell antigen and CDV-specific nucleoprotein. Positive antigen-antibody reaction was visualized by the avidin-biotin-peroxidase complex method on frozen sections. Histologically, neuropathological changes were categorized into acute, subacute, and chronic. In control brains, MHC II expression was weak and predominantly detected on resident microglia of the white matter and on endothelial, perivascular and intravascular cells. In CDV antigen-positive brains, MHC II was mainly found on microglia and to a lesser extent on endothelial, meningeal, choroid plexus epithelial, ependymal and intravascular cells. In addition, virtually all of the perivascular cells expressed MHC II antigen. CDV antigen was demonstrated most frequently in astrocytes. Of the perivascular lymphocytes, the majority were CD3-positive cells, followed by B cells. Only a small proportion of perivascular cells expressed the CD5 antigen. In addition, B cells and CD3 and CD5 antigen-positive cells were found occasionally in subacute and frequently in chronic demyelinating plaques. In acute encephalitis, CDV antigen exhibited a multifocal or diffuse distribution, and MHC II was moderately up-regulated throughout the white matter and accentuated in CDV antigen-positive plaques. In subacute encephalitis, moderate multifocal CDV antigen and moderate to strong diffuse MHC II-specific staining, especially prominent in CDV antigen-positive lesions, were observed. In chronic encephalitis, CDV antigen expression was restricted to single astrocytes at the edge of the lesions or was absent, while MHC II expression, especially prominent on microglia, was strongly up-regulated throughout the white matter, most pronounced in demyelinated plaques. In summary, in acute and subacute lesions without perivascular cuffs, MHC II expression correlated with the presence of CDV antigen. In contrast, in chronic lesions, MHC II expression on microglial cells was the most prominent despite a few CDV antigen-positive astrocytes, indicating that nonviral antigens may play an important role as triggering molecules for the process of demyelination.