Canine microglial cells: stereotypy in immunophenotype and specificity in function?

Microglial cells represent the endogenous immune system of the central nervous system (CNS). Upon pathological insults they reveal their immunological potential aimed at regaining homeostasis. These reactions have long been believed to follow a uniform and unspecific pattern which is irrespective to the underlying disease entity. Evidence is growing that this view seriously underrates microglial competence as the defenders of the CNS. In the present study, microglial cells of 47 dogs were examined ex vivo by means of flow cytometry. Ex vivo examination included immunophenotypic characterization using eight different surface markers and functional studies such as phagocytosis assay and the reactive oxygen species (ROS) generation test. The dogs were classified according to their histopathological diagnoses in disease categories (controls, canine distemper virus (CDV) induced demyelination, other diseases of the CNS) and results of microglial reaction profiles were compared. Immunophenotypic characterization generally revealed relative high conformity in the microglial disease response among the different groups, however the functional response was shown to be more specific. Dogs with intracranial inflammation and dogs with demyelination showed an enhanced phagocytosis, whereas a significant up-regulation of ROS generation was found in dogs with demyelination due to CDV infection. This strongly suggests a specific response of microglia to infection with CDV in the settings of our study and underlines the pivotal role of microglial ROS generation in the pathogenesis of demyelinating diseases, such as canine distemper.     

Partial protection and intrathecal invasion of CD8(+) T cells in acute canine distemper virus infection

Initial non-inflammatory demyelination in canine distemper virus infection (CDV) develops against a background of severe immunosuppression and is therefore, thought to be virus-induced. However, recently we found a marked invasion of T cells throughout the central nervous system (CNS) in dogs with acute distemper despite drastic damage to the immune system. In the present study, this apparent paradox was further investigated by immunophenotyping of lymphocytes, following experimental CDV challenge in vaccinated and non-vaccinated dogs. In contrast to CDV infected, unprotected dogs, vaccinated dogs did not become immunosuppressed and exhibited a strong antiviral immune response following challenge with virulent CDV. In unprotected dogs rapid and drastic lymphopenia was initially due to depletion of T cells. In peripheral blood, CD4(+) T cells were more sensitive and depleted earlier and for a longer time than CD8(+) cells which recovered soon. In the cerebrospinal fluid (CSF) we could observe an increase in the T cell to B cell and CD8(+) to CD4(+) ratios. Thus, partial protection of the CD8(+) cell population could explain why part of the immune function in acute distemper is preserved. As found earlier, T cells invaded the CNS parenchyma in these dogs but also in the protected challenged dogs, which did not develop any CNS disease at all. Since markers of T cell activation were upregulated in both groups of animals, this phenomenon could in part be related to non-specific penetration of activated T cells through the blood brain barrier. However, in diseased animals much larger numbers of T cells were found in the CNS than in the protected dogs, suggesting that massive invasion of T cells in the brain requires CDV expression in the CNS.     

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.     

Immunohistochemical distribution of alpha B-crystallin in the cerebellum of dogs infected with canine distemper virus

The cerebella of 12 dogs infected with canine distemper virus (CDV) and those of three normal dogs were examined. The avidin-biotin-peroxidase complex technique was used to detect alphaB-crystallin (alphaB-c) immunoreactivity and immunolocalisation of the CDV antigen. CDV antigens, immunopositive astrocytes, oligodendrocytes and granular neurons were seen in both the white and grey matter of the infected dogs. In the controls, alphaB-c immunopositive glial cells were seen in the white matter and around the Purkinje cells. In dogs with distemper, alphaB-c immunoreactivity was not observed in some of the glial cells around the Purkinje cells. A significant negative correlation of P < 0.01 level was found between areas of severe demyelination and the number of alphaB-c immunopositive cells in dogs infected with CDV. Such correlation was not observed between mild and moderate demyelinating areas and alphaB-c immunostaining. The alphaB-crystallin/ total number of cells ratio was found to be significant in severely affected demyelinating areas (P < 0.05). These data indicate that there was a relationship between the degrees of CDV associated with demyelination and the level of alphaB-c expression in the glial cells.     

Roles of an extracellular matrix (ECM) receptor and ECM processing enzymes in demyelinating canine distemper encephalitis

Canine distemper virus (CDV) belongs to the genus Morbillivirus of the Paramyxoviridae family. Due to the central nervous system (CNS) tropism of the virus and associated neuropathological changes, demyelinating canine distemper encephalitis (CDE) represents a relevant model for human demyelinating diseases like multiple sclerosis. The present review decribes the role of CD44 antigen (CD44), the principle cell surface receptor for hyaluronate and extracellular matrix (ECM) processing enzymes (matrix metalloproteinases [MMPs]) and their inhibitors (TIMPs) in the pathogenesis of demyelination. In acute and subacute CDE, a plaque-associated CD44 up-regulation is found that parallels astrocyte activation. Likewise, MMPs and TIMPs are prominently up-regulated in these lesions and are expressed mostly by astrocytes and microglia. In chronic lesions, CD44 expression declines together with the number of glial fibrillary acidic protein (GFAP) positive astrocytes. In addition, in this plaque type, CD44 is expressed on the cell membrane of perivascular mononuclear cells. In this phase, a decrease of MMP and TIMP expressions apart from MMP-11, -12, and -13 is obvious. In summary, CD44 and MMPs might be associated with the onset of demyelination and may interact to initiate ECM disturbances. Ligation of CD44 in the early phase may induce chemokines and cytokines and hence initiate and perpetuate the inflammatory process. In the chronic phase, it is conceivable that a MMP-TIMP imbalance may be the motor for lesion progression with a simultaneous influx of CD44-positive activated immune cells.     

Immunohistochemical investigation of cerebellum in dogs infected with canine distemper virus

The cerebella of 21 dogs with canine distemper virus (CDV) infection and four normal dogs were examined histopathologically and immunohistochemically. Cerebella of CDV-infected dogs showed nonsuppurative demyelinating encephalomyelitis, classified as acute, subacute or chronic. Immunolocalisation of CDV antigen also confirmed the infection. Tissues were examined for co-localisation of the CDV antigen with either an astrocyte-specific marker, glial fibrillary acidic protein (GFAP), or an oligodendrocyte-specific marker, galactocerebroside (GalC). Immunoreactive cells were counted in demyelinating areas of the white matter. The number of astrocytes (GFAP positive) was significantly (p < 0.05) higher in CDV-infected dogs compared to controls. In contrast, the number of oligodendrocytes (GalC positive) was significantly (p < 0.001) lower in CDV-infected dogs and was much lower in chronic cases (p < 0.05). Approximately 41% of astrocytes and 17% of oligodendrocytes were immunoreactive for CDV. The ratio of CDV-infected oligodendrocytes and astrocytes remained almost constant during the progression of the disease (P > 0.05). In conclusion, CDV infects both astrocytes and oligodendrocytes. The gradual loss of oligodendrocytes is most likely responsible for the progressive demyelination in CDV infection. Astrocytosis in CDV infection should be further investigated if it occurs to stimulate oligodendrocytes for myelin production to compensate for the loss or to induce oligodendrocyte degeneration.     

Cerebellum progesterone concentration decreased in canine distemper virus infection

Progesterone has neuroprotective effects including augmentation of myelination in the central and peripheral nervous system. This study was designed to determine if demyelinating lesions in the cerebellum resulting from canine distemper virus (CDV) infection are associated with progesterone levels. Progesterone was measured using radioimmunoassay in samples of the cerebellum, corpus callosum, medulla oblongata, parietal, frontal, temporal, and occipital cortices as well as cerebrospinal fluid (CSF) and plasma collected from ten CDV infected and six non-infected dogs. The cerebellum progesterone level was significantly different between CDV infected (0.66+/-0.09 ng/g) and control dogs (1.14+/-0.09 ng/g) (p<0.001); however, no difference was observed for the other CNS regions, plasma and CSF (p>0.05). The cerebellum progesterone level was also significantly different between acute (0.71+/-0.0 5 ng/g) and chronic cases (0.61+/-0.09 ng/g) (p<0.05). The CDV infected cerebella were also categorized histopathologically according to the severity of demyelinating lesions as mild (n=5), moderate (n=2), or severe (n=3) among which the cerebellum progesterone level was significantly different (p<0.05). Progesterone concentration was 0.71+/-0.05 ng/g in mild, 0.65+/-0.10 ng/g in moderate, and 0.56+/-0.07 ng/g in severe cases. In conclusion, progesterone concentration decreases in the cerebellum in CDV infection and the severity of demyelinating lesions is the greatest in cerebella with the lowest progesterone concentrations. The results suggest that local impairment of progesterone metabolism may be associated with the initiation and progression of cerebellar lesions in CDV infection.     

Apoptosis in the cerebellum of dogs with distemper

Canine distemper virus (CDV) may induce multifocal demyelination in the central nervous system of infected dogs. The pathogenesis of this process is not clear. The present work identifies the presence of apoptotic cells in white and grey matter of dogs'cerebellum, naturally infected with CDV. Fifteen dogs with clinical signs of canine distemper that tested positive for CDV nucleoprotein were used. Brain specimens were processed and embedded in paraffin. Sections 5 microm thick were stained with hematoxylin-eosin and Shorr. Other sections were submitted to TUNEL reaction and to immunohistochemistry for CDV nucleoprotein detection. Acute and chronic demyelinated plaques were observed in the white matter, while apoptosis occurred particularly in the granular layer of grey matter. Apoptosis seems to play an important role in the pathogenesis of canine distemper demyelination.     

Pathogenesis and immunopathology of systemic and nervous canine distemper

Canine distemper is a worldwide occurring infectious disease of dogs, caused by a morbillivirus, closely related to measles and rinderpest virus. The natural host range comprises predominantly carnivores. Canine distemper virus (CDV), an enveloped, negative-sense RNA virus, infects different cell types, including epithelial, mesenchymal, neuroendocrine and hematopoietic cells of various organs and tissues. CDV infection of dogs is characterized by a systemic and/or nervous clinical course and viral persistence in selected organs including the central nervous system (CNS) and lymphoid tissue. Main manifestations include respiratory and gastrointestinal signs, immunosuppression and demyelinating leukoencephalomyelitis (DL). Impaired immune function, associated with depletion of lymphoid organs, consists of a viremia-associated loss of lymphocytes, especially of CD4+ T cells, due to lymphoid cell apoptosis in the early phase. After clearance of the virus from the peripheral blood an assumed diminished antigen presentation and altered lymphocyte maturation cause an ongoing immunosuppression despite repopulation of lymphoid organs. The early phase of DL is a sequel of a direct virus-mediated damage and infiltrating CD8+ cytotoxic T cells associated with an up-regulation of pro-inflammatory cytokines such as interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-β. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-γ and IL-1 may occur in advanced lesions. Moreover, an altered balance between matrix metalloproteinases and their inhibitors seems to play a pivotal role for the pathogenesis of DL. Summarized, DL represents a biphasic disease process consisting of an initial direct virus-mediated process and immune-mediated plaque progression. Immunosuppression is due to early virus-mediated lymphocytolysis followed by still poorly understood mechanisms affecting antigen presentation and lymphocyte maturation.     

自发性急性犬瘟热的原发性脱髓性脑病

为了进一步观察犬瘟热病毒引起的原发性脑损伤和包涵体形成的特点，调查脑组织的损伤与神经症状的关系，对10只急性犬瘟热病犬的脑组织进行了详细的病理学研究。为了仔细地观察病变，本试验按照解剖学关系将脑组织分成3个大部分和11个切面，即大脑(4个切面)，脑干(5个切面)和小脑(2个切面)。组织切片经HE、LFB和免疫组织化学染色后进行检查，结果表明：在大脑，脱髓呈弥漫性发生，程度较轻；脑干的周围或靠近第三脑室的白质脱髓较重；小脑在轻度或中度脱髓的基础上常出现严重的多发性脱髓灶。脱髓部呈空泡或海绵状，有少量胶质细胞存在，但无炎性反应。脱髓性病损是非时称性发生，对神经束没有特殊的亲和力。在脑室的室管膜细胞内发现有较多的嗜酸性胞浆或核内包涵体。用抗犬瘟热病毒抗体染色，带有包涵体的室管膜细胞呈现强阳性反应。部分锥体细胞，神经核细胞和漓氏细胞变性、溶解或胞浆深染。胞核浓缩。这种变化以小锥体神经细胞表现得最为明显。根据此研究结果，作者认为由犬瘟热病毒引起的原发性脑组织损伤是一种脱髓性脑病，而不是脑炎变化；位于室管膜细胞内的包涵体对于脑组织犬瘟热的确诊具有重要的作用；由于犬瘟热病毒引起神经细胞的损伤是非特异性的，对脑组织的侵害是非对称性的。对神经束的作用无特殊的亲和力，所以患犬瘟热的犬在临床上可出现不同的神经症状。     

Canine distemper virus-induced depletion of uninfected lymphocytes is associated with apoptosis

Canine distemper virus (CDV), a negative stranded RNA morbillivirus, causes a multisystemic disease in dogs, which is associated with a severe immune suppression. The aim of the study was to examine the influence of early CDV infection on leukocyte depletion, lymphopenia and virus-induced cell death in dogs infected with a virulent CDV strain. From 10 infected dogs, peripheral blood leukocytes were harvested periodically, phenotyped and analyzed for CDV antigen content and apoptosis using Annexin V-FITC and propidium iodide labeling. CDV infection induced a severe CD3+ T cell and CD21+ B cell depletion in all animals at 3 days post-infection (d.p.i.). For dogs with severe distemper, developing virus persistence in the lymphoid tissue and central nervous system, this lymphopenia lasted until the end of the experiment. Increased levels of lymphocyte apoptosis were found at 3 d.p.i., and monocyte apoptosis at 6 d.p.i. This was more prominent in the group of animals with severe distemper. At 3 d.p.i. no leukocyte infection was detectable indicating that the early lymphocyte depletion and apoptosis was not a direct consequence of virus infection. Taken together, our results demonstrate that CDV-induced lymphopenia is an early event and that the degree of lymphocyte depletion correlates with the severity of disease and virus persistence in the lymphoid tissue and central nervous system.     

Immunohistochemical demonstration of the putative canine distemper virus receptor CD150 in dogs with and without distemper

Signaling lymphocyte activation molecule (SLAM) or CD150 can function as a receptor for the canine distemper virus (CDV) in vitro. The expression of SLAM was studied using immunohistochemistry in order to evaluate the presence and distribution of the receptor in dogs in vivo. Additionally, receptor expression was assessed after experimental infection of dogs with CDV. In 7 control dogs without distemper virus, the receptor was found in various tissues, mostly on cells morphologically identified as lymphocytes and macrophages. In 7 dogs with early distemper lesions characterized by presence of the virus, higher numbers of SLAM-expressing cells were found in multiple tissues recognized as targets of CDV compared with those in control dogs. These findings suggest that SLAM, a putative distemper receptor, is expressed in dogs in vivo. Additionally, virus infection is associated with up-regulation of SLAM, potentially causing an amplification of virus in the host.     

Establishment of central nervous system infection by canine distemper virus: breach of the blood-brain barrier and facilitation by antiviral antibody

Morphologic, immunologic and virologic data implicating antiviral antibody in promoting entry of canine distemper virus (CDV) into brain and reticuloendothelial tissues are reviewed. Infection of central nervous system (CNS) endothelium precedes invasion of virus-positive and -negative leukocytes into Virchow-Robin spaces and central nervous system (CNS) parenchyma by 1-3 days. Platelets are implicated in initiation of endothelial infection in that: CDV-infected dogs are thrombocytopenic; platelets from CDV-infected dogs contain IgG-virus complexes on their plasma membranes; platelet microthrombi were observed adjacent to foci of endothelial infection, and; CDV-susceptible ferrets rendered thrombocytopenic by antiplatelet antibody exhibit delayed viral entry into CNS tissues. Renal glomerular-bound IgG, IgM and occasionally CDV antigen were demonstrated in CDV-infected dogs by immunocytochemical techniques. Distemper-infected dogs with inherited C3 deficiency exhibited enhanced renal glomerular disease associated chiefly with deposition of IgM in mesengial regions vs. their homozygous normal CDV-infected littermates. Direct infusion of virus-positive leukocytes, plasma and platelets into the CNS capillary bed via the right carotid artery should establish the primacy of each in the initiation of CNS vascular endothelial infection by CDV.     

Comparison of canine distemper virus strains in gnotobiotic dogs: effects on lymphoid tissues.

The effects of infection on various aspects of lymphoid function in gnotobiotic dogs with 2 virulent strains of canine distemper virus (CDV), Snyder-Hill CDV and R252-CDV, were compared. Both infections resulted in a viremia-related lymphopenia which was nonselective in that the percentages of B and T cells remained unchanged throughout the observation period. Nonfatal Snyder-Hill-CDV infection resulted in a transient depression of in vitro lymphocyte responses to phytohemagglutinin-P, whereas R252-CDV produced prolonged in vitro suppression of phytohemagglutinin-P stimulation. The differences observed are of minor significance and do not explain the differences in central nervous system demyelinating potential between these 1 strains of CVD.     

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.     

犬瘟热病毒研究概况

犬瘟热(CD)是由犬瘟热病毒(CDV)引起的一种急性、高度接触性传染病,流行范围广,发病率、致死率高,临床症状多样。CDV感染宿主广泛,所有日龄的犬都有可能感染。CDV属于副黏病毒科麻疹病毒属,有囊膜包裹的单股负链线性RNA病毒。CDV基因组编码6种蛋白:核衣壳(N)蛋白、磷(P)蛋白、基质膜(M)蛋白、融合(F)蛋白、血凝素(H)蛋白和大(L)蛋白。N、P和L蛋白与病毒复制有关;M蛋白与病毒的装配和出芽有关;F、H蛋白在病毒的侵染过程中起到关键作用。近年来,随着我国宠物业、毛皮经济养殖业的迅速发展,CD在我国的发病率有升高的趋势。论文对CDV分子生物学研究进展进行归纳总结。     

犬瘟热的诊断及其预防免疫的研究进展

本文对犬瘟热（CD）的诊断、预防免疫和免疫失败的影响因素及犬瘟热病毒（CDV）的宿主范围进行了综述。CDV不仅感染陆生食肉动物，而且也感染水生食肉动物，并且其宿主范围还在不断扩大。CDV感染主要采用病毒分离、特异性病毒抗原或特异性核酸检测等方法确诊。疫苗包括灭活的CDV疫苗、麻疹病毒（MV）异源苗及CDV弱毒活苗。疫苗接种犬的免疫反应主要取决于毒株特性及犬的应答能力，只有弱毒活苗能诱导产生持久而坚强的保护力。尽管多年来CDV弱毒活苗的使用控制了CD的发生，但最近免疫过的犬发生CD的病例并不少见。分析免疫失败的原因，主要是母源抗体干扰、疫苗质量差、其它病毒的免疫抑制以及CDV流行株可能发生了变异等因素的影响。     

Urban domestic dog populations as a source of canine distemper virus for wild carnivores in the Coquimbo region of Chile

Urban areas can support dog populations dense enough to maintain canine distemper virus (CDV) and can be a source of infection for rural dogs and free-ranging carnivores. The aim of this study was to investigate the relationships between urban and rural domestic dog and wild carnivore populations and their effects on the epidemiology of CDV to explain retrospectively a CD outbreak in wild foxes in 2003. From 2005 to 2007 a cross-sectional household questionnaire survey was conducted in Coquimbo and Ovalle cities, in three towns and in rural sites along two transects from these cities to the Fray Jorge National Park (FJNP) in the Coquimbo region, Chile. Blood samples were collected from unvaccinated dogs at surveyed households and from free-ranging foxes in rural areas along the transects. The seroprevalence of CDV in domestic dogs was higher in urban than in rural areas and in the later was highest in dogs born before 2001-2002. The seroprevalence of CDV in foxes was higher in areas closer to human settlements. A high seroprevalence in dogs born before 2001-2002 further supports a link between CDV patterns in rural dog and fox populations. In our study area, urban dogs are proposed to be the source of CDV infection to wild carnivores. The large dog population size and density detected in Coquimbo and Ovalle provides optimal conditions for maintaining a large and dense susceptible population of dogs, which can act as a reservoir for highly infectious diseases and could have been the source of infection in the CD outbreak in wild foxes.     

Canine distemper virus infection of canine footpad epidermis

Infection of the footpad epidermis can occur in natural canine distemper virus (CDV) infection of dogs. Footpads from 19 dogs experimentally inoculated with virulent distemper strain A75/17 and from two nonexposed dogs were examined histopathologically and assessed for the presence of viral antigen and nucleoprotein mRNA, as well as number of inflammatory and apoptotic cells. Dogs were divided into four groups based on inoculation status and postmortem examination: inoculated dogs with severe distemper (group 1, n = 7); inoculated dogs with mild distemper (group 2, n = 4); inoculated dogs without distemper (group 3, n = 8); and noninoculated dogs (group 4, n = 2). Footpads from dogs of all groups had a comparably thick epidermis. Eosinophilic viral inclusions and syncytial cells were present in footpad epidermis of one dog of group 1. Footpads of group 1 dogs contained viral antigen and mRNA in the epidermis with strongest staining in a subcorneal location. Additionally, in these dogs footpad dermal structures including eccrine glands and vascular walls were positive for virus particles. No CDV antigen or mRNA was present in the footpad epidermis and dermis of any other dog. Group 1 dogs had more CD3-positive cells and apoptotic cells within the basal layer of the epidermis when compared to the other groups. These findings demonstrate that in experimental infection CDV antigen and mRNA were colocalized in all layers of the infected canine footpad epidermis. The scarcity of overt pathological reactions with absence of keratinocyte degeneration indicates a noncytocidal persisting infection of footpad keratinocytes by CDV.     

Canine distemper virus-associated hypocalcemia.

A retrospective study was done to correlate serum calcium concentrations and parathyroid gland ultrastructure to clinical, immunologic, and pathologic changes experimentally induced in gnotobiotic dogs by canine distemper virus (CDV). Dogs infected with CDV had significantly reduced serum calcium concentrations associated with ultrastructural evidence of parathyroid gland inactivity, degeneration, and viral inclusions. Although CDV-infected dogs exhibited neurologic signs, minimal lesions were present in the central nervous system. It is suggested that viral-induced parathyroid dysfunction may contribute to neutrologic disturbance of CDV infection.