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)-alpha and IL-12 and a lacking response of immunomodulatory cytokines such as IL-10 and transforming growth factor (TGF)-beta. A CD4+-mediated delayed type hypersensitivity and cytotoxic CD8+ T cells contribute to myelin loss in the chronic phase. Additionally, up-regulation of interferon-gamma 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.

Canine distemper of vaccine origin in European mink, Mustela lutreola--a case report.

Cases of canine distemper (CD) related to vaccination of exotic carnivores extend over three decades and have been described in at least nine different species. Our report describes a case of acute CD in a European mink, Mustela lutreola, vaccinated with live attenuated CD vaccine licensed for use in fur-farmed mink. The male mink died of an acute grey matter disease with an unusually long incubation period. A female vaccinated at the same time showed no obvious signs of illness. The diagnosis was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and by subsequent sequencing of the PCR products. The sequenced products of the virus isolated from the mink and of the vaccine batch showed 100% identity. This is the first report in which molecular methods were used to confirm that the disease was caused by the vaccine strain. Based on our findings, it is clearly evident that current CD vaccines cannot be safely used in exotic species.

Increased expression of pro-inflammatory cytokines and lack of up-regulation of anti-inflammatory cytokines in early distemper CNS lesions.

To investigate the pathogenesis of early lesions in canine distemper virus (CDV) leukoencephalomyelitis, the expressions of pro- and anti-inflammatory cytokines such as interleukin (IL)-1beta, IL-2, IL-6, IL-8, IL-10, IL-12, tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma and transforming growth factor (TGF)-beta and the housekeeping genes beta-actin and GAPDH were studied using semi-quantitative RT-PCR. Relative cytokine values were related to the degree of CDV infection, MHC class II expression and infiltration of CD4-, CD8- and CD3epsilon-positive lymphocytes. Actin up-regulation, in contrast to GAPDH, was influenced by CDV infection and therefore could not be used as an internal standard to study cytokine expression. In early CDV infection of the cerebellum, either no detectable lesions or mild infiltration of CD8 positive cells or demyelination and up-regulation of MHC class II antigen were observed. IL-6, -8, -12 and TNF-alpha transcripts were found in 94%, 94%, 78% and 56% of distemper dogs, respectively, compared to 17%, 33%, 0% and 0% in controls, whereas IL-1beta, -2 and IFN-gamma were not detectable in any of the studied cerebella. Conversely, IL-10 and TGF-beta transcripts were present in 83% and 100% of the investigated cerebella of distemper dogs and controls. Relative RT-PCR results, expressed as %GAPDH, revealed a significant up-regulation of IL-6, -8, -12 and TNF-alpha mRNA in distemper dogs; whereas IL-10 and TGF-beta showed only a weak and not significantly increased expression following infection. Relative pro-inflammatory cytokine expression values were highest following CDV infection, indicating that the virus itself directly triggered the up-regulation of the pro-inflammatory cytokines. Succeeding changes, such as lymphocyte infiltration, MHC class II up-regulation and demyelination resulted only in a minor additional increase in cytokine expression, implying a secondary or by-stander mechanism of cytokine activation by these changes. Disease initiation and progression in early distemper leukoencephalomyelitis seemed to be due to a lacking or inappropriate response of the anti-inflammatory cytokines in the presence of a vigorous up-regulation of pro-inflammatory cytokines.

Inflammatory diseases of the central nervous system in dogs.

Inflammatory diseases of the central nervous system (CNS) are important causes of seizures in dogs. Specific diseases include canine distemper, rabies, cryptococcosis, coccidioidomycosis, toxoplasmosis, neosporosis, Rocky Mountain spotted fever, ehrlichiosis, granulomatous meningoencephalomyelitis, and pug dog encephalitis. Inflammatory disorders should be considered when a dog with seizures has persistent neurological deficits, suffers an onset of seizures at less than 1 or greater than 5 years of age, or exhibits signs of systemic illness. A thorough history, examination, and analysis of cerebrospinal fluid are important in the diagnosis of inflammatory diseases. However, even with extensive diagnostic testing, a specific etiology is identified in less than two thirds of dogs with inflammatory diseases of the CNS.

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.

Possible vaccine-induced canine distemper in a South American bush dog (Speothos venaticus).

Suspected vaccine-induced canine distemper was diagnosed in a captive female bush dog (Speothos venaticus). Macroscopic lesions included mild congestion of the gastric mucosa and focal consolidation of the lung. Histopathological lesions included status spongiosis, gliosis, widespread eosinophilic, intranuclear and intracytoplasmic inclusion bodies in neurons, astrocytes and gitter cells of the cerebral, cerebellar and spinal white matter.

Distemper encephalitis in pups after vaccination of the dam.

A five-year-old labrador bitch which had whelped 10 pups three days previously was given booster vaccination against distemper, adenovirus, parvovirus, parainfluenzavirus and leptospirosis. Eighteen days later, signs of central nervous system disease developed in some of the pups, five of which were ultimately euthanased. The cause of the nervous disease was found to be canine distemper, and serological studies showed that the infection was limited to some members of the litter, suggesting that the vaccinal rather than a field virus was more likely to have been responsible.

Vaccine-associated canine distemper infection in a litter of African hunting dogs (Lycaon pictus).

Four, 57 days old, African hunting dog puppies (Lycaon pictus) from one litter died within three weeks following vaccination with modified-live canine distemper virus (CDV) and killed canine adenovirus type 1, canine parvovirus and Leptospira icterohemorrhagiae and canicola. 18 days post vaccination, the animals developed neurologic disease characterized by episodes of grand mal seizures and circling. Macroscopic, histological and immunohistochemical studies revealed acute systemic CDV infection with acute encephalopathy. Virus isolation attempts using primary dog kidney cells, lung macrophages and Vero cells were negative. Therefore, the question whether the infection was the result of vaccination or natural infection remains open. The benefits and risks regarding the use of modified-live CDV vaccines and killed canine distemper vaccines in exotic carnivores are briefly discussed.

Encephalitis induced by a canine distemper virus in squirrel monkeys.

Intracerebral inoculation with canine distemper virus (CDV) caused acute neurological signs of viral encephalitis in squirrel monkeys. Electroencephalogram revealed an abnormal sharp wave and seizure discharges resembling those of epilepsy. There was parenchymal inflammation, perivascular cuffs, neuronal degeneration, and glial reactions. Virus antigen was detected immunohistologically in the neurons and ependymal cells. Thus, CDV infection in squirrel monkeys provides an animal model for viral encephalitis and epilepsy.

A morbillivirus causing mass mortality in seals.

During an outbreak of a serious apparently infectious disease among harbour seals (Phoca vitulina), which started in the Kattegat area in April 1988 and rapidly spread to the North sea, the Wadden sea and the Baltic sea, greater than 17,000 animals died within a period of eight months. In August 1988 it was realized that the clinical symptoms and pathological lesions were similar to those found in canine distemper: apart from general depression and fever, the animals suffered from severe respiratory, gastrointestinal and central nervous disease and a variety of viral, bacterial and parasitic infections were frequently encountered, suggesting a severe malfunctioning of the immune system. At different expert meetings, held in several of the countries involved, possible explanations for the deaths were not only attributed to an infectious agent, but also to effects of overpopulation and environmental pollution. Seroepizootiological studies and the failure of vaccination experiments suggested that a herpesvirus and a picornavirus, which had been isolated from dead seals at the beginning of the outbreak, were opportunistic infections occurring in animals suffering from another infection rather than being the primary cause of the outbreaks. Serological studies were then extended to other viruses of carnivores, known to cause similar symptoms. Screening of a large panel of seal sera from the Netherlands, Denmark, FRG, Sweden and the UK, collected before and during the outbreak, in a virus neutralization test for the presence of canine distemper virus (CDV) neutralizing antibodies, indicated that CDV or a closely related morbillivirus was the primary cause of the disease outbreak.(ABSTRACT TRUNCATED AT 250 WORDS)

Vaccination-induced distemper in kinkajous.

Following vaccination for distemper, using a modified live-virus vaccine developed for dogs, 2 young kinkajous (Potos flavus) developed diarrhea, then central nervous system disease. Clinical signs included myoclonus, head trembling, loss of muscular coordination, and convulsions. One kinkajou gradually recovered; the other seemed to recover, then relapsed and was euthanatized. Microscopic lesions included those of interstitial pneumonia and enteritis and multifocal lymphocytic inflammation, gliosis, spongiosis, and swollen and degenerating axons in the cerebral, cerebellar, and brain stem white matter. Similar lesions were found at all caudally, as exemplified by complete destruction of the dorsal funiculi and dorsal horns of the gray matter of the upper sacral cord segments. Eosinophilic intranuclear inclusions were seen histologically in the glia in the spinal cord, midbrain, and cerebellum, and were confirmed as canine distemper viral inclusions by the fluorescent antibody method. It was concluded that modified live canine distemper virus vaccines should be used with caution or not at all in kinkajous.

Response of gray foxes to modified live-virus canine distemper vaccines.

Ten gray foxes seronegative for canine distemper virus were vaccinated with 1 of 3 commercial modified live-virus canine distemper vaccines. Of 5 foxes receiving vaccine A (chicken tissue culture origin), 4 developed significant titers (greater than or equal to 1:100) of neutralizing antibody to canine distemper virus and remained clinically normal after vaccination. Two of 3 foxes vaccinated with vaccine B (canine cell line origin) and both foxes receiving vaccine C (canine cell line origin) died of vaccine-induced distemper. Five unvaccinated control foxes died of distemper after a known occasion for contact transmission of virus from a fox vaccinated with vaccine B. The results suggested that the chicken tissue culture origin modified live-virus canine distemper vaccine is probably safe for normal adult gray foxes, whereas the canine cell origin vaccines are hazardous. The results of this study tended to corroborate anecdotal experiences of veterinarians who have observed that gray foxes frequently die from distemper soon after vaccination with modified live-virus canine distemper vaccines.