Immunopathogenic and neurological mechanisms of canine distemper virus

Epidemiologic Factors Supporting Triage of Infected Dog Patients Admitted to a Veterinary Hospital Biological Isolation and Containment Unit

The teaching hospital of the Faculty of Veterinary Medicine at the University of Lisbon hosts a Biological Isolation and Containment Unit (BICU) for the hospitalization of both confirmed and suspected animals of an infectious disease. This study targets the BICU dog population to identify and characterize the most frequent infectious diseases recorded in a 7-year period. Several epidemiologic factors were analyzed for their significance to triage infected cases. During the study period, 534 dogs were admitted, of which 263 (49.3%) had a confirmed infectious disease diagnosis: parvovirosis (49.4%; n = 130); leptospirosis (21.7%; n = 57); multidrug-resistant (MDR) bacterial infection; (10.6%; n = 28), and canine distemper (9.9%; n = 26). Several potential risk factors for these diseases were identified: age under 2 years old (p < 0.001), incomplete vaccination for parvovirosis (p < 0.001), age ≥ 10 years old (p < 0.001), and the presence of concomitant disorders for MDR-infected cases (p = 0.03). Logistic regression models were constructed to classify cases and controls. The sensitivity and specificity estimates were very high (>0.83) for parvovirosis, MDR, and distemper infections. A lower sensitivity (0.77) was obtained for identifying cases with leptospirosis. In conclusion, infectious diseases are frequent, hence, it is essential to decrease their occurrence through effective preventive measures such as vaccination. The constructed logistic models can also help in triaging admitted dogs with a potential infectious disease.

Comparison of some cytokines, acute phase proteins and citrulline levels in healthy and canine distemper infected dogs

Canine distemper virus (CDV) is the etiological agent of severe disease in domestic and wild carnivores. Clinical diagnosis of CDV is challenging because of its similarity to other canine respiratory and intestinal diseases. We aimed to determine certain cytokine (interleukin [IL]-1β, IL-2, IL-4, IL-6, IL-10, and tumor necrosis factor-α [TNF-α]), interferon (IFN)-γ, canine serum amyloid A (SAA), and canine citrulline (CIT) levels for the first time in CDV-positive dogs. For this purpose, 10 CDV-positive dogs with compatible clinical findings (i.e., neurological symptoms such as tremors and myoclonus, ocular and nasal discharge, and wheezing) and 10 healthy dogs based on the clinical examinations and rapid test results were enrolled. It was observed that the CIT, INF-γ, IL-1β, IL-2, IL-6, and TNF-α levels were significantly decreased in the CDV-positive dogs than that of the healthy ones (P<0.05). As a result, it was observed that CDV causes immunosuppression and accordingly, the inflammatory response might cause decreased cytokine and acute-phase protein synthesis. Therefore, it was concluded that further investigation of inflammatory pathways and CIT interactions may provide crucial clinical information at different stages of CDV, and aforementioned parameters may serve as important biomarkers for CDV in terms of demonstrating the presence of immunosuppression.

Canine Distemper Virus in Autochtonous and Imported Dogs, Southern Italy (2014–2021)

Simple Summary

In the period 2014–2021, the circulation of CDV in dogs of Southern Italy was investigated. In this time span a reduction in the circulation of CDV was observed, with a higher frequency of detection of the pathogen in imported dogs (18.4%) compared to stray (7.4%) and household (3.9%) animals. These results underline the effectiveness of the prophylaxis strategy on autochthonous dogs as well as the importance of continuous surveillance of CDV, especially in imported dogs.

Abstract

This study aims to investigate the presence of canine distemper virus (CDV) infection in 949 autochthonous or illegally imported dogs from Southern Italy, over a period of eight years (2014–2021). CDV RNA was detected in 6.8% (65/949) of the animals tested, with no detection of CDV in dogs sampled in 2020–2021. The frequency of CDV detection was higher in imported dogs (19/103, 18.3%) with respect to stray (27/365, 7.4%) and household dogs (19/481, 3.9%). On sequence and phylogenetic analyses of selected strains, the analyzed viruses belonged to the Arctic clade, which has already been reported in Italy and in Europe. The results of our study may suggest a reduction of CDV circulation in Southern Italy, while at the same time highlighting the need for strict controls on dog importation, in order to prevent the introduction of viruses from endemic countries.

Phenotypic and Transcriptional Changes of Pulmonary Immune Responses in Dogs Following Canine Distemper Virus Infection

Canine distemper virus (CDV), a morbillivirus within the family Paramyxoviridae, is a highly contagious infectious agent causing a multisystemic, devastating disease in a broad range of host species, characterized by severe immunosuppression, encephalitis and pneumonia. The present study aimed at investigating pulmonary immune responses of CDV-infected dogs in situ using immunohistochemistry and whole transcriptome analyses by bulk RNA sequencing. Spatiotemporal analysis of phenotypic changes revealed pulmonary immune responses primarily driven by MHC-II⁺, Iba-1⁺ and CD204⁺ innate immune cells during acute and subacute infection phases, which paralleled pathologic lesion development and coincided with high viral loads in CDV-infected lungs. CD20⁺ B cell numbers initially declined, followed by lymphoid repopulation in the advanced disease phase. Transcriptome analysis demonstrated an increased expression of transcripts related to innate immunity, antiviral defense mechanisms, type I interferon responses and regulation of cell death in the lung of CDV-infected dogs. Molecular analyses also revealed disturbed cytokine responses with a pro-inflammatory M1 macrophage polarization and impaired mucociliary defense in CDV-infected lungs. The exploratory study provides detailed data on CDV-related pulmonary immune responses, expanding the list of immunologic parameters potentially leading to viral elimination and virus-induced pulmonary immunopathology in canine distemper.

Multiple Receptors Involved in Invasion and Neuropathogenicity of Canine Distemper Virus: A Review

The canine distemper virus (CDV) is a morbillivirus that infects a broad range of terrestrial carnivores, predominantly canines, and is associated with high mortality. Similar to another morbillivirus, measles virus, which infects humans and nonhuman primates, CDV transmission from an infected host to a naïve host depends on two cellular receptors, namely, the signaling lymphocyte activation molecule (SLAM or CD150) and the adherens junction protein nectin-4 (also known as PVRL4). CDV can also invade the central nervous system by anterograde spread through olfactory nerves or in infected lymphocytes through the circulation, thus causing chronic progressive or relapsing demyelination of the brain. However, the absence of the two receptors in the white matter, primary cultured astrocytes, and neurons in the brain was recently demonstrated. Furthermore, a SLAM/nectin-4-blind recombinant CDV exhibits full cell-to-cell transmission in primary astrocytes. This strongly suggests the existence of a third CDV receptor expressed in neural cells, possibly glial cells. In this review, we summarize the recent progress in the study of CDV receptors, highlighting the unidentified glial receptor and its contribution to pathogenicity in the host nervous system. The reviewed studies focus on CDV neuropathogenesis, and neural receptors may provide promising directions for the treatment of neurological diseases caused by CDV. We also present an overview of other neurotropic viruses to promote further research and identification of CDV neural receptors.

Radiographic evidence of metaphyseal sclerosis secondary to canine distemper virus: 4 cases in juvenile dogs

Background

Metaphyseal sclerosis secondary to canine distemper virus has been described histopathologically, but its radiographic appearance has not been described.

Objectives

Describe the radiographic appearance of metaphyseal sclerosis secondary to canine distemper virus in juvenile dogs as distinct from metaphyseal osteopathy (formerly called hypertrophic osteodystrophy).

Animals

Four dogs (2 intact females and 2 intact males) between 2.5 and 4 months of age presented to 2 different veterinary teaching hospitals.

Methods

Retrospective case series in which definitive diagnosis of canine distemper virus based on antemortem positive reverse transcription‐polymerase chain reaction (RT‐PCR) result or necropsy was required.

Results

All 4 dogs were presented for evaluation of neurologic abnormalities, respiratory signs, and lethargy; 2 dogs had gastrointestinal signs and ocular abnormalities. Radiographs on all patients featured multifocal, symmetric, metaphyseal sclerosis, with no evidence of lysis or changes to the adjacent growth plate. The metaphyseal sclerosis was most apparent at the proximal humeral diaphyses and other included long bones. Diagnosis of distemper was confirmed by necropsy (2 of 4 dogs) or positive RT‐PCR results (2 of 4 dogs). Three dogs were euthanized because of progressive illness, and 1 dog was lost to follow‐up.

Conclusion and Clinical Importance

Identification of metaphyseal sclerosis on radiographs during diagnostic evaluation of young dogs should lead to a clinical suspicion of canine distemper virus infection. Sclerosis identified secondary to canine distemper virus is distinct from the necrosis and inflammation of metaphyseal osteopathy.

Molecular and pathological screening of canine distemper virus in Asiatic lions, tigers, leopards, snow leopards, clouded leopards, leopard cats, jungle cats, civet cats, fishing cat, and jaguar of different states, India

The present investigation was conducted to rule out canine distemper (CD) diseases in Indian wild felids (Asiatic lions, tigers, leopards, snow leopards, clouded leopards, leopard cats, jungle cats, civet cats, fishing cat, and jaguar). The collected samples were screened for CD virus (CDV) by histopathology (HP), immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR) targeting H gene and N gene. The HP and IHC of suspected samples portrayed that 22 [11 leopards, 6 lions, 3 tigers, 1 snow leopard and 1 civet cat] out of 129 (17.05%) wild felids were positive for CD. The major pathological consequences were observed in spleen, lung, kidney and brain. The syncytia and intranuclear as well as intracytoplasmic eosinophilic inclusion bodies were seen in CDV infected cells. Although the histopathological lesions in spleen were more specific and consistent, however, the severe demyelinated leukoencephalitis (usually expected in CD infected dog) was not observed in the brain of any Indian wild felids. Conversely, the CDV antigen has been portrayed via IHC in pancreatic islets of Langerhans of tiger species for the first time in this study. Moreover, the concurrent CD and babesiosis has also been observed in a lioness without a usual coffee-coloured urine. The N gene and H gene of CDV isolates were amplified, sequenced and subsequently constructed the phylogenetic tree. The phylogenetic analysis of H gene revealed that the CDV isolates from Indian lion formed separate clade with CDV isolates from Indian dog and Indian palm civet cat. Furthermore, two CDV isolates from Indian tigers formed clade with Onderstepoort vaccine strain and CDV isolates from dogs of Uttar Pradesh, USA and UK. Evidently, CDV is circulating in Indian wild felids and causing diseases in them.

Comparison of lateral flow assay and polymerase chain reaction for diagnosis of canine distemper

In present study, 50 nasal and conjunctival pooled swab samples from 48 dogs, one each from leopard and cat were collected, which were suspected for canine distemper from Anand and Ahmedabad districts during period of January-21 to June-21. Out of the 50 samples, 18% were positive for CD by Lateral flow assay (LFA). Using LFA, one each sample from leopard and cat samples were found negative for CD by LFA. Out of the total 50 (48 dogs, one each from leopard and cat) samples, 14 and 4% were positive by N-gene and H-gene based RT-PCR respectively. Comparative analysis of N and H genes, both the samples positive by H-gene based RT-PCR were also positive by N-gene based RT-PCR, which detected 5 more samples positive than H-gene based RT-PCR. Comparative analysis of N-gene based RT-PCR and LFA, relative sensitivity and specificity were 55.55% and 95.12% respectively. Comparative analysis of H-gene based RT-PCR and LFA relative sensitivity and specificity were 22.22 and 100% respectively.

Detection of Systemic Canine Kobuvirus Infection in Peripheral Tissues and the Central Nervous System of a Fox Infected with Canine Distemper Virus

Canine kobuvirus (CaKV) is a globally distributed pathogen of dogs and is predominantly associated with infection of the gastrointestinal tract. However, an etiological link to enteric disease has not been established since CaKV has been identified in both asymptomatic dogs and animals with diarrheic symptoms. In this study, an extraintestinal CaKV infection was detected by next-generation sequencing in a fox (Vulpes vulpes) in Germany concomitant with a canine distemper virus (canine morbillivirus; CDV) co-infection. Phylogenetic analysis of the complete coding region sequence showed that this strain was most closely related to a CaKV strain detected in a dog in the United Kingdom in 2008. The tissue and cellular tropism of CaKV was characterized by the detection of viral antigens and RNA. CaKV RNA was detected by in situ hybridization in different tissues, including epithelial cells of the stomach and ependymal cells in the brain. The use of a new RT-qPCR assay for CaKV confirmed the systemic distribution of CaKV with viral RNA also detected in the lymph nodes, bladder, trachea, and brain. The detection of a CDV infection in this fox suggests that immunosuppression should be further investigated as a contributing factor to the enhanced extraintestinal spread of CaKV.

Apoptotic investigation of brain tissue cells in dogs naturally infected by canine distemper virus

Background

Canine distemper caused by canine distemper virus that belongs to the Morbillivirus genus of the Paramyxoviridae family is still a global epidemic significant infectious disease, especially in pet dogs in China and serious harm to the development of the dog industry. It has been known that apoptosis caused by the canine distemper virus can show in culture cells, lymphoid tissues, and the cerebellum. However, its occurrence in brain tissue cells remains unclear. To investigate the relationship among canine distemper infecting brain tissues, apoptosis in brain tissue cells, and demyelinating pathogenesis was investigated.

Methods

16 naturally infected dogs that exhibited clinical signs of CD and tested positive for the anti-CDV monoclonal antibody and six healthy dogs that served as the control, were used in the research. Brain specimens were divided into the cerebrum, brain stem, and cerebellum embedded in paraffin and made the sections respectively. Approximately 5 µm-thick sections were stained by hematoxylin–eosin, methyl green pyronin, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling technique, and immunohistochemistry. CDV nucleocapsid protein was detected by immune streptavidin-biotinylated peroxidase complex.

Results

Alterations in the brain tissues of CDV-infected dogs involved both various cells and nerve fibers. CDV had varying degrees of cytotropism to all brain tissue cells; apoptosis also occurred in all brain cells, especially in the endothelia of cerebral vessels, astrocytes, oligodendrocytes, and ependymal cells, the more serious infection, the more obvious apoptosis. Serious infections also involved the pyramidal and Purkinje cells. The nervous fibers exhibited demyelinating lesions (showed small multifocal vacuole), and some axonal neuron atrophy gradually disappeared (formed large vacuole).

Conclusions

Apoptosis in brain tissue cells was mainly related to the propagation path and cytotropism of CDV. The apoptosis of astrocytes, oligodendrocytes, and some neurons may play a significant role in the demyelinating pathogenesis in dogs with acute canine distemper. A lot of diverse nervous signs shown in the clinic may be related to different neuron apoptosis.

First complete genome sequence and molecular characterization of Canine morbillivirus isolated in Central Brazil

The Brazilian regions are still highly endemic areas for Canine morbillivirus [canine distemper virus (CDV)]. However, little is known regarding the genetic variability of the strain circulating in several Brazilian regions. Here, we report the first full-length genome and molecular characterization of CDV isolated from domestic dogs in the Brazilian Center-West region. Sequence alignment and phylogenetic analyses based on deduced amino acid and nucleotide sequences showed that the isolated strain is characterized as the South America-I/Europe genotype. However, it segregates into a CDV subgenotype branch. Interestingly, both H and F proteins have a gain of a potential N-glycosylation sites compared to the Onderstepoort vaccine strain. Therefore, this study provides a reference to further understand the epidemic and molecular characteristics of the CDV in Brazil.

Intake Vaccinations Reduced Signs of Canine Respiratory Disease During an Outbreak at an Animal Shelter

Animal shelters provide an ideal environment for the spread of disease. Dogs are often housed in close quarters with others of unknown vaccine histories, and experience high levels of sustained stress. As a result, Canine Infection Respiratory Disease (CIRD) is often prevalent and difficult to control. The aims of this study were to (1) identify specific pathogens responsible for CIRD in a city shelter in West Texas, USA, and (2) determine whether intake vaccinations decrease proportion of dogs exhibiting signs of CIRD even during an outbreak. A laboratory analysis of conjunctival, pharyngeal, and nasal swabs (n = 15 dogs) and fecal samples (n = 6 kennels) showed prevalence of various CIRD pathogens (e.g., canine adenovirus-2, canine parainfluenza virus, canine distemper virus). All fifteen dogs tested positive for at least one pathogen, with the most prevalent pathogen being Canine Distemper Virus (CDV; n = 12). All of the kennels (n=6) tested positive for Canine Distemper Virus. Health data on dogs (n = 1,258) over the age of 6 weeks were assessed from May to August 2017. Beginning in July, both stray and owner-surrendered dogs were vaccinated with Nobivac^® Canine 1-DAPPv 5 Way and Nobivac^® Intra-Trac^® 3 upon intake, which differed from the previous policy. For each day in the study, we calculated the proportion of dogs in each nasal discharge category, the proportion of dogs observed coughing, and the mean fecal score across all dogs. We conducted a linear regression between the proportion of the shelter vaccinated and the proportion of dogs coughing. At the beginning of the vaccination phase, ~25% of the dogs were coughing. However, as the proportion of the dogs vaccinated increased, the proportion of dogs coughing decreased. There was a significant decrease of 7% of the proportion of dogs coughing when vaccination was at least at 90% compared to when it was <90%. These data suggest that the shelter in this study was experiencing a CIRD outbreak, with CDV being primary pathogen, and that it is possible to substantially reduce illness by implementing a vaccination on intake protocol. The current study provides support for the importance of vaccination in animal shelter welfare.

Contribution of astrocytes and macrophage migration inhibitory factor to immune-mediated canine encephalitis caused by the distemper virus

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that is produced by many cell types in situations of homeostasis or disease. One of its functions is to act as a proinflammatory molecule. In humans, several studies have shown that MIF levels become elevated in the serum, urine, cerebrospinal fluid and tissues of patients with chronic inflammatory diseases (systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, sepsis, atheromas, diabetes and cancer). In dogs, distemper is a viral infectious condition that may lead to demyelination and inflammation in the central nervous system (CNS). In addition to the action of the virus, the inflammatory process may give rise to lesions in the white matter. Therefore, the objectives of the present study were to evaluate the role of MIF in the encephalitis that the canine distemper virus causes and to compare this with immunodetection of major histocompatibility complex-II (MHC-II), CD3 T lymphocytes, MMP-9 and glial fibrillary acidic protein (GFAP; astrocytes) in demyelinated areas of the encephalon, in order to ascertain whether these findings might be related to the severity of the encephalic lesions. To this end, a retrospective study on archived paraffinized blocks was conducted, in which 21 encephala from dogs that had been naturally infected with the canine distemper virus (infected group) and five from dogs that had been free from systemic or CNS-affecting diseases (control group) were used. In the immunohistochemical analysis on the samples, the degree of marking by GFAP, MHC-II, MMP-9 and MIF was greater in the demyelinated areas and in the adjacent neuropil, and this was seen particularly in astrocytes. Detection of CD3 was limited to perivascular cuffs. In areas of liquefactive necrosis, Gitter cells were positive for MMP-9, MIF and MHC-II. Hence, it was concluded that activated astrocytes influenced the afflux of T lymphocytes to the encephalon (encephalitis). In the more advanced phases, activated phagocytes in the areas of liquefactive necrosis (Gitter cells) continued to produce inflammatory mediators even after the astrocytes in these localities had died, thereby worsening the encephalic lesions. Distemper virus-activated astrocytes and microglia produce MIF that results in proinflammatory stimulus on glial cells and brain-infiltrating leukocytes. Therefore, the effect of the inflammatory response is potentiated on the neuropil, resulting in neurological clinical signs.

Antiviral efficacy of favipiravir against canine distemper virus infection in vitro

Background

Canine distemper (CD) is an acute infectious disease with high morbidity rates caused by a highly contagious pathogen (Canine Morbillivirus, also known as canine distemper virus, CDV). CDV can infect a broad range of carnivores resulting in complex clinical signs. Currently, there is no effective method to treat for CDV infections. Favipiravir (T-705), a pyrazine derivative, was shown to be an effective antiviral drug against RNA viruses, acting on RNA-dependent RNA polymerase (RdRp). However, whether the T-705 has antiviral effects following CDV infection is unclear. Here, we investigated the antiviral effect of T-705 against CDV-3 and CDV-11 strains in Vero and DH82 cell lines.

Results

Our data demonstrated that T-705 significantly inhibited the replication of CDV-3 and CDV-11 in both Vero and DH82 cells at different concentrations, ranging from 2.441 μg/ml to 1250 μg/ml. Additionally, T-705 exhibited efficacious antiviral effects when administered at different time points after virus infection. Cytotoxicity tests showed a slight decline in viability in Vero cells after T-705 treatment, and no apparent cytotoxicity was detected in T-705 treated DH82 cells. Comparison of anti-CDV polyclonal serum only inhibition of CDV in supernatant, T-705 directly inhibited viral replication in cells, and indirectly reduced the amount of virions in supernatant. The combination application of T-705 and anti-CDV polyclonal serum exhibited a rapid and robust inhibition against virions in supernatant and virus replication in cells.

Conclusions

Our data strongly indicated that T-705 effectively inhibited viral replication following CDV infection in vitro, and could be a potential candidate for treatment for CD.

Reactive Oxygen Species Are Key Mediators of Demyelination in Canine Distemper Leukoencephalitis but not in Theiler's Murine Encephalomyelitis

(1) Background: Canine distemper virus (CDV)-induced demyelinating leukoencephalitis (CDV-DL) in dogs and Theiler’s murine encephalomyelitis (TME) virus (TMEV)-induced demyelinating leukomyelitis (TMEV-DL) are virus-induced demyelinating conditions mimicking Multiple Sclerosis (MS). Reactive oxygen species (ROS) can induce the degradation of lipids and nucleic acids to characteristic metabolites such as oxidized lipids, malondialdehyde, and 8-hydroxyguanosine. The hypothesis of this study is that ROS are key effector molecules in the pathogenesis of myelin membrane breakdown in CDV-DL and TMEV-DL. (2) Methods: ROS metabolites and antioxidative enzymes were assessed using immunofluorescence in cerebellar lesions of naturally CDV-infected dogs and spinal cord tissue of TMEV-infected mice. The transcription of selected genes involved in ROS generation and detoxification was analyzed using gene-expression microarrays in CDV-DL and TMEV-DL. (3) Results: Immunofluorescence revealed increased amounts of oxidized lipids, malondialdehyde, and 8-hydroxyguanosine in CDV-DL while TMEV-infected mice did not reveal marked changes. In contrast, microarray-analysis showed an upregulated gene expression associated with ROS generation in both diseases. (4) Conclusion: In summary, the present study demonstrates a similar upregulation of gene-expression of ROS generation in CDV-DL and TMEV-DL. However, immunofluorescence revealed increased accumulation of ROS metabolites exclusively in CDV-DL. These results suggest differences in the pathogenesis of demyelination in these two animal models.

Molecular and serological surveys of canine distemper virus: A meta-analysis of cross-sectional studies

BACKGROUND

Canine morbillivirus (canine distemper virus, CDV) persists as a serious threat to the health of domestic dogs and wildlife. Although studies have been conducted on the frequency and risk factors associated with CDV infection, there are no comprehensive data on the current epidemiological magnitude in the domestic dog population at regional and national levels. Therefore, we conducted a cross-sectional study and included our results in a meta-analysis to summarize and combine available data on the frequency and potential risk factors associated with CDV infection.

METHODS

For the cross-sectional study, biological samples from dogs suspected to have canine distemper (CD) were collected and screened for viral RNA. Briefly, the PRISMA protocol was used for the meta-analysis, and data analyses were performed using STATA IC 13.1 software.

RESULTS

CDV RNA was detected in 34% (48/141) of dogs suspected to have CD. Following our meta-analysis, 53 studies were selected for a total of 11,527 dogs. Overall, the pooled frequency of CDV positivity based on molecular and serological results were 33% (95% CI: 23-43) and 46% (95% CI: 36-57), respectively. The pooled subgroup analyses of clinical signs, types of biological samples, diagnostic methods and dog lifestyle had a wide range of CDV positivity (range 8-75%). Free-ranging dogs (OR: 1.44, 95% CI: 1.05-1.97), dogs >24 months old (OR: 1.83, 95% CI: 1.1-3) and unvaccinated dogs (OR: 2.92, 95% CI: 1.26-6.77) were found to be positively associated with CDV infection. In contrast, dogs <12 months old (OR: 0.36, 95% CI: 0.20-0.64) and dogs with a complete anti-CDV vaccination (OR: 0.18, 95% CI: 0.05-0.59) had a negative association.

CONCLUSION

Considering the high frequency of CDV positivity associated with almost all the variables analyzed in dogs, it is necessary to immediately and continuously plan mitigation strategies to reduce the CDV prevalence, especially in determined endemic localities.

Comparative Immunopathology of Cetacean morbillivirus Infection in Free-Ranging Dolphins From Western Mediterranean, Northeast-Central, and Southwestern Atlantic

Cetacean morbillivirus (CeMV; Paramyxoviridae) causes epizootic and interepizootic fatalities in odontocetes and mysticetes worldwide. Studies suggest there is different species-specific susceptibility to CeMV infection, with striped dolphins (Stenella coeruleoalba), bottlenose dolphins (Tursiops truncatus), and Guiana dolphins (Sotalia guianensis) ranking among the most susceptible cetacean hosts. The pathogenesis of CeMV infection is not fully resolved. Since no previous studies have evaluated the organ-specific immunopathogenetic features of CeMV infection in tissues from infected dolphins, this study was aimed at characterizing and comparing immunophenotypic profiles of local immune responses in lymphoid organs (lymph nodes, spleen), lung and CNS in CeMV-molecularly (RT-PCR)-positive cetaceans from Western Mediterranean, Northeast-Central, and Southwestern Atlantic. Immunohistochemical (IHC) analyses targeted molecules of immunologic interest: caspase 3, CD3, CD20, CD57, CD68, FoxP3, MHCII, Iba1, IFNγ, IgG, IL4, IL10, lysozyme, TGFβ, and PAX5. We detected consistent CeMV-associated inflammatory response patterns. Within CNS, inflammation was dominated by CD3⁺ (T cells), and CD20⁺ and PAX5⁺ (B cells) lymphocytes, accompanied by fewer Iba1⁺, CD68⁺, and lysozyme⁺ histiocytes, mainly in striped dolphins and bottlenose dolphins. Multicentric lymphoid depletion was characterized by reduced numbers of T cells and B cells, more pronounced in Guiana dolphins. Striped dolphins and bottlenose dolphins often had hyperplastic (regenerative) phenomena involving the aforementioned cell populations, particularly chronically infected animals. In the lung, there was mild to moderate increase in T cells, B cells, and histiocytes. Additionally, there was a generalized increased expression of caspase 3 in lymphoid, lung, and CNS tissues. Apoptosis, therefore, is believed to play a major role in generalized lymphoid depletion and likely overt immunosuppression during CeMV infection. No differences were detected regarding cytokine immunoreactivity in lymph nodes, spleen, and lung from infected and non-infected dolphins by semiquantitative analysis; however, there was striking immunoreactivity for IFNγ in the CNS of infected dolphins. These novel results set the basis for tissue-specific immunophenotypic responses during CeMV infection in three highly susceptible delphinid species. They also suggest a complex interplay between viral and host's immune factors, thereby contributing to gain valuable insights into similarities, and differences of CeMV infection's immunopathogenesis in relation to body tissues, CeMV strains, and cetacean hosts.

Fusion and hemagglutinin proteins of canine distemper virus promote osteoclast formation through NF-κB dependent and independent mechanisms

Paget's disease (PD) features abnormal osteoclasts (OC) which sharply increase in number and size and then intensely induce bone resorption. The purpose of this study was to determine the direct effects of canine distemper virus (CDV) and its fusion protein and hemagglutinin protein (F + H) on receptor activator of nuclear factor kappa-B ligand (RANKL) induced OC formation in vitro. Immunofluorescence assay, OC morphological and functional detection, intracellular signaling pathway detection, Real-time PCR analysis and ELISA were applied in this study. Immunofluorescence assay provided the conclusive proof that CDV can infect and replicate in RAW264.7 mouse monocyte cell line, primary human peripheral blood mononuclear cells (PBMC) and their further fused OC. Both CDV and F + H significantly promoted OC formation and bone resorption ability induced by RANKL. Meanwhile, intracellular signaling transduction analysis revealed CDV and F + H specifically upregulated the phosphorylation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinase (MAPK) induced by RANKL, respectively. Furthermore, without RANKL stimulation, both CDV and F + H slightly induced OC-like cells formation in RAW264.7 cell line even in the presence of NF-κB inhibitor. F + H upregulate OC differentiation and activity through modulation of NF-κB signaling pathway, and induce OC precursor cells merging dependent on the function of glycoproteins themselves. These results meant that F and H proteins play a pivotal role in CDV supporting OC formation. Moreover, this work further provide a new research direction that F and H proteins in CDV should be considered as a trigger during the pathogenesis of PD.

Development of CDV-specific monoclonal antibodies for differentiation of variable epitopes of nucleocapsid protein

The highly contagious canine distemper viruses (CDVs) are still a major threat to a wide range of natural susceptible hosts. The nucleocapsid (N) protein plays various roles in the virus-induced immune response. But precise mapping of epitopes and antigenic variations in N protein of CDV are still scant. In this study, two monoclonal antibodies (MAbs), designated as F8N and G3N, against the N protein of CDV were generated and characterized. The epitopes recognized by the two MAbs were mapped by truncated N protein fragments expressed in E.coli based on western blotting. The 470ESRYDTQ476 and 385GITKEEAQL393 were identified as the minimal linear epitopes recognized by F8N and G3N, respectively. The amino acid residues of the epitope (385-393aa) were highly conserved in a variety of CDV strains from the databases as well as five CDV strains in this study, indicating that MAb G3N can detect various CDV strains. However, MAb F8N was found not to react with an older CDV 851 strain of the five CDV strains due to both of two amino substitution (S471P and Y473H) in the epitope, whereas either single mutant S471P or Y473H did not eliminate the binding of F8N. Further, the variable epitopes existed in the N protein of six CDV strains resembling CDV3 in phylogenic tree by alignment with sequences from the databases. This is the first record of a precise epitope affecting antigenity of N protein of CDV. These results may facilitate future investigations into the function of NP of CDV and diagnostic methods for CDV infection.

Impacts of canine distemper virus infection on the giant panda population from the perspective of gut microbiota

The recent increase in infectious disease outbreaks has been directly linked to the global loss of biodiversity and the decline of some endangered species populations. Between December 2014 and March 2015, five captive giant pandas died due to canine distemper virus (CDV) infection in China. CDV has taken a heavy toll on tigers and lions in recent years. Here, we describe the first gut microbiome diversity study of CDV-infected pandas. By investigating the influence of CDV infection on gut bacterial communities in infected and uninfected individuals and throughout the course of infection, we found that CDV infection distorted the gut microbiota composition by reducing the prevalence of the dominant genera, Escherichia and Clostridium, and increasing microbial diversity. Our results highlight that increases in intestinal inflammation and changes in the relative abundances of pathogen-containing gut communities occur when individuals become infected with CDV. These results may provide new insights into therapeutics that target the microbiota to attenuate the progression of CDV disease and to reduce the risk of gut-linked disease in individuals with CDV. In addition, our findings underscore the need for better information concerning the dynamics of infection and the damage caused by pathogens in panda populations.

Isolation and phylogenetic analysis of canine distemper virus among domestic dogs in Vietnam

Canine distemper virus (CDV) is one of the most serious pathogens found in many species of carnivores, including domestic dogs. In this study, hemagglutinin (H) genes were detected in five domestic Vietnamese dogs with diarrhea, and two CDVs were successfully isolated from dogs positive for H genes. The complete genome of one isolate, CDV/dog/HCM/33/140816, was determined. Phylogenetic analysis showed that all Vietnamese CDVs belonged to the Asia-1 genotype. In addition, the H proteins of Vietnamese CDV strains were the most homologous to those of Chinese CDVs (98.4% to 99.3% identity). These results indicated that the Asia-1 genotype of CDV was the predominant genotype circulating among the domestic dog population in Vietnam and that transboundary transmission of CDV has occurred between Vietnam and China.

Development and characterization of neutralizing monoclonal antibodies against canine distemper virus hemagglutinin protein

Canine distemper virus (CDV) causes a serious multisystemic disease in dogs and other carnivora. Hemagglutinin (H) protein-specific antibodies are mainly responsible for protective immunity against CDV infection. In the present study, six neutralizing MAbs to the H protein of CDV were newly obtained and characterized by immunizing BALB/c mice with a recent Chinese field isolate. Competitive binding inhibition assay revealed that they recognized four distinct antigenic regions of the H protein. Immunofluorescence assay and western blotting showed that all MAbs recognize the conformational rather than the linear epitopes of the H protein. Furthermore, in immunofluorescence and virus neutralization assays, two of the MAbs were found to react only with the recent Chinese field isolate and not with older CDV strains, including vaccine strain Onderstepoort, indicating there are neutralization-related antigenic variations between the recent Chinese field isolate and the older CDV strains examined in this study. The newly established MAbs are useful for differentiating the expanding CDV strains and could be used in immunotherapy and immunodiagnosis against infection with CDV.

Establishment and characterization of a telomerase-immortalized canine bronchiolar epithelial cell line

Dogs are susceptible to infectious diseases that occur primarily in the respiratory tract. The airway epithelium acts as a first line of defense and is constantly exposed to microorganisms present in the environment. Respiratory epithelial cells have recently gained wide use as a cell model for studying the pathogenesis of human, murine or swine respiratory pathogen infections. However, studies of the pathogenic mechanisms of canine pathogens have been hindered by the lack of reliable respiratory cell lines. Here, we cultured primary canine bronchiolar epithelial cells (CBECs), whose characteristics were confirmed by their expression of the epithelial cell-specific marker cytokeratin 18, and have provided protocols for their isolation and ex vivo expansion. Further, we established immortalized CBECs containing the human telomerase reverse transcriptase (hTERT) gene via transfection of primary CBECs with the recombinant plasmid pEGFP-hTERT. Immortalized bronchiolar epithelial cells (hTERT-CBECs) retain the morphological and functional features of primary CBECs, as indicated by reverse transcriptase polymerase chain reaction, proliferation assays, karyotype analysis, telomerase activity assay, and Western blotting, which demonstrate that hTERT-CBECs have higher telomerase activity, an extended proliferative lifespan, and a diploid complement of chromosomes, even after Passage 50. Moreover, this cell line is not transformed, as evaluated using soft agar assays and tumorigenicity analysis in nude mice, and can therefore be safely used in future studies. The isolation and establishment of stable hTERT-CBECs is of great importance for use as an in vitro model for mechanistic studies of canine pathogenic infections.

Detection and differentiation of wild-type and vaccine strains of canine distemper virus by a duplex reverse transcription polymerase chain reaction

Canine distemper virus (CDV) is the cause of canine distemper (CD) which is a severe and highly contagious disease in dogs. In the present study, a duplex reverse transcription polymerase chain reaction (RT-PCR) method was developed for the detection and differentiation of wild-type and vaccine strains of CDV. Four primers were designed to detect and discriminate the two viruses by generating 638- and 781-bp cDNA products, respectively. Furthermore, the duplex RT-PCR method was used to detect 67 field samples suspected of CD from Guangdong province in China. Results showed that, 33 samples were to be wild-type-like. The duplex RT-PCR method exhibited high specificity and sensitivity which could be used to effectively detect and differentiate wild-type and vaccine CDV, indicating its use for clinical detection and epidemiological surveillance.

New aspects of the pathogenesis of canine distemper leukoencephalitis

Canine distemper virus (CDV) is a member of the genus morbillivirus, which is known to cause a variety of disorders in dogs including demyelinating leukoencephalitis (CDV-DL). In recent years, substantial progress in understanding the pathogenetic mechanisms of CDV-DL has been made. In vivo and in vitro investigations provided new insights into its pathogenesis with special emphasis on axon-myelin-glia interaction, potential endogenous mechanisms of regeneration, and astroglial plasticity. CDV-DL is characterized by lesions with a variable degree of demyelination and mononuclear inflammation accompanied by a dysregulated orchestration of cytokines as well as matrix metalloproteinases and their inhibitors. Despite decades of research, several new aspects of the neuropathogenesis of CDV-DL have been described only recently. Early axonal damage seems to represent an initial and progressive lesion in CDV-DL, which interestingly precedes demyelination. Axonopathy may, thus, function as a potential trigger for subsequent disturbed axon-myelin-glia interactions. In particular, the detection of early axonal damage suggests that demyelination is at least in part a secondary event in CDV-DL, thus challenging the dogma of CDV as a purely primary demyelinating disease. Another unexpected finding refers to the appearance of p75 neurotrophin (NTR)-positive bipolar cells during CDV-DL. As p75NTR is a prototype marker for immature Schwann cells, this finding suggests that Schwann cell remyelination might represent a so far underestimated endogenous mechanism of regeneration, though this hypothesis still remains to be proven. Although it is well known that astrocytes represent the major target of CDV infection in CDV-DL, the detection of infected vimentin-positive astrocytes in chronic lesions indicates a crucial role of this cell population in nervous distemper. While glial fibrillary acidic protein represents the characteristic intermediate filament of mature astrocytes, expression of vimentin is generally restricted to immature or reactive astrocytes. Thus, vimentin-positive astrocytes might constitute an important cell population for CDV persistence and spread, as well as lesion progression. In vitro models, such as dissociated glial cell cultures, as well as organotypic brain slice cultures have contributed to a better insight into mechanisms of infection and certain morphological and molecular aspects of CDV-DL. Summarized, recent in vivo and in vitro studies revealed remarkable new aspects of nervous distemper. These new perceptions substantially improved our understanding of the pathogenesis of CDV-DL and might represent new starting points to develop novel treatment strategies.