Canine distemper virus strains circulating among North American dogs

The evolutionary dynamics history of canine distemper virus through analysis of the hemagglutinin gene during 1930-2020

Canine distemper virus (CDV) is a lethal viral disease of carnivores which is considered to be a serious threat to domestic and wild species. Despite the widespread use of vaccines, CDV still occurs in vaccinated animals and current vaccines does not guarantee complete protection. In this study, a total of 286 hemagglutinin (H) gene sequences of the virus isolated in 25 countries during 90 years (1930-2020) were analyzed by Bayesian maximum likelihood analysis to estimate the population dynamics. We identified the most recent common ancestor (TMRCA) of the virus in 1868 in the USA which arrived in continental Europe in 1948, and from there, the virus spread rapidly to other continents. The Canidae family was identified as the original host as well as a source of the subsequent spread. We identified 11 lineages of geographic co-circulating strains globally. The effective population size experienced a two-phase-exponential growth between 2000-2005 and 2010-2012. Our findings provide a novel insight into the epidemic history of canine distemper virus which may facilitate more effective disease management. This study uses a large set of sequencing data on the H gene of CDV to identify distinct lineages of the virus, track its geographic spread over time, analyze its likelihood of transmission within and between animal families, and provide suggestions for improved strategies to combat the virus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10344-023-01685-z.

GEOGRAPHIC SPREAD OF CANINE DISTEMPER IN WILD CARNIVORES IN MICHIGAN, USA: PATHOLOGY AND EPIDEMIOLOGY, 2008-18

Canine distemper is a widespread disease affecting both domestic and wild carnivores. This investigation of the geographic distribution, wildlife species infected, and relative prevalence rates was conducted over an 11-yr period and helps to document the disease spread, most highly infected wildlife species, and histologic lesions. Animals were collected as found dead, hunter and trapper harvested, and euthanized for displaying signs of abnormal behavior or neurologic disease. This disease appeared to spread from the Lower Peninsula of Michigan into the Upper Peninsula, was most frequently documented in raccoons (Procyon lotor), striped skunks (Mephitis mephitis), and gray fox (Urocyon cinereoargenteus), but also involved additional wildlife species. Three unique wildlife virus strains were identified. Two of these grouped within a separate subclade of the America 2 lineage. A third strain appeared to be a unique sequence type that is not associated with any existing subclade of America 2. We recommend the combined use of routine histology and immunohistochemical staining to confirm the diagnosis, and further recommend that both the lungs and spleen be collected as the optimal tissues to utilize for surveillance purposes.

Genetic characterization of canine distemper virus from wild and domestic animal submissions to diagnostic facilities in Canada

Traditionally considered an agent affecting domestic dogs, canine distemper virus (CDV) is now well known for an ability to infect a broad range of hosts. In Ontario, domestic dogs are routinely vaccinated and clinical disease attributed to CDV infection in this population is infrequent. CDV has been regularly documented in Ontario wildlife spanning at least 4 decades however, the molecular identity of circulating CDV strains is currently unknown. Our objective was to investigate the molecular identities of and genetic relationships between CDV detected in wild and domestic animals from Canada, across multiple host species and over time. Samples were opportunistically collected from submissions to the Ontario-Nunavut node of the Canadian Wildlife Health Cooperative and the Animal Health Laboratory in Guelph, Ontario. RT-PCR was used to confirm CDV diagnosis, and the hemagglutinin gene was sequenced. Phylogenetic relationships were inferred, and the geographic distribution of clades was visualized using a geographic information system. Phenetic relationships between sequences were investigated with a median joining network analysis and through mixed multivariable linear regression. CDV sequences from ten wild and domestic species were characterized into seven lineages, that overlapped geographically and temporally. The predominant lineage circulating in Ontario wildlife, denoted Canada-1, has not been previously described to the authors knowledge. Our analysis indicates that the Canada-1 lineage is most genetically similar to America-1 sequences, however according to current methodology represents a distinct lineage. Multiple co-circulating CDV lineages were also identified, and raccoons appear to play an important role in the maintenance and transmission of these heterogeneous lineages in Ontario. This study also confirmed the presence of CDV from a lineage not found to be circulating in Ontario wildlife, in a domestic dog imported into Ontario from South America. Therefore, travel and the trade of animals may be an important avenue for the introduction of novel CDV lineages. It remains unclear whether and to what extent the genetic heterogeneity identified poses a risk to the efficacy of current vaccines. Increasing viral activity and continued antigenic drift resulting in partial protection or vaccine failure remains a concern.

Prolonged Infection of Canine Distemper Virus in a Mixed-Breed Dog

Canine distemper virus (CDV) is a major viral pathogen in domestic dogs, belonging to the Paramyxoviridae family, in the Morbillivirus genus. It is present worldwide, and a wide range of domestic animals and wild carnivores are at risk. In the absence of vaccination, dogs have a low chance of survival; however, if and when a dog survives, it can take an average of a few weeks to a few months to fully wipe out the virus. In the present study, we traced the course of infection of a 1-year-old mixed-breed male dog. The animal had an unusually long course of persistent CDV infection with a vector-borne heartworm (Dirofilaria immitis) co-infection. The dog excreted the CDV for 17 months with PCR positivity in urine samples collected from February 2019 through June 2020. The sequencing and phylogenetic analysis of the hemagglutinin gene revealed the CDV to be the member of the endemic Arctic-like genetic lineage. To the best of our knowledge, this report represents the longest documented canine infection of CDV. Notably, we highlight the necessity regarding CDV infectivity studies to better comprehend the transmission attributes of the virus.

GENETIC CHARACTERISTICS OF CANINE DISTEMPER VIRUSES CIRCULATING IN WILDLIFE IN THE UNITED STATES

Canine distemper virus (CDV) is a highly contagious disease of wild and domestic mammals. Maintenance of CDV among wildlife plays an important role in the disease epidemiology. Wild animals, including raccoons (Procyon lotor) and gray foxes (Urocyon cinereoargenteus), serve as reservoirs of CDV and hamper the control of the disease. Recently, we discovered that at least three different CDV lineages (America-3 [Edomex], America-4, and America-5] that are genetically different from the available vaccine strains are circulating in domestic dogs in the United States. Because wildlife serve as a reservoir for the virus, it is important to determine if wildlife play a role in the maintenance and spread of these lineages. To determine the genetic characteristics of circulating strains of CDV in wildlife in various geographic regions in the United States, we studied the nucleotide sequences of the hemagglutinin (H) gene of 25 CDV strains detected in nondomestic species. The species included were free-ranging wildlife: three fishers (Martes pennanti), six foxes, one skunk (Mephitis mephitis), 10 raccoons, two wolves (Canis lupus), and one mink (Neovison vison). Strains from two species in managed care, one sloth (Choloepus didactylus) and one red panda (Ailurus fulgens), were also evaluated. Phylogenetic analysis of the H genes indicated that in addition to America-3, America-4, and America-5 lineages, there are at least two other lineages circulating in US wildlife. One of these includes CDV nucleotide sequences that grouped with that of a single CDV isolate previously detected in a raccoon from Rhode Island in 2012. The other lineage is independent and genetically distinct from other CDV strains included in the analysis. Additional genetically variable strains were detected, mainly in raccoons, suggesting that this species may be the host responsible for the genetic variability of newly detected strains in the domestic dog population.

Phylogenetic evidence of the intercontinental circulation of a Canine distemper virus lineage in the Americas

Canine distemper virus (CDV) is the cause of a multisystem disease in domestic dogs and wild animals, infecting more than 20 carnivore and non-carnivore families and even infecting human cell lines in in vitro conditions. Phylogenetic classification based on the hemagglutinin gene shows 17 lineages with a phylogeographic distribution pattern. In Medellín (Colombia), the lineage South America-3 is considered endemic. Phylogenetic studies conducted in Ecuador using fragment coding for the fusion protein signal peptide (Fsp) characterized a new strain belonging to a different lineage. For understanding the distribution of the South America-3 lineage in the north of the South American continent, we characterized CDV from three Colombian cities (Medellín, Bucaramanga, and Bogotá). Using phylogenetic analysis of the hemagglutinin gene and the Fsp region, we confirmed the circulation of CDV South America-3 in different areas of Colombia. We also described, for the first time to our knowledge, the circulation of a new lineage in Medellín that presents a group monophyletic with strains previously characterized in dogs in Ecuador and in wildlife and domestic dogs in the United States, for which we propose the name “South America/North America-4” due its intercontinental distribution. In conclusion, our results indicated that there are at least four different CDV lineages circulating in domestic dogs in South America: the Europe/South America-1 lineage circulating in Brazil, Uruguay, and Argentina; the South America-2 lineage restricted to Argentina; the South America-3 lineage, which has only been reported in Colombia; and lastly an intercontinental lineage present in Colombia, Ecuador, and the United States, referred to here as the “South America/North America-4” lineage.

The Canine Morbillivirus Strain Associated with An Epizootic in Caspian Seals Provides New Insights into the Evolutionary History of this Virus

Canine morbillivirus (canine distemper virus; CDV) is a worldwide distributed morbillivirus that causes sporadic cases and recurrent epizootics among an increasing number of wild, feral, and domestic animal species. We investigated the evolutionary history of CDV strains involved in the 1988 Lake Baikal (CDVPS88) and the 2000 Caspian Sea (CDVPC00) seal die-offs by recovery of full-length sequences from archived material using next-generation sequencing. Bayesian phylogenetic analyses indicated that CDVPC00 constitutes a novel strain in a separate clade (tentatively termed "Caspian") from the America-1 clade, which is comprised of older vaccine strains. The America-1/Caspian monophyletic group is positioned most basally with respect to other clades and is estimated to have separated from other CDV clades around 1832. Our results indicate that CDVPC00 recovered from the epizootic in the Caspian Sea in 2000 belongs to a previously undetected novel clade and constitutes the most ancestral wild-type CDV clade.

Evolution and Interspecies Transmission of Canine Distemper Virus-An Outlook of the Diverse Evolutionary Landscapes of a Multi-Host Virus

Canine distemper virus (CDV) is a worldwide distributed virus which belongs to the genus Morbillivirus within the Paramyxoviridae family. CDV spreads through the lymphatic, epithelial, and nervous systems of domestic dogs and wildlife, in at least six orders and over 20 families of mammals. Due to the high morbidity and mortality rates and broad host range, understanding the epidemiology of CDV is not only important for its control in domestic animals, but also for the development of reliable wildlife conservation strategies. The present review aims to give an outlook of the multiple evolutionary landscapes and factors involved in the transmission of CDV by including epidemiological data from multiple species in urban, wild and peri-urban settings, not only in domestic animal populations but at the wildlife interface. It is clear that different epidemiological scenarios can lead to the presence of CDV in wildlife even in the absence of infection in domestic populations, highlighting the role of CDV in different domestic or wild species without clinical signs of disease mainly acting as reservoirs (peridomestic and mesocarnivores) that are often found in peridomestic habits triggering CDV epidemics. Another scenario is driven by mutations, which generate genetic variation on which random drift and natural selection can act, shaping the genetic structure of CDV populations leading to some fitness compensations between hosts and driving the evolution of specialist and generalist traits in CDV populations. In this scenario, the highly variable protein hemagglutinin (H) determines the cellular and host tropism by binding to signaling lymphocytic activation molecule (SLAM) and nectin-4 receptors of the host; however, the multiple evolutionary events that may have facilitated CDV adaptation to different hosts must be evaluated by complete genome sequencing. This review is focused on the study of CDV interspecies transmission by examining molecular and epidemiological reports based on sequences of the hemagglutinin gene and the growing body of studies of the complete genome; emphasizing the importance of long-term multidisciplinary research that tracks CDV in the presence or absence of clinical signs in wild species, and helping to implement strategies to mitigate the infection. Integrated research incorporating the experience of wildlife managers, behavioral and conservation biologists, veterinarians, virologists, and immunologists (among other scientific areas) and the inclusion of several wild and domestic species is essential for understanding the intricate epidemiological dynamics of CDV in its multiple host infections.

Infection of eight mesocarnivores in New Hampshire and Vermont with a distinct clade of canine distemper virus in 2016-2017

Three fishers (Martes pennanti), 2 gray foxes (Urocyon cinereoargenteus), 1 mink (Neovison vison), 1 skunk (Mephitis mephitis), and 1 raccoon (Procyon lotor), from Vermont and New Hampshire, had lesions on autopsy consistent with canine distemper virus (CDV) infections diagnosed in a 12-mo period in 2016-2017. Lesions of CDV infection were most commonly noted in the lungs (8 of 8 animals), urothelium (5 of 8), biliary tract (5 of 8), gastrointestinal tract (4 of 7), and brain (4 of 6). Splenic lesions were seen in 3 animals. The diagnosis was confirmed via immunohistochemistry and virus isolation. Viral genotyping indicated that all 8 animals were infected with a distinct clade of CDV that has only been reported in wildlife in New England, and this clade of viruses is distinct from vaccine strains. During the 12 mo when these cases occurred, no other CDV clade was identified in any other wildlife or domesticated animal submitted from the 2 states.

Phylogenetic analysis of the wild-type strains of canine distemper virus circulating in the United States

Background

Canine distemper (CD) is a highly contagious, systemic, viral disease of dogs seen worldwide. Despite intensive vaccination in developed countries, recent reports suggest both the re-emergence and increased activity of Canine distemper virus (CDV) worldwide, including the United States. CDV is an RNA virus of the genus Morbillivirus within the family Paramyxoviridae. Viral genomic RNA encodes six structural proteins. Of the six structural proteins, the hemagglutinin (H) gene has the greatest genetic variation and is therefore a suitable target for molecular epidemiological studies. The majority of neutralizing epitopes are found on the H protein, making this gene also important for evaluation of changes over time that may result in antigenic differences among strains. The aim of this study was to determine the phylogenetic relationship of CDV strains circulating in the US.

Methods

Fifty-nine positive canine distemper virus samples collected from dogs from different regions and states from 2014 to 2017 were sequenced with a targeted next-generation sequencing (NGS) method. The sequences of the H, F, and P genes and the matrix-fusion (M-F) intergenic region of the amplified CDVs were analyzed individually.

Results

Sequence analysis of the H gene revealed that there are at least 3 different lineages of CDV currently circulating in the US. These lineages include America-3 (Edomex), America-4, and a clade that was previously reported in association with an outbreak in Wyoming, which was linked to a domestic dog-breeding facility in Kansas in 2010. These lineages differ from the historically identified lineages in the US, including America-1, which contains the majority of the vaccine strains. Genetic differences may result in significant changes to the neutralizing epitopes that consequently may lead to vaccine failure. Phylogenetic analyses of the nucleotide sequences obtained in this study of the F and P genes and the M-F intergenic region with sequences from the GenBank database produced similar findings to the H gene analysis.

Conclusions

The CDV lineages currently circulating in the US differ from the historically identified lineages America-1. Continuous surveillance is required for monitoring circulating CDV strains in the US, to prevent potential vaccine breakthrough events.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1027-2) contains supplementary material, which is available to authorized users.

Antigenic analysis of genetic variants of Canine distemper virus

Canine distemper virus (CDV) is an RNA virus of the genus Morbillivirus within the family Paramyxoviridae. CDV produces multi-systemic disease in dogs and other terrestrial carnivores. With the development of modified live vaccines in the 1950s and 1960s, the disease, with a few exceptions, has been successfully controlled. However, recently the cases of CDV in vaccinated dogs have been increasing throughout the world, including the United States. There are many reasons that can lead to vaccine failure, including antigenic differences between the vaccine strains and the currently circulating wild-type strains. Currently, there are at least three genetically different CDV lineages circulating in the US. Therefore, in this study, we evaluated various wild-type CDV and vaccine isolates to determine if the genetic differences observed among various strains result in significant antigenic differences based on changes to the neutralizing epitopes. The results of a cross-neutralization assay revealed that there are antigenic differences among the tested CDV wild-type isolates as well as between the tested isolates and the vaccine strains currently used in the US. Therefore, these results suggest the need to develop an updated CDV vaccine.

Comparison of reverse-transcription real-time PCR and immunohistochemistry for the detection of canine distemper virus infection in raccoons in Ontario, Canada

Canine distemper virus (CDV) is a widespread morbillivirus that causes subclinical to fatal infections in domestic and wild carnivores. Raccoons ( Procyon lotor) are CDV reservoirs and suffer from associated disease. Aspects of pathogenesis may lead to difficulty in the interpretation of commonly used testing modalities, such as reverse-transcription real-time (RT-rt)PCR and immunohistochemistry (IHC). The reliance upon such tests is greater for wildlife, which are often submitted as carcasses with no clinical history. We compared CDV RT-rtPCR results to immunohistochemistry (the gold standard) in tissues from 74 raccoons. These tests had high kappa agreement (lymph node: 0.9335; lung: 0.8671) and a negative correlation between IHC score and threshold cycle (Ct) value for lymph node and lung (Spearman rank correlation coefficient [ r_s] = -0.8555 and -0.8179, respectively; p < 0.00001). An RT-rtPCR Ct value of 30 in lung and lymph node with sensitivity and specificity of 92.3 and 92.6% and 86.8 and 96.4%, respectively, was suitable for determining CDV involvement. Conjunctival swabs provide an alternative for distemper diagnosis, as there was a strong correlation between Ct values of conjunctival swabs and tissues ( r_s = -0.8498, p < 0.00001, n = 46). This information will aid in more efficient and accurate diagnoses in individuals, small-scale outbreaks, and epidemiologic investigations in wildlife.

Epidemiology and clinical presentation of canine distemper disease in dogs and ferrets in Australia, 2006-2014

OBJECTIVE

To determine the status and distribution of distemper in Australian dogs and ferrets.

DESIGN

Retrospective case series.

METHODS

Cases were identified via a national voluntary disease reporting system, veterinarian groups and a national laboratory database. The geographic distribution, seasonal distribution, signalment and clinical presentation of cases were described using maps and frequency distributions.

RESULTS

A total of 48 individually affected dogs and ferrets in 27 case groups were identified, including eight confirmed case groups (> one individual). Confirmed cases were more common in summer and on the central coast of New South Wales and southern Victoria, and occurred exclusively in young, unvaccinated dogs. For dogs there was no obvious sex predilection. A mortality rate of 100% in ferrets and up to 77% in dogs was estimated. Neurological, gastrointestinal and respiratory were the most commonly reported systems affected in dogs and ferrets. There was no evidence that any large, unreported outbreaks occurred during the study period.

CONCLUSIONS

Continuation of vaccination against canine distemper virus is justified within Australia, particularly for younger dogs. Veterinarians should continue to consider distemper in their differential diagnosis of cases with neurological, gastrointestinal and respiratory presentation.

Detection of respiratory viruses in shelter dogs maintained under varying environmental conditions

Three dog shelters in Rio Grande do Sul were investigated for associations between the occurrence of respiratory viruses and shelter environmental conditions. Nasal secretions randomly collected during the cold season were tested via PCR, and this data collection was followed by nucleotide sequencing of the amplicons. In shelter #1 (poor sanitary and nutritional conditions, high animal density and constant contact between dogs), 78% (58/74) of the nasal samples were positive, 35% (26/74) of which were in single infections and 44% (32/74) of which were in coinfections. Shelters #2 and #3 had satisfactory sanitary and nutritional conditions, outdoors exercise areas (#2) and animal clustering by groups (#3). In shelter #2, 9% (3/35) of the samples were positive for Canine parainfluenza virus (CPIV), and 6% (2/35) were positive for Canid herpesvirus 1 (CaHV-1). In shelter #3, 9% (7/77) of the samples were positive for Canine adenovirus type 2 (CAdV-2), and 1% (1/77) were positive for Canine distemper virus (CDV). The amplicon sequences (CPIV and CDV nucleoprotein gene; CAdV-2 E3 gene; CaHV-1 glycoprotein B gene) showed 94-100% nucleotide identity with GenBank sequences. Our results demonstrate that CPIV, CAdV-2 and CDV are common in dog shelters and that their frequencies appear to be related with environmental and nutritional conditions. These results indicate the need for control/prevention measures, including vaccination and environmental management, to minimize these infections and improve dog health.

Sequencing of emerging canine distemper virus strain reveals new distinct genetic lineage in the United States associated with disease in wildlife and domestic canine populations

BACKGROUND

Recent outbreaks of canine distemper have prompted examination of strains from clinical samples submitted to the University of Tennessee College of Veterinary Medicine (UTCVM) Clinical Virology Lab. We previously described a new strain of CDV that significantly diverged from all genotypes reported to date including America 2, the genotype proposed to be the main lineage currently circulating in the US. The aim of this study was to determine when this new strain appeared and how widespread it is in animal populations, given that it has also been detected in fully vaccinated adult dogs. Additionally, we sequenced complete viral genomes to characterize the strain and determine if variation is confined to known variable regions of the genome or if the changes are also present in more conserved regions.

METHODS

Archived clinical samples were genotyped using real-time RT-PCR amplification and sequencing. The genomes of two unrelated viruses from a dog and fox each from a different state were sequenced and aligned with previously published genomes. Phylogenetic analysis was performed using coding, non-coding and genome-length sequences. Virus neutralization assays were used to evaluate potential antigenic differences between this strain and a vaccine strain and mixed ANOVA test was used to compare the titers.

RESULTS

Genotyping revealed this strain first appeared in 2011 and was detected in dogs from multiple states in the Southeast region of the United States. It was the main strain detected among the clinical samples that were typed from 2011-2013, including wildlife submissions. Genome sequencing demonstrated that it is highly conserved within a new lineage and preliminary serologic testing showed significant differences in neutralizing antibody titers between this strain and the strain commonly used in vaccines.

CONCLUSION

This new strain represents an emerging CDV in domestic dogs in the US, may be associated with a stable reservoir in the wildlife population, and could facilitate vaccine escape.

Recombinant Newcastle disease viral vector expressing hemagglutinin or fusion of canine distemper virus is safe and immunogenic in minks

Canine Distemper Virus (CDV) infects many carnivores and cause several high-mortality disease outbreaks. The current CDV live vaccine cannot be safely used in some exotic species, such as mink and ferret. Here, we generated recombinant lentogenic Newcastle disease virus (NDV) LaSota expressing either envelope glycoproyein, heamagglutinine (H) or fusion protein (F), named as rLa-CDVH and rLa-CDVF, respectively. The feasibility of these recombinant NDVs to serve as live virus-vectored CD vaccine was evaluated in minks. rLa-CDVH induced significant neutralization antibodies (NA) to CDV and provided solid protection against virulent CDV challenge. On the contrast, rLa-CDVF induced much lower NA to CDV and fail to protected mink from virulent CDV challenge. Results suggest that recombinant NDV expressing CDV H is safe and efficient candidate vaccine against CDV in mink, and maybe other host species.

Canine distemper virus antigen detection in external epithelia of recently vaccinated, sick dogs by fluorescence microscopy is a valuable prognostic indicator

Currently, there are no reliable predictors of the clinical outcomes of domesticated dogs that have been recently vaccinated against canine distemper virus (CDV) and develop respiratory disease. In this study, vaccinated dogs from Oklahoma City that were showing clinical signs of respiratory disease were evaluated for CDV antigen using a direct fluorescent antibody test (FAT). Clinical outcomes after standard symptomatic therapy for respiratory disease were recorded, and a statistical analysis of the results was performed. We present our study showing that CDV FAT results were predictive of clinical recovery (prognostic indicator, prospects of clinical recovery) among vaccinated dogs showing clinical signs of respiratory disease. Negative CDV FAT results equated to 80% chances of recovery after symptomatic therapy, compared to 55% chances of recovery when the CDV FAT results were positive. Based on the results of this study, we show that veterinarians can make better informed decisions about the clinical outcomes of suspected CDV cases, with 2-h turnaround times, by using the CDV FAT. Thus, antemortem examination with the CDV FAT on external epithelia of recently vaccinated, sick dogs is a clinically useful diagnostic test and valuable prognostic indicator for veterinarians. Application of the CDV FAT to these samples avoids unnecessary euthanasia of dogs with suspected CDV.

Real-time reverse transcription polymerase chain reaction method for detection of Canine distemper virus modified live vaccine shedding for differentiation from infection with wild-type strains

Canine distemper virus (CDV) remains a common cause of infectious disease in dogs, particularly in high-density housing situations such as shelters. Vaccination of all dogs against CDV is recommended at the time of admission to animal shelters and many use a modified live virus (MLV) vaccine. From a diagnostic standpoint for dogs with suspected CDV infection, this is problematic because highly sensitive diagnostic real-time reverse transcription polymerase chain reaction (RT-PCR) tests are able to detect MLV virus in clinical samples. Real-time PCR can be used to quantitate amount of virus shedding and can differentiate vaccine strains from wild-type strains when shedding is high. However, differentiation by quantitation is not possible in vaccinated animals during acute infection, when shedding is low and could be mistaken for low level vaccine virus shedding. While there are gel-based RT-PCR assays for differentiation of vaccine strains from field strains based on sequence differences, the sensitivity of these assays is unable to match that of the real-time RT-PCR assay currently used in the authors' laboratory. Therefore, a real-time RT-PCR assay was developed that detects CDV MLV vaccine strains and distinguishes them from wild-type strains based on nucleotide sequence differences, rather than the amount of viral RNA in the sample. The test is highly sensitive, with detection of as few as 5 virus genomic copies (corresponding to 10(-1) TCID(50)). Sequencing of the DNA real-time products also allows phylogenetic differentiation of the wild-type strains. This test will aid diagnosis during outbreaks of CDV in recently vaccinated animals.

Rapid and sensitive detection of canine distemper virus by one-tube reverse transcription-insulated isothermal polymerase chain reaction

Background

Canine distemper virus (CDV) has been associated with outbreaks of canine infectious respiratory disease in shelters and boarding kennel environments. POCKIT^TM Nucleic Acid Analyzer is a field-deployable device capable of generating automatically interpreted insulated isothermal polymerase chain reaction (iiPCR) results from extracted nucleic acid within one hour. In this study, reverse transcription iiPCR (RT-iiPCR) was developed to facilitate point-of-need diagnosis of CDV infection.

Results

Analytical sensitivity (limit of detection 95%) of the established CDV RT-iiPCR was about 11 copies of in vitro transcribed RNA per reaction. CDV RT-iiPCR generated positive signals from CDV, but not Bordetella bronchiseptica, canine parvovirus, canine herpesvirus, canine adenovirus 2, canine influenza virus (subtype H3N8), canine parainfluenza virus, and canine respiratory coronavirus. To evaluate accuracy of the established reaction in canine distemper clinical diagnosis, 110 specimens from dogs, raccoons, and foxes suspected with CDV infection were tested simultaneously by CDV RT-iiPCR and real-time RT-PCR. CDV RT-iiPCR demonstrated excellent sensitivity (100%) and specificity (100%), compared to real-time RT-PCR.

Conclusions

The results indicated an excellent correlation between RT-iiPCR and a reference real time RT-PCR method. Working in a lyophilized format, the established method has great potential to be used for point-of-care diagnosis of canine distemper in animals, especially in resource-limited facilities.

Detection and differentiation of field and vaccine strains of canine distemper virus using reverse transcription followed by nested real time PCR (RT-nqPCR) and RFLP analysis

Canine distemper virus (CDV) is the cause of a severe and highly contagious disease in dogs. Practical diagnosis of canine distemper based on clinical signs and laboratory tests are required to confirm CDV infection. The present study aimed to develop a molecular assay to detect and differentiate field and vaccine CDV strains. Reverse transcription followed by nested real time polymerase chain reaction (RT-nqPCR) was developed, which exhibited analytical specificity (all the samples from healthy dogs and other canine infectious agents were not incorrectly detected) and sensitivity (all replicates of a vaccine strain were positive up to the 3125-fold dilution - 10(0.7) TCID50). RT-nqPCR was validated for CDV detection on different clinical samples (blood, urine, rectal and conjunctival swabs) of 103 animals suspected to have distemper. A total of 53 animals were found to be positive based on RT-nqPCR in at least one clinical sample. Blood resulted in more positive samples (50 out of 53, 94.3%), followed by urine (44/53, 83.0%), rectal (38/53, 71%) and conjunctival (27/53, 50.9%) swabs. A commercial immunochromatography (IC) assay had detected CDV in only 30 conjunctival samples of these positive dogs. Nucleoprotein (NC) gene sequencing of 25 samples demonstrated that 23 of them were closer to other Brazilian field strains and the remaining two to vaccine strains. A single nucleotide sequences difference, which creates an Msp I restriction enzyme digestion, was used to differentiate between field and vaccine CDV strains by restriction fragment length polymorphism (RFLP) analysis. The complete assay was more sensitive than was IC for the detection of CDV. Blood was the more frequently positive specimen and the addition of a restriction enzyme step allowed the differentiation of vaccine and Brazilian field strains.

Deduced sequences of the membrane fusion and attachment proteins of canine distemper viruses isolated from dogs and wild animals in Korea

Canine distemper virus (CDV) causes highly contagious respiratory, gastrointestinal, and neurological diseases in wild and domestic animal species. Despite a broad vaccination campaign, the disease is still a serious problem worldwide. In this study, six field CDV strains were isolated from three dogs, two raccoon dogs, and one badger in Korea. The full sequence of the genes encoding fusion (F) and hemagglutinin (H) proteins were compared with those of other CDVs including field and vaccine strains. The phylogenetic analysis for the F and H genes indicated that the two CDV strains isolated from dogs were most closely related to Chinese strains in the Asia-1 genotype. Another four strains were closely related to Japanese strains in the Asia-2 genotype. The six currently isolated strains shared 90.2-92.1% and 88.2-91.8% identities with eight commercial vaccine strains in their nucleotide and amino acid sequences of the F protein, respectively. They also showed 90.1-91.4% and 87.8-90.7% identities with the same vaccine strains in their nucleotide and deduced amino acid sequences of the H protein, respectively. Different N-linked glycosylation sites were identified in the F and H genes of the six isolates from the prototype vaccine strain Onderstepoort. Collectively, these results demonstrate that at least two different CDV genotypes currently exist in Korea. The considerable genetic differences between the vaccine strains and wild-type isolates would be a major factor of the incomplete protection of dogs from CDV infections.

Simultaneous detection of canine respiratory disease associated viruses by a multiplex reverse transcription-polymerase chain reaction assay

A multiplex reverse transcription polymerase chain reaction (mRT-PCR) assay was developed for the simultaneous detection of canine distemper virus (CDV), canine respiratory coronavirus (CRCoV) and canine influenza virus (CIV). These viral pathogens are all causative agents of canine infectious respiratory disease (CIRD). The sensitivity and specificity of the mRT-PCR were determined by comparing it to a rapid antigen test (RAT) or immuno-chromatography test kit and reverse transcription-polymerase chain reaction (RT-PCR) in the detection of CDV, CRCoV and CIV antigens present in 100 clinical samples (nasal swabs and whole blood samples) from 50 dogs with respiratory disease symptoms. This study revealed that mRT-PCR had almost exactly the same performance or results were almost 100% in agreement with that of RT-PCR and RAT both in terms of the assay sensitivity and specificity which was more highly evident in detecting CIV, CDV and CRCoV antigens present in canine nasal swab samples. Therefore, this assay could be a better alternative for the definitive and simultaneous ante-mortem detection of the three viral pathogens that cause CIRD by using nasal swabs.

DNA vaccines encoding proteins from wild-type and attenuated canine distemper virus protect equally well against wild-type virus challenge

Immunity induced by DNA vaccines containing the hemagglutinin (H) and nucleoprotein (N) genes of wild-type and attenuated canine distemper virus (CDV) was investigated in mink (Mustela vison), a highly susceptible natural host of CDV. All DNA-immunized mink seroconverted, and significant levels of virus-neutralizing (VN) antibodies were present on the day of challenge with wild-type CDV. The DNA vaccines also primed the cell-mediated memory responses, as indicated by an early increase in the number of interferon-gamma (IFN-γ)-producing lymphocytes after challenge. Importantly, the wild-type and attenuated CDV DNA vaccines had a long-term protective effect against wild-type CDV challenge. The vaccine-induced immunity induced by the H and N genes from wild-type CDV and those from attenuated CDV was comparable. Because these two DNA vaccines were shown to protect equally well against wild-type virus challenge, it is suggested that the genetic/antigenic heterogeneity between vaccine strains and contemporary wild-type strains are unlikely to cause vaccine failure.

Emergence of Canine Distemper Virus Strains With Modified Molecular Signature and Enhanced Neuronal Tropism Leading to High Mortality in Wild Carnivores

An ongoing canine distemper epidemic was first detected in Switzerland in the spring of 2009. Compared to previous local canine distemper outbreaks, it was characterized by unusually high morbidity and mortality, rapid spread over the country, and susceptibility of several wild carnivore species. Here, the authors describe the associated pathologic changes and phylogenetic and biological features of a multiple highly virulent canine distemper virus (CDV) strain detected in and/or isolated from red foxes ( Vulpes vulpes), Eurasian badgers ( Meles meles), stone ( Martes foina) and pine ( Martes martes) martens, from a Eurasian lynx ( Lynx lynx), and a domestic dog. The main lesions included interstitial to bronchointerstitial pneumonia and meningopolioencephalitis, whereas demyelination—the classic presentation of CDV infection—was observed in few cases only. In the brain lesions, viral inclusions were mainly in the nuclei of the neurons. Some significant differences in brain and lung lesions were observed between foxes and mustelids. Swiss CDV isolates shared together with a Hungarian CDV strain detected in 2004. In vitro analysis of the hemagglutinin protein from one of the Swiss CDV strains revealed functional and structural differences from that of the reference strain A75/17, with the Swiss strain showing increased surface expression and binding efficiency to the signaling lymphocyte activation molecule (SLAM). These features might be part of a novel molecular signature, which might have contributed to an increase in virus pathogenicity, partially explaining the high morbidity and mortality, the rapid spread, and the large host spectrum observed in this outbreak.

Detecção molecular e análise filogenética do gene H de amostras do vírus da cinomose canina em circulação no município de Campinas, São Paulo

O vírus da cinomose canina (CDV), um Morbillivirus da família Paramyxoviridae, é o agente etiológico de doença neurológica e sistêmica em cães. O diagnóstico laboratorial da infecção requer o isolamento viral ou detecção do material genético do vírus em secreções ou tecidos de cães com suspeita clínica da doença. A diversidade genética entre os isolados de CDV pode ser aferida pelo sequenciamento efilogenia molecular do gene que codifica a hemaglutinina viral (gene H), havendo atualmente um especial interesse em comparar as amostras circulantes a campo com o genogrupo América-1, que abrange as cepas presentes nas vacinas disponíveis no mercado. No presente estudo, foi realizada a detecção molecular do gene H de CDV a partir de amostras biológicas colhidas ante- e post- -mortem de 15 cães com sinais clínicos sugestivos de cinomose na região metropolitana de Campinas, São Paulo. Dez dos 15 cães analisados tiveram ao menos um órgão positivo na detecção molecular e os amplicons obtidos foram submetidos ao sequenciamento nucleotídico seguido de análise filogenética molecular. De forma semelhante ao que já foi reportado para estudo analisando a diversidade do gene H em outros países, a reconstrução filogenética obtida para as amostras de casos de cinomose da região de Campinas demonstrou as mesmas foram agrupadas junto a amostras norte-americanas, europeias e japonesas recentes, em um grupo genético distinto do grupo de amostras clássicas de CDV, nomeado America-1, o qual engloba as estirpes vacinais Snyder Hill, Onderstepoort e Lederle.

Canine distemper spillover in domestic dogs from urban wildlife

Canine distemper virus (CDV) causes a major disease of domestic dogs that develops as a serious systemic infection in unvaccinated or improperly vaccinated dogs. Domesticated dogs are the main reservoir of CDV, a multihost pathogen. This virus of the genus Morbillivirus in the family Paramyxoviridae occurs in other carnivorous species including all members of the Canidae and Mustelidae families and in some members of the Procyonidae, Hyaenidae, Ursidae, and Viverridae families. Canine distemper also has been reported in the Felidae family and marine mammals. The spread and incidences of CDV epidemics in dogs and wildlife here and worldwide are increasing.

Phylogenetic analysis of the haemagglutinin gene of canine distemper virus strains detected from breeding foxes, raccoon dogs and minks in China

Canine distemper virus (CDV) infects a variety of carnivores, including wild and domestic Canidae. Genetic/antigenic heterogeneity has been observed among the various CDV strains, notably in the haemagglutinin (H) gene, that appears as a good target to gather epidemiological information. Based on sequence analysis of the H gene, wild-type CDV strains cluster into distinct geographic lineages (genotypes), irrespective of the species of isolation. The sequence of the H gene of 28 CDV strains detected from both vaccinated and non-vaccinated breeding foxes, raccoon dogs and minks from different geographical areas of China during the years 2004-2008 was determined. All the CDV strains but two (strains HL and HLJ2) were characterized as Asia-1 genotype and were highly similar to each other (96.2-99.7% at the amino acid [aa] level) and to other Asia-1 strains (96.1-99.5% aa) previously detected in China. The CDV strains HL and HLJ2 were both collected from foxes in Heilongjiang province in 2005. Strain HL resembled CDVs of the Arctic genotype (GR88-like) and displayed high aa identity (98.0%) to the Chinese canine strain Liu. By converse, strain HLJ2 was barely related to CDVs of the Asia-2 genotype (88.7-90.3% aa identity), and could represent a novel CDV genotype, tentatively proposed as Asia-3. These results suggest that at least three different CDV genotypes, distantly related (81.8-91.6% aa identity) to the vaccine strains, Onderstepoort-like (America-1 genotype), are currently circulating in breeding foxes, raccoon dogs and minks in China, and that the genotype Asia-1 is predominant. Whether the diversity between wild-type CDVs and the vaccine strains may affect, to some extent, the efficacy of the vaccines deserves further investigations.

Diagnostic investigation of emerging viruses of companion animals

In this article, the authors are specifically concerned with the timely and accurate detection of emerging diseases of small animals that are viral in origin. Veterinarians are bound to encounter emerging viruses in their practice. The problem is unavoidable, because viruses are highly mutagenic. Even the immune response dictates the nature of virus that evolves in a host. If the clinical signs and diagnostic methods fail to correlate, the veterinarian should work with the diagnostic laboratory to solve the diagnostic puzzle.