Fatal combined infection with canine distemper virus and orthopoxvirus in a group of Asian marmots (Marmota caudata)

Detection and sequence analysis of Canine morbillivirus in multiple species of the Mustelidae family

BACKGROUND

Canine morbillivirus (canine distemper virus, CDV) is a member of the Paramyxoviridae family. Canine distemper is a serious viral disease that affects many mammalian species, including members of the Mustelidae family. These animals have an elusive nature, which makes related virological studies extremely challenging. There is a significant knowledge gap about the evolution of their viruses and about the possible effects of these viruses to the population dynamics of the host animals. Spleen and lung tissue samples of 170 road-killed mustelids belonging to six species were collected between 1997 and 2022 throughout Hungary and tested for CDV with real-time RT-PCR.

RESULTS

Three species were positive for viral RNA, 2 out of 64 Steppe polecats (Mustela eversmanii), 1 out of 36 European polecats (Mustela putorius) and 2 out of 36 stone martens (Martes foina); all 18 pine martens (Martes martes), 10 least weasels (Mustela nivalis) and 6 stoats (Mustela erminea) tested negative. The complete CDV genome was sequenced in five samples using pan-genotype CDV-specific, amplicon-based Nanopore sequencing. Based on the phylogenetic analysis, all five viral sequences were grouped to the Europe/South America 1 lineage and the distribution of one sequence among trees indicated recombination of the Hemagglutinin gene. We verified the recombination with SimPlot analysis.

CONCLUSIONS

This paper provides the first CDV genome sequences from Steppe polecats and additional complete genomes from European polecats and stone martens. The infected specimens of various species originated from distinct parts of the country over a long time, indicating a wide circulation of CDV among mustelids throughout Hungary. Considering the high virulence of CDV and the presence of the virus in these animals, we highlight the importance of conservation efforts for wild mustelids. In addition, we emphasize the importance of full genomic data acquisition and analysis to better understand the evolution of the virus. Since CDV is prone to recombination, specific genomic segment analyses may provide less representative evolutionary traits than using complete genome sequences.

Neuropathologic and molecular aspects of a canine distemper epizootic in red foxes in Germany

In the last fifteen years, an epidemic of canine distemper virus (CDV) with marked neurotropism has occurred in Europe after a longer period of endemic transmission. Many wildlife species have been infected, with red foxes (Vulpes vulpes) being particularly affected. Given that this species is assumed to mediate cross-species CDV infections to domestic and wild animals, tissue samples from foxes with confirmed CDV infection in North-Western Germany were investigated to better understand the neurotropic aspects of the disease. This analysis included histopathology, virus distribution and cell tropism, phenotyping of inflammatory responses and determination of the genotype of the viruses based on the phylogeny of the hemagglutinin (H) gene. The predominant lesion type is gliosis in both gray and white matter areas associated with an accumulation of Iba1+ macrophages/microglia and upregulation of major histocompatibility complex class II molecules in the brain, while sequestration of CD3+ T and Pax5+ B cell in CDV-infected foxes is limited. Demyelination is found in few foxes, characterized by reduced myelin staining with loss of CNPase+ oligodendrocytes in the cerebellar white matter and brainstem. In addition, axonal damage, characterized by β-amyloid precursor protein expression, is found mainly in these brain regions. In situ hybridization reveals a primary infection of the cerebral and cerebellar gray matter and brain stem. Iba1+ cells and NeuN+ neurons represent the main CDV targets. Sequencing of the CDV H open reading frame from fox tissues reveals that the virus strains belongs to three different sub-lineages of the Europe-1/South America-1 genotype, suggesting independent transmission lines.

Development and Validation of a Pan-Genotypic Real-Time Quantitative Reverse Transcription-PCR Assay To Detect Canine Distemper Virus and Phocine Distemper Virus in Domestic Animals and Wildlife

Canine distemper virus (CDV) is an animal morbillivirus belonging to the family Paramyxoviridae and has caused major epizootics with high mortality levels in susceptible wildlife species. In recent years, the documented genetic diversity of CDV has expanded, with new genotypes identified in India, the Caspian Sea, and North America. However, no quantitative real-time PCR (RT-qPCR) that has been validated for the detection of all genotypes of CDV is currently available. We have therefore established and characterized a pan-genotypic probe-based RT-qPCR assay based on the detection of a conserved region of the phosphoprotein (P) gene of CDV. This assay has been validated using virus strains representative of six genotypes of CDV in different sample types, including frozen tissue, formalin-fixed paraffin-embedded tissue sections, and virus isolates. The primers and probe target sequences were sufficiently conserved to also enable detection of the phocine distemper virus strains responsible for epizootics in harbor seals in the North Sea in 1988 and 2002. Comparison with two recently published RT-qPCR assays for CDV showed that under equivalent conditions the primers and probe set reported in this study were more sensitive in detecting nucleic acids from an Asia-4 genotype, which displays sequence variation in primer and probe binding sites. In summary, this validated new pan-genotypic RT-qPCR assay will facilitate screening of suspected distemper cases caused by novel genotypes for which full genome sequences are unavailable and have utility in detecting multiple CDV strains in geographical regions where multiple genotypes cocirculate in wildlife.

Insight Into an Outbreak of Canine Distemper Virus Infection in Masked Palm Civets in China

In August 2019, a suspected outbreak of canine distemper was observed in a masked palm civet farm that also received stray civets and rescued wild civets in Henan Province of China. A virulent canine distemper virus (CDV) strain, named HN19, from vaccinated masked palm civets was the etiologic agent identified in this outbreak using RT-PCR and sequencing of the complete genome. Serological analysis indicated a lower positive rate of CDV-neutralizing antibody in wild civets than in captive civets. Phylogenetic analysis of viral hemagglutinin (H) and the complete genome showed high identities with Rockborn-like strains at the nucleotide (98.7~99.72%) and the closest nucleotide similarity with a strain that killed lesser pandas in China in 1997, but low identities with America-1 strains (vaccine strains). Most importantly, one distinct amino acid exchange in the H protein at position 540 Asp → Gly (D540G), which confers CDV with an improved ability to adapt and utilize the human receptor, was observed in HN19. This study represents the first reported outbreak of a Rockborn-like CDV strain infection in masked palm civets in China. Based on this report, the existence of Rockborn-like strains in Chinese wild animals may not only cause immune failure in captive animals, but may also confer increased zoonotic potential.

A scoping review of rodent-borne pathogen presence, exposure, and transmission at zoological institutions

BACKGROUND

Rodents are one of the major taxa most likely to carry zoonotic diseases, harboring more than 85 unique zoonotic pathogens. While the significance of rodents' capacity to carry and transmit disease has been characterized in urban settings, the zoo environment is particularly unique given the overlap of collection, free-living, and feeder rodents as well as non-rodent collection animals, staff, and visitors.

ELIGIBILITY CRITERIA

This scoping review examines reports of rodent-borne pathogen detection or transmission in zoo settings extracted from the literature. Papers were included in the final analysis if there was evidence of presence or exposure to a pathogen in a rodent at a zoological institution.

SOURCES OF EVIDENCE

Publications were included from PubMed, CAB Abstracts and Biological Abstracts searched in August 2019.

CHARTING METHODS

Data extracted from publications on pathogen presence/exposure included publication identifiers, study identifiers, infectious agent identifiers, rodent identifiers, and non-rodent collection animal identifiers. Extraction from papers with evidence of disease transmission included number of rodents involved in transmission, non-rodent collection animal species and numbers, and job title of humans involved, diagnostic tests performed, and clinical outcomes.

RESULTS

Aggregate literature examined included 207 publications presenting evidence of pathogen presence and/or exposure in rodents across 43 countries in over 140 zoological institutions. A total of 143 infectious agent genera were identified, comprising 14 viral genera, 31 bacterial genera, 83 parasitic genera, and 15 fungal genera. Of these infectious agents, over 75 % were potentially zoonotic. The most common disease-causing agent genera identified were Leptospira, Toxoplasma, Salmonella, and Yersinia. Additional screening for evidence of pathogen transmission across species yielded 30 publications, indicating an area for future investigation to better inform surveillance and management priorities in order to reduce exposure, infection, and transmission.

CONCLUSIONS

Analyzing the breadth of rodent species and pathogens identified at zoos highlights the unique opportunity zoos have to be at the forefront of the early detection and identification of novel hosts and geographic ranges of rodent-borne pathogens with high impact on both endangered species and people. The overlap of these populations at zoos exemplifies the importance of considering One Health when prioritizing surveillance and risk mitigation of rodent reservoirs at zoos.

Canine Distemper Outbreak by Natural Infection in a Group of Vaccinated Maned Wolves in Captivity

Canine distemper virus (CDV) is one of the most significant infectious disease threats to the health and conservation of free-ranging and captive wild carnivores. CDV vaccination using recombinant canarypox-based vaccines has been recommended for maned wolf (Chrysocyon brachyurus) after the failure of modified live vaccines that induced disease in vaccinated animals. Here, we report a CDV outbreak in a captive population of maned wolves that were previously vaccinated. Five juveniles and one adult from a group of seven maned wolves housed in an outdoor exhibit died in April–May 2013 in a zoo in the Metropolitan Region, Chile. Clinical signs ranged from lethargy to digestive and respiratory signs. Diagnosis of CDV was confirmed by histopathology, antibody assays, and viral molecular detection and characterization. The phylogenetic analyses of the nucleotide sequence of the H gene of the CDV genome identified in the two positive samples suggest a close relation with the lineage Europe 1, commonly found in South America and Chile. CDV infections in maned wolves have not been previously characterized. To the authors’ best knowledge, this is the first report of the clinical presentation of CDV in a canine species previously immunized with a recombinant vaccine.

Human Paramyxovirus Infections Induce T Cells That Cross-React with Zoonotic Henipaviruses

Humans are infected with paramyxoviruses of different genera early in life, which induce cytotoxic T cells that may recognize conserved epitopes. This raises the question of whether cross-reactive T cells induced by antecedent paramyxovirus infections provide partial protection against highly lethal zoonotic Nipah virus infections. By characterizing a measles virus-specific but paramyxovirus cross-reactive human T cell clone, we discovered a highly conserved HLA-B*1501-restricted T cell epitope in the fusion protein. Using peptides, tetramers, and single cell sorting, we isolated a parainfluenza virus-specific T cell clone from a healthy adult and showed that both clones cleared Nipah virus-infected cells. We identified multiple conserved hot spots in paramyxovirus proteomes that contain other potentially cross-reactive epitopes. Our data suggest that, depending on HLA haplotype and history of paramyxovirus exposures, humans may have cross-reactive T cells that provide protection against Nipah virus. The effect of preferential boosting of these cross-reactive epitopes needs to be further studied in light of paramyxovirus vaccination studies.IMPORTANCE Humans encounter multiple paramyxoviruses early in life. This study shows that infection with common paramyxoviruses can induce T cells cross-reactive with the highly pathogenic Nipah virus. This demonstrates that the combination of paramyxovirus infection history and HLA haplotype affects immunity to phylogenetically related zoonotic paramyxoviruses.

Genetic Adaptations, Biases, and Evolutionary Analysis of Canine Distemper Virus Asia-4 Lineage in a Fatal Outbreak of Wild-Caught Civets in Thailand

Canine morbillivirus (CDV) is a serious pathogen that can cause fatal systemic disease in a wide range of domestic and wildlife carnivores. Outbreaks of CDV in wildlife species lead to questions regarding the dispersal of the CDV origin. In the present study, we identified a fatal CDV outbreak in caged wild-caught civets in Thailand. Full-length genetic analysis revealed that CDV from the Asia-4 lineage served as the likely causative agent, which was supported by the viral localization in tissues. Evolutionary analysis based on the CDV hemagglutinin (H) gene revealed that the present civet CDV has co-evolved with CDV strains in dogs in Thailand since about 2014. The codon usage pattern of the CDV H gene revealed that the CDV genome has a selective bias of an A/U-ended codon preference. Furthermore, the codon usage pattern of the CDV Asia-4 strain from potential hosts revealed that the usage pattern was related more to the codon usage of civets than of dogs. This finding may indicate the possibility that the discovered CDV had initially adapted its virulence to infect civets. Therefore, the CDV Asia-4 strain might pose a potential risk to civets. Further epidemiological, evolutionary, and codon usage pattern analyses of other CDV-susceptible hosts are required.

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.

RECENT CHANGES IN INFECTIOUS DISEASES IN EUROPEAN WILDLIFE

Many infectious diseases originating from, or carried by, wildlife affect wildlife conservation and biodiversity, livestock health, or human health. We provide an update on changes in the epidemiology of 25 selected infectious, wildlife-related diseases in Europe (from 2010-16) that had an impact, or may have a future impact, on the health of wildlife, livestock, and humans. These pathogens were selected based on their: 1) identification in recent Europe-wide projects as important surveillance targets, 2) inclusion in European Union legislation as pathogens requiring obligatory surveillance, 3) presence in recent literature on wildlife-related diseases in Europe since 2010, 4) inclusion in key pathogen lists released by the Office International des Epizooties, 5) identification in conference presentations and informal discussions on a group email list by a European network of wildlife disease scientists from the European Wildlife Disease Association, or 6) identification as pathogens with changes in their epidemiology during 2010-16. The wildlife pathogens or diseases included in this review are: avian influenza virus, seal influenza virus, lagoviruses, rabies virus, bat lyssaviruses, filoviruses, canine distemper virus, morbilliviruses in aquatic mammals, bluetongue virus, West Nile virus, hantaviruses, Schmallenberg virus, Crimean-Congo hemorrhagic fever virus, African swine fever virus, amphibian ranavirus, hepatitis E virus, bovine tuberculosis ( Mycobacterium bovis), tularemia ( Francisella tularensis), brucellosis ( Brucella spp.), salmonellosis ( Salmonella spp.), Coxiella burnetii, chytridiomycosis, Echinococcus multilocularis, Leishmania infantum, and chronic wasting disease. Further work is needed to identify all of the key drivers of disease change and emergence, as they appear to be influencing the incidence and spread of these pathogens in Europe. We present a summary of these recent changes during 2010-16 to discuss possible commonalities and drivers of disease change and to identify directions for future work on wildlife-related diseases in Europe. Many of the pathogens are entering Europe from other continents while others are expanding their ranges inside and beyond Europe. Surveillance for these wildlife-related diseases at a continental scale is therefore important for planet-wide assessment, awareness of, and preparedness for the risks they may pose to wildlife, domestic animal, and human health.

Causes of mortality and morbidity in free-ranging mustelids in Switzerland: necropsy data from over 50 years of general health surveillance

BACKGROUND

Although mustelids occur worldwide and include a wide range of species, little is known about the diseases affecting them. Mustelids have regularly been submitted for post mortem investigation in the framework of the program for general wildlife health surveillance in Switzerland, which has been in place for nearly 60 years. We performed a retrospective analysis of the necropsy reports on mustelids submitted to the diagnostic service of the University of Bern. The aims of this study were to present an overview of the causes of mortality and morbidity observed in these carnivores, to assess differences among species, to assess changes in disease detection over the study period, and to describe the pathology of selected diseases.

RESULTS

Five hundred and sixty-six reports from 1958 to 2015 were analyzed. Most animals were stone martens (Martes foina, 46%) and badgers (Meles meles, 44%); the remaining species were polecats (Mustela putorius, 4.7%), pine martens (Martes martes, 2%), stoats (Mustela erminea, 1.4%), weasels (Mustela nivalis, 0.8%) and otters (Lutra lutra, 0.3%). Infectious diseases (n = 262) were frequent and were mostly bacterial or viral; non-infectious conditions (n = 169) were less common and were mostly traumatic or due to metabolic disorders. The most frequent diagnoses included distemper (75% were badgers), amyloidosis (96% were martens), bacterial respiratory infections (all mustelids), biting lice (badgers only) and pulmonary and gastro-intestinal helminths (all species). Less frequent diseases included histoplasmosis (badgers only), aspergillosis, toxoplasmosis, hepatozoonosis, and sarcoptic mange. Lesions due to infection with distemper virus were primarily appreciated in the respiratory tract and central nervous system; they presented species-specific characteristics such as necrosis in the ependyma in badgers and absence of syncytia in stone martens. Amyloidosis in martens was multisystemic in most cases and included both AA and AL amyloidosis; the main macroscopic change was severe splenomegaly.

CONCLUSION

Infectious diseases were the most frequent causes of morbidity and mortality of mustelids, with marked species-specific differences. Lung and skin were the most commonly affected organs. Contagious diseases such as canine distemper, sarcoptic mange and rabies in mustelids showed a similar temporal pattern as in red foxes (Vulpes vulpes), suggesting pathogen spillovers from foxes to mustelids.

Diversity of susceptible hosts in canine distemper virus infection: a systematic review and data synthesis

BACKGROUND

Canine distemper virus (CDV) is the etiological agent of one of the most infectious diseases of domestic dogs, also known as a highly prevalent viral infectious disease of carnivores and posing a conservation threat to endangered species around the world. To get a better panorama of CDV infection in different Orders, a retrospective and documental systematic review of the role of CDV in different non-dog hosts was conducted. The bibliographical data were collected from MedLine/PubMed and Scopus databases. Data related to Order, Family, Genus and Species of the infected animals, the presence or absence of clinical signs, mortality, serological, molecular or antigenic confirmation of CDV infection, geographic location, were collected and summarized.

RESULTS

Two hundred seventeen scientific articles were considered eligible which includes reports of serological evaluation, and antigenic or genomic confirmation of CDV infection in non-dog hosts. CDV infects naturally and experimentally different members of the Orders Carnivora (in 12 Families), Rodentia (four Families), Primates (two Families), Artiodactyla (three Families) and Proboscidea (one Family). The Order Carnivora (excluding domestic dogs) accounts for the vast majority (87.5%) of the records. Clinical disease associated with CDV infection was reported in 51.8% of the records and serological evidence of CDV infection in apparently healthy animals was found in 49.5% of the records. High mortality rate was showed in some of the recorded infections in Orders different to Carnivora. In non-dog hosts, CDV has been reported all continents with the exception of Australasia and in 43 different countries.

CONCLUSIONS

The results of this systematic review demonstrate that CDV is able to infect a very wide range of host species from many different Orders and emphasizes the potential threat of infection for endangered wild species as well as raising concerns about potential zoonotic threats following the cessation of large-scale measles vaccination campaigns in the human population.

Canine distemper virus as a threat to wild tigers in Russia and across their range

Canine distemper virus (CDV) has recently been identified in populations of wild tigers in Russia and India. Tiger populations are generally too small to maintain CDV for long periods, but are at risk of infections arising from more abundant susceptible hosts that constitute a reservoir of infection. Because CDV is an additive mortality factor, it could represent a significant threat to small, isolated tiger populations. In Russia, CDV was associated with the deaths of tigers in 2004 and 2010, and was coincident with a localized decline of tigers in Sikhote-Alin Biosphere Zapovednik (from 25 tigers in 2008 to 9 in 2012). Habitat continuity with surrounding areas likely played an important role in promoting an ongoing recovery. We recommend steps be taken to assess the presence and the impact of CDV in all tiger range states, but should not detract focus away from the primary threats to tigers, which include habitat loss and fragmentation, poaching and retaliatory killing. Research priorities include: (i) recognition and diagnosis of clinical cases of CDV in tigers when they occur; and (ii) collection of baseline data on the health of wild tigers. CDV infection of individual tigers need not imply a conservation threat, and modeling should complement disease surveillance and targeted research to assess the potential impact to tiger populations across the range of ecosystems, population densities and climate extremes occupied by tigers. Describing the role of domestic and wild carnivores as contributors to a local CDV reservoir is an important precursor to considering control measures.

Efficient generation of vesicular stomatitis virus (VSV)-pseudotypes bearing morbilliviral glycoproteins and their use in quantifying virus neutralising antibodies

Morbillivirus neutralising antibodies are traditionally measured using either plaque reduction neutralisation tests (PRNTs) or live virus microneutralisation tests (micro-NTs). While both test formats provide a reliable assessment of the strength and specificity of the humoral response, they are restricted by the limited number of viral strains that can be studied and often present significant biological safety concerns to the operator. In this study, we describe the adaptation of a replication-defective vesicular stomatitis virus (VSVΔG) based pseudotyping system for the measurement of morbillivirus neutralising antibodies. By expressing the haemagglutinin (H) and fusion (F) proteins of canine distemper virus (CDV) on VSVΔG pseudotypes bearing a luciferase marker gene, neutralising antibody titres could be measured rapidly and with high sensitivity. Further, by exchanging the glycoprotein expression construct, responses against distinct viral strains or species may be measured. Using this technique, we demonstrate cross neutralisation between CDV and peste des petits ruminants virus (PPRV). As an example of the value of the technique, we demonstrate that UK dogs vary in the breadth of immunity induced by CDV vaccination; in some dogs the neutralising response is CDV-specific while, in others, the neutralising response extends to the ruminant morbillivirus PPRV. This technique will facilitate a comprehensive comparison of cross-neutralisation to be conducted across the morbilliviruses.

Canine Distemper Virus Fusion Activation: Critical Role of Residue E123 of CD150/SLAM

Measles virus (MeV) and canine distemper virus (CDV) possess tetrameric attachment proteins (H) and trimeric fusion proteins, which cooperate with either SLAM or nectin 4 receptors to trigger membrane fusion for cell entry. While the MeV H-SLAM cocrystal structure revealed the binding interface, two distinct oligomeric H assemblies were also determined. In one of the conformations, two SLAM units were sandwiched between two discrete H head domains, thus spotlighting two binding interfaces ("front" and "back"). Here, we investigated the functional relevance of both interfaces in activating the CDV membrane fusion machinery. While alanine-scanning mutagenesis identified five critical regulatory residues in the front H-binding site of SLAM, the replacement of a conserved glutamate residue (E at position 123, replaced with A [E123A]) led to the most pronounced impact on fusion promotion. Intriguingly, while determination of the interaction of H with the receptor using soluble constructs revealed reduced binding for the identified SLAM mutants, no effect was recorded when physical interaction was investigated with the full-length counterparts of both molecules. Conversely, although mutagenesis of three strategically selected residues within the back H-binding site of SLAM did not substantially affect fusion triggering, nevertheless, the mutants weakened the H-SLAM interaction recorded with the membrane-anchored protein constructs. Collectively, our findings support a mode of binding between the attachment protein and the V domain of SLAM that is common to all morbilliviruses and suggest a major role of the SLAM residue E123, located at the front H-binding site, in triggering the fusion machinery. However, our data additionally support the hypothesis that other microdomain(s) of both glycoproteins (including the back H-binding site) might be required to achieve fully productive H-SLAM interactions.

IMPORTANCE

A complete understanding of the measles virus and canine distemper virus (CDV) cell entry molecular framework is still lacking, thus impeding the rational design of antivirals. Both viruses share many biological features that partially rely on the use of analogous Ig-like host cell receptors, namely, SLAM and nectin 4, for entering immune and epithelial cells, respectively. Here, we provide evidence that the mode of binding between the membrane-distal V domain of SLAM and the attachment protein (H) of morbilliviruses is very likely conserved. Moreover, although structural information revealed two discrete conformational states of H, one of the structures displayed two H-SLAM binding interfaces ("front" and "back"). Our data not only spotlight the front H-binding site of SLAM as the main determinant of membrane fusion promotion but suggest that the triggering efficiency of the viral entry machinery may rely on a local conformational change within the front H-SLAM interactive site rather than the binding affinity.

Pathologic and Molecular Virologic Characterization of a Canine Distemper Outbreak in Farmed Civets

In October 2011, a fatal disease outbreak occurred in 3 civet species farmed for their use in the coffee industry in Thailand. The disease quickly killed 20 animals in a mixed population of Asian palm civets (Paradoxurus hermaphroditus; n = 18), a masked palm civet (Paguma larvata; n = 1), and small Indian civet (Viverricula indica; n = 1). Clinical signs consisted of severe lethargy, weakness, vomiting, and diarrhea with associated dehydration, dyspnea, nasal and footpad hyperkeratosis, and seizures. All civets were positive for canine morbillivirus using the commercial canine distemper virus (CDV) antigen test kit. Consistently observed necropsy findings consisted of severe pneumonia and hemorrhagic enteritis. Microscopic examination revealed severe gastroenteritis, bronchointerstitial pneumonia, lymphadenitis, necrotizing dermatitis, nonsuppurative polioencephalitis, and characteristic intranuclear/intracytoplasmic eosinophilic viral inclusions in multiple tissues. Immunohistochemical analysis revealed immunoreactivity of varying intensity, while virus isolation demonstrated typical cytopathic effects. To confirm CDV infection, reverse transcription-polymerase chain reaction against fusion (F), phosphoprotein (P), and hemagglutinin (H) genes showed bands of expected size using conjunctival swabs (9 civets, 1 dog [Canis lupus familiaris] living on the farm). Phylogenetic analyses and restriction fragment length polymorphism results indicated that the civets were infected by the Asia-1 strain of CDV commonly found in dogs in Thailand. The deduced amino acid sequences of the signaling lymphocyte activation molecule binding region of the CDV-H proteins revealed a Y549H mutation in both CDV-infected Asian palm civets (n = 4) and a co-located dog. We report a canine distemper outbreak in a civet colony with lineage classification and a Y549H mutation in noncanid species in Thailand.

Identification of amino acid substitutions with compensational effects in the attachment protein of canine distemper virus

The hemagglutinin (H) gene of canine distemper virus (CDV) encodes the receptor-binding protein. This protein, together with the fusion (F) protein, is pivotal for infectivity since it contributes to the fusion of the viral envelope with the host cell membrane. Of the two receptors currently known for CDV (nectin-4 and the signaling lymphocyte activation molecule [SLAM]), SLAM is considered the most relevant for host susceptibility. To investigate how evolution might have impacted the host-CDV interaction, we examined the functional properties of a series of missense single nucleotide polymorphisms (SNPs) naturally accumulating within the H-gene sequences during the transition between two distinct but related strains. The two strains, a wild-type strain and a consensus strain, were part of a single continental outbreak in European wildlife and occurred in distinct geographical areas 2 years apart. The deduced amino acid sequence of the two H genes differed at 5 residues. A panel of mutants carrying all the combinations of the SNPs was obtained by site-directed mutagenesis. The selected mutant, wild type, and consensus H proteins were functionally evaluated according to their surface expression, SLAM binding, fusion protein interaction, and cell fusion efficiencies. The results highlight that the most detrimental functional effects are associated with specific sets of SNPs. Strikingly, an efficient compensational system driven by additional SNPs appears to come into play, virtually neutralizing the negative functional effects. This system seems to contribute to the maintenance of the tightly regulated function of the H-gene-encoded attachment protein. Importance: To investigate how evolution might have impacted the host-canine distemper virus (CDV) interaction, we examined the functional properties of naturally occurring single nucleotide polymorphisms (SNPs) in the hemagglutinin gene of two related but distinct strains of CDV. The hemagglutinin gene encodes the attachment protein, which is pivotal for infection. Our results show that few SNPs have a relevant detrimental impact and they generally appear in specific combinations (molecular signatures). These drastic negative changes are neutralized by compensatory mutations, which contribute to maintenance of an overall constant bioactivity of the attachment protein. This compensational mechanism might reflect the reaction of the CDV machinery to the changes occurring in the virus following antigenic variations critical for virulence.

Measles vaccination of nonhuman primates provides partial protection against infection with canine distemper virus

Measles virus (MV) is being considered for global eradication, which would likely reduce compliance with MV vaccination. As a result, children will grow up without MV-specific immunity, creating a potential niche for closely related animal morbilliviruses such as canine distemper virus (CDV). Natural CDV infection causing clinical signs has never been reported in humans, but recent outbreaks in captive macaques have shown that CDV can cause disease in primates. We studied the virulence and tropism of recombinant CDV expressing enhanced green fluorescent protein in naive and measles-vaccinated cynomolgus macaques. In naive animals CDV caused viremia and fever and predominantly infected CD150(+) lymphocytes and dendritic cells. Virus was reisolated from the upper and lower respiratory tracts, but infection of epithelial or neuronal cells was not detectable at the time points examined, and the infections were self-limiting. This demonstrates that CDV readily infects nonhuman primates but suggests that additional mutations are necessary to achieve full virulence in nonnatural hosts. Partial protection against CDV was observed in measles-vaccinated macaques, as demonstrated by accelerated control of virus replication and limited shedding from the upper respiratory tract. While neither CDV infection nor MV vaccination induced detectable cross-reactive neutralizing antibodies, MV-specific neutralizing antibody levels of MV-vaccinated macaques were boosted by CDV challenge infection, suggesting that cross-reactive VN epitopes exist. Rapid increases in white blood cell counts in MV-vaccinated macaques following CDV challenge suggested that cross-reactive cellular immune responses were also present. This study demonstrates that zoonotic morbillivirus infections can be controlled by measles vaccination.

IMPORTANCE

Throughout history viral zoonoses have had a substantial impact on human health. Given the drive toward global eradication of measles, it is essential to understand the zoonotic potential of animal morbilliviruses. Morbilliviruses are thought to have evolved from a common ancestral virus that jumped species and adapted to new hosts. Recently, canine distemper virus (CDV), a morbillivirus normally restricted to carnivores, caused disease outbreaks in nonhuman primates. Here, we report that experimental CDV infection of monkeys resulted in fever and leukopenia. The virus replicated to high levels in lymphocytes but did not spread to epithelial cells or the central nervous system. Importantly, like measles virus in macaques, the infections were self-limiting. In measles-vaccinated macaques CDV was cleared more rapidly, resulting in limited virus shedding from the upper respiratory tract. These studies demonstrate that although CDV can readily infect primates, measles immunity is protective, and CDV infection is self-limiting.

Using the ferret model to study morbillivirus entry, spread, transmission and cross-species infection

Canine distemper virus (CDV) is an animal morbillivirus with a worldwide circulation that infects carnivores, including domestic dogs and an assortment of wildlife hosts. The development of reverse genetics systems for wild-type strains of CDV and the use of the resulting recombinant (r) viruses to infect ferrets by a natural route has shed new light on the temporal pathogenesis of distemper. Combining fluorescent protein expressing recombinant viruses and multimodal, macroscopic and microscopic imaging modalities has highlighted the differential role of the cellular receptors CD150 and PVRL4 in disease progression. This in turn has enabled pathways of viral spread, including multiple routes of entry into the central nervous system, to be mapped with unparalleled sensitivity.