Canine distemper virus in wildlife in south-western Europe

New threats in the recovery of large carnivores inhabiting human-modified landscapes: the case of the Cantabrian brown bear (Ursus arctos)

Understanding mortality causes is important for the conservation of endangered species, especially in small and isolated populations inhabiting anthropized landscapes where both natural and human-caused mortality may hinder the conservation of these species. We investigated the mortality causes of 53 free-ranging brown bears (Ursus arctos) found dead between 1998 and 2023 in the Cantabrian Mountains (northwestern Spain), a highly human-modified region where bears are currently recovering after being critically threatened in the last century. We detected natural traumatic injuries in 52.63% and infectious diseases in 39.47% of the 38 bears for which the mortality causes were registered, with 21.05% of these cases presenting signs of both infectious diseases and traumas. More specifically, almost 30% of the bears died during or after intraspecific fights, including sexually selected infanticide (10.53%). In addition, primary infectious diseases such as infectious canine hepatitis, distemper, clostridiosis and colibacillosis caused the death of 15.79% of the bears. The number of direct human-caused deaths (i.e., shooting, poisoning, snare) decreased over the study period. This study also reveals three new mortality causes triggered by pathogens, two of which-Clostridium novyi and verotoxigenic Escherichia coli-not previously described in ursids, and the other one, canine distemper virus, never reported in brown bears as cause of death. New management strategies for the conservation of Cantabrian bears, which are urgently needed due to the rapid expansion of the population, should consider the mortality causes described in this study and must promote further research to elucidate how the high prevalence of infectious diseases may threaten the current recovery of the population.

Canine distemper virus (CDV)-neutralizing activities of an anti-CDV canine-derived single-chain variable antibody fragment 4-15 (scFv 4-15) screened by phage display technology

Canine distemper virus (CDV) is a highly contagious pathogen that causes severe diarrhea, fever and vomiting in domestic dogs, posing a serious threat to the dog breeding industry. Currently, there are no effective therapeutic agents for emergency treatment despite the availability of vaccines against CDV infection. Single-chain fragment variable (scFv) antibody has been demonstrated to effectively inhibit virus infections, suggesting a potential candidate as a therapeutic agent for canine distemper. In this study, a phage-displayed scFv library was constructed from the peripheral blood lymphocytes of dog immunized intramuscularly with live-attenuated CDV vaccine, and was subjected to four rounds of pannings against CDV. Subsequent indirect enzyme-linked immunosorbent assay screening revealed high-affinity scFv antibodies specific to CDV, and indirect immunofluorescence assay screening revealed CDV-neutralizing activity of scFv antibodies. Our results showed that a scFv antibody 4-15 (scFv 4-15) with high-affinity binding to CDV and neutralizing activity against CDV was obtained, which displayed effective therapeutic potential in vivo for dogs challenged with a lethal dose of CDV. Conclusively, the scFv 4-15 with high-affinity binding and neutralizing activity to CDV that was obtained by phage display technology provides a promising candidate for the therapeutic agents against CDV infection.

Study of Canine Distemper Virus Presence in Catalonia's Wild Carnivores through H Gene Amplification and Sequencing

Canine distemper virus (CDV) is recognised worldwide as an important pathogen in both domestic and wild carnivores. Few data are available on its impact and spread on the wildlife/wildlife-domestic animal-environment interface. This study, aimed at developing a conservation-oriented control strategy, analysed 89 sick or deceased animals from 2019 to 2023 at the Wildlife Rehabilitation Centre in Torreferrussa. RT-PCR and sequencing of the partial H gene were used to detect and analyse CDV in tissues. The total positive percentage was 20.22% (18/89), comprising 13 red foxes (44.8%), 4 European badgers (28.6%), and 1 American mink (4.5%), while 24 Eurasian otters tested negative. Phylogenetic analysis indicated that all of the CDV strains belong to the European lineage. Geographically distant individuals and different species shared the same viral strain, suggesting a strong capacity of CDV for interspecies and long-distance transmission. This calls for further research, particularly focusing on potential impacts of CDV on endangered carnivores.

Greater predisposition to second generation anticoagulant rodenticide exposure in red foxes (Vulpes vulpes) weakened by suspected infectious disease

Anticoagulant rodenticide (AR) exposure in wild carnivores is a current and global concern due to continuous and widespread use worldwide. We studied the prevalence of ARs in liver samples of 25 red foxes (Vulpes vulpes), 3 European badgers (Meles meles) and 2 genets (Genneta genneta) from Alicante (Spanish Levante region) obtained in 2021 and 2022. In addition to trauma, poisoning by pesticides is the most frequent cause of death in wild carnivores in this region. The present research aims to explain a possible association between the fact of suffering from an infectious disease and the increase in ARs concentrations in the affected animals. Both first- and second-generation ARs were analysed by HPLC/MS/TOF in liver samples. Apart from the cause of death, the influence of other variables such as age, sex and body weight were also assessed on AR liver concentrations. Potential health risks for individuals and populations in the study area have also been studied. Our research detected higher AR concentrations in the group of red foxes clinically diagnosed with infectious disease compared to the group of apparently healthy red foxes, mostly killed by trauma. Furthermore, our results lead us to suggest that red fox could be considered a good sentinel species for the risk of exposure to ARs in other wild mammals. All the livers analysed contained ARs and the most detected compounds in red fox were difenacoum, bromadiolone, brodifacoum, present in all the samples analysed, and flocoumafen (in 96 %). Additionally, 53 % of the animals had at least one second generation anticoagulant rodenticide (SGAR) above the threshold value reported as triggering adverse health effects (200 ng/g). Regarding this, the level of risk in red fox in this area might be classified as high and worrying. Moreover, we suggest that individuals and populations with weakened health due to other diseases (for example, infectious or parasitic diseases) might be more prone to high exposure to anticoagulant rodenticides and, very probably, would be more sensitive to suffering serious effects at lower doses of ARs.

Survey of Common Infectious Diseases in Urban Foxes (Vulpes spp.) in Southeastern Iran

The red fox (Vulpes vulpes) is one of the most common species of wild Canidae and is relatively abundant in Iran. Foxes (Vulpes spp.) transmit many zoonotic diseases, the most important of which are visceral leishmaniasis, rabies, hydatidosis, toxocariasis, and trichinellosis. In this study, visceral leishmaniasis, rabies, ectoparasites, canine gastrointestinal helminths, dermatophytosis, distemper, parvovirus infection, and heartworm infections were evaluated among live-trapped and rescued foxes injured by traffic road accidents referred to the teaching hospital of Kerman, Iran, veterinary faculty. Skin scraping and direct microscopic examination were used to detect ectoparasites and dermatophytosis. Immunochromatography rapid kits were used to detect dirofilariasis, parvovirus infection, and distemper. Necropsy was used to check for gastrointestinal parasites. Rabies and visceral leishmaniosis were screened for with direct fluorescent antibody test and ELISA methods, respectively. Gastrointestinal helminth infections, including Toxocara canis, Taenia taeniaeformis, Dipylidium caninum, Joyeuxiella echinorhyncoids, Toxascaris leonina, Taenia hydatigena, Echinococcus granulosus, Rictolaria spp., Oxynema spp., Macracanthorhynchus hirudinaceus, and Physaloptera spp., were detected. Skin scrapings showed dermatophytosis and various ectoparasites, including Rhipicephalus sanguineus, Ctenocephalides canis and Ctenocephalides felis, and Sarcoptes scabiei, in foxes with dermal lesions. Distemper and parvovirus infection (26.66%) were the common viral diseases, and rabies infection rate was quite high (16.66%). Dirofilariasis and leishmaniasis were detected in 10% of the population. This study showed that urban foxes which often cohabit with humans and domestic animals are carriers of many different pathogens. This interaction may facilitate indirect cross-species transmission of zoonotic disease. Periodic health monitoring and multidisciplinary cooperation for the diagnosis, control, and prevention of these zoonoses is highly recommended.

Serological and molecular survey of canine distemper virus in red foxes (Vulpes vulpes): Exploring cut-off values and the use of protein A in ELISA tests

The wide distribution and ecological plasticity of the red fox (Vulpes vulpes) make it a potential reservoir for many infectious diseases shared with domestic and wild carnivores. One of such diseases is canine distemper, which is caused by an RNA virus and its main domestic reservoir is the dog. However, other carnivores can also participate in its maintenance, as shown by the recent upsurge of reported cases in wildlife in many parts of the world, and by the fact that red foxes may act as true reservoirs for canine distemper virus (CDV). The lack of validated serological tests for wildlife or other non-target species may be a handicap for monitoring this virus. In this study, serological assays were compared in 147 red fox sera using a commercial ELISA validated for its use in dogs and a non-specific modified ELISA with Protein A peroxidase conjugate to detect bound antibodies. In addition, the presence of CDV RNA in brain, spleen, lung, and liver samples from 144 foxes was investigated by a RT-qPCR. Through the comparison of the results of both ELISAs and the use of a finite mixture model of the optical density values obtained by both techniques, we adjusted the cut-off point of the commercial ELISA to obtain the seroprevalence in foxes. The overall seroprevalence detected was 53.7% (79/147) and 57.1% (84/147) by the commercial and modified ELISA, respectively, with a moderate agreement according to Cohen's Kappa statistic (κ = 0.491, z = 5.97, p < 0.0001). CDV RNA was detected in 30 out of 144 foxes, which resulted in 20.8% of CDV-infected foxes. At individual level, the results obtained by relating the serological status and the presence/absence of RNA in different organs were explained in terms of the pathogenesis of the infection. Our results highlight the convenience of adjusting the cut-off point when using an ELISA assay developed in domestic dogs for its use in foxes. Moreover, Protein A is confirmed to be a good alternative to be used in red foxes, presenting a good reactivity towards its IgG.

Phenotypic Characterization of Encephalitis in the BRAINS of Badgers Naturally Infected with Canine Distemper Virus

Canine distemper virus (CDV) affects a huge diversity of domestic and wild carnivores, with increasing numbers of mortality events worldwide. The local cell-mediated immune response elicited against a natural infection is an important factor in determining the outcome of CDV infection. Therefore, the purposes of this study were to describe the local immune response within the central nervous systems (CNSs) of seven badgers naturally infected with CDV in Asturias (Atlantic Spain) and to determine the phenotype and distribution of microglial cells, T and B lymphocytes, and astrocytes in the foci of gliosis located in the thalamus and cerebellum using immunohistochemistry. The immunohistochemical assessment demonstrated the presence of Iba1-positive microglia and GFAP-positive astrocytes in the foci of gliosis, whereas T (CD3-negative) or B (CD20-negative) lymphocytes in those same lesions were absent. Our results also revealed that the badgers with natural CDV encephalitis presented lesions mostly located in the white matter of the thalamus and cerebellum, suggesting a CDV-specific tropism for the white matter of badger brains in those locations. The knowledge gained in the field of the immunopathogenesis of distemper disease affecting the CNSs of badgers could help to clarify CDV disease patterns in this species.

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.

Phylogenetic characterization of the canine distemper virus isolated from veterinary clinics in the Mekong Delta, Vietnam

Background and Aim

Canine distemper (CD) caused by the CD virus (CDV) has a high mortality rate that severely affects dog populations and other terrestrial carnivores worldwide. However, the genetics of CDV strains circulating in various regions in Vietnam, especially the Mekong Delta, remains unclear. This study aimed to characterize the molecular status of CDV strains circulating in the Mekong Delta, Vietnam.

Materials and Methods

Ocular/nasal swabs were collected from 550 dogs with clinically suspected CDV infection from veterinary clinics in three Vietnamese provinces. A reverse transcription-polymerase chain reaction on the part of the hemagglutinin gene was performed. A phylogenetic tree was constructed to analyze the relationship between the detected CDV and GenBank sequences.

Results

The molecular study demonstrated that 4.18% (23/550) of the dogs were positive for CDV. The clinical findings revealed that the positive dogs exhibited clinical signs of distemper. The phylogenetic analysis indicated that the identified CDV sequences were clustered in the same branch with the genotype Asia-1 and distantly related to the vaccine strains. Notably, the CDV sequences detected in this study were grouped with the sequences previously found in southeast Vietnam; however, they were distant from those found in the north.

Conclusion

The present study confirmed the presence of CDV and to the best of our knowledge, highlighted for the first time that the CDV strains circulating in the Mekong Delta of Vietnam belong to the genotype Asia-1.

Canine Distemper Virus in Tigers (Panthera tigris) and Leopards (P. pardus) in Nepal

From wild dogs (Lycaon pictus) in the Serengeti to tigers (Panthera tigris altaica) in the Russian Far East, canine distemper virus (CDV) has been repeatedly identified as a threat to wild carnivores. Between 2020 and 2022, six Indian leopards (P. pardus fusca) presented to Nepali authorities with fatal neurological disease, consistent with CDV. Here, we report the findings of a serosurvey of wild felids from Nepal. A total of 48 serum samples were tested, comprising 28 Bengal tigers (P. t. tigris) and 20 Indian leopards. Neutralizing antibodies were identified in three tigers and six leopards, equating to seroprevalences of 11% (CI: 2.8-29.3%, n = 28) and 30% (CI: 12.8-54.3%, n = 20), respectively. More than one-third of seropositive animals were symptomatic, and three died within a week of being sampled. The predation of domestic dogs (Canis lupus familiaris) has been posited as a potential route of infection. A comparison of existing diet studies revealed that while leopards in Nepal frequently predate on dogs, tigers do not, potentially supporting this hypothesis. However, further work, including molecular analyses, would be needed to confirm this.

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.

Detection and Molecular Characterization of Canine Distemper Virus in Wildlife from Northern Italy

Canine distemper virus (CDV) is a fatal, highly contagious disease found in wild and domestic carnivores. Several outbreaks have occurred in wildlife in Italy in recent years. This study aims to detect CDV in wildlife following the increasing mortality of foxes (Vulpes vulpes) in the Emilia-Romagna region (northern Italy) observed in 2021. Sixty-seven foxes and one badger (Meles meles) were subjected to necropsy followed by histological examination and were analyzed with molecular techniques to detect the presence of CDV. Of the tested animals, 16% (nine foxes and one badger) were positive for CDV. Phylogenetic analysis showed two different lineages based on complete H gene sequences. The Europe/South America-1 lineage was detected in one fox from Modena, which resembled the CDV variant associated with a previous outbreak in northern Italy in 2018, while the European Wildlife lineage was detected in animals from the Rimini province. Amino acid analysis highlighted a Y549H mutation in all sequences collected, which is commonly associated with increased virulence.

Self-assembling ferritin nanoparticles coupled with linear sequences from canine distemper virus haemagglutinin protein elicit robust immune responses

BACKGROUND

Canine distemper virus (CDV), which is highly infectious, has caused outbreaks of varying scales in domestic and wild animals worldwide, so the development of a high-efficiency vaccine has broad application prospects. Currently, the commercial vaccine of CDV is an attenuated vaccine, which has the disadvantages of a complex preparation process, high cost and safety risk. It is necessary to develop a safe and effective CDV vaccine that is easy to produce on a large scale. In this study, sequences of CDV haemagglutinin (HA) from the Yanaka strain were aligned, and three potential linear sequences, termed YaH₃, YaH₄, and YaH₅, were collected. To increase the immunogenicity of the epitopes, ferritin was employed as a self-assembling nanoparticle element. The ferritin-coupled forms were termed YaH₃F, YaH₄F, and YaH₅F, respectively. A full-length HA sequence coupled with ferritin was also constructed as a DNA vaccine to compare the immunogenicity of nanoparticles in prokaryotic expression.

RESULT

The self-assembly morphology of the proteins from prokaryotic expression was verified by transmission electron microscopy. All the proteins self-assembled into nanoparticles. The expression of the DNA vaccine YaHF in HEK-293T cells was also confirmed in vitro. After subcutaneous injection of epitope nanoparticles or intramuscular injection of DNA YaHF, all vaccines induced strong serum titres, and long-term potency of antibodies in serum could be detected after 84 days. Strong anti-CDV neutralizing activities were observed in both the YaH₄F group and YaHF group. According to antibody typing and cytokine detection, YaH₄F can induce both Th1 and Th2 immune responses. The results of flow cytometry detection indicated that compared with the control group, all the immunogens elicited an increase in CD3. Simultaneously, the serum antibodies induced by YaH₄F and YaHF could significantly enhance the ADCC effect compared with the control group, indicating that the antibodies in the serum effectively recognized the antigens on the cell surface and induced NK cells to kill infected cells directly.

CONCLUSIONS

YaH₄F self-assembling nanoparticle obtained by prokaryotic expression has no less of an immune effect than YaHF, and H₄ has great potential to become a key target for the easy and rapid preparation of epitope vaccines.