SEROLOGIC RESPONSE TO CANINE DISTEMPER VACCINATION IN CAPTIVE LINNAEUS'S TWO-TOED SLOTHS ( CHOLOEPUS DIDACTYLUS) AFTER A FATAL CANINE DISTEMPER VIRUS OUTBREAK

Safety and Immunogenicity of Morbillivirus canis Vaccines for Domestic and Wild Animals: A Scoping Review

Morbillivirus canis (canine distemper virus (CDV)) is recognized as a multihost pathogen responsible for a transmissible disease affecting both domestic and wild animals. A considerable portion of wildlife populations remain unvaccinated due to a lack of safety and immunogenicity data on existing vaccines for the prevention of CDV infection in these species. This review aimed to assess the current state of CDV vaccination research for both domestic and wild animals and to explore novel vaccine candidates through in vivo studies. It also sought to synthesize the scattered information from the extensive scientific literature on CDV vaccine research, identify key researchers in the field, and highlight areas where research on CDV vaccination is lacking. A scoping review was conducted across four databases following the PRISMA-ScR protocol, with information analyzed using absolute and relative frequencies and 95% confidence intervals (CIs) for study number proportions. Among the 2321 articles retrieved, 68 met the inclusion criteria and focused on CDV vaccines in various animal species, such as dogs, ferrets, minks, and mice. Most of the scientific community involved in this research was in the USA, Canada, France, and Denmark. Various vaccine types, including MLV CDV, recombinant virus, DNA plasmids, inactivated CDV, and MLV measles virus (MeV), were identified, along with diverse immunization routes and schedules employed in experimental and commercial vaccines. Safety and efficacy data were summarized. Notably, 37 studies reported postimmunization CDV challenge, primarily in dogs, revealing the survival rates of vaccinated animals. In summary, CDV vaccines generally demonstrate an acceptable safety profile in dogs and show promise as a means of controlling CDV. However, significant gaps in vaccine research persist, particularly concerning wildlife reservoirs, indicating the need for further investigation.

A Bacterium-like Particle Vaccine Displaying Envelope Proteins of Canine Distemper Virus Can Induce Immune Responses in Mice and Dogs

Canine distemper virus (CDV) can cause fatal infections in giant pandas. Vaccination is crucial to prevent CDV infection in giant pandas. In this study, two bacterium-like particle vaccines F3-GEM and H4-GEM displaying the trimeric F protein or tetrameric H protein of CDV were constructed based on the Gram-positive enhanced-matrix protein anchor (GEM-PA) surface display system. Electron microscopy and Western blot results revealed that the F or H protein was successfully anchored on the surface of GEM particles. Furthermore, one more bacterium-like particle vaccine F3 and H4-GEM was also designed, a mixture consisting of F3-GEM and H4-GEM at a ratio of 1:1. To evaluate the effect of the three vaccines, mice were immunized with F3-GEM, H4-GEM or F3 and H4-GEM. It was found that the level of IgG-specific antibodies and neutralizing antibodies in the F3 and H4-GEM group was higher than the other two groups. Additionally, F3 and H4-GEM also increased the secretion of Th1-related and Th2-related cytokines. Moreover, F3 and H4-GEM induce IgG and neutralizing antibodies' response in dogs. Conclusions: In summary, F3 and H4-GEM can provoke better immune responses to CDV in mice and dogs. The bacterium-like particle vaccine F3 and H4-GEM might be a potential vaccine candidate for giant pandas against CDV infection.

Investigation of Chlamydia sp., Morbillivirus sp., Parvovirus sp., Leishmania sp. and Alphacoronavirus sp. in captive giant anteaters (Myrmecophaga tridactyla)

ABSTRACT This research aimed to investigate the occurrence of Chlamydia sp., Morbillivirus sp., Parvovirus sp., Leishmania sp. and Alphacoronavirus sp. in captive giant anteaters. Blood and fecal samples were taken from 16 animals in institutions from the states of Minas Gerais, Bahia and Distrito Federal, which had been in captivity for at least a year. A commercial rapid chromatographic immunoassay test was used for detecting coronavirus and parvovirus antigens, in addition to antibodies against leishmaniasis, all results being negative. In the case of the test for antibodies against distemper, four (4/16; 25%) anteaters had an average titration, two (2/16; 12.5%) a low titration and ten (10/16; 62.5%) were non-reactive. Using the DOT-ELISA (dot blotting) method for detection of immunoglobulin G, only one specimen obtained a 1 : 40 titration. For the polymerase chain reaction tests for Leishmania and Chlamydia, all samples were negative.

SENTINEL COYOTE PATHOGEN SURVEY TO ASSESS DECLINING BLACK-FOOTED FERRET (MUSTELA NIGRIPES) POPULATION IN SOUTH DAKOTA, USA

As part of the national recovery effort, endangered black-footed ferrets (Mustela nigripes) were reintroduced to the Cheyenne River Sioux Reservation in South Dakota, US in 2000. Despite an encouraging start, numbers of ferrets at the site have declined. In an effort to determine possible causes of the population decline, we undertook a pathogen survey in 2012 to detect exposure to West Nile virus (WNV), canine distemper virus (CDV), plague (Yersinia pestis), tularemia (Francisella tularensis), and heartworm (Dirofilaria immitis) using coyotes (Canis latrans) as a sentinel animal. The highest seroprevalence was for WNV with 71% (20/28) of coyotes testing antibody-positive. Seroprevalence of CDV and plague were lower, 27% and 13%, respectively. No evidence of active infection with tularemia or heartworm was seen in the coyotes sampled. As this study did not sample black-footed ferrets themselves, the definitive cause for the decline of this population cannot be determined. However, the presence of coyotes seropositive for two diseases, plague and CDV, lethal to black-footed ferrets, indicated the potential for exposure and infection. The high seroprevalence of WNV in the coyotes indicated a wide exposure to the virus; therefore, exposure of black-footed ferrets to the virus is also likely. Due to the ability of WNV to cause fatal disease in other species, studies may be useful to elucidate the impact that WNV could have on the success of reintroduced black-footed ferrets as well as factors influencing the spread and incidence of the disease in a prairie ecosystem.

Serologic Survey of Selected Pathogens in Free-Ranging Bengal Tigers (Panthera tigris tigris) in Nepal

Serum samples of 11 Bengal tigers (Panthera tigris tigris) from Chitwan National Park in Nepal, collected between 2011-17, were evaluated for the presence of antibodies to eight diseases commonly investigated in large felids. This initial serologic survey was done to establish baseline information to understand the exposure of Nepal's free-ranging tiger population to these diseases. Tiger serum samples collected opportunistically during encounters such as translocation, human conflict, and injury were placed in cold storage for later use. Frozen serum samples were assessed for feline coronavirus (FCoV), feline immunodeficiency virus, feline leukemia virus, feline herpesvirus (FHV), canine distemper virus, canine parvovirus-2 (CPV-2), leptospirosis (LEP; seven serovars), and toxoplasmosis (TOX). Six tigers were found to be positive for LEP, eight for CPV-2, five for FHV, one for FCoV, and 10 for TOX. Tigers, like other wild felids, have been exposed to these common pathogens, but further research is needed to determine the significance of these pathogens to the Nepali population.

IDLY INFECTED: A REVIEW OF INFECTIOUS AGENTS IN POPULATIONS OF TWO- AND THREE-TOED SLOTHS (CHOLOEPUS SPECIES AND BRADYPUS SPECIES)

Two- and three-toed sloths (Choloepus spp. and Bradypus spp.) have become popular animals in American culture and in American zoos, where they are frequently used as animal ambassadors. Despite the increased focus on sloth species, the prevalence of infectious diseases in sloth populations and the associated clinical consequences are relatively unknown. This study reviewed all published literature from 1809 to 2019 that examined infectious agents in both captive and wild populations of either two- or three-toed sloths. Online databases were electronically searched for relevant manuscripts using strings of inclusion and exclusion terms, resulting in an initial identification of 5,364 articles. After removing duplications and conducting two relevance screenings, 57 manuscripts were included in the full review. A total of 1,769 individual two-toed sloths and 879 individual three-toed sloths were accounted for in the included studies, with evidence of infection or exposure to infectious agents in 647 (36.6%) and 222 (25.3%) individual two- and three-toed sloths, respectively. Approximately 74% of documented infections were cryptic fungal, parasitic, and viral infections. The remaining 26% of infections represent those that were associated with clinical signs of disease. The infectious agents reported were bacterial (84), parasitic (20), viral (9), and fungal (4). Significant knowledge gaps remain regarding clinical and subclinical infectious disease prevalence and impact in both free-ranging and captive sloths.

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.

Cross-species transmission and evolutionary dynamics of canine distemper virus during a spillover in African lions of Serengeti National Park

The outcome of pathogen spillover from a reservoir to a novel host population can range from a "dead-end" when there is no onward transmission in the recipient population, to epidemic spread and even establishment in new hosts. Understanding the evolutionary epidemiology of spillover events leading to discrete outcomes in novel hosts is key to predicting risk and can lead to a better understanding of the mechanisms of emergence. Here we use a Bayesian phylodynamic approach to examine cross-species transmission and evolutionary dynamics during a canine distemper virus (CDV) spillover event causing clinical disease and population decline in an African lion population (Panthera leo) in the Serengeti Ecological Region between 1993 and 1994. Using 21 near-complete viral genomes from four species we found that this large-scale outbreak was likely  ignited by a single cross-species spillover event from a canid reservoir to noncanid hosts <1 year before disease detection and explosive spread of CDV in lions. Cross-species transmission from other noncanid species probably fuelled the high prevalence of CDV across spatially structured lion prides. Multiple lines of evidence suggest that spotted hyenas (Crocuta crocuta) could have acted as the proximate source of CDV exposure in lions. We report 13 nucleotide substitutions segregating CDV strains found in canids and noncanids. Our results are consistent with the hypothesis that virus evolution played a role in CDV emergence in noncanid hosts following spillover during the outbreak, suggest that host barriers to clinical infection can limit outcomes of CDV spillover in novel host species.

Natural Canine Distemper Virus Infection in Linnaeus's 2-Toed Sloths (Choloepus didactylus)

An outbreak of canine distemper virus in a private zoo in eastern Tennessee in July 2016 led to fatal clinical disease in 5 adult, wild-caught Linnaeus's 2-toed sloths (Choloepus didactylus). Clinical signs included hyporexia, lethargy, mucopurulent nasal discharge, and oral and facial ulcers. At necropsy, affected animals had crusts and ulcers on the lips, nose, tongue, and oral cavity. Microscopically, all sloths had widespread, random, hepatic necrosis; lymphoid depletion; and bronchointerstitial pneumonia. The central nervous system did not contain gross or histopathologic lesions in any of the 5 sloths, although immunoreactivity for viral antigen was present within vessel walls. Epithelial cells and histiocytes within numerous organs contained intranuclear and intracytoplasmic inclusions and occasional syncytial cells. Canine distemper virus was confirmed with immunohistochemistry and virus isolation. Viral sequencing identified the novel American-4 strain prevalent in eastern Tennessee wildlife. This is the first pathologic characterization of canine distemper virus infection in sloths (family Choloepodidae, order Pilosa) and emphasizes the significant morbidity and mortality in this species.

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.

Histopathological Characteristics and Expression of CDV-NP Antigen in the Brain of Serologically Positive Spontaneously Infected Red Foxes (Vulpes Vulpes) In Western Serbia

Canine distemper virus (CDV) is a worldwide distributed RNA virus that can cause severe disease in carnivore and non-carnivore species. Red foxes are highly susceptible and may act as a reservoir of the virus. As in other wild species, distemper in red foxes can manifest as acute, systemic and chronic nervous form. In the present study, we detected antibodies against CDV among red foxes in Western Serbia, and analyzed histopathologically and immunohistochemically for CDV nuclear protein antigen (CDV-NP) brain samples derived from seropositive animals. Seroprevalence of CDV antibodies was 36.8%. Histopathological changes included gliosis, neuronal degeneration, satellitosis, mononuclear inflammation, demyelination and presence of inclusion bodies. Immunostaining showed a diffuse presence of CDV-NP antigen, mainly in the cytoplasm of astrocytes and neurons. Results of this work contribute to the opinion that red foxes act as a potential reservoir of CDV and underline the importance of routine vaccination of dogs that could come in close contact with these animals. Potential active surveillance program would give a better insight in the degree of CDV infection in wildlife.

Canine distemper virus active infection in order Pilosa, family Myrmecophagidae, species Tamandua tetradactyla

Canine distemper virus (CDV) is a highly contagious disease pathogen which causes disease in the domestic dog and species classified in the Canidae, Procyonidae, Mustelidae, Hyaenidae, Ursidae, Viveridae, Felidae, Tayassuidae, and Cercopithecidae families. A combined strategy that involved the direct sequencing of amplicons from genes coding for nucleocapsid, large polymerase, and hemagglutinin proteins of CDV, as well as the pathological findings and the immunohistochemical detection of viral nucleocapsid protein in diverse tissues, confirmed the participation of CDV in the development of a neurological disease in a southern tamandua (Tamandua tetradactyla) from Midwestern Brazil. Phylogenetic analysis based on the hemagglutinin gene sequences revealed that the strain from this study grouped with isolates from the Europe 1/South America 1 lineage. The specific polymorphisms at the SLAM receptor-binding site of the hemagglutinin gene, previously linked to disease emergence in novel hosts, were not detected in this genome. These findings represent the first description of CDV-induced infection in the Tamandua tetradactyla and extend the distribution of this infection to include members of the family Myrmecophagidae, order Pilosa.

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.