High pathogenic avian influenza A(H5) viruses of clade 2.3.4.4b in Europe-Why trends of virus evolution are more difficult to predict

Since 2016, A(H5Nx) high pathogenic avian influenza (HPAI) virus of clade 2.3.4.4b has become one of the most serious global threats not only to wild and domestic birds, but also to public health. In recent years, important changes in the ecology, epidemiology, and evolution of this virus have been reported, with an unprecedented global diffusion and variety of affected birds and mammalian species. After the two consecutive and devastating epidemic waves in Europe in 2020-2021 and 2021-2022, with the second one recognized as one of the largest epidemics recorded so far, this clade has begun to circulate endemically in European wild bird populations. This study used the complete genomes of 1,956 European HPAI A(H5Nx) viruses to investigate the virus evolution during this varying epidemiological outline. We investigated the spatiotemporal patterns of A(H5Nx) virus diffusion to/from and within Europe during the 2020-2021 and 2021-2022 epidemic waves, providing evidence of ongoing changes in transmission dynamics and disease epidemiology. We demonstrated the high genetic diversity of the circulating viruses, which have undergone frequent reassortment events, providing for the first time a complete overview and a proposed nomenclature of the multiple genotypes circulating in Europe in 2020-2022. We described the emergence of a new genotype with gull adapted genes, which offered the virus the opportunity to occupy new ecological niches, driving the disease endemicity in the European wild bird population. The high propensity of the virus for reassortment, its jumps to a progressively wider number of host species, including mammals, and the rapid acquisition of adaptive mutations make the trend of virus evolution and spread difficult to predict in this unfailing evolving scenario.

First record of Risso's dolphin Grampus griseus (Cuvier, 1812) in Icelandic waters

In July 2022, two Risso's dolphins were reported stranded in Hrútafjörður (N65° 09,503; W21° 05,529), a fjord in northern Iceland. These events represent the first confirmed observations and strandings of Risso's dolphins in Icelandic waters. Given the uniqueness of these events, a decision was made to conduct full necropsies on these individuals. This study reports findings from viral and parasitological investigations, morphological and fitness measurements, as well as stomach and intestine content analysis for each of the Risso's dolphin specimens. The results of the necropsies do not suggest any other cause of death than lack of food and exhaustion. A large plastic fragment in one individual's stomach supports these suggestions. The presence of those specimens in the middle of the subarctic ocean illustrates ongoing changes in spatial distribution expanding northward, impacting not only Risso's dolphins but more generally marine life and biodiversity.

First Report of Resistance to Ivermectin in Parascaris univalens in Iceland

Horses in Iceland have been isolated for more than 1,000 yr but still harbor a similar range of gastrointestinal parasites as do horses across the world. The long isolation of the horses and their parasites presumably means that no resistance genes have been introduced into the Parascaris spp. population. It is therefore of particular interest to investigate the efficacy of ivermectin on Parascaris spp. infecting Icelandic foals. Potential treatment failure of ivermectin in Iceland will add substantial new information on how resistance can arise independently. This study aimed to determine the efficacy of subcutaneous injection of ivermectin for the treatment of Parascaris spp. infection in foals and to identify the Parascaris species present in the west and north of Iceland. A fecal egg count reduction (FECR) test (FECRT) was performed on 50 foals from 8 farms, including an untreated control group of 6 foals, from September to November 2019. The foals were between 3 and 5 mo of age at the start of the study and had not previously been treated with anthelmintic drugs. Each foal was treated subcutaneously with off-label use of Ivomec® injection 10 mg/ml or Noromectin® 1% at a dose of 0.2 mg/kg. The FECR for each farm was calculated in 2 ways, by the eggCounts package in R and by the Presidente formula (FECRT). Both calculation methods resulted in efficacy levels between 0% and 80.78%, indicating ivermectin resistance on all farms. We also confirmed, by karyotyping, that the species of equine ascarid present in the west and north of Iceland is Parascaris univalens. This study provides evidence for treatment failure of ivermectin against P. univalens infection in foals. Since Icelandic horses have been isolated on the island for more than 1,000 yr, this implies that resistance alleles have developed independently in the Icelandic Parascaris population. The actual clinical impact of ivermectin resistance is unknown but another drug of choice should be considered to treat Parascaris infection in foals in Iceland.

Deiminated proteins and extracellular vesicles as novel biomarkers in pinnipeds: Grey seal (Halichoerus gryptus) and harbour seal (Phoca vitulina)

Peptidylarginine deiminases (PADs) are phylogenetically conserved calcium-dependent enzymes which post-translationally convert arginine into citrulline in target proteins in an irreversible manner, leading to functional and structural changes in target proteins. Protein deimination can cause the generation of neo-epitopes, affect gene regulation and also allow for protein moonlighting and therefore facilitate multifaceted functions of the same protein. PADs are furthermore a key regulator of cellular release of extracellular vesicle (EVs), which are found in most body fluids and participate in cellular communication via transfer of cargo proteins and genetic material. In this study, post-translationally deiminated proteins and EVs were assessed in sera of two seal species, grey seal and harbour seal. We report a poly-dispersed population of serum-EVs, which were positive for phylogenetically conserved EV-specific markers and characterised by transmission electron microscopy. A number of deiminated proteins critical for immune and metabolic functions were identified in the seal sera and varied somewhat between the two species under study, while some targets were in common. EV profiles of the seal sera further revealed that key microRNAs for inflammation, immunity and hypoxia also vary between the two species. Protein deimination and EVs profiles may be useful biomarkers for assessing health status of sea mammals, which face environmental challenges, including opportunistic infection, pollution and shifting habitat due to global warming.

Deiminated proteins and extracellular vesicles - Novel serum biomarkers in whales and orca

Peptidylarginine deiminases (PADs) are a family of phylogenetically conserved calcium-dependent enzymes which cause post-translational protein deimination. This can result in neoepitope generation, affect gene regulation and allow for protein moonlighting via functional and structural changes in target proteins. Extracellular vesicles (EVs) carry cargo proteins and genetic material and are released from cells as part of cellular communication. EVs are found in most body fluids where they can be useful biomarkers for assessment of health status. Here, serum-derived EVs were profiled, and post-translationally deiminated proteins and EV-related microRNAs are described in 5 ceataceans: minke whale, fin whale, humpback whale, Cuvier's beaked whale and orca. EV-serum profiles were assessed by transmission electron microscopy and nanoparticle tracking analysis. EV profiles varied between the 5 species and were identified to contain deiminated proteins and selected key inflammatory and metabolic microRNAs. A range of proteins, critical for immune responses and metabolism were identified to be deiminated in cetacean sera, with some shared KEGG pathways of deiminated proteins relating to immunity and physiology, while some KEGG pathways were species-specific. This is the first study to characterise and profile EVs and to report deiminated proteins and putative effects of protein-protein interaction networks via such post-translationald deimination in cetaceans, revealing key immune and metabolic factors to undergo this post-translational modification. Deiminated proteins and EVs profiles may possibly be developed as new biomarkers for assessing health status of sea mammals.

The effect of maternal immunity on the equine gammaherpesvirus type 2 and 5 viral load and antibody response

Two types of gammaherpesviruses (γEHV) are known to infect horses, EHV-2 and EHV-5. Foals become infected early in life, probably via the upper respiratory tract, despite maternal antibodies. In this study, we analyzed samples from a herd of mares and their foals. The foals were followed from birth to 22 months of age and the dams during the first 6 months postpartum. Blood and nasal swab samples were taken regularly for evaluation of antibody responses, virus isolation and viral load by qPCR. EHV-2 was isolated on day 5, and EHV-5 on day 12, earlier than previously reported. γEHV specific antibodies were not detectable in serum of foals before colostrum intake but peaked a few days after colostrum. Overall, EHV-2 viral load peaked in nasal swab at three to four months of age, paralleled with decline in maternal antibodies, but EHV-5 viral load did not peak until month 12. Maternal antibodies had a notable effect on the viral load and induction of endogenous antibody production. Foals were grouped in two groups depending on the mare’s γEHV specific total IgG levels in serum at birth, group-high and group-low. Group-high had higher levels of maternal γEHV specific total IgG and IgG4/7 for the first 3 months, but when the endogenous production had superseded maternal antibodies, group-low was higher. The maternal antibodies had an effect on the γEHV viral load. Group-low peaked in EHV-2 viral load one month earlier than group-high. These effects were more evident for EHV-5, as there were seven months between the viral load peaks for the groups. The study provides information on how maternal antibody transfer affects γEHV shedding and antibody production in offspring. It also extends our knowledge on the occurrence of EHV-2 and EHV-5 infection in foals during the first two years of life.

Neonatal Immunization with a Single IL-4/Antigen Dose Induces Increased Antibody Responses after Challenge Infection with Equine Herpesvirus Type 1 (EHV-1) at Weanling Age

Neonatal foals respond poorly to conventional vaccines. These vaccines typically target T-helper (Th) cell dependent B-cell activation. However, Th2-cell immunity is impaired in foals during the first three months of life. In contrast, neonatal basophils are potent interleukin-4 (IL-4) producers. The purpose of this study was to develop a novel vaccine triggering the natural capacity of neonatal basophils to secrete IL-4 and to evaluate if vaccination resulted in B-cell activation and antibody production against EHV-1 glycoprotein C (gC). Neonatal vaccination was performed by oral biotinylated IgE (IgE-bio) treatment at birth followed by intramuscular injection of a single dose of streptavidin-conjugated gC/IL-4 fusion protein (Sav-gC/IL-4) for crosslinking of receptor-bound IgE-bio (group 1). Neonates in group 2 received the intramuscular Sav-gC/IL-4 vaccine only. Group 3 remained non-vaccinated at birth. After vaccination, gC antibody production was not detectable. The ability of the vaccine to induce protection was evaluated by an EHV-1 challenge infection after weaning at 7 months of age. Groups 1 and 2 responded to EHV-1 infection with an earlier onset and overall significantly increased anti-gC serum antibody responses compared to control group 3. In addition, group 1 weanlings had a decreased initial fever peak after infection indicating partial protection from EHV-1 infection. This suggested that the neonatal vaccination induced a memory B-cell response at birth that was recalled at weanling age after EHV-1 challenge. In conclusion, early stimulation of neonatal immunity via the innate arm of the immune system can induce partial protection and increased antibody responses against EHV-1.

Establishment and characterization of fetal equine kidney and lung cells with extended lifespan. Susceptibility to equine gammaherpesvirus infection and transfection efficiency

Due to the slow growth of equine gammaherpesviruses, isolation of these viruses requires cells that can be propagated long term and show clear cytopathy following infection. Equine cell lines with extended lifespan were established from primary cells originating from equine fetal kidney and lung by transfecting the cells with the retroviral vector LXSN116E6E7 containing the human papilloma virus oncogenes 16 E6 and E7. The transfected equine kidney cell line and equine lung cell line can be propagated for more than 40 passages, whereas the corresponding primary cells only for 10-12 passages. The primary cells and the derived cell lines can be infected with equine gammaherpesvirus 2 (EHV-2) with similar efficiency. However EHV-5 can be grown to a substantially higher titer in the kidney cell line than their primary counterpart, with cytopathic effect visible three days earlier than in the primary cells. Due to rapid cell growth the lung cell line is difficult to use for virus production. The kidney cell line was four times more susceptible to transfection as compared to the primary kidney cells. On the other hand no difference was between the lung cell line and the primary lung cells in transfection efficiency. The cell lines can be a valuable tool for investigating gammaherpesviruses, and possibly other viruses infecting horses.

Validation and evaluation of VapA-specific IgG and IgG subclass enzyme-linked immunosorbent assays (ELISAs) to identify foals with Rhodococcus equi pneumonia

REASONS FOR PERFORMING STUDY

Rhodococcus equi (Rhodococcus hoagii/Prescottella equi) is a common cause of foal pneumonia, but its diagnosis remains a challenge for equine veterinarians. While the VapA-specific (virulence-associated protein A) immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) has low sensitivity and specificity for detecting pneumonic foals, little is known about VapA-specific IgG subclasses.

OBJECTIVES

To evaluate the performance of VapA-specific ELISA for IgG and its subclasses IgGa, IgGb and IgG(T) in the early diagnosis of pneumonia caused by R. equi.

STUDY DESIGN

Assay validation followed by assessment of diagnostic performance using archived samples from animals of known status.

METHODS

Serum samples from exposed (n = 125) and nonexposed adult horses (n = 10) and from experimentally challenged and naturally infected foals were used for ELISA validation. Post mortem and tissue culture records of the last 24 years from the Institute for Experimental Pathology at the University of Iceland in Keldur, Iceland laboratory were evaluated to confirm the absence of R. equi cases in Iceland. The diagnostic performance of VapA-specific IgG and its subclasses was evaluated using banked serum samples from pneumonic (n = 21) and healthy foals (n = 80). To evaluate each IgG assay, a cut-off value was selected based on receiver operating characteristic curve analysis and used to calculate sensitivity and specificity. The intra- and interassay coefficients of variation were calculated for each ELISA.

RESULTS

Using sera from Iceland, where R. equi infection has not been reported, the VapA-specific IgG ELISA differentiated exposed from nonexposed horses. When used to identify infected foals, VapA-specific IgG, IgGa and IgGb had no diagnostic value. In contrast, IgG(T) had high sensitivity and specificity.

CONCLUSIONS

Horses from Iceland are not exposed to VapA(+) R. equi and can serve as negative controls. VapA-specific IgG subclasses, with the exception of IgG(T), are poor predictors of disease. Further investigation on the use of IgG(T) as a diagnostic tool in field conditions is needed.

Serological markers of Bornavirus infection found in horses in Iceland

Background

In a stable of eight horses in Northern Iceland, six horses presented with clinical signs, such as ataxia and reduced appetite, leading to euthanasia of one severely affected horse. Serological investigations revealed no evidence of active equine herpes virus type 1 infection, a common source of central nervous system disease in horses, nor equine arteritis virus and West Nile virus. Another neurotropic virus, Borna disease virus, was therefore included in the differential diagnosis list.

Findings

Serological investigations revealed antibodies against Borna disease virus in four of five horses with neurological signs in the affected stable. One horse without clinical signs was seronegative. Four clinically healthy horses in the stable that arrived and were sampled one year after the outbreak were found seronegative, whereas one of four investigated healthy horses in an unaffected stable was seropositive.

Conclusions

This report contains the first evidence of antibodies to Borna disease virus in Iceland. Whether Borna disease virus was the cause of the neurological signs could however not be confirmed by pathology or molecular detection of the virus. As Iceland has very restricted legislation regarding animal imports, the questions of how this virus has entered the country and to what extent markers of Bornavirus infection can be found in humans and animals in Iceland remain to be answered.

Genetic diversity of equine gammaherpesviruses (γ-EHV) and isolation of a syncytium forming EHV-2 strain from a horse in Iceland

The horse population in Iceland is a special breed, isolated from other equines for at least one thousand years. This provides an exceptional opportunity to investigate old and new pathogens in a genetically closed herd. Both types of equine gammaherpesviruses, EHV-2 and EHV-5, are common in Iceland. Genetic variation was examined by sequencing four genes, glycoprotein B (gB), glycoprotein H (gH), DNA polymerase and DNA terminase for 12 Icelandic and seven foreign EHV-2 strains. One Icelandic virus isolate, gEHV-Dv, induced syncytium formation, an uncharacteristic cytopathy for EHV-2 in equine kidney cells. When sequenced, the glycoprotein genes were different from both EHV-2 and EHV-5, but the polymerase and terminase genes had 98-99% identity to EHV-2. Therefore the gEHV-Dv strain can be considered a variant of EHV-2. Substantial genetic variability was seen within the EHV-2 glycoprotein genes but limited in the polymerase and terminase genes. The Icelandic EHV-2 strains do not seem to differ phylogenetically from the foreign viruses, despite isolation for over a thousand years.

Mutations in MITF and PAX3 cause "splashed white" and other white spotting phenotypes in horses

During fetal development neural-crest-derived melanoblasts migrate across the entire body surface and differentiate into melanocytes, the pigment-producing cells. Alterations in this precisely regulated process can lead to white spotting patterns. White spotting patterns in horses are a complex trait with a large phenotypic variance ranging from minimal white markings up to completely white horses. The "splashed white" pattern is primarily characterized by an extremely large blaze, often accompanied by extended white markings at the distal limbs and blue eyes. Some, but not all, splashed white horses are deaf. We analyzed a Quarter Horse family segregating for the splashed white coat color. Genome-wide linkage analysis in 31 horses gave a positive LOD score of 1.6 in a region on chromosome 6 containing the PAX3 gene. However, the linkage data were not in agreement with a monogenic inheritance of a single fully penetrant mutation. We sequenced the PAX3 gene and identified a missense mutation in some, but not all, splashed white Quarter Horses. Genome-wide association analysis indicated a potential second signal near MITF. We therefore sequenced the MITF gene and found a 10 bp insertion in the melanocyte-specific promoter. The MITF promoter variant was present in some splashed white Quarter Horses from the studied family, but also in splashed white horses from other horse breeds. Finally, we identified two additional non-synonymous mutations in the MITF gene in unrelated horses with white spotting phenotypes. Thus, several independent mutations in MITF and PAX3 together with known variants in the EDNRB and KIT genes explain a large proportion of horses with the more extreme white spotting phenotypes.

In vitro analysis of expression vectors for DNA vaccination of horses: the effect of a Kozak sequence

One of the prerequisite for developing DNA vaccines for horses are vectors that are efficiently expressed in horse cells.

We have analysed the ectopic expression of the human serum albumin gene in primary horse cells from different tissues. The vectors used are of pcDNA and pUC origin and include the cytomegalovirus (CMV) promoter. The pUC vectors contain CMV intron A whereas the pcDNA vectors do not.

Insertion of intron A diminished the expression from the pcDNA vectors whereas insertion of a Kozak sequence upstream of the gene in two types of pUC vectors increased significantly the in vitro expression in primary horse cells derived from skin, lung, duodenum and kidney.

We report for the first time the significance of full consensus Kozak sequences for protein expression in horse cells in vitro.

Study of equid herpesviruses 2 and 5 in Iceland with a type-specific polymerase chain reaction

The horse population in Iceland is a special breed, isolated from other horses for at least 1000 years. This provides an exceptional opportunity to investigate old and new pathogens in an inbred herd with few infectious diseases. We have developed a high sensitivity semi-nested PCR to study equid gammaherpesviruses 2 and 5 (EHV-2 and 5) in Iceland. The first PCR is group specific, the second type-specific, targeting a 113bp sequence in the glyB gene. DNA isolated from white blood cells and 18 different organs was tested for the presence of EHV-2 and 5. This was done in adult horses and foals, healthy and with various enteric infections. Both virus types were easily detected in all types of organs tested or EHV-2 in 79% cases and EHV-5 in 63%. In DNA from PBMC or buffy-coat EHV-2 was found in 20% cases and EHV-5 in 10%, all except one positive were foals. Co-culture of PBMC on fetal horse kidney cells was efficient for detecting EHV-2 but not for EHV-5. We verify here for the first time infections with EHV-2 and 5 in horses in Iceland and show that both viruses are common.

Vaccination of sheep with Maedi-visna virus gag gene and protein, beneficial or harmful?

In spite of intense efforts no vaccine is yet available that protects against lentiviral infections. Sheep were immunised eight times over a period of 2.5 years with the maedi-visna (MVV) gag gene on two different vectors, 2 sheep with VR1012-gag-CTE and 2 sheep with pcDNA3.1-gag-CTE. All sheep responded to some of the mature MVV Gag proteins in Western blot (WB). Three of them responded to the virus in lymphocyte proliferation test. The sheep received a boost with recombinant Gag protein resulting in elevated antibody response. However, when they were challenged intratracheally with MVV they all became immediately infected as judged by a strong rise in antibody titer and virus isolation from blood. It is therefore clear that the vaccination gave no protection. It is even possible that it facilitated infectivity since virus was isolated earlier from all the vaccinated sheep than from any of the unvaccinated sheep infected in the same way with the same dose.

Simultaneous mutations in CA and Vif of Maedi-Visna virus cause attenuated replication in macrophages and reduced infectivity in vivo

Maedi-visna virus (MVV) is a lentivirus of sheep sharing several key features with the primate lentiviruses. The virus causes slowly progressive diseases, mainly in the lungs and the central nervous system of sheep. Here, we investigate the molecular basis for the differential growth phenotypes of two MVV isolates. One of the isolates, KV1772, replicates well in a number of cell lines and is highly pathogenic in sheep. The second isolate, KS1, no longer grows on macrophages or causes disease. The two virus isolates differ by 129 nucleotide substitutions and two deletions of 3 and 15 nucleotides in the env gene. To determine the molecular nature of the lesions responsible for the restrictive growth phenotype, chimeric viruses were constructed and used to map the phenotype. An L120R mutation in the CA domain, together with a P205S mutation in Vif (but neither alone), could fully convert KV1772 to the restrictive growth phenotype. These results suggest a functional interaction between CA and Vif in MVV replication, a property that may relate to the innate antiretroviral defense mechanisms in sheep.

Mucosal vaccination with an attenuated maedi–visna virus clone

Four sheep were infected intratracheally with an attenuated molecular clone of maedi-visna virus (MVV). All four became infected. Ten months later these sheep were challenged intratracheally with a genetically similar but pathogenic clone of MVV. Four unvaccinated sheep were infected simultaneously. All sheep became infected by the challenge virus. The vaccinated sheep were not protected against superinfection with the challenge clone. However, virus was isolated more frequently from the blood of the unvaccinated controls than of the vaccinated animals and ten times more frequently from lungs of unvaccinated sheep than from lungs of vaccinated sheep at sacrifice, indicating partial protection.

Listeria monocytogenes in horses in Iceland

Twenty isolates of Listeria monocytogenes associated with five confirmed and four suspected incidents of listeriosis in horses in Iceland were characterised by serotyping, pulsed-field gel electrophoresis and ribotyping. Semiquantitative estimates of the numbers of L monocytogenes were made on faeces from horses with clinical signs of listeriosis and on grass silage fed to them. Large numbers of L monocytogenes were often found in the faeces of horses with severe signs of disease. The 20 isolates could be divided into six genotypes, each incident involving only one genotype. One serovar 1/2a genotype was associated with three confirmed incidents of listeriosis in 1991, 1993 and 1997. In one incident, the same genotype was isolated from the organs of a horse with listeriosis and from the spoiled grass silage fed to it.

The vif gene of maedi-visna virus is essential for infectivity in vivo and in vitro

We have investigated the role of vif in maedi-visna virus (MVV), a lentivirus of sheep, by studying in vitro replication of vif-deleted MVV in several cell types, and the effects of vif deletion on in vivo infection. By measuring RT activity, we found that in comparison to wild-type MVV, growth of vif-deleted MVV was similar in fetal ovine synovial (FOS) cells, highly attenuated in sheep choroid plexus (SCP) cells, and not detectable in macrophages, natural target cells of MVV. Productive infection by vif-deleted MVV could not be demonstrated in sheep. An increased mutation frequency was observed in DNA produced by endogenous reverse transcription of viral RNA in vif-deleted virions, indicating the existence of a factor comparable in action to human APOBEC3G. These results suggest that the vif gene of MVV is essential for infectivity and that the Vif protein protects the viral genome from enpackaged mutagenic activities.

Intratracheal inoculation as an efficient route of experimental infection with maedi-visna virus

Maedi-visna virus (MVV) spreads horizontally via the respiratory route. In order to establish an experimental mucosal infection route, we compared intranasal and intratracheal inoculation using the infectious MVV molecular clone KV1772-kv72/67. For intranasal infection 0.5 x 10(3)-0.5 x 10(7) TCID50 of virus was sprayed into the nostrils of the sheep. For the intratracheal infection 10(0)-10(6) TCID50 of virus was injected into the trachea. Successful infection was indicated by development of MVV specific antibodies and virus isolation over a period of 6 months. In the intranasal infection, only the sheep receiving the highest dose i.e., 0.5 x 10(7) TCID50, became infected, suggesting that intranasal application was not an efficient mode of infection. In the intratracheal infection, the sheep infectious dose 50% was 10(1) TCID50 and virus could be isolated from the central nervous system 4 months post infection with 10(4) TCID50. Therefore it is concluded that intratracheal infection is a very efficient route for experimental inoculation with MVV.

Comparative analysis of the attachment protein gene (H) of dolphin morbillivirus

DMV, dolphin morbillivirus, a paramyxovirus of uncertain origin recently emerged in Mediterranean dolphins. This study presents the complete nucleotide sequence of the hemagglutinin (H) gene including the gene boundaries. The single open reading frame of the DMV H gene encodes a protein of 604 residues which exhibits overall sequence characteristics similar to the H genes of other morbilliviruses. When compared to its closest homologues, measles virus (MV) and rinderpest virus (RPV), DMV has, respectively, 44 and 46% of amino acid residues in identical positions. The primary sequence of the DMV H protein is markedly less conserved than that of the fusion protein. The comparative data at the genomic level correspond with cross-neutralization studies with different morbilliviruses. Retrospective serogical studies dating back to 1983 indicate DMV-like infections in whales of the eastern Atlantic. The presented data support and extend previous studies suggesting that this novel morbillivirus is one of the phylogenetically oldest morbilliviruses known to circulate today. The relationship of DMV and established morbilliviruses to the newly emerged candidate morbillivirus infecting horse and man is discussed.

Studies on manifestations of canine distemper virus infection in an urban dog population

An upsurge of canine distemper was recognized at the beginning of 1991 in the urban dog population of the Copenhagen area. The outbreak had the characteristics of a virulent morbillivirus introduction in a partly immune population, where the disease primarily was manifested in young individuals. Testing of single serum samples for the presence of canine distemper virus (CDV) IgM antibodies using an IgM ELISA confirmed current and recent CDV infections in an urban dog population, where the use of attenuated CDV vaccines was widespread. In 49 out of 66 sera from clinical cases suspected of canine distemper we detected CDV IgM antibodies, as compared to the detection of viral antigen by indirect immunofluorescence in 27 of 65 specimens of conjunctival cells. The antigenic make-up of isolates from acute and subacute clinical cases was investigated with a panel of 51 monoclonal antibodies directed against CDV and the related phocine distemper virus. The isolates exhibited an homogeneous reaction pattern and shared overall antigenic characteristics of the CDV prototype. The majority of cases were diagnosed among unvaccinated dogs and individuals with unknown or obscure vaccination record. However, severe clinical cases were also diagnosed in vaccinated individuals.

Infection studies with canine distemper virus in harbour seals

Infection studies in harbour seal (Phoca vitulina) were conducted with the Snyder-Hill strain of canine distemper virus (CDV) that is virulent for dog and mink. The inoculated seals showed clinical symptoms which were to some degree similar to those observed in CDV infections of sensitive species of carnivores. Viral replication in lymphoid cells was followed by an extended period of immunosuppression. The results did not provide conclusive evidence for viral replication in surface epithelia of seals, and accordingly no spread of the infection to contact seals and mink was demonstrated. The pathogenicity of the infection did not increase upon a second viral passage in seal. The serological data showed that CDV-infected seals mounted an early virus specific antibody response. Overall, the results indicated that the harbour seal was not especially sensitive to CDV infection. The differences in the in vivo biological properties of CDV and PDV add to the distinction between these viruses at the genomic and antigenic levels.

Round table on morbilliviruses in marine mammals

Since 1988 morbilliviruses have been increasingly recognized and held responsible for mass mortality amongst harbour seals (Phoca vitulina) and other seal species. Virus isolations and characterization proved that morbilliviruses from seals in Northwest Europe were genetically distinct from other known members of this group including canine distemper virus (CDV), rinderpest virus, peste des petits ruminants virus and measles virus. An epidemic in Baikal seals in 1987 was apparently caused by a morbillivirus closely related to CDV so that two morbilliviruses have now been identified in two geographically distant seal populations, with only the group of isolates from Northwest Europe forming a new member of the genus morbillivirus: phocid distemper virus (PDV). Because of distemper-like disease, the Baikal seal morbillivirus was tentatively named PDV-2 in spite of its possible identity with CDV. The appearance of morbilliviruses in the Mediterranean Sea causing high mortality amongst dolphins should further increase the research activities on protection strategies for endangered species of marine mammals.

Antigenic relationships between field isolates of morbilliviruses from different carnivores

The antigenic relationships between PDV and isolates of morbilliviruses from carnivores suffering from distemper were investigated. Fourteen isolates, originating from terrestrial carnivores and harbour seals from 1985-1991 from Denmark, Norway, Greenland, and the U.S.A. were reacted in IFA and ELISA with monoclonal antibodies (MAbs) directed against four virion proteins (NP, P, F, and H). The MAbs comprised a newly completed panel of 36 anti-PDV MAbs and 39 previously developed anti-CDV MAbs. The antigenic make-up of the isolates separated them into the CDV prototype group and the PDV prototype group, having the antigenic characteristics of the reference vaccine strains of CDV and the Danish PDV isolate, respectively. The minor antigenic variations within the CDV group contrasted markedly to the differences encountered between the CDV and PDV group. The PDV group included isolates made in 1988 from diseased seals of Danish and Norwegian waters and isolates made in 1989 from distemper outbreaks in Danish mink farms. In contrast, the other distemper isolates investigated, including isolates from 1986 from a corresponding Danish mink farm, revealed the antigenic characteristics of CDV. Our results strongly indicate that PDV was recently transmitted from diseased seals to terrestrial carnivores causing distemper epizootics among farmed mink.

Coronavirus infection in mink (Mustela vison). Serological evidence of infection with a coronavirus related to transmissible gastroenteritis virus and porcine epidemic diarrhea virus

Antibodies to a transmissible gastroenteritis virus (TGEV)-related coronavirus have been demonstrated in mink sera by indirect immunofluorescence, peroxidase-linked antibody assays and immunoblotting. This is the first serological evidence of a specific coronavirus infection in mink. The putative mink coronavirus (MCV) seems to be widespread in the Danish mink population with a prevalence approaching 100%. Analysis by immunoblotting has shown that MCV is closely related to TGEV by the spike (S), matrix (M) and nucleoprotein (N) polypeptides. Furthermore, antibodies to MCV also cross-reacted with N and M polypeptides of porcine epidemic diarrhea virus (PEDV). Thus MCV may occupy an intermediate position between the TGEV group of coronavirus and PEDV. The possibility that MCV may be associated with syndromes of acute enteritis in preweaning mink is discussed.

Immunological relationships between phocid and canine distemper virus studied with monoclonal antibodies

The immunological relationships between distemper viruses, isolated from a seal and mink in Denmark and from a dog in Greenland, were investigated with 39 previously developed monoclonal antibodies (MAbs) directed against four major structural proteins of canine distemper virus (CDV). They were also investigated with 16 newly developed MAbs directed against the fusion (F) and large glycoprotein (named H in analogy with measles virus) of phocid distemper virus (PDV) isolated from a harbour seal (Phoca vitulina). These MAbs were reacted with the three different isolated viruses and with the LEC strain of measles virus, in ELISA and immunofluorescence tests. In addition, immunoprecipitation tests were carried out with some of the cross-reacting antibodies. All 55 MAbs reacted identically with distemper virus isolated from seals or mink. When the MAbs produced against CDV were tested, 37 of 39 antibodies reacted with a virus isolated from a sled dog diseased in an outbreak of distemper in Greenland prior to the epizootic among seals in the North Sea. Of the 39 antibodies, 25 reacted with PDV and distemper virus isolated from mink. Of these antibodies, only three of the nine antibodies directed against the H protein of CDV cross-reacted with PDV and distemper virus from mink. Eleven MAbs, reacting with six epitopes of the H protein of PDV, were produced. All 11 antibodies reacted with distemper virus from mink, two of the antibodies reacted with CDV and none reacted with measles virus. All five antibodies reacting with three different epitopes of the F protein of PDV reacted with distemper virus from mink and CDV. Of these five antibodies three, directed against two epitopes, reacted with measles virus. Of the two envelope proteins, the H protein shows pronounced immunological differences between PDV and CDV. In contrast, immunologically the F protein appears to be well conserved among morbilliviruses. It is concluded that the virus causing the epizootic in seals in the North Sea in 1988 may have infected mink on land, or, alternatively, the virus in the sea may have originated from virus-infected mink.

Infection studies in mink with seal-derived morbillivirus

Morbillivirus derived from diseased harbour seals (Phoca vitulina) has characteristics of acute virulent canine distemper virus infection in mink. The infection induced a disease resembling the acute systemic and nervous form of canine distemper.