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Borrelia burgdorferi can induce Lyme disease. Approved Lyme vaccines for horses are currently not available. In an effort to protect horses, veterinarians are using Lyme vaccines licensed for dogs. However, data to assess the response of horses to, or determine the efficacy of this off-label vaccine use are missing. Here, antibodies against outer surface protein A (OspA), OspC, and OspF were quantified in diagnostic serum submissions from horses with a history of vaccination with canine Lyme vaccines. The results suggested that many horses respond with low and often short-lasting antibody responses. Subsequently, four experimental vaccination trials were performed. First, we investigated antibody responses to three canine vaccines in B. burgdorferi-naïve horses. One killed bacterin vaccine induced antibodies against OspC. OspA antibodies were low for all three vaccines and lasted less than 16weeks. The second trial tested the impact of the vaccine dose using the OspA/OspC inducing bacterin vaccine in horses. A 2mL dose produced higher OspA and OspC antibody values than a 1mL dose. However, the antibody response again quickly declined, independent of dose. Third, the horses were vaccinated with 2 doses of a recombinant OspA vaccine. Previous vaccination and/or environmental exposure enhanced the magnitude and longevity of the OspA antibody response to about 20weeks. Last, the influence of intramuscular versus subcutaneous vaccine administration was investigated for the recombinant OspA vaccine. OspA antibody responses were not influenced by injection route. The current work highlights that commercial Lyme vaccines for dogs induce only transient antibody responses in horses which can also be of low magnitude. Protection from infection with B. burgdorferi should not be automatically assumed after vaccinating horses with Lyme vaccines for dogs.

A previously unrecognized virus belonging to the subfamily Pneumovirinae and most closely related to murine pneumovirus (MPV) was identified in domestic dogs in 2 related animal shelters. Additional diagnostic testing yielded 3 new viral isolates and identified 6 additional PCR positive dogs from other USA locations indicating that its distribution is not geographically limited. Nucleotide sequences encompassing 9 of the 10 genes were compared to the only 2 available MPV strains, 15 and J3666. Several features distinguished the canine pneumovirus (CnPnV) from the murine strains. Two regions of diversity were identified in the amino-proximal region of P and the overlapping P2 ORF was only 54 amino acids (aa) compared to 137aa in MPV. The G protein had an amino-terminal cytoplasmic tail 18aa longer than in the MPV strains. The CnPnV SH protein showed the highest divergence with only 90.2% aa identity when compared to MPV strain 15. Like strain 15, the CnPnV SH ORF coded for a protein of 92aa while J3666 has a 114aa variant. Comparison of CnPnV isolates at culture passages 4 and 17 revealed 7nt differences within the 8598nt sequenced. Of note was a substitution at nt 364 in G resulting in a termination codon that would produce a truncated G protein of 122aa. Analysis of early passage and ex vivo samples showed the termination codon in G to be predominant after 6 days in culture indicating rapid selection of the mutation in A72 cells.

West Nile virus (WNV) is a zoonotic pathogen of global importance. In horses with neurological signs, detection of WNV-specific immunoglobulin M (IgM) in serum is widely used to identify clinical cases of WNV encephalitis. Here, we describe the development of two monoclonal antibodies (mAbs) to equine IgM which were used in a WNV IgM-specific enzyme-linked immunosorbent assay (ELISA). Their performance was compared to an established assay based on polyclonal anti-IgM. Check test serum samples from the National Veterinary Service Laboratory (NVSL) were used to evaluate the performance of the three anti-IgM antibodies. The anti-IgM 1-22 mAb correctly identified all NVSL samples. Both the polyclonal antibody and monoclonal anti-IgM 2B-63 identified eight out of ten samples correctly. The three assays were then compared using serum samples from clinically healthy animals (n=33) and horses with neurological signs (n=21). High Spearman rank correlations (0.76-0.86) were found among the ELISA results. Inter-test agreements (weighted kappa) for assay interpretation resulted in strong agreement (0.95) of the results obtained by the mAbs and moderate agreements when monoclonal and polyclonal anti-IgM-based assays were compared. To determine the analytical sensitivities of anti-WNV IgM detection, serial dilutions of WNV IgM-positive serum samples were analyzed. The highest sensitivity was obtained by using the anti-IgM 1-22 mAb to capture IgM from equine serum. In conclusion, the use of monoclonal anti-IgM antibodies can improve the sensitivity of IgM detection in the acute phase of WN disease.

Phylogenetic and antigenic analyses indicate that recent circulating equine-2 influenza viruses in the United States have been alternating between two genetic and antigenic distinct lineages since 1996. The evolution rates for these two lineages, the Kentucky and the Florida lineage, are very similar. For the earlier isolates in the Kentucky lineage, there are multiple and sequential nonsynonymous substitutions at antigenic sites B and D. However, there are no changes at any of these antigenic sites for KY98 and OK00. In the Florida lineage, except for NY99 with one amino acid substitution at antigenic site B, viruses in this lineage do not have nonsynonymous substitutions at any of the antigenic sites. The lack of amino acid substitutions at these antigenic sites suggests a mechanism other than immune selection is responsible for the maintenance of these viral lineages. Serological analysis indicates that these two lineages are antigenic distinct, and the pattern of reactivity of horse sera towards these two lineages alternates in consecutive years, parallel to the "switching" of virus lineage seen in the phylogenetic tree. This alternate circulation may play a role in the maintenance of these two lineages of equine-2 influenza virus.

Lyme disease, a bacterial illness caused by Borrelia burgdorferi, is thought to be most prevalent in the heavily tick-infested areas of the northeastern United States. Serum samples from 196 asymptomatic horses residing in the Pacific northwest were tested for the presence of antibodies to Borrelia burgdorferi , using the canine SNAP 4DX (IDEXX Laboratories, Inc., Maine) and the enzyme-linked immunosorbent assay (ELISA). Positive samples were confirmed by Western blot analysis. The ELISA and Western blot analyses identified 29 of 196 horses that had antibodies for Borrelia burgdorferi, whereas the Canine SNAP 4DX only identified 2 of 196 horses as positive for an antibody titer. These results indicate that 14.8% of horses residing in the northwestern United States have been exposed to B. burgdorferi.