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BackgroundThe lungworm Dictyocaulus viviparus, causing parasitic bronchitis in cattle, induces a temporary protective immunity that prevents clinical disease. A radiation-attenuated larvae based vaccine is commercially available in a few European countries, but has the disadvantages of a live vaccine. As a recombinant subunit vaccine would overcome these disadvantages, the parasite’s muscle protein paramyosin (PMY) was tested as a recombinant vaccine antigen.MethodsD. viviparus-PMY was recombinantly expressed in Escherichia coli as a glutathione-S-transferase (GST)-fused protein. Emulsified in adjuvant Saponin Quil A, the protein was given intramuscularly into calves. Two independent recombinant PMY (rPMY) vaccination trials with negative control groups (first trial: adjuvant only; second trial: non-fused GST) as well as an additional positive control group in the second trial, using the Bovilis©Dictol live vaccine to verify vaccination results, were performed. To determine the vaccination success, shedding of larvae as well as worm burden and worm sizes were analyzed. Additionally, ELISA-based determination of development of immunglobulins IgM, IgA, IgE, IgG as well as the subclasses IgG1 and IgG2 was performed. To analyze PMY localization in the bovine lungworm, immunohistochemical staining of adult worms was carried out.ResultsImmunohistochemical staining revealed that PMY is part of the bovine lungworm’s pharyngeal and body wall muscles. Vaccination with rPMY resulted in 47% [geometric mean: 67%] and 57% (geometric mean: 71%) reduction of larvae shedding in the first and second vaccination trial, respectively. Worm burden was reduced by 54% (geometric mean: 86%) and 31% (geometric mean: 68%), respectively, and worms of rPMY-vaccinated cattle were significantly shorter in both trials. Furthermore, ELISAs showed a clear antibody response towards rPMY with exception of IgE for which titers could not be detected. After challenge infection, rPMY antibodies were only exceptionally elevated among study animals indicating PMY to be a hidden antigen.ConclusionsEven though vaccination with the attenuated live vaccine was with 94% (geometric mean: 95%) reduction in larvae shedding and 93% (geometric mean: 94%) reduction in worm burden superior to rPMY vaccination, results using the latter are promising and show the potential for further development of a recombinant PMY-based vaccine against the bovine lungworm.

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Major sperm proteins (MSPs) represent a protein family occurring in nematodes only. Identification of the 3' and 5' untranslated region (UTR) completed the so far partial msp complementary DNA sequences of the bovine lungworm Dictyocaulus viviparus. The full-length transcript contains sequence tracts consistent with the Kozak and polyadenylation consensus sequence. On genomic level, three full-length sequences differing in three nucleotides were determined containing a 65-bp phase zero intron. Conceptual translation inferred two MSP isoforms due to one substitution within the 126-amino acid polypeptide. Bioinformatic analysis predicted that bovine lungworm MSP folds into an immunoglobulin-like seven-stranded beta sandwich as known for Caenorhabditis elegans and Ascaris suum. Furthermore, bovine lungworm MSP is confidentially predicted to be N-terminal-acetylated and secreted via a non-classical pathway. Quantitative real-time polymerase chain reaction analysis using ten developmental lungworm stages showed that msp is transcribed mainly in adult male parasites and in some degree in hypobiotic L5. However, marginal msp transcription was detectable in all of the investigated developmental lungworm stages.

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