Molecular study of an outer fragment of Haemophilus parasuis neuraminidase and utility with diagnostic and immunogen purposes

- A neuraminidase fragment from 15 H. parasuis reference serotypes was analysed.
- The β-barrel fragment was quite similar for all serotypes, except for serotype 2.
- Serovars 6 and 7 or 12 and 13 shared between them the same nucleotidic sequence.
- This outer fragment could be used as a suitable diagnostic tool for H. parasuis.
- It could be also tested for studying vaccines to all serovars except serovar 2.

Haemophilus parasuis is a swine pathogenic organism, being the causative agent of Glässer's disease. It has got some virulence factors, some of which act as potential candidates for the vaccine developing. Among them there is the neuraminidase enzyme, which is located inside the outer membrane and contains a β-barrel domain with seven external loops. By using the polymerase chain reaction technique, the β-barrel fragment was amplified, sequenced and analysed for the 15 H. parasuis reference serotypes. The results showed a small diversity for them, except for serotype 2, which has a deletion that covers the loops with potential to be used as vaccine antigen. However, some of the other serotypes showed the same nucleotidic sequence between them, such those 6 and 7 or those 12 and 13. This fact was also confirmed by means of phylogenetic analysis. For these reasons, the tested fragment might result in a putative candidate for the development of subunit vaccines against all the serotypes causing Glässer's disease outbreaks, with the exception of serotype 2, alone or in combination with other proven immunogenicity molecules. Anyway, further studies should be carried out in pigs in order to confirm this hypothesis. Finally, this outer fragment of H. parasuis neuraminidase could be used as a suitable diagnostic tool at a species level, for instance, by PCR.