Rahul Nelli, working at the School of Veterinary Medicine and Science at the University of Nottingham, and co-workers have compared human- and avian-type sialic acid influenza receptors in the pig. Their paper, published in BMC Veterinary Research, suggests that pigs are no more likely to be the host of virus reassortment than humans. The researchers also noted abundant receptors in the pig's intestine.

A major determinant of influenza infection is the presence of virus receptors on susceptible host cells to which the viral haemagglutinin is able to bind, accoridng to Nelli and co-authors. Avian viruses preferentially bind to sialic acid α2,3-galactose (SAα2,3-Gal) linked receptors, whereas human strains bind to sialic acid α2,6-galactose (SAα2,6-Gal) linked receptors.

To date, there has been no detailed account published on the distribution of SA receptors in the pig, a model host that is susceptible to avian and human influenza subtypes, thus with potential for virus reassortment. The group examined the relative expression and spatial distribution of SAα2,3-GalG(1-3)GalNAc and SAα2,6-Gal receptors in all major organs from normal post-weaned pigs by binding with lectins Maackia amurensis agglutinins (MAA II) and Sambucus nigra agglutinin (SNA) respectively.

Results

Both SA α2,3-Gal and SA α2,6-Gal receptors were extensively detected in all major porcine organs. Furthermore, distribution of both SA receptors in the pig respiratory tract closely resembled the published data of the human tract. Similar expression patterns of SA receptors between pig and human in other major organs were found, with exception of the intestinal tract. Unlike the limited reports on the scarcity of influenza receptors in human intestines, the researchers found increasing presence of SAα2,3-Gal and SAα2,6-Gal receptors from duodenum to colon in the pig.

Conclusions

The extensive presence of SAα2,3-Gal and SAα2,6-Gal receptors in all major organs examined suggests that each major organ may be permissive to influenza virus entry or infection. The high similarity of SA expression patterns between pig and human, in particular in the respiratory tract, suggests that pigs are not more likely to be potential hosts for virus reassortment than humans. Their finding of relative abundance of SA receptors in the pig intestines highlights a need for clarification on the presence of SA receptors in the human intestinal tract, concluded Nell and co-authors.

Reference

Nelli R.K., S.V. Kuchipudi, G.A. White, B. Baquero Perez, S.P. Dunham and K-C. Chang. 2010. Comparative distribution of human and avian type sialic acid influenza receptors in the pig. BMC Veterinary Research 2010, 6:4. doi:10.1186/1746-6148-6-4.

Further Reading

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You can view the full report (as a provisional PDF) by clicking here.