PGD is a multifactorial worldwide disease with both infectious and non-infectious causes. PGD leads to significant problems in Atlantic salmon (Salmo salar) and many other species.
Among the infectious causes are viruses (Atlantic salmon paramyxovirus-ASPV, Salmon gill poxvirus-SGPV), bacteria (Tenacibaculum maritimus, Piscichlamydia salmones, Candidatus Clavochlamydia salmonis), parasites (Neoparamoeba perurans, Loma salmonae, Ichthyobodo spp., Trichodina sp.). Non-infectious causes include phytoplankton and zooplankton.
Gross pathological changes include “clubbing”, in which thickened white areas of hyperplastic epithelium can be easily seen, mainly at the ends or distal third of the filaments.
The hyperplasia leads to compromised gas exchange, as well as all of the other metabolic and homeostatic mechanisms for which the gills are responsible, plus impaired clearance mechanisms.
- Gjessing, M. C., Thoen, E., Tengs, T., Skotheim, S. A., & Dale, O. B. (2017). Salmon gill poxvirus, a recently characterized infectious agent of multifactorial gill disease in freshwater‐and seawater‐reared Atlantic salmon. Journal of fish diseases, 40(10), 1253-1265.
- Mitchell, S. O., & Rodger, H. D. (2011). A review of infectious gill disease in marine salmonid fish. Journal of fish diseases, 34(6), 411-432.
- Nylund, S., Andersen, L., Sævareid, I., Plarre, H., Watanabe, K., Arnesen, C. E., … & Nylund, A. (2011). Diseases of farmed Atlantic salmon Salmo salar associated with infections by the microsporidian Paranucleospora theridion. Diseases of Aquatic Organisms, 94(1), 41-57.