Development of a diagnostic molecular marker forPhilonemaspp. (Nematoda; Dracunculoidea) infecting salmonids in British Columbia

Abstract

We developed a species specific DNA probe based on differential PCR amplification that distinguishes two congeneric nematode parasites of salmonids in British Columbia: Philonema agubernaculum Simon and Simon, 1936, usually parasitic in lake resident rainbow trout, Oncorhynchus mykiss; and P. oncorhynchi Kuitunen-Ekbaum, 1933, parasitic in anadromous sockeye salmon, O. nerka. The region differentially amplified was the D3 expansion domain of the 28S rDNA. Sequences of the two species differ in two parts of the domain, one a single base substitution and the other a three base duplication in P. oncorhynchi. A primer specific to P. oncorhynchi (amplifying P. oncorhynchi, not P. agubernaculum) was defined in the duplication region. Using differential amplification, we showed that sockeye smolts are infected with P. agubernaculum, although returning adults harbour only P. oncorhynchi. This technique could conceivably be used to quantify the frequency of heterologous infections in the wild, before infecting worms are identifiable at the species level based on morphological criteria.