Investigations on the role of the salmon louse, Lepeophtheirus salmonis (Caligidae), as a vector in the transmission of Aeromonas salmonicida subsp. salmonicida.

Abstract

A bacteria-parasite challenge model was used to study the role of sea lice, Lepeophtheirus salmonis (Copepoda), as a vector of Aeromonas salmonicida subsp. salmonicida. Three hypotheses were tested: (i) L.&#xa0;salmonis can acquire A.&#xa0;salmonicida subsp. salmonicida via water bath exposure; (ii) L.&#xa0;salmonis can acquire the bacteria via parasitizing infected Atlantic salmon, Salmo salar; and (iii) L.&#xa0;salmonis can transmit the bacteria to na&#xef;ve Atlantic salmon via parasitism. Adult L.&#xa0;salmonis exposed to varying A.&#xa0;salmonicida subsp. salmonicida suspensions (10(1) -10(7) &#xa0;cells&#xa0;mL(-1) ) for 1.0, 3.0 or 6.0&#xa0;h acquired the bacteria externally (12.5-100%) and internally (10.0-100%), with higher prevalences associated with the highest concentrations and exposures. After exposure to 10(7) &#xa0;cells&#xa0;mL(-1) , viable A.&#xa0;salmonicida subsp. salmonicida could be isolated from the external carapace of L.&#xa0;salmonis for 120&#xa0;h. Lepeophtheirus salmonis also acquired the bacteria externally and internally from parasitizing infected fish. Bacterial transmission was observed only when L.&#xa0;salmonis had acquired the pathogen internally via feeding on 'donor fish' and then by parasitizing smaller (<50&#xa0;g) 'naive' fish. Under specific experimental conditions, L.&#xa0;salmonis can transfer A.&#xa0;salmonicida subsp. salmonicida via parasitism; however, its role as a mechanical or biological vector was not defined.