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To better understand the role of vector transmission of aquatic viruses, we established an in vivo virus−parasite challenge specifically to address (1) whether Lepeophtheirus salmonis can acquire infectious haematopoietic necrosis virus (IHNV) after water bath exposure or via parasitizing infected Atlantic salmon Salmo salar and if so, define the duration of this association and (2) whether L. salmonis can transmit IHNV to naïve Atlantic salmon and whether this transmission requires attachment to the host. Salmon lice which were water bath-exposed to 1 × 10 5 plaque-forming units (pfu) ml −1 of IHNV for 1 h acquired the virus (2.1 × 10 4 pfu g ) and remained viruspositive for 12 h. IHNV-positive salmon lice generated through water bath exposure or after parasitizing infected Atlantic salmon successfully transmitted IHNV, resulting in 76.5 and 86.6% of the exposed Atlantic salmon testing positive for IHNV, respectively. In a second experiment, only salmon lice that became IHNV-positive through water bath exposure transmitted IHNV to 20% of the naïve fish, and no virus was transmitted when IHNV-infected salmon lice were cohabitated but restrained from attaching to naïve fish. Under laboratory conditions, adult L. salmonis can acquire IHNV and transmit it to naïve Atlantic salmon through parasitism. However, the ephemeral association of IHNV with L. salmonis indicates that the salmon louse act as a mechanical rather than a biological vector or reservoir. 97: 155-165, 2011 156 ing the last epidemic (2001−2003) the average cumulative mortality of Atlantic salmon on infected farms was 58% (Saksida 2006), highlighting the significant economic cost of this disease. KEY WORDS: Sea lice · Lepeophteirus salmonis · Infectious heamatopoietic necrosis virus (IHNV) · Disease vector · Virus transmission · Atlantic salmon · Salmo salar Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSDis Aquat OrgQuestions concerning the epidemiology of IHNV, such as the source of infection, mode of transmission, and mechanism that perpetuates the virus among salmonid populations, are yet to be fully addressed (Bootland & Leong 1999). Laboratory studies have clearly demonstrated water exposure as an effective mode of IHNV transmission to both Pacific and Atlantic salmon in salt-and freshwater (Traxler et al. 1993, Wolf 1988. Moreover, epidemiological investigation of the spatial and temporal occurrence of IHNV in saltwater-farmed Atlantic salmon suggest that waterborne transmission may have played a role in the spread of virus between farms located in close proximity to each other (Saksida 2006). However, alternative modes of IHNV transmission, including the potential for transfer by aquatic invertebrates, cannot be discounted.The topic of piscine ectoparasites as vectors for pathogens has been reviewed by Cusack & Cone (1986), focusing on tissue feeding species with monoxenous life cycles. The authors hypothesize that while moving between hosts such species may contribute to dis...

A study was carried out to determine the effect of Lernaeocera branchialis on Atlantic cod infected in the laboratory and in the field and also to ascertain its effect on cod-ranching. Sixty-four percent (308) of 481 cod acquired infections in the laboratory and 33% (159) of the infected fish died over a 4-yr period. About 74% of the deaths occurred within 4 mo of the infection. Monthly samples of cod collected adjacent to a cod-ranching operation showed an initial prevalence of 30% that subsequently decreased in the following 2 mo to 15%. Prevalence of the infection also decreased among the initial field sample of cod that were kept alive, from 30 to 17% during the same 2-mo period and to 9% after 8 mo and was associated with death caused by the parasite. Cod examined at intervals after infection showed evidence of reduced weight gain, lower liver somatic index, liver lipid, and blood values than controls. A field sample taken from the same area during the summer of the following year indicated a prevalence of 12%. This higher than usual prevalence (4-6%) was associated with retention of the intermediate host, Cyclopterus lumpus, that provided an additional source of infective stages. It is likely that increased parasitism could affect the success of the cod-ranching operation in view of the parasite's devastating effects on its hosts.

Using standard OIE bacteriological screening protocols, we sampled the external carapace and internal stomach contents of motile stages (preadult and adult) of Lepeophtheirus salmonis collected from farmed Atlantic salmon from May 2007 to April 2008 in British Columbia, Canada. Three potentially pathogenic bacteria (Tenacibaculum maritimum, Pseudomonas fluorescens, and Vibrio spp.) were isolated from external (58-100%) and internal (12.5-100%) samples of sea lice. The prevalence of bacteria was higher from lice collected during the months with higher water temperatures and among adult lice. These preliminary results have led to a comprehensive, multi-year study where we plan to examine the possible role of sea lice as a vector for disease.