THE ROLE OF EPIDEMIOLOGY IN THE SURVEILLANCE AND CONTROL OF PREVALENT FISH DISEASES – THE CASE OF THE SEA LICE IN FARMED SALMONIDS IN CHILE

Chile is the second larger producer of farmed salmon in the world. The sea lice Caligus rogercresseyi is one of the most challenging fish health problems for this industry because of its complex control (as the sea lice quickly develops tolerance to chemotherapeutants), and due to the fact that it is ubiquitous in sea water. In Chile, sea lice is under an official surveillance and control program administered by the health authority SERNAPESCA.

The aim of this abstract was to highlight the role of epidemiology in surveillance and control of prevalent aquatic disease, such as the case of sea lice.

Surveillance of sea lice in Chile involves weekly reports of sea lice levels for every single farm rearing Atlantic salmon or rainbow trout. The amount of surveillance data makes it difficult to appreciate spatial and temporal distribution patterns of sea lice. Using quantitative epidemiological approaches such as linear mixed effects models it was possible to observe that sea lice: 1) has a clear east-west spatial pattern (Fig. 1); 2) increases over the salmon production cycle (Fig. 2A); and 3) has decreased over the last 6 years (Fig. 2B). Epidemiological methods have been also used to investigate the recent expansion of sea lice to regions where it was thought that environmental conditions were not optimal for their development.

In terms of control, epidemiological quantitative methods have been successfully used to: 1) evaluate the field efficacy of antiparasitic drugs on different sea lice developmental stages (i.e. juvenile, adult males, gravid females); 2) to provide the first evidence of the sensitivity loss of sea lice to the organophosphate azamethiphos; and 3) to demonstrate the beneficial effect of the synchronization of antiparasitic treatments among farms within an area.