Salmon Aquaculture and Transmission of the Fish Tapeworm

quaculture of salmon constitutes a rapidly growing worldwide industry with an expanding globalized market (1,2). Although this industry has several economic benefits, according to recent reports it is also accompanied by effects that are detrimental to human and animal health and the environment (1,2). Aquaculture has been implicated in the transmission of infectious diseases. For example, in caged fish aquaculture, bacterial and parasitic diseases can be transmitted to wild fish (1,2). Furthermore, aquaculture raised fish may be susceptible to the microorganisms and parasites of wild fish (1,3). However, in spite of the accepted fact that parasitic worms can be transmitted to humans by free-ranging fish (4), until recently, few examples have been reported of pathogens that could be transmitted to humans directly by the products and subproducts of salmon aquaculture. I discuss here information indicating that salmon aquaculture may be involved in expanding the range of fish tapeworm infections in nature and to humans. Several recent publications report outbreaks of human cases of infection by the fish tapeworm Diphyllobothrium latum in Brazil (5–9). These infections have been epidemiologically linked to consumption of raw salmon produced by the aquaculture industry in southern Chile, thousands of miles away (5–9). Infections by D. latum have been detected in several cities in Brazil (5–9), and in a tourist who traveled there from Europe (10). These cases of diphyl-lobothriasis are noteworthy because this parasite was totally unknown to clinicians and parasitologists in Brazil, where it does not appear to have an endemic life cycle (5–9). D. latum is transmitted to humans by plerocercoid lar-vae present in fish meat and visceral organs (www.dpd.cdc.gov/dpdx). D. latum and the closely related sea gull tapeworm, D. dendriticum, have well-established endemic life cycles in a series of glacial lakes that dot Region XIX and Region X in northern Chilean Patagonia. Infections with these parasites have been detected in this geographic area since the 1950s in persons who ingested uncooked fish from these lakes and also in animals (11–14). The link that closes the epidemiologic chain between the Brazilian outbreak of fish tapeworm infections and the aquaculture of salmon in southern Chile is that some of the freshwater lakes where D. latum and D. dendriticum are endemic are used to grow the freshwater stages of juvenile salmon, or smolt, in cages (15). Smolt are temporarily grown in these lakes to accelerate their growth before they are transported to cages in the …