Parasites of Imported and Non-Native Wild Asian Swamp Eels

Science Center Objects

In parts of Asia, wild-caught and aquaculture-reared swamp eels are widely consumed as food by humans and are a common source of human gnathostomiasis, a food-borne zoonosis caused by parasitic nematodes of the genus Gnathostoma spp. In humans, the larvae of these nematodes can cause tissue damage and, in some instances, death. Over the past two decades, many thousands of Asian swamp eels have been legally shipped live from Asia to North America where they are distributed to numerous ethnic food markets in the USA and parts of Canada.  

Parasites of Imported and Non-Native Wild Asian Swamp Eels
Asian swamp eels have been legally shipped from Asia to North America where they are distributed to ethnic food markets. 

The Science Issue and Relevance: Introduced wild populations of non-native Asian swamp eels (Synbranchidae: Monopterus spp) are established in Florida, Georgia, New Jersey, and Hawai’i. Over the past two decades, many thousands of Asian swamp eels have been legally shipped live from Asia to North America where they are distributed to numerous ethnic food markets in the USA and parts of Canada. Live food markets are most likely the source of most of the known wild populations. In parts of Asia, wild-caught and aquaculture-reared swamp eels are widely consumed as food by humans and are a common source of human gnathostomiasis, a food-borne zoonosis caused by parasitic nematodes of the genus Gnathostoma spp. In humans, the larvae of these nematodes can cause tissue damage and, in some instances, death. A preliminary survey documented a substantial parasite burden in both market and wild swamp eels in the USA. More recently, Dr. Nico and USGS collaborator Dr. Rebecca Cole examined a small number of Asian swamp eels from markets in several cities in the USA and confirmed the presence of Gnathostoma spp. The focus of the present study is to more fully document the species and diversity of Gnathostoma spp and other potentially harmful macroparasites infecting introduced swamp eels, including eels imported live into food markets and specimens from non-native wild populations. Wider geographic and more intensive sampling of both market eels and non-native wild populations is necessary to assess the potential for these and other parasites to become established in the United States.

Methodology for Addressing the Issue: The current phase involves resampling of market eels and also targeting larger, older specimens in all or most USA wild populations for parasites. For comparative purposes, a few samples of certain other live freshwater fishes imported live and sold live in US food markets will also be examined. Identification of parasites will be based on morphological characters and in some situations augmented with molecular characterizations.

Parasites of Imported and Non-Native Wild Asian Swamp Eels
Swamp eels are a common source of human gnathostomiasis, a food-borne zoonosis caused by parasitic nematodes of the genus Gnathostoma spp.

Future Needs: Increased global trade of live fish increases the risk that gnathostomes and other fish-borne parasites will be introduced into regions along with their introduced hosts. The current research will: 1) more fully document prevalence of zoonotic Gnathostoma species and other potentially harmful parasites in swamp eels; 2) broaden the investigation to include swamp eels and a few other imported live fish from food markets in previously unsampled areas of the USA and perhaps Canada, 3) more thoroughly sample wild populations in Florida and New Jersey; and 4) attempt to obtain samples and analyze the parasites of introduced wild populations present in Georgia and Hawaii, populations whose parasites have not previously been investigated. This research is being funded by the USGS Invasive Species Program and addresses prevention, early detection and rapid assessment of new invaders, monitoring and forecasting of invasive species, effects of invasive species, control and management of invasive species, and information management.