Snail Trail for Parasites Expands

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The invasive giant African land snail is expanding its range in Miami, and with it, the range of the parasitic rat lungworm, according to new U.S. Geological Survey led research.

KEARNEYSVILLE, W.Va. – The invasive giant African land snail is expanding its range in Miami, and with it, the range of the parasitic rat lungworm, according to new U.S. Geological Survey led research.

Image: Giant African Land Snail
A large giant African land snail sitting on a gloved hand.  The snail is approximately 8 inches long and covers the entire hand.  
Public domain

Giant African land snails, along with other species of snails and slugs, are an intermediate host for the rat lungworm, a parasitic nematode. Other snails, flatworms, frogs, freshwater prawns and land crabs have been shown to carry the parasite. Wildlife and humans may become infected through contamination from ingesting raw or undercooked snails and slugs. Exposure can result in mild to severe symptoms and can also lead to eosinophilic meningitis.

In this study, giant African land snails were collected from the 21 core areas that were routinely monitored by the Florida Department of Agriculture and Consumer Services in Miami, Florida. Snails tested positive for the rat lungworm in seven of the core areas. Previously only one core area was found to be positive for the rat lungworm.

“Most snails are large, five to eight inches long and four inches in diameter, so it proved more accurate to take multiple tissue samples from each snail to test for infectivity,” said Deborah Iwanowicz, a USGS biologist and lead author of the study. “Collecting just one additional sample per snail increased the number of snails testing positive for the rat lungworm by 13 percent.  This allowed us to confirm that the parasite is not uniformly distributed throughout the snail.”

Giant African land snails are native to East Africa but have expanded globally to areas such as Sierra Lion, Liberia, Ivory Coast, American Samoa, Guadaloupe, East Asia, India, Ghana and the United States.  There are established populations in Hawaii and eradication efforts are underway in Florida to combat the recent introduction. These snails can spawn multiple times within a season producing approximately 400 eggs in a clutch.

According to the U.S. Department of Agriculture Animal and Plant Health Inspection Service, other suitable habitat can be found in Alabama, Arizona, California, Georgia, Kentucky, Louisiana, Maryland, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Texas and Virginia.

“These land snails are known to consume over 500 species of plants and can withstand severe weather by going dormant for a couple months to over a year.  Their range expansion could have deleterious effects on food crops and spread disease well north of the Miami area” said biologist and lead author Deborah Iwanowicz.

Along with parasite monitoring, the USGS is examining the genetic makeup of snails caught in Florida and comparing them to snails found globally to determine the Florida snail invasion history.

“Knowing the origins of the snails that are spreading in Miami may help agriculture and wildlife officials as they look into strategies to prevent the further spread of this harmful invasive,” said Iwanowicz. 

“The spread of Angiostrongylus cantonensis, the rat lungworm, in giant African land snails (Lissachatina fulica) in Florida” by D.D. Iwanowicz, L. R. Sanders, W.B. Schill, M.V. Xayavong, A. J. da Silva , Y. Qvarnstrom and T. Smith,  is available in the Journal of Wildlife Diseases online.

Map of Miami showing locations where Giant African land snails were collected in May 2013.
Locations in the Miami area where Giant African land snails were collected in May 2013. Sources for map include: Esri, DeLorme, HERE, USGS, Intermap P Corp., NRCAN, Esri Japan, METI, Esri Chinga (Hong Kong), Esri (Thailand), Tom Tom.