GIANT INVASIVE SNAILS TAKE HOLD IN LOCAL LAKES, CITY REVEALS AFTER ECM INQUIRY

These large snails can potentially transmit rat lung worm disease

By Miriam Raftery

Photo:  Channeled apple snail laying a mass of pink eggs  by Katasha Cornwell, Fl. Dept. of Transportation:

October 28, 2021 (San Diego) – What are those pink clusters on rocks at Lake Murray and Lake Miramar?  After an East County Magazine inquiry, an official with the city of San Diego confirmed that they are eggs laid by Channeled Apple Snails. Also known as the “golden snail,” the crustacean is an invasive species from South America with potential to become a serious agricultural pest—and also potential to transmit rat lung disease. 

They are listed as a restricted species prohibited in California – but they are now found in several California counties and a handful of other states including Florida, Alabama, Arizona, and Idaho.

ECM sent an inquiry to the city after spotting an image on social media of the unidentified pink masses (photo, right) at Lake Murray.  Arian Collins, Supervising Public Information Officer for the City of San Diego, confirmed, “The City of San Diego has been aware of and monitoring the presence of Channeled Apple Snails in Murray and Miramar reservoirs for more than a decade. The California Department of Fish and Wildlife is also aware of the snails in both reservoirs.”

So why hasn’t the city eradicated the snails, notified the media, or posted any warning signs for the public in the past decade – since handling  or consuming these snails raw can potentially transmit rat lungworm, which can cause a fatal form of meningitis?

Collins replied, “Unfortunately, once a population of the snails has established, it’s almost impossible to remove it entirely. The City’s team of biologists concluded that the overall effect of the snails on the ecosystem has been minor and has no effect on drinking water quality.”

Elsewhere, however, the snails have wreaked havoc.  Up to three inches in length, these giant snails from the Amazon and Plata basins in South America are astoundingly adaptable. They have both gills and lungs – enabling them to breathe in and out of water. They can withstand heat and cooler temperatures. They can even float!

Each female snail lays egg masses that contain 200 to 600 eggs, soon sending hundreds of offspring slithering into the environment.  The snails tend to stay submerged at night, emerging to forage voraciously during the day.

When Channeled Apple Snails were introduced into Asia and Hawaii in the 1980s as a potential gourmet food source, the market dried up. But snails released into the wild soon threatened Asian rice crops as well as taro fields in Hawaii used to make poi.  They were brought to the U.S. mainland via the aquarium trade before being released illegally into the wild.

According to the U.S. Fish and Wildlife Service, numerous attempts to eradicate the snails have failed including widespread use of pesticides with serious health and environmental consequences.  Lack of natural predators allows the snails to proliferate and potentially push out native species. 

Use of ducks to eat the snails has helped, but the best way to destroy them is to hand-crush the snails and eggs, or knock the eggs into the water with a high-powered water spray. Whether the City of San Diego has tried any of these methods is unclear.

If images of giant snails give you thoughts of making home-prepared escargot, think twice.  Channeled Apple Snails, like other snail and slug species, can carry rat lung worm, a parasite capable of transmitting rat lungworm diseases and sometimes, a fatal form of meningitis.  According to the U.S. Centers for Disease Control entry on rat lung disease, the parasitic illness can be transmitted by eating raw snails, or even by handling them, as well as by touching or eating  vegetation or unwashed produce such as lettuce that snails have crawled over and left a trail of slime on. If you must handle snails, wear gloves and if you cook them, boil thoroughly.

Photos, right:  rat lung worm, courtesy of the U.S. Centers for Disease Control

While most people recover without treatment and the parasite eventually dies, some people may develop symptoms including headache, stiff neck, tingling, painful skin, low-grade fever, nausea and vomiting – early signs of meningitis. If you have these symptoms, you should seek medical treatment immediately and let the doctor know if you’ve handled or consumed raw or undercooked snails, frogs or shrimp, which can also carry rat lungworms.

ECM asked the County’s Health and Human Services Agency how many cases of rat lung disease have been reported locally in the past 20 years, to assess whether there has been a rise in cases since the introduction of the invasive snails.

Sarah Sweeney, communications officer for the County of San Diego Health & Human Services Agency responded, “I can confirm that County Public Health Services have nothing on record of any cases being identified in San Diego County.”

Troublingly, however, she cautioned, “Note that it is not a reportable disease.”  So withno mandate for medical professionals to report suspected or confirmed cases, there is no real way of knowing whether or not the invasive snails slithering into our region have sickened unsuspecting San Diego residents.