Schistosomiasis is caused by parasitic worms excreted by snails in water. They penetrate the skin, grow in blood vessels, multiply, and cause bladder bleeding, liver damage, kidney failure, and cancer. Rat lungworms, carried by snails, are transmitted through uncooked snail meat. They eat their way to the brain, causing meningitis. Avoid raw snail meat and meat from unreliable sources.
Snails could be among the deadliest animals if you look at the official number of people who die each year because of them! According to an infographic released by Bill Gates, animals like sharks kill about 10 people a year, lions 100 and crocodiles 1,000, despite having among the most fearsome reputations. However, freshwater snails are responsible for thousands of deaths every year through a disease called schistosomiasis. Snails may also carry thousands of “rat lungworms” which can cause meningitis if ingested by humans.1 2
Risks that Snails Pose
Freshwater Snail and Schistosomiasis
Schistosomiasis is an acute and chronic disease caused by parasitic worms. The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite, known as cercariae, emerges from the snail, hence contaminating water.
Schistosomiasis is transmitted by contact with contaminated fresh water (lakes and ponds, rivers, dams) inhabited by snails carrying the parasite. Swimming, bathing, fishing, and even domestic chores such as laundry and herding livestock can put people at risk of contracting the disease.
Among human diseases caused by parasites, schistosomiasis ranks second behind malaria in terms of its social, economic, and public health impact in tropical and subtropical regions of the world. Worldwide, more than 700 million people are at risk of infection and more than 207 million people are infected.3 4
Role of Snails in the Transmission of Schistosomiasis
People suffering from schistosomiasis contaminate freshwater sources with excreta containing parasite eggs. These hatch in water and the hatched eggs become ready to infect any freshwater snails in their path. Inside the snails, the young worms grow capable of burrowing back into human skin. Larvae emerge from the snails and swim in the water until they come into contact with a human and penetrate the skin.
Once inside the body, the larvae develop into male and female worms which pair up and live together in the blood vessels for years. Female worms release thousands of eggs, which are passed out of the body in the urine and feces. If people urinate or defecate in freshwater bodies, the eggs migrate to snails where they eventually hatch and begin the cycle again.
Inside the Human Body
Inside the human body, female worms grow into adults and lay eggs that migrate through the body for release in feces. The eggs of these worms can damage the intestines, bladder, and other organs. If a person does not receive treatment and the eggs stay in the body, he or she may eventually experience long-term problems, which include:
- Bleeding of the bladder
- Ulceration of the bladder
- Liver damage
- Eventual kidney failure
- Children with repeated infection can develop anemia, malnutrition, and learning disabilities.5
Giant African Snails and Meningitis
Meningitis is the swelling of the membranes around the brain and spinal cord. It can be triggered by viruses, bacteria, or a fungal infection. Snails harboring a rat parasite called lungworm can lead to meningitis.
During the course of its natural life cycle, the lungworm shuttles between two creatures. In its adult phase, it burrows around in the lung of a rat. At some point, it produces larva that migrates to the feces of the rat. Snails, while grazing on leaves, eat the rat feces among other things. The larvae infect the snails, living in them until they are almost mature, at which point the snails are eaten by rats. The cycle of life begins all over again.
The parasite only gets passed to humans when people eat uncooked snail meat.
Inside the Human Body
Once consumed, the parasites eat their way to the central nervous system, where they eventually die. On ingesting a snail infected by the worms, which will eventually reach the brain, human beings can contract eosinophilic meningitis. Symptoms include headaches, numbness, spasms, and in the most serious cases – death.6 7
Should I Stay Away from Snail Meat?
Snails are considered a delicacy in many parts of the world. So should you run a mile when served some? Not really. Snails served in restaurants are usually bred in captivity and/or purged extensively to remove toxins. Avoid eating them if the meat is from unreliable or dodgy sources. According to a Florida Department of Agriculture and Consumer Services entomologist, “Most of the infections and deaths from snail-transmitted diseases apparently come from eating raw or undercooked snails or ingesting slime residue left on fresh fruits and vegetables.” Do avoid eating uncooked snail meat or wild snails at all costs.8
Snails do have a bad reputation, but with adequate precautions, they can also continue to coexist safely in the aquatic environment. Improvement of sanitary facilities for safe disposal of human waste; provision of safe drinking water; reduction of contact with contaminated water; and snail control are some preventive measures to reduce the hazards snails pose.9
References [ + ]
|1.||↑||The Deadliest Animal in the World, Gatesnotes.|
|2.||↑||Snails, Slugs, and Semi-slugs: A Parasitic Disease in Paradise, Centers for Disease Control and Prevention.|
|3.||↑||Schistosomiasis, Neglected Tropical Disease.|
|4, 5, 9.||↑||Parasites – Schistosomiasis, Centers for Disease Control and Prevention.|
|6.||↑||Tsai, Hung-chin, Yung-Ching Liu, Calvin M. Kunin, Ping-hong Lai, Susan Shin-jung Lee, Yao-Shen Chen, Shue-Ren Wann et al. “Eosinophilic meningitis caused by angiostrongylus cantonensis associated with eating raw snails: correlation of brain magneticresonance imaging scans with clinical findings.” The American journal of tropical medicine and hygiene 68, no. 3 (2003): 281-285.|
|7.||↑||Ohlweiler, Fernanda Pires, Marisa Cristina de Almeida Guimarães, Fernanda Yoshika Takahashi, and Juliana Manas Eduardo. “Current distribution of Achatina fulica, in the State of São Paulo including records of Aelurostrongylus abstrusus (Nematoda) larvae infestation.” Revista do Instituto de Medicina Tropical de São Paulo 52, no. 4 (2010): 211-214.|
|8.||↑||Some Health Risks With Eating Giant African Land Snail, WLRN.|