Gastropod-borne parasitic diseases (GPDs) are a group of infectious diseases that require a gastropod species to serve as an intermediate host for a parasitic organism (typically a nematode or trematode) that can infect humans upon ingesting the parasite or coming into contact with contaminated water sources. These diseases can cause a range of symptoms, from mild discomfort to severe, life-threatening conditions, with them being prevalent in many parts of the world, particularly in developing regions. Preventive measures such as proper sanitation and hygiene practices, avoiding contact with infected gastropods and cooking or boiling food properly can help to reduce the risk of these diseases.
Gastropod-borne parasitic diseases affects over 300 million people worldwide and makes up several of the Neglected Tropical Diseases (NTDs) listed by the World Health Organisation. They are a significant public health concern in developing countries and are caused by various nematode and trematode species that use gastropods as their intermediate hosts. Gastropods are known to host several helminthic parasites due to their ability to thrive in different ecosystems. Gastropod-borne parasitic diseases have a significant impact on human, livestock and companion animal health. Over 140 gastropod species from 20 families are known intermediate hosts for nematode and trematode species that affect hundreds of millions of people in around 90 countries. Moreover, its estimated over 18,000 digenean trematode species and approximately 50 metastrongyloid nematode species use gastropods as their intermediate hosts and are of medical or veterinary importance. Gastropod-borne parasitic diseases are a significant public health problem in endemic areas and can lead to chronic malnutrition and other long-term health problems. Control measures such as health education campaigns, improved sanitation and hygiene practices and better food safety measures can help to reduce the prevalence of gastropod-borne parasitic diseases.
Trematodes Trematodes (commonly known as flukes) are a subclass of the Trematoda and are obligatory internal parasites. The Digenea consist of around 80 families and 6,000 described species, with only a dozen species known to actively infect humans. The most well-known and predominate gastropod-borne parasitic disease is schistosomiasis, while other less known GPDs include Amphistomiasis, Brachylaimiasis, Clinostomiasis, Clonorchiasis, Dicrocoeliasis, Echinostomiasis, Eurytrematosis, Fasciolopsiasis, Fascioliasis, Haplorchiasis, Heterophyiasis, Metagonimiasis, Metorchiasis, Nanophyetiasis, Neodiplostomiasis, Opisthorchiasis, Paragonimiasis and Philophthalmiasis (commonly grouped as foodborne trematodiasis). Theses trematode diseases cause significant morbidity and mortality in humans, especially in developing countries and have a significant impact on livestock and companion animal health. Both schistosomiasis and foodborne trematodiases are significant public health problem in endemic areas and are identified as a Neglected tropical diseases by the World Health Organisation (WHO).
Amphistomiasis Amphistomiasis (also known as paramphistomiasis) is a parasitic infection caused by several genera of intestinal flukes that belong to the superfamily Paramphistomoidea (Calicophoron, Carmyerius, Cotylophoron, Explanatum, Gastrodiscoides, Gigantocotyle, Paramphistomum and Watsonius). These parasites commonly infect the digestive tract of ruminants (such as cattle, sheep, and goats), with species like Gastrodiscoides hominis and. Watsonius watsoni infecting humans. Amphistomiasis is primarily found in Asia, Guyana, Zambia, Nigeria and Russia in areas where people have close contact with infected livestock. The transmission of amphistomiasis is associated with the ingestion of undercooked (or raw) freshwater plants contaminated with the metacercarial stage of the parasite. However, other organisms like fish and freshwater invertebrates can also contain these metacercaria. The larvae then migrate to the rumen or abomasum of the host animal, where they attach themselves to the mucosa and feed on blood. The trematode then infects the intestinal wall of the host, leading to chronic inflammation and damage. Symptoms of amphistomiasis can include abdominal pain, diarrhea, vomiting, fatigue, and weight loss. In severe cases, the infection can lead to intestinal obstruction, liver damage, and other complications. Amphistomiasis is typically diagnosed through the identification of eggs or adult trematodes in fecal samples or through endoscopic examination of the intestines. Treatment usually involves anthelmintic medications such as praziquantel, to kill the adult worms and prevent further damage to the intestinal wall.
Brachylaimiasis
Brachylaimiasis is a parasitic infection caused by the intestinal trematode genus, Brachylaima, which infects various animals and one species (B. cribbi) known to infect humans. The life cycle of Brachylaima involves a two (or more) intermediate terrestrial gastropod host being infected through the ingestion of eggs excreted by an infected definitive host. After ingestion, it takes one to three months for an asexual sporocyst to be created and start to produce cercariae within the first intermediate gastropod host. These cercariae are secreted through the mucus of the first intermediate gastropod host and seek out to infect other gastropods through skin to skin contact. The first intermediate gastropod host can also act as both the first and second intermediate host, as infected snails shedding cercariae in their mucus can infect themselves, making them a first and second intermediate host simultaneously. The successful cercariae develop into mature metacercariae after four months and can survive up to another four months within the second gastropod host. The transmission cycle is completed when the secondary intermediate gastropod host is ingested by a bird, mammal, or reptile definitive host and the metacercariae reaches the intestines.
Of the species of Brachylaima investigated, only B. cribbi has been found to cause infection within humans, with the only cases been described in Australia. The symptoms of brachylaimiasis in humans include abdominal pain, diarrhea, vomiting, fever, anemia and eosinophilia. The infection is usually mild or self-limiting, but can be chronic and severe in rare cases. Brachylaimiasis is usually treated with the anthelminthic drug, praziquantel, which is effective against most trematode infections. The prevention of brachylaimiasis involves avoiding the consumption of undercooked (or raw) snails and slugs or unwashed vegetables (such as lettuce or spinach) contaminated with the slime/faeces/corpses of a second intermediate gastropod host.
Clinostomiasis Clinostomiasis is a parasitic infection caused by the esophageal trematode species, Clinostomum complanatum.
Clonorchiasis
Clonorchiasis is a parasitic infection caused by the Chinese liver fluke, Clonorchis sinensis. The disease is prevalent in East Asia, including China, Korea, Vietnam and parts of Russia. The transmission of clonorchiasis occurs through the ingestion of raw or undercooked fish that are infected with the larvae of Clonorchis sinensis. Once inside the human body, the larvae develop into adult flukes in the bile ducts of the liver. The adult flukes can cause inflammation and blockage of the bile ducts, which can lead to liver damage and other complications.
Symptoms of clonorchiasis may not appear immediately after infection but can manifest as early as a few days or up to several months later. The most common symptoms include abdominal pain, diarrhea, nausea, vomiting, fever and jaundice. In some cases, the infection may be asymptomatic and individuals may not show any signs of the disease. Diagnosis of clonorchiasis is made through a combination of medical history, physical examination and laboratory tests. Imaging tests such as ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) may also be used to detect the presence of the liver fluke in the bile ducts. The treatment of clonorchiasis involves the use of anthelmintic medications, such as praziquantel or albendazole to kill the adult flukes. However, if the infection has caused significant damage to the liver, additional medical treatment may be necessary. The prevention of clonorchiasis involves properly cooking or freezing caught fish as it can kill the larvae inside and prevent infection.
Dicrocoeliasis Dicrocoeliasis is a parasitic infection caused by the liver fluke genus, Dicrocoelium
Echinostomiasis Echinostomiasis is a parasitic infection caused by several species of intestinal fluke from the family, Echinostomatidae. The most common cause of echinostomiasis is from the members of the genus, Echinostoma. These parasites are found worldwide, but are particularly common in South East Asia such as South Korea and the Philippines. The infection is usually acquired via the consumption of undercooked (or raw) freshwater fish, amphibians, mollusks or crustaceans contaminated with infective metacercaria. Symptoms of echinostomiasis can include abdominal pain, diarrhea, nausea, vomiting and weight loss. In some cases, the infection can lead to more severe complications such as intestinal obstruction or inflammation. Echinostomiasis is diagnosed by examining stool samples for the presence of adult worms or eggs. Treatment typically involves the use of anthelmintic medications such as praziquantel or albendazole. Prevention involves avoiding the consumption of raw or undercooked meat.
Eurytrematosis
Eurytrematosis is a parasitic infection caused by the pancreatic trematode genus, Eurytrema. This trematode genus primarily affects ruminants such as cattle and sheep, but has been known to infect humans as well. The transmission cycle of eurytrematosis starts with eggs being excreted by an infected definitive host and being ingested by a terrestrial gastropod host. After ingestion, the eggs hatch and after several months, asexual sporocyst are created and start to produce cercariae, that are expelled into the environment by the first intermediate gastropod host. These cercariae are secreted through the mucus of the first intermediate gastropod host and are ingested by the second intermediate hosts, which is an insect species such as a grasshopper (Orthoptera) or an ant. The successful cercariae develop into mature metacercariae and wait for months within the second intermediate insect host. The transmission cycle is then completed when the second intermediate host is accidentally ingested by a ruminant, where the adult parasites are then able to reside in the bile ducts of the liver and the pancreatic ducts. In humans, accidental infection can occur through the consumption of contaminated water or food.