Trematodiasis is a group of parasitic infections caused by different species of flukes, in humans mainly by digenean trematodes. Symptoms can range from mild to severe depending on the species, number and location of trematodes in the infected organism. Symptoms depend on the type of trematode present, and include chest and abdominal pain, high temperature (fever), digestion issues, cough and shortness of breath (dyspnea), diarrhoea and change in appetite. Trematodiases can be transmitted through food or water that contains larval forms of the parasite. Infections can be transmitted through aquatic organisms which act as a host for the maturity of the parasite. Foodborne trematodiasis is transmitted when organisms ingest contaminated undercooked food including aquatic plants and organisms. Other trematodiases caused by the blood flukes of the genus Schistosoma are transmitted by contact with water contaminated by swimming larvae of a different stage of development or infective stage than in foodborne trematodes. This article focuses on foodborne trematodiases. Trematodiases can be prevented and controlled through public health programs aimed at educating people about how contaminated water and food can lead to infections. Education programs include raising awareness about the transmission of trematodiases through the consumption of food that is not cooked well such as fish, molluscs, and other aquatic animals and plants. Sanitation and distribution of clean water are also used to control the spread of trematodiases on a larger scale. Foodborne trematodiases that involve the lung, liver and intestines are classified as a neglected tropical disease, as is schistosomiasis. Cases of trematodiases that can be transmitted through food has affected over 70 countries globally, with the most impacted countries located in Latin America and Asia. According to the World Health Organization recorded that there are approximately 200,000 cases of foodborne trematodiases that are caused by four kinds of trematodes: Clonorchis, Fasciola, Opisthorchis, and Paragonimus. The majority of cases are from East and Southeast Asia. Schistosomiasis is an environmentally-acquired trematodiasis accounting for over 200 million cases annually, most of which are in Africa. The urinary blood fluke (Schistosoma haematobium), the Southeast Asian liver fluke (Opisthorchis viverrini) and the Chinese liver fluke (Clonorchis sinensis) are recognised by the International Agency for Research on Cancer as a Group 1 biological carcinogens in humans.
Signs and symptoms Most cases of trematodiases show no symptoms. Infected organisms that show symptoms will range in severity depending on the number of parasites. When the number of trematodes is high, signs of infection include severe pain in the abdomen. The signs and symptoms of the disease is also impacted by the location and spread of the parasite in the body. Tissues in organs are damaged when infected by the parasite. This damage can be mechanical as the parasite attaches to the walls of the host, as well as chemical. Symptoms of lung fluke infections (Paragonimus) depend on the parasite’s stage in its life cycle, and how it travels around in the lung. Trematodiases that impact the lungs can cause cough, headache, chest pain, high temperature and change in appetite. Intestinal trematodiases infect the gastrointestinal tract. Symptoms of intestinal fluke infections can range from mild to severe symptoms depending on the length of time that the parasite spends in the body. Signs and symptoms that arise in infected organisms include headache, indigestion problems such as diarrhoea, high temperature, and pain in the abdomen which can also lead to malnutrition as the infected organism’s appetite is lost. In intestinal trematodiases, the walls of the intestine can be damaged, which can lead to ulcers in some infected organisms. Trematodiases caused by liver trematodes infect the host’s liver, gall bladder and bile duct and can cause inflammation within these organs. Symptoms vary from case to case and include abdominal pain, loss of appetite, problems with indigestion including diarrhoea and constipation, whereas in some cases, no symptoms are shown. Opisthorchis viverrini damages the bile duct when in the adult stage of the life cycle, forming the cancer cholangiocarcinoma. Blood flukes can cause the trematodiases schistosomiasis which can cause reactions on skin. When infected, the host can also experience symptoms such as nausea, lack of appetite, diarrhoea, and abdominal pain.
Causes Trematodiases are zoonotic infections caused by trematodes. In foodborne trematodiases, these parasites are transferred from animals to humans. Transmission of trematodiases can occur through the consumption of water and food that is contaminated with trematodes in the larval stages of their life cycle. In a host organism, eggs of trematodes can spread through faeces, and sputum if the host is infected by a lung fluke. Once these reach water, they infect aquatic snails which act as intermediate hosts for trematodiases that are transmitted through food. A second host will depend on the species of trematode, and are usually aquatic animals Some trematodiases such as schistosomiasis can also be transmitted when the skin comes in contact with water containing the parasite. Trematodes all have different life cycles in which they can reproduce asexually and sexually. When trematodes are at the metacercariae stage in their life cycle, humans and other definitive hosts such as mammals and birds can be infected. In humans, adult trematodes can survive for 25 years.
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