Carcinogenic parasite

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Carcinogenic parasites are parasitic organisms that depend on other organisms (called hosts) for their survival, and cause cancer in such hosts. Three species of flukes (trematodes) are medically-proven carcinogenic parasites, namely the urinary blood fluke ( Schistosoma haematobium ), the Southeast Asian liver fluke ( Opisthorchis viverrini ) and the Chinese liver fluke ( Clonorchis sinensis ). S. haematobium is prevalent in Africa and the Middle East, and is the leading cause of bladder cancer (only next to tobacco smoking). O. viverrini and C. sinensis are both found in eastern and southeastern Asia, and are responsible for cholangiocarcinoma (cancer of the bile ducts). The International Agency for Research on Cancer declared them in 2009 as a Group 1 biological carcinogens in humans. [1]

Contents

Other parasites are also linked to various cancers. Among protozoan parasites, Toxoplasma gondii , Cryptosporidium parvum , Trichomonas vaginalis and Theileria are associated with specific cancer cells. Plasmodium falciparum can also be an indirect cause of cancer. Tapeworms such as Echinococcus granulosus and Taenia solium may directly or indirectly cause cancer. Liver flukes such as Opisthorchis viverrini and Platynosomum fastosum can cause cancer in domesticated animals. Roundworms such as Strongyloides stercoralis , Heterakis gallinarum , and Trichuris muris are known to cause cancer in animals. [2]

History

A rat roundworm Gongylonema neoplasticum was the first parasite discovered—allegedly—to cause cancer. A Danish physician Johannes Fibiger discovered it in 1907, and experimentally showed that he could induce stomach cancer in rats using the roundworm infection in 1913. In 1914, he gave the name Spiroptera (Gongylonema) neoplastica, but later changed it to Spiroptera carcinoma. [3] Fibiger won the 1926 Nobel Prize in Physiology or Medicine "for his discovery of the Spiroptera carcinoma". However, his interpretation was later found to be false, and that the roundworm was not carcinogenic on its own. [4] [5] Fibiger's Nobel Prize was described as "one of the biggest blunders made by the Karolinska Institute." [6]

The first true carcinogenic parasite discovered was Schistosoma haematobium. Theodor Maximillian Bilharz, a German physician at the Kasr el-Aini Hospital in Cairo recovered the adult fluke from a dead soldier in 1851. He named it Distomum haematobium. The disease is often called bilharzia in honour of the discoverer. [7] The infectivity and life cycle was discovered by Scottish physician Robert Thomson Leiper in 1915. [8] A British Surgeon Reginald Harrison, at the Liverpool Royal Infirmary, was the first to note its role in cancer. In 1889, he found that four people out of five cancer victims had bilharzia. A German physician Carl Goebel confirmed in 1903 that bladder tumour occurred in most bilharzia patients. By 1905, he was convinced that carcinoma of bladder was due to bilharzia. [9]

Group 1 carcinogens in human

Three flukes, urinary blood fluke (Schistosoma haematobium), Southeast Asian liver fluke (Opisthorchis viverrini) and Chinese liver fluke (Clonorchis sinensis) are classified as Group 1 carcinogens, i.e. they are substantiated and directly cancer-causing agents. [1]

Schistosoma haematobium

S. haematobium is a digenetic trematode found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. [10] It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer (only next to tobacco smoking). [11] [12] Its life cycle is transmission between humans and freshwater snail, species of Bulinus. The larvae live in water bodies from where they infect the hosts by penetrating the skin. Adults are found in the venous plexuses around the urinary bladder and the released eggs travels to the wall of the urine bladder causing haematuria and fibrosis of the bladder. The bladder becomes calcified, and there is increased pressure on ureters and kidneys (hydronephrosis). Inflammation of the genitals due to S. haematobium may contribute to the propagation of HIV. [13] Antigens produced by the eggs induce granuloma formation. Granulomata in turn coalesce to form tubercles, nodules or masses that often ulcerate. This creates the pathological lesions found in the bladder wall, ureter and renal; and also tumour, both benign and malignant. [14] [15]

Opisthorchis viverrini

O. viverrini is a food-borne liver fluke that mainly attacks the area of the bile duct. Infection with the parasite, called opisthorchiasis is the major cause of cholangiocarcinoma, a cancer of the bile ducts, in northern Thailand, the Lao People's Democratic Republic, Vietnam and Cambodia. [16] O. viverrini has three successive host for its life cycle – the first intermediate hosts are freshwater snails of the genus Bithynia, the second intermediate hosts are different cyprinid fish, and humans are the definitive hosts. [17] Generally opisthorchiasis due to O. viverrini is harmless without any clinical symptoms, but in rare cases, cholangitis, cholecystitis, and cholangiocarcinoma can develop. O. viverrini invades the bile ducts and, rarely, the gall bladder and pancreatic duct. Heavy infection can produce problems such as fibrosis in the liver, gall bladder and bile ducts. [18] Pathological effects on the bile ducts including inflammation, epithelial desquamation, goblet cell metaplasia, epithelial and adenomatous hyperplasia and periductal fibrosis collectively promote cholangiocarcinoma. [19] Though it is not immediately life-threatening, cancer develops after 30–40 years, and the ensuing death is rapid—within 3–6 months of diagnosis. [20]

Clonorchis sinensis

C. sinensis is also a food-borne liver fluke. It is the most prevalent human trematode in Asia, and is found in Korea, China, Vietnam and also Russia. 85% of the cases are found in China. [21] It is transmitted similarly to O. viverrini, but the species of snails are varied, of which Parafossarulus manchouricus is the most common. The cyprinid fish hosts are also different. [22] General clonorchiasis is indicated with fatigue, abdominal discomfort, anorexia, weight loss, diarrhea, liver cirrhosis and jaundice. The most severe infections cause cholangiocarcinoma and hepatic carcinoma. [23]

Indirect or putative carcinogens

Infection with malarial parasite Plasmodium falciparum is classified by IARC as probable (Group 2A) carcinogen. Schistosoma japonicum is a possible (Group 2B) carcinogen. There is a close association between the cat liver fluke Opisthorchis felineus and bile duct cancer among people in Russia. [24] [25]

Toxoplasma gondii and eye cancer (intraocular lymphoma) was detected by PCR from two human cases. [26] Strongyloides stercoralis eggs and adult worms may be linked with gastric adenocarcinoma and colon adenocarcinoma in Korea. [27] [2] Cryptosporidium parvum infection is associated with colorectal carcinoma. [28] [29]

Carcinogens in animals

The roundworm Trichuris muris infection can increase the number of tumours in mice. [30] Heavy infection with the trematode Platynosomum fastosum is associated with cholangiocarcinoma in cats. [31] Cryptosporidium parvum infection can be the cause of carcinoma in the gut of mice. [29] [32]

Related Research Articles

<span class="mw-page-title-main">Schistosomiasis</span> Human disease caused by parasitic worms called schistosomes

Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a disease caused by parasitic flatworms called schistosomes. The urinary tract or the intestines may be infected. Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience liver damage, kidney failure, infertility, or bladder cancer. In children, it may cause poor growth and learning difficulty.

<span class="mw-page-title-main">Trematoda</span> Class of parasitic flatworms

Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.

<i>Schistosoma</i> Genus of flukes

Schistosoma is a genus of trematodes, commonly known as blood flukes. They are parasitic flatworms responsible for a highly significant group of infections in humans termed schistosomiasis, which is considered by the World Health Organization as the second-most socioeconomically devastating parasitic disease, with hundreds of millions infected worldwide.

<i>Clonorchis sinensis</i> Species of fluke

Clonorchis sinensis, the Chinese liver fluke, is a liver fluke belonging to the class Trematoda, phylum Platyhelminthes. It infects fish-eating mammals, including humans. In humans, it infects the common bile duct and gall bladder, feeding on bile. It was discovered by British physician James McConnell at the Medical College Hospital in Calcutta (Kolkata) in 1874. The first description was given by Thomas Spencer Cobbold, who named it Distoma sinense. The fluke passes its lifecycle in three different hosts, namely freshwater snail as first intermediate hosts, freshwater fish as second intermediate host, and mammals as definitive hosts.

<span class="mw-page-title-main">Klatskin tumor</span> Medical condition

A Klatskin tumor is a cholangiocarcinoma occurring at the confluence of the right and left hepatic bile ducts. The disease was named after Gerald Klatskin, who in 1965 described 15 cases and found some characteristics for this type of cholangiocarcinoma

<span class="mw-page-title-main">Praziquantel</span> Medication

Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat schistosomiasis, clonorchiasis, opisthorchiasis, tapeworm infections, cysticercosis, echinococcosis, paragonimiasis, fasciolopsiasis, and fasciolosis. It should not be used for worm infections of the eye. It is taken by mouth.

<span class="mw-page-title-main">Clonorchiasis</span> Infectious disease caused by fish parasites

Clonorchiasis is an infectious disease caused by the Chinese liver fluke and two related species. Clonorchiasis is a known risk factor for the development of cholangiocarcinoma, a neoplasm of the biliary system.

Schistosoma japonicum is an important parasite and one of the major infectious agents of schistosomiasis. This parasite has a very wide host range, infecting at least 31 species of wild mammals, including nine carnivores, 16 rodents, one primate (human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Travelers should be well-aware of where this parasite might be a problem and how to prevent the infection. S. japonicum occurs in the Far East, such as China, the Philippines, Indonesia and Southeast Asia.

<i>Schistosoma mansoni</i> Species of fluke

Schistosoma mansoni is a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma). The adult lives in the blood vessels near the human intestine. It causes intestinal schistosomiasis. Clinical symptoms are caused by the eggs. As the leading cause of schistosomiasis in the world, it is the most prevalent parasite in humans. It is classified as a neglected tropical disease. As of 2021, the World Health Organization reports that 251.4 million people have schistosomiasis and most of it is due to S. mansoni. It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname.

<i>Schistosoma haematobium</i> Species of fluke

Schistosoma haematobium is a species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). It is found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is the leading cause of bladder cancer. The diseases are caused by the eggs.

Opisthorchis viverrini, common name Southeast Asian liver fluke, is a food-borne trematode parasite from the family Opisthorchiidae that infects the bile duct. People are infected after eating raw or undercooked fish. Infection with the parasite is called opisthorchiasis. O. viverrini infection also increases the risk of cholangiocarcinoma, a cancer of the bile ducts.

<span class="mw-page-title-main">Theodor Bilharz</span> German physician

Theodor Maximilian Bilharz was a German physician who made pioneering discoveries in the field of parasitology. His contributions led to the foundation of tropical medicine. He is best remembered as the discoverer of the blood fluke Schistosoma haematobium, the causative parasite of bloody urine (haematuria) known since ancient times in Egypt. The parasite, as the cause of bladder cancer, is declared by the International Agency for Research on Cancer as Group 1 carcinogen. The infection is known by an eponymous term bilharzia or bilharziasis, as well as by schistosomiasis.

<i>Opisthorchis felineus</i> Species of fluke

Opisthorchis felineus, the Siberian liver fluke or cat liver fluke, is a trematode parasite that infects the liver in mammals. It was first discovered in 1884 in a cat's liver by Sebastiano Rivolta of Italy. In 1891, Russian parasitologist, Konstantin Nikolaevich Vinogradov (1847–1906) found it in a human, and named the parasite a "Siberian liver fluke". In the 1930s, helminthologist Hans Vogel of Hamburg published an article describing the life cycle of Opisthorchis felineus. Felineus infections may also involve the pancreatic ducts. Diagnosis of Opisthorchis infection is based on microscopic identification of parasite eggs in stool specimens. Safe and effective medication is available to treat Opisthorchis infections. Adequately freezing or cooking fish will kill the parasite.

Opisthorchiasis is a parasitic disease caused by certain species of genus Opisthorchis. Chronic infection may lead to cholangiocarcinoma, a cancer of the bile ducts.

<span class="mw-page-title-main">Liver fluke</span> Group of liver parasites

Liver fluke is a collective name of a polyphyletic group of parasitic trematodes under the phylum Platyhelminthes. They are principally parasites of the liver of various mammals, including humans. Capable of moving along the blood circulation, they can occur also in bile ducts, gallbladder, and liver parenchyma. In these organs, they produce pathological lesions leading to parasitic diseases. They have complex life cycles requiring two or three different hosts, with free-living larval stages in water.

<span class="mw-page-title-main">Koi (dish)</span> Lao-Thai salad dish with raw beef

Koi is a "salad" dish of the Lao people living in modern-day Laos and Isan, Thailand, consisting of raw meat denatured by acidity, usually from lime juice. Common varieties include koi kung, with shrimp as the main ingredient, and koi paa /koi pla, which consists of minced or finely chopped raw fish in spicy salad dressing.

Schistosoma bovis is a two-host blood fluke, that causes intestinal schistosomiasis in ruminants in North Africa, Mediterranean Europe and the Middle East. S. bovis is mostly transmitted by Bulinus freshwater snail species. It is one of nine haematobium group species and exists in the same geographical areas as Schistosoma haematobium, with which it can hybridise. S. bovis-haematobium hybrids can infect humans, and have been reported in Senegal since 2009, and a 2013 outbreak in Corsica.

<span class="mw-page-title-main">Trematodiasis</span> Medical condition

Trematodiasis is a group of parasitic infections due different species of flukes, the trematodes. Symptoms can range from mild to severe depending on the species, number and location of trematodes in the infected organism. Symptoms depend on type of trematode present, and include chest and abdominal pain, high temperature, digestion issues, cough and shortness of breath, diarrhoea and change in appetite.

The Integrated Opisthorchiasis Control Program, commonly known as the "Lawa Project", located in Khon Kaen Province, Thailand, is an effort to reduce chronic infection by the Southeast Asian liver fluke among the native peoples of Isan, the northeast region of Thailand. The project operates under the aegis of the Tropical Disease Research Laboratory, Department of Pathology, Faculty of Medicine, Khon Kaen University. It is directed by Banchob Sripa. Its aim is to eliminate the practice of consuming raw or undercooked fish, the major cause of liver fluke infection and bile duct cancer in the region. The project is unique in that it follows the principles of EcoHealth, a One Health approach to improving human and animal health. The project has been the subject of newspaper and TV reports by BBC, The New York Times, and The Guardian.

<span class="mw-page-title-main">Gastropod-borne parasitic disease</span> Medical condition

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 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.

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