Carcinogenic parasite

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]

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]


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 humanEdit

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 haematobiumEdit

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 viverriniEdit

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 sinensisEdit

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 carcinogensEdit

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 animalsEdit

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]


  1. ^ a b Bouvard, V; Baan, R; Straif, K; Grosse, Y; Secretan, B; El Ghissassi, F; Benbrahim-Tallaa, L; Guha, N; et al. (2009). "A review of human carcinogens--Part B: biological agents" (PDF). The Lancet. 10 (4): 321–322. doi:10.1016/S1470-2045(09)70096-8. PMID 19350698.
  2. ^ a b Machicado, Claudia; Marcos, Luis A. (2016). "Carcinogenesis associated with parasites other than Schistosoma, Opisthorchis and Clonorchis: A systematic review". International Journal of Cancer. 138 (12): 2915–2921. doi:10.1002/ijc.30028. PMID 26840624.
  3. ^ Lalchhandama, K. (2017). "The making of oncology: The tales of false carcinogenic worms". Science Vision. 17 (1): 33–52. doi:10.33493/scivis.17.01.06.
  4. ^ Oettlé, A. G. (1962). "A historical review of past histopathological material at the South African Institute for Medical Research between 1911 and 1927". South African Medical Journal. 36 (31): 628–631.
  5. ^ Clemmesen, J (1978). "Johannes Fibiger. Gongylonema and vitamin A in carcinogenesis". Acta Pathologica et Microbiologica Scandinavica. 270 (Suppl): 1–13. PMID 362817.
  6. ^ Norrby, Erling (2010). Nobel Prizes and Life Sciences. Singapore: World Scientific Publishing Co. p. 115. ISBN 978-9-81-429937-4.
  7. ^ Grove, D.I. (1990). A History of Human Helminthology. Wallingford, Oxon (UK): C.A.B. International. p. 188. ISBN 978-0-85198-689-0.
  8. ^ Barakat, Rashida M.R. (2013). "Epidemiology of Schistosomiasis in Egypt: Travel through Time: Review". Journal of Advanced Research. 4 (5): 425–432. doi:10.1016/j.jare.2012.07.003. PMC 4293883. PMID 25685449.
  9. ^ Berry, A.; Iriart, X.; Fillaux, J.; Magnaval, J.-F. (2017). "Schistosomose urogénitale et cancer [Urinary schistosomiasis and cancer]". Bulletin de la Société de Pathologie Exotique. 110 (1): 68–75. doi:10.1007/s13149-017-0547-4. PMID 28185084. S2CID 195078476.
  10. ^ Anon (2017). "Schistosomiasis". WHO Fact Sheet. WHO Media Centre. Retrieved 12 December 2017.
  11. ^ Antoni, S.; Ferlay, J.; Soerjomataram, I.; Znaor, A.; Jemal, A.; Bray, F. (2017). "Bladder Cancer incidence and mortality: A global overview and recent trends". European Urology. 71 (1): 96–108. doi:10.1016/j.eururo.2016.06.010. PMID 27370177.
  12. ^ Khurana S, Dubey ML, Malla N (April 2005). "Association of parasitic infections and cancers". Indian J Med Microbiol. 23 (2): 74–79. doi:10.1016/S0300-483X(01)00357-2. PMID 15928434.
  13. ^ Leutscher, Peter D. C.; Pedersen, Mette; Raharisolo, Clairette; Jensen, Jørgen Skov; Hoffmann, Steen; Lisse, Ida; Ostrowski, Sisse R.; Reimert, Claus M.; Mauclere, Philippe; Ullum, Henrik (2005). "Increased Prevalence of Leukocytes and Elevated Cytokine Levels in Semen from Schistosoma haematobium–Infected Individuals". The Journal of Infectious Diseases. 191 (10): 1639–1647. doi:10.1086/429334. PMID 15838790.
  14. ^ Mills, E.A.; Machattie, C.; Chadwick, C.R. (1936). "Schistosoma haematobium and its life cycle in Iraq". Transactions of the Royal Society of Tropical Medicine and Hygiene. 30 (3): 317–334. doi:10.1016/S0035-9203(36)90068-8.
  15. ^ Ibrahim, H. (1948). "Bilharziasis and bilharzial cancer of the bladder". Annals of the Royal College of Surgeons of England. 2 (3): 129–141. PMC 1940191. PMID 18908968.
  16. ^ Dao, Thanh Thi Ha; Bui, Tuan Van; Abatih, Emmanuel Nji; Gabriël, Sarah; Nguyen, Thanh Thi Giang; Huynh, Quang Hong; Nguyen, Chuong Van; Dorny, Pierre (2016). "Opisthorchis viverrini infections and associated risk factors in a lowland area of Binh Dinh Province, Central Vietnam". Acta Tropica. 157: 151–157. doi:10.1016/j.actatropica.2016.01.029. PMID 26872984.
  17. ^ King, S.; Scholz, T. Š. (2001). "Trematodes of the family Opisthorchiidae: A minireview". The Korean Journal of Parasitology. 39 (3): 209–221. doi:10.3347/kjp.2001.39.3.209. PMC 2721069. PMID 11590910.
  18. ^ Hitanant, Sawadh; Tan-Ngarm Trong, Danai; Damrongsak, Chiamchitt; Chinapak, Orapan; Boonyapisit, Sasiprapa; Plengvanit, Ukrist; Viranuvatti, Vikit (1987). "Peritoneoscopic findings in 203 patients with Opisthorchis viverrini infection". Gastrointestinal Endoscopy. 33 (1): 18–20. doi:10.1016/S0016-5107(87)71478-3. PMID 2951293.
  19. ^ Pairojkul, C; Shirai, T; Hirohashi, S; Thamavit, W; Bhudhisawat, W; Uttaravicien, T; Itoh, M; Ito, N (1991). "Multistage carcinogenesis of liver-fluke-associated cholangiocarcinoma in Thailand". Princess Takamatsu Symposia. 22: 77–86. PMID 1668894.
  20. ^ Sripa, Banchob; Kaewkes, Sasithorn; Sithithaworn, Paiboon; Mairiang, Eimorn; Laha, Thewarach; Smout, Michael; Pairojkul, Chawalit; Bhudhisawasdi, Vajaraphongsa; et al. (2007). "Liver Fluke Induces Cholangiocarcinoma". PLOS Medicine. 4 (7): e201. doi:10.1371/journal.pmed.0040201. PMC 1913093. PMID 17622191.
  21. ^ Hong, Sung-Tae; Fang, Yueyi (2012). "Clonorchis sinensis and clonorchiasis, an update". Parasitology International. 61 (1): 17–24. doi:10.1016/j.parint.2011.06.007. PMID 21741496.
  22. ^ Tang, Ze-Li; Huang, Yan; Yu, Xin-Bing (6 July 2016). "Current status and perspectives of Clonorchis sinensis and clonorchiasis: epidemiology, pathogenesis, omics, prevention and control". Infectious Diseases of Poverty. 5 (1): 71. doi:10.1186/s40249-016-0166-1. PMC 4933995. PMID 27384714.
  23. ^ Sripa B, Brindley PJ, Mulvenna J, Laha T, Smout MJ, Mairiang E, Bethony JM, Loukas A (2012). "The tumorigenic liver fluke Opisthorchis viverrini--multiple pathways to cancer". Trends in Parasitology. 28 (10): 395–407. doi:10.1016/ PMC 3682777. PMID 22947297.
  24. ^ Pakharukova, Mariya Y.; Mordvinov, Viatcheslav A. (2016). "The liver fluke Opisthorchis felineus: biology, epidemiology and carcinogenic potential". Transactions of the Royal Society of Tropical Medicine and Hygiene. 110 (1): 28–36. doi:10.1093/trstmh/trv085. PMID 26740360.
  25. ^ Fedorova, Olga S.; Kovshirina, Yulia V.; Kovshirina, Anna E.; Fedotova, Marina M.; Deev, Ivan A.; Petrovskiy, Fedor I.; Filimonov, Aleksandr V.; Dmitrieva, Alla I.; et al. (2017). "Opisthorchis felineus infection and cholangiocarcinoma in the Russian Federation: A review of medical statistics". Parasitology International. 66 (4): 365–371. doi:10.1016/j.parint.2016.07.010. PMID 27474689.
  26. ^ Shen, De Fen; Herbort, Carl P; Tuaillon, Nadine; Buggage, Ronald R; Egwuagu, Charles E; Chan, Chi-Chao (2001). "Detection of Toxoplasma Gondii DNA in Primary Intraocular B-Cell Lymphoma". Modern Pathology. 14 (10): 995–999. doi:10.1038/modpathol.3880424. PMID 11598169.
  27. ^ Seo, An Na; Goo, Youn-Kyoung; Chung, Dong-Il; Hong, Yeonchul; Kwon, Ohkyoung; Bae, Han-Ik (2015). "Comorbid Gastric Adenocarcinoma and Gastric and Duodenal Strongyloides stercoralis Infection: A Case Report". The Korean Journal of Parasitology. 53 (1): 95–99. doi:10.3347/kjp.2015.53.1.95. PMC 4384790. PMID 25748714.
  28. ^ Sulżyc-Bielicka, Violetta; Kołodziejczyk, Lidia; Jaczewska, Sylwia; Bielicki, Dariusz; Safranow, Krzysztof; Bielicki, Paweł; Kładny, Józef; Rogowski, Wojciech (2018). Ganti, Apar Kishor (ed.). "Colorectal cancer and Cryptosporidium spp. infection". PLOS ONE. 13 (4): e0195834. Bibcode:2018PLoSO..1395834S. doi:10.1371/journal.pone.0195834. PMC 5908144. PMID 29672572.
  29. ^ a b Benamrouz, S.; Conseil, V.; Creusy, C.; Calderon, E.; Dei-Cas, E.; Certad, G. (2012). "Parasites and malignancies, a review, with emphasis on digestive cancer induced by Cryptosporidium parvum (Alveolata: Apicomplexa)". Parasite. 19 (2): 101–115. doi:10.1051/parasite/2012192101. PMC 3671432. PMID 22348213.
  30. ^ Hayes, Kelly S.; Cliffe, Laura J.; Bancroft, Alison J.; Forman, Simon P.; Thompson, Seona; Booth, Cath; Grencis, Richard K. (2017). "Chronic Trichuris muris infection causes neoplastic change in the intestine and exacerbates tumour formation in APC min/+ mice". PLOS Neglected Tropical Diseases. 11 (6): e0005708. doi:10.1371/journal.pntd.0005708. PMC 5501682. PMID 28650985.
  31. ^ Andrade, R.L.F.S.; Dantas, A.F.M.; Pimentel, L.A.; Galiza, G.J.N.; Carvalho, F.K.L.; Costa, V. M.M.; Riet-Correa, F. (2012). "Platynosomum fastosum-induced cholangiocarcinomas in cats". Veterinary Parasitology. 190 (1–2): 277–280. doi:10.1016/j.vetpar.2012.04.015. PMID 22963714.
  32. ^ Machicado, Claudia; Marcos, Luis A. (2016-06-15). "Carcinogenesis associated with parasites other than Schistosoma, Opisthorchis and Clonorchis: A systematic review: Carcinogenesis associated with parasites". International Journal of Cancer. 138 (12): 2915–2921. doi:10.1002/ijc.30028. PMID 26840624.