Database of Food Borne Human Pathogens
Bacteria, Virus, Fungi, Protozoa, Helminths
Helminths Food Pathogen
Helminths are large, eukaryotic and multicellular organisms. They are commonly known as parasitic worms or intestinal worms, although not all helminths are intestinal parasites. Helminth includes three major groups: cestodes (tapeworms), trematodes (flukes) and nematodes (roundworms). These organisms are microscopic but when they develop into adults can be seen with naked eyes.
Helminths form three main life-cycle stages: eggs, larvae and adults. Adult worms infect definitive hosts (those in which sexual development occurs) whereas larval stages may be free-living or parasitize invertebrate vectors, intermediate or paratenic hosts. Nematodes produce eggs that embryonate in utero or outside the host. The emergent larvae undergo 4 metamorphoses (moults) before they mature as adult male or female worms. Cestode eggs released from gravid segments embryonate to produce 6-hooked embryos (hexacanth oncospheres) which are ingested by intermediate hosts. The oncospheres penetrate host tissues and become metacestodes (encysted larvae). When eaten by definitive hosts, they excyst and form adult tapeworms. Trematodes have more complex life-cycles where ‘larval’ stages undergo asexual amplification in snail intermediate hosts. Eggs hatch to release free-swimming miracidia which actively infect snails and multiply in sac-like sporocysts to produce numerous rediae. These stages mature to cercariae which are released from the snails and either actively infect new definitive hosts or form encysted metacercariae on aquatic vegetation which is eaten by definitive hosts.
Helminths are transmitted to the final host in several ways. The most common infection is through ingestion of contaminated vegetables, drinking water, and raw or undercooked meat. Contaminated food may contain eggs of nematodes such as Ascaris, Enterobius, and Trichuris; cestodes such as Taenia, Hymenolepis, and Echinococcus; and treamtodes such as Fasciola.
The main effects derived from intestinal helminth infection are sickness, tiredness and diminished physical fitness due to the deprivation of essential nutrients caused by the presence of worms in the intestine.
The parasitic nematode Angiostrongylus cantonensis is responsible for the human disease known as angiostrongyliasis or rat lungworm disease, a major cause of eosinophilic meningitis. Neurological damage appears to be caused both by the physical damage caused by the movement of the worms in the brain and by the inflammation caused by the immune reaction to the worms, which seems to be a more intense reaction to the dead than to the live worms.
Pinworm has the broadest geographic range of any helminth, and is the most prevalent helminth infection in the USA and Western Europe. It is commonly found in school-aged children, though it is seen in adults as well.
It is also known as the Human Whipworm. has a narrow anterior esophageal end and shorter and thicker posterior anus. These pinkish-white worms are threaded through the mucosa. They attach to the host through their slender anterior end and feed on tissue secretions instead of blood. Their characteristic eggs are barrel-shaped and brown, and have bipolar protuberances.
Dioctophyme renale, commonly referred to as the "giant kidney worm"  is a parasitic roundworm whose mature form is found in the kidneys of mammals. D. renale is distributed worldwide, but is less common in Africa and Oceania. It affects fish eating mammals, particularly mink  and dogs. Human infestation is rare, but results in destruction of the kidneys. Upon diagnosis through tissue sampling, the only treatment is surgical excision.
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Toxocara canis is gonochoristic, adult worms measure from 9 to 18 cm, are yellow-white in color, and occur in the intestine of the definitive host. In adult dogs, the infection is usually asymptomatic. The adult canis has a round body with spiky cranial and caudal parts, covered by yellow cuticula.
Anisakis is a genus of parasitic nematodes, which have life cycles involving fish and marine mammals. They are infective to humans and cause anisakiasis. People who produce immunoglobulin E in response to this parasite may subsequently have an allergic reaction, including anaphylaxis, after eating fish that have been infected with Anisakis species.
Strongyloides stercoralis is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. Its common name is threadworm. The Strongyloides stercoralis nematode can parasitize humans. The adult parasitic stage lives in tunnels in the mucosa of the small intestine.
Gnathostoma spinigerum is a parasitic nematode that causes gnathostomiasis in humans, As a nematode, Gnathostoma spinigerum has cylindrical, a cuticle layer with three main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals.
T r i c h i n e l l a s p i r a l i s h a s t h e u n i q u e a b i l i t y t o m a k e i t s e l f a t h o m e b y c r e a t i n g a n d h i d i n g i n a n e w t y p e o f c e l l i n t h e h o s t b o d y t h a t i s t h e n u r s e c e l l .
Fasciola hepatica is also known as the common liver fluke or sheep liver fluke. It is a parasitic trematode which infects the livers of various mammals, including humans. It is one of the largest flukes of the world.
Diphyllobothrium is a genus of tapeworm which can cause diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriosis is Diphyllobothrium latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode that infects fish and mammals.
Clonorchis sinensis is also known as Chinese liver fluke, is a human liver fluke. This parasite lives in the liver of humans, and is found mainly in the common bile duct and gall bladder, feeding on bile and causes inflammatory and proliferative alterations.
Fasciolopsis buski is commonly called the giant intestinal fluke, because it is an exceptionally large parasitic fluke, and the largest known to parasitise humans. The fluke differs from most species that parasitise large mammals, in that they inhabit the gut rather than the liver as Fasciola species do. Fasciolopsis buski generally occupies the upper region of the small intestine, but in heavy infestations can also be found in the stomach and lower regions of the intestine. Fasciolopsis buski is the cause of the pathological condition fasciolopsiasis
Paragonimus westermani is the major species of lung fluke that infects humans, causing paragonimiasis. The species sometimes is called the Japanese Lung fluke or Oriental Lung fluke. Human infections are most common in eastern Asia and in South America. Paragonimus westermani was discovered when two Bengal tigers died of paragonimiasis in zoos in Europe in 1878. Several years later Infections in humans were recognised in Formosa.
Schistosoma mansoni is a significant parasite of humans, a trematode that is one of the major agents of the disease schistosomiasis which is one type of helminthiasis, a neglected tropical disease. The schistosomiasis caused by Schistosoma mansoni is intestinal schistosomiasis.
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 9 carnivores, 16 rodents, one primate (Human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Schistosoma japonicum is the only human blood fluke that occurs in China and Philippines.
Echinococcus multilocularis is a cyclophyllid tapeworm. produces the disease known as echinococcosis in certain terrestrial mammals, including wolves, foxes, jackals, coyotes, domestic dogs and humans. Unlike E. granulosus, E. multilocularis produces many small cysts (also referred to as locules) that spread throughout the internal organs of the infected animal. Ingestion of these cysts, usually by a canid eating an infected rodent, results in a heavy infestation of tapeworms.
Taenia spp. are long, segmented, parasitic tapeworms (family Taeniidae, subclass
Cestoda). These parasites have an indirect life cycle, cycling between a definitive and
an intermediate host. they are zoonotic, with humans serving
as the definitive host, the intermediate host, or both. Non
-zoonotic species of Taenia also exist.