Some types of helminthiases are classified as neglected tropical diseases. They include:

- Soil-transmitted helminthiases

- Roundworm infections such as lymphatic filariasis, dracunculiasis, and onchocerciasis

- Trematode infections, such as schistosomiasis, and food-borne trematodiases, including fascioliasis, clonorchiasis, opisthorchiasis, and paragonimiasis

- Tapeworm infections such as cysticercosis, taeniasis, and echinococcosis

Areas with the highest prevalence of helminthiasis are tropical and subtropical areas including sub-Saharan Africa, central and east Asia, and the Americas.

The fundamental prevention strategy is hygiene and sanitation. Secondary measures include stricter meat-inspection standards, livestock confinement, health education, safe meat preparation, mass drug therapy, and identifying and treating human and pig carriers. Moreover, a high level of sanitation and prevention of human faecal contamination of pig feeds also plays a major role in prevention. Infection can be prevented with proper disposal of human faeces around pigs, cooking meat thoroughly and/or freezing the meat at −10 °C for 5 days. For human cysticercosis, dirty hands are attributed to be the primary cause, and especially common among food handlers.

Proper cooking of meat is an effective prevention. For example, cooking (56 °C for 5 minutes) of beef viscera destroys cysticerci. Refrigeration, freezing (−10 °C for 9 days) or long periods of salting is also lethal to cysticerci. Inspection of beef and proper disposal of human excreta are also important measures.

Avoid ingestion of raw freshwater fish. Adequate cooking or freezing of freshwater fish will kill the encysted fish tapeworm larvae. Also, because human feces is an important mechanism for spreading eggs, proper disposal of sewage can cut down on infection of fish and thus of humans.

Most occurrences are found in areas that lack adequate sanitation and include Southeast Asia, West Africa, and East Africa.

"H. nana" lodges itself in the intestines and absorbs nutrients from the intestinal lumen. In human adults, the tapeworm is more of a nuisance than a health problem, but in small children, many "H. nana" worms can be dangerous. Usually, the larvae of this tapeworm cause the most problem in children; they burrow into the walls of the intestine, and if enough tapeworms are present in the child, severe damage can be inflicted. This is done by absorbing all the nutrients from the food the child eats. Usually, a single tapeworm will not cause health issues. "H. nana" usually will not cause deaths unless in extreme circumstances and usually in young children or in people who have weakened immune systems. In some parts of the world, individuals who are heavily infected are a result of internal autoinfection.

The definitive hosts for these "Taenia" species are canids. The adult tapeworms live in the intestines of animals like dogs, foxes, and coyotes. Intermediate hosts such as rabbits, goats, sheep, horses, cattle and sometimes humans get the disease by inadvertently ingesting tapeworm eggs (gravid proglottids) that have been passed in the feces of an infected canid. This can happen from ingesting food, water or soil that has been contaminated by dog feces. The disease cannot be transmitted from one intermediate host to another, but it is still not a good idea to eat meat that presents with cystic nodules from coenurosis.

The total global infection is estimated to be between 40 and 60 million people. In the US, the incidence of infection is low, but 25% of cattle sold are still infected.

Good hygiene, public health and sanitation programs, and elimination of infected rats help to prevent the spread of hymenolepiasis. Preventing fecal contamination of food and water in institutions and crowded areas is of primary importance. General sanitation and rodent and insect control (especially control of fleas and grain insects) are also essential for prevention of "H. nana" infection.

Tapeworm infection can also be caused by eating raw or undercooked meat from an animal that has the larvae of the tapeworm, grouped in cysts (coenuri) in its muscle tissue. Once ingested, the larvae then develop into adult tapeworms in the intestines.

Adult tapeworms can measure up to long and can survive as long as 25 years. Some tapeworms attach themselves to the walls of the intestine, where they cause irritation or mild inflammation, while others may pass through to the stool and exit the body.

Unlike other tapeworms, the dwarf tapeworm can complete its entire life cycle — egg to larva to adult tapeworm — in one host. This is the most common tapeworm infection in the world and can be transmitted between humans.

Even while being treated for certain tapeworm infections, reinfection can result from ingesting tapeworm eggs shed by the adult worm into

the stool, as a result of insufficient personal hygiene.

Sparganosis is endemic or potentially endemic in 48 countries, and although rare, cases have been described in Asia, Africa, Australia, South America, and the United States. The majority of cases occur in Southeast Asia and Eastern Africa. Ocular sparganosis is especially prevalent in China and Vietnam. The highest numbers of cases occur in Korea and Japan. As of 2003, only seven cases of sparganosis had ever been described in Europe.

In Latin America, an estimated 75 million persons live in endemic areas and 400,000 people have symptomatic disease. Some studies suggest that the prevalence of cysticercosis in Mexico is between 3.1 and 3.9 percent. Other studies have found the seroprevalence in areas of Guatemala, Bolivia, and Peru as high as 20 percent in humans, and 37 percent in pigs. In Ethiopia, Kenya and the Democratic Republic of Congo around 10% of the population is infected, in Madagascar 16%. The distribution of cysticercosis coincides with the distribution of "T. solium". Cysticercosis is the most common cause of symptomatic epilepsy worldwide.

Prevalence rates in the United States have shown immigrants from Mexico, Central and South America, and Southeast Asia account for most of the domestic cases of cysticercosis.

In 1990 and 1991, four unrelated members of an Orthodox Jewish community in New York City developed recurrent seizures and brain lesions, which were found to have been caused by "T. solium". All of the families had housekeepers from Latin American countries and were suspected to be source of the infections.

This disease is very rare in humans and only about 100 cases have ever been recorded. It is a more common problem in sheep and cattle and can be problematic for farmers in endemic regions of the world. Most human cases occur in developing countries such as India and Sub Saharan Africa where the dog population is not controlled or treated for tapeworm, and in areas lacking proper sanitation. "T. multiceps" has been reported in regions all over the world (both human and animal infections) and is the most common coenurosis causing species. "T. serialis" has been seen in North America, Europe and Africa, and "T. brauni" and "T. glomerata" have only been seen in Africa. This disease still occurs, even in developed countries. Some of the most recent reported cases occurred in France, Italy, Israel, Canada and the United States. Some experts suspect under reporting of this disease, especially in impoverished and developing countries where reporting technologies are more difficult to obtain. The global prevalence might be much higher than present data suggest.

"Taenia solium" is found worldwide, but is more common where pork is part of the diet. Cysticercosis is most prevalent where humans live in close contact with pigs. Therefore, high prevalences are reported in Mexico, Latin America, West Africa, Russia, India, Pakistan, North-East China, and Southeast Asia. In Europe it is most widespread among Slavic people.

The frequency has decreased in developed countries owing to stricter meat inspection, better hygiene and better sanitation of facilities.

Because sparganosis is a rare infection, public health strategies have not made its prevention a priority. Public health strategies focusing on providing basic access to clean water may help to reduce future sparganosis infections. In their retrospective study of 25 cases of cerebral sparganosis, Song et al. found that 12 patients (48%) had eaten raw or uncooked frog or snake that was infected with sparganum, 5 patients (20%) had applied an animal's flesh as a poultice to an open wound, 4 patients had drunk contaminated water, and the cause of infection was not known for 4 patients. As a result of these findings, Song et al. conclude that health education about sparganosis and the importance of food sanitation should be implemented in all rural endemic areas. It has been recommended that water consumed in endemic areas should be boiled or treated to prevent ingestion of Cyclops or Spirometra larvae. Especially in areas where ponds or ditches provide potential habitats for infected copepods, public health strategies should include education campaigns about how to identify drinking water that could potentially be infected. Strategies should warn people against ingesting the raw flesh of the intermediate hosts, such as snakes and frogs, and against using them as poultices.

There is a negative association between an infection with the parasite "T. gondii" and multiple sclerosis, therefore, researchers have concluded that toxoplasmosis infection could be considered a protective factor.

Deworming treatments in infected children may have some nutritional benefit, as worms are often partially responsible for malnutrition. However, in areas where these infections are common, there is strong evidence that mass deworming campaigns do not have a positive effect on children's average nutritional status, levels of blood haemoglobin, cognitive abilities, performance at school or survival. To achieve health gains in the longer term, improvements in sanitation and hygiene behaviours are also required, together with deworming treatments.

There are 21.4 million people infected with trachoma, of whom 2.2 million are partially blind and 1.2 million are blind. It is found in Africa, Asia, Central and South America, Middle East, and Australia. The disease disproportionately affects women and children. The mortality risk is very low, although multiple re-infections eventually lead to blindness. The symptoms are internally scarred eyelids, followed by eyelids turning inward. Trachoma is caused by a micro-organism that spreads through eye discharges (on hands, cloth, etc.) and by "eye-seeking flies".

It is treated with antibiotics. The only known prevention method is interpersonal hygiene.

Diphyllobothriasis is the infection caused by tapeworms of the Diphyllobothrium genus, commonly "Diphyllobothrium latum" and "Diphyllobothrium nihonkaiense".

In most of the current studies where positive correlations have been found between "T. gondii" antibody titers and certain behavioral traits or neurological disorders, "T. gondii" seropositivity tests are conducted after the onset of the examined disease or behavioral trait; that is, it is often unclear whether infection with the parasite increases the chances of having a certain trait or disorder, or if having a certain trait or disorder increases the chances of becoming infected with the parasite. Groups of individuals with certain behavioral traits or neurological disorders may share certain behavioral tendencies that increase the likelihood of exposure to and infection with "T. gondii"; as a result, it is difficult to confirm causal relationships between "T. gondii" infections and associated neurological disorders or behavioral traits. Provided there is in fact a causal link between "T. gondii" and schizophrenia, studies have yet to determine why some individuals with latent toxoplasmosis develop schizophrenia while others do not, however, some plausible explanations include differing genetic susceptibility, parasite strain differences, and differences in the route of the acquired "T. gondii" infection.

Helminths are extremely successful parasites capable of establishing long-lasting infections within a host. During this time, helminths compete with the host organism's cells for nutrient resources and thus possess the potential to cause harm. However, the number of organisms hosted by individuals undergoing helminthic therapy is very small and any side effects are typically only encountered in the first three months of infection. In the long term, the vast majority of clinically infected individuals are asymptomatic, with no significant nutrient loss. In fact, nutrient uptake can be enhanced in some subjects who are hosting a small number of helminths. If the side effects from helminthic therapy were to become unmanageable, they can be alleviated by the use of anthelminthic medications.[1][7][8] The most common clinical symptoms which may be encountered while undergoing helminthic therapy can include:

- Fatigue

- Gastrointestinal discomfort

- Anemia

- Fever

- Abdominal pain

- Weight loss

- Anorexia

- Diarrhea

- General malaise

The capture, transportation and culture of bait fish can spread damaging organisms between ecosystems, endangering them. In 2007, several American states, including Michigan, enacted regulations designed to slow the spread of fish diseases, including viral hemorrhagic septicemia, by bait fish. Because of the risk of transmitting "Myxobolus cerebralis" (whirling disease), trout and salmon should not be used as bait. Anglers may increase the possibility of contamination by emptying bait buckets into fishing venues and collecting or using bait improperly. The transportation of fish from one location to another can break the law and cause the introduction of fish and parasites alien to the ecosystem.

Although coenurosis is more commonly associated with domestic animals, it has also been documented in wildlife. It has been found in mountain ungulates in the French Alps. It is believed that the ungulates are being contaminated by infected sheepdogs. Understanding how this disease is transmitted from sheepdogs to wild animals is important in managing the spread of this potentially dangerous zoonotic disease. A potential management strategy would be for farmers to properly dispose of carcasses that they find on their land. In wild gelada monkeys in Ethiopia, coenurosis was found to affect the fitness of these primates. Mortality increased and fertility was inhibited. The disease has also been documented in wild sheep and other ruminants and rarely documented in rodents, horses, and cats. Very few cases have been identified but this could be due to limited research on wild coenurosis. Animals infected with this disease tend to hide or take cover from predators and therefore may not be seen by humans. However, coenurosis has been known to increase mortality and decrease fertility in wild animal populations.

Coenurosis (a.k.a. Caenurosis and Coenuriasis, gid or sturdy in the vernacular) is a parasitic infection that develops in the intermediate hosts of some tapeworm species ("Taenia multiceps", "T. serialis, T. brauni," or "T. glomerata") and are caused by the coenurus, the larval stage of these worms. This disease occurs mainly in sheep and other ungulates, but occasionally can occur in humans too by accidental ingestion of worms' eggs.

Adult worms of these species develop in the small intesine of the definitive hosts (dogs, foxes, and other canids), causing a disease from the group of taeniasis. Humans cannot be definitive hosts for these species of tapeworms.

Though not a health concern in thoroughly cooked fish, parasites are a concern when human consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. The popularity of such raw fish dishes makes it important for consumers to be aware of this risk. Raw fish should be frozen to an internal temperature of −20 °C (−4 °F) for at least 7 days to kill parasites. It is important to be aware that home freezers may not be cold enough to kill parasites.

Traditionally, fish that live all or part of their lives in fresh water were considered unsuitable for sashimi due to the possibility of parasites (see Sashimi article). Parasitic infections from freshwater fish are a serious problem in some parts of the world, particularly Southeast Asia. Fish that spend part of their life cycle in salt water, like salmon, can also be a problem. A study in Seattle, Washington showed that 100% of wild salmon had roundworm larvae capable of infecting people. In the same study farm raised salmon did not have any roundworm larvae.

Parasite infection by raw fish is rare in the developed world (fewer than 40 cases per year in the U.S.), and involves mainly three kinds of parasites: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). Infection by the fish tapeworm "Diphyllobothrium latum" is seen in countries where people eat raw or undercooked fish, such as some countries in Asia, Eastern Europe, Scandinavia, Africa, and North and South America. Infection risk of anisakis is particularly higher in fishes which may live in a river such as salmon ("shake") in Salmonidae, mackerel ("saba"). Such parasite infections can generally be avoided by boiling, burning, preserving in salt or vinegar, or freezing overnight. Even Japanese people never eat raw salmon or ikura (salmon roe), and even if they seem raw, these foods are not raw but are frozen overnight to prevent infections from parasites, particularly anisakis.

Below are some life cycles of fish parasites that can infect humans: