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.

Latest estimates indicate that the total annual death toll which is directly attributable is as high as 135,000. The death toll due to the malnutrition link is likely to be much higher.

The World Health Organization estimates that globally more than 1.5 billion people (24% of the total population) have a soil-transmitted helminth infection. Over 270 million preschool-age children and over 600 million school-age children live in areas where these parasites are intensively transmitted, and are in need of treatment and preventive interventions. Latest estimates indicate that more than 880 million children are in need of treatment from STH infections.

By type of parasitic worm the breakdown is:

- approximately 807-1,121 million with ascaris

- approximately 576-740 million with hookworm

- approximately 604-795 million with whipworm

Mammals can get parasites from contaminated food or water, bug bites, or sexual contact. Ingestion of contaminated water can produce Giardia infections.

Parasites normally enter the body through the skin or mouth. Close contact with pets can lead to parasite infestation as dogs and cats are host to many parasites.

Other risks that can lead people to acquire parasites are walking barefeet, inadequate disposal of feces, lack of hygiene, close contact with someone carrying specific parasites, and eating undercooked foods, unwashed fruits and vegetables or foods from contaminated regions.

Parasites can also be transferred to their host by the bite of an insect vector, i.e. mosquito, bed bug, fleas.

Infection of "T. trichiura" is most frequent in areas with tropical weather and poor sanitation practices. Trichuriasis occurs frequently in areas in which untreated human feces is used as fertilizer or where open defecation takes place. Trichuriasis infection prevalence is 50 to 80 percent in some regions of Asia (noted especially in China and Korea) and also occurs in rural areas of the southeastern United States.

Good hygiene is necessary to avoid reinfection. The Rockefeller Foundation's hookworm campaign in Mexico in the 1920s was extremely effective at eliminating hookworm from humans with the use of anthelmintics. However, preventative measures were not adequately introduced to the people that were treated. Therefore, the rate of reinfection was extremely high and the project evaluated through any sort of scientific method was a marked failure. More education was needed to inform the people of the importance of wearing shoes, using latrines (better access to sanitation), and good hygiene.

Intestinal parasite prevention methods are not isolated to specific geographical areas; however, many of the research-based interventions have primarily taken place in underdeveloped countries and regions, where sanitation is a large concern for spreading disease.Current best practice behaviors that prevent intestinal parasites include: using proper hand washing practices, using correctly-built latrines with ample ventilation, having a piped water source, and wearing shoes. Currently, in some parts of Ethiopia where disease prevalence is high, up to 80% of people in a population lack access to washing facilities. While is this high, 93% did have access to a latrine, but only 29.2% of those latrines had proper construction to decrease parasitic infections.Behavioral interventions have focused on promoting washing, sometimes with soap, in context of education at schools and child care facilities. In recent studies, the best interventions follow a multidisciplinary approach by:

- Increasing environmental sanitation to promote hand washing and shoe wearing habits

- Educating children at young ages at school and at home

Specific evidence-based interventions that may lower disease prevalence include:

- Interventions at schools, focusing on the construction of pit latrines (ventilated and improved), providing clean drinking water and educating the students about hygiene

- The SAFE (surgery, antibiotics, facial cleanliness, environmental sanitation) strategy to address trachoma, primarily the facial cleanliness and the environmental sanitation components

- Hand-washing with soap at critical times and nail clipping to decrease reinfection rates, although further research is needed to develop and implement similar interventions at scale

- Programs combining anthelmintic drug administration with interventions to increase environmental sanitation (such as decreasing fecal contamination)

The prevalence of intestinal parasites is the highest among children that are living in the poorest communities in developing nations. The most common causes of intestinal parasites are through consumption of contaminated water, infected soil, inadequate sanitation and hygiene, and improper hygiene. Specifically, lack of access to facilities for safe disposal of human waste can result in intestinal parasites and disease. Poor hygiene habits or lacking available hygiene resources, such as hand washing facilities, also negatively impact rates of disease. Parasitic contamination can also occur from eating raw vegetables and fruits, soil-eating behavior, and lack of available safe water.

Parasites can get into the intestine by going through the mouth from uncooked or unwashed food, contaminated water or hands, or by skin contact with larva infected soil; they can also be transferred by the sexual act of anilingus in some cases.

When the organisms are swallowed, they move into the intestine, where they can reproduce and cause symptoms. Children are particularly susceptible if they are not thoroughly cleaned after coming into contact with infected soil that is present in environments that they may frequently visit such as sandboxes and school playgrounds. People in developing countries are also at particular risk due to drinking water from sources that may be contaminated with parasites that colonize the gastrointestinal tract.

Infection can be avoided by proper disposal of human feces, avoiding fecal contamination of food, not eating dirt, and avoiding crops fertilized with untreated human feces. Simple and effective proper hygiene such as washing hands and food is recommended for control.

Improved facilities for feces disposal have decreased the incidence of whipworm. Handwashing before food handling, and avoiding ingestion of soil by thorough washing of food that may have been contaminated with egg-containing soil are other preventive measures. Improvement of sanitation systems, as well as improved facilities for feces disposal, have helped to limit defecation onto soil and contain potentially infectious feces from bodily contact.

A study in a Brazillian urban centre demonstrated a significant reduction in prevalence and incidence of soil-transmitted helminthiasis, including trichuriasis, following implementation of a citywide sanitation program. A 33% reduction in the prevalence of trichuriasis and a 26% reduction in the incidence of trichuriasis was found in a study performed on 890 children ages 7–14 years old within 24 different sentinel areas chosen to represent the varied environmental conditions throughout the city of Salvador, Bahia, Brazil. Control of soil fertilizers has helped eliminate the potential for contact of human fecal matter and fertilizer in the soil.

Control of this parasite should be directed against reducing the level of

environmental contamination. Treatment of heavily infected individuals is one

way to reduce the source of contamination (one study has estimated that 60% of

the total worm burden resides in less than 10% of the population). Other

obvious methods are to improve access to sanitation, e.g. toilets, but also

convincing people to maintaining them in a clean, functional state, thereby making

them conducive to use.

Roughly 0.8-1.3 billion individuals are infected with this intestinal worm, primarily in Africa and Asia. About 120 to 220 million of these cases are symptomatic.

As of 2010 Ascariasis caused about 2,700 directly attributable deaths, down from 3,400 in 1990. The indirectly attributable deaths due to the malnutrition link may be much higher.

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.

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.

"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.

Education, improved sanitation, and controlled disposal of human feces are critical for prevention. Nonetheless, wearing shoes in endemic areas helps reduce the prevalence of infection.

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.

Necatoriasis is caused by "N. americanus". "N. americanus" can be divided into two areas – larvae and adult stage. The third stage larvae are guided to human skin by following thermal gradients. Typically, the larvae enter through the hands and feet following contact with contaminated soil. A papular, pruritic, itchy rash will develop around the site of entry into the human host. This is also known as "ground itch". Generally, migration through the lungs is asymptomatic but a mild cough and pharyngeal irritation may occur during larval migration in the airways. Once larvae break through the alveoli and are swallowed, they enter the gastrointestinal tract and attach to the intestinal mucosa where they mature into adult worms. The hookworms attach to the mucosal lining using their cutting plates which allows them to penetrate blood vessels and feed on the host's blood supply. Each worm consumes 30μl of blood per day. The major issue results from this intestinal blood loss which can lead to iron-deficiency anemia in moderate to heavy infections. Other common symptoms include epigastric pain and tenderness, nausea, exertional dyspnea, pain in lower extremities and in joints, sternal pain, headache, fatigue, and impotence. Death is rare in humans.

The clinical aspects of ancylostomiasis were first described in Europe as "miner's anaemia". During the construction of the Gotthard Tunnel in Switzerland (1871–1881), a large number of miners suffered from severe anaemia of unknown cause. Medical investigations let to the understanding that it was caused by "Ancylostoma duodenale" (favoured by high temperatures and humidity) and to "major advances in parasitology, by way of research into the aetiology, epidemiology and treatment of ancylostomiasis".

Hookworms still account for high proportion of debilitating disease in the tropics and 50-60,000 deaths per year can be attributed to this disease.

Parasitic worms have been used as a medical treatment for various diseases, particularly those involving an overactive immune response. As humans have evolved with parasitic worms, proponents argue they are needed for a healthy immune system. Scientists are looking for a connection between the prevention and control of parasitic worms and the increase in allergies such as hay-fever in developed countries. Parasitic worms may be able to damp down the immune system of their host, making it easier for them to live in the intestine without coming under attack. This may be one mechanism for their proposed medicinal effect.

One study suggests a link between the rising rates of metabolic syndrome in the developed worlds and the largely successful efforts of Westerners to eliminate intestinal parasites. The work suggests eosinophils (a type of white blood cell) in fat tissue play an important role in preventing insulin resistance by secreting interleukin 4, which in turn switches macrophages into "alternative activation". Alternatively-activated macrophages are important to maintaining glucose homeostasis (i.e., blood sugar regulation). Helminth infection causes an increase in eosinophils. In the study, the authors fed rodents a high-fat diet to induce metabolic syndrome, and then injected them with helminths. Helminth infestation improved the rodents' metabolism. The authors concluded:

Although sparse in blood of persons in developed countries, eosinophils are often elevated in individuals in rural developing countries where intestinal parasitism is prevalent and metabolic syndrome rare. We speculate that eosinophils may have evolved to optimize metabolic homeostasis during chronic infections by ubiquitous intestinal parasites….

Parasitic infections can usually be treated with antiparasitic drugs.

Albendazole and mebendazole have been the treatments administered to entire populations to control hookworm infection. However, it is a costly option and both children and adults become reinfected within a few months after deparasitation occurs raising concerns because the treatment has to repeatedly be administered and drug resistance may occur.

Another medication administered to kill worm infections has been pyrantel pamoate. For some parasitic diseases, there is no treatment and, in the case of serious symptoms, medication intended to kill the parasite is administered, whereas, in other cases, symptom relief options are used. Recent papers have also proposed the use of viruses to treat infections caused by protozoa.

The most common medications used to treat coccidian infections are in the sulfonamide antibiotic family.

Depending on the pathogen and the condition of the animal, untreated coccidiosis may clear of its own accord, or become severe and damaging, and sometimes cause death.

Coccidiosis is a significant disease for chickens, especially affecting the young chicks. It can be fatal or leave the bird with compromised digestion. There are chick feed mixes that contain a coccidiostat to manage exposure levels and control disease. In an outbreak, coccidiocidal medications are given. Examples are toltrazuril (Baycox) or amprolium. After multiple infections, surviving chickens become resistant to the coccidia.

Helminths (), also commonly known as parasitic worms, are large multicellular organisms, which can generally be seen with the naked eye when they are mature. They are often referred to as intestinal worms even though not all helminths reside in the intestines. For example, schistosomes are not intestinal worms, but rather reside in blood vessels. The word helminth comes from Greek "hélmins", a kind of worm.

There is no consensus on the taxonomy of helminths. It is simply a commonly used term to describe certain worms with some similarities. These are flatworms (platyhelminthes), namely cestodes (tapeworms) and trematodes (flukes), and roundworms or nemathelminths (nematodes) – both of these are parasitic worm types – and the annelida, which are not parasitic or at the most ectoparasites like the leeches.

Helminths are worm-like organisms living in and feeding on living hosts. They receive nourishment and protection while disrupting their hosts' nutrient absorption. This can cause weakness and disease of the host. Those helminths that live inside the digestive tract are called intestinal parasites. They can live inside humans and other animals. In their adult form, helminths cannot multiply in humans. Helminths are able to survive in their mammalian hosts for many years due to their ability to manipulate the immune response by secreting immunomodulatory products. All helminths produce eggs (also called ova) for reproduction. These eggs have a strong shell that protects them against a range of environmental conditions. The eggs can therefore survive in the environment, outside their hosts, for many months or years.

Many, but not all, of the worms referred to as helminths belong to the group of intestinal parasites. An infection by a helminth is known as helminthiasis, helminth infection or intestinal worm infection. There is a naming convention which applies to all helminths: the ending "-asis" (or in veterinary science: "-osis") is added at the end of the name of the worm to denote the infection with that particular worm. For example, "Ascaris" is the name of a type of helminth, and ascariasis is the name of the infectious disease caused by that helminth.

Because of Eustrongylides species’ complex life cycle with various host species, preventing infection and controlling outbreaks is difficult. Outbreaks of this disease are closely linked to agricultural runoff and urban development Eutrophication of water bodies supports high population levels of oligochaete worms, which causes increased numbers of infected fish that eat the worms, and then the birds who eat the fish.

One way to prevent Eustrongylidosis is to control oligochaete populations. Outbreaks of this parasite are closely linked to high numbers of oligochaete worms in the area’s waterways. This is because the worms are essential for Eustrongylides species to reproduce. Oligochaete populations can be controlled by monitoring nutrient levels in the water, because high nutrient levels support oligochaete populations. They can also be controlled by decreasing the level of oxygen in the water. Encouraging responsible farming practices in order to reduce chemical run-off will help prevent this disease from occurring.

Managers need to be diligent in catching the symptoms of the parasite before it can become an outbreak. Once an outbreak of Eustrongylidosis has occurred, there is little that ecosystem managers can do to stop the spread in oligochaetes, fish and birds. Traditional anthelminthics (dewormers) are not effective in fish because they kill parasites that live inside the gastrointestinal tract, whereas Eustrongylides species live outside the stomach in the body cavity. The parasites can only be removed from fish surgically, which is not feasible. In order to completely stop the Eustrongylides life cycle in fish, all fish in an affected area must be culled.

Surgical removal of the parasite from wading birds is a viable option, but this would also not be feasible for a large number of birds, and it would not stop the cycle of infection.