Types of parasitic helminths
Of all the known helminth species, the most important helminths with respect to understanding their transmission pathways, their control, inactivation and enumeration in samples of human excreta from dried feces, faecal sludge, wastewater, and sewage sludge are:
soil-transmitted helminths, including Ascaris lumbricoides (the most common worldwide), Trichuris trichiura, Necator americanus, Strongyloides stercoralis and Ancylostoma duodenale
Hymenolepis nana
Taenia saginata
Enterobius
Fasciola hepatica
Schistosoma mansoni
Toxocara canis
Toxocara catiHelminthiases are classified as follows (the disease names end with "-sis" and the causative worms are in brackets):

Roundworm infection (nematodiasis)
Filariasis (Wuchereria bancrofti, Brugia malayi infection)
Onchocerciasis (Onchocerca volvulus infection)
Soil-transmitted helminthiasis – this includes ascariasis (Ascaris lumbricoides infection), trichuriasis (Trichuris infection), and hookworm infection (includes necatoriasis and Ancylostoma duodenale infection)
Trichostrongyliasis (Trichostrongylus spp. infection)
Dracunculiasis (guinea worm infection)
Baylisascaris (raccoon roundworm, may be transmitted to pets, livestock, and humans)

Tapeworm infection (cestodiasis)
Echinococcosis (Echinococcus infection)
Hymenolepiasis (Hymenolepis infection)
Taeniasis/cysticercosis (Taenia infection)
Coenurosis (T. multiceps, T. serialis, T. glomerata, and T. brauni infection)

Trematode infection (trematodiasis)
Amphistomiasis (amphistomes infection)
Clonorchiasis (Clonorchis sinensis infection)
Fascioliasis (Fasciola infection)
Fasciolopsiasis (Fasciolopsis buski infection)
Opisthorchiasis (Opisthorchis infection)
Paragonimiasis (Paragonimus infection)
Schistosomiasis/bilharziasis (Schistosoma infection)

Acanthocephala infection
Moniliformis infection

Transmission
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 trematodes such as Fasciola. Raw or undercooked meats are the major sources of Taenia (pork, beef and venison), Trichinella (pork and bear), Diphyllobothrium (fish), Clonorchis (fish), and Paragonimus (crustaceans).
Epidemiology
Areas with the highest prevalence of helminthiasis are tropical and subtropical areas including sub-Saharan Africa, central and east Asia, and the Americas. Neglected tropical diseases
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

Prevalence
The soil-transmitted helminths (A. lumbricoides, T. trichiura, N. americanus, A. duodenale), schistosomes, and filarial worms collectively infect more than a quarter of the human population worldwide at any one time, far surpassing HIV and malaria together. Schistosomiasis is the second most prevalent parasitic disease of humans after malaria.In 2014–15, the WHO estimated that approximately 2 billion people were infected with soil-transmitted helminthiases, 249 million with schistosomiasis, 56 million people with food-borne trematodiasis, 120 million with lymphatic filariasis, 37 million people with onchocerciasis, and 1 million people with echinococcosis. Another source estimated a much higher figure of 3.5 billion infected with one or more soil-transmitted helminths.In 2014, only 148 people were reported to have dracunculiasis because of a successful eradication campaign for that particular helminth, which is easier to eradicate than other helminths as it is transmitted only by drinking contaminated water.Because of their high mobility and lower standards of hygiene, school-age children are particularly vulnerable to helminthiasis. Most children from developing nations will have at least one infestation.