Wound myiasis occurs when fly larvae infest open wounds. It has been a serious complication of war wounds in tropical areas, and is sometimes seen in neglected wounds in most parts of the world. Predisposing factors include poor socioeconomic conditions, extremes of age, neglect, mental disability, psychiatric illness, alcoholism, diabetes, and vascular occlusive disease.

About 14 million people, mainly children, are treated annually for head lice in the United States alone. Only a small proportion of those treated, however, may have objective evidence of an extant infestation. High levels of louse infestations have also been reported from all over the world including Denmark, Sweden, U.K., France and Australia.

Normally head lice infest a new host only by close contact between individuals, making social contacts among children and parent child interactions more likely routes of infestation than shared combs, brushes, towels, clothing, beds or closets. Head-to-head contact is by far the most common route of lice transmission.

The United Kingdom's National Health Service, and many American health agencies, report that lice "prefer" clean hair, because it's easier to attach eggs and to cling to the strands.

Head lice ("Pediculus humanus capitis") are not known to be vectors of diseases, unlike body lice ("Pediculus humanus humanus"), which are known vectors of epidemic or louse-borne typhus ("Rickettsia prowazekii"), trench fever ("Rochalimaea quintana") and louse-borne relapsing fever ("Borrelia recurrentis").

Myiasis of the human eye or ophthalmomyiasis can be caused by "Hypoderma tarandi", a parasitic botfly of caribou. It is known to lead to uveitis, glaucoma, and retinal detachment.

Human ophthalmomyiasis, both external and internal, has been caused by the larvae of the botfly.

By one author's count, 257 human cases of "Thelazia callipaeda" had been reported worldwide by the year 2000, though thelaziasis is still considered to be a rare disease.

Various livestock and wildlife surveys suggest that thelaziasis is quite common among animals.

- A slaughterhouse survey in Canada found that about one-third (32%) of cattle over an 8-month period were infested with eyeworms.

- A survey of horses in Kentucky revealed a 42% rate of infestation with "Thelazia lacrymalis".

- In Wyoming and Utah, a survey of hunter-harvested mule deer found 15% to be infested by "Thelazia californiensis".

- A survey of various sites in Italy found 23-60% of dogs, 5% of foxes and 4 out of 4 cats to be infested with "Thelazia callipaeda".

This condition, is caused by body louse ("Pediculus humanus humanus", sometimes called "Pediculus humanus corporis") is a louse which infests humans and is adapted to lay eggs in clothing, rather than at the base of hairs, and is thus of recent evolutionary origin. Pediculosis is a more serious threat due to possible contagion of diseases such as typhus. Epidemiology and treatment of human body lice is described in the article on body lice.

Metagonimiasis infections are endemic or potentially endemic in 19 countries including Japan, Korea, China, Taiwan, the Balkans, Spain, Indonesia, the Philippines and Russia. Human infections outside endemic areas may result from ingesting pickled fish or sushi made from fish imported from endemic areas.

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.

Bed bug bites are caused by bed bugs primarily of two species "Cimex lectularius" (the common bed bug) and "Cimex hemipterus". Infestation is rarely due to a lack of hygiene. These insects feed exclusively on blood and may survive a year without eating. They are attracted by body warmth and carbon dioxide. Transfer to new places is usually in the personal effects of the human they feed upon.

Dwellings can become infested with bed bugs in a variety of ways, such as:

- Bugs and eggs inadvertently brought in from other infested dwellings on a visiting person's clothing or luggage;

- Infested items (such as furniture especially beds or couches, clothing, or backpacks) brought in a home or business;

- Nearby dwellings or infested items, if easy routes are available for travel, e.g. through ducts or false ceilings;

- Wild animals (such as bats or birds) that may also harbour bed bugs or related species such as the bat bug;

- People visiting an infested area (e.g. dwelling, means of transport, entertainment venue, or lodging) and carrying the bugs to another area on their clothing, luggage, or bodies. Bedbugs are increasingly found in air travel.

- Though bed bugs will feed on pets, they do not live or travel on the skin of their hosts, and pets are not believed a factor in their spread.

Several public health prevention strategies could help lower the rates of metagonimiasis. One is to control the intermediate host (snails). This can be done through use of molluscidals. Another is to use education to ensure all people, especially in areas were the disease regularly occurs, fully cook all fish. This could potentially be problematic and not as effective as hoped as many of the people affected by metagonimiasis eat raw or pickled fish as part of a traditional, long-seated dietary practice. Additionally, implementing more sanitary water conditions would reduce the continual reintroduction of eggs to water sources, thus restarting the lifecycle. Complete control of metagonimiasis presents several potential problems because it does have several reservoir hosts, thus eradication is unlikely.

Head lice are generally spread through direct head-to-head contact with an infested person. Transmission by sharing bedding or clothing such as headwear is much less common. The cause of head lice infestations is not related to cleanliness. Neither hair length nor how often the hair is brushed affect the risk of infection.

Body lice are spread through direct contact with the body, clothing, or other personal items of a person already carrying lice. Pubic lice are most often spread by intimate contact with an infested person. Head lice occur on the head hair, body lice on the clothing, and pubic lice mainly on the hair near the groin. Lice cannot burrow into the skin.

Other lice that infest humans are the body louse and the crab louse. The claws of these three species are adapted to attachment to specific hair diameters.

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

Body lice frequently lay their eggs on or near the seams of clothing. They must feed on blood and usually only move to the skin to feed. They exist worldwide and infest people of all races and can therefore spread rapidly under crowded living conditions where hygiene is poor (homeless, refugees, victims of war or natural disasters).

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

The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually. It is estimated between 1 and 20% of specific groups in Europe are infected.

Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice. Lice infestation during that same period was more prevalent than chickenpox.

About 6–12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world, including Israel, Denmark, Sweden, U.K., France, and Australia.

The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e.g. school), and socioeconomic status were found to be significant factors in head louse infestation. Children between 4 and 13 years of age are the most frequently infested group. In the U.S., African-American children have lower rates of infestation.

The United Kingdom's National Health Service and many American health agencies report that lice "prefer" clean hair because it's easier to attach eggs and to cling to the strands; however, this is often contested.

Head lice ("Pediculus humanus capitis") infestation is most frequent on children aged 3–10 and their families. Females get head lice twice as often as males, and infestation in persons of or other black descent is rare because of hair consistency. But these children may have nits that hatch and the live lice could be transferred by head contact to other children.

Body lice are spread through prolonged direct physical contact with a person who has them or through contact with articles such as clothing, beds, bed linens, or towels that have been in contact with an infested person. In the United States, body lice infestations are rare, typically found mainly in homeless transient populations who do not have access to bathing and regular changes of clean clothes. Infestation is unlikely to persist on anyone who bathes regularly and who has at least weekly access to freshly laundered clothing and bedding.

Although louse-borne (epidemic) typhus is no longer widespread, outbreaks of this disease still occur during times of war, civil unrest, natural or man-made disasters, and in prisons where people live together in unsanitary conditions. Louse-borne typhus still exists in places where climate, chronic poverty, and social customs or war and social upheaval prevent regular changes and laundering of clothing.

Because they live so close to the outside of the body, "Thelazia" is one of the few nematode infections which can be treated topically.

Topical treatment of livestock, dogs and cats with organophosphates (such as ecothiopate iodide or isofluorophate) and systemic treatment with anthelmintics (such as ivermectin, levamisole, and doramectin) are recommended by the Merck Veterinary Manual. Other sources have reported positive results treating dogs with moxidectin, imidacloprid, or milbemycin oxime.

For the treatment of human cases, removal of the worm is suggested. Topical treatment with cocaine or thiabendazole have also been reported to kill the worms in human cases.

Because most, if not all, species of "Thelazia" are spread by flies, sanitary practices which reduce the presence of flies will also reduce the spread of thelaziasis.

Pinworm infection occurs worldwide, and is the most common helminth (i.e., parasitic worm) infection in the United States and Western Europe. In the United States, a study by the Center of Disease Control reported an overall incidence rate of 11.4% among people of all ages. Pinworms are particularly common in children, with prevalence rates in this age group having been reported as high as 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, and 29% in Denmark. Finger sucking has been shown to increase both incidence and relapse rates, and nail biting has been similarly associated. Because it spreads from host to host through contamination, enterobiasis is common among people living in close contact, and tends to occur in all people within a household. The prevalence of pinworms is not associated with gender, nor with any particular social class, race, or culture. Pinworms are an exception to the tenet that intestinal parasites are uncommon in affluent communities.

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.

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.

"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.

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.

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

A number of other symptoms may occur from either the bite of the bed bugs or from their exposure. Anaphylaxis from the injection of serum and other nonspecific proteins has been rarely documented. Due to each bite taking a tiny amount of blood, chronic or severe infestation may lead to anemia. Bacterial skin infection may occur due to skin break down from scratching.

Systemic poisoning may occur if the bites are numerous. Exposure to bed bugs may trigger an asthma attack via the effects of airborne allergens although evidence of this association is limited. There is no evidence that bed bugs transmit infectious diseases even though they appear physically capable of carrying pathogens and this possibility has been investigated. The bite itself may be painful thus resulting in poor sleep and worse work performance.

Similar to humans, pets can also be bitten by bed bugs. The signs left by the bites are the same as in case of people and cause identical symptoms (skin irritation, scratching etc).

Pinworm infection cannot be totally prevented under most circumstances. This is due to the prevalence of the parasite and the ease of transmission through soiled night clothes, airborne eggs, contaminated furniture, toys and other objects. Infection may occur in the highest strata of society, where hygiene and nutritional status are typically high. The stigma associated with pinworm infection is hence considered a possible over-emphasis. Counselling is sometimes needed for upset parents that have discovered their children are infected, as they may not realize how prevalent the infection is.

Preventative action revolves around personal hygiene and the cleanliness of the living quarters. The "rate" of reinfection can be reduced through hygienic measures, and this is recommended especially in recurring cases.

The main measures are keeping fingernails short, and washing and scrubbing hands and fingers carefully, especially after defecation and before meals. Under ideal conditions, bed covers, sleeping garments, and hand towels should be changed daily. Simple laundering of clothes and linen disinfects them. Children should wear gloves while asleep, and the bedroom floor should be kept clean. Food should be covered to limit contamination with dust-borne parasite eggs. Household detergents have little effect on the viability of pinworm eggs, and cleaning the bathroom with a damp cloth moistened with an antibacterial agent or bleach will merely spread the still-viable eggs. Similarly, shaking clothes and bed linen will detach and spread the eggs.

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.