The symptoms of this infection depends on where the larvae migrates into the body when swallowed, however the most common symptoms are :

- Swelling

- Symptoms resembling those of an allergic reaction

- Skin eruptions

- Eye and neurological symptoms.

Most of the mites which cause this affliction to humans are from the order Acari, hence the name Acariasis. The entire taxonomic classification to order would be:

- Kingdom: Animalia

- Phylum: Arthropoda

- Subphylum: Chelicerata

- Class: Arachnida

- Order: Acari (At the order level, there is still substantial argument among researchers as to how to categorize Acari. Some call it a subclass, others a superorder, "Acarina".)

Specific species involved include:

- Acariformes

- Trombidiformes

- "Trombicula" species (trombiculosis or chiggers)

- "Demodex" species (Demodicosis)

- "Pyemotes tritici"

- "Cheyletiella"

- Sarcoptiformes

- "Sarcoptes scabiei" (Scabies)

- Parasitiformes

- "Dermanyssus gallinae"

- "Liponyssoides sanguineus"

- "Ornithonyssus bacoti", "Ornithonyssus bursa", "Ornithonyssus sylviarum"

- Another candidate is "Androlaelaps casalis". However, based on this mite's life style as a predator on other mite species (such as the previously-mentioned "Dermanyssus gallinae"), it is highly unlikely to be a cause of acariasis.

Some of these reflect reports existing of human infestation by mites previously believed not to prey on humans.

Symptoms of parasites may not always be obvious. However, such symptoms may mimic anemia or a hormone deficiency. Some of the symptoms caused by several worm infestation can include itching affecting the anus or the vaginal area, abdominal pain, weight loss, increased appetite, bowel obstructions, diarrhea, and vomiting eventually leading to dehydration, sleeping problems, worms present in the vomit or stools, anemia, aching muscles or joints, general malaise, allergies, fatigue, nervousness. Symptoms may also be confused with pneumonia or food poisoning.

The effects caused by parasitic diseases range from mild discomfort to death.

The nematode parasites "Necator americanus" and "Ancylostoma duodenale" cause human hookworm infection, which leads to anaemia and protein malnutrition. This infection affects approximately 740 million people in the developing countries, including children and adults, of the tropics specifically in poor rural areas located in sub-Saharan Africa, Latin America, South-East Asia and China.

Chronic hookworm in children leads to impaired physical and intellectual development, school performance and attendance are reduced.

Pregnant women affected by a hookworm infection can also develop aneamia, which results in negative outcomes both for the mother and the infant. Some of them are: low birth weight, impaired milk production, as well as increased risk of death for the mother and the baby.

Strongyloides infection occurs in five forms. On acquiring the infection, there may be respiratory symptoms (Löffler's syndrome). The infection may then become chronic with mainly digestive symptoms. On reinfection (when larvae migrate through the body), there may be respiratory, skin and digestive symptoms. Finally, the hyperinfection syndrome causes symptoms in many organ systems, including the central nervous system.

Although organisms such as bacteria function as parasites, the usage of the term "parasitic disease" is usually more restricted. The three main types of organisms causing these conditions are protozoa (causing protozoan infection), helminths (helminthiasis), and ectoparasites. Protozoa and helminths are usually endoparasites (usually living inside the body of the host), while ectoparasites usually live on the surface of the host. Occasionally the definition of "parasitic disease" is restricted to diseases due to endoparasites.

Frequently asymptomatic. Gastrointestinal system symptoms include abdominal pain and diarrhea. Pulmonary symptoms (including Löffler's syndrome) can occur during pulmonary migration of the filariform larvae. Dermatologic manifestations include urticarial rashes in the buttocks and waist areas as well as larva currens. Eosinophilia is generally present.

Strongyloidiasis can become chronic and then become completely asymptomatic.

There are several complications with the terminology:

Acariasis is a term for a rash, caused by mites, sometimes with a papillae (pruritic dermatitis), and usually accompanied by severe itching sensations. An example of such an infection is scabies.

The closely related term, mange, is commonly used with domestic animals (pets) and also livestock and wild mammals, whenever hair-loss is involved. "Sarcoptes" and "Demodex" species are involved in mange, but both of these genera are also involved in human skin diseases (by convention only, not called mange). "Sarcoptes" in humans is especially severe symptomatically, and causes the condition scabies noted above.

Another genus of mite which causing itching but rarely causes hair loss because it burrows only at the keratin level, is "Cheyletiella." Various species of this genus of mite also affect a wide variety of mammals, including humans.

Mite infestation sometimes implies an ectoparasitic, cutaneous condition such as dermatitis. However, it is possible for mites to invade the gastrointestinal and urinary tracts.

MeSH uses the term "Mite Infestations" as pertaining to Acariformes. However, mites not in this grouping can be associated with human disease. (See "Classification", below.)

The term Acari refers to ticks and mites together, which can cause ambiguity. (Mites are a paraphyletic grouping).

Mites can be associated with disease in at least three different ways: (1) cutaneous dermatitis, (2) production of allergin, and (3) as a vector for parasitic diseases. The language used to describe mite infestation often does not distinguish among these.

Mange is a class of skin diseases caused by parasitic mites. Since mites also infect plants, birds, and reptiles, the term "mange", suggesting poor condition of the hairy coat due to the infection, is sometimes reserved only for pathological mite-infestation of nonhuman mammals. Thus, mange includes mite-associated skin disease in domestic animals (cats and dogs), in livestock (such as sheep scab), and in wild animals (for example, coyotes, cougars, and bears). Since mites belong to the arachnid subclass Acari (also called Acarina), another term for mite infestation is acariasis.

Parasitic mites that cause mange in mammals embed themselves either in skin or hair follicles in the animal, depending upon their genus. "Sarcoptes" spp. burrow into skin, while "Demodex" spp. live in follicles.

In humans, these two types of mite infections, which would otherwise be known as "mange" in furry mammals, are instead known respectively as scabies and demodicosis.

Sarcoptic mange, also known as canine scabies, is a highly contagious infestation of "Sarcoptes scabiei canis", a burrowing mite. The canine sarcoptic mite can also infest cats, pigs, horses, sheep, and various other species. The human analog of burrowing mite infection, due to a closely related species, is called scabies (the "seven year itch").

All these burrowing mites are in the family Sarcoptidae. They dig into and through the skin, causing intense itching from an allergic reaction to the mite, and crusting that can quickly become infected. Hair loss and crusting frequently appear first on elbows and ears. Skin damage can occur from the dog's intense scratching and biting. Secondary skin infection is also common. Dogs with chronic sarcoptic mange are often in poor condition, and in both animals and humans, immune suppression from starvation or any other disease causes this type of mange to develop into a highly crusted form in which the burden of mites is far higher than in healthy specimens.

Swimmer’s itch or cercarial dermatitis, is a short-term immune reaction occurring in the skin of humans that have been infected by water-borne schistosomatidae. Symptoms, which include itchy, raised papules, commonly occur within hours of infection and do not generally last more than a week. It is common in freshwater, brackish and marine habitats worldwide. Incidence may be on the rise, although this may also be attributed to better monitoring. Nevertheless, the condition has been regarded as emerging infectious disease.

There are no permanent effects to people from this condition. Orally administered hydroxyzine, an antihistamine, is sometimes prescribed to treat swimmer's itch and similar dermal allergic reactions. In addition, bathing in oatmeal, baking soda, or Epsom salts can also provide relief of symptoms.

Because the larvae are in an abnormal host, they do not mature to adults but instead migrate

through the skin until killed by the host's inflammatory response. This migration causes

local intense itching and a red serpiginous lesion. Treatment with a single dose of oral ivermectin results in cure rates of 94–100%.

The infection is usually contracted by persons walking barefoot over

contaminated soil. In penetrating the skin, the larvae may cause an allergic

reaction. It is from the itchy patch at the site of entry that the early

infection gets its nickname "ground itch". Once larvae have broken through the skin,

they enter the bloodstream and are carried to the lungs (unlike ascarids,

however, hookworms do not usually cause pneumonia). The larvae migrate from

the lungs up the windpipe to be swallowed and carried back down to the

intestine. If humans come into contact with larvae of the dog hookworm or the

cat hookworm, or of certain other hookworms that do not infect humans, the

larvae may penetrate the skin. Sometimes, the larvae are unable to complete their

migratory cycle in humans. Instead, the larvae migrate just below the skin

producing snake-like markings. This is referred to as a creeping eruption or

cutaneous larva migrans.

An ectoparasitic infestation is a parasitic disease caused by organisms that live primarily on the surface of the host.

Examples:

- Scabies

- Crab louse (pubic lice)

- Pediculosis (head lice)

- "Lernaeocera branchialis" (cod worm)

How myiasis affects the human body depends on where the larvae are located. Larvae may infect dead, necrotic (prematurely dying) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal tract, or in genitourinary sites. They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can reach the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis.

Several different presentations of myiasis and their symptoms:

The main symptom is itching, usually in the pubic-hair area, resulting from hypersensitivity to louse saliva, which can become stronger over two or more weeks following initial infestation. In some infestations, a characteristic grey-blue or slate coloration macule appears ("maculae caeruleae") at the feeding site, which may last for days. Nits or live lice may also be visible to the unaided eye. Adult lice can sometimes be seen crawling on the skin.

Nosocomial myiasis is myiasis acquired in a hospital setting. It is quite frequent, as patients with open wounds or sores can be infested if flies are present. To prevent nosocomial myiasis, hospital rooms must be kept free of flies.

Hypodermyasis is a parasitic infection by the larvae of warble flies, most notably "Hypoderma lineatum" and "Hypoderma bovis". These flies mostly infect cattle in the warmer areas of the northern hemisphere. Humans become hosts when they inadvertently swallow the eggs of those flies.

Most conditions of STH have a light worm burden and usually have no discernible symptoms. Heavy infections however cause a range of health problems, including abdominal pain, diarrhoea, blood and protein loss, rectal prolapse, and physical and mental retardation.

Severe ascariasis is typically a pneumonia, as the larvae invades lungs, producing fever, cough and dyspnoea during early stage of infection.

Hookworm infections insinuate a skin reaction (dermatitis), increased white blood cells (eosinophils), a pulmonary reaction (pneumonitis), and skin rash (urticarial).

Iron deficiency anaemia due to blood loss is a common symptom.

Pediculosis pubis (also known as "crabs" and "pubic lice") is a disease caused by the pubic louse, "Pthirus pubis", a parasitic insect notorious for infesting human pubic hair. The species may also live on other areas with hair, including the eyelashes, causing pediculosis ciliaris. Infestation usually leads to intense itching in the pubic area. Treatment with topic agents such as permethrin or pyrethrin with piperonyl butoxide is effective. Worldwide, pediculosis pubis affects about 2% of the population.

Swimmer’s itch probably has been around as long as humans. The condition was known to exist as early as the 1800s, but it was not until 1928 that a biologist found that the dermatitis was caused by the larval stage of a group of flatworm parasites in the family Schistosomatidae. The genera most commonly associated with swimmer’s itch in humans are Trichobilharzia and Gigantobilharzia. It can also be caused by schistosome parasites of non-avian vertebrates, such as "Schistosomatium douthitti", which infects snails and rodents. Other taxa reported to cause the reaction include "Bilharziella polonica" and "Schistosoma bovis". In marine habitats, especially along the coasts, swimmer’s itch can occur as well.

These parasites use both freshwater snails and vertebrates as hosts in their parasitic life cycles as follows:

1. Once a schistosome egg is immersed in water, a short-lived, non-feeding, free-living stage known as the miracidium emerges. The miracidium uses cilia to follow chemical and physical cues thought to increase its chances of finding the first intermediate host in its life cycle, a freshwater snail.

2. After infecting a snail, it develops into a mother sporocyst, which in turn undergoes asexual reproduction, yielding large numbers of daughter sporocysts, which asexually produce another short-lived, free-living stage, the cercaria.

3. Cercariae use a tail-like appendage (often forked in genera causing swimmer’s itch) to swim to the surface of the water; and use various physical and chemical cue in order to locate the next and final (definitive) host in the life cycle, a bird. These larvae can accidentally come into contact with the skin of a swimmer. The cercaria penetrates the skin and dies in the skin immediately. The cercariae cannot infect humans, but they cause an inflammatory immune reaction. This reaction causes initially mildly itchy spots on the skin. Within hours, these spots become raised papules which are intensely itchy. Each papule corresponds to the penetration site of a single parasite.

4. After locating a bird, the parasite penetrates through the skin (usually the feet), dropping the forked tail in the process. Inside the circulatory system, the immature worms (schistosomula) develop into mature male and female worms, mate and migrate through the host’s circulatory system (or nervous system in case of "T. regenti") to the final location (veins feeding the gastrointestinal tract) within the host body. There they lay eggs in the small veins in the intestinal mucosa from which they make their way into the lumen of the gut, and are dumped into the water when the bird defecates. One European species, "Trichobilharzia regenti", instead infects the bird host’s nasal tissues and larvae hatch from the eggs directly in the tissue during drinking/feeding of the infected birds.

Symptoms becomes evident only when the intensity of infection is relatively high. Thus the degree of negative outcomes is directly related to worm burden; more worms means greater severity of disease.

Light infestations (<100 worms) frequently have no symptoms. Heavier infestations, especially in small children, can present gastrointestinal problems including abdominal pain and distension, bloody or mucus-filled diarrhea, and tenesmus (feeling of incomplete defecation, generally accompanied by involuntary straining). Mechanical damage to the intestinal mucosa may occur, as well as toxic or inflammatory damage to the intestines of the host. While appendicitis may be brought on by damage and edema of the adjacent tissue, if there are large numbers of worms or larvae present, it has been suggested that the embedding of the worms into the ileocecal region may also make the host susceptible to bacterial infection. A severe infection with high numbers of embedded worms in the rectum leads to edema, which can cause rectal prolapse, although this is typically only seen in small children. The prolapsed, inflamed and edematous rectal tissue may even show visible worms.

Growth retardation, weight loss, nutritional deficiencies, and anemia (due to long-standing blood loss) are also characteristic of infection, and these symptoms are more prevalent and severe in children. It does not commonly cause eosinophilia.

Coinfection of "T. trichiura" with other parasites is common and with larger worm burdens can cause both exacerbation of dangerous trichuriasis symptoms such as massive gastrointestinal bleeding (shown to be especially dramatic with coinfection with "Salmonella typhi") and exacerbation of symptoms and pathogenesis of the other parasitic infection (as is typical with coinfection with "Schistosoma mansoni", in which higher worm burden and liver egg burden is common). Parasitic coinfection with HIV/AIDS, tuberculosis, and malaria is also common, especially in Sub-saharan Africa, and helminth coinfection adversely affects the natural history and progression of HIV/AIDS, tuberculosis, and malaria and can increase clinical malaria severity. In a study performed in Senegal, infections of soil-transmitted helminths like "T. trichiura" (as well as schistosome infections independently) showed enhanced risk and increased the incidence of malaria.

Heavy infestations may have bloody diarrhea. Long-standing blood loss may lead to iron-deficiency anemia. Vitamin A deficiency may also result due to infection.

One third of individuals with pinworm infection are totally asymptomatic. The main symptoms are pruritus ani and perineal pruritus, i.e., itching in and around the anus and around the perineum. The itching occurs mainly during the night, and is caused by the female pinworms migrating to lay eggs around the anus. Both the migrating females and the clumps of eggs are irritating, but the mechanisms causing the intense pruritus have not been explained. The intensity of the itching varies, and it can be described as tickling, crawling sensations, or even acute pain. The itching leads to continuously scratching the area around the anus, which can further result in tearing of the skin and complications such as secondary bacterial infections, including bacterial dermatitis (i.e., skin inflammation) and folliculitis (i.e., hair follicle inflammation). General symptoms are insomnia (i.e., persistent difficulties to sleep) and restlessness. A considerable proportion of children suffer from loss of appetite, weight loss, irritability, emotional instability, and enuresis (i.e., inability to control urination).

Pinworms cannot damage the skin, and they do not normally migrate through tissues. However, in women they may move onto the vulva and into the vagina, from there moving to the external orifice of the uterus, and onwards to the uterine cavity, fallopian tubes, ovaries, and peritoneal cavity. This can cause vulvovaginitis, i.e. an inflammation of the vulva and vagina. This causes vaginal discharge and pruritus vulvae, i.e., itchiness of the vulva. The pinworms can also enter the urethra, and presumably, they carry intestinal bacteria with them. According to Gutierrez (2000), a statistically significant correlation between pinworm infection and urinary tract infections has been shown; however, Burkhart & Burkhart (2005) maintain that the incidence of pinworms as a cause of urinary tract infections remains unknown. Incidentally, one report indicated that 36% of young girls with a urinary tract infection also had pinworms. Dysuria (i.e., painful urination) has been associated with pinworm infection.

The relationship between pinworm infestation and appendicitis has been researched, but there is a lack of clear consensus on the matter: while Gutierres (2005) maintains that there exists a consensus that pinworms do not produce the inflammatory reaction, Cook (1994) states that it is controversial whether pinworms are causatively related to acute appendicitis, and Burkhart & Burkhart (2004) state that pinworm infection causes symptoms of appendicitis to surface.

The signs and symptoms of helminthiasis depend on a number of factors including: the site of the infestation within the body; the type of worm involved; the number of worms and their volume; the type of damage the infesting worms cause; and, the immunological response of the body. Where the burden of parasites in the body is light, there may be no symptoms.

Certain worms may cause particular constellations of symptoms. For instance, taeniasis can lead to seizures due to neurocysticercosis.

The first potential reaction is an itchy, papular rash that results from cercariae penetrating the skin, often in a person's first infection. The round bumps are usually one to three centimeters across. Because people living in affected areas have often been repeatedly exposed, acute reactions are more common in tourists and migrants. The rash can occur between the first few hours and a week after exposure and lasts for several days. A similar, more severe reaction called "swimmer's itch" reaction can also be caused by cercariae from animal trematodes that often infect birds.