"Taenia saginata" infection is asymptomatic, but heavy infection causes weight loss, dizziness, abdominal pain, diarrhea, headaches, nausea, constipation, chronic indigestion, and loss of appetite. It can cause antigen reaction that induce allergic reaction. It is also a rare cause of ileus, pancreatitis, cholecystitis, and cholangitis.

Clinical presentation of sparganosis most often occurs after the larvae have migrated to a subcutaneous location. The destination of the larvae is often a tissue or muscle in the chest, abdominal wall, extremities, or scrotum, although other sites include the eyes, brain, urinary tract, pleura, pericardium, and spinal canal. The early stages of disease in humans are often asymptomatic, but the spargana typically cause a painful inflammatory reaction in the tissues surrounding the subcutaneous site as they grow. Discrete subcutaneous nodules develop that may appear and disappear over a period of time. The nodules usually itch, swell, turn red, and migrate, and are often accompanied by painful edema. Seizures, hemiparesis, and headaches are also common symptoms of sparganosis, especially cerebral sparganosis, and eosinophilia is a common sign. Clinical symptoms also vary according to the location of the sparganum; possible symptoms include elephantiasis from location in the lymph channels, peritonitis from location in the intestinal perforation, and brain abscesses from location in the brain. In genital sparganosis, subcutaneous nodules are present in the groin, labia, or scrotum and may appear tumor-like.

Ocular sparganosis a particularly well-described type of sparganosis. Early signs of the ocular form include eye pain, epiphora (excessive watering of the eye), and/or ptosis (drooping of the upper eyelid). Other signs include periorbital edema and/or edematous swelling that resembles Romana’s sign in Chagas disease, lacrimation, orbital cellulitis, exophthalmos (protrusion of the eyeball), and/or an exposed cornea ulcer. The most common sign at presentation is a mass lesion in the eye. If untreated, ocular sparganosis can lead to blindness.

In one case of brain infestation by "Spirometra erinaceieuropaei", a man sought treatment on suffering headaches, seizures, memory flashbacks and strange smells. Magnetic resonance imaging (MRI) scans showed a cluster of rings, initially in the right medial temporal lobe, but moving over time to the other side of the brain. The cause was not determined for four years; ultimately a biopsy was performed and a 1 cm-long tapeworm was found and removed. The patient continued to suffer symptoms.

Although tapeworms in the intestine usually cause no symptoms, some people experience upper abdominal discomfort, diarrhea, and loss of appetite. Anemia may develop in people with the fish tapeworm. Infection is generally recognized when the infected person passes segments of proglottids in the stool (which look like white worms), especially if a segment is moving.

Rarely, worms may cause obstruction of the intestine, and very rarely, T. solium larvae can migrate to the brain causing severe headaches, seizures and other neurological problems. Neurocysticercosis can progress for years before the patient displays symptoms.

In at least one case, cancer cells from a tapeworm spread to the human host in an immunocompromised man, producing swelling, obstructions, and other conventional symptoms of human-originated cancer.

Hymenolepiasis is infestation by one of two species of tapeworm: "Hymenolepis nana" or "H. diminuta". Alternative names are dwarf tapeworm infection and rat tapeworm infection. The disease is a type of helminthiasis which is classified as a neglected tropical disease.

Taeniasis is generally asymptomatic and is diagnosed when a portion of the worm is passed in the stool. It is not fatal, although cysticercosis can cause epilepsy and neurocysticercosis can be fatal.

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

In humans, this parasitic infection causes a variety of symptoms, depending on where the cyst occurs. The tapeworm larvae group together to form fluid filled cysts in various body tissues. These cysts start out small, but as the larvae grow, the cyst can reach the size of an egg. The cysts of "T. multiceps" are usually between 2 and 6 cm in diameter and are most commonly found in the CNS and can contain anywhere from a few to over a hundred worm larvae within them. "T serialis" and "T. glomerata" cysts present in the CNS, muscles, or subcutaneous tissue, and "T. brauni" cysts occupy these same areas but occur in the eye more frequently than the other three species.

When the cyst occurs in the brain, as it often does, the infected individual may experience headaches, seizures, vomiting, paralysis affecting one side of the body (hemiplegia), paralysis involving one limb (monoplegia), and loss of ability to coordinate muscles and muscle movements. Many of these symptoms are due to the buildup of inter-cranial pressure from the growing cyst or from the cyst pressing on other parts of brain.

When the cyst occurs in the spinal cord, it can cause severe pain and inflammation, and loss of feeling in some nerves.

When the cyst occurs in the eyes, it causes decreased vision and headaches.

In the muscular and subcutaneous tissues, the cyst causes disfiguring nodules that can protrude out of the body. These nodules can be painful, uncomfortable, and can cause loss of muscle function.

Diphyllobothriasis can last for decades if untreated. Most infections are asymptomatic. Manifestations may include abdominal discomfort, diarrhea, vomiting and weight loss. Vitamin B12 deficiency with subsequent megaloblastic anemia may occur, but has not for several decades in "D. latum" infections, possibly because of improved nutrition. In one test, nearly half of the ingested vitamin was absorbed by "D. latum" in otherwise healthy patients, while 80-100% was absorbed by the worm in patients with anemia. It is not known why anemia occurs in some cases but not others. Massive infections may result in intestinal obstruction. Migration of proglottids can cause cholecystitis or cholangitis.

Females cases are disproportionately reported, most likely due to the higher likelihood for them to be involved in meal preparation, rather than any morphological differences.

Tapeworm infection is the infestation of the digestive tract by a species of parasitic flatworm (known as a cestode), called tapeworms. Live tapeworm larvae grouped in cysts (coenuri)are sometimes ingested by consuming undercooked meat. Once inside the digestive tract, a larva can grow into a very large adult tapeworm. Additionally, many tapeworm larvae cause symptoms in an intermediate host. For example, cysticercosis is a disease involving larval tapeworms in the human body.

Cysticerci can develop in any voluntary muscles in humans. Invasion of muscle by cysticerci can cause myositis, with fever, eosinophilia, and muscular pseudohypertrophy, which initiates with muscle swelling and later progress to atrophy and fibrosis. In most cases, it is asymptomatic since the cysticerci die and become calcified.

The term neurocysticercosis is generally accepted to refer to cysts in the parenchyma of the brain. It presents with seizures and, less commonly, headaches. Cysticerca in brain parenchyma are usually 5–20 mm in diameter. In subarachnoid space and fissures, lesions may be as large as 6 cm in diameter and lobulated. They may be numerous and life-threatening.

Cysts located within the ventricles of the brain can block the outflow of cerebrospinal fluid and present with symptoms of increased intracranial pressure.

Racemose neurocysticercosis refers to cysts in the subarachnoid space. These can occasionally grow into large lobulated masses causing pressure on surrounding structures.

Neurocysticercosis involving the spinal cord, most commonly presenting as back pain and radiculopathy.

"Hymenolepis" worms live in the intestines of rats and are common in warm climates, and are generally found in the feces of rats, which are consumed by their secondary hosts—beetles. The worms mature into a life form referred to as a "cysticercoid" in the insect; in "H. nana," the insect is always a beetle.

Humans and other animals become infected when they intentionally or unintentionally eat material contaminated by insects. In an infected person, it is possible for the worm's entire lifecycle to be completed in the bowel, so infection can persist for years if left untreated.

"H. nana" infections are much more common than "H. diminuta" infections in humans because, in addition to being spread by insects, the disease can be spread directly from person to person by eggs in feces. When this happens, "H. nana" oncosphere larvae encyst in the intestinal wall and develop into cysticercoids and then adults. These infections were previously common in the southeastern USA, and have been described in crowded environments and individuals confined to institutions. However, the disease occurs throughout the world. "H. nana" infections can grow worse over time because, unlike in most tapeworms, "H. nana" eggs can hatch and develop without ever leaving the definitive host.

There are no specific symptoms or signs of hookworm infection, but they give rise to a combination of intestinal inflammation and progressive iron-deficiency anemia and protein deficiency. Coughing, chest pain, wheezing, and fever will sometimes result from severe infection. Epigastric pains, indigestion, nausea, vomiting, constipation, and diarrhea can occur early or in later stages as well, although gastrointestinal symptoms tend to improve with time. Signs of advanced severe infection are those of anemia and protein deficiency, including emaciation, cardiac failure and abdominal distension with ascites.

Larval invasion of the skin (mostly in the Americas) can produce a skin disease called cutaneous larva migrans also known as "creeping eruption". The hosts of these worms are not human and the larvae can only penetrate the upper five layers of the skin, where they give rise to intense, local itching, usually on the foot or lower leg, known as "ground itch". This infection is due to larvae from the "A. Braziliense" hookworm. The larvae migrate in tortuous tunnels between the "stratum basale" and "stratum corneum" of the skin, causing serpiginous vesicular lesions. With advancing movement of the larvae, the rear portions of the lesions become dry and crusty. The lesions are typically intensely itchy.

Sparganosis is a parasitic infection caused by the plerocercoid larvae of the genus "Spirometra" including , "S. ranarum", "S. mansonoides" and "S. erinacei". It was first described by Patrick Manson from China in 1882, and the first human case was reported by Charles Wardell Stiles from Florida in 1908. The infection is transmitted by ingestion of contaminated water, ingestion of a second intermediate host such as a frog or snake, or contact between a second intermediate host and an open wound or mucous membrane. Humans are the accidental hosts in the life cycle, while dogs, cats, and other mammals are definitive hosts. Copepods (freshwater crustaceans) are the first intermediate hosts, and various amphibians and reptiles are second intermediate hosts.

Once a human becomes infected, the plerocercoid larvae migrate to a subcutaneous location, where they typically develop into a painful nodule. Migration to the brain results in cerebral sparganosis, while migration to the eyes results in ocular sparganosis. Sparganosis is most prevalent in Eastern Asia, although cases have been described in countries throughout the world. In total, approximately 300 cases have been described in the literature up to 2003. Diagnosis is typically not made until the sparganum larva has been surgically removed. Praziquantel is the drug of choice, although its efficacy is unknown and surgical removal of the sparganum is generally the best treatment. Public health interventions should focus on water and dietary sanitation, as well as education about the disease in rural areas and discouragement of the use of poultices.

The term "hookworm" is sometimes used to refer to hookworm infection. A hookworm is a type of parasitic worm (helminth).

Coenurosis is a parasitic infection that results when humans ingest the eggs of dog tapeworm species "Taenia multiceps", "T. serialis, T. brauni," or "T. glomerata."

It is important to distinguish that there is a very significant difference between intestinal human tapeworm infection and human coenurosis. Humans are the definitive hosts for some tapeworm species, the most common being "T. saginata" and "T. solium" (beef and pork tapeworms). This means that these species can develop into full grown, reproductively capable adult worms within the human body. People infected with these species have a tapeworm infection. In contrast, the four species that cause human coenurosis can only grow into mature, reproductively capable worms inside their definitive hosts, canids such as dogs, wolves, foxes and coyotes. Humans who ingest eggs from any of these four species of "Taenia" become intermediate hosts, or places where the eggs can mature into larvae but not into adult worms. When humans ingest these eggs, the eggs develop into tapeworm larvae that group within cysts known as coenuri, which can be seen in the central nervous system, muscles, and subcutaneous tissues of infected humans. People with coenurosis do not develop a tapeworm infection because the larvae of coenurosis-causing parasites cannot develop into worms inside of humans.

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.

Dientamoebiasis is a medical condition caused by infection with "Dientamoeba fragilis", a single-cell parasite that infects the lower gastrointestinal tract of humans. It is an important cause of traveler's diarrhea, chronic abdominal pain, chronic fatigue, and failure to thrive in children.

In the human manifestation of the disease, "E. granulosus", "E. multilocularis", "E. oligarthrus" and "E. vogeli" are localized in the liver (in 75% of cases), the lungs (in 5–15% of cases) and other organs in the body such as the spleen, brain, heart, and kidneys (in 10–20% of cases). In the patients who are infected with "E. granulosus" and therefore have cystic echinococcosis, the disease develops as a slow-growing mass in the body. These slow-growing masses, often called cysts, are also found in patients that are infected with alveolar and polycystic echinococcosis. The cysts found in those with cystic echinococcosis are usually filled with a clear fluid called hydatid fluid, are spherical, and typically consist of one compartment and are usually only found in one area of the body. While the cysts found in those with alveolar and polycystic echinococcosis are similar to those found in those with cystic echinococcosis, the alveolar and polycystic echinococcosis cysts usually have multiple compartments and have infiltrative as opposed to expansive growth.

Depending on the location of the cyst in the body, the patient could be asymptomatic even though the cysts have grown to be very large, or be symptomatic even if the cysts are absolutely tiny. If the patient is symptomatic, the symptoms will depend largely on where the cysts are located. For instance, if the patient has cysts in the lungs and is symptomatic, they will have a cough, shortness of breath and/or pain in the chest. On the other hand, if the patient has cysts in the liver and is symptomatic, they will suffer from abdominal pain, abnormal abdominal tenderness, hepatomegaly with an abdominal mass, jaundice, fever and/or anaphylactic reaction. In addition, if the cysts were to rupture while in the body, whether during surgical extraction of the cysts or by trauma to the body, the patient would most likely go into anaphylactic shock and suffer from high fever, pruritus (itching), edema (swelling) of the lips and eyelids, dyspnea, stridor and rhinorrhea.

Unlike intermediate hosts, definitive hosts are usually not hurt very much by the infection. Sometimes, a lack of certain vitamins and minerals can be caused in the host by the very high demand of the parasite.

The incubation period for all species of "Echinococcus" can be months to years, or even decades. It largely depends on the location of the cyst in the body and how fast the cyst is growing.

In extreme cases of intestinal infestation, the mass and volume of the worms may cause the outer layers of the intestinal wall, such as the muscular layer, to tear. This may lead to peritonitis, volvulus, and gangrene of the intestine.

Researchers have published conflicting reports concerning whether "Blastocystis" causes symptoms in humans, with one of the earliest reports in 1916. The incidence of reports associated with symptoms began to increase in 1984, with physicians from Saudi Arabia reporting symptoms in humans and US physicians reporting symptoms in individuals with travel to less developed countries. A lively debate ensued in the early 1990s, with some physicians objecting to publication of reports that "Blastocystis" caused disease. Some researchers believe the debate has been resolved by finding of multiple species of "Blastocystis" that can infect humans, with some causing symptoms and others being harmless (see Genetics and Symptoms).

A few of most commonly reported symptoms are:

- abdominal pain

- itching, usually anal itching

- constipation

- diarrhea

- watery or loose stools

- weight loss

- fatigue

- flatulence

Some less commonly reported symptoms include:

- Skin rash

- Headache, depression

- Arthritic symptoms and joint pain

- Intestinal inflammation

Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.

Specific defences are specialised responses to particular pathogens recognised by the fish's body, that is adaptative immune responses. In recent years, vaccines have become widely used in aquaculture and ornamental fish, for example vaccines for furunculosis in farmed salmon and koi herpes virus in koi.

Some commercially important fish diseases are VHS, ich and whirling disease.

The most commonly reported symptoms in conjunction with infection with "D. fragilis" include abdominal pain (69%) and diarrhea (61%). Diarrhea may be intermittent and may not be present in all cases. It is often chronic, lasting over two weeks. The degree of symptoms may vary from asymptomatic to severe, and can include weight loss, vomiting, fever, and involvement of other digestive organs.

Symptoms may be more severe in children. Additional symptoms reported have included:

1. Weight loss

2. Fatigue

3. Nausea and vomiting

4. Fever

5. Urticaria (skin rash)

6. Pruritus (itchiness)

7. Biliary infection

The most common form found in humans is cystic echinococcosis (also known as unilocular echinococcosis), which is caused by "Echinococcus granulosus sensu lato". The second most common form is alveolar echinococcosis (also known as alveolar colloid of the liver, alveolar hydatid disease, alveolococcosis, multilocular echinococcosis, "small fox tapeworm"), which is caused by "Echinococcus multilocularis" and the third is polycystic echinococcosis (also known as human polycystic hydatid disease, neotropical echinococcosis), which is caused by "Echinococcus vogeli" and very rarely, "Echinococcus oligarthrus". Alveolar and polycystic echinococcosis are rarely diagnosed in humans and are not as widespread as cystic echinococcosis, but polycystic echinococcosis is relatively new on the medical scene and is often left out of conversations dealing with echinococcosis, and alveolar echinococcosis is a serious disease that has not only a significantly high fatality rate, but the potential to become an emerging disease in many countries.

Blastocystosis refers to a medical condition caused by infection with "Blastocystis". "Blastocystis" is a protozoal, single-celled parasite that inhabits the gastrointestinal tracts of humans and other animals. Many different types of "Blastocystis" exist, and they can infect humans, farm animals, birds, rodents, amphibians, reptiles, fish, and even cockroaches. Blastocystosis has been found to be a possible risk factor for development of IBS (Irritable Bowel Syndrome).