Diagnosis rests on the microscopic identification of larvae (rhabditiform and occasionally filariform) in the stool or duodenal fluid. Examination of many samples may be necessary, and not always sufficient, because direct stool examination is relatively insensitive, with a single sample only able to detect larvae in about 25% of cases. It can take 4 weeks from initial infection to the passage of larvae in the stool.

The stool can be examined in wet mounts:

- directly

- after concentration (formalin-ethyl acetate)

- after recovery of the larvae by the Baermann funnel technique

- after culture by the Harada-Mori filter paper technique

- after culture in agar plates

Culture techniques are the most sensitive, but are not routinely available in the West. In the UK, culture is available at either of the Schools of Tropical Medicine in Liverpool or London. Direct examination must be done on stool that is freshly collected and not allowed to cool down, because hookworm eggs hatch on cooling and the larvae are very difficult to distinguish from Strongyloides.

Finding Strongyloides in the stool is negative in up to 70% of tests. It is important to undergo frequent stool sampling as well as duodenal biopsy if a bad infection is suspected. The duodenal fluid can be examined using techniques such as the Enterotest string or duodenal aspiration. Larvae may be detected in sputum from patients with disseminated strongyloidiasis.

Given the poor ability of stool examination to diagnose strongyloides, detecting antibodies by ELISA can be useful. Serology can cross-react with other parasites, remain positive for years after successful treatment or be falsely negative in immunocompromised patients. Infected patients will also often have an elevated eosinophil count, with an average of absolute eosinophil count of 1000 in one series. The combination of clinical suspicion, a positive antibody and a peripheral eosinophilia can be strongly suggestive of infection.

Specific helminths can be identified through microscopic examination of their eggs (ova) found in faecal samples. The number of eggs is measured in units of eggs per gram. However, it does not quantify mixed infections, and in practice, is inaccurate for quantifying the eggs of schistosomes and soil-transmitted helmiths. Sophisticated tests such as serological assays, antigen tests, and molecular diagnosis are also available; however, they are time-consuming, expensive and not always reliable.

For medical purposes, the exact number of helminth eggs is less important and therefore most diagnoses are made simply by identifying the appearance of the worm or eggs in feces. Due to the large quantity of eggs laid, physicians can diagnose using only one or two fecal smears. The Kato technique (also called the Kato-Katz technique) is a laboratory method for preparing human stool samples prior to searching for parasite eggs. Eggs per gram is a laboratory test that determines the number of eggs per gram of feces in patients suspected of having a parasitological infection, such as schistosomiasis.

For the purpose of setting treatment standards and reuse legislation, it is important to be able to determine the amount of helminth eggs in an environmental sample with some accuracy. The detection of viable helminth eggs in samples of wastewater, sludge or fresh feces (as a diagnostic tool for the infection helminthiasis) is not straight forward. In fact, many laboratories in developing countries lack the right equipment or skilled staff required to do so. An important step in the analytical methods is usually the concentration of the eggs in the sample, especially in the case of wastewater samples. A concentration step may not be required in samples of dried feces, e.g. samples collected from urine-diverting dry toilets.

Antibody detection can be useful to indicate schistosome infection in people who have traveled to areas where schistosomiasis is common and in whom eggs cannot be demonstrated in fecal or urine specimens. Test sensitivity and specificity vary widely among the many tests reported for the serologic diagnosis of schistosomiasis and are dependent on both the type of antigen preparations used (crude, purified, adult worm, egg, cercarial) and the test procedure.

At CDC, a combination of tests with purified adult worm antigens is used for antibody detection. All serum specimens are tested by FAST-ELISA using "S. mansoni" adult microsomal antigen (MAMA). A positive reaction (greater than 9 units/µl serum) indicates infection with "Schistosoma" species. Sensitivity for "S. mansoni" infection is 99 percent, 95 percent for "S. haematobium" infection, and less than 50 percent for "S. japonicum" infection. Specificity of this assay for detecting schistosome infection is 99 percent. Because test sensitivity with the FAST-ELISA is reduced for species other than "S. mansoni", immunoblots of the species appropriate to the patient's travel history are also tested to ensure detection of "S. haematobium" and "S. japonicum" infections. Immunoblots with adult worm microsomal antigens are species-specific and so a positive reaction indicates the infecting species. The presence of antibody is indicative only of schistosome infection at some time and cannot be correlated with clinical status, worm burden, egg production, or prognosis. Where a person has traveled can help determine what "Schistosoma" species to test for by immunoblot.

In 2005, a field evaluation of a novel handheld microscope was undertaken in Uganda for the diagnosis of intestinal schistosomiasis by a team led by Russell Stothard from the Natural History Museum of London, working with the Schistosomiasis Control Initiative, London.

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.

Anecdotal data gathered from helminth self-treaters and their physicians and presented in socio-medical studies suggest that a much larger number of diseases may be amenable to helminthic therapy than are currently being investigated by formal clinical trials.

Diagnosis of infection is confirmed by the identification of eggs in stools. Eggs of "S. mansoni" are approximately 140 by 60 µm in size, and have a lateral spine. The diagnosis is improved by the use of the Kato-Katz technique (a semi-quantitative stool examination technique). Other methods that can be used are enzyme-linked immunosorbent assay (ELISA), circumoval precipitation test, and alkaline phosphatase immunoassay.

Microscopic identification of eggs in stool or urine is the most practical method for diagnosis. Stool examination should be performed when infection with "S. mansoni" or "S. japonicum" is suspected, and urine examination should be performed if "S. haematobium" is suspected. Eggs can be present in the stool in infections with all "Schistosoma" species. The examination can be performed on a simple smear (1 to 2 mg of fecal material). Since eggs may be passed intermittently or in small amounts, their detection will be enhanced by repeated examinations and/or concentration procedures. In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique. Eggs can be found in the urine in infections with "S. haematobium" (recommended time for collection: between noon and 3 PM) and with "S. japonicum". Quantification is possible by using filtration through a nucleopore filter membrane of a standard volume of urine followed by egg counts on the membrane. Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for "S. haematobium") may demonstrate eggs when stool or urine examinations are negative.

Diagnosis of taeniasis is mainly using stool sample, particularly by identifying the eggs. However, this has limitation at the species level because tapeworms basically have similar eggs. Examination of the scolex or the gravid proglottids can resolve the exact species. But body segments are not often available, therefore, laborious histological observation of the uterine branches and PCR detection of ribosomal 5.8S gene are sometimes necessary. Ziehl–Neelsen stain is also used for "T. saginata" and "T. solium", in most cases only the former will stain, but the method is not entirely reliable. Loop-mediated isothermal amplification (LAMP) is highly sensitive (~2.5 times that of multiplex PCR), without false positives, for differentiating the taenid species from faecal samples.

To date the most relevant test for "T. asiatica" is by enzyme-linked immunoelectrotransfer blot (EITB). EITB can effectively identify asiatica from other taenid infections since the serological test indicates an immunoblot band of 21.5 kDa exhibited specifically by "T. asiatica". Even though it gives 100% sensitivity, it has not been tested with human sera for cross-reactivity, and it may show a high false positive result.

In regions where helminthiasis is common, mass deworming treatments may be performed, particularly among school-age children, who are a high-risk group. Most of these initiatives are undertaken by the World Health Organization (WHO) with positive outcomes in many regions. Deworming programs can improve school attendance by 25 percent. Although deworming improves the health of an individual, outcomes from mass deworming campaigns, such as reduced deaths or increases in cognitive ability, nutritional benefits, physical growth, and performance, are uncertain or not apparent.

The presence of "T. cruzi" is diagnostic of Chagas disease. It can be detected by microscopic examination of fresh anticoagulated blood, or its buffy coat, for motile parasites; or by preparation of thin and thick blood smears stained with Giemsa, for direct visualization of parasites. Microscopically, "T. cruzi" can be confused with "Trypanosoma rangeli", which is not known to be pathogenic in humans. Isolation of "T. cruzi" can occur by inoculation into mice, by culture in specialized media (for example, NNN, LIT); and by xenodiagnosis, where uninfected Reduviidae bugs are fed on the patient's blood, and their gut contents examined for parasites.

Various immunoassays for "T. cruzi" are available and can be used to distinguish among strains (zymodemes of "T.cruzi" with divergent pathogenicities). These tests include: detecting complement fixation, indirect hemagglutination, indirect fluorescence assays, radioimmunoassays, and ELISA. Alternatively, diagnosis and strain identification can be made using polymerase chain reaction (PCR).

Finding "Toxocara" larvae within a patient is the only definitive diagnosis for toxocariasis; however, biopsies to look for second stage larvae in humans are generally not very effective. PCR, ELISA, and serological testing are more commonly used to diagnose "Toxocara" infection. Serological tests are dependent on the number of larvae within the patient, and are unfortunately not very specific. ELISAs are much more reliable and currently have a 78% sensitivity and a 90% specificity. A 2007 study announced an ELISA specific to "Toxocara canis", which will minimize false positives from cross reactions with similar roundworms and will help distinguish if a patient is infected with "T. canis" or "T. cati". OLM is often diagnosed after a clinical examination. Granulomas can be found throughout the body and can be visualized using ultrasound, MRI, and CT technologies.

An epidemiological investigation can be done to determine a patient's exposure to raw infected meat. Often, an infection arises from home-preparation of contaminated meat, in which case microscopy of the meat may be used to determine the infection. Exposure determination does not have to be directly from a laboratory-confirmed infected animal. Indirect exposure criteria include the consumption of products from a laboratory-confirmed infected animal, or sharing of a common exposure with a laboratory-confirmed infected human.

Blood tests and microscopy can be used to aid in the diagnosis of trichinosis. Blood tests include a complete blood count for eosinophilia, creatine phosphokinase activity, and various immunoassays such as ELISA for larval antigens.

A blood smear is a simple and fairly accurate diagnostic tool, provided the blood sample is taken during the period in the day when the juveniles are in the peripheral circulation. Technicians analyzing the blood smear must be able to distinguish between "W. bancrofti" and other parasites potentially present.

A polymerase chain reaction test can also be performed to detect a minute fraction, as little as 1 pg, of filarial DNA.

Some infected people do not have microfilariae in their blood. As a result, tests aimed to detect antigens from adult worms can be used.

Ultrasonography can also be used to detect the movements and noises caused by the movement of adult worms.

Dead, calcified worms can be detected by X-ray examinations.

The drug of choice for the treatment of uncomplicated strongyloidiasis is ivermectin. Ivermectin does not kill the "Strongyloides" larvae, only the adult worms, therefore repeat dosing may be necessary to properly eradicate the infection. There is an auto-infective cycle of roughly two weeks in which Ivermectin should be re-administered however additional dosing may still be necessary as it will not kill "Strongyloides" in the blood or larvae deep within the bowels or diverticula. Other drugs that are effective are albendazole and thiabendazole (25 mg/kg twice daily for 5 days—400 mg maximum (generally)). All patients who are at risk of disseminated strongyloidiasis should be treated. The optimal duration of treatment for patients with disseminated infections is not clear.

Treatment of strongyloidiasis can be difficult and "Strongyloides" has been known to live in individuals for decades; even after treatment. Continued treatment is thus necessary even if symptoms resolve.

Because of the high cost of Stromectol, the veterinary formula Ivomec can be used. Government programs are needed to help citizens finance lifelong medication.

Clothes and sheets must be washed with enzyme washing powder and dried on hot daily.

There is currently no vaccine against Chagas disease. Prevention is generally focused on decreasing the numbers of the insect that spreads it ("Triatoma") and decreasing their contact with humans. This is done by using sprays and paints containing insecticides (synthetic pyrethroids), and improving housing and sanitary conditions in rural areas. For urban dwellers, spending vacations and camping out in the wilderness or sleeping at hostels or mud houses in endemic areas can be dangerous; a mosquito net is recommended. Some measures of vector control include:

- A yeast trap can be used for monitoring infestations of certain species of triatomine bugs ("Triatoma sordida", "Triatoma brasiliensis", "Triatoma pseudomaculata", and "Panstrongylus megistus").

- Promising results were gained with the treatment of vector habitats with the fungus "Beauveria bassiana".

- Targeting the symbionts of Triatominae through paratransgenesis can be done.

A number of potential vaccines are currently being tested. Vaccination with "Trypanosoma rangeli" has produced positive results in animal models. More recently, the potential of DNA vaccines for immunotherapy of acute and chronic Chagas disease is being tested by several research groups.

Blood transfusion was formerly the second-most common mode of transmission for Chagas disease, but the development and implementation of blood bank screening tests has dramatically reduced this risk in the 21st century. Blood donations in all endemic Latin American countries undergo Chagas screening, and testing is expanding in countries, such as France, Spain and the United States, that have significant or growing populations of immigrants from endemic areas. In Spain, donors are evaluated with a questionnaire to identify individuals at risk of Chagas exposure for screening tests.

The US FDA has approved two Chagas tests, including one approved in April 2010, and has published guidelines that recommend testing of all donated blood and tissue products. While these tests are not required in US, an estimated 75–90% of the blood supply is currently tested for Chagas, including all units collected by the American Red Cross, which accounts for 40% of the U.S. blood supply. The Chagas Biovigilance Network reports current incidents of Chagas-positive blood products in the United States, as reported by labs using the screening test approved by the FDA in 2007.

"N. fowleri" can be grown in several kinds of liquid axenic media or on non-nutrient agar plates coated with bacteria. "Escherichia coli" can be used to overlay the non-nutrient agar plate and a drop of cerebrospinal fluid sediment is added to it. Plates are then incubated at 37 °C and checked daily for clearing of the agar in thin tracks, which indicate the trophozoites have fed on the bacteria. Detection in water is performed by centrifuging a water sample with "E. coli" added, then applying the pellet to a non-nutrient agar plate. After several days, the plate is microscopically inspected and "Naegleria" cysts are identified by their morphology. Final confirmation of the species' identity can be performed by various molecular or biochemical methods.

Confirmation of "Naegleria" presence can be done by a so-called flagellation test, where the organism is exposed to a hypotonic environment (distilled water). "Naegleria", in contrast to other amoebae, differentiates within two hours into the flagellate state.

Pathogenicity can be further confirmed by exposure to high temperature (42 °C): "Naegleria fowleri" is able to grow at this temperature, but the nonpathogenic "Naegleria gruberi" is not.

Evidence in support of the idea that helminthic infections reduce the severity of autoimmune diseases is primarily derived from animal models. Studies conducted on mice and rat models of colitis, muscular sclerosis, type 1 diabetes, and asthma have shown helminth-infected subjects to display protection from the disease. While helminths are often considered a homogenous group, considerable differences exist between species and the utilization of species in clinical research varies between human and animal trials. As such, caution must be exercised when interpreting the results from animal models.

Helminthic therapy is currently being studied as a treatment for several (non-viral) autoimmune diseases in humans including celiac disease, Crohn's disease, multiple sclerosis, ulcerative colitis, and atherosclerosis. It is currently unknown which clinical dose or species of helminth is the most effective method of treatment. Hookworms have been linked to reduced risk of developing asthma, while "Ascaris lumbricoides" (roundworm infection) was associated with an "increased" risk of asthma. Similarly, "Hymenolepis nana", "Trichoris trichiura", "Ascaris lumbricoides", "Strongyloides stercolaris", "Enterobius vermicularis", and "Trichuris suis" ova have all been found to lower the number of symptom exacerbations, reduce the number of symptom relapses, and decrease the number of new or enlarging brain lesions in patients with multiple sclerosis at doses ranging from 1,180 to 9,340 eggs per gram. However, "Ascaris lumbricoides", "Strongyloides stercolaris" and "Enterobius vermicularis" are not considered suitable for therapeutic use in humans because they do not meet the criteria for a therapeutic helminth.

"Trichuris suis" ova has been used in most cases to treat autoimmune disorders because it is thought to be non-pathogenic in humans and therefore has been rendered as safe.

The use of "Trichuris suis" ova has been granted by the USA Food and Drug Administration as an investigational medicinal product (IMP). While in the UK, the hookworm "Necator americanus" has been granted an IMP license by the Medicines and Healthcare Regulatory Authority. This hookworm is likely to be relatively safe, although it can cause temporary gastrointestinal side effects, especially following the initial inoculation and with larger doses.

The general ideal characteristics for a therapeutic helminth are as follows:

- Little or no pathogenic potential

- Does not multiply in the host

- Cannot be directly spread to close contacts

- Produces a self-limited colonization in humans

- Produces an asymptomatic colonization in humans

- Does not alter behaviour in patients with depressed immunity

- Is not affected by most commonly used medications

- Can be eradicated with an anti-helminthic drug

- Can be isolated free of other potential pathogens

- Can be isolated or produced in large numbers

- Can be made stable for transport and storage

- Easy to administer

The use of trypanotolerant breeds for livestock farming should be considered if the disease is widespread.

Fly control is another option but is difficult to implement.

The main approaches to controlling African trypanosomiasis are to reduce the reservoirs of infection and the presence of the tsetse fly. Screening of people at risk helps identify patients at an early stage. Diagnosis should be made as early as possible and before the advanced stage to avoid complicated, difficult and risky treatment procedures.

One strategy for the prevention of infection transmission between cats and people is to better educate people on the behaviour that puts them at risk for becoming infected.

Those at the highest risk of contracting a disease from a cat are those with behaviors that include: being licked, sharing food, sharing kithchen utensils, kissing, and sleeping with a cat. The very young, the elderly and those who are immunocompromised increase their risk of becoming infected when sleeping with their cats (and dogs). The CDC recommends that cat owners not allow a cat to lick your face because it can result in disease transmission. If someone is licked on their face, mucous membranes or an open wound, the risk for infection is reduced if the area is immediately washed with soap and water. Maintaining the health of the animal by regular inspection for fleas and ticks, scheduling deworming medications along with veterinary exams will also reduce the risk of acquiring a feline zoonosis.

Recommendations for the prevention of ringworm transmission to people include:

- regularly vacuuming areas of the home that pets commonly visit helps to remove fur or flakes of skin

- washing the hands with soap and running water after playing with or petting your pet.

- wearing gloves and long sleeves when handling cats infected with.

- disinfect areas the pet has spent time in, including surfaces and bedding.

- the spores of this fungus can be killed with common disinfectants like chlorine bleach diluted 1:10 (1/4 cup in 1 gallon of water), benzalkonium chloride, or strong detergents.

- not handling cats with ringworm by those whose immune system is weak in any way (if you have HIV/AIDS, are undergoing cancer treatment, or are taking medications that suppress the immune system, for example).

- taking the cat to the veterinarian if ringworm infection is suspected.

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.

Prevention focuses on protecting against mosquito bites in endemic regions. Insect repellents and mosquito nets are useful to protect against mosquito bites. Public education efforts must also be made within the endemic areas of the world to successfully lower the prevalence of "W. bancrofti" infections.

The fundamental prevention strategy is hygiene and sanitation. Secondary measures include stricter meat-inspection standards, livestock confinement, health education, safe meat preparation, mass drug therapy, and identifying and treating human and pig carriers. Moreover, a high level of sanitation and prevention of human faecal contamination of pig feeds also plays a major role in prevention. Infection can be prevented with proper disposal of human faeces around pigs, cooking meat thoroughly and/or freezing the meat at −10 °C for 5 days. For human cysticercosis, dirty hands are attributed to be the primary cause, and especially common among food handlers.

Proper cooking of meat is an effective prevention. For example, cooking (56 °C for 5 minutes) of beef viscera destroys cysticerci. Refrigeration, freezing (−10 °C for 9 days) or long periods of salting is also lethal to cysticerci. Inspection of beef and proper disposal of human excreta are also important measures.

Some treatments for infection with "Toxocara cati" include drugs designed to cause the adult worms to become partially anaesthetized and detach from the intestinal lining, allowing them to be excreted live in the feces. Such medications include piperazine and pyrantel. These are frequently combined with the drug praziquantel which appears to cause the worm to lose its resistance to being digested by the host animal. Other effective treatments include ivermectin, milbemycin, and selamectin. Dichlorvos has also been proven to be effective as a poison, though moves to ban it over concerns about its toxicity have made it unavailable in some areas.

Treatment for wild felids, however, is difficult for this parasite, as detection is the best way to find which individuals have the parasite. This can be difficult as infected species are hard to detect. Once detected, the infected individuals would have to be removed from the population, in order to lower the risk of continual exposure to the parasites.

A primary method that has been used to lower the amount of infection is removal through hunting. Removal can also occur through landowners, as Dare and Watkins (2012) discovered through their research on cougars. Both hunters and landowners can provide samples that can be used to detect the presence of feline roundworm in the area, as well as help remove it from the population. This method is more practical than administering medications to wild populations, as wild animals, as mentioned before, are harder to find in order to administer medicinal care.

Medicinal care, however, is also another method used in round worm studies; such as the experiment on managing raccoon roundworm done by Smyser et al. (2013) in which they implemented medical baiting. However, medicine is often expensive and the success of the baiting depends on if the infected individuals consume the bait. Additionally, it can be costly (in time and resources) to check on baited areas. Removal by hunting allows agencies to reduce costs and gives agencies a more improved chance of removing infected individuals.