Parasitic infections are conditions or illnesses caused by parasites living within and reproducing within the body. Identifying parasitic infections can be challenging due to subtle signs and non-specific symptoms that often develop slowly over time.Β
The most common symptoms of parasitic infections include weight loss, intestinal gas, cramping, and headaches. These symptoms overlap with many chronic health concerns, allowing parasitic infections to mimic other conditions, such as other infections or inflammatory disorders.Β
The most common parasitic infections in the United States include Giardia, Toxoplasma, roundworm, hookworm, and pinworm.Β
If a parasitic infection is suspected, accurate and comprehensive testing may help healthcare providers understand potential causes and support informed care decisions. A thorough history of the patient's illness and travel history is also essential for diagnosis.
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Understanding Parasitic Infections
Ectoparasites, protozoa, and helminths are the three main classes of parasites associated with common parasitic infections in humans.
Ectoparasites
Ectoparasites live on the host's exterior and include ticks, lice, fleas, and mites. They can act as carriers for blood infections that may impact humans and animals.
Helminths
Helminths are multi-celled parasitic worms that infect the gastrointestinal tract, including roundworms, tapeworms, and flukes.Β
Once adults, helminths are visible to the naked eye and range from 1mm to 1 meter in length. Adult helminths exit the host through the stool. Still, the eggs remain in the intestine, creating an opportunity for spreading to others who come into contact with stool-contaminated food, water, and surfaces.
Protozoa
Protozoa are microscopic, single-cell parasites that can infect the gastrointestinal tract, the blood, or bodily tissues. Tens of thousands of protozoa are classified based on their method of locomotion.Β
Protozoa spread when stool or soil contaminated with eggs is ingested, most often through water and produce. They differ from helminths because of their small size and ability to replicate inside the host.
The most common types of protozoa include:Β
- Amoebas: Amoebas employ "false feet," or pseudopods, for mobility (e.g., Entamoeba histolytica)
- Ciliates: Ciliates are defined by their delicate and short cilia, hair-like structures used for locomotion and gathering food (e.g., Balantidium coli)
- Flagellates: Whip-like flagella allow them to assess their surroundings and move around. (e.g., Giardia intestinalis or Trichomonas vaginalis)
- Sporozoans: Sporozoans are non-flagellated, non-ciliated, and non-amoeboid protozoa. They are unable to move in their adult state. (e.g, Plasmodium and Cryptosporidium)
Signs and Symptoms of Parasitic Infections
Since different parasites may contribute to varying health impacts, symptoms of parasitic infections can range widely. Some patients with parasitic infections are unaware of any symptoms, while others experience several, including some that are quite serious.
Gastrointestinal complaints are the most common symptom of intestinal parasitic infections. These include changes in stool, diarrhea, nausea, and vomiting.Β
Other systemic symptoms are possible, including fever, fatigue, teeth grinding, and muscle and joint pain.Β
People with certain parasitic infections can experience skin symptoms such as hives, rashes, general itching, and rectal itching.Β
Parasitic infections are most often assumed to be intestinal. However, it is essential to note that some parasitic infections occur in the blood, the organs, and the urogenital tract.Β
Trichomoniasis is a sexually transmitted infection (STI) of the lower genital tract caused by a parasitic protozoan called Trichomonas vaginalis.Β Although symptoms vary, most people with trichomoniasis cannot tell they have the infection as symptoms come and go.Β
In women, the vagina and urethra are involved; and in men, the urethra is affected. Symptoms include foul-smelling discharge, genital irritation, redness, burning, and itching. Pain with intercourse and lower abdominal discomfort can also be present.Β
Babesiosis is an illness associated with a protozoan parasite that can infect red blood cells. Many Babesia species are found in animals, though only a few may affect humans.
Babesia microti is the most common species that infects humans in the United States.Β It spreads through tick bites, primarily the deer tick.Β Symptoms of Babesiosis are similar to the flu and include fever, chills, headache, fatigue, and joint pain.
Importance of Comprehensive Testing
Early and accurate testing for potential parasitic infections may help in assessing health impacts, supporting patient care, and minimizing risks associated with parasite exposure. However, parasitic diseases may fail to be identified due to the subtle ways they can present, including symptoms that coincide with various health concerns.Β
Current detection methods include laboratory testing along with consideration of travel history, clinical history, and the patient's geographical exposure.Β
Challenges of Diagnosing Parasitic Infections
One of the challenges in diagnosing parasitic infections is the variability in the complexity of parasite lifecycles. Some parasites complete their lifecycle in a single host (simple lifecycle parasites, or SLPs), while others require multiple, successive hosts.Β
Some complex lifecycle parasites (CLPs) require multiple hosts to complete their life span. These parasites are notable for potentially impacting human and animal health, with examples including those associated with toxoplasmosis, malaria, Lyme disease, and sleeping sickness.Β
Complex lifecycle parasites (CLPs) contribute to the difficulty of diagnosing infection. CLPs can be more challenging to diagnose due to their multiple lifecycle stages, long incubation times, and challenges identifying larvae versus adults in various stages.
Examples of parasites with complex lifecycles include:
- Plasmodium (malaria)
- Taenia (tapeworm)
- Toxoplasma gondii (toxoplasmosis)
These species employ multiple hosts throughout their developmental stages to complete their lifecycle.
Diagnostic Methods for Parasitic Infections
Several types of tests are employed to diagnose parasitic diseases. Clinicians order particular tests based on each individual's symptoms and signs.Β Β
Microscopy
An ova and parasite test (O&P) is a stool test commonly ordered when a parasite infection of the gastrointestinal tract is suspected. The CDC recommends that at least three stool samples, collected on separate days, be examined during an O&P. This test uses the naked eye and microscopy to assess for eggs, larvae, and adult parasites.Β
Microscopy, such as that used in an O&P, may offer advantages, including simplicity, specificity, and low cost. Limitations of microscopy include subjective and time-consuming interpretation, the short duration required to maintain a viable sample, and low sensitivity, which is particularly challenging in early infection.
Blood Testing: Serology
Blood testing can also be conducted to detect parasitic infections. Blood smears and serology testing are the two most common types of blood tests ordered for parasite detection.Β
A blood smear is a test used to look for parasites under a microscope that can be found in the blood. Examples of parasites in the blood are babesiosis, a tick-borne illness, and malaria.Β Β Β
Serology tests look for antibodies to parasites made by the immune system when fighting the infection. For example, a serology test identifies toxoplasma-specific antibodies.Β
Enzyme-linked immunosorbent assay (ELISA) is a type of serology test that can detect antibodies to parasites. ELISA testing may provide a cost-effective option for detecting antibodies associated with certain parasites, as it identifies antibodies attached to corresponding antigens.Β
Rapid diagnostic tests (RDTs) are a group of serology tests with short performance times that allow for quick clinical decision-making when addressing suspected parasite infections. They look for specific antigens produced by parasites.Β
RDTs may be advantageous due to their ease of use, minimal lab equipment requirements, and prompt results, offering clinicians timely insights to support health assessments.
Blood Testing: Polymerase Chain Reaction (PCR)
While microscopic techniques and blood testing have been the gold standard of parasite testing, molecular testing techniques are also valuable.Β Β
Some protozoan infections are easier to identify via polymerase chain reaction (PCR) methodology. This method employs diagnostic primers and tests DNA preparations extracted from fecal samples. PCR is used when microscopic detection is difficult, especially if there is a low number of parasites in the stool sample.Β
Real-time PCR is another molecular technique that monitors the progress of the reaction in real-time, compared to the end-point detection available with standard PCR. This improves the lab results' rapidity, accuracy, and sensitivity.Β
Studies suggest that molecular assays, such as PCR, may offer useful alternatives to microscopy and serology. These methods are highly sensitive and specific, showing promise in identifying particular parasitic species and tracking health progress.
ImagingΒ
Imaging studies, including X-ray, Computerized Axial Tomography (CAT), ultrasound, and Magnetic Resonance Imaging (MRI) scans, may be useful in identifying the presence of tissue-invasive endoparasites.
This type of testing is useful when looking for tissue-invasive endoparasites that can reside in specific organs. Examples are tapeworms, flukes, and various protozoans such as Entamoeba histolytica, a protozoan considered a worldwide, tissue-invasive pathogen.Β
Emerging Diagnostic Techniques
In addition, some exciting emerging diagnostic techniques are at the forefront. Genome analysis with Next-Generation Sequencing (NGS) has shown promise in supporting parasite research and testing. The NGS technique allows for high-resolution data differentiating pathogen strains that differ by as little as one single-nucleotide polymorphism (SNP).Β
Another emerging laboratory method is metabolomics. This method can detect parasites and their interactions with hosts, identify biomarkers to diagnose, stage, and predict the direction of parasitic disease, and assess the interactions between the host, the parasite, and the microbiome.Β Β
While these newer techniques are still in their early stages, some functional medicine test panels offer a more comprehensive view by combining various tests to assess for parasites.Β
In addition to an O&P investigation, several functional medicine laboratories offer comprehensive stool panels that assess the microbiome's overall health and reveal effective and efficient treatment options that protect it.Β
These panels combine microscopy, stool culture, and PCR techniques. Many of these panels also include inflammatory markers such as calprotectin and lactoferrin, stool pH, enzyme assays, and assessment of beneficial and dysbiotic bacteria in the gut, offering a more complete stool assessment.
Best Practices for Practitioners
Parasitic infection may be worth considering as part of a differential diagnosis in patients with broad symptoms potentially associated with parasitic exposure. These include a history of chronic gastrointestinal concerns, dermatological complaints, anal itching, and unexplained weight loss.Β Β
Parasitic illness should be considered in patients with coinciding travel history, poor living conditions, and habitation in susceptible geographic locations.Β If a parasitic infection is suspected, testing should be initiated after appropriate history and physical exam is acquired.Β
Due to its low cost and simplicity, an O&P x 3 is a valid first step in lab testing for parasites. However, the following steps are at the healthcare provider's discretion.Β
Prioritizing which tests to order will vary greatly and depend on the patient's symptoms and the location of the suspected parasite in the body. These factors will determine whether further blood or stool testing is valuable.Β
While serology testing and blood smears may be helpful in parasite diagnosis, other blood testing, such as a complete blood count (CBC) and chemistry panel (CMP), may also be valuable to rule out anemias, deficiencies, and organ involvement.Β
Combining stool and blood testing may be beneficial for a more thorough evaluation of the patient. However, it is crucial to keep in mind that false negatives can occur, as some assessments for parasites do not differentiate between a current and a previous infection.Β
Comprehensive stool assessments available through some functional medicine labs may provide healthcare practitioners with valuable insights, as they offer a wide range of information within a single test panel.Β
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Key Takeaways
- If a parasitic infection is suspected, accurate and comprehensive testing may support healthcare providers in understanding potential causes and developing informed care plans.
- Early and accurate diagnosis of parasitic infection is essential for managing the severity of the illness, improving patient outcomes, and minimizing the spread of disease.
- Current detection and diagnosis methods employ laboratory testing, travel history, clinical history, and the patient's geography.
- An (O&P) is a stool test commonly ordered when a parasite infection of the gastrointestinal tract is suspected.Β
- Blood testing, including serology and blood smears, may provide helpful insights in cases of suspected parasitic exposure.
- PCR and real-time PCR are sensitive and specific methods that can assist in identifying specific parasitic species and in monitoring health progress.
- Imaging studies may be of most value when testing for tissue-invasive endoparasites.
- Several functional medicine laboratories offer comprehensive stool test panels that employ O&P x 3 and other markers that assess the microbiome's overall health.
- Next Generation Sequencing and Metabolomics are two emerging laboratory techniques that offer great promise for the future of parasite detection and treatment.
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