There are many types of parasitic diseases, and if intestinal parasitic infections caused by helminths or protozoa are not properly identified and treated, their morbidity and mortality can increase. While these diseases are generally considered to be only found in developing countries, there is a trend towards an increasing number of cases of parasitic infections in developed countries as global tourism and migration increase.
Recently, the Medscape medical website introduced several common intestinal parasitic infections, aiming to raise awareness among healthcare professionals about the characteristics, life history, diagnosis, and treatment of common intestinal parasites.
Figure 1. Hookworm adheres to the intestinal mucosa (Image: CDC)
worm
1. Tapeworms
Tapeworms belong to the order tapeworms of the phylum Obpenidae, including taenia schizocephalus, taenia hymenopsis, tapeworm compound holes, echinococcum tapeworms, and taenia terrestrium. Tapeworms are long and mostly segmented. Adult tapeworms have no digestive tract and absorb nutrients through the cortex. Adults have a head (called a cephalic segment), a neck, and a segmented body, and are hermaphrodite.
Tapeworms require 1-2 intermediate hosts in their life history. Usually, the eggs are released from the host into the environment and then ingested by the intermediate host. The eggs hatch in the intermediate host, and then the larvae enter the host tissue and become encapsulates. The primary host ingests the capsule by eating the meat of the intermediate host.
Figure 2. Life history of Echinococcus tapeworm (Image: CDC)
The life history of Echinococcus tapeworm is shown in Figure 2. Humans are the primary hosts for tapeworms, taenia and taenia membranium, but they may also be intermediate hosts for Echinoccus and Taenia diastiformis. Typical routes of infection are fecal-oral transmission or consumption of contaminated, undercooked meat.
The most common symptoms of most tapeworm infections are abdominal pain, anorexia, weight loss, and malaise. Taenia schizophalum absorbs most of its vitamin B12, resulting in megaloblastic anemia in the host. Taenia porcine can parasitize cysticercosis in the central nervous system, causing neurocysticercosis and inducing epilepsy.
Figure 3. Echinoccus fine-grained tapeworm (Image: CDC/Peter M. Cchantz)
Echinococcum fine-grained tapeworm can slowly parasitize echinococcal sacs over time, eventually having a huge impact on the affected organs. Lesions of the affected organs are cellular and may not develop symptoms until 5 to 15 years after infection. Cystic rupture can cause fever, itching, urticaria, eosinophilia, and allergic reactions. Patients with liver involvement and symptoms may have mortality rates of more than 2% to 4% if left untreated, and echinococcosis can be estimated to be more than 90% after 10 to 15 years if left untreated.
Tapeworm infection can be diagnosed by collecting 2 to 3 stool samples to examine the eggs and parasites. Enzyme-linked immunosorbent assay (ELISA), western blotting, and polymerase chain reaction (PCR) may be helpful in definitive diagnosis; their sensitivity and specificity vary depending on the tapeworm species involved.
Figure 4. A cystic lesion on the left side of the midranial fossa, consistent with an imaging diagnosis of neurocysticercosis (Credit: Dr. Lars Grimm)
Imaging tests are usually used to evaluate for cerebral cysticercosis (CT/MRI) and echinococcosis cysts (CT/MRI/ultrasonography). MRI T2-weighted images suggest a cystic lesion on the left side of the midranial fossa, consistent with imaging diagnosis of neurocysticercosis.
Treatment of most tapeworm infections includes deworming, such as praziquantel, niclosamide, and albendazole. Surgical treatment is usually the option for patients with symptoms of local infection, including surgical excision and aspiration.
2. Pinworms
Figure 5. Perianal pinworm (Image: Medscape/Joseph J Bocka)
Pinworms (human pinworms) are the most common intestinal parasite in the United States. Pinworms parasitize the small intestine, but pregnant females can migrate to the anus and lay eggs in the folds of the perianal skin, especially at night (figure 5). The hatched larvae migrate back to the anus and lower end of the small intestine, causing reverse infection. Eggs can be discharged into the air or onto the surface of pollutants and then ingested by the host.
Most infected patients are asymptomatic. The most common symptom is itching of the anus. However, it should be noted that pinworm infection is also an uncommon trigger for appendicitis in children, with a global incidence of 0.2% to 41.8%.
Pinworm disease can be diagnosed by looking at eggs obtained by a microscope perianal swab and female pinworms (the ideal sampling time is in the morning). Treatment involves taking deworming medications (mebendazole, bis-hydroxynaphthalazine, or albendazole) throughout the family while all clothes and bedding are cleaned.
3. Roundworms
Roundworms are the most common helminth infection worldwide. Human roundworms are the largest genus of roundworms that infect humans, can be up to 35 cm long, and can survive in the small intestine for up to 2 years. His life history is complex and can involve a variety of human organs (Figure 6).
Figure 6. Life history of roundworms (Image: CDC)
Females are fertilized by nearby males and lay about 200,000 eggs a day. Fertilized eggs survive in the soil for up to 17 months, cause infection by being ingested by the host, and then hatch in the host's small intestine. The second stage larvae pass through the wall of the small intestine and migrate through the portal system to the liver and lungs. The larvae can be coughed up and then swallowed into the digestive tract, where they develop into adults.
Adults feed on the products of digestion, resulting in a lack of protein, calories or vitamin A in children and malnutrition. Because roundworms do not multiply in the host, infection is limited to 2 years unless re-infection occurs.
Although most infected individuals are asymptomatic, patients may present with growth retardation, ascaria pneumonia, eosinophilia, bowel or pancreatic obstruction, and hepatobiliary duct injury. Roundworms are diagnosed primarily by looking for fecal eggs and parasites. Abdominal x-ray may reveal signs of intestinal obstruction, and ultrasonography may reveal single worms or twisted adult worms.
Figure 7.400 unstained unstained unfertilized roundworm eggs under × magnification (Credit: DR. CDC/Mae Melvin)
Albendazole, mebendazole, or ivermectin monotherapy are usually effective in eradicating roundworms. Deworming is not recommended during acute pneumonia, not only because ascaria pneumonia is a self-limiting disease, but also because of the high risk of pneumonia at the time of larval death. Endoscopic retrograde cholangiopancreatography (ERCP) can be used to diagnose and treat infections of the bile duct system.
Most adults spontaneously migrate from the small intestine and biliary system, but refractory cases may require surgery. Prophylactic medication may be used as a short course of treatment, but water sources, the environment and hygiene must be improved to prevent re-infection in the long term.
4. Hookworms
Human hookworms, mainly duodenal hookworms and Hookworms of the Americas, are infected in about 576-740 million people worldwide. Hookworms are the second most common trigger for worm infection (roundworms in place 1).
Figure 8. Hookworm life history (Image source: CDC)
In soils contaminated with human feces, hookworms can quickly penetrate the skin and enter the human body. It is common for hookworms to appear where they penetrate the skin (local skin symptoms including severe allergic itching). The larvae burrow into the microvenous veins and follow the bloodstream to the lungs, penetrating the capillaries into the alveoli, causing asymptomatic alveolitis with eosinophilia. Coughing and swallowing transport the larvae to the intestines, where the larvae then develop into adults. Adults feed on blood from the capillaries of the mucous membranes.
About 5 weeks after the initial infection, the female produces thousands of eggs each day into the soil. If there is no re-exposure infection, the infection disappears after the adult dies. The life cycle of the plate-mouth nematode is 3-10 years, and the hookworm is 1-3 years.
Patients may present with diarrhea, vague abdominal pain, cramping, or nausea. Diagnosis can be confirmed by examination of fecal eggs and parasites. A complete blood count may reveal both iron deficiency anemia and eosinophilia. Iron supplementation can treat anemia, either monotherapy with albendazole or mebendazole, or once daily with thiamethiazide bisparabenate for 3 days, which can effectively clear the infection.
5. Intestinal flukes
Intestinal flukes belong to the class of trematodes, are hermaphroditic, flattened, and range in length from a few millimeters to a few centimeters. The most commonly infected human intestinal flukes are Ginger Flakes Brucella (Figure 9), Xenomorphic Trematodes, Lateral Trematodes Yokogawa, and Trematodes spinosa, of which Ginger Flakes Brucellois is the largest and most common human gut fluke.
Figure 9. Left is an unstained Brinell ginger flake egg under 500x magnification, and the right is an adult Brinze ginger flake (Image: CDC on the left; CDC/Georgia Public Health Department on the right)
The life history of each species of intestinal fluke is very complex, involving multiple intermediate hosts such as snails, fish, tadpoles, or vegetables. Humans are infected primarily by ingesting raw or undercooked intermediate hosts. The developing larvae adhere to the wall of the small intestine and then develop into adults over several months. Adults can cause inflammation, ulceration, and mucus secretion of tissues at the site of adsorption.
Most infected patients are asymptomatic, but some develop loose stools, weight loss, malaise, and nonspecific abdominal pain. Patients with severe infections may alternate diarrhoea and constipation, edema of the face, abdominal wall and lower extremities, anorexia, nausea, and vomiting.
Examination of eggs and parasites in the stool confirms the diagnosis. Triple doses of praziquantel therapy for more than 1 day adequately clear the infection.
6. Microsporidium
Microsporidium is a spore-producing parasite that grows within obligate cells. There are more than 1200 genera in the microspore phylum, most of which can cause infection in humans. The two most important are microsporidium encephalitis and intestinal microsporidium. Most infected patients have HIV or other immunosuppressive diseases, including organ transplant patients, people with diabetes, children, and the elderly.
Microsporidium disease is infected by human-to-human or waterborne transmission of ingested or inhaled microsporidium spores. The spores protrude from the electrode tube and inject infectious spore plastin into the host. The spores multiply within the cell by a dichotomy and eventually destroy the cell, releasing more spores (Figure 10).
Patients with enteric microsporidium disease may present with chronic nonspoemic diarrhea, weight loss, abdominal pain, nausea, vomiting, and malnutrition. Transmission through spores can also present with cholecystitis, renal failure, and muscle, brain, and respiratory infections.
Figure 10. Electron microscope image of microsporidia encephalitis spores rupturing from a eukaryotic cell (Image source: CDC, USA)
Microsporidium can be diagnosed by microscopic examination of the stool, but this does not distinguish between infected microsporidium species. Cytological and histological examination may be helpful in the diagnosis. In addition, immunofluorescence tests (IFAs) and PCR can also be used. Albendazole treatment for 2 to 4 weeks is effective for most eyes, intestines, and disseminated microsporidium.
protozoan
1. Colonis
Possynos disease is an intestinal infection caused by protozoan colonic vivocilli (figure 11). Its main host is pigs, so pig farmers or pig by-product merchants are at high risk of infection.
Figure 11. Possylium colon (Image: CDC/Oregon Public Health Laboratory)
Humans infect infected cysts by ingesting contaminated food or water, and then the manoidal valloids migrate to the large intestine, cecum, and terminals of the ileum. There, then, trophozoites develop, which are copied and bound by a dichotomy by consuming bacteria. The trophozoites predominantly parasitize the lumen of the intestine, but may penetrate the mucous membranes and cause ulcers.
Although most immunocompetent patients are asymptomatic, patients may present with mucoid bloody stools, nausea, vomiting, abdominal pain, anorexia, weight loss, fever, colitis, and dehydration.
Diagnosis is confirmed by wet smear of stool specimens (1000×x magnification). The trophozoite is large, covered with cilia, and has spiral-shaped movements, and these features identify the trophozoite. Treatment includes fluid and electrolyte replacement and treatment with tetracycline, metronidazole, or diiodoquinoline. There are currently no large-scale reports of antibiotic resistance.
2. Fragile binuclear amoeba
Fragile binucleated amoebas are flagellar protozoa (figure 12) that causes large intestinal infection. It is usually thought to be transmitted by human-human fecal-oral transmission or co-infection with pinworm eggs (human pinworms). However, the life history of the fragile binuclear amoeba is not yet fully understood.
Figure 12. Fragile dual-core amoeba (Image source: CDC)
The trophozoite infects the mucosal trap cells of the large intestine, causing an eosinophilic inflammatory response. Abdominal pain and non-bloody diarrhea are the most common symptoms, but symptoms such as anorexia, weight loss, nausea, vomiting, flatulence, headache, fever, malaise, and fatigue can also occur.
Diagnosis is mainly by microscopic observation of long-lasting stained fresh stool smears (trichromatic) that can reveal characteristic polymorphic trophozoites (commonly binuclear) with up to four nuclei, which are characteristic of their chromatin aggregates. Treatment is primarily anthelminthic, such as diiodoquinoline (the drug of choice), metronidazole, tetracycline, or paromycin.
3. Giardia
Giardiasis is a major diarrhoeal disease prevalent worldwide. In the United States, giardiasis is the most commonly diagnosed intestinal parasitic disease. Giardiasis is usually caused by Giardia. The route of infection is mainly through ingestion of giardia capsules from contaminated water sources, followed by decanting, reproduction and cloning of the capsules in the upper part of the small intestine. The capsules remain viable in ice water for 2 to 3 months, and 10-25 sacs can cause infection. The exact pathophysiology mechanism is not yet clear.
Most infections are asymptomatic, and asymptomatic carriers are common. Human-to-human transmission due to poor personal and environmental hygiene is the main route of infection. Patients with symptomatic infection may present with sudden diarrhea, watery diarrhea, abdominal cramps, vomiting, fever, malaise, anorexia, lactose intolerance, and weight loss. Symptoms can last up to 3 weeks, with more than 50% of patients losing an average of 10 pounds. There is no significant change on physical examination, and stool tests are often heme-negative.
Figure 13. Electron microscope scan images showing giardia sacs (bottom left) and trophozoites (bottom right) (Credit: DR. CDC/Stan Erlandsen, USA)
Stool examination of sacs or trophozoites, ELISA or IFA methods to detect fecal antigens, or a very small number of duodenal samples may be helpful in diagnosis. Treatment consists mainly of fluid and electrolyte replacement, along with insect repellents such as albendazole or metronidazole.
4. Hemolytic endomegalyb
Amoebic disease is caused by histolytic amoeba protozoa and is mainly infected by ingestion of cysts in soil, food, or water contaminated with feces. Amoeba capsules develop into trophoblasts in the cecum, terminal ileum, and colon. The trophozoite crosses the barrier of the colonic mucosa, destroys tissues, and causes secretory bloody diarrhea and colitis. Hematogenous transmission can cause trophozoites to accumulate in the liver, brain, and lungs, leading to abscess formation.
Microscopic examination of fecal cysts and trophozoites, as well as ELISA, IFA, indirect hemagglutination tests, PCR, etc., can diagnose intrahistolytic amoeba. Diiodoquinoline or paromycin may treat patients with asymptomatic amoebiasis. Patients with symptomatic bowel or parenteral disease are treated with metronidazole or tetracycline, followed by diiodoquinoline or paronomycin. Parenteral amoebic abscesses generally require drainage and treatment with metronidazole or tetracycline.
Figure 14. Picture on the left shows a composite micrograph of the tissue-lysolytic amoeba capsule (iodine staining) and trophozoites (Giemsa staining) (Image source: CDC, USA); the picture on the right is a three-color microscope of the tissue-lysolytic amoeba trophozoite (Image source: CDC/Mae Melvin and Dr. Greene)
5. Cryptosporidium
Cryptosporidium disease is an infection caused by protozoa of the cryptosporidium genus, most commonly in human cryptosporidium or cryptosporidium microsporidium. Transmission routes are mainly human-to-human fecal-oral transmission, but animal transmission to humans or waterborne transmission can also occur.
Cryptosporidium oocysts are highly infectious, with 10-1000 oocysts causing infection. The oocyst invades intestinal cells but parasitizes within the vacuoles formed between the host cell membrane and cytoplasm. They cause diarrhea by increasing intestinal permeability, secreting chlorides, and causing malabsorption in the small intestine.
Figure 15. Cryptosporidium life history (Image adapted from CDC/Alexander j da Silva and Melanie Moser)
In healthy adults, cryptosporidiosis presents primarily as self-limiting diarrhea that lasts up to 4 weeks. But in children and immunodeficient patients such as AIDS, it can cause persistent severe diarrhea.
Microscopic examination of stool (modified acid-antacy staining reveals red-stained round oocysts, Figure 16), antigen testing, or PCR can help diagnose cryptosporidiosis. Treatment with nizonide shortens the duration of diarrhea in immunocompetent patients, but is not effective in patients with AIDS. Symptomatic treatments such as rehydration fluids, nutritional support, and anti-exercise drugs can help prevent subsequent morbidity.
Figure 16. Modified Nichys' acid-resistant staining for Cryptosporidium oocysts (Credit: CDC/Oregon Public Health Laboratory)
6. Spore coccidioides such as Besteni
Isosporangiosis is a diarrheal disease caused by sporecoccidioides such as Besperiococcus beetle. Infection is transmitted through human-to-human fecal mouth, and no animal carnivost reservoir has been found. The host becomes infected by ingesting an oocyst containing sporangia, which desaccesticles and releases the asspores. The sporozoites invade the mucosal epithelial cells of the distal and proximal jejunum of the duodenum and reproduce asexually asexually, with the final product being the oocyst and released into the feces.
Although no toxins have been found, symptoms of isosporidiosis indicate that they are toxin-mediated diseases. Symptoms include extensive watery non-bloody diarrhea, crampy abdominal pain, malaise, anorexia, vomiting, and fever. Infants, children, and immunodeficient patients may present with persistent severe diarrhea.
Figure 17. Life history of isosporidium (image adapted from CDC)
Diagnosis can be confirmed by microscopic examination of stool samples by wet tablets or modified acid-antacid staining (Figure 18 left). Ultraviolet autofluorescence microscopy (Figure 18 right) is also helpful in the diagnosis.
Figure 18. Isosporidium, the left picture is a modified acid-resistant staining method, and the right picture is an image under an ultraviolet autofluorescence microscope (Image source: CDC, USA)
Fluid and electrolyte supplementation and oral co-trimoxazole are effective in the treatment of other spore coccidiosis. Ciprofloxacin is a second-line alternative. Long-term suppressive therapy may be required in patients with co-AIDS infection.
In summary, most intestinal parasitic infections are caused by eating food or water contaminated with parasite eggs. Therefore, paying attention to dietary hygiene, not eating undercooked meat and not drinking raw water, while maintaining good personal hygiene, can help reduce intestinal parasitic infections.