NEMATODESNematodes are elongated, symmetric roundworms andconstitute one of the largest phyla in the animal kingdom.Most nematode species are free-living, but some have evolvedinto parasites of plants and animals, including humans.Parasitic nematodes of medical significance may be classifiedas intestinal or tissue nematodes.All are zoonotic infections caused by incidental exposuretoinfectious nematodes.
INTESTINAL NEMATODES• More than a billion people worldwide are infected with one or more species of intestinal nematodes.• These parasites are most common in regions with poor fecal sanitation, particularly in developing countries in the tropics and subtropics• Although nematode infections are not usually fatal, they contribute to malnutrition and diminished work capacity.• Humans may on occasion be infected with nematode parasites that ordinarily infect animals; these are zoonotic parasites.
Trichinellosis / Trichinosis Трихинелоза• Develops after the ingestion of meat containing larves of Trichinella spiralis - pork or meat from a carnivore.• While most infections are mild and asymptomatic, but heavy infections can cause:- severe enteritis,- periorbital edema,- myositis,- death
Five species of Trichinella are now recognized as causes of infection in humans. Two species are distributed worldwide:- Trichinella spiralis, which is found in a great variety of carnivorous and omnivorous animals,- Trichinella pseudospiralis, which is found in mammals and birds.- Trichinella nativa is present in Arctic regions and infects bears;- Trichinella nelsoni is found in equatorial Africa, where it is common among felid predators and scavengers such as hyenas and bush pigs;- Trichinella britovi is found in temperate areas of Europe and western Asia among carnivores but not among domestic swine.
Life Cycle- After the consumption of meat by the host, encysted larvae are liberated by digestive acid and pepsin.- The larvae invade the small – bowel mucosa and mature rapidly into adult worms.- After about 1 week, female worms release newborn larvae that migrate via the circulation to striated muscle.- The larvae of all species except T. pseudospiralis then encyst in the muscle cell
• Human trichinosis is most often caused by the ingestion of infected pork products and thus can occur in almost any location where the meat of domestic or wild swine is eaten.• Human trichinosis also may be acquired from the meat of other animals, including:- dogs (in parts of Asia and Africa),- horses (in Italy and France), and- bears and walruses (in northern regions).
Pathogenesis And Clinical Features• Clinical symptoms of trichinosis arise from the successive phases of parasite enteric invasion, larval migration, and muscle encystment.• Most light infections (those with fewer than 10 larvae per gram of muscle) are asymptomatic,• whereas heavy infections (which can involve more than 50 larvae per gram of muscle) can be life- threatening.• Invasion by large numbers of parasites provokes diarrhea during the first week after infection.• Abdominal pain, constipation, nausea, or vomiting also may be prominent.• The prolonged and fulminant diarrhea noted probably reflects a response to repeated infection.
The migrating Trichinella larvae provoke a markedlocal and systemic hypersensitivity reaction:- fever- hypereosinophilia,- Periorbital and facial edema- hemorrhages in the subconjunctivae, retina,- nail beds ("splinter" hemorrhages).
Hypersensitivity reaction:- Periorbital and facial edema
• dysphagia sometimes develops• Myocarditis with tachyarrhythmias or heart failure,• less commonly, encephalitis or pneumonitis may develop and accounts for most deaths of patients with trichinosis.• A maculopapular rash, headache, cough, dyspnea
2 to 3 weeks after infection there are symptoms:• myositis with myalgias,• muscle edema,• weakness develop, usually• with the inflammatory reactions to migrating larvae.• The most commonly involved muscle groups include:- the extraocular muscles;- the biceps; and- the muscles of the jaw, neck, lower back, and diaphragm Peaking about 3 weeks after infection, symptoms subside only gradually during a prolonged convalescence.
Laboratory Findings And Diagnosis• Blood eosinophilia develops in more than 90 % of patients with symptomatic trichinosis and may peak at a level of greater than 50 %• Serum levels of IgE and• muscle enzymes, including- creatine phosphokinase,- lactate dehydrogenase, and- aspartate aminotransferase, are elevated in most symptomatic patients.
Epidemiological Diagnosis- Patients should be questioned about their consumption of pork or wild-animal meat and about illness in other individuals who ate the same meat.- A presumptive clinical diagnosis can be based on fevers, eosinophilia, periorbital edema, and myalgias after a suspect meal.- Arise in the titer of parasite-specific antibody, which usually does not occur until after the third week of infection, confirms the diagnosis.- Alternatively, a definitive diagnosis requires surgical biopsy of at least 1 g of involved muscle; the yields are highest near tendon insertions. The fresh muscle tissue should be compressed between glass slides and examined microscopically
TREATMENT Current anthelmintic drugs are ineffective against Trichinella larvae in muscle. Glucocorticoids like prednisone (1mg/kg daily for 5 days) are beneficial for severe myositis and myocarditis. Mebendazole, like thiabendazole, appears to be active against enteric stages of the parasite, but its efficacy against encysted larvae has not been conclusively demonstrated.• Mebendazole (Vermox) tb. 0,1 gr., 20 mg/kg /day, 3x1, 10-14 days; children - 5 mg/ kg/day• Albendazole (Zentel) tb. 0,2 gr, 10 mg/kg /day, 7-10 days• Pyrantel (Combartin) tb. 0,25 gr 10 mg/kg/twice a day, 5 days• antipyretics, and analgesics.
Prevention Larvae may be killed by:- cooking pork until it is no longer pink or- by freezing it at -15°C for 3 weeks.- However, Arctic T. nativa larvae in walrus or bear meat are relatively resistant and may remain viable despite freezing.
Ascariasis/Ascaridosis/Ascaris lumbricoides is thelargest intestinal nematodeparasite of humans, reachingup to 40 cm in length.1 billion people are infectedworldwide.Most infected individualshave low worm burdens andare asymptomatic. Clinicaldisease arises frompulmonary and intestinalcomplications.
Life Cycle• Adult worms live in the lumen of the small intestine.• Mature female Ascaris worms are producing up to 240,000 eggs a day, which pass with the feces.• Ascarid eggs, which are remarkably resistant to environmental stresses, become infective after several weeks of maturation in the soil and can remain infective for years.• After infective eggs are swallowed, larvae hatched in the intestine invade the mucosa, migrate via the circulation to the lungs, break into the alveoli, ascend the bronchial tree, and return via swallowing to the small intestine, where they develop into adult worms.
Between 2 and 3 months elapse between initial infection and egg production.• The adult worms live for approximately 1 to 2 years.Epidemiology• Ascaris is widely distributed in tropical and subtropical regions as well as in other humid areas.• Transmission typically occurs via fecally contaminated soil
Clinical Features During the lung phase of larval migration, about 9 to 12 days after egg ingestion, patients may develop an:- irritating nonproductive cough and- burning substernal discomfort that is aggravated by coughing or deep inspiration.- Dyspnea and blood-tinged sputum are less common.- Fever is usually reported, with temperatures sometimes exceeding 38.5°C.- Chest x-rays may reveal evidence of eosinophilic pneumonitis (Loefflers syndrome), with round or oval infiltrates a few millimeters to several centimeters in size. These infiltrates may be transient and intermittent.
• Adult worms in the small intestine usually cause no symptoms.• In heavy infections, particularly in children, a large bolus of entangled worms can cause pain and small-bowel obstruction,• complicated by perforation• A large worm can enter in the biliary tree, causing biliary colic, cholecystitis, holangitis, pancreatitis, and intrahepatic abscesses.• Migration of an adult worm up the esophagus can provoke coughing and oral expulsion of the worm.• intestinal and biliary ascariasis can rival acute appendicitis and gallstones as causes of surgical acute abdomen.
Laboratory Findings• Microscopic detection of characteristic Ascaris eggs (65 by 45 um) in fecal samples.• Larvae can be found in sputum• A plain abdominal film• Worms can be detected by ultrasound and cholangiopancreatograpy
TREATMENT- Mebendazole 2 x 0,2 gr. 3 days- Albendazole 0,4 gr. These benzimidazoles are contraindicated in pregnancy• Pyrantel pamoate – 10 mg/kg and• piperazine citrate are safe in pregnancy
TRICHURIASISMost invasions with thewhipworm Trichuris trichiuraare asymptomatic, butheavy infections may causegastrointestinal symptoms.Like the other soil-transmittedhelminths, whipworm isdistributed globally in thetropics and subtropics and ismost common among poorchildren.
Life CycleThe adult worms reside in thecolon and cecum, into thesuperficial mucosa.Thousands of eggs laid daily byadult female worms pass via thefeces and mature in the soil.After ingestion, infective eggshatch in the duodenum, releasinglarvae that mature beforemigrating to the large bowel.The entire cycle takes about 3months, and adult worms may livefor several years.
Clinical FeaturesMost infected individuals have no symptomsHeavy infections may result in abdominalpain, anorexia, and bloody or mucoid diarrhea resemblinginflammatory bowel disease.Rectal prolapse can result from massive infections inchildren, who often suffer from malnourishment and otherdiarrheal illnesses.
Diagnosis The characteristic - 50- by 20-um lemon-shaped whipworm eggs are readily detected on stool examination. Treatment• Adult worms, which are 3 to 5 cm long, occasionally can be seen on proctoscopy.- Mebendazole- Albendazole- Pyrantel pamoate
ENTEROBIOSIS PINWORM Enterobius vermicularis is more common in temperate countries than in the tropics.• Enterobius adult worms are about 1 cm long and dwell in the bowel lumen.• The gravid female worm migrates nocturnally out into the perianal region and releases up to 10,000 immature eggs.
Life Cycle The eggs become infective within hours and are transmitted via hand-to-mouth passage.This life cycle takes about 1 month, and adult worms survive for about 2 months.Self- infection results from perianal scratching and transport of infective eggs on the hands or under the nails to the mouth.Owing to the ease of person-to- person spread, pinworm infections are common among family members andinstitutionalized populations.
Clinical Features• Most pinworm infections are asymptomatic.• Perianal pruritus is the cardinal symptom. The itching is often worse at night owing to the nocturnal migration of the female worms, and it may lead to excoriation and bacterial superinfection.• Heavy infections have been claimed to cause abdominal pain and weight loss.• On rare occasions, pinworms invade the female genital tract, causing vulvovaginitis and pelvic or peritoneal granulomas.• Eosinophilia or elevated levels of serum IgE are rare.
DiagnosisSince pinworm eggs are not usuallyreleased in the bowel, the diagnosiscannot be made by looking for eggsin the feces.Instead, eggs deposited in theperianal region are detected by theapplication of clear cellulose tape tothe perianal region in the morning.After the tape is transferred to amicroscope slide, will reveal thecharacteristic pinworm eggs, whichare oval, measure 55 by 25 um, andare flattened along one side.
TREATMENTMebendazole 2 x 0,2 gr. 3 daysAlbendazole 0,4 gr. These benzimidazoles are contraindicated in pregnancyPyrantel pamoate – 10 mg/kg andpiperazine citrate are safe in pregnancy All affected individuals should be given a dose of mebendazole or pyrantel pamoate, with treatment repeated after 10 to 14 days.• Treatment of household members is also advocated to eliminate asymptomatic reservoirs of potential reinfection.