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Tissue And Blood Helminths

Trichinella Potential Severity

Usually asymptomatic, but heavy infections can lead to severe myocarditis, pneumonia, and encephalitis that can be fatal.

Prevalence, Epidemiology, and Life Cycle

Trichinosis is found worldwide, wherever contaminated meat is undercooked.

Trichinella is a roundworm whose larvae are released from cyst walls in contaminated meat by acid-pepsin digestion in the stomach. Upon entering the small intestine, larvae invade the intestinal microvilli and develop into adult worms.

Females then release larvae that enter the bloodstream and seed skeletal and cardiac muscle. The larvae grow in individual muscle fibers and eventually become surrounded by a cyst wall. Once encysted, the larvae can remain viable for many years. If the cyst-containing muscle tissue is ingested, Trichinella is able to take up residence in the new host.

The domestic animal that primarily becomes infected with Trichinella is the pig. In many countries, including the United States, pigs are fed with grain, which explaining the low incidence of trichinosis. In the United States, laws were enacted to prevent the feeding of uncooked garbage to pigs, and as a result, fewer than 100 trichinosis cases are reported annually.

Most cases of trichinosis result from improperly processed pork, but undercooked bear, walrus, cougar, wild boar, and horse meat have also been sources of Trichinella infection.

Clinical Presentation

Symptoms correlate with the numbers of worms in tissues. Because the number of cysts ingested is often low, most infections are asymptomatic. Heavier infestations can result in diarrhea, abdominal pain, and vomiting during the intestinal phase, followed in 1 to 2 weeks by fever, periorbital edema, subconjunctival hemorrhages, and chemosis. Muscle pain, swelling, and weakness are common.

The extraocular muscles are frequently involved first, followed by the neck and back, arms and legs. Occasionally, a macular or petechial diffuse body rash may be seen. These symptoms usually peak within 2 to 3 weeks, but they may be followed by a prolonged period of muscle weakness. Death is uncommon, but can result from severe myocarditis leading to congestive heart failure. Fatal encephalitis and pneumonia have also been reported.

About Trichinosis

  1. Caused by ingesting larvae cysts, primarily from pork.
  2. Uncommon in countries that don't feed pigs uncooked garbage.
  3. Larvae infect skeletal and cardiac muscle.
  4. Light infections are often asymptomatic.
  5. Heavy infection causes abdominal pain and diarrhea, followed by fever, periorbital edema, muscle pain (ocular muscles firsthand myocarditis, associated with marked eosinophilia and increased creatine phosphokinase.
  6. Diagnosis is made by muscle biopsy, ELISA, or clinical signs.
Tissue And Blood Helminths

Diagnosis and Treatment

An elevated peripheral eosinophil count associated with periorbital edema, myositis, and fever strongly suggest the diagnosis. Eosinophil counts are often very high. Serum creatine phosphokinase is also elevated, reflecting muscle damage. A specific diagnosis requires biopsy of a symptomatic muscle to demonstrate Trichinella larvae. Because exposure history and the clinical manifestations are usually distinct, a biopsy is rarely required.

Antibody to Trichinella increases within 3 weeks and can be detected by ELISA. Mebendazole is recommended for treatment. Myositis may be reduced by using a dosing regimen that starts with a lower dose for 3 days, and then follows with higher doses for 10 days. Albendazole can be given as alternative therapy. In critically ill patients, corticosteroids (prednisone 50 mg daily for 10 to 15 days) may be helpful, but no controlled trials have been conducted proving efficacy. Cooking meat above 55°C until all pink flesh is browned kills encysted larvae and prevents trichinosis.

Echinococcosis Potential Severity

Infections with Echinococcus multilocularis usually lead to symptomatic disease; patients infected with Echinococcus granulosus may remain asymptomatic. Extensive disease causes significant morbidity and mortality

Prevalence, Epidemiology, and Life Cycle

Echinococcus is member of the cestode (tapeworm) family. Infections with Echinococcus granulosus are found worldwide, including in Africa, the Middle East, southern Europe, Latin America, and the southwestern United States.

A second species, Echinococcus multilocularis is found in northern Europe, Asia, the northern United States, and the Arctic. Humans represent an inadvertent intermediate host, the infection being contracted by ingestion of food contaminated with viable parasite eggs. Echinococcus is carried in the feces of sheep, goats, camels, horses, and domestic dogs that live around livestock. In the southwestern United States, most cases are contracted from sheep dogs. The primary host for Echinococcus multilocularis is the fox, and domestic cats and dogs become secondarily infected.

Because eggs are partially resistant to drying and can remain viable for many weeks, food can become contaminated without coming in direct contact with infected animals. Ingested eggs hatch in the intestine, forming oncospheres that penetrate the bowel wall, enter the bloodstream, and are deposited in various organs — most commonly the liver and lungs, and less frequently the brain, heart, and bones — where they encyst. The resulting hydatid cysts consist of a germinal membrane that produces multiple tapeworm heads and that also undergoes budding to form multiple, septated daughter cysts within the primary cyst. Cysts can survive in the host for decades.

A 33-year-old woman, an immigrant from Jordan, presented with a chief complaint of bloody cough and shortness of breath for a periodof! weeks. At age 22,she had undergone a computed tomography scan of the abdomen as part of a workup for polycystic ovaries. She was noted at that time to have a large liver cyst consistent with Echinococcus. Although she was asymptomatic, resection of the left lobe of the liver was performed that year. Despite surgical resection, she experienced recurrent cysts and on three occasions underwent percutaneous aspiration followed by injection of hypertonic saline.

One month before admission and 6 years after her last aspiration and injection procedure, she began coughing up blood. At the same time, she noted shortness of breath. She received several courses of oral antibiotics, but failed to improve. Her coughing then became productive of gelatinous, foul-smelling serosanguinous fluid. Pulmonary exam revealed decreased breath sounds and dullness to percussion at the right base. Bronchial breath sounds and E-to-A changes were noted in the right posterior mid-lung field. The liver was not palpable. A CTscan of the chest and abdomen revealed a fluid collection over the dome of the liver and an 8×5-cm abscess in the right lower lobe that contained an air-fluid level.

Clinical Presentation

Most patients with echinococcosis are asymptomatic, the infection being detected incidentally on an imaging study. Symptoms generally develop when the hydatid cyst reaches a size of 8 to 10 cm and begins compressing vital structures or eroding into the biliary tract or a pulmonary bronchus. The cysts can also become superinfected, resulting in a bacterial abscess. Cyst leakage or rupture can result in an anaphylactic reaction, causing fever and hypotension. Cysts can also develop in the brain, heart, kidneys, eyes, and bones. Asymptomatic disease caused by Echinococcus granulosus rarely progresses; however, 90% of cases of asymptomatic Echinococcus multilocularis infection eventually progress to symptomatic disease.

Diagnosis and Treatment

Ultrasonography, computed tomography scan, or magnetic resonance imaging reveal a characteristic hydatid cyst with a distinct septated structure representing daughter cysts. Often, tapeworm heads can also be visualized. The stage of infection can be classified based on ultrasound findings, but computed tomography scan has been found to be the most effective diagnostic method for delineating the extent of disease. The diagnosis can be confirmed by ELISA, which is highly sensitive for liver cysts, but less sensitive for cysts in other organs. Complete surgical resection of the hydatid cyst is often recommended in symptomatic disease. The cyst should be removed intact, taking great care to avoid a rupture, which will spread the infection by daughter cysts.

To reduce the risk of spread, aspiration of the cyst is recommended — a procedure that involves removing a fraction of the contents and instilling a hypertonic saline solution (30% NaCl), iodophore, or 95% ethanol to kill the germinal layer and daughter cysts. Surgical resection should be performed 30 minutes after instillation of the solution. In cases with biliary communication, the foregoing cidal agents are not recommended because of the risk of inducing sclerosing cholangitis. As compared with medical treatment alone, debulk-ing of cysts does not improve outcome, but it may relieve symptoms in specific cases.

Treatment in the periopera-tive period with three to four cycles of albendazole 400 mg twice daily for 4 weeks, followed by a 2-week rest period is generally recommended to limit the risk of intraoperative dissemination. The same medical therapy is recommended for patients with inoperable hydatid cyst. In selected cases, computed tomography or ultrasound has been used to guide percutaneous needle aspiration drainage and instillation of cidal agents (hypertonic saline or ethanol) to sterilize the cyst, followed by re-aspiration after 15 minutes to remove the cidal agent ("PAIR"). The PAIR treatment is often curative, and it is becoming the treatment of choice. The efficacy of PAIR has not be confirmed by randomized trials, however.

About Echinococcus

  1. Spread primarily by domestic dogs, who excrete eggs in their feces. Eggs survive in dust and contaminate food.
  2. Eggs hatch in the intestine and oncospheres enter the bloodstream, where they migrate to the liver or lung, or (less commonly) to the brain, where they form hydatid cysts.
  3. Hydatid cysts survive and grow over decades, causing symptoms when they reach 8 to 10 cm in diameter.
  4. Diagnosis is made by computed tomography scan or ultrasonography.
  5. Treatment involves administration of albendazole, combined with surgical resection preceded by instillation of an agent cidal to the germinal layer. Alternatively, percutaneous needle drainage and cidal agent instillation ("PAIR") maybe curative.

Cysticercosis

Potential Severity

Causes neurologic complications in a significant number of infected patients many years after the initial infection.

Prevalence, Epidemiology, and Life Cycle

Taenia solium is another cestode (tapeworm) common in Central and South America, Mexico, the Philippines, Southeast Asia, India, Africa, and southern Europe. Like Echinococcus, Taenia can be contracted by ingesting viable eggs or by eating raw or undercooked pork containing encysted larvae. Once ingested, the eggs hatch or the encysted larvae are released into the stomach, where they migrate into the intestine and develop into adult worms that can reach 8 m in length. Autoinfection can occur as a result of regurgitation of eggs into the stomach or accidental ingestion of eggs from the host's own feces.

Clinical Presentation

Adult intestinal worms rarely cause symptoms. However, larvae can penetrate the intestine, enter the bloodstream and eventually encyst in the brain, causing neurocysticercosis. Cysts may lodge in the cerebral ventricles (causing hydrocephalus), the spinal cord (resulting in cord compression and paraplegia), the subarachnoid space (causing chronic meningitis), or the cerebral cortex (causing seizures). Cysts may remain asymptomatic for many years, becoming clinically apparent only when the larvae die, an event associated with cyst swelling and increased inflammation. Larvae also encyst in other tissues (skin and muscle), but rarely cause symptoms. Eye involvement is also reported.

Diagnosis and Treatment

Computed tomography or nuclear magnetic resonance scan are the preferred diagnostic studies, demonstrating discrete cysts that may enhance following the administration of contrast media depending on the degree of surrounding inflammation. In Central nervous system infection, multiple lesions are generally detected. Older lesions are often calcified. In the absence of cerebral edema, lumbar puncture can be performed.

Tissue And Blood Helminths

Analysis of the cerebrospinal fluid usually reveals lymphocytes or eosinophils accompanied by low glucose and elevated protein. Serologic tests detecting antibody directed against Taenia solium may be positive, particularly in patients with multiple cysts. Treatment for neurocysticercosis is complex and controversial.

Albendazole and praziquantel may kill livingcysts, but larval death results in increased inflammation and edema, and may exacerbate symptoms.

A recent randomized trial and a meta-analysis suggested that in symptomatic patients with cortical lesions, albendazole combined with oral dexamethasone (2 mg three times daily) or oral prednisone (40 mg daily) enhances resolution of the lesions and reduces the incidence of seizures. Surgical resection of cysts may be required depending on the symptoms and on size and location of the offending cyst. Antiepileptic medications should be used to control seizures.

About Cysticercosis (Taenia solium infection)

  1. Contracted by ingesting eggs in fecally contaminated food or encysted larvae in undercooked pork.
  2. Larvae enter the bloodstream, encysting primarily in the brain.
  3. Symptoms develop after many years when the larvae die, causing increased inflammation.
  4. Can cause seizures, hydrocephalus, paraplegia, and meningitis.
  5. Diagnosis is made by computed tomography scan, magnetic resonance imaging, or serology.
  6. Treatment involves administration of albendazole plus corticosteroids for symptomatic disease; surgical resection can be performed in selected patients.

Schistosomiasis

Potential Severity

Usually a chronic disorder resulting in debilitating complications. Occasionally fatal during the early stage of infection as a result of a severe serum-sickness syndrome.

Prevalence, Epidemiology, and Life Cycle

Schistosoma mansoni, S. haematobium, and S. japonicum are members of the fluke (trematode) family. Schistosomes are estimated to infect between 200 and 300 million people worldwide.

Primary infection does not occur in the United States because the critical intermediate host — a specific type of freshwater snail — is absent. However, approximately 400,000 imported cases occur in immigrants from Puerto Rico, South America (particularly Brazil), the Middle East, and the Philippines. S. mansoni is found primarily in South America, the Caribbean, Africa, and countries of the Arab Middle East. S. haematobium is found in Africa and the Middle East, and S. japonicum is  found primarily in China and  the Philippines. Two other strains that have more recently been found to cause disease are S. intercalatum (Western and Central Africa) and S. mekongi (Indochina).

The parasite is contracted by exposure to fresh water containing infectious cercariae. The fork-tailed cercariae are able to swim to and penetrate the skin of people wading in stagnant infested freshwater pools or rice paddies. Once inside the host, cercariae lose their tails and mature into schistosomulae that enter the bloodstream. From the bloodstream, they penetrate the lung and liver, where over a period of 6 weeks, they mature to adult worms.

The adult worms then migrate through the venous plexus to various sites, depending on the Schis-tosoma strain. S. mansoni worms take up residence in the inferior mesenteric veins responsible for venous drainage of the large intestine; S.japonicum, in the superior mesenteric veins that drain the small intestine, and S. haematobium, in the vesicular plexus that drains the urinary bladder.

Once resident in the host, the worms can live for decades, releasing eggs into the bowel or bladder. Improper handling of contaminated stool and urine leads to egg contamination of water.

Eggs hatch in fresh water, forming miracidia whose cilia enable them to swim and infect freshwater snails. Each species of schis-tosome requires a specific freshwater snail intermediate, which explains the geographic distribution of each strain. The miracidia multiply within the snail, and within 4 to 6 weeks, they release large numbers of cercariae capable of infecting humans.

About the Life Cycle of Schistosoma

  1. Cercariae swimming in fresh water can penetrate human skin.
  2. Cercariae mature into schistosomulae that enter the bloodstream and migrate to the liver and lung, where they mature.
  3. Mature worms migrate to the venous system of the small (S. japonicum) or large bowel (S. mansoni) or to the bladder venous plexus (S. haematobium).
  4. The worms release eggs into stool or urine for many years, resulting in contamination of fresh water.
  5. Freshwater snails are infected by miracidia, a necessary step in the production of cercariae and infection of humans.

A 32-year-old man was evaluated for a lesion of the urinary bladder. He had been well until 16 months earlier. Soon after returning from a 1-week vacation in Malawi, he had an episode of perineal pain associated with painful ejaculation and brown-colored ejaculate. His condition improved after treatment with ciprofloxacin. Four months before the evaluation, this patient had begun experiencing urinary frequency, with intermittent passage of small blood clots in the urine. His symptoms failed to improve on ciprofloxacin treatment. An epidemiologic history noted frequent travel outside the United States.

Most recently, the man had traveled to Malawi with his wife. While there, he had repeatedly swum in a lake that he was assured was "safe." A laboratory workup showed a normal peripheral white blood cell count and differential. Urinalysis confirmed hematuria. Cytology found no malignant cells. A urogram and ultrasound demonstrated a round structure, 8x 10 mm in diameter, adherent to the bladder wall.

Cystoscopic examination disclosed multiple, slightly raised, polypoid lesions that were less than 5 mm in diameter. The lesions were erythe-matous, with focal yellow areas. Low-power microscopic examination of material from a bladder biopsy revealed a polypoid inflammatory lesion of the bladder mucosa with dense inflammatory infiltrate surrounding clusters of eggs in the submucosa.

At higher magnification, the granulomas were found to contain clusters of helminthic eggs surrounded by epithelioid histio-cytes, chronic inflammatory cells, and eosinophils. The eggs were oval and had a terminal spine characteristic ofS. haematobium. The man's wife was subsequently examined, and Schistosoma eggs were found in her urine. Both were treated with praziquantel, and the eggs disappeared from both patients'urine.

Clinical Presentation

The three stages of the disease correspond to the life cycle of the parasite in the human host. The first stage occurs at the time of penetration and is commonly termed "swimmer's itch." A very itchy macular papular rash develops within 24 hours of the cercariae penetrating the skin. The lesions spontaneously resolve as the organisms spread to the bloodstream. An avian schistosome is also able to penetrate the skin, but it is not capable of entering the bloodstream. This benign form of swimmer's itch is common in the Great Lakes of the north-central United States and in freshwater lakes in Europe.

The second stage of clinical disease occurs 4 to 8 weeks later, when the worms mature and begin releasing eggs. Patients develop a serum-sickness-like syndrome as they react with elevated levels of immunoglobulin E and peripheral eosinophilia to egg antigens. Fever, headache, cough, chills, and sweating are accompanied by lymphadenopathy and hepatosplenomegaly. This clinical constellation has been called "Katayama fever" and is most commonly associated with S. japonicum. The symptoms usually resolve spontaneously, but in heavy infections, this acute reaction can be fatal. The third, chronic, stage results from granulomatous reactions to egg deposition in the intestine, liver, bladder, and (less commonly) the lung and Central nervous system.

Granulomatous reactions in the bowel can lead to chronic diarrhea, abdominal pain, and blood loss. Eggs may enter the portal venous system and gain entry to the liver, where chronic inflammation is followed by fibrosis leading to portal hypertension, splenomegaly, and bleeding esophageal varices. Because the hepatic parenchyma is seldom compromised, liver function tests are usually normal. Peripheral eosinophilia is commonly encountered.

Hepatosplenomegaly with normal liver function tests, peripheral eosinophilia, and a history of residence in an endemic area should raise the possibility of chronic hepatic schistosomiasis. The development of collateral venous channels in association with portal hypertension can result in egg deposition in the pulmonary arteries, causing pulmonary hypertension and right-sided congestive heart failure.

Deposition of eggs in the Central nervous system is less common and can cause seizures or, if eggs are deposited in the region of the spinal cord, transverse myelitis. In S. haematobium, eggs are deposited in the bladder wall, leading to hematuria, bladder obstruction, hydronephrosis, and recurrent urinary tract infections. Bladder cancer may also complicate chronic S. haematobium infection.

Diagnosis and Treatment

Demonstration of eggs in the stool or urine allows a specific diagnosis to be made. Quantitative egg counts are helpful in assessing the intensity of the infection. Urine is best collected between noon and 2 PM. Passing the urine through a 10-mm filter concentrates the eggs. Eggs may also be identified on tissue biopsies. Rectal biopsy is particularly helpful in diagnosing S. mansoni.

The eggs of 5. mansoni, S. japonicum, and S. haematobium have distinct morphologies, allowing them to be readily identified using a low-power (100X) microscope. In chronic disease, the egg burden may be low, making the diagnosis difficult. Anti-schistosome antibody tests are now available for detecting chronically infected patients; however, the specificity and sensitivity of these tests limit their value.

Furthermore, the tests cannot be used in lifelong residents of endemic areas, because serology in these individuals is frequently positive in the absence of active infection. Praziquantel is effective treatment for all forms of schistosomiasis. Side effects of treatment are mild and include fever, abdominal discomfort, and headache.

Clinical Presentation of Schistosomiasis

  1. Skin penetration causes "swimmer's itch."
  2. A serum-sickness syndrome with eosinophilia and high immunoglobulin E levels may follow.This constellation of symptoms is called Katayama fever.
  3. Granulomatous reaction to egg deposition leads to chronic diarrhea, portal hypertension and hepatosplenomegaly, and pulmonary hypertension in Schistosoma mansoni and S. japonicum.
  4. Eggs deposited in the bladder can lead to hematuria, bladder obstruction, hydronephrosis, recurrent urinary tract infections, and sometimes bladder cancer in cases of S. haematobium.
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