NEMATODES

Nematodes are elongated, symmetric roundworms and

constitute one of the largest phyla in the animal kingdom.

Most nematode species are free-living, but some have evolved

into parasites of plants and animals, including humans.

Parasitic nematodes of medical significance may be classified

as intestinal or tissue nematodes.

All are zoonotic infections caused by incidental exposure

toinfectious 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

marked

local 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 the

largest intestinal nematode

parasite of humans, reaching

up to 40 cm in length.

1 billion people are infected

worldwide.

Most infected individuals

have low worm burdens and

are asymptomatic. Clinical

disease arises from

pulmonary and intestinal

complications.

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 (Loeffler's 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

TRICHURIASIS

Most invasions with the whipworm Trichuris trichiuraare asymptomatic, but

heavy infections may cause gastrointestinal symptoms.

Like the other soil-transmitted helminths, whipworm is distributed globally in the tropics and subtropics and is most common among poor children.

Life Cycle

The adult worms reside in the colon and cecum, into the superficial mucosa.

Thousands of eggs laid daily by adult female worms pass via the feces and mature in the soil.

After ingestion, infective eggs hatch in the duodenum, releasing larvae that mature before migrating to the large bowel.

The entire cycle takes about 3 months, and adult worms may live for several years.

Clinical Features

Most infected individuals have no symptoms

Heavy infections may result in abdominal

pain, anorexia, and bloody or mucoid diarrhea resembling

inflammatory bowel disease.

Rectal prolapse can result from massive infections in

children, who often suffer from malnourishment and other

diarrheal 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.

Diagnosis

Since pinworm eggs are not usually released in the bowel, the diagnosis cannot be made by looking for eggs in the feces.

Instead, eggs deposited in the perianal region are detected by the application of clear cellulose tape to the perianal region in the morning.

After the tape is transferred to a microscope slide, will reveal the characteristic pinworm eggs, which are oval, measure 55 by 25 um, and are flattened along one side.

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

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.