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with E. histolytica, flies and cockroaches can be responsible for mechanical transmission. Human-tohuman and animalto-human transmission are probably more common than suspected. B. hominis is a common intestinal parasite of humans

and animals, with a worldwide distribution. Depending on the geographic location, it may be detected in 1% to 40% of

fecal specimens. B. hominis may be the most common parasite found in the intestinal tract. Pathogenesis and Spectrum of

Disease B. hominis can cause diarrhea, cramps, nausea, fever, vomiting, abdominal pain, and urticaria and may require

therapy. A possible relationship between B. hominis and intestinal obstruction and perhaps even infective arthritis has

been suggested. In patients with other underlying conditions, the symptoms may be more pronounced. The incidence of

this organism appears to be higher than suspected in stools submitted for parasite examination. In symptomatic patients in

whom no other etiologic agent has been identified, B. hominis should certainly be considered the possible pathogen. It has

been suggested that proteases of genetic subtype 3 could be considered a virulence factor responsible for protein

degradation and subsequent pathogenesis.

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Laboratory Diagnosis:

Routine Methods. Routine stool examinations are very effective in recovering and identifying B. hominis; the permanent

stained smear is the procedure of choice, because examination of wet preparations may not easily reveal the organism. If

the fresh stool is rinsed in water before fixation (for the concentration method), B. hominis organisms, other than the

cysts, are destroyed, and a false-negative report may result. The organisms should be quantitated in the report (i.e., rare,

few, moderate, or many). It is also important to remember that other possible pathogens should be adequately ruled out

before a patient is treated for B. hominis.

Antigen Detection. Fecal immunoassays to detect B.hominis antigen have been developed but are not yet commercially

available. The technique currently used is the enzyme-linked immunosorbent assay (ELISA).

Antibody Detection. ELISA and fluorescent antibody tests have been developed to detect serum antibody to B. hominis

infections. A strong antibody response is consistent with the ability of this organism to cause symptoms. Also,

demonstration of serum antibody production both during and after B. hominis symptomatic disease is immunologic

evidence for the pathogenic role for this protozoan, although it may take 2 years or longer with chronic infections to

develop a serologic response.

Therapy:

Although clinical evidence is limited, studies have been done on the in vitro susceptibility of B. hominis to

numerousdrugs. Currently, metronidazole (Flagyl) appears to be the most appropriate drug. Diiodohydroxyquin

(Yodoxin) also has been effective, and dosage schedules for these two drugs are as recommended for other intestinal

protozoa. The development of new drug sensitivity assays may improve researchers’ ability to evaluate the activities of

various drugs against this organism.

Prevention:

Prevention requires improved personal hygiene and sanitary conditions, in addition to proper disposal of fecal material.

FLAGELLATES:

The Mastigophora, or flagellates, have specialized locomotor organelles called flagella; these are long, thin, cytoplasmic

extensions that may vary in number and position, depending on the species. Different genera of flagellates may live in the

intestinal tract, the bloodstream, or various tissues.

Four common species of flagellates are found in the intestinal tract: Giardia lamblia, Dientamoeba fragilis, Chilomastix

mesnili, and Pentatrichomonas hominis (Figures 48-16 to 48-23). Several other smaller, nonpathogenic flagellates, such

as Enteromonas hominis and Retortamonas intestinalis (see Figure 48-16) G. lamblia and D. fragilis are the flagellates

considered pathogenic. D. fragilis has been associated with diarrhea, nausea, vomiting, and other nonspecific intestinal

complaints. Trichomonas vaginalis is pathogenic but occurs in the urogenital tract. Trichomonas tenax is occasionally

found in the mouth and may be associated with poor oral hygiene.

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Giardia lamblia:

General Characteristics:

G. lamblia is the most common cause of intestinal infection worldwide.

Other than B. hominis, G. lamblia (also called G. duodenalis and G. intestinalis) is probably the most common protozoan

organism identified in individuals in the United States. It causes symptoms ranging from mild diarrhea, flatulence, and

vague abdominal pains to acute, severe diarrhea to steatorrhea and a typical malabsorption syndrome. Various

documented waterborne and food-borne outbreaks have occurred during the past several years. A number of animals may

serve as reservoir hosts for G. lamblia. Differentiation of flagellates is based on overall shape, numbers, an arrangements

of flagella. Both the trophozoite and cyst stages are included in the life cycle of G. lamblia. Trophozoites divide by means

of longitudinal binary fission, producing two daughter trophozoites. The organism is found most commonly in the crypts

in the duodenum. Trophozoites are the intestinal dwelling stage and attach to the epithelium of the host villi by means of

the ventral disk. The attachment is substantial and results in disk “impression prints” when the organism detaches from

the surface of the epithelium.Trophozoites may remain attached to or may detach from the mucosal surface. Because the

epithelial surface sloughs off the tip of the villus every 72 hours, the trophozoites apparently detach at that time. G.

lamblia trophozoites are teardrop shaped and have been described as “someone looking at you”. Cyst formation takes

place as the organisms move down through the jejunum after exposure to biliary secretions. The trophozoites retract the

flagella into the axonemes, the cytoplasm becomes condensed, and the cyst wall is secreted (see Figures 13 to 14).

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the cyst matures, the internal structures are doubled, so that when excystation occurs, the cytoplasm divides, producing

two trophozoites. Excystation occurs in the duodenum or appropriate culture medium.

Epidemiology:

Transmission of G. lamblia occurs by ingestion of viable cysts. Although contaminated food or drink may be the

source, intimate contact with an infected individual may also result in transmission of the organism. This organism is

found more frequently in children or in groups living in close quarters. Outbreaks have been associated with poor

sanitation facilities or sanitation breakdowns, as evidenced by infections of travelers and campers. Limited information is

available on seasonal variations in giardiasis. Some data suggest an association with the cooler, wetter months of the year,

which may implicate environmental conditions as advantageous to cyst survival.

Certain occupations may place an individual at risk for infection, such as sewage and irrigation workers, who may be

exposed to infective cysts. In situations in which young children are grouped together, such as in nursery schools, an

increased incidence of exposure and subsequent infection of both children and staff members may be seen. A high

incidence of giardiasis occurs in patients with immunodeficiency syndromes, particularly in those with common variable

hypogammaglobulinemia.

Giardiasis is the most common cause of diarrhea in these patients and may be associated with mild to severe villus

atrophy An estimated 200 million people in Asia, Africa, and Latin America have symptomatic infections. In the United

States, approximately 20,000 cases are reported yearly. However, an estimated 2 million cases may occur annually.

Figure 14 A, Giardia lamblia trophozoite. B, G. lamblia trophozoite, iodine stain. C, G. lamblia cysts

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Pathogenesis and Spectrum of Disease:

The incubation period for giardiasis ranges from approximately 12 to 20 days. Giardiasis may not be recognized as the

cause, because the infection mimics acute viral. enteritis, bacillary dysentery, bacterial or other food poisonings, acute

intestinal amebiasis, or “traveler’s diarrhea” (toxigenic Escherichia coli). However, the type of diarrhea plus the lack of

blood, mucus, and cellular exudate is consistent with giardiasis.

Asymptomatic Infection. Although the parasites in the crypts of the duodenal mucosa may reach very highnumbers, they

may not cause a pathologic condition. The organisms feed on the mucous secretions and do not penetrate the mucosa.

Although organisms have been seen in biopsy material obtained from inside the intestinal mucosa, others have been seen

attached to the epithelium.

Intestinal Disease. For unknown reasons, symptomatic patients may have irritation of the mucosal lining, increased

mucus secretion, and dehydration. The onset may be accompanied by nausea, anorexia, malaise, lowgrade fever, and

chills, in addition to a sudden onset of explosive, watery, foul-smelling diarrhea. Other symptoms include epigastric pain,

flatulence, and diarrhea with increased amounts of fat and mucus in the stool but no blood. Weight loss often

accompanies these symptoms. Although some speculate that the organisms coating the mucosal lining may act to prevent

fat absorption, this does not completely explain the prevention of the uptake of other substances normally absorbed at

other intestinal levels. Severe malabsorption has also been linked with isolated levothyroxine malabsorption, leading to

severe hypothyroidism and secondary impairmen of pancreatic function. In both cases, treatment with metronidazole led

to complete remission of symptoms. Occasionally the gallbladder is involved, resulting in gallbladder colic and jaundice.

G. lamblia also has been identified in bronchoalveolar lavage fluid.

Chronic Disease. The acute phase often is followed by a subacute or chronic phase. Symptoms include recurrent, brief

episodes of loose, foul-smelling stools and possibly increased distention and foul flatus. Between episodes of mushy

stools, the patient may have normal stools or may be constipated. Abdominal discomfort includes marked distention and

belching with a rotten-egg taste. Chronic disease must be differentiated from amebiasis; disease caused by other intestinal

parasites (e.g., D. fragilis, Cryptosporidium spp., Cyclospora cayetanensis, Isospora belli, Strongyloides stercoralis);

inflammatory bowel disease; and irritable colon. On the basis of symptoms such as upper intestinal discomfort, heartburn,

and belching, giardiasis must also be differentiated from duodenal ulcer, hiatal hernia, and gallbladder and pancreatic

disease.

Laboratory Diagnosis:

Routine Methods. Routine stool examinations are normally recommended for the recovery and identification of

intestinal protozoa. However, in the case of G. lamblia, because the organisms are attached securely to the mucosa by

means of the sucking disk, a series of five or six stool samples may be examined without recovering the organism. The

organisms also tend to be passed in the stool on a cyclic basis. The Entero-Test capsule can be helpful for recovering the

organisms, as can the duodenal aspirate. Although cysts often can be identified on the wet stool preparation, many

infections may be missed without examination of a permanent stained smear. If material from the string test or mucus

from a duodenal aspirate is submitted, it should be examined as a wet preparation for motility; however, motility may be

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represented by nothing more than a slight flutter of the flagella, because the organism is caught up in the mucus. After

diagnosis, the positive specimen can be preserved as a permanent stain.

Antigen Detection. The development of fecal immunoassays to detect Giardia antigen in stool has dramatically

improved the sensitivity seen with the routine O&P examination. The ELISA has been used to detect Giardia antigen in

feces. Fluorescent methods with monoclonal antibodies have also proven extremely sensitive and specific in detecting G.

lamblia in fecal specimens. Other products are available as a cartridge format that uses an immunochromatographic strip–

based detection system for G. lamblia and/or Cryptosporidium spp. Any antigen detection system should always be

reviewed for compatibility with stools submitted in preservatives rather than fresh specimens. Some limitations exist on

the use of kits for organisms in the genus Entamoeba. However, commercial reagent kits for detecting Giardia and

Cryptosporidium spp. can be used with formalin-based stool preservatives or with fresh or frozen specimens. Many of

these cartridge format tests provide an answer within 10 minutes and are equal to or better than other immunoassays with

regard to sensitivity and specificity. Many of these newer methods are being used to test patients suspected of having

giardiasis or those who may be involved in an outbreak. The detection of antigen in stool or visual identification of

organisms by using monoclonal antibody reagents indicates current infection. The value of these detection assays as

rapid, reliable immunodiagnostic procedures has been emphasized by the increase in Giardia infections and the greater

awareness of particular incidences (e.g., nursery school settings). Because the organisms are shed so sporadically, use of a

fecal immunoassay does not eliminate the need to analyze multiple stool specimens for sensitive detection of G. lamblia;

a minimum of two stools should be tested. If the first specimen is negative, it may represent a false negative.

Histology. Trophozoites are detectable in the duodenum and proximal jejunum; however, mucosal invasion generally has

been found in areas where necrosis or mechanical trauma was present.

Apparently, patients with giardiasis also have reduced mucosal surface areas compared with control patients.

Nucleic Acid-Based Techniques: Currently, there are no molecular-based assays commercially available for the

detection of G. lamblia.

Prevention:

The most effective practice for preventing the spread of infection in the child care setting is thorough hand washing by

the children, staff members, and visitors. Filtration systems have also been recommended, although they have certain

drawbacks, such as clogging.

Chilomastix mesnili:

General Characteristics

The C. mesnili trophozoite is pear shaped, measuring 6 to 24 μm long and 4 to 8 μm wide. It has a single nucleus and a

distinct oral groove, or cytostome (mouth), close to the nucleus. Flagella are difficult to see without obvious motility in a

wet preparation. The morphology can be

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seen on the permanent stained smear; the cytostome may be visible in some trophozoites. The cysts are pear or lemon

shaped and range from 6 to 10 μm long and 4 to 6 μm wide . They have a single nucleus and a typical curved cytostomal

fibril, called the shepherd’s crook. The cyst’s definitive morphology can be seen on a permanent stain.

Epidemiology:

C. mesnili tends to have a cosmopolitan distribution, although it is found more frequently in warm

climates.Transmission occurs through ingestion of infective cysts.

Pathogeneis and Spectrum of Disease:

C. mesnili is considered nonpathogenic and does not cause disease.

Laboratory Diagnosis

Although cysts sometimes can be seen in a wet preparation, definitive identification of C. mesnili relies on

examination of permanent stained smears.

Therapy

Specific treatment is not recommended for C. mesnili. Because these nonpathogenic organisms are acquired

through fecal-oral contamination.

Prevention:

Prevention depends on adequate disposal of human excreta and improved personal hygiene, preventive

measures that apply to most of the intestinal protozoa.

Dientamoeba fragilis

General Characteristics:

D. fragilis was described in 1918. D. fragilis tends to be common in some pediatric populations, and the incidence is

higher for patients under 20 years of age in some studies. Some speculate that D. fragilis may be infrequently recovered

and identified; a low incidence or absence from survey studies may be due to poor laboratory techniques and a general

lack of knowledge about the organism. The D. fragilis trophozoite is characterized as having one nucleus (20% to 40%) or

two nuclei (60% to 80%). The nuclear chromatin usually is fragmented into three to five granules, and normally no

peripheral chromatin is seen on the nuclear membrane. The cytoplasm is usually vacuolated and may contain ingested

debris and some large, uniform granules. The cytoplasm can also appear uniform and clean with few inclusions. Size and

shape vary considerably among organisms, even on a single smear(Figure 15)

Pathogenesis and Spectrum of Disease:

D. fragilis has been associated with a wide range of symptoms. Case reports of children infected with D.

fragilis reveal a number of symptoms, including intermittent diarrhea, abdominal pain, nausea, anorexia,

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malaise, fatigue, poor weight gain, and unexplained eosinophilia. The most common symptoms in patients

infected with this parasite appear to be intermittent diarrhea and fatigue. In some patients, both the organism

and the symptoms persist or reappear until appropriate treatment is initiated.

Laboratory Diagnosis:

Routine Methods. Diagnosis of D. fragilis infections depends on proper collection and processing techniques

(a minimum of three fecal specimens). Although the survival time for this parasite has been reported as 24 to 48

hours in the trophozoite form, the survival time in terms of morphology is limited, and stool specimens must be

examined immediately or preserved in a suitable fixative soon after defecation. It is particularly important to

examine permanent stained smears of stool with an oil immersion objective (×100).These trophozoites have

been recovered in formed stool; therefore, a permanent stained smear must be prepared for every stool sample

submitted for examination. Organisms seen in direct wet mounts may appear as refractile, round forms; the

nuclear structure cannot be seen without examination of the permanent stained smear.

Antibody Detection. On indirect immunofluorescence assay, serum samples from patients with confirmed D.

fragilis infections showed positive titers, and all matched controls had positive titers ranging from 20 to 160.

However, these tests are not routinely used, nor are the reagents commercially available.

Therapy:

Clinical improvement has been seen in adults receiving tetracycline, and symptomatic relief has been observed

in children receiving diiodohydroxyquin, metronidazole, or tetracycline.

Prevention:

Fecal-oral transmission has not been documented; therefore, it is difficult to speculate about preventive

measures. However, if transmission does occur from ingestion of certain helminth eggs, the appropriate hygiene

and sanitary measures to prevent contamination with fecal material are appropriate.

Figure 15Trophozoites of Dientamoeba fragilis

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Pentatrichomonas hominis:

P. hominis is probably the most commonly identified flagellate, other than G. lamblia and D. fragilis. P. hominis has

been recovered from all parts of the world, in both warm and temperate climates, and is considered nonpathogenic and

noninvasive. It is not known to have a cyst stage P. hominis trophozoites live in the cecum and feed on bacteria. The

trophozoite measures 5 to 15 μm long and 7 to 10 μm wide. It has a pyriform membrane, which aid identification of the

organism. The undulating membrane extends the entire length of the body, in contrast to that seen in the pathogen T.

vaginalis (on which the membrane extends halfway down the body).

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vaccines are either ineffective in those most at risk (infants) or provide only short-term protection

(everyone else).

The advent of conjugate subunit vaccines heralded a new age for immunization against diseases

caused by encapsulated organisms such as meningococcus, Haemophilus influenzae type b (Hib)

and pneumococcus.

WHO recommends that children receive Haemophilus influenzae type b (Hib) and pneumococcal

conjugate vaccines. In addition,.

Toxoid vaccines

Toxoid vaccines are based on the toxin produced by certain bacteria (e.g. tetanus or diphtheria).

The toxin invades the bloodstream and is largely responsible for the symptoms of the disease. The

protein-based toxin is rendered harmless (toxoid) and used as the antigen in the vaccine to elicit

immunity.

To increase the immune response, the toxoid is adsorbed to aluminium or calcium salts, which serve

as adjuvants.

Components of a vaccine

Vaccines include a variety of ingredients including antigens, stabilizers, adjuvants, antibiotics, and

preservatives.

 Antigens

Antigens are the components derived from the structure of disease-causing organisms, which are

recognized as ‘foreign’ by the immune system and trigger a protective immune response to the

vaccine.

 Stabilizers

Stabilizers are used to help the vaccine maintain its effectiveness during storage. Bacterial vaccines

can become unstable due to hydrolysis and aggregation of protein and carbohydrate molecules.

Stabilizing agents include MgCl2 (for OPV), MgSO4 (for measles), lactose-sorbitol and sorbitolgelatine.

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Adjuvants

Adjuvants are added to vaccines to simulate the production of tibodies against the vaccine to make

it more effective.

Adjuvants have been used for decades to improve the immune response to vaccine antigens, most

often in inactivated (killed) vaccines. In conventional vaccines, adding adjuvants into vaccine

formulations is aimed at enhancing, accelerating and prolonging the specific immune response to

vaccine antigens.

Aluminium salts example

Aluminium salts are among the oldest adjuvants that are commonly used. They slow the escape of

the antigen

from the site of injection thereby lengthening the duration of contact between the antigen and the

immune system (i.e. macrophages and other antigen-receptive cells).

Antibiotics

Antibiotics (in trace amounts) are used during the manufacturing phase to prevent bacterial

contamination of the tissue culture cells in which the viruses are grown. Usually only trace amounts

appear in vaccines, for example, MMR vaccine and IPV each contain less than 25 micrograms of

neomycin per dose .Persons who are known to be allergic to neomycin should be closely observed

after vaccination so that any allergic reaction can treated at once.

Preservatives

Preservatives are added to multidose vaccines to prevent bacterial and fungal growth. They include a

variety of substances, for example Thiomersal, Formaldehyde, or Phenol derivatives.

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Vaccine Development

The development process for vaccines is unique. Vaccine development is highly capital intensive and

risky. Given the importance of safety with biologics, the vaccine industry is highly regulated

Research to discover new vaccine antigens and novel approaches to immunization usually takes

several years, and costs tens of millions of dollars.(Table 2-8)

Once a discovery is made, several developments must be undertaken to reach the licensing stage.

The development of each of these processes is very lengthy, requiring on average 10–15 years. The

total development costs can reach close to $US1 billion

Vaccine Manufacturing

The manufacture of vaccines is achieved from the propagation of living microorganisms. Some of

these may be dangerous human pathogens. Therefore, the manufacture of vaccines is conducted in a

highly regulated and controlled environment.

All vaccine manufacturers are subject to national and international regulatory control and must

comply with specifications for Good Manufacturing Practices (GMP). These requirements vary

between countries, but the fundamentals are common .

Manufacturing is conducted in an aseptic environment and closely monitored by quality control

measures. Vaccines also require a strict cold chain to maintain their stability. Under most

circumstances vaccines are shipped and stored under refrigeration .(Table 2-9)

Table (2-8) The main steps for vaccine development

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Regulatory process for vaccines under development

Because of their biological nature and because they are largely administered to healthy individuals,

the entire vaccine development and manufacturing process is regulated.

Before vaccines are licensed, the three successive phases of clinical development must be approved

by a national regulatory authority and may only proceed from one phase to the next upon approval

of the national regulator.

The regulator has the authority to refuse or withdraw a product license if the manufacturer is not

compliant with current regulations.(Figure2-106)

Technologies for vaccine development.

Since the times of Pasteur, vaccines have been developed using empirical approaches consisting

mostly of killed or live-attenuated microorganisms, partially purified components of pathogens

(subunit vaccines), detoxified toxins or polysaccharides.

These vaccines have been very successful in eliminating many devastating diseases.

During the past 30 years, subsequent waves of new technologies have made possible vaccines that

were impossible with the empirical approaches. These include recombinant DNA technology,

glycoconjugation, reverse vaccinology and many emerging next-generation technologies, such as

novel adjuvants, synthetic biology and structure-based vaccine design (structural

vaccinology)(Figure2-107)

Table (2-9) Vaccine meutecting steps

Figure (2-106) Regular steps for vaccine under development

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Vaccine efficacy

Vaccine efficacy varies according to the type of vaccine and the manner in which the vaccine antigen

is processed by the immune system.

Vaccine efficacy may also vary between different populations. However, in general, the efficacy of

licensed vaccines ranges from above 70% to almost 100.

In other words, vaccines could be expected to reduce the attack rates in the vaccinated population by

70–100% compared to the attack rates in the unvaccinated population.

Figure(2-107) Technology for vaccine development

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Production of Licensed US Influenza Vaccines: by Growing Viral Isolates in Embryonated

Chicken Eggs

Figure (2-108)Vaccine efficacy

Figure(2-109) Influenza Vaccines production steps

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Gardasil

A genetically engineered vaccine

Gardasil, a genetically engineered vaccine, prevents cervical cancer by blocking infection with the

two viruses that together cause about 70 percent of cervical cancers. HPV 16 and 18, both sexually

transmitted viruses, are two of the 100-plus types of human papilloma virus.(Figure2-110)

Vaccines and bananas

Bananas have potential to become the world's first edible vaccine due to Agrobacterium. An edible

vaccine doesn't need sterile syringes, costly refrigeration, or multiple injections. According to the

World Health Organization (WHO), more than 2 million children die worldwide each year from

diarrhea that can be prevented easily with vaccines.(Figure 2-111)

Vaccine trails in Alzheimer's disease

Figure2-110)labelling for Gardasil

Figure(2-111)An edible vaccine

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The most promising areas of Alzheimer’s disease research involves vaccine-based therapies which

stimulate the body to produce antibodies to amyloid-beta protein and remove it from the brain.

(Figure 2-112)

Figure(2-112)Vaccine trails Alzheimer

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The field of parasitology is often associated with tropical areas; however, many parasitic organisms that

infect humans are worldwide in distribution and occur with some frequency in the temperate zones.

Also, an increase in the number of compromised patients, particularly those who are immunodeficient or

immunosuppressed, has led to increased interest in the field of parasitology. These individuals are greatly at

risk for certain parasitic infections. Parasites of humans are classified into six major divisions:

1. Protozoa (amebae, flagellates, ciliates, sporozoans, coccidia, microsporidia)

2. Nematoda or roundworms

3. Platyhelminthes, or flatworms (cestodes, trematodes)

4. Pentastomids, or tongue worms

5. Acanthocephala, or thorny-headed worms

6. Arthropoda (e.g., insects, spiders, mites, ticks)

The Parasites to be considerd:

1)Protozoa:

A-Intestinal:

1- Amebae (intestinal):

Entamoeba histolytica

2- Flagellates (intestinal):

Giardia lamblia†

Chilomastix mesnili

Dientamoeba fragilis

Pentatrichomonas hominis

3- Ciliates (intestinal):

Balantidium coli

4- Coccidia, Microsporidia (intestinal):

Cryptosporidium spp.

Cyclospora cayetanensis

Isospora (Cystoisospora) belli

Sarcocystis hominis

Sarcocystis suihominis

5- Microsporidia (intestinal):

Enterocytozoon bieneusi

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Encephalitozoon spp.

B- Blood and Tissue Protozoa (Sporozoa, Flagellates):

1-Sporozoa (Malaria and Babesiosis)

Plasmodium vivax

Plasmodium ovale

Plasmodium malariae

Plasmodium falciparum

Plasmodium knowlesi

Babesia spp.

2-Flagellates (Leishmaniae, Trypanosomes)

Leishmania tropica complex

Leishmania mexicana complex

Leishmania braziliensis complex

Leishmania donovani complex

Leishmania peruviana

Trypanosoma brucei gambiense

Trypanosoma brucei rhodesiense

Trypanosoma cruzi

Trypanosoma rangeli

C- Other Body Sites: Amebae, Flagellates, Coccidia.

1-Amebae

Naegleria fowleri

Acanthamoeba spp.

Balamuthia mandrillaris

2-Flagellates

Trichomonas vaginalis

Trichomonas tenax

3-Coccidia (Other Body Sites)

Toxoplasma gondii

2)Nematoda or round worms:

A-Intestinal Nematodes (Roundworms):

Helminths

Nematodes

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Ascaris lumbricoides

Enterobius vermicularis (pinworm)

Strongyloides stercoralis (threadworm)

Trichostrongylus spp.

Trichuris trichiura (whipworm)

Capillaria philippinensis (hookworms)

Ancylostoma duodenale (Old World)

Necator americanus (New World)

B-Tissue Nematodes (Roundworms):

Helminths

Trichinella spiralis

Visceral larva migrans (Toxocara canis or Toxocara cati)

Ocular larva migrans (Toxocara canis or Toxocara cati)

Cutaneous larva migrans (Ancylostoma braziliense or

Ancylostoma caninum)

Dracunculus medinensis

Parastrongylus (Angiostrongylus cantonensis )

Parastrongylus (Angiostrongylus costaricensis )

Gnathostoma spinigerum )

C-Blood and Tissue (Filarial) Nematodes:

Mansonella streptocerca

Mansonella perstans

3)Platyhelminthes or flatworms:(Cestodes, Trematodes)

3.1.Cestodes:

A-Intestinal Cestodes (Tapeworms):

Diphyllobothrium latum

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B-Tissue Cestodes(Tapeworms):

Tissue (Larval Forms)

Taenia solium

Echinococcus granulosus

Echinococcus multilocularis

Taenia multiceps

Spirometra mansonoides

3.2. Trematodes:

A-Intestinal Trematodes

Helminths Trematodes (Flukes) Intestinal Like:

Fasciolopsis buski

Heterophyes heterophyes

Metagonimus yokogawai

B-Liver and Lung Trematodes

Clonorchis (Opisthorchis) sinensis

Opisthorchis viverrini

Fasciola hepatica

Paragonimus westermani

Paragonimus mexicanus

C-Blood Trematodes

Schistosoma mansoni

Schistosoma haematobium

Schistosoma japonicum

Schistosoma intercalatum

Schistosoma mekongi

Protozoa:

The protozoa are unicellular eukaryotic organisms, most of which are microscopic. They have a number of

specialized organelles that are responsible for life functions and that allow further division of the group into classes.

Most protozoa multiply by binary fission and are ubiquitous worldwide.

The clinically relevant intestinal protozoa are generally considered to be Entamoeba histolytica, Blastocystis

hominis, Giardia lamblia, Dientamoeba fragilis, Balantidium coli, Isospora (Cystoisospora) belli, Cryptosporidium

spp., Cyclospora cayetanensis, and the microsporidia.

(Table 1 ):Description of the More Common Groups of Human Parasites.

Parasite Group Description

Flagellates Trypanosomatid protozoa; morphologic forms are identified based on the position,

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(trypanosomes length, and

attachment site of the flagella. At some time in their life cycle, these protozoa have the

trypomastigote form with the typical undulating membrane and free flagellum at the

anterior end.

Transmission is typically through an insect vector.

Some organisms cause African sleeping sickness (e.g., Trypanosoma brucei gambiense,

T. b.

rhodesiense). The etiologic agent of American trypanosomiasis is T. cruzi, which has

amastigote and

trypomastigote stages in the mammalian host and an epimastigote form in the arthropod

host

Nematodes,

intestinal

Helminthic parasites; roundworms.

Nematodes have separate sexes, are elongate-cylindrical and bilaterally symmetrical

with a triradiate

symmetry at the anterior end. Nematodes have an outer cuticle layer, no circular

muscles, and a

pseudocele that contains all systems (digestive, excretory, nervous, reproductive).

Transmission is by ingestion of eggs or by skin penetration of larval forms from the soil.

Examples: Ascaris, Enterobius, Trichuris, and Strongyloides spp. and hookworm.

Nematodes,

tissue

Helminthic parasites; roundworms.

Many of these organisms are rarely seen in the United States; however, some are

important and are

found worldwide. Diagnosis may be difficult if the only specimens are obtained through

biopsy and/or

autopsy, and interpretation must be based on examination of histologic preparations.

Examples: Trichinella spp., visceral larva migrans (VLM), ocular larva migrans (OLM),

Helminthic round worms.

Transmission is via arthropods.

Adult worms tend to live in the tissues or lymphatics of the vertebrate host. The

diagnosis is made on

the basis of recovery and identification of the larval worms (microfilariae) in the blood,

other body

fluids, or skin.

Examples: Wuchereria, Brugia, Loa, and Onchocerca spp

Cestodes,

intestinal

Helminthic tapeworms. Adult tapeworm consists of a chain of egg-producing units

called proglottids,

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which develop from the neck region of the attachment organ (scolex). Food is absorbed

through the

worm’s integument. The intermediate host contains the larval forms that are acquired

through

ingestion of the adult tapeworm eggs.

Transmission is through the ingestion of larval forms in poorly cooked or raw meat or

freshwater fish.

Examples: Dipylidium caninum (infection is acquired by accidental ingestion of dog

fleas).

Hymenolepis nana and H. diminuta are transmitted via ingestion of certain arthropods

(fleas, beetles).

Also, H. nana can be transmitted through egg ingestion (life cycle can bypass the

intermediate beetle

host).

Humans can serve as both the intermediate and definitive hosts in H. nana and Taenia

solium infections

Cestodes, tissue Tissue tapeworms.

Transmission is through ingestion of certain tapeworm eggs or accidental contact with

certain larval

forms, leading to tissue infection. Humans serve as the accidental intermediate host.

Examples: Taenia solium, Echinococcus granulosus, and several other species.

Trematodes,

intestinal

Flatworms that are exclusively parasitic. Except for the schistosomes (blood flukes),

flukes are

hermaphroditic. They may be flattened; most have oral and ventral suckers.

Transmission: Intestinal trematodes require a freshwater snail to serve as an intermediate

host; these

infections are food borne (freshwater fish, mollusks, or plants).

Example: Fasciolopsis buski, the giant intestinal fluke.

Trematodes,

liver, lung

Transmission: Liver and lung trematodes require a freshwater snail to serve as an

intermediate host;

these infections are food borne (freshwater fish, crayfish or crabs, or plants).

Examples: Public health concerns include cholangiocarcinoma associated with

Clonorchis and

Opisthorchis infections, severe liver disease associated with Fasciola infections, and

misdiagnosis of

tuberculosis in individuals infected with Paragonimus spp.

Trematodes,

blood

Schistosomes; sexes are separate. Males are characterized by an infolded body that

forms the

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gynecophoral canal in which the female worm is held during copulation and oviposition.

Transmission: Infection is acquired by skin penetration by the cercarial forms that are

released from

freshwater snails. The adult worms reside in the blood vessels over the small intestine,

large

intestine, or bladder. Examples: Schistosoma mansoni, S. haematobium, and S.

japonicum

Amebae:

Amebae, includes the organisms capable of movement by means of cytoplasmic protrusions called

pseudopodia. This group includes free-living organisms, in addition to nonpathogenic and pathogenic

organisms found in the intestinal tract and other areas of the body. (see Table 1).

Occasionally, when fresh stool material is examined as a direct wet mount, motile trophozoites may be seen, as

well as other, nonparasitic structure.

Entamoeba histolytica:

General Characteristics:

Living trophozoites (motile feeding stage) of E. histolytica vary in size from about 12 to 60 μm in diameter.

Organisms recovered from diarrheic or dysenteric stools generally are larger than those in formed stool from an

asymptomatic individual. The motility has been described as rapid and unidirectional. Although this

characteristic motility is often described, amebiasis rarely is diagnosed on the basis of motility seen in a direct

mount. The cytoplasm is differentiated into a clear outer ectoplasm and

a more granular inner endoplasm. E. histolytica has directional and progressive motility, whereas the other

amebae tend to move more slowly and at random. However, motility is rarely seen even in a fresh wet mount

from a patient with diarrhea or dysentery. The cytoplasm is generally more finely granular, and the presence of

red blood cells (RBCs) in the cytoplasm is considered diagnostic for E. histolytica (Figure1).

Figure 1 Entamoeba histolytica trophozoite containing ingested red blood cells.

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Permanent stained smears demonstrate accurate morphology compared with other techniques. When the

organism is examined on a permanent stained smear(trichrome or iron-hematoxylin stain), the morphologicthe

cyst matures (metacyst) (see Figure2,3),

nuclear division occurs, with the production of four nuclei. Often chromatoidals may be absent in the mature cyst.

Cyst morphology does not differentiate E. histolytica from E. dispar. Cyst formation occurs only in the intestinal

tract; once the stool has left the body, cyst formation does not occur. The one-, two-, and fournucleated cysts are

infective and represent the mode of transmission from one host to another.

Epidemiology:

Amebiasis is caused by infection with the true pathogen, Entamoeba histolytica. Recent evidence from molecular

studies confirms the differentiation of pathogenic E. histolytica and nonpathogenic E. dispar as two distinct species.

E. histolytica is considered the etiologic agent of amebic colitis and extraintestinal abscesses (amebic liver abscess),

whereas nonpathogenic E. dispar produces no intestinal symptoms and is not invasive in humans.

Figure2: Entamoeba histolytica/Entamoeba dispar cyst.

Figure 3: Entamoeba dispar trophozoite; no ingested red blood cells are

present.

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Infection is acquired through the fecal-oral route from infective cysts contained in the feces. These cysts can be

ingested in contaminated food or drink or contracted from fomites or various sexual practices that could include

accidental ingestion of fecal organisms.

The infection occurs worldwide, particularly in areas with poor sanitation. It is estimated that E. histolytica

infection kills more than 100,000 people each year.

Pathogenesis and Spectrum of Disease:

The pathogenesis of E. histolytica is related to the organism’s ability to directly lyse host cells and cause tissue

destruction.

Amebic lesions show evidence of cell lysis, tissue necrosis, and damage to the extracellular matrix. Evidence

indicates that E. histolytica trophozoites interact with the host through a series of steps: adhesion to the target cell,

phagocytosis, and cytopathic effect.

Numerous other parasite factors also play a role. From the perspective of the host, E. histolytica induces both

humoral and cellular immune responses; cell-mediated immunity is the major human host defense against this

complementresistant cytolytic protozoan.

The presentations of disease are seen with invasion of the intestinal mucosa or dissemination to other organs (most

often the liver) or both. However, it is estimated that a small proportion (2% to 8%) of infected individuals have

invasive disease beyond the lumen of the bowel. Also, organisms may be spontaneously eliminated with

no disease symptoms Blood flow from the mesenteric veins surrounding the intestine returns blood, via the

portal vein, to the liver, most commonly the upper right lobe Amebae in the submucosa can be carried by the

bloodstream to the liver. The onset of symptoms may be gradual or sudden; upper right abdominal pain and

fever (38° to 39°C) are the most consistent findings. Although the liver may be enlarged and tender, liver

function tests may be normal or slightly abnormal (jaundice is rare). The abscess can be visualized

radiologically, sonically, or by radionuclear scan; most patients have a single abscess in the right lobe of the

liver. The most common complication is rupture of the abscess into the pleural space. An abscess also can

extend into the peritoneum and through the skin. Hematogenous spread to the brain, lung, pericardium, and

other sites is possible ( figure 4).

Laboratory Diagnosis:

Routine Methods: The standard O&P examination is the recommended procedure for recovery and identification of

E. histolytica in stool specimens. Microscopic examination of a direct saline wet mount may reveal motile

trophozoites, which may contain RBCs. However, trophozoites with RBCs are found only in a limited number of

cases. In many patients who do not present with acute dysentery, trophozoites may be present but do not contain

RBCs, and the organisms may be pathogenic E. histolytica or nonpathogenic E. dispar.

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An asymptomatic individual may have few trophozoites and possibly only cysts in the stool. Although the

concentration technique is helpful for demonstrating cysts, the most important technique for the recovery and

identification of protozoan organisms is the permanent stained smear (normally stained with trichrome or ironhematoxylin). A minimum of three specimens collected over not more than 10 days may be required for

identification. Sigmoidoscopy specimens may be very helpful for identifying organisms. At least six areas of the

mucosa should be sampled. Smears from these areas should be examined after permanent staining. However, these

specimens are not considered a substitute for the recommended minimum of three stool specimens submitted for

O&P examination (direct, concentration, and permanent stained smear).

Liver aspirate material is rarely examined, and often the specimen was not collected properly. Aspirated material

must be aliquoted into several different containers as it is removed from the abscess; amebae may be found only in

the last portion of the aspirated material, theoretically material from the abscess wall, not necrotic debris from the

abscess center.

Antigen Detection: A number of enzyme immunoassay reagents are commercially available, and their specificity and

sensitivity provide excellent options for the clinical laboratory. These tests can differentiate the E. histolytica/ E.

dispar group from the rest of the Entamoeba species, such as nonpathogenic Entamoeba coli or Entamoeba

hartmanni. Other test reagents can distinguish between E. histolytica and E. dispar . These kits require fresh or frozen

stool;

Antibody Detection. Serologic testing for intestinal disease is rarely recommended unless the patient has true

dysentery; even in these cases, the titer (e.g., indirect hemagglutination) may be low and thus difficult to interpret. A

definitive diagnosis of intestinal amebiasis should not be made without demonstrating the presence of the organisms.

In patients suspected of having extraintestinal disease, serologic tests are diagnostically more effective. Indirect

hemagglutination and indirect fluorescent antibody tests have been reported positive with titers greater

than or equal to 1 : 256 and greater than or equal to 1 : 200, respectively, in almost 100% of cases of amebic liver

abscess. In the absence of STAT serologic tests for amebiasis (tests with very short turnaround times for results), the

decision on diagnosis must be made on clinical grounds and on the basis of results of other diagnostic tests, such as

scans.

Histology. A histologic diagnosis of amebiasis can be made when the trophozoites in the tissue are identified.

Organisms must be differentiated from host cells . Periodic acid-Schiff (PAS) staining often is used to help locate the

organisms, which appear bright pink with a green-blue background (depending on the counterstain used).

Nucleic Acid-Based Techniques : Nucleic acid-based amplification methods, including polymerase chain reaction

, have been developed for the identification of E. histolytica. Stool specimens, however, may contain inhibitors that

would prevent accurate detection using amplification methods. These tests are not widely used, because they require

more technical expertise and currently have not proven to be more sensitive than antigen-based immunoassays.

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Therapy:

Two classes of drugs are used in the treatment of amebic infections: luminal amebicides, such as iodoquinol

or diloxanide furoate, and tissue amebicides, such as metronidazole, chloroquine, or dehydroemetine. Because

of the differences in drug efficacy, it is important that the laboratory report indicates whether cysts,

trophozoites, or both are present in the stool specimen.

Prevention:

Humans are the reservoir host for E. histolytica, and infection can be transmitted to other humans, primates, dogs,

cats, and possibly pigs. Accidental consumption of sewage-contaminated water provides another route of infection.

Amebiasis is considered a zoonotic waterborne infection. The cyst stages are resistant to environmental conditions

and can remain viable in the soil for 8 days at 28° to 34°C, for 40 days at 2° to 6°C, and for 60 days at 0°C. Cysts

normally are removed by sand filtration or destroyed by 200 ppm of iodine, 5% to 10% acetic acid,

or boiling. However, an asymptomatic carrier who is a food handler generally is thought to play the most important

role in transmission. Proper disposal of contaminated feces is considered the most important preventive measure.

Although vaccines have been discussed as a possibility for eliminating human disease, nothing currently is available.

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Figure 4: A to C, Trophozoites of Entamoeba histolytica (note ingested red blood cells). D, Trophozoite of E.

histolytica/E. dispar. E, Early cyst of E. histolytica/E. dispar. F to H, Trophozoites of Entamoeba coli. I and J, Cysts

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Entamoeba coli:

General Characteristics

The life cycle of E. coli is identical to that of E. dispar. After digestion of infective cysts, the organisms excyst in the

intestinal tract and produce trophozoites. Cyst formation occurs as the gut contents move through the intestinal tract;

the excreted cysts are the infective form that is transmitted to humans and some animals. E. coli trophozoites are

somewhat larger than those of E. histolytica and E. dispar and range from 15 to 50 μm in Diameter.

Motility is sluggish with broad, short pseudopods. In wet preparations, differentiating nonpathogenic E. coli from

pathogenic E. histolytica is almost impossible. On the permanent stained smear viewed at a higher magnification, the

cytoplasm is granular with vacuoles containing bacteria, yeasts, and other food materials. The nucleus has a large

blotlike karyosome that may be eccentric rather than centrally located. The chromatin on the nuclear membrane tends

to be clumped and irregular. Although rare, if RBCs are present in the intestinal tract, E. coli may ingest them rather

than bacteria.

Early cysts often contain chromatoidal bars, which tend to be splinter shaped and irregular. Eventually, the nuclei

divide until the mature cyst, containing eight nuclei, is formed (see Figures 4).

In rare cases, the number of nuclei reaches 16.The cysts measure 10 to 35 μm in diameter, and as they mature, the

chromatoidal bars disappear. When the cyst of E. coli matures, it becomes more refractive to fixation; therefore, the

cyst may be seen on the wet preparation but not on the permanent stained smear. Occasionally, on trichrome smears,

the cysts appear distorted and somewhat pink (Figure 5,6).

Figure 5: Entamoeba coli trophozoite. Figure 6 Entamoeba coli cyst (trichrome stain) (poor

preservation; typical appearance of some E. coli cysts).

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Epidemiology:

Transmission occurs through the ingestion of mature cysts from contaminated food or water. The organism is readily

acquired, and in some warmer climates or areas with primitive hygienic conditions, the colonization rate can be quite

high.

Pathogenesis and Spectrum of Disease:

E. coli are considered nonpathogenic and do not cause disease.

Laboratory Diagnosis:

Unless the mature cyst with eight nuclei is seen, the morphologies of E. histolytica, E. dispar, E. moshkovskii, and

E. coli are similar in the trophozoite and immature cyst stages. E. moshkovskii is typically a free-living amoeba

isolatedin river or stream sediment and rarely infects humans. Definitive identification relies on examination of

permanent stained smears.

Therapy:

Specific treatment is not recommended for the nonpathogen E. coli. Correct differentiation among the species is

critical to good patient care. Because the amebae are acquired through fecal-oral contamination, pathogens and

nonpathogens can be found in the same patient. If few E. histolytica/E. dispar organisms are present among many E.

coli organisms, extended microscopic examination and/or the use of species-specific immunoassay testing may be

required to make the correct

Identification

Prevention:

Prevention depends on adequate disposal of human excreta and improved personal hygiene, preventive measures that

apply to most of the intestinal protozoa.

Figure 7 A, Entamoeba hartmanni

trophozoite. B, E. hartmanni

cyst.

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Entamoeba hartmanni:

General Characteristics:

The life cycle of E. hartmanni is similar to that of E. dispar, with differences in size (Figures 7 and 8). In wet

preparations, E. hartmanni trophozoites range in size from 4 to 12 μm in diameter, and cysts range in size from 5 to

10 μm in diameter. On the permanent stained smear, the cysts, primarily, tend to shrink as a result of dehydration;

therefore, the sizes of all the organisms, including pathogenic E. histolytica, may be somewhat smaller (1 to 1.5 μm)

than the wet preparation measurements. Trophozoites do not ingest RBCs, and the motility is usually less rapid ,The

morphologic characteristics of E. hartmanni are very similar to those of E. histolytica, with two exceptions.

Frequently, E. hartmanni cysts may contain only one or two nuclei, even though the mature cyst contains four nuclei.

Mature cysts of E. hartmanni also retain their chromatoidal bars, a characteristic not usually seen in E. histolytica/E.

dispar. E. hartmanni’s chromatoidal bars are similar to those of E. histolytica and E. dispar but smaller and more

numerous. At the species level, differentiation between E. hartmanni and E. histolytica/E. dispar depends on size;

therefore, laboratories are required to use calibrated microscopes that are checked periodically for accuracy.

Epidemiology:

Transmission occurs through the ingestion of mature cysts from contaminated food or water. If accurate

identifications have been recorded, the colonization rate tends to match that of E. histolytica.

Pathogenesis and Spectrum of Disease:

E. hartmanni is considered nonpathogenic and does not cause disease.

Laboratory Diagnosis: