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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

Entamoeba dispar

Entamoeba coli

Entamoeba hartmanni

Endolimax nana

Iodamoeba bütschlii

Blastocystis hominis

 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:

Nematodes

Wuchereria bancrofti

Brugia malayi

Brugia timori

Loa loa

Onchocerca volvulus

Mansonella ozzardi

Mansonella streptocerca

Mansonella perstans

3)Platyhelminthes or flatworms:(Cestodes, Trematodes)

 3.1.Cestodes:

 A-Intestinal Cestodes (Tapeworms):

Diphyllobothrium latum

Dipylidium caninum

Hymenolepis nana

Hymenolepis diminuta

Taenia solium

Taenia saginata

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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),

cutaneous larva

migrans (CLM).

Nematodes,

filarial

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

of E. coli.

A B C

D E F

G H I

J

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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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SectionIII– Parasitology By Nada Sajet

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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SectionIII– Parasitology By Nada Sajet

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: