Protozoa 2

OPTOMETRY · SEMESTER 2

Microbiology and Parasitology

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PROTOZOA OF MEDICAL IMPORTANCE

Learning Objectives

By the end of this session, students are expected to be able to:
Describe general characteristics of Protozoa
List Protozoa of medical importance
Explain mode of transmission of protozoa of medial importance
Describe life cycle of Protozoa of medical importance
List specimens collected to diagnose protozoa of medical importance

List drugs of choice to treat protozoa of medical importance

List Protozoa of medical importance

Entamoeba histolytica
Entamoeba coli
Giardia lamblia
Trichomonas vaginalis
Trichomonas hominis

Balantidium coli

Cryptosporidium parvum

Isospora belli
Trypanasomes
Plasmodium spp
Leishmania
Toxoplasma spp

List Protozoa of medical importance

Mode of transmission of protozoa of medial importance

Oral-anal sexual cotanct
Ingestion of contaminated food and drinks
Blood transfusion
Congenital transmission
Vector-borne bite
Sexual contact

Penetration

Cryptosporidium parvum

Cryptosporidium parvum: Is a tiny coccidian parasite that causes outbreaks of diarrhoea (cryptosporidiosis )

It is one of several species that cause cryptosporidiosis, a parasitic disease of the mammalian intestinal tract.
Cryptosporidium is a protozoan pathogen of the Phylum Apicomplexa

Characteristics of Cryptosporidium Parvum

The sporozoite measures 2-6 μm diameter.

Cryptosporidium is capable of completing its life cycle within a single host, resulting in microbial cyst stages (oocyst).

Oocysts are rounded and measure 4.2 to 5.4 μm in diameter.
Oocysts are excreted in feces and are capable of transmission to a new host.

Sporozoites are sometimes visible inside the oocysts, In modified acid-fast stain oocysts appear as bright pink to red organisms containing some dark granules and usually have a central clear area.

Morphological Features of Cryptosporidium Parvum Oocyst

Life Cycle of Cryptosporidium Parvum

The life cycle of Cryptosporidium parvum consists of an asexual stage and a sexual stage
The life cycle begins with oocysts
Oocysts are infective at the time of excretion
The ingested oocysts excysts when reaches the small intestine release four (4) sporozoites
The sporozoites invade epithelial cells of small intestine and become intracellular, settling in the cell surface called the parasitopharous vacuole .

Inside the cells the sporozoites develop into trophozoites , the feeding stage

Trophozoites undergo merogony (asexual division ) forming meronts containing merozoites
And merozoites are released to infect the new cells
Some merozoites develop into microgametocytes and Macrogametocytes

Life Cycle of Cryptosporidium Parvum cont..

These initiate the sexual life cycle after microgametes to fertilize the macrogametocytes forming a zygote later on, the zygote develop to form oocyst Thick- walled oocysts are passed in stool and can infect others Thin -walled oocyst can cause auto infection within the same host

Life Cycle of Cryptosporidium Parvum

Disease caused by cryptosporidium parvum

Cryptosporidium parvum causes cryptosporidiosis characterized by unremitting, profuse diarrhea This leads to malabsorption , dehydration, chronic diarrhoea , electrolyte imbalance ,severe weight loss and wasting.

In immunocompetent the disease is always self limiting but severe in immunosuppressed patient such as HIV infected people

Diagnosis

Specimen
o Stool
o Serum
Technique
o Microscopy
Wet mount
Modified ZN stain

o Serological tests

Characteristics of Isospora Belli

It is opportunistic parasite associated with AIDS

The oocyst is elongated-ellipsoid constricted at one end asymmetrical at the other end (rugby ball shape)
The wall is smooth, colourless and refractive
Its size measures about 28 x 14μm
The sporocyst and sporozoite are subspheroid to ellipsoid measuring 14 x 10 μm in size

Medical Importance of Isospora Belli

Isospora belli causes isosporiasis

o Diarrhoea (usually self-limiting) in immunocompetent patients o Chronic diarrhoea in the immunocompromised patients like in HIV&AIDS which is characterized with body wasting , electrolyte imbalance , profuse diarrhoea

Diagnosis

Specimen
o Stool
o Serum
Technique
o Microscopy
Wet mount
Modified ZN stain
o Serological tests

ELISA

Specimens collected to diagnose protozoa of medical importance

Fresh stools
Rectal scrapings
Liver aspirate
Blood
Mucosal scraping (from the sigmoid colon)
Bone marrow lymph nodes fluid, Liver and spleen aspirates.
Urine

High Vaginal Smear

Overview of Trichomonas Vaginalis

The Trichomonas vaginalis are flagellate protozoa (mastigophora) that are characterized by having an undulating membrane and a number of flagella.

They are adapted to living in the genital urinary tract of man.
Trichomonas vaginalis is responsible for causing a sexually transmitted disease called Trichomoniasis

Characteristics of Trichomonas Vaginalis

Trichomonas vaginalis is a colourless pear-shaped, with a short undulating membrane supported by a single flagellum and four anterior flagella

It measures about 10 x 7μm, though its length may vary from 5 to 30μm and its width from 2 to 14μm
The organism moves with a characteristic wobbling and rotating motion
The nonpathogenic trichomonads, Trichomonas hominis and Trichomonas tenax, cannot readily be distinguished from Trichomonas vaginalis when alive

•It is actively phagocytic

Optimal growth occurs under moderately anaerobic conditions
Reproduction is by binary fission
Unlike many pathogenic protozoa don’t form cyst

Morphological Features of Trichomonas Trophozoites

A: Normal trophozoite
B: Round form after division

C: Common form seen in stained preparation

Mode of Transmission

Transmission is primarily by unprotected sexual intercourse
Contaminated towels and examination instruments and materials
Infants may be infected during birth (congenital )

Life Cycle of Trichomonas Vaginalis

Life Cycle

Trichomonas vaginalis resides in the female lower genital tract and the male urethra and prostate.
In the genital tract the parasite replicates by binary fission.

The parasite does not appear to have a cyst form, and does not survive well in the external environment.

Trichomonas vaginalis is transmitted to another person (man being the only known host) by unprotected sexual intercourse

Transmission can occur from female to male, male to female, or female to female partner

In female trophozoites inhabit the vagina and cervix, feeding on epithelial cells and bacteria.

In male they colonize the urethra and prostate.

They replicate by binary fission

Medical Importance of Trichomonas Vaginalis

Disease Caused by Trichomonas vaginalis
Trichomoniasis associated with
Vaginitis and cervicitis (inflammation of vagina and cervix).
Pelvic inflammatory disease risk increases and sometime associated with
Froth, yellow green vaginal discharge
Strong unpleasant fish smell
Itching or irritation inside the vagina
Pain during sex and burning sensation during urination
Urethritis (inflammation of the urethra).

Prostatitis (inflammation of the prostate).

Laboratory diagnosis

Laboratory specimen
Vaginal swabs
Urine samples (first-void urine)
Vaginal secretions/discharge
Urethral swabs

First-void urine

Laboratory technique

Direct wet preparation

Culture

Drugs of choice

Metronidazole
Secnidazole

Tinidazole

References

Arcari, M., Baxendine, A. & Bennett, C. E. (2000). The Ciliates, Coccidia and

Microsporidia. Diagnosing Medical Parasites through Coprological Techniques.

Becker, F.J. & Silverton, R.E. (1985). Introduction to Medical Laboratory Technology (6th ed.). London: Butterworth.
Brooks, G.F., Carroll, K.C., Butel, J.S. et al. (2007). Jawetz, Melnick, & Adelberg'smMedical Microbiology (24th ed.). USA: The McGraw-Hill Companies, Inc.
Brown, H.W. (1968). Basic Clinical Parasitology (3rd ed). New York: Meredith
Corporation.
CDC (2007). Laboratory Identification of Parasites of Public Health Concern.

“Cryptosporidiosis.” Retrieved March 27th, 2010 from http://www.dpd.cdc.gov/dpdx/mHTML/Cryptosporidiosis.htm

CDC (2009). DPDx, Laboratory Identification of Parasites of Public Health Concern.m

Retrieved Ma

Cook, G. (2000). Manson’s Tropical Diseases (22nd ed.). London: WB Saunders Company Ltd.

Harwood, R.F., James, M.T., (1979). Entomology in Human and Animal Health (7th ed.). Washington: State University Pulman.
Levinson, W. (2004). Medical Microbiology and Immunology. (8th ed.). Examination &, Board Review. New York: International Edition Lange Medical Books /McGraw Hill Medical Publishing & Davson.
Mike, S. (2004). Medical Entomology for Students. London: Oxford University Press.
Monica, C. (1987). Medical Laboratory Manual for Tropical Countries. Volume 1 (2nd ed.). Oxford: ELBS Butterworth, Heinemann Ltd.