overview of parasites

1. General Parasitology and
Overview of Parasitic Infections

2. GENERAL PARASITOLOGY
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3. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PARASITOLOGY
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▰ Parasite is a living organism, which lives in or upon another organism (host)
and derives nutrients directly from it, without giving any benefit to the host.
▰ Medical Parasitology - study of animal parasites, which infect and produce
diseases in human beings.

4. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PARASITOLOGY (Cont..)
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Parasites may be classified as:
▰ Ectoparasites
▰ Endoparasites

5. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PARASITOLOGY (Cont..)
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Ectoparasites:
▰ Inhabit the surface of the body of the host without penetrating into the tissues
(e.g., fleas or ticks).
▰ Serve as important vectors transmitting the pathogenic microbes.
▰ Infection produced by these parasites - infestation.

6. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PARASITOLOGY (Cont..)
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Endoparasites:
▰ Parasites, that live within the body of the host (e.g., Leishmania).
▰ Invasion by the endoparasite is called as infection.

7. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PARASITOLOGY (Cont..)
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▰ Endoparasites are further classified into protozoa and helminths.

8. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Medically important protozoans and helminths
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Medically important protozoans
Amoeba
 Entamoeba histolytica
 Free-living amoebae: Naegleria, Acanthamoeba, Balamuthia
Flagellates
 Intestinal Flagellate: Giardia
 Genital Flagellate: Trichomonas
 Hemoflagellates: Leishmania and Trypanosoma
Apicomplexa
 Malaria parasites and Babesia
 Opportunistic coccidian parasites : Toxoplasma, Cryptosporidium, Cyclospora, Cystoisospora, Sarcocystis
Miscellaneous Protozoa : Balantidium coli, Blastocystis and Microsporidia*

9. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Medically important protozoans and helminths
(Cont..)
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Medically important helminths
Cestodes
Diphyllobothrium, Taenia, Echinococcus, Hymenolepis, Dipylidium and others
Trematodes or Flukes
Schistosoma, Fasciola, Clonorchis, Opisthorchis, Fasciolopsis, Paragonimus and others
Intestinal Nematodes
Trichuris, Enterobius, Hookworm, Strongyloides, Ascaris and others
Somatic Nematodes
Filarial nematodes, Dracunculus and Trichinella

10. LIFE CYCLE OF PARASITES
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11. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
LIFE CYCLE OF PARASITES
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▰ Depends up on three factors: host, mode of transmission and infective form.
Host:
▰ Organism, which harbors the parasite and provides the nourishment and
shelter.
▰ Can be classified into definitive host (where the parasite undergoes sexual
cycle) or intermediate host (where the parasite undergoes asexual cycle).

12. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
LIFE CYCLE OF PARASITES (Cont..)
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▰ In direct/simple life cycle - parasite requires only one host to complete its
development.
▰ In indirect/complex life cycle - parasite requires two/ three hosts (one
definitive host and another one or two intermediate host/s) to complete its
development.

13. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
LIFE CYCLE OF PARASITES (Cont..)
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Infective form:
▰ Morphological form of the parasite which is transmitted to man.
Autoinfection:
▰ Few intestinal parasites may infect the same person by contaminated hand
(external autoinfection) or by reverse peristalsis (internal autoinfection). It is
▰ Observed in: Cryptosporidium parvum, Taenia solium, Enterobius vermicularis,
Strongyloides stercoralis and Hymenolepis nana.

14. LABORATORY DIAGNOSIS OF
PARASITIC DISEASES
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15. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Examination of Feces
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▰ As many parasites inhabit in the intestinal tract, stool examination is the most
common diagnostic technique used for the diagnosis of parasitic infections.

16. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Specimen Collection
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▰ Stool specimens should be collected in
a wide-mouthed, clean, leak-proof,
screw capped containers and should
be handled carefully to avoid acquiring
infection from organisms present in
stool.

17. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Specimen Collection (Cont..)
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Timing:
▰ Collected before starting anti-parasitic drugs and closer to the onset of
symptoms.
Frequency:
▰ At least three stool specimens collected on alternate days (within 10 days)
(except for intestinal amoebiasis - six specimens may be recommended).

18. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Specimen Collection (Cont..)
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When to examine:
▰ Liquid stool specimens - examined within 30 minutes,
▰ Semisolid stools - within 1hr.
▰ Formed stools - up to 24 hours after collection.
For monitoring response to therapy:
▰ Repeat stool examination - 3 to 4 weeks after the therapy for intestinal
protozoan infection, and 5–6 weeks for Taenia infection.

19. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Specimen Collection (Cont..)
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If delay in transport:
▰ Fecal specimens should be kept at room temperature;
▰ Preservatives (e.g. 10% formalin) - used to maintain the morphology of the
parasitic cysts and eggs.
Specimens other than stool:
 Perianal Swabs (cellophane tape or NIH swab)
 Duodenal Contents

20. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Macroscopic Examination
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▰ Mucoid bloody stool: acute amoebic dysentery, intestinal schistosomiasis,
and invasive balantidiasis.
▰ Color: Dark red stool - upper gastrointestinal tract (GIT) bleeding and a bright
red stool - bleeding from lower GIT.
▰ Frothy pale offensive stool (containing fat) - found in giardiasis.

21. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Microscopic Examination
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▰ Includes direct wet mount examination
▰ Permanent staining methods.

22. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Permanent Stained Smear
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▰ Required for accurate detection of protozoan cysts and trophozoites by
staining their internal structures.
▰ Commonly used methods are:
 Iron-hematoxylin stain
 Trichrome stain
 Modified acid-fast stain - useful for coccidian parasites such as
Cryptosporidium, Cyclospora and Cystoisospora

23. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Concentration Techniques
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▰ If the parasite output is low in feces (egg, cysts, trophozoites and larvae) and
direct examination may not be able to detect the parasites, then the stool
specimens need to be concentrated.
▰ These methods are also useful in epidemiological analysis and for assessing the
treatment response.
▰ The eggs, cysts and larvae are recovered after concentration procedures; but, the
trophozoites get destroyed.

24. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Commonly used concentration techniques
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▰ Sedimentation techniques
▰ Floatation techniques
▰ Zinc sulphate flotation concentration technique
▰ Sheather’s sugar flotation technique

25. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Examination of Blood
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▰ Useful in diagnosis of infection caused by blood parasites like Plasmodium,
Trypanosoma, Leishmania, Babesia, Wuchereria bancrofti, Brugia malayi, Loa
loa and Mansonella.

26. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Examination of Blood (Cont..)
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▰ Various methods of examination of blood include:
 Direct wet mount examination
 Examination of blood smears (thin smear and thick smear)
 Quantitative buffy coat (QBC)
 Concentration of blood

27. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Immunodiagnostic Methods
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▰ Detection of parasite specific antibodies in serum, and detection of circulating
parasitic antigen in the serum.
▰ These methods are useful when:
 Parasites are detected only during the early stages of the disease
 Parasites occur in very small numbers
 Parasites reside in internal organs and morphological identification is not
possible
 When other techniques like culture are time consuming

28. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Molecular Methods
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▰ Polymerase chain reaction (PCR) and real time PCR.
▰ LAMP assay: developed for visceral leishmaniasis and malaria.
▰ BioFire FilmArray: It is an automated multiplex nested PCR. The
gastrointestinal panel can simultaneously detect 22 enteric pathogens,
including 4 parasites such as—E. histolytica, G. lamblia, Cryptosporidium,
Cyclospora.

29. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Other Diagnostic Modalities
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▰ Culture techniques
▰ Imaging techniques
▰ Intra-dermal skin tests
▰ Xenodiagnostic technique
▰ Animal inoculation methods

30. TREATMENT OF PARASITIC
DISEASES
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31. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Anti-parasitic agents
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Protozoa Anti-parasitic agents
Entamoeba histolytica Metronidazole, tinidazole Diloxanide furoate
Giardia species Metronidazole, tinidazole
Trichomonas Metronidazole, tinidazole
Trypanosoma cruzi Benznidazole, nifurtimox
Trypanosoma brucei Pentamidine, suramin
Leishmania donovani Amphotericin B, Antimonials Paromomycin, Miltefosine
Plasmodium species Chloroquine, Quinine, Artemisinin derivative Primaquine,
Mefloquine, Sulfadoxine-pyrimethamine Lumefantrine

32. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Anti-parasitic agents (Cont..)
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Protozoa Anti-parasitic agents
Cryptosporidium Nitazoxanide
Cyclospora Cotrimoxazole
Cystoisospora Cotrimoxazole
Toxoplasma Cotrimoxazole, spiramycin
Microsporidia Albendazole
Balantidium coli Tetracycline
Cestodes Praziquantel, Niclosamide, Albendazole
Trematodes Praziquantel, Triclabendazole for Fasciola hepatica

33. Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
Anti-parasitic agents (Cont..)
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Protozoa Anti-parasitic agents
Intestinal nematodes Mebendazole, albendazole, Pyrantel pamoate
Ivermectin (for Strongyloides)
Filarial nematodes Diethylcarbamazine (DEC) Albendazole,
Ivermectin

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36. THANK YOU
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