Introduction to Medical Parasitology

1. INTRODUCTION TO MEDICAL PARASITOLOGY
MR. MANOJ MEHTA

2. Introduction
• Parasite : A living organism which receives nourishment and shelter
from another organism where it lives.
• Parasitology is the study of parasites, their hosts, and the relationship
between them
• Medical Parasitology: "the study and medical implications of
parasites that infect humans”

3. FEATURES OF PARASITES
1. Smaller than their host,
2. numerous number than host
3. Short life span than their host, and
4. Have greater reproductive potential than their host

4. ASSOCIATION OF ORGANISMS
• Parasitism:-A relationship in which an organism (the parasite)
benefits from the association with another organism (the host) whereas
the host is harmed in some way.
• Commensalism:- A relationship in which one organism,the commensal
, is benefited whereas the other organism;the host is neither harmed or
helped by the association.
• Mutualism:- A relationship in which both patterned are benefit.
• Symbiosis:- Permanent association between two different organisms, so
dependant on each other, that their life part is impossible

5. CLASSIFICATION OFPARASITES :-
A. According to their habitat:
1. Ectoparasites: parasites living on or affecting the skin surface of the host.
e.g. lice, tick, etc.
2. Endoparasites: Parasites living within the body of the host.
e.g. Leishmania species, Ascaris lumbricoides, etc.
II. According to their dependence on the host:
1. Permanent (obligate) parasites: parasite living permanently in a host and
cannot live without a host
e.g. Trichomonos species.,Plasmodium secies.
2.Temporary (facultative) parasite: The parasite is capable of independent
existence in addition to parasitic life.
E.g. Strongyloids stercolaris, Naegleria fowleri, etc

6. III. According to their Pathogenicity:
1. Pathogenic parasites:- It causes disease in the host.
E.g. E. histolytica
2. Non-Pathogenic (commensal) parasite:-The parasite derives food and
protection from the host without causing harm to the host.
E.g. Entamoeba coli
3. Opportunistic parasites:- Parasites which cause mild disease in
immunologically healthy individuals, but they cause severe disease in
immuno-deficient hosts.
E.g. Pneumocystis carnii, Toxcoplasma gondii, Isospora belli

7. HOST
Host :- In the parasitism, the partners which provide the food and shelter for
parasites, and to some degree are injured by this association, are scientifically
called as hosts. -larger, more complex and better regulated bodies
Types of Hosts:-
1. Definitive host:- is the host in which the parasite become sexually mature
(♂♀) (where the adult worm harbor or undergoing sexual reproduction).
Ex. Man
2. Intermediate host:- is host in which the parasite undergoes larval
development but does not reach sexual maturity, parasites often can undergo
asexual reproduction in this type of host.
Ex: Taenia adult------ man
Larva –--- cattle

9. VECTOR
Vector:- Any arthropod or other living carrier which transports a pathogenic
microorganisms from an infected to non-infected host.
A. Biological vectors:-Those vectors that complete the life cycle a parasite
E.g.Anopheles(VectorofPlasmodium),Phlebotomus(Vectorof Leishmania),
Glossina(vectorofTrypanosoma),Simulium(VectorofOnchocerca),etc.
B. Mechanical (transport) Vectors: They are passive carriers of parasites, not
essential in the life cycle.
E.g. House fly and Chocroach as a mechanical vector for Amoebae,
Giardia, etc.

10. MODE OFTRANSMISSION
• Horizontal Direct Mode of Transmission:
-By Feco-oral route: Most intestinal parasites transmitted in this way.
• - Sexual intercourse
• - Blood transfusion
• - Direct skin penetration (soil transmitted helminthes)
• II. Vertical Direct Mode of Transmission: Transmission of the parasite is
from the mother to child through: - Congenital / transplacental
• - Transmammary (breast milk)
• Indirect Mode of Transmission requires biological vectors and/or one or
more intermediate hosts for transmission.

11. I. By ingesting infective stage of parasites:
• 1. In food, water or from hands that have been contaminated with faeces, E.g. E.
histolytica, E. vermicularis
• 2. In raw or undercooked meat, e.g. T. saginata, T. solium, T. spiralis
• 3. In raw or undercooked fish, crab, or water vegetation e.g. intestinal flukes
• 4. Water containing Cyclopes e.g., D. medinensis Parasitology
II. Penetration of Skin When in Contact with
1.Faecally polluted soil, e.g., S.stercoralis, Hook worms
2. Water containing infective stages of the parasite E.g., Cercaria of Schistosome species.
III. Through Insect Bite e.g, filarial worms, Trypanosoma species, Plasmodium species ,
Leishmania species IV. Sexual Contact, e.g., Trichomonas vaginalis
IV.Transplacental, e.g., T. gondii
V. Kissing, e.g., Trichomonas gingivalis, Trichomonas tenax

12. Types of Specimen
• Stool :-.e. g., intestinal nematodes, cestodes, trematodes and protozoa.
• Blood :- e.g., Haemoparasites Urine :- e.g., S. hematobium, T. vaginalis,
• Sputum :- e.g., P. westermani. Skin :- e.g., L. aethopica, O. volvulus, D.
medinensis and E. vermiculari
• Cerebro-Spinal fluid:- e.g., Trypanosoma rhodisense and Naegleria fowleri.
• Bone marrow:- e.g., L. donovani and T.gondii
• Lymphgland aspirates:- e.g Trypanosoma rhodisense, L..donovani and T.
gondii
• Liver aspirate :e.g.,E.histolytica, L..donovani and T.gondii
• Spleen aspirate:- e.g L..donovani and T.gondii
• Muscle biopsy:- e.g., T. spiralis Rectal scraping:- e.g., Schistosoma species
Duodenal aspirate:- e.g., G. lamblia, F. hepatica and S. stercoralis
• Bronchial biopsy :- e.g., P.carnii Perianal swab:- e.g.,E.vermicularis

13. IMPORTANCE of PARASITE
• More importance in developing countries where the social and economic
conditions require great deal of improvement in terms of better clothing,
shelter, food, provisions of wells and latrines and sewages and other
waste disposal facilities together with the means of controlling vectors.
• Most of the developing countries lie within the tropics where provides
better environmental conditions for larval development of parasites than
that of temprate regions, but also provides better conditions for the
multiplication of vectors.

14. AIM OFTHE STUDYPARASITE
-To understand the concepts of parasitism, the relationships between parasites
and hosts, between parasites and environment and the cultural and
socioeconomic factors affecting the transmission of parasites
- Know the general epidemiological aspects of parasites that affect human
- Apply simple preventive measures for specific parasites
- Know the life cycle of specific parasites and identify the important parasitic
agents affecting human health
- Apply the necessary procedures for the diagnosis of parasites in the medical
laboratory and reporting of results properly
- Apply the basic methods of specimens collection, preservation and processing
- Keep up the basic laboratory safety regulation

15. Classification of parasites
• General classification: animal parasites are classified according to international code taxonomy –
Each parasite belong to a:
•
• In classification, scientific parasitic name is of 2 parts:
Genus name and species name. Ex: Plasmodium Falciperum
Genetic name (one word): plasmodium
Species name (two words): plasmodium falciperum.
• Genus: means group of close related species.
• Species: means population with the same genetic characters.

16. Classification of parasites
Paraistes
Protozoa Helminthes
Intestinal
Blood and
tissue
Urogenital Cestodes Trematodes Nematodes

17. Classification of Protozoan
SUBKINGDOM Class Species- examples
Protozoa Rhizopods E. histolytica
Flagellates G. lamblia
Sporozoa P. falciparum,
P. vivax,
P. malariae,
P. ovale
Ciliates B. coli

18. Difference between protozoa and metazoa

19. Characteristics of protozoa
1. Protozoa are unicellular (eukaryotic) or acellular organisms which are capable of
performing all the vital functions of life.
2. Protozoan is measured in microns (size vary from 2-150 µ).
3. Cytoplasmic extension in form of pseudopodia, flagellae or cilia are responsible
for locomotion.
4. Nucleus may be compact with diffuse chromatin or vesicular with central or
eccentric karyosome (DNA) and peripheral chromatin (RNA).
5. Respiration is mostly anaerobic.
6. Secretion: Protozoa secrete digestive enzymes, toxins, cytolysin and antigenic
substances.
7. Reproduction: may be asexual or sexual.

20. PROTOZOA
• Single-celled Eukaryotes
• Free-living or parasitic
2 forms:
1. Cyst form (infective for humans) &
2. Trophozoite form
Protozoa
Intestinal Blood and tissue
Entamoeba histolytica
Giardia lamblia
Cryptosporidium
Malaria
Toxoplasma
Trypanosoma
Leishmaina
Urogenital tract
Trichononas Vaginalis

21. According to Mode of locomotion, protozoa are classified into the following
groups:
•Class: Rhizopoda: Protozoa move by pseudopodia.
Entamoeba histolytica
•Class: Mastigophora: Protozoa move by flagellae.
Gastrointestinal flagellates: Giardia intestinalis
Genitourinary flagellates: Trichomonas vaginalis
Blood and Tissue flagellates: Trypanosoma gambiense, Trypanosoma
rhodesiense , and Leishmania species.
•Class: Ciliophora: Protozoa move by cilia. Balantidium coli
•Class: Sporozoa: Protozoa have no motor organelles .
Plasmodium species, and Toxoplasma gondii.
Protozoa

22. • According to the body systems Protozoa are mainly classified into:
1. Haemopoietic parasites.
2. Intestinal parasites.
3. Genitourinary parasites.
4. Cutaneous parasites.
5. Others.
 Haemopoietic parasites:
• 1. Plasmodium species.
• 2. Leishmania species.
• 3. Trypanosoma species.
• 4. Toxoplasma species.

23.  Intestinal parasites:
 1. Entamoeba histolytica.
 2. Blantidium coli.
 3. Giardia lamblia.
 4. Cryptosporidium parvum.
 5. Isospora belli.
 Genitourinary parasites:
 Trichomonas vaginalis

24. Helminthes
Nematodes
(round worms)
Ascaris
lumbricoides
(Roundworm)
Cystods
(flat worms)
Taenia saginata
Trematodes
(fluks)
Bilharzia
(Schistosomiasis)

25. Helminthes can be classified into the following:
1- Trematodes (flukes): are members of Platyhelminthes.
Trematoda are flattened- leaf shaped non-segmented hermaphrodites except
Schistosoma species.
Examples
. Schistosoma mansoni
 Schistosoma haematobium
 Schistosoma japonicum
 Hermaphroditic flukes
Classification of Helminths

26. 2-Cestoda
Flattened-segmented Platyhelminthes, hermaphroditic worms (Tapeworm) with body
differentiated into:
•Scolex: 1-2 mm, carries, organ of fixation in the form of suckers or bothria.
•Neck actively dividing parts which gives rise to segments
•Segments start with immature segments followed by mature segments with well-developed
reproductive organs and then by gravid segments with well gravid uterus.
Classification of Helminths
example
 1 Taenia saginata and Taenia solium.
 2. Hymenolepis nana.
 3. Diphyllobothrium latum.
 4. Dipylidium caninum.
 5. Echinococcus granulosus.
 6. Echinococcus multilocularis.

27. 3- Nematoda:
 Nematodes are cylindrical non-segmented unisexual worms.
 They have body cavity containing fluids in which organs float.
 Anal and genital opening are separate in female and united in male (Cloaca).
 Mouth may be provided with lips, papillae and teeth
o Intestinal Nematodes
• Ascaris lumbricoides
• Hookworms
• Enterobius vermicularis
• Trichuris trichiura
o Tissue Nematodes
• Wuchereria bancrofti
• Brugia malayi
• Brugia timori
• Loa loa
• Onchocerca volvulus
• Dracunculus medinensis
• Trchinella spiralis