1. INTRODUCTION TO PARASITOLOGY
SAMUEL AGUAZIM, M.D.
INTRODUCTION
TO PARASITOLOGY

2. Is the mighty lion a despicable parasite?
The benefit in the relationship between lion and wildebeest seems highly skewed in favor of the lion

3. Who is a parasite?
Parasites are usually much smaller than their hosts, they also do not kill before they eat.

4. Disease terminology
Prepatency: infected but parasite presence can not be detected yet
Patency: established infection, parasite stages can be detected (malaria parasites in blood smears, worm eggs in feces etc.)
Incubation period: time between infection and the development of symptoms
Acute disease can lead to crisis which can resolve in spontaneous healing, chronic infection or death
Convalescence: Period after healing, absence of infectious agents, no symptoms, in certain case immunity to reinfection

5. Why study Parasitology?
Many of these parasites are causative agents of major public health problems of the world.
Recent estimates of prevalence of parasites in the world are:
Ascaris billion Hookworms billion Whipworms billion Filarial worms million Malaria million Schistosomes million Amebiasis million Taenia tapeworms million Clonorchis million Chagas’ Disease million  
These parasites cause untold suffering and death in the world today.

6. Epidemiology
Although parasitic infections occur globally, the majority occur in tropical regions, where there is poverty, poor sanitation and personal hygiene
Often entire communities may be infected with multiple, different organisms which remain untreated because treatment is neither accessible nor affordable
Effective prevention and control requires "mass intervention strategies” and intense community education. Examples include:
General improved sanitation: pit latrines, fresh water wells, piped water
Vector control: insecticide impregnated bed nets, spraying of houses with residual insecticides, drainage, landfill
Mass screening and drug administration programmes which may need to be repeated at regular intervals

7. The burden of some major parasitic infections
Parasite
Diseases
No. people infected
Deaths/yr
Plasmodium
malaria
273 million
1.12 million
Soil transmitted helminths:
Roundworm (Ascaris)
Whipworm (Trichuris)
Hookworm (Ancylostoma and Necator)
Pnemonitis, intestinal obstruction
Bloody diarrhoea, rectal prolapse
Coughing, wheezing, abdominal pain and anaemia
2 billion
200,000
Schistosoma
Renal tract and intestinal disease
200 million
15,000
Filariae
Lymphatic filariasis and elephantiasis
120 million
Not fatal but 40 million disfigured or incapacitated
Trypanasoma cruzi
Chagas disease (cardiovascular)
13 million
14,000
African trypanosomes
African sleeping sickness
0.3 – 0.5 million
48,000
Leishamania
Cutaneous, mucocutaneous and visceral leishmaniasis
12 million; 2 million new cases/yr
50,000

8. Taxonomic classification of protozoa
Sub kingdom
Phylum
Sub-phylum
Genus- examples
Species- examples
Protozoa
Sarcomastig-ophora
further divided into
Sarcodina-- - move by pseudopodia
Entamoeba
E. histolytica
Mastigophora
move by flagella
Giardia
G. lamblia
Apicomplexa
no organelle of
locomotion
Plasmodium
P. falciparum,
P. vivax,
P. malariae,
P. ovale
Ciliophora
move by cillia
Balantidium
B. coli
Microspora
Spore-forming
Enterocyto-zoa
E. bienusi

9. Introduction to Medical Parasitology
Definition of Medical Parasitology
Conceptions related to medical Parasitology
Relationships between parasite and host
The basic factors of transmission of parasitic diseases
The preventive measures of parasitic diseases

10. Definition of Medical Parasitology
Medical Parasitology Parasites Parasitic diseases
Morphology
Life Cycle
Pathogenesis
Diagnosis
Treatment
Transmission
Prevention

11. Conceptions related to medical Parasitology
Symbiosis
Parasite and type of parasites
Host and common type of host
Life cycle and type of life cycle

12. Symbiosis
------The relationship between two living things (animals). Two living things live together and involve protection or other advantages to one or both partner.
Commensalism
Mutualism
Parasitism*

13. Commensalism
Both partners are able to lead independent lives, but one may gain advantage from the association when they are together and least not damage to the other.
Fig. A female pea crab in the mantle cavity of its mussel host. The crab does not damage the mussel and uses its shell purely for protection

14. Mutualism
Mutualism is a permanent association between two different organisms that life apart is impossible, two partners benefit each other, such as termites and flagellates.
The mutuals are metabolically dependent on one another; one cannot survive in the absence of the other.

15. Parasitism
An association which is beneficial to one partner and harmful to the other partner. The former that is beneficial to is called parasite, the latter that is harmful to is called host. Human / Hookworm

16. Parasite and the type of parasites
Parasite: It is an animal that is dependent
on another animal (host) for its
survival.
Type of parasites
Protozoa(ffff
Nematodes
Parasites Helminths Trematodes Endo-
Cestodes
Arthropods Ecto-

17. Examples of important intestinal protozoa
Transmitted by the faecal-oral route and cause diarrhoea
Giardia lamblia: world-wide distribution, lives in the small intestine and results in malabsorption
Entamoeba histolytica: may invade the colon and cause bloody diarrhoea – amoebic dysentery. Also causes ameobic liver abscess.
Cryptosporidium parvum: more prevalent in the immunocompromised
Cyclospora cyatenensis - parasitises the small intestinal mucosa and may cause diarrhoea for several weeks
Balantidium coli: a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulceration
Enterocytozoon bienusi: a microsporidian that parasitises the small intestine. Also more common in the immunocompromised.

18. Examples of important systemic protozoa
Detected in the blood
Plasmodium: the cause of malaria. There are 4 species that infect man: P. falciparum, P. vivax, P. ovale and P. malariae
Toxoplasma gondi: transmitted by the ingestion of oocysts from cat faeces. Infection can lead to ocular problems and is also a cause of neonatal toxoplasmosis
Leishmania: transmitted by sand flies, can lead to visceral, cutaneous and mucocutaneous leishmaniasis
Trypanosoma: haemoflagellates which cause
In Africa - sleeping sickness (transmitted by the Tsetse fly)
In South America - Chagas disease (transmitted by the Reduviid bug)
Typical lesion of cutaneous leishmaniasis
Tsetse fly – the vector of African trypanosomiasis It has a painful bite!

21. Endoparasite and ectoparasite
----A parasite which lives in or on the body of the host is called endoparasite (protozoa and heminthes) or ectoparasite (arthropods).

22. HOST AND TYPES OF HOST
HOST: an organism that harbor the parasite, usually larger than the parasite. It supplies the parasite with nourishment and shelter, it is the injured partner.

23. A carrier is a person who harbours parasite has no clinical symptoms, is an important source of infection in epidemiology.

24. Intermediate host : Harbours larval or asexually reproductive stage of a parasite, according to priority they are classified into first intermediate host, second intermediate host and third intermediate host.
Definitive (final) host: Harbours adult or sexually reproductive stage of a parasite

25. Life cycle and type of life cycle
Life cycle : The whole process of parasite growing and developing.
The direct life-cycle : Only one host (no intermediate host).
The indirect life cycle : Life cycle with more than one host (intermediate host and final host).

28. Relationship (Effect) between parasite and host
injure to
Parasites harbor in Host (animal or human)
to response immune produce
Effects of the parasites on the host
Effects of the host on the parasites

29. Effects of parasites on the host
Depriving the host of essential substance
Hookworm Suck blood Anemia
Mechanical effects of parasites on the host
Ascaris Perforate/Obstruction
Toxic and allergy effect
E.H Proteolytic enzyme Necrosis
Parasite antigen Immune system
e.g. Anaphylaxis
Immune response
Allergy/ Hypersensitivity

30. Effects of the host on the parasites
----The host can produce certain degree resistance to parasites in human body or re-infection. The resistance (Immunity) is not very strong. In general, It don’t wipe out parasites completely, but may limit the number of parasites and establish balance with parasites.
Innate immunity
Acquired immunity

31. Innate immunity
Barrier : Prevent parasites to invade in certain degree. Skin/Mucous membrane/Placenta.
Acid in skin or stomach can cause damage of the parasites.
Phagocytosis of phagocyte.
----Non-specific/effective against a wide range of parasitic infection/controlled by genetical factors. But not very strong!

32. Acquired immunity Mechanism : cellular and humoral immunity.
Sterilizing immunity : Wipe out the parasites completely, meanwhile get a long-term specific resistance to re-infection. Rare!
Non-sterilizing immunity : Wipe out most of the parasites, but not completely. Common! No parasite, no immunity!

33. The basic factor of transmission of parasitic diseases
Parasitic diseases Infectious diseases Transmission
The source of the infection
The routes of transmission
The susceptible host
----The combined effect of those factors determine the dispensability and the prevalence of the parasites at a given time and place and regulate the incidence of the parasitic diseases in certain local population.

34. The source of the infection
Patient : Persons who have parasites in their body and show clinical symptoms.
Carrier : Persons who have parasites in their body, not show symptoms.
Reservoir host : Animals that harbors the same species of parasites as man. Sometimes, the parasites in animals can transmit into human.

35. The routes of transmission I
Congenital transmission : From mother to infant. Toxoplasmosis
Contact transmission : Direct contact---Trichomonas vaginalis; Indirect contact---Ascaris lumbricodes
Food transmission : The infectious stage of parasites contaminated food / The meat of the intermediate hosts containing infectious stage of parasites.

36. The routes of transmission II
Water transmission : Drink or contact the water contaminated the infectious stage of parasites.
Soil transmission : Contamination of the soil by feces containing the certain stage of parasites and this stage can develop into stage.
Arthropod transmission : Vectors of certain parasitic diseases.

37. The susceptible host
----In general, most people is the susceptible host (Why?). The parasite reaching a susceptible host must gain entrance and set up a favorable residence in order to complete its life cycle and cause the transmission of parasitic diseases.

38. The prevention measures of the parasitic diseases
Controlling the source of the infection.
----Treatment of the patients, carriers and reservoir hosts.
Intervention at the routes of transmission
----Managing feces and water resource,controlling or eliminating vectors and intermediate hosts.
Protecting the susceptible hosts.
----Paying attention to personal hygiene, changing bad eating habit, taking medicine.

39. THANK YOU FOR YOUR ATTENTION!