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

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

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

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

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 1.5 billion Hookworms 1.3 billion Whipworms 1 billion Filarial worms 657 million Malaria 500 million Schistosomes 270 million Amebiasis 50 million Taenia tapeworms 50 million Clonorchis 20 million Chagas’ Disease 15 million   These parasites cause untold suffering and death in the world today.

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

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

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

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

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

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

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*

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

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.

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

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-

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.

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!

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

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.

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

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

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).

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

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

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

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!

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!

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.

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.

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.

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.

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.

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.

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