Intro to Medical Parasitology

• Lecture: Introduction to Medical Parasitology
• Instructor: Prof. Khalifa E. Khalifa, Ass. Prof. Nora Aboelfetouh
• Program: Medicine and Surgery Program, Spring 2025

Objectives

• Understand the meaning of "Medical Parasitology."
• Define basic terms in "Medical Parasitology."
• Discuss relationships between living organisms, focusing on parasitism and commensalism.
• List and define types of hosts and parasites.
• Recall study objectives of Medical Parasitology: geographical distribution, morphology, life cycle, pathogenesis, clinical picture, diagnosis, treatment, prevention, and control.
• Apply study objectives to individual parasites studied during the course.

Medical Parasitology

• Medical Parasitology is the biological science that deals with morphology, biology, pathogenesis, clinical manifestations, diagnosis, prevention, and control of human parasites.

Associations Between Organisms

• Associations between organisms include parasitism, commensalism, mutualism, and symbiosis.
• Parasitism: one organism benefits (parasite) to the detriment of the other (host/patient); Giardia intestinalis causes diarrhea in humans.
• Commensalism: one organism benefits without harming the other; Entamoeba coli lives in the human large intestine without causing disease.

Parasites

• A parasite is a living organism (uni- or multicellular) that lives in or on a larger organism (host); it causes harm to the host, resulting in parasitic disease.

Types of Parasites based on Habitat

• Ectoparasites: live on the surface of hosts, causing infestation.
• Endoparasites: live inside the body of hosts (small intestine, large intestine, etc.).

Types of Parasites based on Number of Hosts

• Monoxenous: require only one host to complete its life cycle; Ascaris lumbricoides and Trichuris trichiura.
• Heteroxenous: require two (diheteroxenous) or more (polyxenous) hosts to complete its life cycle; Fasciola and Heterophyes heterophyes.

Types of Parasites based on Association with Hosts

• Obligatory: cannot survive outside the host.
• Facultative: capable of free living outside their host under favorable conditions and can hide inside the host under unfavorable conditions; Strongyloides stercoralis.
• Temporary: visits the host from time to time for a meal; mosquitoes.
• Permanent: always fixed to their hosts; lice.
• Accidental: affects unusual hosts.
• Opportunistic: causes severe disease in immuno-compromised hosts; Cryptosporidium hominis.

Types of Hosts

• Final or definitive host (DH): harbors the adult stages or sexually reproducing forms where the parasite reaches maturity.
• Intermediate host (IH): harbors the larval stages or asexually reproducing forms.
• Reservoir host (RH): harbors the same species and stages as humans; maintains the parasite's life cycle in nature and serves as a source of re-infection.
• Vector: an arthropod that transmits parasites from one host to another.

Natural vs. Accidental Hosts

• Natural: a parasite completes its life cycle.
• Accidental: a parasite may or may not complete its life cycle.
• High Host Specificity: develops only in one host.
• Low Host Specificity: develops in several hosts.

Study Objectives in Parasitology

• Locate Geographical Distribution.
• Describe Morphology (Adult, Larva, Eggs, Trophozoite, Cyst).
• Name the definitive host, intermediate host(s), and reservoir hosts.
• Name the habitat where the parasite lives inside the host (bile duct, small intestine, etc.).

Describing the Life Cycle includes

• Cycle inside the definitive host (DH).
• Exit route (urine, stool, sputum, insects, etc.).
• Cycle in intermediate host (IH), if present.
• Infective stage.
• Mode, route, and source of infection.
• Diagnostic stage.
• Discuss the pathogenesis and pathology: -General effects: fever, allergy, nervous irritability, anaphylaxis, malnutrition, anemia. -Local effects: mechanical obstruction, pressure symptoms, tissue lysis, local skin manifestations, disturbed function such as diarrhea and/or skin nodule.
• Correlate the clinical manifestations with the pathology induced.

Methods of Diagnosis

• Clinical: recognizing symptoms and signs.
• Laboratory: using direct and indirect techniques.
  • Direct: finding diagnostic stages (egg, larva, trophozoites, cyst) through parasitological methods.
  • Indirect: detecting antibodies and antigens in blood samples; Enzyme Linked Immunosorbent Assay (ELISA), Indirect Haemagglutination Assay (IHA), Immunochromatographic technique (ICT).
  • Molecular: detecting parasite genes by PCR.
• Imaging techniques: X-ray, CT, and sonography.
• Prescribe the treatment of choice.
• Describe and apply proper control and preventive measures by understanding factors favoring parasitic infection.

Components to be studied for Parasites and Diseases

• Parasites: Morphology, Habitat, DH/IH/RH, and Life Cycle with stages and modes.
• Disease: Epidemiology, Pathogenesis, Clinical Manifestations, Diagnosis (Clinical/Laboratory/Imaging), Treatment, and Prevention.

Parasite Nomenclature

• Kingdom: Animalia
• Phylum: Platyhelminthes
• Class: Cestoda
• Order: Cyclophyllidea
• Family: Taeniidae
• Genus: Taenia (italic, initial capital letter)
• Species: saginata solium (italic, initial small letter)

Areas of Study

• Helminthology: multicellular worms; GIT, Blood, Urogenital & Respiratory Modules.
• Protozoology: unicellular; GIT, Blood, Urogenital & CNS Modules.
• Entomology: arthropods; Musculoskeletal & Skin, Blood, Resp. Modules.

Direct and Indirect Life Cycles

• Parasite life cycles are the pathway of development from one stage to the next.
• Direct Life Cycle: completed in one host; monoxenous parasites.
• Indirect Life Cycle: completed in more than one host; heteroxenous parasites.

Main Components of Life Cycle

• Habitat: specific organ/tissue where the parasite resides (GIT, urogenital, respiratory, blood, CNS).
• Hosts: Definitive Host (DH), Intermediate Host (IH), Reservoir Host (RH).
• Infective Stage: Egg, Larva, Trophozoite, Cyst, Oocyst.
• Mode of Infection: ingestion, inhalation, blood transfusion, sexual intercourse, insect bite, penetration of skin, etc.
• Diagnostic Stage: Egg, Larva, Trophozoite, Cyst, Oocyst.
• Source of Infection: person, food (vegetables, meat, fish), water, air, soil, self-infection.
• Route of Infection/Entry: oral, skin, parenteral (injection).
• Route of Exit: stool, urine, sputum, insect vectors.

Importance of Studying the Life Cycle

• Predict clinical manifestations based on habitat.
• Diagnose infections and select proper diagnostic sample timing.
• Design control and prevention strategies; considering infection mode and hosts.

Transmission of Parasitic Infection

• Oral transmission (foodborne): Improperly cooked meat/fish, unwashed fruits/vegetables.
• Skin penetration: Active, or via skin contact.
• Autoinfection: Self-infection, external or internal.
• Congenital (transplacental).
• Sexual transmission.
• Blood transfusion and organ transplantation.
• Inhalation followed by swallowing.
• Vector transmission: Biological or Mechanical.

Effects of Parasites on Host

• Systemic Effects include inflammatory cytokines; anemia, eosinophilia, malnutrition, allergic reaction, autoimmune disorders, impaired immunity and/or immunomodulation.
• Local Effects include disturbed processes, tissue destruction, space-occupying lesions, chronic inflammation, malignant transformation, obstruction, skin issues, and RBC destruction.

Clinical Manifestations

• Intestinal Parasites cause pain, nausea/vomiting, indigestion, allergic manifestations, vitamin deficiency, malabsorption, anaemia, & dysentery.
• Blood Parasites cause fever, chills, toxemia, splenomegaly, lymphadenopathy, anaemia, thrombocytopenia, encephalitis, and coma.
• Tissue Parasites cause fever, chills, toxic/allergic reaction, anemia, liver/lung/skin issues, motor or sensory loss, bone fractures & eye issues