Schistosomiasis and Sleeping Sickness Quiz

General Parasitology

• A parasite is a living organism that gets its nourishment and other needs from a host.
• A host is an organism that supports a parasite.
• Parasites in medical parasitology include protozoa, helminthes, and some arthropods.
• Hosts vary depending on the life cycle stage of the parasite.

Different Kinds of Parasites

• Ectoparasite: Lives on the outer surface of the host (e.g., lice, ticks, mites).
• Endoparasite: Lives inside the host's body (e.g., Entamoeba histolytica).
• Obligate Parasite: Entirely dependent on the host for its life cycle (e.g., Plasmodium spp).
• Facultative Parasite: Can live as a parasite or non-parasitic depending on the environment (e.g., Naegleria fowleri).
• Accidental Parasite: Attacks an unnatural host and survives (e.g., Hymenolepis diminuta).
• Erratic Parasite: Wanders into an organ it is not usually found in (e.g., Entamoeba histolytica in the liver or lung).

Different Kinds of Hosts

• Definitive Host: Harbors the adult stage or where the parasite reproduces sexually.
• Intermediate Host: Harbors larval stages or asexual reproduction.
• Paratenic Host: A temporary refuge and vehicle for the parasite to reach the definitive host.
• Reservoir Host: A host that keeps the parasite alive and available for transmission to another host.
• Natural Host: A naturally infected host for a specific parasite.
• Accidental Host: A host that is not usually infected, but can harbor a parasite.

Three Common Symbiotic Relationships

• Mutualism (+,+): Both partners benefit, completely dependent on each other. (e.g., protozoa and termite)
• Commensalism (+,0): One partner benefits, and the other is not harmed or benefitted. (e.g., normal floras in the human body)
• Parasitism (+,-): One partner benefits (parasite) and the other is harmed (host). (e.g., worms like lumbricoides, Ascaris )

Effect of Parasites on the Host

• Direct effects: Mechanical injury (pressure), blockage of vessels, production of toxic substances, and deprivation of nutrients.
• Indirect effects: Immunological reaction causing tissue damage (e.g., nephritis). Excessive proliferation of tissues due to invasion.

Basic Concepts in Medical Parasitology

• Morphology: Size, shape, colour, and position of organelles. Important in lab diagnosis to distinguish between pathogenic and commensal organisms (e.g., Entamoeba histolytica and Entamoeba coli).
• Geographical Distribution: Depends on host, presence of vector, environmental conditions, and transmission mechanisms (e.g., food habits).

Life Cycle of Parasites

• The route a parasite takes from entry to exit of the host, including time outside the host.
• Can be simple (one host) or complex (multiple hosts).
• This information helps understand the symptomatology and pathology of the parasite and provides information for diagnosis, treatment, epidemiology, prevention, and control.

Host-Parasite Relationship

• Carrier state: Perfect balance between parasite destruction and host repair.
• Disease state: Parasite dominates leading to a disease condition.
• Parasite destruction: Host prevails, eliminating the parasite.

Laboratory Diagnosis

• Blood: Examination for parasites in the blood (e.g., malaria, filariasis).
• Stool: Examination for intestinal or biliary tract parasites (e.g., amoebiasis, giardiasis).
• Urine: Examination for parasites localized to the urinary tract (e.g., schistosomiasis).
• Sputum: Examination for parasites in the respiratory tract (e.g., paragonimiasis).
• Biopsy: Examination of tissues (e.g., kala-azar, cysticercosis, trichinosis, Chagas disease, Onchocerciasis).
• Urethral/vaginal discharge: Examination for T. vaginalis.
• Indirect evidences: changes in blood, e.g., eosinophilia, indicating tissue invasion by helminthes, or reduced white blood cells.

Treatment

• Chemotherapy with specific drugs is used to treat parasitic infections, often targeting rapidly proliferating parasite cells to inhibit nucleic acid or protein synthesis or specific metabolic pathways (e.g., folate).

Prevention and Control

• Implementing measures to break parasite transmission cycles, reduce infection sources, control vector populations, and improve hygiene.

Classification of Medical Parasitology

• Parasites belong to kingdoms Protista and Animalia.
• Protista includes protozoa (microscopic single-celled eukaryotes)
• Helminthes are macroscopic, multicellular worms. (medical parasitology is divided into these groups: protozoology, helminthology, entomology)

Protozoa

• Single-celled, morphologically and functionally complete organisms.
• Composed of cytoplasm (outer hyaline ectoplasm, inner granular endoplasm), responsible for protection, movement, ingestion, excretion, respiration, and digestion.
• Nuclei function in reproduction and maintaining life.
• Resistant cyst stage to survive adverse conditions.

Reproduction of Protozoa

• Asexual: Simple binary fission, multiple fission (schizogony).
• Sexual: Conjugation, syngamy.

Prevalence of Protozoa

• Ubiquitous in moist environments (sea, soil, fresh water).
• Varying survival strategies in adverse environments.

Morphology of Protozoa

• Predominantly microscopic, 2 to >100µm.
• Nucleus with clumped or dispersed chromatin and nucleolus (karyosome) useful for species differentiation.

Pathogenesis of Protozoa

• Entry and establishment in the host.
• Attachment, replication, and colonization.
• Harmful effects (toxins).
• Immune evasion.

Antiprotozoal Agents

Targeting rapidly proliferating parasite cells, inhibiting nucleic acid/protein synthesis, or specific metabolic pathways (e.g., folate).

Important Pathogenic Protozoa

• Table detailing protozoan species, their location in the host, and common diseases.

Amoebiasis

• Primitive unicellular microorganisms.
• Two stages: active feeding (trophozoite), & dormant, infectious (cyst)
• Binary fission, formation of numerous trophozoites within a mature cyst.
• Pseudopodia for movement.

Entamoeba histolytica (Morphological Features)

• Trophozoites vary in size (10-60µm), moving rapidly, progressing, and unidirectional through pseudopods.

• Nucleus with evenly arranged chromatin, compact, centrally located karyosome.

• Cytoplasm is finely granular, with ingested bacteria and debris.

• In severe cases, RBCs might be visible—a diagnostic feature.

• Cysts range from 10-20µm.

• Immature cysts have inclusions (glycogen and chromatoidal bars).

• Maturing cysts lose inclusions.

Life Cycle of Entamoeba histolytica

• Ingestion of cysts.
• Excystation and penetration of the colon wall.
• Multiplication by binary fission.
• Diagnosis and stool samples (trophozoites or cysts).
• Pathogenesis, including ulcers, extraintestinal involvement (liver).

Other types of Non-pathogenic Protozoa

• Species like Entamoeba gingivalis, Entamoeba coli, Endolimax nana, Iodamoeba buetschlii, are common commensals of the intestinal tract. Details of these vary in morphological characteristics and prevalence.

Mastigophora (Pathogenic Flagellates)

• Protozoan group with whip-like appendages called flagella for motility.
• Includes luminal, hemoflagellates, and genital flagellates.

Giardia lamblia

• Pathogenic flagellate

• Pear-shaped trophozoite with suction disc attachment; a four nucleus double walled cyst

• Transmission through contaminated food and water, resistant cysts survive outside hosts/water purifying facilities.

• Pathogenesis involves invasion of bowel mucosa, with mucous secretions & dehydration as a symptom

• Diagnosis is with stool samples.

• Treatment typically with quinacrine hydrochloride or metronidazole.

Trichomonas vaginalis

• Pear-shaped trophozoite with undulating membrane and 4 flagella.
• Found in urethra, vagina, and prostate.
• Sexually transmitted predominantly.
• Inflammation and vaginal discharge symptomatic.
• Treatment with metronidazole for both partners.

Coccdia (Sporozoa)

• Apicomplexa class
• Spore-forming protozoa.
• Intracellular parasites; common in blood, tissues, and body fluids.
• Toxoplasma gondii, a member of this group, causes toxoplasmosis.

Malaria

• Caused by Plasmodium sp
• Two hosts: Vertebrate (humans- intermediate) and Invertebrate (mosquito- definitive).
• Life cycle stages: pre-erythrocytic schizogne, erythrocytic schizogne, and gametogony.
• Transmission via an Anopheles mosquito bite.

Medically Important Ciliates (Balantidiasis)

• The ciliate Balantidium coli is the only pathogenic member.
• Simple life cycle: Ingestion of infectious cysts → excystation → invasion of trophozoites → tissue invasion, and intestinal ulcers.
• Clinical findings are similar to amebiasis—abdominal pain, bloody stools, tenderness, anorexia & low level fever.
• Diagnosis is through microscopic fecal examinations.
• Treatment with tetracycline, metronidazole, or iodoquinol.

Medically Important Helminths

• Introduction: a general overview of parasitic helminths, noting their significance, their range of habitats, and the fact that they cause morbidity and mortality.
• Sources of parasitic helminthes: the ways they cause infection.
• The groupings and classification of Trematodes, Nematodes & Cestodes as different 'flat' worms.

• Trematodes (Flukes): Blood flukes (Schistosoma spp.), Intestinal flukes (Fasciola hepatica, Fasciolopsis buski), Liver flukes (Clonorchis sinensis) and Lung flukes (Paragonimus westermani). Each fluke species has specific characteristics, habitats, lifecycle, symptoms, and methods of diagnosis and treatment.

• Nematodes (Roundworms): These worms feature an unsegmented, elongated, cylindrical body. They are considered parasites of humans, plants, and animals. A description (morphology) should include specifics of the various nematodes like Ascaris lumbricoides, Hookworms, Strongyloides stercoralis Enterobius vermicularis, Trichuris trichuira, Dracunculus medinensis, Trichinella, and Larva Migrans. Each species has particular details in their life cycle, symptoms, morphology, diagnosis, and treatment methods.

• Cestodes (Tapeworms): The worms in this group are flat, ribbon-like structures without a digestive tract. The key differences for the various tapeworm species should be noted - differences in lifecycle, symptoms, morphology, diagnosis, and treatment; examples include Taenia saginata, Taenia solium, Diphyllobothrium latum.

Summary of specific helminthic diseases (e.g., Schistosomiasis, Ascariasis, Hookworm)

For each of the helminthic diseases mentioned above provide an outline of the disease, including: • Causative organism (scientific name)

• Site of infection in host (anatomy and organs affected)

• Life cycle (including stages): How the parasite spreads and infects the host (e.g., soil, intermediate vector, other mammals, transmission mechanisms).

• Morphology of parasite involved/infected host organs.

• Clinical features (symptoms)

• Diagnosis (how is the diagnosis determined)

• Treatment (common method or medications used)

• Epidemiology (prevalence and risk factors)

• Prevention (measures taken to prevent transmission/ infection).

Test your knowledge on schistosomiasis and sleeping sickness with this quiz. Covering key aspects such as species, habitats, symptoms, and immune responses, it's designed for students in parasitology or related fields. Challenge yourself and improve your understanding of these significant infections.