10-Protozoa and Helminthology

General Classification of Protozoa and Helminthology

• Overview: Microbiology - 10 covers Protozoa and Helminthology at the University of Pécs, Faculty of Health Sciences.

• Eukaryotic Classification of Protozoa:

  • a. Flagellates: Represented by species such as Giardia intestinalis.

  • b. Amebae: Represented by the genus Entamoeba.

  • c. Sporozoa: Represented by the genus Plasmodium.

  • d. Ciliates: Represented by Balantidium coli.

Eukaryotic Cell Structure

• Core Components: Protozoa are unicellular eukaryotic organisms featuring a complex internal structure.

• Major Organelles and Structures:

  • Nucleus and Nucleolus.

  • Nuclear membrane with pores.

  • Golgi apparatus.

  • Rough endoplasmic reticulum (with ribosomes) and Smooth endoplasmic reticulum.

  • Mitochondrion (energy production).

  • Lysosome.

  • Microtubules and Microfilaments (cytoskeleton).

  • Cell membrane and Glycocalyx/Microvilli.

• Specialized or Conditional Structures (not present in all cell types):

  • Chloroplast.

  • Cell wall.

  • Centrioles.

  • Flagellum.

Protozoan General Characteristics and Structure

• Unicellularity: Protozoans are single-celled eukaryotic organisms.

• Serious Human Diseases: They are responsible for significant global illnesses, including ameobiasis, Chaga’s disease, malaria, African sleeping sickness, leishmaniasis, and toxoplasmosis.

• Functional Anatomy:

  • Nucleus: Contains the genetic material.

  • Plasma: Differentiated into two layers.

  • Ectoplasm: Outer layer providing protection against external influences, facilitating the ability to move, and aiding in nutrition.

  • Endoplasm: Inner layer containing undigested food grains, stored proteins, and glycogen.

Reproduction and Life Cycles

• Reproductive Modes: Protozoa utilize both asexual and sexual pathways.

  • Asexual Reproduction: The parent cell divides to produce one or more offspring cells. This is the most common form of division.

  • Sexual Reproduction: Involves the merging of gametes.

• Cyclical Phases: Reproduction often involves alternating sexual and asexual phases.

• Host Definitions:

  • Final Host (Definitive Host): The organism in which the sexual reproduction of the parasite takes place.

  • Intermediate Host: The organism in which the asexual reproduction of the Protozoa takes place.

Epidemiology and Prevention of Parasitic Infections

• Geographical Distribution: Parasitic infections occur worldwide but are disproportionately common in tropical areas and regions where hygiene is poor.

• Social Impact: Often entire communities are infected. Treatment is frequently inaccessible or unaffordable.

• Preventative Measures:

  • Sanitation: Use of latrines and construction of landfills.

  • Water Supply: Access to fresh wells and running water.

  • Vector Control: Use of mosquito netting, insect spraying, insect control, and general sanitation.

  • Public Health: Regular screening of populations at specified intervals.

Statistics on Major Parasitic Infections

• Plasmodium (Malaria):

  • Infected count: $273 \times 10^{6}$.

  • Deaths per year: $1.12 \times 10^{6}$.

• Soil-transmitted Helminths (Roundworm/Ascaris, Whipworm/Trichuris, Hookworm/Ancylostoma and Necator):

  • Symptoms: Pneumonia, intestinal obstruction, bloody stools, cough, wheezing, abdominal pain.

  • Infected count: $2 \times 10^{9}$.

  • Deaths per year: $200,000$.

• Schistosoma (Kidney and bowel disease):

  • Infected count: $200 \times 10^{6}$.

  • Deaths per year: $15,000$.

• Trypanosoma cruzi (Chagas disease - cardiovascular focus):

  • Infected count: $13 \times 10^{6}$.

  • Deaths per year: $14,000$.

• African Trypanosomes (Sleeping sickness):

  • Infected count: $0.3 \times 10^{6}$ to $0.5 \times 10^{6}$.

  • Deaths per year: $48,000$.

• Leishmania (Diseases of skin, mucous membranes, internal organs):

  • Infected count: $12 \times 10^{6}$ ($2 \times 10^{6}$ new cases per year).

  • Deaths per year: $50,000$.

Protozoa Living in Blood and Tissues

• Flagellata:

  • Trypanosoma brucei gambiense and T. brucei rhodesiense: Cause African Sleeping Sickness.

  • Trypanosoma cruzi: Causes American Trypanosomiasis (Chagas disease).

  • Leishmania donovani: Causes visceral leishmaniasis.

  • Leishmania tropica: Causes cutaneous leishmaniasis.

  • Leishmania brasiliensis: Causes mucocutaneous leishmaniasis.

• Sporozoa:

  • Plasmodium spp. (P. falciparum, P. vivax, P. ovale, P. malariae): Cause malaria.

  • Toxoplasma gondii: Causes toxoplasmosis.

Trypanosomiasis: Sleeping Sickness and Chagas Disease

• West African Sleeping Sickness (T. brucei gambiense) and East African Sleeping Sickness (T. brucei rhodesiense):

  • Cases: Approximately $0.5 \times 10^{6}$ cases per year.

  • Vector: The tsetse fly (Glossina sp.).

  • Phase 1 Symptoms: Muscle pain and joint pain.

  • Phase 2 Symptoms: Swollen lymph nodes, lethargy, meningoencephalitis, and coma.

• Chagas Disease (T. cruzi):

  • Geographic Focus: Latin/South America.

  • Prevalence/Lethality: $12 - 19 \times 10^{6}$ cases; $10\%$ lethality.

  • Vector: The kissing bug.

  • Infection Mechanism: Bug feces are inoculated into a cutaneous portal (local lesion).

  • Symptoms: Fever, swelling of lymph nodes, spleen, and liver.

  • Organ Damage: Heart muscle (cardiomegaly) and large intestine damage; chronic inflammation in organs, specifically heart and brain.

  • Note: Adults are often asymptomatic carriers.

Malaria (Plasmodium species)

• Transmission:

  • Vector and Final Host: Female Anopheles mosquito.

  • Intermediate Host: Humans and monkeys.

• Clinical Symptoms and Pathology: Alternating fever, hemorrhage, tissue necrosis, and renal impairment.

• Malaria Forms and Fever Patterns:

  • P. falciparum: Malaria tropica. Incubation of $7 - 30$ days ($90\%$) or longer ($10\%$). Fever is irregular or even continuous.

  • P. malariae: Malaria quartana. Incubation of $16 - 50$ days. Fever attacks recur every $72$ hours.

  • P. ovale: Malaria tertiana. Incubation of $12 - 18$ days ($90\%$) or longer ($10\%$). Fever attacks recur every $48$ hours.

  • P. vivax: Malaria tertiana. Incubation of $12 - 18$ days ($90\%$) or longer ($10\%$). Fever attacks recur every $48$ hours.

• Human Life Cycle Stages:

  • Exo-erythrocytic Cycle: Sporozoites injected by mosquito blood meal; infect liver cells; form schizonts; rupture to release merozoites.

  • Erythrocytic Cycle: Merozoites infect red blood cells; form immature trophozoites (ring stage), then mature trophozoites, then schizonts; rupture releases more merozoites.

  • Gametogony: Formation of gametocytes (macrogametocytes and microgametocytes) ingested by mosquitoes.

• Diagnosis and Late Symptoms:

  • Methodology: Giemsa stain of blood samples.

  • Clinical markers: Fever, chills, head/joint/muscle pain (flu-like) moving to high fever ($41\,^{\circ}\text{C}$), vomiting, anemia, and liver failure.

Toxoplasmosis (Toxoplasma gondii)

• Parasite Nature: Extensive distribution; intracellular parasite.

• Hosts:

  • Final Host: Cats (harbor oocysts in the GI tract).

  • Vector: Rats (often part of the cycle).

  • Intermediate Host: Humans and other mammals.

• Transmission: Ingestion of raw meat containing tissue cysts (bradyzoites) or substances contaminated by cat feces (oocysts on fruits, vegetables, soil, or litter).

• Clinical Risk:

  • Most cases are unnoticed (asymptomatic).

  • Pregnancy: Risks include stillbirth or fetal abnormalities.

  • Immunocompromised (AIDS): Risks include brain lesions, heart damage, and lung damage.

Protozoa Living in Body Cavities

• Entamoeba histolytica (Amoebiasis):

  • Disease: Amoebic dysentery.

  • Geographic focus: South/West Africa, Southeast Asia, Mexico, Latin America.

  • Transmission: Water, vegetables, fruits contaminated with cysts.

  • Biological Process: Cyst enters the body, turns into a trophozoite in the intestine.

  • Pathology: Necrosis, ulcerative inflammation. Symptoms include mucous/purulent stools and lower abdominal cramps.

  • Mortality: $40,000$ to $100,000$ deaths per year.

• Trichomonas vaginalis (Trichomoniasis):

  • Nature: Most frequent sexually transmitted disease (STD).

  • Prevalence: $7.4 \times 10^{6}$ new cases per year.

  • Features: Does not form cysts. Obligate parasite of the urogenital tract. Multiplies by longitudinal binary fission.

  • Symptoms (Women): Greenish-yellow, frothy, strong-smelling vaginal discharge; itching; dysuria; painful contact.

  • Symptoms (Men): Often linked to prostate cancer risk.

  • Complications: Premature labor and cervical cancer.

• Giardia lamblia (Giardiasis):

  • Nature: Pathogenic flagellate.

  • Lifecycle: Cysts enter the duodenum, germinate, and travel to the jejunum to multiply.

  • Reservoirs: Beavers, cattle, coyotes, cats, and humans.

  • Transmission: Contaminated food and water.

  • Symptoms: Diarrhea, abdominal pain.

Leishmaniasis

• Causative Agent: More than $20$ species of Leishmania parasites.

• Vector: The sand fly.

• Distribution: Found on every continent except Australia and Antarctica. High prevalence in the Middle East, North Africa, Southern Europe, Central America, and South America.

• Clinical Forms:

  • Cutaneous Leishmaniasis: Most common form; causes skin sores.

  • Visceral Leishmaniasis (Kala-azar): Affects spleen, liver, and bone marrow. Symptoms include weight loss, anemia, leukopenia (low white count), and thrombocytopenia (low platelet count). Potentially lethal.

  • Mucosal Leishmaniasis: Parasites spread from the skin to mucous membranes of the nose, mouth, or throat.

Introduction to Helminths

• General Characteristics: Multicellular animals with specialized organs for reproduction, digestion, movement, and protection.

• Parasitic Mechanics: Possess mouthparts for attachment. Most are hermaphroditic (well-developed sex organs producing eggs and sperm).

• Adverse Effects on Host:

  • Mechanical damage.

  • Deprivation of nutrients.

  • Toxic effects from metabolites and toxins.

• Epidemiology:

  • $50$ human-parasitizing species.

  • Human role: Often the definitive host and sole biological reservoir.

• Classification:

  • Nematodes: e.g., Ascaris lumbricoides.

  • Trematoda: e.g., Fasciola hepatica.

  • Cestoda: e.g., Taenia.

Specific Nematodes (Roundworms)

• Enterobius vermicularis (Pinworm):

  • Epidemiology: Common in children's communities; hands contaminated with eggs ($500 \times 10^{6}$ cases/year).

  • Symptoms: Anal itching and restlessness.

  • Compilations: Appendicitis and bacterial dermatitis.

  • Lifecycle: Gravid females migrate to the perianal region at night to lay eggs.

• Ascaris lumbricoides (Roundworm):

  • Size: Largest intestinal nematode ($15 - 25\,\text{cm}$).

  • Lifecycle: Ingested eggs \rightarrow larvae hatch in small intestine \rightarrow enter bloodstream \rightarrow travel to lungs \rightarrow esophagus \rightarrow return to small intestine to mature.

  • Symptoms: Pneumonia (eosinophilia), malnutrition, and ileus (intestinal obstruction).

Cestoda (Tapeworms)

• General Features: Range from $0.5\,\text{cm}$ to $15\,\text{m}$ in length. Parasitize the gut. Extraintestinal larvae can cause serious disease (e.g., echinococcosis).

• Taenia saginata (Smooth-headed tapeworm):

  • Size: $3 - 10\,\text{m}$.

  • Final Host: Humans.

  • Intermediate Host: Cattle.

  • Transmission: Undercooked beef containing cysticercus larvae.

• Taenia solium (Hookhead tapeworm):

  • Size: $2 - 5\,\text{m}$.

  • Final Host: Humans.

  • Intermediate Host: Pigs.

  • Pathology: Can cause cysticercosis (larvae encysted in brain or muscle; retinitis in eyes).

Trematoda (Flukes: Schistosomiasis)

• Agent: Schistosoma species (Blood fluke).

• Prevalence: Hundreds of millions infected.

• Intermediate Host: Snail.

• Transmission: Larvae penetrate the skin during outdoor bathing or washing in contaminated water.

• Symptoms: Frequent urination, bloody diarrhea, lower abdominal pain, cirrhosis, and ascites.

• Legal Status: Notifiable disease.