Parasitology Notes

Introduction to Parasitology

• Parasitology: Study of parasites.
• Parasites: Microorganisms deriving food from/at host's expense.
• Symbiosis: Unlike organisms coexisting.
  • Mutualism: Both benefit (e.g., intestinal flora producing vitamin K).
  • Commensalism: One benefits, the other is unharmed (e.g., normal flora on the human body).
  • Parasitism: One benefits at the other's detriment (parasite deprives host).
• Parasite Classification:
  • Protozoa: Single-celled.
    • Sporozoa: No movement.
    • Sarcodina: Pseudopodia (amoebas).
    • Mastigophora: Flagella (flagellates).
    • Ciliata: Cilia (ciliates).
  • Metazoan (Helminths): Multicellular.
    • Platyhelminthes (flatworms): Cestoda (tapeworms), Trematoda (flukes).
    • Nemathelminthes (roundworms).
• Vector: Organism transmitting disease.
• Parasite Habitat:
  • Ectoparasites: Live outside host (infestation).
  • Endoparasites: Live inside host (infection).
• Parasite Independence:
  • Obligate: Requires a host (e.g., Plasmodium).
  • Facultative: Can live independently.
• Parasite Mode of Living:
  • Permanent: Lives in host from early life (e.g., head lice).
  • Intermittent: Visits host to feed (e.g., mosquito).
  • Incidental: Unusual host (e.g., dog tapeworm in humans).
  • Transitory: Larva in host, free-living adult (e.g., Echinococcus granulosus).
  • Erratic: Unusual organ (e.g., Ascaris lumbricoides).
  • Aberrant: No further development (e.g., dog roundworm in human).
• Host: Organism harboring the parasite.
  • Definitive: Adult/sexual stage.
  • Intermediate: Larval/asexual stage.
  • Paratenic: Transport host (no parasite development).
  • Reservoir: Vertebrate host, source of infection.
  • Accidental: Not usual host (zoonosis in humans).
  • Aberrant: Parasite cannot complete development.
• Sources of Infection: Contaminated soil/water, food, vectors, animals, other persons, auto-infection.
• Mode of Transmission:
  • Oral: Contaminated water/food.
  • Skin: Hookworms, Strongyloides.
  • Direct: Sexual intercourse (e.g., Trichomonas vaginalis).
  • Transmammary: Milk (e.g., Strongyloides).
  • Transplacental: Congenital (e.g., Toxoplasma gondii).
  • Inhalation: Airborne (e.g., Enterobius vermicularis eggs).
  • Vector: Arthropod bites (e.g., mosquitoes for malaria).
  • Iatrogenic: Blood transfusion.
• Portal of Exit:
  • Anus: Roundworm eggs.
  • Urine: Trichomonas vaginalis, Strongyloides stercoralis, Schistosoma haematobium.
  • Sputum: Lung fluke, Ascaris lumbricoides larvae.
  • Vaginal Discharge: T. vaginalis.
• Pathogenesis: Disease development.
  • Inapparent Infection: No symptoms.
  • Mechanisms: Lytic necrosis (Entamoeba histolytica), traumatic damage, host tissue reaction, neoplastic growth, toxic/allergy phenomena.

Protozoa Characteristics

• Single-celled eukaryotes.
• May be facultative parasites.
• Chemo-heterotrophs.
• Motile (flagella, cilia, pseudopods), except sporozoa.
• Specialized organelles.
• Cytoplasm: Ectoplasm (outer), Endoplasm (inner).
• Size: 3-300 micrometers.
• Reproduction:
  • Binary fission (asexual).
  • Syngamy (sexual, union of cells).
• Transmission:
  • Intestinal: Person-to-person, contaminated food/water.
  • Blood/Tissue: Direct contact, vectors.
• Life Cycle:
  • Cyst: Infective, dormant, non-motile.
  • Trophozoite: Pathogenic, motile, feeding.

Subphylum Sarcodina

• Motility via pseudopodia.
• Many are harmless.
• Naegleria Fowleri:
  • Free-living amoeba found in soil and freshwater.
  • Causes meningoencephalitis.
  • Acquired intranasally from contaminated water.
  • Treatment: Amphotericin B.
• Acanthamoeba Castellani:
  • Survives in cold water.
  • Causes keratitis (contact lens users) and granulomatous amoebic encephalitis.
  • Treatment: Pentamidine, Ketoconazole, or Flucytosine.
• Entamoeba Histolytica:
  • Causes amebiasis.
  • Transmission: Ingestion of cysts in contaminated food and water.
  • Symptoms: Dysentery, abdominal discomfort, liver abscess.
  • Treatment: Metronidazole (symptomatic), Iodoquinol (asymptomatic).

Subphylum Mastigophora

• Motility via flagella.
• Leishmania spp.:
  • Hemoflagellates.
  • Transmitted by sandflies.
  • Leishmania Donovani: Causes Kala-azar (visceral leishmaniasis).
    • Symptoms: Fever, weight loss, splenomegaly.
  • Leishmania Tropica & Leishmania Braziliensis: Cause cutaneous and mucocutaneous leishmaniasis.
    • Symptoms: Skin lesions, destruction of nasal cartilage.
• Giardia Lambia:
  • Causes giardiasis (traveler’s diarrhea).
  • Transmission: Ingestion of cysts in contaminated water/food.
  • Symptoms: Non-bloody diarrhea, nausea, flatulence.
  • Treatment: Metronidazole, Tinidazole.
• Trichomonas Vaginalis:
  • Causes trichomoniasis vaginitis.
  • Transmission: Sexual contact.
  • Symptoms: Foul-smelling discharge, itching, strawberry cervix (women), urethritis (men).
  • Treatment: Metronidazole (both partners).
• Trypanosoma Brucei Gambiense & Trypanosoma Brucei Rhodesiense:
  • Cause African trypanosomiasis (sleeping sickness).
  • Vector: Tsetse fly (Glossina).
  • Symptoms: Skin ulcer, fever, lymphadenopathy, encephalitis.
  • Treatment: Suramin, Pentamidine.
• Trypanosoma Cruzi:
  • Causes Chaga’s disease (American trypanosomiasis).
  • Vector: Reduviid bug (Triatoma).
  • Symptoms: Facial edema, lymphadenopathy, megacolon, myocarditis, cardiac arrhythmia.
  • Treatment: Nifurtimox, Benznidazole.

Phylum Ciliophora

• Motility via cilia.
• Balantidium Coli:
  • Causes balantidiasis/dysentery.
  • Transmission: Ingestion of cysts in contaminated food/water.
  • Symptoms: Liquid stools with pus, blood, mucus.
  • Treatment: Tetracycline.

Subphylum Apicomplexa

• Non-motile.
• Plasmodium:
  • Causes malaria (P. vivax, P. malariae, P. ovale, P. falciparum).
  • Vector: Female Anopheles mosquito.
  • Symptoms: Splenomegaly, anemia; cold, hot, and sweating stages.
• Toxoplasma Gondii:
  • Causes toxoplasmosis.
  • Transmission: Undercooked meat, contaminated cat feces, transplacental.
  • Symptoms: Asymptomatic, mononucleosis-like, congenital infections (stillbirth, encephalitis).
  • Treatment: Pyrimethamine and sulfadiazine.

Cestodes (Tapeworms)

• Flatworms with scolex (head), body (proglottids), and neck.
• Hermaphroditic.
• Taenia Saginata (Beef Tapeworm):
  • Transmission: Ingestion of raw/undercooked beef (cysticercus).
  • Symptoms: Mild abdominal cramps, malaise.
  • Treatment: Praziquantel.
• Taenia Solium (Pork Tapeworm):
  • Transmission: Ingestion of raw/undercooked pork (cysticercus cellulosae).
  • Can cause taeniasis (larvae) or cysticercosis (eggs).
  • Symptoms: Muscle pain, neurocysticercosis (seizures, headache).
  • Treatment: Praziquantel (intestinal), Albendazole (cysticercosis).
• Diphyllobothrium Latum (Fish Tapeworm):
  • Transmission: Ingestion of raw/undercooked fish.
  • Symptoms: Abdominal discomfort, diarrhea, vitamin B12 deficiency.
  • Treatment: Praziquantel, vitamin B12.
• Hymenolepis Nana (Dwarf Tapeworm):
  • Transmission: Ingestion of eggs, accidental ingestion of beetles.
  • Symptoms: Abdominal pain, asymptomatic, autoinfection.
  • Treatment: Praziquantel.
• Ecchinococcus Granulosus (Dog Tapeworm):
  • Zoonotic; causes hydatid cyst disease.
  • Transmission: Ingestion of food/water contaminated by dog feces.
  • Symptoms: Liver dysfunction, pulmonary cyst, cerebral cyst.
  • Treatment: Albendazole, surgical removal of cyst.

Trematodes (Flukes)

• Fleshy, leaf-shaped worms.
• Most are hermaphroditic except Schistosoma spp.
• Schistosoma Spp (Blood Fluke):
  • Dioecious, intravascular parasites.
  • Transmission: Skin penetration by cercariae.
  • Schistosoma Mansoni: Damages distal colon.
  • Schistosoma Japonicum: Damages small and large intestines.
    • Causes Katayama’s Disease
  • Schistosoma Haematobium: Damages bladder wall.
    • Causes Vesical bilharziasis
  • Treatment: Praziquantel.
• Clonorchis Sinensis (Asian Liver Fluke or Chinese Liver Fluke):
  • Transmission: Ingestion of undercooked/raw freshwater fish (metacercariae).
  • Symptoms: Abdominal pain, hepatomegaly, cholangiocarcinoma.
• Fasciola Hepatica (Sheep Liver Fluke):
  • Transmission: Ingestion of metacercariae encysted on aquatic plants.
  • Symptoms: Liver tenderness, hepatomegaly.
• Paragonimus Westermani (Oriental Lung Fluke):
  • Transmission: Ingestion of undercooked/raw crab meat (metacercariae).
  • Symptoms: Chronic cough producing bloody sputum.
• Fasciolopsis Buski (Large Intestinal Fluke):
  • Transmission: Ingestion.
  • Symptoms: Abscess formation, ulceration, hemorrhage, edema.

Nematodes (Roundworms)

• Unsegmented, cylindrical worms.
• Separate sexes.
• Ascaris Lumbricoides:
  • Transmission: Ingestion of eggs.
  • Habitat: Small intestine.
  • Symptoms: Intermittent colicky pain, loss of appetite, abdominal distension.
• Enterobius Vermicularis:
  • Transmission: Ingestion and auto-infection.
  • Symptoms: Pruritus in perianal area.
• Trichuris Trichiura:
  • Transmission: Ingestion.
  • Habitat: Large intestine.
  • Symptoms: Asymptomatic; heavy infection leads to rectal prolapse.
• Hookworm (Ancylostoma Duodenale and Necator Americanus):
  • Transmission: Skin penetration.
  • Symptoms: Pneumonia-like symptoms, microcytic, hypochromic anemia.
• Strongyloides Stercoralis:
  • Transmission: Skin penetration and auto-infection.
  • Habitat: Small intestine.
  • Symptoms: Pneumonitis; dissemination in immunocompromised.
• Capillaria Philippinensis:
  • Transmission: Ingestion of undercooked/raw freshwater fish.
  • Habitat: Small intestine.
  • Symptoms: Chronic diarrhea, weight loss, low-electrolyte level.
• Trichinella Spiralis:
  • Transmission: Ingestion of infected animal meat (undercooked).
  • Symptoms: Larvae migration and muscle invasion causing myalgia.
• Wuchereria Bancrofti and Brugia Malayi:
  • Transmission: Mosquito bite.
  • Symptoms: Lymphatic obstruction, edema (elephantiasis).

Rickettsial Infections

• Transmitted by arthropods (ticks, mites, lice, fleas) or inhalation (Q fever).
• Small, gram-negative, obligate intracellular parasites.
• Vectors:
  • Rocky Mountain Spotted Fever: R. rickettsii, tick-borne.
  • Ehrlichiosis: E. chaffeensis, ticks.
  • Rickettsialpox: R. akari, mite-borne.
  • Scrub Typhus: R. tsutsugamushi, mites.
  • Epidemic Typhus: R. prowazekii, louse-borne.
  • Murine Typhus: R. typhi, flea-borne.
  • Q Fever: C. burnetii, none.
• Spotted Fever Group:
  • Rickettsiapox: Eschar; fever, headache, chills, myalgia; treatment: Doxycycline
• Epidemic Typhus (Louse-Borne Typhus): Rickettsia Prowazekii
  • transferred via lice; rashes occur; treatment: hygiene.
• Murine Thyphus: Rickettia typhi & Rickettsia felis
  • transferred via fleas; mild signs and symptons
• Scrub Typhus: Orientia tsutsugamushi(Rickettsia tsutsugamushi)
  • transferred via mites; like epidemic typhus except for eschar.
• Q Fever (Query Group): Coxiella burnetti
  • transferred via Inhalation of dust w/ organism or aerosols; like influenzia and non-baterial pneuomonia.
• Relasping Fever: Borrelia recurrentis
  • transferred via lice and ticks, causes fever, headache, loss of apetite. DOC: Tetracycline
• Lyme Disease(Lyme Borreliosis): Borrelia burgdorferi ,flexible spirochete w/ coarse irregular coils
  • transferred via arthropod-borne ticks, stage 1: painless red rash which creates circular marks, Second Stage:Few weeks or months, third Stage: arthritis with large joints(knees).

Other Systemic Infections

• Dengue Fever:
  • Vector: Aedes aegypti, Aedes albopictus.
  • Symptoms: High-grade fever, muscle and bone pains (break-bone fever), rash.
  • Dengue Hemorrhagic Fever/Dengue Shock Syndrome: Increased risk of bleeding and shock.
• Chikungunya:
  • Vector: Aedes aegypti.
  • Symptoms: Severe muscle and joint pains.
• Zika:
  • Vector: Aedes aegypti, Aedes albopictus.
  • Linked to microcephaly in newborns.
• Leptospirosis:
  • Transmission: Contact with contaminated water.
  • Symptoms: Biphasic; flue-like, meningitis, renal and liver damage (Weil’s Disease).
  • Treatment: Penicillin; prophylaxis: Doxycycline.