Parasitology Notes

Parasitology: Introduction to Protozoa

Significance of Parasitology

  • Parasitism: One organism benefits, the other is harmed.
  • High prevalence of parasitic infections globally (e.g., toxoplasmosis).
  • Significant mortality (e.g., malaria).
  • Impact on quality of life.
  • Vector-borne transmission (mosquitoes, ticks).
  • Geographical distribution correlates with vector occurrence.
  • Climate change affects vector distribution.
  • Complex life cycles with multiple stages and intermediate hosts.

Classification of Parasites

  • Protozoa: Single-celled parasites.
  • Worms: Multicellular parasites; both found in body cavities or tissues.
  • Ectoparasites: Fleas, mites, lice; primarily unpleasant but can spread diseases.

Medically Relevant Protozoa

  • GI Tract: Entamoeba histolytica, Giardia duodenalis, Cryptosporidium spp.
  • Vagina: Trichomonas vaginalis.
  • Tissues: Free-living amoebae (Acanthamoeba, Naegleria), Plasmodia, Babesia, Toxoplasma gondii, Leishmania, Trypanosoma.

Protozoan Forms

  • Trophozoite: Actively living, multiplying form; low environmental resistance.
  • Cyst: Survival form in the environment.

Entamoeba histolytica

  • Causes intestinal amebiasis.
  • Symptoms range from asymptomatic to amebic colitis, dysentery, chronic infections (peritonitis, perforations, granulomas).
  • Extraintestinal amebiasis: liver abscess (most common), pleuropulmonary abscess, brain abscess, skin lesions.

Diagnosis of Entamoeba histolytica

  • Microscopy: Stool or tissue samples; can be challenging due to similar species.
  • Antigen detection: Immunochromatography, EIA.
  • Antibody detection: For extraintestinal manifestations, EIA.
  • Molecular methods: PCR.

Giardia duodenalis

  • Epidemiology: Worldwide, more prevalent in warm climates and in children.
  • Clinical picture: Ranges from asymptomatic to severe diarrhea, malabsorption. Acute cases: diarrhea, abdominal pain, bloating, nausea, vomiting (1-3 weeks). Chronic cases: recurrent symptoms, malabsorption, debilitation.
  • Transmission: Many animal reservoirs; contaminated water.

Diagnosis of Giardia duodenalis

  • Microscopy: Stool (trophozoites in liquid, cysts in formed stool), duodenal fluid. Requires repeated tests.
  • Antigen detection: Immunochromatography; more sensitive than microscopy.

Cryptosporidia

  • Symptoms: Self-limiting diarrhea in immunocompetent patients (2-3 weeks); severe complications in immunocompromised patients (malabsorption, wasting).
  • Extraintestinal cryptosporidiosis: Pulmonary or biliary tract involvement.

Diagnosis of Cryptosporidia

  • Microscopy: Acid-fast staining.
  • Direct fluorescent antibody, EIA: Most sensitive and specific.
  • Rapid immunochromatographic assays are available.

Trichomonas vaginalis

  • Causes trichomoniasis, a common non-viral STI.
  • Women: vaginitis, vulvar/cervical lesions, dysuria.
  • Men: urethritis, prostatitis.
  • Often asymptomatic.
  • Humans are the only host; no cyst form.
  • Co-factor in HIV transmission.
Increased risk for:
  • preterm birth
  • premature rupture of membranes
  • cervical cancer
Treatment
  • Treatment of sexual partner(s) is important

Diagnosis of Trichomonas vaginalis

  • Microscopy: Vaginal discharge (women), urethral/prostatic secretions (men).
  • Culture: Sensitive, but takes time.
  • PCR

Free-Living Amoebae: Acanthamoeba, Naegleria

  • Acanthamoeba:
    • Acanthamoeba Keratitis: corneal infection, contact lens wearers. Can cause permanent visual impairment
    • Granulomatous Amebic Encephalitis (GAE): brain and spinal cord infection, immunocompromised individuals.
    • Disseminated Infection: skin, sinuses, lungs, immunocompromised.
  • Naegleria fowleri:
    • Primary Amebic Meningoencephalitis (PAM): rapid CNS degeneration, high fatality rate. Symptoms similar to bacterial meningitis, rapid onset after nasal exposure to contaminated fresh water.

Leishmaniasis

  • Vector-borne disease transmitted by sandflies.
  • Clinical Manifestations:
    • Cutaneous
    • Visceral
    • Mucosal (mucocutaneous)

African Trypanosomiasis: Sleeping Sickness

  • Vector: Tsetse fly
  • Trypanosoma brucei gambiense & Trypanosoma brucei rhodesiense
  • Symptoms: chancre, fever, headache, confusion, personality changes.

South American Trypanosomiasis: Chagas Disease

  • Vector: Triatomine bug (kissing bug)
  • Trypanosoma cruzi
  • Transmission: bug feces, blood transfusion, organ transplantation, congenital, oral.
  • Forms: Acute, Chronic, Asymptomatic

Malaria

  • Caused by Plasmodia; vector-borne (Anopheles mosquito).
  • High mortality among parasitic diseases.
  • Symptoms: fever, chills, headache, myalgias. Severe forms involve CNS, renal failure, anemia.
Transmission
  • Anopheles mosquitos

Diagnosis

  • Thin/Thick Smear (Giemsa staining)
  • Rapid diagnostic tests (immunochromatography).
  • Molecular Diagnosis (PCR)
Treatment
  • Artemisinin-based combination therapy (ACT).
  • Primaquine: P. vivax and P. ovale

Toxoplasmosis

  • Toxoplasma gondii: Infects warm-blooded animals, including humans.
  • Transmission: Food/water contaminated with cat feces, undercooked meat, congenital.
  • Symptoms: Asymptomatic or mild lymphadenopathy in immunocompetent individuals. Severe CNS disease in immunocompromised.
  • Congenital Toxoplasmosis: Acute infection during pregnancy can lead to severe outcomes.

Worms

  • Multicellular parasites (Helminths).
Types:
  • Trematodes (Flukes)
  • Cestodes (Tapeworms)
  • Nematodes (Roundworms)

Schistosomiasis

  • Parasitic disease.
  • Transmission: cercariae penetrate skin
  • Symptoms: Cercaria dermatitis, acute and chronic schistosomiasis, haematuria, blood in sperm, scarring, bladder cancer
Schistosoma Species
  • Schistosoma haematobium
  • Schistosoma mansoni
  • Schistosoma japonicum
  • Schistosoma mekongi
  • Schistosoma intercalatum

Echinococcosis

Echinococcosis granulosus
  • Cystic echinococcosis (CE), mostly in the liver
Echinococcus multilocularis
  • Alveolar echinococcosis (AE), slow growing cyst in the liver

Taeniasis

Three main species
  • Taenia saginata
  • Taenia solium
  • Taenia asiatica
  • Intermediate host: cattle, pigs
  • Asymptomatic or mild symptoms

Nematodes (roundworms)

Enterobius vermicularis
  • Pinworm.
  • Perianal pruritus (itching).
Strongyloides stercoralis
  • Penetrate skin.
  • Complicated parasitic life cycle: free living cycle and parasitic cycle; autoinfection
Hookworms
  • Ancylostoma duodenale, Necator americanus
  • cutaneous larva migrans