Protozoans and Helminths Diseases of Man Notes

MODULE IV-B: PROTOZOANS AND HELMINTHS DISEASES OF MAN

COMPONENTS IN THE LIFE CYCLE

• Source of Infection:
  • Parasite comes in contact with soil, water, or other intermediate hosts.
• Mode of Transmission:
  • Parasites come in contact with humans.
• Infective Stage:
  • Parasite enters and establishes residence in or on humans.
• Pathogenic Stage:
  • Parasite multiplies and competes with humans for nutritional needs.
• Diagnostic Stage:
  • Parasite emerges from humans.

CLASSIFICATION OF PARASITES

• Two Major Groups:
  1. Single-celled protozoa (Sub-kingdom Protozoa)
  • Reproduce through binary fission.
  • Types:
    • Amoeba and Flagellates (Phylum Sarcomastigophora):
      • Amoeba moves via pseudopodia.
      • Flagellates have one or more whip-like flagella for movement.
    • Sporozoa (Phylum Apicomplexa):
      • Undergo both sexual and asexual reproduction.
      • Lack any organ for motility.
    • Ciliates (Phylum Ciliophora):
      • Possess rows or patches of cilia as organs of locomotion.
  1. Multi-cellular metazoan (Sub-kingdom Metazoan) (Helminths or Worms):
  • Two Phyla:
    • Nemathelminthes (Roundworms)
    • Platyhelminthes (Flatworms)
  • Two Classes:
    • Trematoda (Flukes)
    • Cestoda (Tapeworms)

PROTOZOA

Definition of Terms

• Infective Stage:
  • Stage of the parasite entering the host or the stage present in the source of infection.
• Pathogenic Stage:
  • Stage responsible for organ damage in the host leading to clinical manifestations.
• Encystation:
  • Process where trophozoites convert to cyst forms.
• Excystation:
  • Process where cysts convert to trophozoite forms.

INTESTINAL AND UROGENITAL PROTOZOA

Entamoeba histolytica

• Important Properties:
  • Intestinal and tissue amoeba.
  • Only known pathogenic intestinal amoeba.
• Life Cycle:
  • Ingestion of cyst from contaminated food/water.
  • Excystation occurs in the ileum, then colonization in the cecum and colon leading to encystation and fecal excretion.
• Epidemiology and Pathogenesis:
  • Common in tropical countries with poor sanitation.
  • Transmission via cyst ingestion.
  • Can invade portal circulation, leading to liver abscess.

DISEASE: AMOEBIASIS

• Signs and Symptoms:
  1. Acute Intestinal Amoebiasis:
  • Dysentery, lower abdominal discomfort, flatulence, tenesmus.
  1. Chronic Infection:
  • Occasional diarrhea, weight loss, fatigue.
    • Extrantestinal Amoebiasis:
  • Amoebic liver abscess presenting with upper quadrant pain, weight loss, fever, and a tender, enlarged liver.
• Laboratory Diagnosis:
  • Stool examination.
• Treatment:
  • Metronidazole; surgical drainage if necessary.
• Prevention and Control:
  • Good hygiene practices, proper handwashing, waste disposal, and thorough washing/cooking vegetables.

Giardia lamblia (Giardia intestinalis)

• Important Properties:
  • Exists as a cyst and trophozoite form.
  • Trophozoite shape: pear-shaped or teardrop-shaped with four pairs of flagella and a sucking disc.
  • Cyst: oval, thick-walled with four nuclei.
• Life Cycle:
  • Ingestion of cyst from fecally contaminated water/food, excystation in the stomach, trophozoites attach to the duodenal mucosa causing inflammation.

DISEASE: GIARDIASIS

• Signs and Symptoms:
  • Bloody, foul-smelling diarrhea, nausea, loss of appetite, flatulence, abdominal cramps, steatorrhea, typically afebrile.
• Laboratory Diagnostics:
  • Stool exam, string test.
• Treatment:
  • Metronidazole.
• Prevention and Control:
  • Proper handwashing, boiling/filtering drinking water, proper waste disposal.

Trichomonas vaginalis

• Important Properties:
  • Pear-shaped organism with central nucleus, four anterior flagella, and undulating membrane.
  • Exists only in trophozoite form.
• Life Cycle:
  • Transmitted by sexual intercourse, invades vaginal mucosa.
• Epidemiology and Pathogenesis:
  • Mainly transmitted through sexual contact; significant in women and prostate.

DISEASE: TRICHOMONIASIS

• Signs and Symptoms:
  • Infection in Males: Prostatitis, urethritis.
  • Infection in Females: Scant, watery vaginal discharge, foul-smelling greenish yellow liquid, pruritus, burning sensation, "strawberry cervix."
• Laboratory Diagnosis:
  • Wet mount of vaginal/prostatic secretions, urine, urethral discharges.
• Treatment:
  • Metronidazole.
• Prevention and Control:
  • Use condoms, practice safe sex, maintain acidic pH of the vagina.

BALANTIDIUM COLI

• Important Properties:
  • Largest intestinal protozoan infective to humans.
  • Exhibits rotary boring motility due to cilia.
• Mode of Transmission:
  • Fecal-oral route.
• Life Cycle:
  • Cysts ingested from contaminated water (pig feces), undergo excystation in small intestines, increase in number in large intestines, leading to ulceration.

DISEASE: BALANTIDIASIS

• Signs and Symptoms:
  • Acute infections lead to liquid stools with pus, blood, mucus; chronic infections show alternating diarrhea and constipation, tender colon, anemia, cachexia.
• Laboratory Diagnosis:
  • Stool examination.
• Treatment:
  • Oxytetracycline, Metronidazole.
• Prevention and Control:
  • Maintain sanitary hygiene, proper disposal of pig feces, and boiling drinking water.

BLOOD AND TISSUE PROTOZOA

ACANTHAMOEBA

• Important Properties:
  • Free-living amoeba causing brain inflammation.
  • Infects primarily immunocompromised patients, found in contaminated freshwater, and survives in cold water.

DISEASES:

1. Granulomatous Amoebic Encephalitis (GAE):
   • Infection mainly in immunocompromised individuals.
   • Symptoms include headache, seizures, stiff neck, nausea, vomiting.
   • Laboratory Diagnosis: Histologic examination of corneal scrapings.
2. Keratitis:
   • Severe eye pain, potential loss of vision.

• Treatment:
  • Propamidine.
• Prevention and Control:
  • Adequate boiling of drinking water, regular disinfection of contact lenses.

NAEGLERIA

• Important Properties:
  • Free-living protozoan, can survive in thermal springs.
• Life Cycle:
  • Parasite penetrates nasal mucosa, causing meningoencephalitis.

DISEASE: PRIMARY AMOEBIC MENINGOENCEPHALITIS

• Signs and Symptoms:
  • Sore throat, nausea, vomiting, fever, headache, meningeal irritation.
• Laboratory Diagnosis:
  • Demonstration of trophozoite in CSF.
• Treatment:
  • Amphotericin B with Miconazole and Rifampicin.
• Prevention and Control:
  • Adequate chlorination of swimming pools and hot tubs.

TOXOPLASMA GONDII

• Important Properties:
  • Definitive hosts: domestic cats, other felines; intermediate hosts: humans and mammals.
• Life Cycle:
  • Ingested by humans, oocyst releases sporozoites in intestines, which invade tissue.

DISEASE: TOXOPLASMOSIS

• Signs and Symptoms:
  • Acute infections may lead to chills, fever, headache, lymphadenitis; chronic can lead to encephalitis, chorioretinitis, and blindness.
• Laboratory Diagnosis:
  • Immunofluorescence assay, microscopic examination of cyst in tissues.
• Treatment:
  • Pyrimethamine plus Sulfadiazine for immunocompromised; Clindamycin for pregnant women.
• Prevention and Control:
  • Adequate cooking of meat, pregnant women avoid cats and raw meat.

PLASMODIUM SPP. (e.g., Plasmodium falciparum)

• Mode of Transmission:
  • Bite from female Anopheles mosquito, blood transfusion.
• Two Stages:
  1. Asexual Stage (Schizogony): In human host (intermediate).
  2. Sexual Stage (Sporogony): In mosquito (definitive).

DISEASE: MALARIA

• Signs and Symptoms:
  • Three stages of paroxysms:
  1. Cold Stage: chills, headache, myalgia.
  2. Hot Stage: spiking fever, shaking chills, nausea.
  3. Sweating Stage: drenching sweats, splenomegaly, anemia.
• Laboratory Diagnosis:
  • Thin and thick blood smears for Plasmodium spp. identification.
• Treatment:
  • Chloroquine or parenteral quinine.
• Prevention and Control:
  • Prophylaxis for travelers with Doxycycline, mosquito nets, insect repellant, insecticide sprays.