Parasites

Protozoa and Intestinal Parasites Overview

• Types of Parasites to Cover:

  • Intestinal Parasites:

  • Protozoa and Helminths

  • Notable Parasites:

  • Entamoeba histolytica (Amoebas)

  • Giardia lamblia (Flagellates)

  • Trichomonas vaginalis (Flagellate)

  • Cryptosporidium parvum (Sporozoa)

  • Schistosoma (Fluke)

  • Taenia (Tapeworm)

  • Enterobius vermicularis (Pinworm)

  • Trichuris trichiura (Whipworm)

  • Ascaris lumbricoides (Roundworm)

  • Necator americanus (Hookworm)

  • Wuchereria bancrofti (Filariasis)

  • Loa loa (African eye worm)

  • Dracunculus medinensis (Guinea worm)

Intestinal Amebiasis: Entamoeba histolytica

• Characteristics:

  • Protozoan type (Amoebae)

  • Infective cysts are shed in feces and can excyst into trophozoites in the human body.

  • Humans are the only carriers.

• Epidemiology:

  • Symptoms correlate with tissue destruction in the large intestine.

  • Primarily found in tropical/subtropical regions with poor sanitation.

  • U.S. prevalence: 1% to 2%.

  • Main transmission through contaminated food or water; also linked to oral-anal sexual practices.

• Disease Pathogenesis:

  • Interaction can lead to pathogenic outcomes in the large intestine including flask-shaped ulcerations.

  • Invades deeper mucosa extending into the peritoneal cavity affecting neutrophils and colonic epithelial cells.

• Clinical Features:

  • Symptoms include:

  • Abdominal pain

  • Cramping

  • Colitis with diarrhea (bloody stools in severe cases)

  • Extraintestinal issues like fever and leukocytosis with possible liver abscesses (commonly in the right lobe).

• Diagnosis & Treatment:

  • Diagnosis through microscopy (trophozoites and cysts in feces).

  • Other tests include serology and PCR.

  • Treatment typically involves Metronidazole.

Giardia lamblia

• Characteristics:

  • Flagellate protozoan with cyst and trophozoite forms.

  • Trophozoites exhibit falling leaf motility and have a tear-drop shape (12-15 micrometers).

  • They have 2 nuclei and a ventral adhesion disk with 4 flagella.

• Epidemiology & Transmission:

  • Widely distributed; found in streams and lakes.

  • Fecal-oral transmission, common in children and daycare settings.

  • Resistant to everyday chlorine water treatment.

• Life Cycle:

  • Ingestion of cysts, release of trophozoites in the duodenum.

  • Trophozoites replicate via binary fission and can affect the intestinal lining.

• Clinical Features:

  • Symptoms include:

  • Fatty, foul-smelling diarrhea (steatorrhea)

  • Abdominal cramps

  • No prominent tissue necrosis but with malabsorption issues.

• Diagnosis & Treatment:

  • Testing involves stool specimens over multiple days and may include antigen detection assays.

  • Treatment options: Tinidazole or Metronidazole.

Trichomonas vaginalis

• Characteristics:

  • A flagellate protozoan with motility derived from an undulating membrane; found primarily in the genital tract.

  • Detected primarily as a trophozoite.

• Pathogenesis & Clinical Features:

  • Causes irritation and inflammation leading to ulcerations, increasing STI transmission risk.

  • Symptoms include:

  • Vulvar itching/burning

  • Frothy discharge with rancid odor.

• Diagnosis & Treatment:

  • Diagnosis via nucleic acid amplification tests or microscopy of discharges.

  • Treatment includes Metronidazole.

Cryptosporidium parvum

• Characteristics:

  • Sporozoa type with complex life cycle involving both asexual and sexual reproduction.

  • Transmitted through fecal-oral routes, especially in immunocompromised hosts.

• Epidemiology & Clinical Features:

  • Causes watery diarrhea and associated gastrointestinal symptoms.

  • Self-limiting gastroenteritis in healthy individuals but severe in immunocompromised patients.

• Life Cycle:

  • Ingestion of sporulated oocysts, excystation, and succession of asexual and sexual reproduction leading to oocyst formation.

• Diagnosis & Treatment:

  • Diagnosis via visualizing oocysts; treatment typically with Nitazoxanide.

Helminths Overview

• Trematodes (Flukes):

  • Schistosoma species: notable for cylindrical shape and separate male/female forms.

  • Transmission via skin penetration in freshwater environments.

• Cestodes (Tapeworms):

  • Taenia species: infection via undercooked meat in endemic regions; life cycle involves proglottids and egg development.

• Nematodes (Roundworms):

  • Enterobius vermicularis (Pinworm): commonly asymptomatic but can cause intense itching.

  • Ascaris lumbricoides: large roundworm with a life cycle involving larval migration from gut to lungs.

  • Necator americanus: hookworm that causes anemia and may lead to severe gastrointestinal issues.

Diagnosis & Treatment of Helminths

• Common Diagnostic Techniques:

  • Microscopy for eggs in stool samples.

• Treatment Options:

  • Varies by species but often includes Benzimidazoles (Albendazole, Mebendazole) or Praziquantel for flukes and tapeworms.

Blood and Tissue Protozoa

• Notable Types:

  • Plasmodium (causing malaria), Babesia (tick-borne illness), Toxoplasma gondii (zoonotic infection), Trypanosoma (Chagas disease).

• Plasmodium:

  • Infection cycles through humans and mosquitoes, with significant morbidity & mortality especially in Africa.

  • Parasite replication in the liver and erythrocytic stages causes associated symptoms such as chills and fever.

• Diagnosis involves blood films and molecular diagnostics.

• Treatment for Plasmodium infections includes various antimalarial drugs like Chloroquine, and treatment for specific species such as Primaquine for P. vivax.