Parasitology: Clinical Pathology

• Parasitology, focusing on Clinical Pathology.

What is a Parasite?

• A parasite is an organism that lives in or on another organism (host).
• It derives nutrients at the host's expense.
• Parasites do not necessarily cause disease.
• Hosts may be harmed and suffer consequences with parasitic disease.

Curriculum Objectives

• Understand life cycles with examples.
• Describe the clinical syndrome, diagnosis, and treatment of parasitic infections:
  • Gastrointestinal parasitic infections: Giardiasis, Cryptosporidiosis, Amoebiasis, Ascariasis, Strongyloidiasis.
  • Blood/Tissue parasitic infections: Malaria, Schistosomiasis, Hydatid disease (Echinococcus), (Trichomoniasis).

Approaching Parasites

• Distribution: Where they are found globally/environment.
• Life Cycles: How they survive and breed.
  • Direct transmission occurs from one host to the next.
  • Indirect transmission involves an intermediate host or vector.
• Clinical Manifestations: How parasites affect the host.
• Diagnosis: How parasites are identified.
• Treatment: How to eliminate parasites.
• Control: How to prevent infections.

Classification of Parasites

• Protozoa (microscopic): Single-celled organisms such as Giardia, Trichomonas, Entamoeba histolytica, Malaria, and Crytosporidia.
  • They transmit via GI - faeco-oral or Blood/tissue – vector.
• Helminths (macroscopic): Multicellular and do not multiply in humans.
  • Nematodes (roundworms): Ascaris and Strongyloides.
  • Transmission routes are faeco-oral or transcutaneous.
  • Platyhelminths: Cestodes (Taenia, Echinococcus) and Trematodes (Schistosoma).
• Ectoparasites (Arthropods): Mites, Lice, Ticks, and Fleas.

Giardiasis (Giardia lamblia)

• Protozoa of the flagellate type.
• Global distribution.
• Direct life cycle.
• Symptoms appear 1-2 weeks post-infection, but may often be asymptomatic.
• Clinical symptoms: Diarrhoea (floating pale stool), flatulence, bloating, sulfurous burps, and fatigue.
• Diagnosis and Treatment: Diagnosed stool OCP but are treated with Metronidazole (or Tinidazole), and Controlled by good Sanitation & Hygiene.

Cryptosporidiosis (Cryptosporida spp.)

• Distribution: Widespread where faecal matter contaminates.
• Life Cycle: Direct.
• Onset in humans occurs 2-10 days after exposure.
• Common symptoms: Watery diarrhoea, stomach cramps/pain, dehydration, nausea and vomiting, fever, and weight loss.
• Diagnosis: Stool OCP, microscopy (acid-fast staining), direct fluorescent antibody [DFA], or enzyme immunoassays.
• Treatment: Hydration with possibilities of spontaneous resolution.
  • Immunosuppressed patients may have prolonged infections.
  • Nitazoxanide may be considered.
• Control: Sanitation and hygiene.
  • Use good hand hygiene, don't swallow pool.
  • Boil water for a minute (3 mins above 2,000m), and/or filter.
  • Use barrier precautions for sex.

Ascaris lumbricoides

• Soil transmitted helminth nematode.
• Distribution is mostly tropical and sub-tropical.
• Life cycle: Direct.
• Often asymptomatic, with possible mild abdominal discomfort or intestinal obstruction.
• Diagnosis: Stool OCP
• Treatment: Albendazole or Mebendazole and treated with Control: Sanitation and hygiene.

Strongyloidiasis (Strongyloides stercoralis)

• Helminth - Nematode type.
• Distribution: Global.
• Life Cycle: Direct.
• Clinical Presentation: Asymptomatic or symptoms include rash, GI symptoms, dry cough/itchy throat, oesinophilia (75%), and hyperinfection/dissemination (Mortality 90%).
• Diagnosis: Serology and Stool OCP.
• Treatment: Ivermectin 200mcg/kg.
  • Repeat doses are given if immunosuppressed after 14 days.
  • Daily treatment is given if hyperinfection until negative for 2 weeks.
• Control Sanitation and hygiene.

Malaria (Plasmodium spp.)

• Spread through the bite of the female anopheles mosquito
• The 5 species are; plasmodium falciparum, plasmodium vivax, plasmodium ovale, plasmodium malariae, plasmodium knowlesi
• Kills a child every 40 seconds
• Kills over one million people mostly children each year
• Ninety percent of all malaria infections are in sub-saharan Africa
• Diagnosis: Malaria screen, LAMP or Rapid antigen test, Blood film (thick and thin), PCR (reference lab)

Cystic Echinococcosis

• Tapeworm found in dogs, sheep, cattle, goats and pigs
• Most Human infections are asymptomatic
• Has slowly enlarging cysts in the liver, lungs and other organs that go unnoticed for years.

Trichomonas vaginalis (Protozoa - flagellate)

• Parasitic protozoa
• Life Cycles: Direct, parasite multiplies by binary fission
• Often asymptomatic but can cause mild irritation, urination irritation alongside discharge in women and if untreated can for months or increase the risk of STI's
• Highest Sensitivity can be found by NAAT Nucleic Acid Amplification test