L6 Medical Parasitology Overview

Medical Parasitology

• Medical parasitology is the study of parasites and their relationships with hosts.
• Parasitology is traditionally restricted to protozoa, helminths (worms), and arthropods (medical insects).
• Parasites can be microorganisms that live either within or on another organism (host).

Module Objectives

• Recognize the basic concepts of human parasites and parasitic diseases.
• Describe different types of parasites transmitted through food and their associated diseases.

Impact of Intestinal Parasitic Infections

• Intestinal parasitic infections negatively impact nutrition.
• Undernutrition can increase the likelihood of parasitic infection.
• Adult worms residing in the small intestine can interfere with host nutrition and damage the intestinal mucosa, which hinders nutrient absorption.
• Hookworm infection is a significant cause of nutritional deficiencies, specifically iron deficiency anemia.

Host-Parasite Relationships

Commensalism

• One organism, the commensal, feeds on substances consumed by the host.
• The relationship benefits one organism, while the other remains unaffected (neither benefit nor harmed).
• Entamoeba coli is a non-pathogenic species often found as a commensal parasite in the human gastrointestinal tract.

Mutualism

• Mutualist (organism) and host depend on each other physiologically.
• Both organisms benefit from the ecological interaction, as they both gain an advantage from their relationship.
• The alligator and birds relationship is an example, as birds clean the alligator's teeth; in turn, birds gain food.

Parasitism

• Parasite benefits, while the host is harmed (causing disease).

• Parasite dependency on the host can be permanent or temporary.

• Obligatory parasites are reliant on the host for their physiological survival. They cannot live without the host.

• Facultative parasites can exist as free-living organisms but can also become parasitic.

• Parasites can cause different types of diseases, depending on the parasite's specifics.

• Major types of parasites are categorized based on their location in the host body; endoparasites and ectoparasites.

• Endoparasites reside within the host's body (e.g., alimentary tract, liver, lungs, urinary bladder, or blood).

• Examples include malaria parasites (Plasmodium spp) and sleeping sickness parasites (Trypanosoma spp). These parasites have infective stages in the host's blood that are transmitted to new hosts through the bite of an insect.

• Ectoparasites are attached to the host's outer surface (e.g., bed bugs, ticks, and lice).

Host Classification

• (1) Definitive host:*
• The host where the parasite reaches sexual maturity.
• Example: Mosquitoes are the definitive host for malaria. Humans are the definitive host for taeniasis.
• (2) Intermediate host:*
• A temporary but essential environment for parasite development.
• Example: Humans serve as an intermediate host for malaria. Pigs and cattle serve as intermediate hosts for taeniasis.
• (3) Transfer host (mechanical vector):*
• Not essential to the parasite's life cycle, but utilized as a temporary vehicle for reaching a host.
• Example: House flies (Musca domestica) are transport hosts for various protozoan and viral/bacterial pathogens.

Vectors

• An arthropod or invertebrate serving as a host and carrier for a parasite.
• Essential for the completion of the parasite's life cycle.
• Examples of vectors for parasites transmitted to humans or vertebrates include mosquitoes (malaria), sand flies (leishmaniasis), and tsetse flies (African trypanosomiasis).

Reservoir Host

• Infected animals that serve as sources of infective organisms for humans.
• Example: Rodents are reservoir hosts for leishmaniasis.

Classification of Medically Important Parasites

• Protozoa (unicellular)
• Flatworms (trematodes and cestodes)
• Roundworms (nematodes)
• Arthropods (insects, ticks, and lice)

Transmission of Parasitic Diseases

• Food: Foodborne parasites are transmitted via food, water, soil, or person-to-person contact. Foods prone to contamination include undercooked seafood, undercooked meat, and raw vegetables. Common foodborne parasites include protozoa (Giardia intestinalis, Entamoeba histolytica, Toxoplasma gondii, Cryptosporidium spp), nematodes (Ascaris lumbricoides, Enterobius vermicularis, Trichuris trichiura), and cestodes (Taenia spp, Hymenolepis nana). Symptoms vary depending on the specific parasite but may include abdominal pain, diarrhea, muscle pain, cough, skin lesions, malnutrition, and neurological symptoms.
• Water: Water can become contaminated with parasites, causing illness. Common waterborne parasites include Entamoeba histolytica (amebiasis), Giardia intestinalis (giardiasis), and Schistosoma spp (schistosomiasis). Infection occurs by swallowing contaminated water.
• Animals: Zoonotic diseases spread between animals and humans. Foods from infected animals - cows, pigs - can be sources for these kinds of infections. Examples include Taenia spp. and Trichinella spiralis.
• Blood: Bloodborne parasites can be transmitted by blood transfusion. Parasites can be found in blood. Parasites that circulate in the blood stream include Babesia, Plasmodium, and Trypanosoma. Vectors carry these blood-borne parasites.
• Insects: Insects act as vectors for various diseases. They transmit the parasites to humans. Parasites must undergo development in the insect for transmission.
• Congenital: Infections transmitted from a mother to her child during pregnancy or childbirth. Examples include Toxoplasma gondii, Trypanosoma cruzi, and Plasmodium spp.

Assignment: Foodborne Parasites and Nutrition

• Aim: Explore the interconnections between foodborne parasites and nutrition. Understand the role of parasites in food safety and contributing to malnutrition, particularly in vulnerable populations.
• Objectives: Identify common foodborne parasites and their transmission routes, analyze nutritional challenges from parasitic infections, explore prevention strategies, and evaluate the role of nutrition in building immunity to parasitic infections.
• Topics: Investigate how foodborne parasites contribute to malnutrition, why populations with poor sanitation and food insecurity are more susceptible, effects on specific nutrients and long-term consequences, strategies to reduce incidence in malnourished communities, and the roles of climate change and globalization in spreading foodborne parasites and their nutritional impact.
• Structure: Include an introduction (background on foodborne parasites), main body (evidence-based research and discussions), conclusion (summarizing findings, recommendations), references, length (at least 2000 words, excluding front page), and formatting (APA style, 12-point Times New Roman, double-spaced).