Parasite Survival Strategies

The Parasite's To Do List

• Parasites have seven key tasks to perform in order to survive and reproduce within a host. These include achieving transmission and entry, migrating to the appropriate tissue or site, maintaining their position, finding a mate, successfully reproducing, undergoing developmental changes, and coping with host changes while evading the immune system.
• Transmission and entry can occur through diverse pathways including fecal-oral, trophic, direct penetration, vector-borne, sexual transmission, vertical transmission, and horizontal transmission.
• Transmission via vectors can be categorized by vector competence and vector capacity.
• Fecal-oral transmission is a common route for parasites such as Giardia, Entamoeba, and Cryptosporidium.
• Direct penetration is utilized by parasites like Schistosoma cercariae and hookworm L3 larvae.
• Vector competence refers to the ability of a vector to become infected and transmit a parasite. This categorization further separates into biological vectors, which require the parasite to undergo essential development or reproduction, and mechanical vectors, which simply transport parasites.
• Vector capacity considers extrinsic factors including feeding frequency on the host, time spent on the host, lifespan, abundance, and dispersal ability of the vector.
• Within biological vectors, parasites can exhibit cyclodevelopmental transmission, where they develop but don't multiply, propagative transmission, where they multiply but don't develop, or cyclopropagative transmission, where they undergo both development and multiplication.
• Sexual transmission is observed in parasites like Trypanosoma equiperdum, Trichomonas vaginalis, and Tritrichomonas foetus.
• Vertical transmission occurs from mother to offspring via the placenta, transovarian transfer, or via feeding, with examples including Toxoplasma gondii, Toxocara canis, and Babesia bigmina.
• Horizontal transmission involves contact with infected individuals or abiotic factors, excluding parent-progeny relationships, and is seen in many ectoparasites, aerosols, water, and contaminated surfaces.
• Certain parasites, like trematodes Opisthorchis viverrini and Clonorchis sinensis, can induce neoplasia, an abnormal proliferation of cells.

Pathology Resulting from Parasitic Infections

• Parasites can cause pathology by altering host cellular growth patterns, interfering with nutrient acquisition, releasing toxins, and inducing immune responses.
• Neoplasia, a key pathology, is characterized by abnormal cell proliferation.
• Spirocerca lupi, a nematode, is known to induce esophageal carcinomas.
• Parasites can interfere with host nutrient acquisition by diverting nutrients to themselves.
• Diphyllobothrium latum, a tapeworm, can cause vitamin B12 deficiency, leading to megaloblastic anemia and neuron demyelination.
• Giardia lamblia infection impairs nutrient absorption, resulting in lactose and fat malabsorption.
• Intestinal protozoa like Giardia, Cryptosporidium, and others can impair Na+ absorption and increase luminal Cl- secretion.
• Plasmodium and hookworm infections cause erythrocyte destruction, leading to anemia.

Introduction to Protozoa

• Protozoa are diverse single-celled eukaryotic organisms characterized by several key features, including locomotion, nuclei & mitochondria.
• Protozoa use three primary modes of locomotion: pseudopodia, cilia, and flagella.
• Protozoa possess various nuclear types based on nucleolus arrangement, including granular, vesicular, peripheral, and complex.
• Some protozoa exhibit degenerate mitochondria-related organelles (MROs) with reduced functions, or structures associated with mitochondria, such as kinetoplasts.
• The origin of mitochondria predates the divergence of eukaryotes.
• All eukaryotes have mitochondria or mitochondria-related organelles (MROs).

Intestinal Physiology

• The intestinal epithelium plays a crucial role in nutrient absorption and barrier function.
• Intestinal pathology caused by parasites can involve inflammation, disruption of the epithelial barrier, electrolyte imbalance, and diarrhea.
• Reactive oxygen species (ROS) play a significant role in intestinal pathology, as they can damage macromolecules and contribute to inflammation.
• ROS are produced as a by-product of aerobic metabolism, and mechanisms for detoxification are essential.
• Cytokines are involved in immune responses and can contribute to intestinal pathology by stimulating ion secretion, altering paracellular permeability, increasing ROS production, and causing epithelial disruption.
• Diarrhea, a common symptom of intestinal pathology, can be categorized into osmotic, secretory, and inflammatory types.
• Secretory diarrhea results from overstimulation of intestinal secretory cells, often triggered by toxins produced by bacteria.
• Inflammatory diarrhea is associated with inflammation of the intestinal lining, a process frequently triggered by invasive parasites or bacterial toxins.
• Osmotic diarrhea arises from increased osmotic pressure within the intestinal lumen due to poorly absorbed substances, such as undigested sugars or malabsorbed nutrients.

Test your knowledge on the essential tasks parasites undertake to thrive within hosts. This quiz covers various transmission pathways, migration strategies, and the methods used by parasites to evade host defenses. Dive into the fascinating world of parasite biology and survival!