Pathogens: Disease-Causing Agents Overview

Pathogens: Disease-Causing Agents

• Pathogens are microorganisms that cause illness by infecting the body and overcoming the immune system.
• They include bacteria, viruses, fungi, helminths, protozoans, and prions.
• Pathogens gain entry through mucous membranes (e.g., open wounds, eyes, nose, mouth).
• Replication within the host can be localized or systemic.

Types of Pathogens

Bacteria

• Bacteria are unicellular organisms, many beneficial, some harmful.
• Antibiotic overuse can lead to antibiotic-resistant strains.
• ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) are highly antibiotic-resistant.
• They cause diseases such as sepsis, lung infections, and necrotizing fasciitis.
• Antibiotics can be used to kill or prevent the replication of non-resistant bacteria.

Viruses

• Viruses are smaller than bacteria, not cell-like, and debated as living.
• They require a host cell for replication through lytic or lysogenic cycles.
• Examples include the influenza virus (common flu), norovirus, and measles virus.
• Symptoms vary (e.g., cough, fever, body aches, gastrointestinal distress, skin rash).
• Antibiotics are ineffective against viruses. Vaccination and symptom management are key.

Fungi

• Fungi are eukaryotic organisms, found in the environment and body.
• Infections can be exogenous (external) or endogenous (internal, from overgrowth).
• Examples include candidiasis (yeast infection) and ringworm (skin infection).
• Antifungals (e.g., nystatin, fluconazole) are used to treat fungal infections.

Protozoa

• Protozoa are single-celled organisms, sometimes transmitted by vectors (e.g., mosquitoes).
• They cause localized or systemic diseases.
• Examples include Giardia (intestinal infection) and Plasmodium (malaria).
• Diagnosis and treatment may involve stool/blood tests and strong antibiotics (e.g., azithromycin).

Helminths

• Helminths are large, multicellular parasites (worms).
• Unlike other pathogens, they often don't replicate inside the host.
• Categories include flatworms, thorny-headed worms, and roundworms.
• Can cause chronic inflammatory disease if untreated.
• Examples are hookworms and roundworms like Ascaris.
• Treated with anthelmintic medications (e.g., albendazole, mebendazole).

Prions

• Prions are misfolded proteins that cause normally-folded proteins to misfold.
• Not considered living.
• Related to diseases like Mad Cow disease and Gerstmann-Sträussler-Scheinker disease (GSS).
• Often result in rapidly progressing dementia and death.

Prevention

• Preventing infection includes handwashing, safe sex practices, vaccination, avoiding shared items, insect bite protection, proper food handling, and bathroom hygiene.