Mortality and morbidity rates for infectious diseases vary greatly by geographical location. World Health Organization (WHO) statistics provide striking documentation that deaths due to infectious diseases are much higher in poor countries than in the countries with the highest income levels. It is particularly striking that malaria and tuberculosis are significant causes of death in low-resource countries, whereas these diseases are rarely fatal in wealthy countries. Other infectious diseases that significantly cause death in low-resource countries are pneumonia, diarrhea, and HIV infection. The top ten causes of death in lower and middle-resource countries In lower and middle-resource countries also include lower respiratory infections, tuberculosis, and diarrheal diseases.
- Define infection and identify the differences between colonization and infection, giving specific examples of each.
- How does infection start, and what is the usual course?
- What factors influence the course of an infection? Give specific examples of different trajectories of infection.
Full Answer Section
2. How Infection Starts and Usual Course:
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Entry: Infections typically begin when microorganisms enter the body through various portals of entry, such as:
- Breaches in the skin: Cuts, wounds, insect bites
- Respiratory tract: Inhalation of airborne pathogens
- Gastrointestinal tract: Ingestion of contaminated food or water
- Urogenital tract: Sexual transmission
- Mucous membranes: Eyes, nose, mouth
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Establishment: The microorganisms then attach to host cells and begin to multiply.
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Host Response: The host's immune system recognizes the invading pathogens and initiates a response, which may include:
- Innate Immunity: Immediate, non-specific defenses, such as physical barriers (skin, mucous membranes), phagocytosis (engulfment of pathogens by immune cells), and the inflammatory response.
- Adaptive Immunity: A more specific and long-lasting response, involving the production of antibodies and the activation of T cells.
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Outcome: The course of an infection can vary widely:
- Resolution: The host successfully clears the infection, and the individual recovers fully.
- Chronic Infection: The infection persists for a long time, often with ongoing symptoms.
- Latent Infection: The pathogen remains dormant in the body for a period of time and may reactivate later.
- Death: In some cases, the infection can overwhelm the host's immune system, leading to severe illness and death.
3. Factors Influencing the Course of Infection:
- Virulence of the Pathogen: The ability of the pathogen to cause disease.
- Host Factors:
- Immune System: A weakened immune system (e.g., due to HIV/AIDS, malnutrition, age) increases susceptibility to infection and can worsen the course of disease.
- Age: Very young children and older adults are often more susceptible to infection.
- Underlying Medical Conditions: Chronic diseases (e.g., diabetes, cancer) can weaken the immune system and increase the risk of infection.
- Nutrition: Poor nutrition can impair immune function.
- Genetics: Genetic factors can influence susceptibility to certain infections.
- Environmental Factors:
- Overcrowding: Increases the risk of transmission of infectious diseases.
- Poor sanitation and hygiene: Contributes to the spread of infectious diseases.
- Climate: Certain climates may be more conducive to the transmission of certain infectious diseases (e.g., malaria in tropical regions).
- Treatment:
- Availability and access to appropriate treatment: Early diagnosis and effective treatment can significantly improve outcomes.
- Antimicrobial resistance: The emergence of antibiotic-resistant bacteria can complicate the treatment of infections.
Examples of Different Trajectories of Infection:
- Acute Infection: A short-term infection, such as the common cold, that resolves quickly with or without treatment.
- Chronic Infection: A long-term infection, such as tuberculosis or HIV, that can persist for years or even a lifetime.
- Latent Infection: An infection that remains dormant in the body for a period of time, such as herpes simplex virus.
- Subclinical Infection: An infection that occurs without any noticeable symptoms.