Communicable Diseases Lecture Notes

Communicable Diseases Disease Concepts 1. communicable disease: transmission of an agent (or its by-product) from reservoir to host. 2. agent: a factor that must be present for a disease to occur in a susceptible host. 3. infection: growth of a pathogenic microbe in a host (with or without evidence of disease) (also called "sepsis"). 4. pathogenicity: capable of producing disease. 5. virulence: harmfulness of a disease. 6. reservoir: any place where an infectious agent depends primarily for survival. 7. host: any animal infected by an agent; may be diseased or may be intermediate host. 8. incubation period: time interval between exposure to infectious agent and first sign or symptom of disease. 9. carrier: person or animal that harbors an organism of disease without showing symptoms. 10. asymptomatic carrier: never shows symptoms (also called "inapparent infection"). 11. transmission: any mechanism by which a susceptible human host is exposed to an infectious agent. 12. fomites: inanimate objects (other than food, water) which harbor or transmit infectious organisms. 13. vector: insect or other animal that may transfer pathogens to humans. 14. infestation: humans, animals: lodgment, development, and reproduction of arthropods on the surface of the body or in clothing. articles, premises: harboring or sheltering animals (especially arthropods or rodents). Disease Controls Objective: The fundamental purpose of environmental health is to prevent disease from occurring. The purpose of this section is to discuss the different types of prevention and to start applying them in the analysis of the various disease in this section. From the standpoint of our model of communicable disease, we can divide controls into 3 basic categories. This approach may actually be more helpful in divising strategies for controlling the spread of communicable disease. 1. Control the agent: For example, we can remove agents before their entry into air, water, and soil. If it is a chemical agent, this may involve simple changes in production processes. If it is a microbial agent, it may involve prohibiting consumption of affected foods, or use of bactericides on preparation surfaces. 2. Control the environment: For example, we can control control vectors, or treat polluted air, water, and soil. We can also prevent access to an area. 3. Control the host: For example, we can take steps to protect the young, the old, and the sick, each of whom may be the high risk individuals. This may involve personal hygiene, immunizations, or health education. Selected Airborne Diseases 1. Common cold agent: reservoir: transmission: 2. Influenza: agent: reservoir: transmission: rhinoviruses, coronaviruses, others human direct contact influenza viruses (3 major serotypes): type A: widespread, pandemics type B: local epidemics type C: only in sporadic cases human same as cold 3. Tuberculosis: agent: reservoir: transmission: Mycobacterium primarily human primarily droplet nuclei 4. Coccidioidomycosis: agent: reservoir: Coccidioides immitis (fungus) soil transmission: 5. Pneumonia: reservoir: transmission various agents: airborne inflammation of the lungs with congestion (not a specific disease, but a pathological term -- i.e., symptoms) essentially human generally direct, sometimes airborne 5. pneumococcal pneumonia (Streptococcus pneumoniae) 6. mycoplasmal pneumonia (Mycoplasma pneumoniae) 7. pneumocystis pneumonia (Pneumocystis carinii) 8. chlamydial pneumonia (Chlamydia trachomatis) 9. others: various viruses, rikettsias (Q fever), Legionella, worms (nematodes), etc.