Communicable Diseases
1. communicable transmission
disease: 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 time interval between exposure
period: 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, lodgment, development, and reproduction
animals: of arthropods on the surface of the
body or in clothing.
articles, harboring or sheltering animals
premises: (especially arthropods or rodents).
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.
1. Common cold
agent: rhinoviruses, coronaviruses, others
reservoir: human
transmission: direct contact
2. Influenza:
agent: influenza viruses (3 major serotypes):
type A: widespread, pandemics
type B: local epidemics
type C: only in sporadic cases
reservoir: human
transmission: same as cold
3. Tuberculosis:
agent: Mycobacterium
reservoir: primarily human
transmission: primarily droplet nuclei
4. Coccidioidomycosis:
agent: Coccidioides immitis (fungus)
reservoir: soil
transmission: airborne
5. Pneumonia: inflammation of the lungs with congestion
(not a specific disease, but a pathological
term -- i.e., symptoms)
reservoir: essentially human
transmission generally direct, sometimes airborne
various agents:
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.
Test your knowledge with a: quiz
For more information, try: diseases