Communicable Diseases
Figure 2.10: The Burden of Disease by Group of Cause, Percent of Deaths, 2001
Data from Lopez AD, et al Global Burden of Disease and Risk Factors.
Washington, DC and New York: The World Bank and Oxford University Press;
2006:8.
Table 2.5: The Ten Leading Causes of Death in Children Ages 0-14, by Broad Income Group, 2001
Adapted with permission from: Lopez A, Begg S, Bos E. Demographic and
Epidemiological Characteristics of Major Regions, 1990-2001. In: Lopez A,
Mathers C, Ezzati M, Jamison D, Murray C, eds. Global Burden of Disease and
Risk Factors. Washington, DC and New York: The World Bank and Oxford
University Press; 2006:70.
Key Terms
• Communicable diseases includes:
– Those caused by infectious agents, such as:
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Malaria
HIV/AIDS
TB
Cholera
– Those caused by parasites, such as:
• Hookworm
• Filariasis
Studying Communicable Diseases
• Many aspects to the study of communicable
diseases
– Infectious organism and its transmission vector
• Life cycle and reservoir (where it lives) of the infectious
organism/parasite and/or transmission vector
• Cycle of infection
– Human to human; host to insect to human…
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Pathology of the organism in the body
Diagnosis
Treatment
Prevention
Modes of Transmission
• Direct contact - person to person
– Contact with an infected skin lesion
– Contact with blood or other body fluids
• Contact with fecal material of a sick person and then
touch your eyes, nose….
– Breathe in droplets expelled by coughing/sneezing
sick person (some consider this airborne)
– Sexual contact
– Needle sharing
Modes of Transmission
• Airborne
– Pathogen is aerosolized, attached to dust…in the
air
– Become infected by breathing in the infected air
– Isolation of the infected individual is
recommended to prevent transmission
– Examples: SARS (TB , influenza)
Modes of Transmission
• Vector-borne
– Spread by an animal - often by the bite of an infected
insect
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Rabies – animal bite
Malaria – mosquito
Lyme disease - ticks
Dengue fever – mosquito
– Insect itself is often infected by biting an infected
carrier
• Rodent with plague  tick  human
• Livestock with African sleeping sickness  tsetse fly 
human
Modes of Transmission
• Food and water borne
– Infection occurs with ingestion of contaminated food
or water
• Water borne:
– Cholera
– Hepatitis A
• Food borne – often fecally contaminated or
contaminated water used to cook foods
– Salmonella
– E. coli
Modes of Transmission
• Mother-to-child (MTC)
– Referred to as vertical transmission
– Infection is passed from mother to fetus during
pregnancy or mother to infant through breast milk
More Key Terms
• Infection – occurs when the infectious agent
begins to reproduce in the body
– may result in a “case” – person with disease
(symptoms)
– Can be infected without disease!
• Typhoid Mary
• Pathogenicity – # with disease (symptoms) per #
infected
• Virulence - # with severe illness or death per #
with disease
– Aka case fatality rate
More Key Terms
• Infectivity – capacity of the organism to cause
infection in a susceptible individual
• Measure infectivity by:
– Secondary attack rate – average number of other
people one sick person infects
• # infected/# susceptible people exposed
• Prions
Infectious Agents
– Protein based infectious particles
• Viruses
– Genetic material (DNA, ssDNA, RNA…) inside a protein capsid
– Many are vaccine preventable
• Bacteria
– Prokaryotes
– Some vaccine preventable
• Protozoa
– Eukaryotes
• Fungus
– Eukaryotes (molds and yeast)
• Worms
– Parasitic multi-celled eukaryotes
Timeline of Infection
Pre-Clinical
Phase
• Infection occurs
• Disease can be detected through lab work
Contagious
• Infected person may become contagious before or
after symptoms begin
Clinical Phase
• Symptoms develop
• Person recovers with or without immunity or dies
Major Infectious Diseases Worldwide
• HIV/AIDS
– Virus
• Malaria
– protozoa
• Tuberculosis (TB)
– bacteria
• Measles
– virus
Neglected Tropical Diseases (NTD)
• Diseases that have a significant impact on
health and quality of life, but are generally not
deadly
• http://www.who.int/neglected_diseases/en/
– ~23 minute video on the forgotten diseases
• http://whqlibdoc.who.int/publications/2010/9
789241564090_eng.pdf