Biology 261

• new natural pathogen for
• which the individual host, and sometimes the entire species, has not developed
• resistance; rabid and dramatic onset.

• they themselves show few
• (or perhaps no) symptoms, but are actively carrying and shedding the pathogen.

• (long-term infections)
• caused by well-adapted pathogen libing in balance with its host, taking what it
• needs for existence and causing only a minimum of harm.

• - arises as the result of infection (or intoxication) of a large
• number of people from a contaminated common source such as food or water.

• constantly present with low
• incidence in a population.

• when a number of cases are
• observed, usually in a relatively short period of time, in an area previously
• experiencing only sporadic cases of the disease.

unusually high numbers.

• the study of the
• occurrence, distribution, and determinants of health and disease in a
• population and control of a disease in a population

• Inanimate agents such as
• bedding, toys, books, and surgical instruments can also transmit disease.

• the resistance of a group
• to infection due to immunity of a high proportion of the members of the group.

• the disease incidence shows
• a relatively slow, progressive rise and a gradual decline

• the number of new cases of an individual
• disease in a population in a given time period.

• the incidence of disease in
• populations and includes both fatal and nonfatal diseases.

• The incidence of death in a
• population

- widespread, usually worldwide, epidemic.

• the number of total cases
• (new and existing) of an individual disease in a population in a given time
• period.

• restricts the movement of a person with active
• infection to prevent spread of the pathogen to other people.

• the observation,
• recognition, and reporting of disease as they occur

- living agents transmitting pathogens.

• food and water are
• potential disease vihicles.

• a disease that primarily
• infects animals but is occasionally transmitted to humans.

Epidemiology is the study of the occurrence, distribution, and determinants of health and disease in a population, and control of a disease in a population.

• Infectious diseases were the leading causes of death in 1900, whereas today they are much less important.
• Heart disease and cancer

1) Infection

2) Incubation period

3) Acute period

4) Decline period – rapid by crisis or slow by lysis

5) Convalescence period

Endemic disease is constantly present with low incidence in a population.

Epidemic disease is unusually high numbers

Pandemic disease is a widely distributed epidemic.

Reservoirs or sites in which infectious agents remain viable and from which infection of individuals may occur. (may be either animate or inanimate)

• Acute infections or new natural pathogen for which the individual
• host, and sometime the entire species, has not developed resistance: rapid and
• dramatic onset.

Chronic infections (long-term infections) or caused by well-adapted pathogen living in balance with its host, taking what it needs for existence and causing only minimum harm.

• - Anthrax: Causative agent: Bacillus anthracis Infection sources: Milk or meat from infected
• animals Control measures: Destruction of
• infected animals

• - Bacillary dysentery: Causative agent: Shigella dysenteriae Infection sources: Fecal contamination of
• food and water Control measures:
• Detection and control of carriers; oversight of food handlers; decontamination
• of water supplies

- Botulism: Causative agent: Clostridium botulinum Infection sources: Soil-contaminated food Control measures: Proper preservation of food

• - Cholera: Causative agent: Vibrio cholerae Infection sources: Fecal contamination of
• food and water Control measures:
• Decontamination of public water sources; immunization

• - Giardiasis: Causative agent: Giardia spp. Infection sources: Fecal contamination of
• water Control measures: Decontamination
• of public water sources

• - Hepatitis: Causative agent: Hepatitis A, B, C, D, E Infection sources: Infected humans Control measures: Decontamination of
• contaminated fluids and fomites; immunization if available (A and B)

• - Typhoid fever: Causative agent: Salmonella typhi Infection sources: Fecal contamination of
• food and water Control measures:
• Decontamination of public water sources; oversight of food handlers;
• pasteurization of milk; immunization

• - Diphtheria: Causative agent: Corynebacterium diphtheria Infection sources: Human cases and carriers;
• infected food and fomites Control
• measures: Immunization; quarantine of infected individuals

• - Tuberculosis: Causative agent: Mycobacterium tuberculosis Infection sources: Sputum from human cases;
• infected milk Control measures:Treatment
• with isoniazid; pasteurization of milk

• - Whooping cough: Causative agent: Bordetella pertussis Infection sources: Human cases Control measures: Immunization; case
• isolation

• - German measles: Causative agent: Rubella virus Infection sources: Human cases Control measures: Immunization; avoid contact
• between infected individuals and pregnant women

• - AIDS: Causative agent: Human immunodeficiency virus (HIV) Infection sources: Infected body fluids,
• especially blood and semen Control
• measures: Treatment with metabolic inhibitors (not curative)

• - Malaria: Causative agent: Plasmodium spp. Infection sources: Bite from Anopheles
• mosquito Control measures: Control
• mosquito population; treat infected humans with antimalarial drugs

• - Plague: Causative agent: Yersinia pestis Infection sources: Bite from flea Control measures: Control rodent populations;
• immunization

• - Rocky Mountain spotted fever: Causative agent: Rickettsia
• rickettsii Infection sources: Bite from
• infected tick Control measures: Avoid
• tick exposure; treat infected individuals with antibiotics

• - Rabies: Causative agent: Rabies virus Infection sources: Bite by carnivores,
• contact with infected neural tissue
• Control measures: Avoid animal bites; immunization of animal handlers
• and exposed individuals

• - Tularemia: Causative agent: Francisella tularensis Infection sources: Contact with rabbits Control measures: Avoid contact with rabbits;
• treat infected individuals with antibiotics

- Common-source epidemics: cholera

- Host to host epidemics: Influenza and chickenpox

- Vectors: West Nile virus

• - Direct contact: Common cold, influenza, syphilis (Treponema
• pallidum), and gonorrhea (Neisseria gonorrhoeae)

• - A reservoir is a site in shich infectious agents remain viable and
• from which infection of individuals may occur.

• - Soil (Clostridium tetani [the causal agent of tetanus]), organisms
• (staphylococci and streptococci [cause: diphtheria, gonorrhea, and mumps])

• - As the host population develops resistance, the spread of the
• pathogen is checked, and eventually a balance is reached in which host and
• pathogen are in equilibrium.

• - Herd immunity is the resistance of a group to infection due to
• immunity of a high proportion of the members of the group.If a high proportion
• of individual sin a group are immune to an infectious agent, then the whole
• population will be protected.

- No, if a population is 70% immunized it will be absent from the population, the immunized individuals protect the rest of the population because they cannot acquire and pass on the pathogen, thus breaking the cycle of infection.

- The most cases of AIDS is found in Sub-Saharan Africa.

- Transmitted during sexual activity or by blood-contaminated needles.

• • Staphylococcus spp., particularly S. aureus., cause wound and
• blood infections, pneumonia.

• • Escherichia
• coli , Enterococcus spp., Pseudomonas
• aeruginosa, Candida albicans, Klebsiella pneumonia - urinary
• infections.

• • Staphylococcus spp., Enterococcus spp. and Escherichia coli
• have tendency to have multiple drug resistance

Major factors leas=ding to a spread of nosocomial infections:

• -
• Many patients have low resistance to infectious disease because of
• their illness

• - Healthcare facilities treat infectious disease patients, and these
• patients may be pathogen reservoirs

- Multiple patients in rooms and wards increace the chance of cross-infection

- Healthcare personnel move from patient to patient, increasing the probability of transfer of pathogens

- Healthcare procedures such as hypodermic injection, spinal puncture, and removal of tissue samples or fluids, breach the skin barrier and may introduce pathogens into the patient

- In maternity wards of hospitals, newborn infants are unusually susceptible to certain infections because they lack well-developed defense mechanisms

• - Surgical procedures expose internal organs to sources of contamination, and the sress of surgery often diminishes the resistance of the
• patient to infection

- Certain therapeutic drugs, such as steroids used for controlling inflammation, increase the susceptibility to infection

• - Use of antibiotics to control infections selects for
• antibiotic-resistant organisms.

• Control directed against reservoir

• – Eradication for wild and domestic animal reservoirs: rabies carriers
• and insects.

– Isolation for human carriers.

• Control of transmission

– Water treatment, food quality control, masks.

• Immunization

• – Smallpox, diphtheria, tetanus, whooping cough, measles, mumps,
• rubella, polio. Hepatitis A and B. Bacterial pneumonia and meningitis.

• Quarantine -

• – time limit for quarantine is the longest period of the
• communicability of the given disease

• – Cholera, plague, yellow fever, relapsing fever, typhoid fever,
• smallpox. Ebola hemorrhagic fever and meningitis is some cases.

• Surveillance, reportable diseases in Table 33.5

• Pathogen Eradication

– Small pox in 1980.

• – Polio, leprosy, Chagas’ disease, dracunculiasis are targeted as of
• now.

– Candidates syphilis and rabies.

• Causes of death in the Americas and Africa, 2002. (a) Africa; (b) the Americas. There were 10.7 million deaths in Africa, 6.7 million due to infectious diseases. There were 6 million deaths in the Americas, 623,000 due
• to infectious diseases.

1. Human demographics.

– Cities versus country living.

– Sexual and other risk behavior.

2. Technology and industry.

– General improvement in public health

– Nocosomial diseases

– Transportation, central distribution

• 3. Economic development and
• land use.

• –
• Lyme disease in the US

– Rift Valley disease in Egypt.

• 4. International travel and
• commerce.

– West Nile virus, Marburg (Ebola) virus

• 5. Microbial adaptation and
• change.

– RNA viruses: SARS, influenza and HIV virus.

• 6. Breakdown of public
• health measures.

– Cryptosporidium outbreak in Wisconsin

– Diphtheria in the Soviet Union

• 7. Abnormal natural
• occurrences that upset the usual host-pathogen balance.

– Hantavirus and mice

• Recognition of the disease

– Surveillance

• – Clinical syndromes: (1) acute respiratory disease, (2) encephalitis
• and aseptic meningitis, (3) hemorrhagic fever, (4) acute diarrhea, (5)
• clustering of high fever cases, (6) unusual clustering of any disease or
• deaths, and (7) resistance to common drug or treatment.

• Intervention to prevent transmission

• Bacillus anthracis

• Small pox

• Yersinia pestis

• Brucella abortus

• •
• Francisella tularensis

• Salmonella spp.

• Rabies virus

• Ebola virus

• Huntaviruses

• Botulinum E toxin.