Dr. Wael H. Mansy, MDAssistant Professor

College of Pharmacy King Saud University

Infectious Diseases

Infectious Diseases

Study Objectives: to know 1. What is an infectious disease??2. What is an infection??3. Causes of re-emerging of the problem of the infectious diseases4. Microbiological Classification of Infectious Diseases.5. Means of Transmission of Infectious Diseases.6. The action of pathogen in infectious process (pathogenicity)7. What is infectivity ,virulence, Immunogenicity and incubation period .8. Manifestations of infectious process (Infection spectrum).9. The immune reaction of host in infectious process.10. Common symptoms and signs.

Infectious disease is:① A group of common diseases

② Caused by different pathogens

③ Possessing infectivity.

④ To form epidemic.

⑤ Infectious disease is a threat to the health of people.

What is an infectious diseases??

Infectious Diseases

A case is a risk factor …Infection in one person can be transmitted to others

What is an infectious disease??

Infectious Diseases

Definition of infection① Complex process of interaction between pathogen

and human body

② Infection is composed of three factors: pathogen, host and environment

③ There are commensalisms and opportunistic infection

What is an infection??

Infectious Diseases

Causes of re-emerging of the problem of the infectious diseases:

Infectious Diseases

1. Loss of Antibiotic Effectiveness.

2. Increased Population Density: Transmission from person to person is more likely.

3. Travel: Travelers may bring back pathogens.

4. Global Warming: May affect rainfall or other factors that currently affect diseases

or their carriers.

5. Biological Warfare or Terrorist Attacks: There have recently been a number of

threats of such attacks involving anthrax.

6. New Routes of transmission: Organ Transplants.

7. Complacency and Ignorance: Many, possibly most, people do not wash their hands

after using the toilet.

Bacterial Gram-negativeGram-positive

Viral DNA virusRNA virusEnveloped vs non-enveloped

Fungal DisseminatedLocalized

Parasitic ProtozoaHelminths

Microbiological Classification of Infectious Diseases

Contact Requires direct or indirect contact (fomite, blood, or body fluid)

Food or WaterIngestion of contaminated food or water

Airborne Inhalation of contaminated air

Vector-borne Dependent on biology of vector as well as infectivity of organism

Perinatal

Sexual

Similar to contact infection, however, the contact may occur in utero or during delivery. transmission by sexual intercourse.

Means of Transmission of Infectious Diseases

Factors Influencing Disease Transmission

• Weather• Housing• Geography• Occupational setting• Air quality• Food

EnvironmentAgent

Host• Age• Sex• Genotype• Behaviour• Nutritional status•Health status

• Infectivity• Pathogenicity• Virulence• Immunogenicity• Antigenic stability• Survival

The pathogenicity of pathogen is related to :

1. Invasiveness

2. virulent

3. Number of pathogen

4. Mutation (variability)

Pathogenicity What does pathogenicity mean???

It means the ability of a microbiological agent to induce disease

Infectious DiseasesFactors Influencing Disease Transmission( Agent)

Infectivity: Ability of agent to cause infectionNumber of infectious particles requiredIn person-to-person transmission, secondary attack rate is a measure of

infectivity

Infectious Diseases

Virulence :Severity of the disease after infection occurs.

Measured by case fatality rate or proportion of clinical cases that develop severe

disease.

Factors Influencing Disease Transmission( Agent)

Immunogenicity Ability of an organism to produce an immune response that provides protection

against reinfection with the same or similar agent

Can be life long or for limited periods

Important information for development of vaccines

Infectious DiseasesFactors Influencing Disease Transmission( Agent)

Infection and ImmunityManifestations of infectious process (Infection spectrum):1) Clearance of pathogen (no infection)2) Covert infection (subclinical infection)3) Overt infection (Clinical infection or apparent infection)4) Carrier states

Health carrier after covert infection. Convalescent carrier after overt infection. Incubatory carrier before onset of disease.

According to carrier time : #acute (transient) carrier #chronic carrier5) Latent infection.

Infectious Diseases

Direct tissue invasion: like smallpox

Production of a toxin: anthrax produce toxins that invade and

destroy tissue

Immunologic enhancement or allergic reaction

Persistent or latent infection

Enhancement of host susceptibility to drugs

Immune suppression

Pathogenetic Mechanisms:

Infectious Diseases

Cases Index – the first case identified Primary – the case that brings the infection into a population Secondary – infected by a primary case Tertiary – infected by a secondary case

Transmission

Infectious Diseases

P

S

S

T

Susceptible

Immune

Sub-clinical

Clinical

ST

Incubation period

Time between exposure and onset of symptoms or signs of infection.

Each disease has typical incubation period but varies widely.

Requires replication of the organism to some threshold level for producing

symptoms

Infectious Diseases

Tuberculosis Scarlet Fever tetanus Gonorrhea Diptheria Streptococcal Infections Pneumonia (can also be viral or fungal) Pertussis Bubonic Plague There are many others.

Bacterial Diseases

*Common Cold

*Influenza

*AIDS/HIV

*Herpes (Simplex and Zoster)

*Hepatitis A,B,C, D, E, F and G.

*Measles, Mumps and Rubella.

*Poliomyelitis.

*Infectious mononucleosis.

Viral Diseases

*Organisms, but without chlorophyll

*Generally life off of dead organisms or dead material within a living organism.

*Some are single cell organisms (yeast)

*Some are multi-cell organisms (mushrooms)

*Many are extremely valuable:

-yeasts give us bread and alcohol

-mushrooms.

*Can cause disease by releasing enzymes that damage cells or by producing toxins. Some mushrooms produce VERY deadly toxins.

Fungi

Fungal Diseases-Candidiasis.-Athlete’s foot - Tinea pedis-Jock itch - Tinea cruris-Nail fungus - Tineu unguis-Ringworm-Histoplasmosis-Over-the-counter medications are usually effective for mild

infections, except of the nails.-Systemic treatments can be prescribed for serious infections,

including the nails, and for histoplasmosis.

Fever: Three stages : effervescence fastigium deffervescence Five kinds of fever: *Sustained fever.

*Remittent fever: one that shows significant variations in 24 hours but without return to normal temperature. ,

*Intermittent fever: an attack of malaria or other fever, with recurring fever episodes separated by times of normal temperature ,

*Relapsing fever: alternating periods of fever and apyrexia, each lasting from five to seven days.

*Saddle type fever.

*Irregular fever.

Common symptoms and signs

Infectious Diseases

Mechanism of Fever

• Temperature is ultimately regulated in the hypothalamus. A

trigger of the fever, called a pyrogen, causes a release of

prostaglandin E2 (PGE2). PGE2 then in turn acts on the

hypothalamus, which generates a systemic response back to

the rest of the body, causing heat-creating effects to match a

new temperature level.

• A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body.

• The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen.

• Cytokines (especially interleukin 1) are a part of the innate immune system, are produced by phagocytic cells, and cause the increase in the thermoregulatory set-point in the hypothalamus. Other examples of endogenous pyrogens are interleukin 6 (IL-6), and tumor necrosis factor-alpha.

Mechanism of Fever

Rash eruption Date of eruption 1st: chickenpox 2nd: scarlet fever 3rd: smallpox 4th: measles 5th: typhus 6th: typhoid fever Location of eruption Form of rash Exanthema : *maculo-papular rash: A maculopapular rash is a flat, red area on the

skin that is covered with small confluent bumps e.g. measles.*Petechia: *Vesiculo-pustular rash *Urtecaria. Enanthema

Common symptoms and signsInfectious Diseases

Toxemic symptoms Mononuclear phagocyte system reactions Hepato- splenomegaly Lymph nodes enlargement Clinical types

acute, sub acute, mild, common, severe, fulminant, typical, atypical, abortive, ambulatory

Infectious DiseasesCommon symptoms and signs