infectious diseases

54
Dr Adam Ibrahim MBBS Amoud University Infectiou s Diseases

Upload: adam-ibrahim

Post on 03-Jun-2015

206 views

Category:

Documents


2 download

TRANSCRIPT

Page 1: Infectious diseases

Dr Adam Ibrahim MBBS

Amoud University

Infectious Diseases

LDSD
From BioEdOnline Christine Hermann PhD
Page 2: Infectious diseases

Introduction of infectious disease

Overview Classification of disease Stage of infectious disease Epidemiological aspects of infectious disease

(in a population and individual level) Pathogens Disease Laboratory diagnosis of infectious disease

Page 3: Infectious diseases

Overview

¨ Infection is the term used to indicate the presence of an infectious agent in an individual or population.

¨ Infectious diseases are the invasion of a host organism by microbes.

¨ Microbes that cause illness are also known as pathogens.

Page 4: Infectious diseases

¨ The most common pathogens are bacteria and viruses; some kinds of fungi and protozoa, also cause disease.

¨ An organism that a microbe infects is known as the host for that microbe.

Page 5: Infectious diseases

¨ Infectious diseases remain a leading cause of death and disability.

¨ Advances in the control of diseases such as tuberculosis (TB), malaria, and smallpox after the Second World War led to hopes that the threat from infectious disease would diminish.

Page 6: Infectious diseases

¨ Factors such as increasing international travel and trade, the breakdown of public health systems in some countries due to war or economic decline and growing resistance to existing antibiotics have meant that infectious diseases continue to be a significant risk to health

Page 7: Infectious diseases

¨ There has been ongoing progress in controlling some vaccine-preventable childhood diseases such as polio, diphtheria and invasive Haemophilus influenza type b infection (Hib).

¨ However, new previously unknown diseases have appeared in the past 25 years such as acquired immune deficiency syndrome (AIDS) and hepatitis C.

Page 8: Infectious diseases

¨ Well-known diseases such as measles have become more common again after a period of decline.

Page 9: Infectious diseases

Human activities that have led to the emergence and spread of new diseases

Encroachment on wildlife habitats. The construction of new villages and housing developments in rural areas brings people into contact with animals--and the microbes they harbor.

Changes in agriculture. Destroying rain forests.

Page 10: Infectious diseases

Uncontrolled urbanizationModern transport.High-speed globe-trotting. With

international jet-airplane travel, people infected with a new disease can carry the disease to the far side of the world before their first symptoms appear.

Page 11: Infectious diseases

Koch’s Postulates

¨ Koch developed four criteria to demon- strate that a specific disease is caused by a particular agent.1. The specific agent must be associated with every

case of the disease.2. The agent must be isolated from a diseased host and

grown in culture.3. When the culture-grown agent is introduced into a

healthy susceptible host, the agent must cause the same disease.

4. The same agent must again be isolated from the infected experimental host.

Page 12: Infectious diseases

Infectious vs. noninfectious disease

¨ Any disease caused by a pathogen is an infectious disease; any disease not caused by a pathogen is a non-infectious disease

¨ Not all infectious diseases are spread from host to host.

Page 13: Infectious diseases

¨ Not all infectious diseases are associated with pathogen infection of the host (e.g., intoxications can result from exposure to secreted toxin rather than the secreting organism).

Page 14: Infectious diseases

Classification Of Disease

¨ Diseases may be classified in a number of ways, many of which we will subsequently discuss,

¨ including:– Infectious disease– Communicable disease– Noncommunicable disease– Contagious disease

Page 15: Infectious diseases

Communicable disease

¨ A communicable disease is an infectious disease that may be passed from individual to individual.

¨ Yet, not all infectious diseases are considered communicable

¨ A more narrow definition of communicable disease is one that is infectious during the incubation or recovery (convalescence) periods of a disease

Page 16: Infectious diseases

Noncommunicable disease¨ A noncommunicable disease is an infectious disease

that is not spread from individual to individual but instead is acquired from an inanimate object or other species

¨ Noncommunicable infectious disease may be differentiated into three categories: Infections caused by opportunists arising from an

individual’s own microflora

Poisonings following ingestion of secreted exotoxins

Infections acquired from organisms found in the environment (other than from individuals of one's own species

Page 17: Infectious diseases

Contagious disease

¨ A communicable diseases that is easily passed from individual to individual is said to be contagious

¨ Yes, not all communicable disease are considered contagious (though certainly all contagious diseases are considered communicable)

Page 18: Infectious diseases

TYPES OF INFECTIOUS DISEASE

¨ Infectious disease can be described as being

Acute, chronic, sub acute, latent, or as an in apparent (subclinical) infection

Local, focal, or systemic

Septicemia, bacteremia, viremia, or toxemia

A primary/ secondary infection, super infection, or a mixed infection

Page 19: Infectious diseases

Classification of Infectious Disease¨ By duration

– Acute – develops and runs its course quickly.– Chronic – develops more slowly and is usually less severe, but may

persist for a long, indefinite period of time.– Latent – characterized by periods of no symptoms between outbreaks

of illness.¨ By location

– Local – confined to a specific area of the body.– Systemic – a generalized illness that infects most of the body with

pathogens distributed widely in tissues.¨ By timing

– Primary – initial infection in a previously healthy person.– Secondary – infection that occurs in a person weakened by a primary

infection.

Page 20: Infectious diseases

Phases of Infectious Disease

¨ Diseases caused by infectious agents usually run a standard course that is associated with different signs and symptoms.

¨ Before we describe these different phases of infectious diseases, we must first define the terms, “signs” and “symptoms.”

Page 21: Infectious diseases

¨ Signs of an infectious disease are characteristics of a disease that can be observed by examining a patient.

¨ They include things such as fever, coughing, rash, vomiting, and diarrhea.

¨ Symptoms, on the other hand, can be felt only by the patient. They include pain, headache, and nausea.

Page 22: Infectious diseases

STAGES OF INFECTIOUS DISEASE

¨ Infectious diseases tend to occur in stages including (in typical order) Incubation period

Prodromal phase (not typical)

Invasive phase

Decline phase

Convalescence period

Sequelae (not typical)

Page 23: Infectious diseases

Phases of Infectious Disease

¨ Incubation period – time between infection and the appearance of signs and symptoms.

¨ Prodromal phase – mild, nonspecific symptoms that signal onset of some diseases.

¨ Clinical phase – a person experiences typical signs and symptoms of disease.

¨ Decline phase - subsidence of symptoms.¨ Recovery phase – symptoms have disappeared,

tissues heal, and the body regains strength.

Page 24: Infectious diseases

Infection in Individuals – definition

¨ Depending upon the host-microbe interaction, infection can be: Silent (inapparent, asymptomatic, subclinical),

or

Overt, causing a disease of infection.¨ Silent or asymptomatic infections, such as

HIV infection during the early phase, can still be infectious.

Page 25: Infectious diseases

¨ A carrier is a person who is infected with an organism but shows no evidence of disease, although disease may have been present earlier

¨ Acute infection implies a 'short-lived' infection, such as influenza, with or without symptoms; the period of infectivity is also short.

Page 26: Infectious diseases

¨ Chronic infection refers to a 'long-standing' condition during which the pathogen continually replicates and the patient may be persistently infectious to others, e.g., hepatitis B infection.

¨ Latent infection refers to a persistent infection with the possibility of intermittent shedding of pathogens, e.g., varicella zoster virus causing shingles or herpes simplex virus causing cold sores or genital herpes

Page 27: Infectious diseases

Infection in Populations

¨ Endemic infection refers to infection or disease that occurs regularly at low or moderate frequency.

¨ Pandemics are global epidemics. The size of 'outbreaks is dependant upon factors such as the ratio of susceptible to immune subjects, period of infectivity, population density, etc.

Page 28: Infectious diseases

Spread of Infection

¨ With respect to the spread of infection, people can be divided in to : Those who are susceptible,

Those who are infected but are not yet infectious,

Those who are infected and infectious, and

Those who are immune.

Recovery from infection usually gives

immunity.

Page 29: Infectious diseases

Means of transmission

¨ Contact requires direct or indirect contact ( fomites, blood, or body fluids)

Food ingestion of contaminated food or water water

Airborne inhalation of contaminated air

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

Perinatal similar to contact infection, however, the contact may occur in uterus or during the delivery

Page 30: Infectious diseases

Robin Cochran-Dirksen (Many slides from BioEdOnline Baylor Christine Herrmann PhD)

Transmission of Infectious Diseases

¨ Agents that cause infectious diseases can be transmitted in many ways.– Through the air– Through contaminated food or water– Through body fluids– By direct contact with contaminated

objects– By animal vectors such as insects, birds,

bats, etc.

Courtesy of VOA

Chinese students wearing masks during a

SARS outbreak

Courtesy of CDC

Aedes aegypti mosquito Known to transmit

Dengue fever

Page 31: Infectious diseases

Incubation Period

¨ The incubation period is defined as the time between exposure to the onset of symptoms or other signs of infection.

¨ Diseases have incubation periods that vary widely

Page 32: Infectious diseases

Infectivity

Ability of agent to cause infection

Number of infectious particles required

In person-to-person transmission, secondary attack rate is a measure of infectivity

In person-to-person transmission, the higher the infectivity, the more secondary infections. For example, the infectivity of tuberculosis is low and the infectivity of smallpox is high.

Page 33: Infectious diseases

Pathogenicity

Ability of a microbiological agent to induce disease

Because the smallpox virus can produce disease relatively easily, it is considered to have high pathogenicity.

Polio has low pathogenicity.

Page 34: Infectious diseases

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

Page 35: Infectious diseases

Herd immunity

When the number of immune persons is high enough that it is unlikely that a susceptible person will have contact with an infected person

Level of immunity required is dependent on the characteristics of the infectious disease

Page 36: Infectious diseases

Pathogenic mechanism

¨ Direct tissue invasion¨ Production of a toxin¨ Immunologic enhancement or allergic

reaction¨ Persistent or latent infection¨ Enhancement of host susceptibility to

drugs¨ Immune suppression

Page 37: Infectious diseases

Pathogen

¨ The pathogens fall into five main groups:

1. Viruses

2. Bacteria

3. Fungi

4. Protozoa

5. Helminthes

Page 38: Infectious diseases

Definitions

¨ Commensalism: Literally `eating at the same table'! This refers to a neutral situation where the host and bacteria live together, but have no effect on each other's life cycle - either positive or negative..

¨ Parasitism: This describes an unequal relationship where one organism clearly benefits from an association to the detriment of another.

Page 39: Infectious diseases

¨ Opportunistic infection: This occurs when the normal human defences are so weakened that it allows infection to take place by organisms that would not generally be able to cause infection in a healthy human.

Page 40: Infectious diseases

¨ Nosocomial infection: These are infections that are transmitted in hospitals.

¨ Some of these may be opportunistic infections mentioned above affecting seriously ill patients, others, for example infections with Methicillin-Resistant Staphylococcus aureus (MRSA), may occur because of the special nature of the hospital environment

Page 41: Infectious diseases

Bacterial pathogenesis

¨ Host susceptibility¨ Bacterial infectivity¨ Host resistance¨ Genetic and molecular basis for virulence¨ Host mediated pathogenesis¨ Intracellular growth¨ Virulence factors

Page 42: Infectious diseases

Disease

¨ Disease is a disturbance in the state of health (of the host) wherein the body cannot carry out all its normal functions

¨ When an infection causes disease, the effects of the disease range from mild to severe

¨ Disease, or illness, is characterized by changes in the host that interfere with normal function

Page 43: Infectious diseases

Production of Disease

¨ Once a bacterium has entered the body, there are a number of ways in which it can cause disease.

Local Effects

Distant Effects( Endotoxin and exotoxins)

Evasion of Host Defences

Page 44: Infectious diseases

Virulence factors

¨ Properties of a pathogens that allow them to cause disease are termed virulence factors

¨ Virulence factors may distinguish a pathogenic microorganism from otherwise identical non-pathogenic microorganisms by allowing pathogens to invade, adhere to, and colonize a host, and then harm the host

Page 45: Infectious diseases

Types of virulence factors

¨ The following are types of virulence factors: Adherence Factors: Many pathogenic bacteria

colonize mucosal sites by using pili (fimbriae) to adhere to cells.

Invasion Factors: Surface components that allow the bacterium to invade host cells can be encoded on plasmids, but more often are on the chromosome.

Page 46: Infectious diseases

Capsules: Many bacteria are surrounded by capsules that protect them from opsonization and phagocytosis.

Endotoxins: The lipopolysaccharide endotoxins on Gram-negative bacteria cause fever, changes in blood pressure, inflammation, lethal shock, and many other toxic events.

Exotoxins: Exotoxins include several types of protein toxins and enzymes produced and/or secreted from pathogenic bacteria. Major categories include cytotoxins, neurotoxins, and enterotoxins.

Page 47: Infectious diseases

Laboratory diagnosis of infectious disease¨ Is based one or more of the following:

Direct examination of the specimen by microscopic examination or antigenic technique.

Isolation of organism in culture Sero – diagnosis.Molecular genetic detection.

Page 48: Infectious diseases

Laboratory diagnosis of bacteria and fungal infection¨ Microscopy : gram stain remain extremely

useful diagnostic technique because it is a rapid and inexpensive method. Isolation and identification of organism: blood culture , CSF culture . urine/stool/genital/throat/respiratory culture.

Page 49: Infectious diseases

Laboratory diagnosis of viruses infection By electronic microscopy Antigenic detection Viral isolation in culture Serologic detection Detection of viral genome by molecular

biology technique

Page 50: Infectious diseases

Laboratory diagnosis of parasitic infection.¨ Most parasites are detected by

– Microscopic examination of clinical specimen: – e.g. plasmodium, bobesai spp; leishmania spp;

helminthes egg, etc.– Blood smear – Fecal specimen.

¨ Serological diagnosis are good for trichinella, toxoplasmosis, and strongyloidiasis.

Page 51: Infectious diseases

Principles of Antibacterial Therapy

¨ age-appropriate antibiotic dosing and toxicities must also be considered.

¨ Specific antibiotic therapy based → microbiologic diagnosis → supported by antimicrobial susceptibility testing.

¨ Common practice is based on a clinical diagnosis with empirical use of antibacterial agents.

Page 52: Infectious diseases

Empiric use of antibacterial agents

¨ Appropriate empirical use of antibacterial agents in infants and children is essential.

¨ A complete history + physical examination+ appropriate laboratory + radiographic studies= specific diagnoses= empiric antibacterial use.

¨ Antibiotic action is related to achieving therapeutic levels at the site of infection.

Page 53: Infectious diseases

The Patterns Of Antimicrobial Resistance¨ Resistance to penicillin and cephalosporin

antibiotics.¨ Antimicrobial resistance occurs through

many modifications of the bacterial genome

Page 54: Infectious diseases

Thank you for your attention