DISEASE: A Pathological condition of body parts (or) tissue characterized by an identifiable group of signs & symptoms. INFECTIOUS DISEASE: Diseased caused by an infectious agents such as bacterium, virus, protozoan (or) fungus that can be passed on to others. (also communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness (i. e, characteristic medical signs/symptoms of disease). INFECTION: Is the colonization of a host organisms by parasite species. (occurs when an infectious agents enters the body and begins to reproduce may (or) may not lead to disease. INFECTIVITY: The ability of an organisms to enter, survive and multiply in the host. INFECTIOUSNESS OF DISEASE: Indicates the comparative ease with which the disease is transmitted to other hosts.
PATHOGEN: Infectious agent that cause disease (or) microorganism capable of causing disease. PATHOLOGY: The study of the structural and functional manifestations of disease. PATHOLOGIST: A physician who was specialized in pathology. PATHOGENICITY: The ability to cause disease. PATHOGENESIS: The steps (or) mechanisms involved in the development of disease. HOST: An organism infected by another organism.
VIRULENCE: The relative ability of an agent to cause rapid and severe disease in host. is used as synonym for pathogenic. is used to express a measure or degree of pathogenicity. is used in reference to the severity of the infectious diseases that are caused by the pathogens. Virulence factors: The physical attributes or properties of pathogens that enable them to escape various host defense mechanisms and cause disease.
Infectious diseases are a leading cause of death worldwide. Responsible for a quarter to a third of all deaths worldwide. Account for more than half of all death in children under the age of 5. Of the top ten causes of death compiled by the world Heath organization, five are due to infectious diseases. In addition to human toll, infectious diseases present a large financial burden.
Top causes of death, according to the World Health Organization report for the calendar year 2001
Top 10 Causes of death in the worldThe top ten causes of death according to the World Health Organization are responsible for 52% of the all deaths in the world; that is 30 million deaths per year. 10. Road traffic accidents Road traffic accidents cause 1,210,000 deaths per year, that is 2.1% of all deaths 9. Diabetes Diabetes causes 1,260,000 deaths per year, that is 2.2% of all deaths 8. Tuberculosis Tuberculosis causes 1,340,000 deaths per year, that is 2.4% of all deaths 7. Lung Cancer Lung cancer causes 1,390,000 deaths per year, that is 2.4% of all deaths 6. AIDS AIDS causes 1,780,000 deaths per year, that is 3.1% of all deaths 5. Diarrhoeal diseases Diarrhoeal diseases cause 2,460,000 deaths per year, that is 4.3% of all deaths 4. Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease causes 3,280,000 deaths per year, that is 5.8% of all deaths 3. Lower respiratory infections Lower respiratory infections cause 3,460,000 deaths per year, that is 6.1% of all deaths 2. Stroke and other cerebrovascular disease Stroke and other cerebrovascular diseases cause 6,150,000 deaths per year, that is 10.8% of all deaths 1. Ischaemic heart disease Ischaemic heart disease causes 7,250,000 deaths per year, that is 12.8% of all deaths
The World Health Organization collects information on global deaths by International Classification of Disease (ICD) code categories. The following table lists the top infectious disease killers which caused more than 100,000 deaths in 2002 (estimated).The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly everydisease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases includepertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratoryand diarrheal deaths.
Infectious agents have probably always caused disease in humans. Through the centuries, these disease have resulted in significant losses of human life. Small Pox has been described in ancient Egyptian and Chinese writings and many have been responsible for more deaths than all others infectious diseases combined. There is evidence that malaria and poliomyelitis have existed since ancient times. In the 14th Century, the bubonic plague (or) Black Death, killed about 20 million people in Europe alone. In the 20th Century, the 1918 influenza may have killed up to 50 million people world wide. Close to 20 million people have died of AIDS to date.
1973 – A young Bangladeshi girl infected with smallpox. A Pandemic (global epidemic) affects over an extensive geographical area. Plague of Justinian – (541-750) killed 50% & 60% - Europe population. The Black Death of 1347 to 1352 killed 25 million in Europe over 5 years. Smallpox, measles & typhus – 15th & 16th Centuries – Central & South America by European explorers – pandemic in Mexico (1518 and 1568) to fall 20 - 30 million. Smallpox killed 60 million Europeans during 18th Century Tuberculosis killed one-quarter of adult population of Europe in 19th Century. Influenza Pandemic (1918)(Spanish Flu) killed 25-50 million people . Now Influenza kills about 250,000 to 500,000 worldwide each year.
East German postage stamps depicting four antique microscopes. Advancements in microscopy were essential to the early study of infectious diseases. Ideas of contagion became more popular in Europe – through writing of the Italian monk Girolamo Fracastoro. Anton Van Leeuwenhoek (1632 – 1723) – Advanced the science of microscopy. John Snow and William Budd – demonstrated contagiousness of typhoid and cholera through contaminated water (mid-19th Century). Louis Pasteur – proved beyond doubt that certain diseases are caused by infectious agents & developed rabies vaccine. Robert Koch – provided the study of infectious diseases with scientific basis – Koch’s Postulates. Edward Jenner, Jonas Salk and Albert Sabin – smallpox & polio vaccines. Alexander Fleming - World’s first antibiotic Penicillin which Florey & Chain then developed.
Koch developed four criteria to demonstrate 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 to isolated from the infected experimental host.
BY DURATION: - Acute : develops and runs its cause quickly (has rapid onset followed by a relatively rapid recovery; Measles, mumps and influenza – etc.). - Chronic: develops more slowly (insidious onset) and is usually less server, but may persist for long indefinite period of time. (tuberculosis, leprosy (Hansen disease) and syphilis – etc.). - Latent : Characterized by periods of no symptoms between outbreaks of illness.(Herpes Infections) (Some come on more suddenly than a chronic disease but less suddenly than an acute disease: Subacute Diseases) eg., Bacterial endocarditis.
BY LOCATION: Localized Infection: Confined to a specific area of the body. Eg: Pimples, boils and abscess - etc. Systemic Infection: A generalized illness that infects most of the body with pathogens distributed widely in tissue. (Generalized Infection) Eg: Miliary Tuberculosis – etc. BY SYMTOMS/Evidence/Appearence:(ache or pain, a ringing in the ears (tinnitus), blurred vision, nausea, dizziness, itching and chills) Symptomatic : (Clinical) The patient experiencing symptoms. Asymptomatic : (Subclinical Disease) The patient is unware of because he or she is not experienceing any symptoms. (Eg: Gonorrhea, Trichomoniasis – etc.) (A sign of a disease : defined as some type of objective evidence of a disease) Palpating, Abnormal heart or breath sounds, blood pressure, pulse rate and laboratory results - etc.) Enlarged liver (Hepatomegaly) , Spleen (splenomegaly).
BY TIMINGS: Primary Infection: Initial infection in a previously healthy person. ( cause disease as a result of their presence or activity with the normal, healthy host, and their intrinsic virulence – to reproduce and spread) Secondary Infection: Infection that occurs in a person weakened by a primary infection.
MOST infectious agents that cause disease are microscopic in size an thus are called Microbes (or) Microorganisms: Different groups of agents that cause disease are: Bacteria Viruses Protozoa (Protists) Fungi Helminthes Prions
Agents that cause infectious diseases can be transmitted in many ways. Through the air Through contaminated food (or) water Through body fluids By direct contract with contaminated objects. By animal vectors such as insects, birds, bats etc., (Aedes aegypti mosquto – tranmit Dengue fever) Transmission may occur through several different mechanisms. Respiratory diseases and meningitis are commonly acquired by contact with aerosolized droplets, spread by sneezing, coughing, talking, kissing or even singing. Gastrointestinal diseases are often acquired by ingesting contaminated food and water. Sexually transmitted diseases are acquired through contact with bodily fluids, generally as a result of sexual activity. Some infectious agents may be spread as a result of contact with a contaminated, inanimate object (known as a fomite), such as a coin passed from one person to another. While other diseases penetrate the skin directly
The Incubation Period : Time between infection and appearance of signs and symptoms. The Prodromal Period (or) Phase: Mild, nonspecific symptoms that signal onset of some disease. The Period of ILLNESS (or)Clinical phase: A person experiences typical signs and symptoms of disease Decline Phase: subsidence of symptoms. The convalescent Period (or) Recovery Phase: Symptoms have disappeared, tissues heal and the body regains strength.
Production of poisons, such as toxins and enzymes that destroy cells and tissues. Direct invasion and destruction of host cells. Triggering responses from the host’s immune system leading to disease signs and symptoms.
ENTRY: into the body Penetration of skin or mucous membranes Inoculation of pathogen into bodily tissues Inhalation (Respiratory tract) Ingestion (Gastrointestinal tract) Introduction (Genitourinary tact) or (directly into the blood/blood transfusion). Use of shared needles by intravenous drug abusers. ATTACHMENT : To some tissue(s) within the body. MULTIPLICATION: In one location of the body (Localized infection) or multiply throughout the body (systemic infection) INVASION/SPREAD EVASION OF HOST DEFENSES DAMAGE TO HOST TISSUE(s): The damage may be so extensive as to cause the death of the patient
Extreme fatigue which may be ongoing for more than 2-3 months. Continued weight loss. Low grade or spiking fever Night sweats and chills Vague body aches and pain
Vaccines Antimicrobial drugs Good Personal Hygiene and Sanitation Protection against mosquitoes Quarantine
Emerging diseases are those that have recently appeared within a population, (or) whose incidence (or) geographic range is increasing rapidly. Disease can emerge (or) re-emerge due to: Appearance of a previously unknown agent. Evaluation of a new infectious agent. Spread of an infectious agent to a new host. Spread of an infectious agent to new locations. Acquisition of resistance to antimicrobial drugs. Deliberate introduction into a population.
The medical treatment of infectious diseases falls into the medical field of Infectiology and in some cases the study of propation pertains to the field of Epidemiology.Initially diagnosed by Primary care physicians or Internal Medicine specialists.(general practitioners, laboratory scientists, Immunologists, bacteriologists and other specialists).An infectious disease team may be altered when: The disease has not been definitively diagnosed after an initial workup. The patient is immunocompromised (e.g., AIDS or after Chemotherapy) The infectious agent is of an uncommon nature (e.g. tropical diseases) The disease has not responded to first line antibiotics. The disease might be dangerous to other patients, and the patient might have to be isolated.