Infection and disease

Infection and disease

• Infection: Entry of “infectious” organisms inside the body, their multiplication

• Disease: Cell / tissue damage, signs and symptoms

All infections may not necessarily cause disease

Microbes come in different shapes and sizes

Bacteria

Parasites

Protozoa

Viruses

Fungi

Historical perspective

Evidence from mummies

Egyptian pharaoh Ramses V

Unknown child from Naples

Source: http://plaza.ufl.edu/

Egyptian art tells us about polio

Source: The Art Archive at Art Resource, NY

Supernatural explanations for infectious diseases

Source: Infectious Disease Epidemiology, Nelson and Williams

Climate, soil etc believed to make one sick

Hippocrates

• Dismissed supernatural explanations

• Seasonal changes in disease patterns

• Fever and swelling – immune response

Hippocrates (460-377 BC)

Fracastoro

• First to propose that infectious diseases were caused by invisible, minute, self-replicating seeds

• Proposed transmission by direct contact, air and through objects

• Described several infectious diseases including syphilis

(1478-1553)

Renaissance era in medicine(14-17 century)

Foundations of modern medicine

• Anatomy

• Physiology

• Circulation

• Brain

• Surgical instruments

• hygiene

Hospitals and hygiene

First microscope (1600s)

Leeuwenhoek

LensSample

Focus

First vaccine

• Edward Jenner (1749-1823)

• World’s first vaccine – against small pox

• Father of immunology

Louis Pastuer (1822-1895)

• Fermentation

• Pasteurization

• Vaccine development

Robert Koch (1843-1910)

• Koch’s postulates

• Gold standard in microbiology

• Fathers of Microbiology - Robert Koch - Louis Pasteur

Koch’s postulates

First set of rules on how to link a disease to an infectious agent. Still used

Several bacterial agents were discovered in the 1800s

Year Disease/organism

1874 Leprosy

1882 Cholera streptococcus

1884 Diptheria

1884 Typhoid

1884 Tetanus

1892 Gas gangrene

1894 Plague

Self-experimentation to prove Koch’s postulates

• Inoculate organism into one’s own body to prove disease etiology / pathogenesis

• Yellow fever / hookworms / Hepatitis E virus

Reservoirs and vectors

• Transmission of plague from rats to humans

• Transmission of yellow fever through Aedes aegypti

First established viral disease with obligate cycle in insect no human to human transmission

• Transmission of malarial parasite (Plasmodium falciparum through Aedes aegypti)

Disarming the microbe

• Alexander Fleming discovered penicillin in September 1928.

• World’s first antibiotic

“That’s funny”

Penicillin: Miracle cure

Terminology…• Incidence Fraction of a population that

newly contracts a disease during a specific time. (Eg. Influenza virus)

• Prevalence Fraction of a population having a specific disease at a given time. (eg. HIV)

• Endemic disease Disease constantly present in a population. (eg. Malaria)

• Epidemic disease Disease acquired by many hosts in a given area in a short

time. (Eg. Dengue epidemic in Delhi)

• Pandemic disease Worldwide epidemic (eg. Influenza pandemic).

Major pandemics

• Bubonic plague (1347-1351): ~ 200 million dead

• Influenza (1918-1919): ~ 100 million dead

Control of infectious diseases: 20th century

• Foundation of the Center for Disease Control and Prevention (CDC)

• Understanding disease biology/pathology

• Development of molecular microbiology

• Development of vaccines

• Development of antimicrobial drugs

Source: Infectious Disease Epidemiology, Nelson and Williams

Year Disease/organism

1798 Smallpox

1896 Cholera

1897 Plague

1927 Tetanus

1927 Tuberculosis

1955 Polio

1970 Anthrax

1998 Rotavirus

Development of vaccines

Discovery of antimicrobial drugs

• 1928 – penicillin

• 1928 to 1962: 15 classes of antibiotics

Control of infectious diseases

Disease 1900: Annual Morbidity

2000: Annual Morbidity

Percent decrease

Smallpox 48164 0 100Polio 16316 0 100Diptheria 175885 1 100Measles 503282 89 100

Role of vaccines and antibiotics

How does the future look? 15 classes of antibiotics

3 classes of antibiotics

BLEAK ; increase in drug-resistance /void in drug discovery

Normal microbiota and the host:

• Locations of normal microbiota on and in the human body

Normal microbiota and the host:

• Transient microbiota may be present for days, weeks, or months

• Normal microbiota permanently colonize the host

• Symbiosis is the relationship between normal microbiota and the host

Normal microbiota: how the host benefits ?

• Microbial antagonism is competition between microbes.

• Normal microbiota protect the host by: – occupying niches that pathogens might occupy– producing acids– producing bacteriocins

• Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect.

Microbes

• Are invisible to the naked eye

• Are everywhere around us, inside us, on us, in our food, in our homes, in the air we breathe and the water we wash in.

• Are mostly useful, but some are harmful

• Have been around for 3.8 bn years.

Microbes exist in huge numbers

In one single teaspoon of garden soil, there are over 100,000 microbes.

In 1ltr of seawater, there are over 1bn microbes.

On your skin there are more microbes than there are people in the world.

There are so many microbes, that scientists have only named <1% of them.

Microbes outnumber all other species and make up most of the living matter on the planet