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 Protozoa Bacteria Viruses Fungi Parasites

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 Climate, soil etc believed to make one sick Source: Infectious Disease Epidemiology, Nelson and Williams

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) Focus Sample Lens Leeuwenhoek

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 Typhoid 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

Development of vaccines Year Disease/organism 1798 Smallpox 1896 Cholera 1897 Plague 1927 Tetanus Tuberculosis 1955 Polio 1970 Anthrax 1998 Rotavirus Source: Infectious Disease Epidemiology, Nelson and Williams

Discovery of antimicrobial drugs 1928 – penicillin 1928 to 1962: 15 classes of antibiotics

Control of infectious diseases 1900: Annual Morbidity 2000: Annual Morbidity Percent decrease Smallpox 48164 100 Polio 16316 Diptheria 175885 1 Measles 503282 89 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