AIDS Lec 1 Epidemics

Ch.1-2

Epidemic

quick widespread occurrence of infectious disease in community (like smallpox, plague, measles)

Plague of Ashdod

painting by Nicolas Poussin about stolen Ark of the Covenant by Philistines during battle in Samuel 1, Old Testament

Bubonic Plague

bacterial infection that killed thousands in Europe, swells the lymph nodes, armpits, groin, and neck

Plague of Athens (430 BC)

-pustular rash, high fever, and diarrhea

-attributed to smallpox, typhus, or measles

-during Peloponnesian War (Athens lost to Sparta)

Plague of Justinian (542-543)

-infection in port cities of the Roman Empire

-lasted 200 years

-25-50 million dead

-bubonic plague (Yersinia pestis)

-led to Dark Ages

-defeated by Visgoths, then Muslims

Antonine Plague (165-180 AD)

-devastated by Roman Empire

-suspected to be smallpox or measles

-killed ~1/3 of the population

Black Death (1346-53)

-75-200 million people died

-likely pneumonic plague (Yersinia pestis)

-led to fear of foreigners

Smallpox Epidemic (1518)

-Europeans brought smallpox to the New World

-33% killed in a few months

-reduced Aztec population from 25-30 M to 1.5 M

Girolamo Fracastoro (1546)

-proposes that epidemic diseases are caused by tiny

"spores" that could transmit infection by direct or indirect contact

Friedrich Gustav Jakob Henle (1840)

-proposes the Germ Theory: contagious diseases are spread by microorganisms (pathogens) that infect (enter) susceptible people to cause disease

John Snow (1854)

-epidemiology, mapped chlorera in London, water contaminated pump

Robert Koch and Friedrich Loeffler (1884)

-Koch’s postulates, 4 criteria relationship between microbe and infectious disease

Viruses

-require host cell machinery to replicate: (rhinovirus/the common cold, HIV/AIDS, influenza/the flu)

Bacteria

-prokaryotic, can be free living, some are obligate or obligate intracellular pathogens (Salmonella, Staphylococcus, Strep)

Fungi

-eukaryotic pathogens, typically extracellular, cell wall can be targeted by drugs (Candida/thrush, Athletes foot)

Protozoan Parasites

-unicellular eukaryotes, some can also be free-living, some must live inside host cells while others are extracellular in a host

Helminth Parasites

-multicellular “worms” aka helminths

Koch’s Postulates

1. Not found in healthy people 2. Isolated from host and grown in pure culture 3. Causes same disease in healthy person 4. Can be re-isolated from diseased and is original to causative agent

Epidemic Plague (1894)

-Yersinia pestis bacterium spread by rats & fleas in southern China & Hong Kong

Pandemic Influenza (1918)

-infected 500 million people across the world

-killed 50-100 million: 3-5% of the world's population

-predominantly killed healthy young adults (excessive immune response)

-spread exacerbated by World War 1

-lack of transparency by governments

-first use of masks

Polio (early to mid 20th)

-improvements in sanitation delayed exposure to the poliovirus

-infection of infants causes a mild gastrointestinal infection

-infection of children or adults causes paralytic disease

-50,000 deaths in 50 years

-vaccines developed in 1952 and 1957

Syphillis (early to mid 20th)

-sexually transmitted chronic infectious phase without symptoms

-untreated led to death

-“a social disease”

-blamed prostitutes & immigrants

-20,000 prostitutes quarantined or jailed during WWI

-army discouraged access to condoms

-cure in 1909

-the epidemic was only controlled 40 years later

-elimination of repressive approaches

-new antibiotics (penicillin)

Before Germ Theory

-warfare, strangers, changes in appearance (pustules, buboes)

-rapid death, high rates of death

-loss of military, agriculture & social structure

After Germ Theory

-infectious agent (germ), mechanism(s) of spread, manifestations of infection

Rate of Transmission

-efficiency of transmitting the infectious

agent

-two factors affect transmission rate:

Inherent efficiency (ease with which

the agent infects a susceptible host)

Encounter rate between infected and

uninfected persons

HIV

the pathogen* that can infect humans and

leads to AIDS.

HIV transmission

sex, injection drug use, pregnancy, occupational exposure, transfushion/transplant

Disease Syndrome

a set of signs & symptoms that occur together

during a particular type of illness

Stages of HIV

1. Asymptomatic but transmits 2. Incubation period (10+ years) 3. AIDS, progressive loss of immune system function

AIDS

-caused by the Human Immunodeficiency

Virus (HIV)

-Characterized by severe damage to the

immune system

-An important clue was the development of

a lung infection (pneumonia) caused by a

fungus called Pneumocystis in AIDs patients

Patients undergoing chemotherapy for

immune system cancers (lymphomas) also

got Pneumocystis infections

AIDS Consequences

-loss of key elements of the immune response

-“Secondary infections” caused by bacteria, protozoa, fungi, and other viruses (opportunistic infections) are often the cause of death

-loss of immune system also permits development of cancer:

lymphomas and Kaposi’s sarcoma frequently develop in AIDS patients

-brain cell damage from HIV leads to loss of mental function, referred to as AIDS dementia

Emergence

-observed clustering of cases of rare diseases (1981):

Pneumocystis carinii pneumonia, Kaposi’s sarcoma (cancer), persistent lymphadenopathy

-diverse risk groups suggested that AIDS is caused by an infection

-Gay men

-Hemophiliacs

-Injection drug users

-Pasteur Institute (France) Lymphadenopathy-Associated Virus (1983)

-National Cancer Institute HTLV-III (1984)

HIV causes AIDS

-persons having unprotected sex

-transfusion recipients

-persons with hemophilia

-sex partners of infected persons

-children born to infected women

-health care workers (by being stuck with a needle used on HIV-infected patient)

Which racial groups are more affected?

black, latino

Men and women are equally affected T or F?

true