Chapter One: The Nature of Plagues
- Incubation period: interval of time required for development of a disease
- Latent period: seemingly inactive period between exposure to an infection and subsequent illness
- Parasite virulence: capacity of a parasite to cause disease
-Bacteria, fungi, protozoa – single cell parasites
- Herd Immunity - the state in which immunization levels are so high that even the small minority not immunized will still be protected.
- Parasites – Entities that are unable to survive on their own (life dependent) and require another living being for their nourishment; parasitism
is not disgusting, simply a means to an end. We do the same – eating and breathing – in order to survive.
- R0 - basic reproductive ratio of the disease or the multiplier of the disease.
- Transmission – the movement of a parasite from host to host – whether by direct or indirect means
- Types of parasites: virus, bacteria, microparasite, macroparasite.
- If the value for R0 is larger than 1, the “seeds” of the infection will lead to an ever-expanding spread of the disease – an epidemic or a
- If the value for R0 is less than 1, each infection produces few than one transmission stage and the parasite cannot establish itself.
- Three factors that influence the occurrence of a disease: host, environment, agent.
Portal of Entry:
- Dermal – through the skin ex. fungus. , Ingestion – through the mouth, Inhalation – during respiration. - Aspiration – airway entry.
- Clinical disease: Classic and severe disease, moderate severity mild illness, Subclinical disease: infection without clinical illness
(asymptomatic infection; shows no symptoms), exposure without infection.
- Plagues derived from ‘plaga’ (to strike a blow that wounds), epidemic (Greek origin) ‘epi’ (among) and ‘demos’ (the people). Def. of plague:
highly infectious, usually fatal epidemic disease.
Legionnaire’s Disease Outbreak – Philadelphia 1976
- Peter Turner, WWII veteran, fell ill following a stay at a hotel in Pennsylvania for a legionnaires’ convention.
- Early symptoms: high fever, chills, headache, and muscle ache and pains, dry couch, chest pains, shortness of breath, vomiting, and diarrhea.
- Final symptoms (a week later): lungs filled with fluid and pus, confusion, disorientation, hallucinations, and loss of memory.
- 221 others legionnaires also became ill and 33 of them including Turner died of pneumonia.
- Pathway of spread of disease: *aspiration* of bacteria (called Legionella) in *aerosolized* water from AC, while in lobby of the Bellevue-
- 11,000 documented cases of Legionnaire’s disease annual in the US and estimates of 100,000 with a fatality rate of 15%.
Toxic Shock Syndrome (TSS)
- Mary Benton. Symptoms: vomiting, high fever, light-headedness and fainting, sore throat, muscle ache. A day later, rash appeared and eyes
become blot-shot. Within 3 to 4 days, confusion, fatigue, weakness, thirst, rapid pulse, skin became cool and moist, rapid breathing. Followed
by sudden drop in BP.
- She died within 48 hours while under care from multiorgan failures. Bacterium staphylococcus aerus found in vaginal sample.
- From 1979 – 1996 in affected 5296 women, average age – 22, with peak death rate of 4%.
Chapter 2 – Plagues, the Price of Being Sedentary
- Approximately 5,500 years ago, Uruk, was established in Mesopotamia (present-day Iraq).
o First undisputed city- place where farmers do not exist.
- Three revolutions: tool-making, agricultural, scientific/industrial revolution.
Chapter Three: Plagues of Antiquity
- Plagues first recorded when we became farmers.
- Characterised by parasites with long lived transmission stages
- The Pharaohs’ Plague (Blood Fluke or snail fever or endemic hematuria or schistosomiasis or bilharzia) à
à 1900 BC
- Arman Ruffer (1859-1917) found many calcified eggs of blood fluke in the kidneys of many mummies.
- Fossil snails have been found in the well water of Jericho (fossil snails are capable of transmitting blood fluke disease).
- Blood fluke is not a fatal disease, but a corrosive one.
- Napoleon’s army during the invasion of Egypt (1799-1801) were the first Europeans to get this disease.
- In 1851 Theodor Bilharz found connection b/w hematurai and parasite when worm found in man’s blood vessel during an autopsy.
- He named the worm Distomum (meaning “two mouths”).
- The name was changed to Schistosoma (“from the Greek words schisto [“split”] and soma [“body”]”).
- The snails Bulinus and biomphalaria were identified as the vectors. The infection was transmitted by bathing in infested water.
- The adult worms develop in blood vessels close to the bladder and small intestine are ~10 mm in length.
- The passage of eggs through the bladder wall and small intestines that causes bleeding and gives the sign of hematuria.
- The eggs spread throughout the body via bloodstream and accumulate in various organs. The eggs also scatter up and block the normal
blood flow which can lead to tissue death.
- The earliest signs of this disease occur in 1-2 months and are: fever, chills, sweating, headache, and cough.
- In 6-12 months, the accumulation of organs creates organ enlargement (especially the liver and spleen), and abdomen to become bloated,
appetite diminishes, blood loss leads to anaemia, and there is dysentery”.
- Schistosomiasis is an arithmetic disease: how severe the symptoms are depends on how many worms there are.
- Current diagnosis for schistosomiasis is by examining stools and urine under microscope and finding eggs.
- Fresh water, sanitary waste removal, and fresh water supply for bathing are good ways to reduce human exposure. Also irrigation channels
lined with cement to keep snails out and keep water away from snails for 2-3 days, the time for miracidia to go away.