HLTA01 - Chapter 3

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University of Toronto Scarborough
Health Studies
Caroline Barakat

HLTA01 Plagues and People: Chapter 3 - Many agricultural practices (plants, animals) were sustained by the Nile - People of Egypt had gotten snail fever - Civilization at this time depended on the water of rivers and the Nile for their farming o The water was favorable for snail fever caused by the blood fluke - Blood fluke disease was known as the “Plague of the Pharaohs” o Not fatal o Seasonal problems and then moved to all year problem - Civilization began to collapse due to agriculture and copper based weapons - Source of snail fever was unknown because the transmission stages of the parasites were microscopic o Nothing was invented at the time to see the stages o Eggs, miracidia, and cercariae (parasites) o The adult worms were also very tiny  The lived in small blood vessels Search for the Destroyer - Blood fluke disease -> snail fever -> endemic hematuria o Feces, urine, water, snails, and a flatworm - First people to experience the disease were the troops in Napoleon’s army (1799-1801) - Symptom – bloody urine o Baron Jean (military surgeon) had believed that this symptom was due to the high heat - 1851; Theodor Bilharz – discovered a connection between the disease and parasites o Found worms in blood vessels during an autopsy on a young man - The disease is now called schistosomiasis/ bilharzias - He saw microscopic egg with a pointed spine in female worms o They were found in the bladder and embryos were found in the eggs o The eggs released ciliated larva that swam around for around an hour and then disintegrated - 1863; Jon Harley – found shistosome eggs in blood-tinged urine o He didn’t know how the disease was transmitted - Suspected that humans got the disease by eating infected snails or drinking water that was contaminated by the ciliated larvae (miracidia) - 1870; Spencer Cobbald –stated that eggs hatched in fresh/ brackish water rather than in urine - 1904; Japanese physicians o Found related blood flukes (schistisoma japonicum) o Infected humans o The eggs didn’t have a spine - 1905; Patrick Monson – found eggs with the spines on the side (schistisoma mansomi) - These were the 3 known species of human-infecting blood flukes - Miracidia able to penetrate freshwater snails - Tailed larvae (cercariae) come from infected snails o Directly penetrated mice skin in experiments - WWI troops/ soldiers caught the infection by bathing in infested water - Doctors were still unsure if the infection could be transmitted by ingestion o Leiper used an acid similar to stomach acid and found that the cercariae were killed in it - Leiper proved that S. mansomi and S. haematobium were different o Cercariae hatched from biomphalaria – eggs with lateral spines o Bulinus – eggs with a terminal spine - S.mansomi – found in the liver - S.haematobium – found in the bladder - Cycle of snail fever o Eggs released larva in fresh water, miracidia found appropriate/ suitable snails and penetrated soft tissues (in their feet), migrated to liver and formed into sporocyst, parasites increased by asexual reproduction (6-7 weeks), snails shed fork-tailed cercariae which swam and penetrated human skin, developed into adult worms (5-8 weeks) Snail Fever, the Disease - Adult worms were about 10 mm in length - Males; had a groove going lengthwise(gynecephoric canal) where the female worm resided o They both had two suckers; one at the head and one at the end - Adult schistosomes live in blood vessels close to bladder and small intestine - Paired worms (form groove) move to smaller veins o Female worms leave fertilized eggs - Pathology results from eggs not worms - Eggs moved to the veins’ walls and bladder or intestine o Pushed there from the host’s inflammatory response - Bleeding – caused by eggs passing through the bladder - Eggs are eliminated by urine or feces after entering bladder/ intestine o However over 2/3 of the eggs stay in the veins because they are washed back by the blood stream o They then scatter around the body and stay in various organs (mostly in liver and spleen) - Amount of eggs blocks normal blood flow – lead to tissue death - Earliest signs of infections o 1-2 months - Fever, chills, sweating, coughing o 6 months to 1 year later – appetite diminishes, and the amount of blood loss leads to anemia  Eggs produce organ enlargement - Severity depended on the amount of worms and eggs present Where Snail Fever is Found - Wars and human migration o Blood flukes of East African lakes to the Nile River o Distributed along trade routes - Possibly introduced into America by African slaves - Present day there are about 200 million people infected with schistosomes - Infectious disease is still continued o Although people use the water for working, bathing, drinking, washing clothes and swimming, they may also sometimes use it as an outdoor toilet o Highest incidence of the disease is found in children o Aswan High Dam of England  Favorable conditions for snails carrying schistosomes - Disease is associated with agriculture o Also been a military problem (U.S. troops) - Originated most likely from animals in rain forests - Skin rash and pustules are the furthest they can go now because they can’t migrate past the human skin (cercariae) Snail Fever Today - Light microscope - Prevention – education on disease and its transmission process o Providing safe water supply and sanitary disposal of human wastes - Treatments; 1918 (tartaremetic compound), 1929 (stibophen injection) o Both resulted in many deaths - Praziquantel (biltricide) - No preventive vaccine or drug for the disease - Disease will continue to live if people continue to urinate and defecate in the same water where vector snails reside and expose their bare skin by using the water for agricultural purposes Plague of Athens - Land and climate in Greece was poor o Resulte
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