Introduction to Epidemiology 6th Edition by Ray M Merrill

Exercise 4

What did Snow observe regarding the association between city size and length of epidemic?

Step 1 of 2

Cholera is an intestinal disease and is caused by strains of bacterium Vibrio cholerae. Major symptoms of this disease include diarrhea, muscle cramps and vomiting. In severe cases, diarrhea leads to electrolyte imbalance and dehydration, due to excessive loss of water. It is both endemic (found in particular area) as well as epidemic (widespread occurrence) disease. Unhygienic food habits are the major cause of the transmission of this disease. Hence, it is prevailed more in the developing countries, where most of the poor people, drink, wash, eat, and sleep together.

Bacterium causing fowl cholera was grown in cultures, first by Louis Pasteur. He deliberately injected this culture into the fowl to confirm their action. When this culture was injected after two months to the fresh stock of fowl, they did not develop the disease, indicating that attenuation has weakened the bacterial culture.

When the fresh culture of bacterium was inoculated in the previously survived fowls, they first developed the disease and then recovered after sometime, indicating, that an organism who has already been exposed to a disease, does not get infected by it on second exposure.