Biology

Antonie van leeuwenhoek, first to observe microorganisms using a microscope. He invented more than 500 simple microscopes. Though they are not that much powerful as compound microscope but they rule the world for more than a decade. Leeuwenhoeks simple microscopes magnified objects to over 200 times actual size, with clearer and brighter images than any of his predecessors had achieved. He was the first person to observe company of living animalcules (bacteria) in tooth plaque. Of course, nobody else knew their significance in causing disease. His other discoveries included algae, blood cells, sperm cells, foraminifera, nematodes and rotifers. He observed blood flow in capillaries and the pattern of muscle fibers. In fact he initiated the field of bacteriology and microbiology without which Edward Jenner has no role in inventing the vaccine for small pox which was caused by variola. Edward Jenner of course a great scientist who saved so many lives by inventing vaccine for small pox but he could not consider as a all-time great microbiologist when compare to Antonie van leeuwenhoek who is considered as father of microbiology.
For finding out the vaccine the disease must be known and the organism must be isolated from a diseased organism and can be able to produce disease symptoms when introduced into a healthy organism. This can be otherwise famously known as Koch Postulates, developed in 19th century as general guidelines to identify  HYPERLINK httpen.wikipedia.orgwikiPathogen o Pathogen pathogens. Attempts made to apply Kochs postulates to the diagnosis of viral diseases at a time when viruses could not be isolated in culture, which is otherwise impossible.
Disease Epidemics
The massive outbreak of plague occurred in 1348-49 which had a long-term impact on socio economic conditions of Europe population. The main symptom of this plague is a swollen, painful lymph gland called a bubo, usually in the groin, armpit, or neck. So this can be otherwise called as bubonic plague. Actually it is a vector born disease, which can spread by fleas to humans from rodents. Millions of people in Europe died from plague in the Middle Ages, when human homes and places of work were inhabited by flea-infested rats. It is a disease of rodents caused by Yersinia pestis . The outbreak of disease occurred due to favorable weather conditions and less life spawn of the vector fleas.  Disease can be controlled by either reducing the flea or by reducing the rodent population. Reduce rodent habitat like rock piles, junk, cluttered firewood etc., which can reduce rodent population.
Some medical historians think that the bacterium became less virulent others that the disease vectors host became increasingly separated from human beings as brick houses replaced timber-framed dwellings others emphasize the importance of quarantine measures in restricting plague in Europe. The United States Centers for Disease Control (CDC) monitor these outbreaks, and make efforts to control the disease in rodent populations where it is still active. Plague still poses a significant threat to human health. The use of antibiotics such as tetracycline and streptomycin for the treatment of plague has been recommended by the WHO Expert Committee, which leads to the development of antibiotic-resistant Y. pestis strains. So several alternatives came into existence like immunotherapy, non-pathogen-specific immunomodulatory therapy, phage therapy, bacteriocin therapy, and treatment with inhibitors of virulence factors.