They hygiene movement world wide at the end of the 1800s world wide played a major impact on improving health. Prior to 1900 with the poor elimination of feces, food, and lack of individual hygiene lead to massive epidemics associated with vermin.
By Edal Anton Lefterov - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16005971
Rates have been a common plague of mankind since the dawn of man. It appears that the Plague was spread world wide in relation to the spread of rats. A major reason for this has been the lack of sanitary controls, and before the past century rodenticide was not very effective. During the past century control of rats have been improved. Also there has not been a major outbreak of plague for a few centuries.
One of the major afflictions of vermin is that of mosquito born disease. Early this century, for example with the building of the Panama canal, thousands died as the result of mosquito born disease such as yellow fever. Massive drives have taken place to reduce the breeding grounds for Mosquitos. DDT played a significant role in mosquito reduction, yet at the same time the environmental damage was seen. Mosquito born disease such as Dengue, Zika, and Malaria are still being fought. However, the number of deaths of Mosquito born disease have been markedly reduced.
One of the major sources of disease is flies and horse droppings. Before Automobiles horses were the primary means of transportation. However, there was not a means to rapidly clean up the droppings. Flies love droppings as only 50% of the nutrients that go in a horses month, come out the back of the horses. The droppings breed bacteria and flies carry these germs into houses. Fortunately sanitation methods have reduced droppings, also the reduction of horses as transportation with cars and bicycles reduced dropping and flies carrying disease.
Once again, the world should be proud of what it has accomplished with hygiene.