Zoonoses, diseases that are transmitted from animals to humans, stem from bacterial, viral, parasitic, or fungal infection of an animal host that spreads to humans through bite, scratch, or ingestion.  Zoonotic diseases have had a major impact on human civilization throughout history and have shaped modern societies, governments, and farming practices.

Plague

Plague is one of the most devastating human diseases of all time. Plague is caused by the bacteria Yersinia pestis and is transmitted to humans through the bite of a flea. Plague is carried by small rodents such as rats, mice, and squirrels, which have lived among humans and their food supplies for centuries. Plague has had an enormous impact on human civilization, effecting art, literature, culture, and even human populations.

Although the presence of plague has been noted throughout human history, there have been three major epidemics that have been devastating to the human population. The first epidemic, The Justinian Plague, began in the middle of the 6th century in the Byzantine Empire. Over a 200-year period, it is thought that nearly 25 million people died of plague. The second epidemic, referred to as The Great Plague or the Black Death, occurred during the 14th century. The Great Plague began in China and travelled by established trade routes throughout Asia and Europe, ultimately killing millions of people and wiping out 60% of the population of Europe.  The third plague, The Modern Plague, began in China in the late 19th century and eventually killed 10 million worldwide. Rat-infested shipping containers and merchant ships, along with rat fleas, are considered to be likely reasons for the spread of plague. Today, outbreaks of plague still exist in parts of Asia, Africa, and western regions of the United States, which can be treated with antibiotics.

Bovine Tuberculosis

Bovine TB is caused by the Mycobacterium bovis bacteria and is transmitted to humans through consumption of unpasteurized dairy products or direct contact with an infected animal.
 

Bovine tuberculosis (TB) was once a significant cause of death in 19th century Europe and North America.  The large number of deaths were thought to be associated with the urbanization of cities and towns, which moved people farther away from the rural farmland where milk was produced and increased the time between harvesting and delivery of milk to consumers.  This increased time from harvest to consumption provided ample opportunity for bacteria to grow and replicate to unsafe levels.

In 1882, the German microbiologist Robert Koch identified bovine TB as an infectious threat to humans. In Great Britain, A Royal Commission of Tuberculosis was established to tackle this issue. However, it was not until 1907 when the Royal Commission declared that TB was transmissible through infected milk and measures should be taken to prevent consumption of contaminated milk. Early efforts at eradicating TB in Great Britain focused on management of infected cow herds, by improving living conditions and removal of cows known to be infected. However, rates of bovine TB were still high, and from 1912 to 1937, up to 65000 people are though to have died in Great Britain alone.

Thanks to the efforts of the French scientist, Louis Pasteur, the process of pasteurization was developed to kill microorganisms in milk and other beverages using heat. In 1925, pasteurization of milk was proved to be a safe and effective means of removing dangerous pathogens from raw milk.  Shortly after, pasteurization of dairy products to increase public safety became more common in developing countries.  The United States instituted mandatory pasteurization of milk for public consumption in the 1930’s, an effort spearheaded by Dr. Alice Catherine Evans from the U.S. Department of Agriculture.  In 1943, Dr. G. S. Wilson of the London School of Hygiene and Tropical Medicine declared that pasteurization of milk is the only immediate solution for supplying safe milk to the British public.  In the 1950s, British government entities instituted a compulsory TB eradication plan that focused on cattle testing and herd management, and pasteurization of commercially sold milk soon followed.