**2. Historical impacts of military operations**

While the preceding examples are broadly based and were influenced by the general movement of people and goods, military operations have directly or indirectly influenced the regional and global spread of diseases. When militaries invade new areas, they are exposed to new ecological habits, tend to cause the displacement of people including civilians and military personnel, and modify the local infrastructure, which may promote disease or disease re-emergence. For example, during the Siege of Caffa in 1346, members of the Mongol Tartar Army are thought to have introduced plague to the residents of Caffa, either intentionally by the hurling of plague infected bodies over the walls, or unintentionally through rodent to rodent transmission. Infected residents and military personnel fleeing the city by boat are thought to have transmitted the disease to Mediterranean ports, where it rapidly spread throughout western Europe [11]. Evidence indicates smallpox was also instrumental in affecting outcomes during military campaigns in the New World. For example, because of the decimation of the native people due to the introduction of smallpox by the Spanish, Hernan Cortes was able to conquer the Aztec Empire and much of modern Mexico. Similarly, during the Pontiac Rebellion and the siege of Fort Pitt, Field Marshall Amherst and Colonel Henry Bouquet of the British Army are thought to have used smallpox inoculated goods such as blankets to transmit smallpox to the Native Americans to expatriate them from the territory [12]. While impossible to prove, this act and the incidental exposure of Native Americans in the area to smallpox may have been responsible for the deaths of up to 1.5 million people [13].

75 to 200 million people across Europe [2], the importation of smallpox to the America's in the fifteenth through nineteenth centuries [3] and cholera transported to the Baltics, Mexico and the United States by troops, ships and immigrants in the 1830's [4]. Examples of vector and vector borne-disease invasions facilitated by the movement of people include species of the *Aedes* mosquito, to include *Aedes aegypti* thought to have been brought to the Americas during the slave trade [5] and which is the primary vector of the recently introduced Zika virus in the western hemisphere, and *Aedes albopictus*, a competent vector of arboviruses such as West Nile virus, dengue and yellow fever, thought to have been introduced to the New World since 1930, and *Anopheles* species to include *Anopheles gambiae* which was the vector responsible for importing *Plasmodium falciparum* malaria from West Africa to South America in 1930 [4]. All are thought to have been brought from Africa and Asia to the Americas through the transport of goods and people by ships and airplanes. More recent examples include the introduction of

Another aspect of increased mobilization is the speed at which diseases can be spread. While the speed of spread may be affected by the causative agent, there is no doubt mass global transport may increase the pace at which diseases can be spread. For example, the 1957 influenza pandemic which originated in China was able to spread from its epicenter to a global distribution within 6 months due to regular air travel across the globe [7]. Similarly, severe acute respiratory syndrome (SARS), a disease caused by a coronavirus, was able to spread from a single source in southern China to people in 26 different countries within the course of 3 months [8]. Intense monitoring and isolation of infected individuals may have reduced the transmission and avoided another large-scale pandemic. While both influenza and SARS are respiratory infections, the global spread of other types of diseases has been shown to have been facilitated by mass global transportation. One such disease is the Human Immunodeficiency Virus (HIV) and its associated disease Acquired Immune Deficiency Syndrome (AIDS). While genetic analyses indicate that HIV made the jump from chimpanzees to humans approximately 70 years ago [9] in western Africa, the disease started to spread in the 1970's and 1980's due to travel, especially of certain groups such as immigrants, mass goods transporters and military personnel. While the majority of HIV positive individuals still live in Africa, by 2016, an estimated 36.7 million people across 125 different countries were HIV positive. Due to movement of peoples, the disease increased from an estimated 10,000 to 300,000 cases to 36.7

While the preceding examples are broadly based and were influenced by the general movement of people and goods, military operations have directly or indirectly influenced the regional and global spread of diseases. When militaries invade new areas, they are exposed to new ecological habits, tend to cause the displacement of people including civilians and military personnel, and modify the local infrastructure, which may promote disease or disease re-emergence. For example, during the Siege of Caffa in 1346, members of the Mongol Tartar Army are thought to have introduced plague to the residents of Caffa, either intentionally

the East Asian tick to New Jersey in the eastern United States [6].

million cases in only 35 years [10].

86 Current Issues in Global Health

**2. Historical impacts of military operations**

Other diseases, while not used to fight a war, have impacted the outcome of wars or even been used as a reason to start wars. The British defeat at the Battle of Cartagena in 1741 by the Spanish is thought to have been facilitated by the substantial loss of British sailors and troops to disease, particularly yellow fever. The British also lost a substantial number of soldiers to yellow fever during their peaceful occupation of Havana, Cuba during the Seven Years War, losing more men than they did in operations in North America during the same time [14]. Other armies were not immune to the impacts of yellow fever. From 1801 to 1803, Napoleon's largest expeditionary force was destroyed by yellow fever during the Haitian-French War, with over half of the deaths caused by yellow fever [15]. Beginning in 1894, the southern US began to experience an outbreak of yellow fever. The source was thought to be Cuban immigrants and fishermen operating in US waters. US government officials sought to curb the outbreak in the US by sending epidemiologists to Cuba to try and reduce a concurrent outbreak in Cuba. When the outbreak continued, the US officials approached Spain to address the outbreak. However, the Spanish response was to quash a rebellion occurring in Cuba at the time, increasing the cases of yellow fever. As a pretext to stop the outbreak, on April 25, 1898, the United States declared war on Spain. In the lead up to the war, US trainees located in camps in the southern US also contracted yellow fever, seriously impacting the US's ability to wage war. By 1900, US researchers had determined yellow fever was caused by the bite of a mosquito and by 1901, yellow fever had been eradicated from Cuba [16].

During the early part of the twentieth century, influenza was the primary disease influenced by the massive movement of people. The primary factor driving this mass movement of people was World War I. From July 1914 to November 1918, more than 70 million military personnel were mobilized in support of the war effort [17]. During this time, a new strain of the influenza virus, H1N1, began to circulate among troops in Europe and was carried across the globe as troops moved from Europe back to their home countries. The disease spread rapidly through militaries, especially among camps found across the United States. At its height, the admission rates among these camps was 361 per 1000 individuals. This infection of training camps provided a ready source of movement of the virus back to Europe as troops moved back and forth [18]. At the height of the infection, over 500 million people were infected globally, and 50 to 100 million people died, resulting in a global reduction in life expectancy of over 10 years [4].
