So I’m sure by now you will have heard of the Zika virus. An obscure virus discovered in the late 40s, it has sky-rocketed to everyone’s attention recently with its potential links to the birth-defect microcephaly and the neurological disorder Guillain-Barre syndrome. In response, a number of South American nations have asked women to not get pregnant, apparently taking a leaf from the the US’s famously successful absitence campaign.

In response, some are predicting that the extremely conservative governments in the region will have to loosen their restrictions on abortion. If this were to occur, it would be a large change for the region. It would not, however, be the first time mosquitoes have played a significant role in the course of history.

One of the most deadly mosquito borne diseases is Yellow Fever. These days, 85% of those who contract it have no or mild symptoms. For the other 15%, there is no treatment and even with modern medicine, up to 50% will die. Horribly. Vomiting blood, which one scholar describes as looking “like coffee grounds” (p. 110). Charming.

Nevertheless, whilst unfortunate for sufferers, that symptom is great for historians as it is distinctive.¹ This allows historians to track its effects across history, particularly in the Caribbean.

For our purposes, the most important thing about Yellow fever is that although it has a high mortality rate, if you manage to live through it, you will be immune to it for life. This, combined with the fact that children generally only get minor symptoms of the disease, means that any population that has grown up around it will largely be immune, whilst any population that enters a Yellow Fever area is going to have a bad time. This is broadly similar to malaria where, while you don’t get immunity for life, each time you get it, you become a little more resistant to the disease.

What does this mean for history? In the Early Modern Period,² for a variety of reasons that I don’t have time to go into here, the British Empire was waxing in the Americas, whilst the Spanish Empire was waning. Nevertheless, gold and silver were still flooding out of Spain’s colonies.

One its key possessions was Cartagena in Colombia, a bustling port city. Knowing it was a prime target, the Spaniards had the city well defended. Fortifications were layered, with troops able to give ground in pieces during the course of the siege. This was crucial, for while the fortifications at Cartagena were strong, the British were arriving with 29,000 men against just over 4,000 Spaniards, of which just over half were professional soldiers.

The attack began on the 13th of March 1741. At first the British out gunned the Spanish, blasting two minor forts into submission. Then they began to falter. The British forces launched a spectacularly inept assault against the key fort guarding the city. Many of the soldiers abandoned their ladders on the trek through the jungle. Those that did bring their ladders quickly found that they weren’t tall enough to scale the walls.

Even so, it was disease that took the real toll. By the time the fighting ceased, the British had lost over 8,000 men, and McNeill estimates that only 6% of casualties were due to fighting. And things only got worse. After retreating from Cartagena, “unaccountably undeterred” (p. 166) the British forces attempted to raid several other Spanish possessions in the Caribbean. Again, disease continued to scour the British ranks. By the time the British returned home, of the 29,000 in the force, 22,000 are thought to have perished. Only 1,000 of them are thought to have been direct casualties of war.

Possibly the most astounding aspect of the whole affair is, despite Erica Charters’s counter-claim, the utter lack of compassion shown for the rank and file. Admittedly, they did often build hospitals and, where possible, provided fresh fruit. Though as pointed out by Harrison, this was largely for reasons of economics more than anything else—as warfare became more specialised, training new troops became more expensive. Nevertheless, such mortality was generally seen as “the inevitable cost of war and commerce in a hot climate” (p. 16).

Whilst this has been a single example of the effects of mosquito borne viruses on history, it is far from the only one. Mosquitoes proved a valuable ally to the home side in almost every conflict in the Caribbean, from assaults on the French possessions of Martinique and Guadeloupe, to the American Revolution itself. Even when the British were victorious, such as with the invasion of Havana in 1762, after victory, the troops garrisoned there lost so many men to disease during the occupation, that Britain had to trade it back as a concession after the war had ended.

And to think, all of that didn’t even include the fact that mosquitoes make the single most annoying sound in the world. Nevertheless, they serve as an excellent reminder that for all we tend to focus on the movers and shakers of history, often the smallest things can have gigantic impacts.

Academic Sources

Charter, E 2014, Disease, war, and the imperial state : the welfare of the British armed forces during the Seven Years’ War, University of Chicago Press, London.

Harrison, M 2010, Medicine in an age of Commerce and Empire: Britain and its Tropical Colonies 1660-1830, Oxford University Press, Oxford.

McNeill, JR 2013, Mosquito Empires: Ecology and War in the Greater Caribbean, 1620-1914, Cambridge University Press, New York.

McNeill, JR 2013, “Mosquito Revolutions: Disease, War, and Independence in the U.S. South, Haiti, and Venezuela, 1776-1825”, Juniata, vol. 14, 2014, pp. 107-123.