Yellow fever is a serious viral haemorrhagic disease transmitted by infected mosquitos and endemic to tropical areas of Africa and Central and South America. In the 1800s the American South experienced yellow fever epidemics that killed thousands. People didn’t know what caused the fever or how it spread.

In 1888, a saloonkeeper named Richard McCormick living in Jacksonville, Florida fell sick with the dreaded disease. The townspeople acted swiftly sending McCormick into quarantine and burning all of his belongings, including the entire hotel where his saloon was located.

Despite these efforts at containment, one citizen after another fell sick and many died. The governor had the streets covered in lime and bichloride of mercury and at night barrels of tar were burned and ammunition was fired at the sky to rid the air of infection.¹

The yellow fever mystery was solved years before in the 1870’s when a Cuban epidemiologist named Carlos Finlay suggested that mosquitos transmitted yellow fever to humans. His ideas were dismissed as ludicrous.²

Then, in the 1900’s U.S. Army physicians James Carroll and Walter Reed decided to test Finley’s theories. Carroll allowed an infected mosquito to feed on him and developed yellow fever. Reed presented the findings to the medical profession and received much of the credit for “beating” yellow fever.³ 

This story illuminates how important it is for the health community to understand how different pathogens are transmitted. If the townspeople had understood that yellow fever is transmitted by infected mosquitos they would have behaved in ways that would have protected more people from contracting the disease (and they wouldn’t have burned down a hotel).

In this chapter, we’ll (A.) preview key terminology, (B.) discuss the chain of infection, and (C.) examine modes of transmission. We’ll end the chapter with (D.) some learning games  and a quiz.

Learning Objectives

Having completed this chapter you will be able to meet these learning objectives:

• Define these terms: Disease reservoir, portal of exit, mode of transmission, portal of entry, susceptible host, and zoonotic disease.
• List the three types of disease reservoirs.
• Compare and contrast active carriers of disease, with asymptomatic carriers, and passive carriers.
• Describe one portal of exit for a disease and one portal of entry for a disease.
• List three factors that make a possible host more susceptible to disease.
• Define these modes of transmission: Direct contact, indirect contact, droplet contact, vector transmission, and vehicle transmission.
• Compare and contrast direct contact with indirect contact.
• List five possible fomites that might convey disease.
• Describe one way infected droplets spread disease.
• Compare and contrast vector transmission with vehicle transmission.

References

1. “The Yellow Fever Epidemic Of 1888.” JAMA: The Journal of the American Medical Association, XII, no. 1, 1889, p. 22., doi:10.1001/jama.1889.02400780024005.
2. “Carlos Finlay.” Wikipedia, Wikimedia Foundation, 10 Feb. 2020, en.wikipedia.org/wiki/Carlos_Finlay.
3. “Walter Reed.” Wikipedia, Wikimedia Foundation, 1 Apr. 2020, en.wikipedia.org/wiki/Walter_Reed.