Introduction
Yellow fever (YF) is an infectious disease spread by mosquitoes and caused by a single-stranded positive RNA virus belonging to the arbovirus family Flavivirus. The yellow fever virus circulates primarily in temperate and tropical areas of Africa and South America. The worst epidemic in North America happened in 1793 in Philadelphia, where 5,000 people died, and a third of the city’s inhabitants were evacuated (Jácome et al. 1).
The virus is transmitted by mosquitoes that feed on infected wild animals in the forest before feeding on humans traversing the forest. After 3–6 days of incubation, the YF virus can produce a variety of clinical manifestations, ranging from a self-limiting or moderate febrile illness along with flu-like symptoms in most cases to severe hemorrhage and infection of the liver.
The Origin of the Disease
At first, it was thought that YF had come from the Americas, where the first Spanish invaders had found it at the end of the sixteenth century. It is assumed that infected African captives shipped to the Caribbean and southern America introduced the illness to the Americas. Even though the first historically documented YF epidemic emerged in Guadeloupe in 1647, the identification of putative or probable cases before that year led to the identification of YF existence in the New World (Gianchecchi et al. 2). Epidemiological and genetic research supports the theory that the yellow fever virus emerged from Africa and was brought to Western America in the 16th century through the trade of captives from endemic African nations (Gianchecchi et al. 2). Molecular studies have revealed a greater genetic heterogeneity of yellow fever in Africa, proving evidence for its origin.
At the beginning of the 19th century, yellow fever was a reported and dreaded disease in the western and coastal areas of West Africa despite its unknown etiology and mechanism of transmission. Traditionally known as “yellow jack” due to the yellow quarantine banner on ships, the disease frightened people and hampered commerce (Gianchecchi et al. 2). The illness manifested in epidemic and endemic forms and was linked to ports. However, not much was known about it. Comparing the number of outbreaks in Africa and Europe between the 17th and 19th centuries, the Americas were more affected due to a combination of socioeconomic, ecological, and demographic factors (Gianchecchi et al. 3).
The densely populated areas of the coastal cities of the United States (US) provided a favorable environment for the propagation of the YF virus brought by ships from the Caribbean, with constant epidemics hitting cities including New York City and Philadelphia, resulting in the deaths of hundreds of thousands of Americans. (Gianchecchi et al. 3). In Africa, however, the lower population density did not facilitate the spread of YF.
The Transmission Cycles of the Disease
There are three different types of transmission cycles for yellow fever. In the most common cycle, the sylvatic, the primary hosts are nonhuman primates. The vectors of infection are mosquito species, Sabethes spp or Aedes spp. End-hosts, such as humans, join the cycle and become affected not only when they live in the region but also when they visit the sylvatic wooded regions as workers and tourists.
Humans are the primary recipients and Ae. Aegypti is the primary carrier in the urban cycle (Jácome et al. 2). The Savannah cycle, also known as the intermediary cycle, was first documented in Africa but may also apply to some areas of South America. It develops when humans reside in regions of emergence at the border of African savannahs, where they may get infected with a virus conveyed by a sylvatic mosquito and cause minor rural epidemics.
The Impact of the Disease on Individuals
Throughout human history, yellow fever has brought immense pain and devastation to the populations of the Americas, Africa, and Europe. It caused economic devastation in its aftermath and acted as a barrier to development. Yellow fever-infected ships were frequently quarantined, causing significant delays and financial losses for the maritime industry (Tuells et al. 7).
The disease also enormously affected agriculture, as it frequently killed livestock and rendered crop production problematic. The elevated death rate among those infected with yellow fever was a significant additional effect. Yellow fever epidemics frequently resulted in the death of thousands of individuals in a short time, causing substantial economic and social setbacks.
The Spread of the Disease
From the 17th century to the end of the 19th century, it was believed that YF transmission could occur through water or human contact, with the pathogen entering the body through the respiratory system. After the epidemic developed in Philadelphia in 1793, in which the dearth of direct contact between individuals could not have contributed to their spread, the theory regarding the mode of disease transmission changed gradually. It was believed that YF could not be transmitted through direct contact between individuals. Walter Reed performed the first research that cast some light on YF transmission (Gianchecchi et al. 3).
Reed’s study expanded upon the 1881 findings of Cuban physician Carlos Finlay. Finlay furthered studies into the mode of transmission by proposing that Aedes aegypti could be the mosquito liable for the disease’s transmission (Gianchecchi et al. 3). Finlay performed experiments and determined that YF disease was spread by an infected mosquito biting a healthy individual. It took, however, several years for his hypothesis to become widely adopted.
Thirteen soldiers fell sick and died from YF, for every soldier killed in action. Surgeon General George Sternberg dispatched Walter Reed and his team to Cuba to discover what triggered the outbreak. Reed’s research validated Finlay’s previous contention that a filterable chemical in sick patients’ blood was responsible for the illness (Gianchecchi et al. 3). Additionally, Reed’s research inspired General William Godas to launch initiatives against urban mosquito vectors, eradicating the illness in 1902. (Gianchecchi et al. 3) (Gianchecchi et al. 3). The attempts to curb and avert the spread of contagious illnesses are indebted to the pioneering work of Reed and Godas, who made significant contributions to the field of public health.
Combatting the Disease
Before the founding of the United States, not much was done to avert the spread of infectious illnesses such as YF. During periods when YF was prevalent, various methods were employed to combat the disease. Frequently, quarantine was used to avert the propagation of yellow fever. To stop the infection from spreading, diseased persons were segregated from other community members, and occasionally, entire villages or towns were put under quarantine.
At times, state and local administrations attempted to enforce quarantine rules. In 1878, Congress was compelled by the persistence of YF outbreaks to enact federal quarantine legislation. (Centers for Disease Control and Prevention par. 3) This legislation did not violate state sovereignty and prepared a path for federal participation in quarantine measures. In addition, enhanced hygiene and sanitation measures prevented the propagation of yellow fever. This consisted of efforts such as enhancing waste management and handwashing.
Reforms Initiated After the Event
Outbreaks of yellow fever sparked the creation of novel public health initiatives. In 1936, the live, attenuated YV 17D vaccine was invented. (Espinal et al. 4). The vaccine is extensively utilized for YF protection in travelers, regular immunization of neonates in endemic regions, and response to outbreaks. The 17D YF vaccine produces a rapid, extremely robust, and essentially everlasting adaptive immune reaction.
States in the Americas followed the Pan American Health Organization (PAHO) technical advisory group guidelines to avert and manage yellow fever in the zone. This included the introduction of the YF vaccine universally into national immunization schemes for children aged one year in nations with endemic transmission (Espinal et al. 4). Travelers to areas where YF transmission is possible were also advised to be vaccinated.
In addition, efforts were made to reduce mosquito populations through better drainage and hygiene. Reforms included using long-lasting pesticide-treated materials, such as nets and covers, primarily targeting adult mosquitoes and larvicides to manage larval stages. (Espinal et al. 3). Some environmental changes were made, such as eliminating stagnant water, controlling garbage, installing channeled water, and constructing obstacles. Notably, regular vector control and emergency actions can considerably lower vector populations but cannot eradicate mosquitoes.
Conclusion
Yellow fever remains a major global health problem, especially in some parts of America and sub-Saharan Africa. In regions with low immunization rates and inadequate mosquito control, the illness still causes outbreaks and epidemics despite a safe and efficient vaccine. The prevalence and spread of the virus are currently being studied to properly prepare for future epidemics and increase immunization rates and mosquito control methods.
Works Cited
Centers for Disease Control and Prevention. “History of Quarantine.” CDC, 2019. Web.
Espinal, Marcos A., et al. “Emerging and Reemerging Aedes-Transmitted Arbovirus Infections in the Region of the Americas: Implications for Health Policy.” American Journal of Public Health vol, 109 no.3, 2019, pp. 1-6. Web.
Gianchecchi, Elena, et al. “Yellow Fever: Origin, Epidemiology, Preventive Strategies and Future Prospects – ProQuest.” Proquest.com, vol. 10, no.3, 2022, pp. 1-17. Web.
Jácome, Rodrigo, et al. “A Yellow Flag on the Horizon: The Looming Threat of Yellow Fever to North America.” International Journal of Infectious Diseases, vol. 87. 2019, pp. 1-8. Web.
Tuells, Jose, et al. “Yellow Fever: A Perennial Threat.” Archives of Medical Research, vol. 53, no. 7. 2022, pp 1-9. Web.