Free to follow every thread. No paywall, no dead ends.
Yellow fever: the story on HearLore | HearLore
Yellow fever
The first definitive outbreak of yellow fever in the New World occurred on the island of Barbados in 1647, marking the beginning of a centuries-long terror that would reshape the Americas. This disease, known to the indigenous Mayan people of the Yucatán Peninsula as xekik or blood vomit, was not merely a fever but a terrifying journey into the liver. While most infections resulted in a brief, flu-like illness, approximately 15% of those infected would enter a toxic phase where the liver failed, turning the skin yellow and causing the mouth, nose, and eyes to bleed. This hemorrhagic state produced vomit containing blood, earning the disease its Spanish name, vomito negro, or black vomit. The mortality rate for those who reached this stage was catastrophic, ranging from 20 to 50 percent, making yellow fever one of the most feared infectious diseases of the 18th and 19th centuries. The disease originated in Africa, where local populations had developed acquired immunity through childhood exposure, but when the virus and its vector, the Aedes aegypti mosquito, were transferred to the Americas via the trafficking of enslaved Africans, they found a population with no natural defenses. The result was a series of epidemics that killed thousands, paralyzed navies, and altered the course of history.
The Mosquito Hypothesis
For centuries, the cause of yellow fever remained a mystery, with theories ranging from putrid miasma in the air to astrological alignments proposed by the Ottawa Prophet Ezekiel Stone Wiggins during an 1888 epidemic in Jacksonville. It was not until 1881 that Carlos Finlay, a Cuban-Spanish doctor and scientist, proposed that the disease was transmitted by a specific mosquito rather than by direct contact or bad air. His hypothesis was initially dismissed by the medical establishment until the Spanish-American War of the 1890s, where U.S. Army doctors suffered staggering losses, forcing a reevaluation of the problem. In 1900, a team led by Walter Reed, including doctors James Carroll, Aristides Agramonte, and Jesse William Lazear, set out to prove Finlay's theory. They conducted experiments that involved allowing mosquitoes to bite infected patients and then biting healthy volunteers, a process that required the first known use of medical consent forms to ensure participants understood the risks. The team successfully proved that the Aedes aegypti mosquito was the vector, making yellow fever the first virus shown to be transmitted by mosquitoes. This discovery allowed William Gorgas to eradicate yellow fever from Havana and later during the construction of the Panama Canal, where previous French efforts had failed due to high mortality rates from the disease and malaria. Despite Reed receiving much of the credit in American history books, he fully acknowledged Finlay's foundational work, though historians note that the acceptance of Finlay's research was a contentious issue that often overlooked the contributions of less prominent scientists.
When did the first definitive outbreak of yellow fever occur in the New World?
The first definitive outbreak of yellow fever in the New World occurred on the island of Barbados in 1647. This event marked the beginning of a centuries-long terror that would reshape the Americas.
Who discovered that yellow fever is transmitted by mosquitoes?
Carlos Finlay, a Cuban-Spanish doctor and scientist, proposed that the disease was transmitted by a specific mosquito in 1881. A team led by Walter Reed in 1900 successfully proved that the Aedes aegypti mosquito was the vector.
When was the yellow fever virus first isolated and who developed the 17D vaccine?
The yellow fever virus became the first human virus to be isolated in 1927 in West Africa. Max Theiler led the completion of the 17D yellow fever vaccine in 1937, for which he was awarded the Nobel Prize in Physiology or Medicine.
How did William Gorgas help complete the construction of the Panama Canal?
William Gorgas launched a massive sanitation campaign in 1904 to eradicate the Aedes aegypti mosquito from the area. His methods included spraying insecticides, eliminating breeding sites, and improving drainage, which transformed the swampy conditions into a habitable zone for workers.
Why has yellow fever not been eradicated from South America and Africa?
Yellow fever persists in a sylvatic cycle involving wild primates and forest-dwelling mosquitoes, making eradication impossible without eliminating all vectors. The disease circulates among nonhuman primates and mosquitoes of the genus Haemagogus and Sabethes in South America and the genus Aedes in Africa.
When did the first appearance of yellow fever occur in recorded history in Asia?
The first appearance of the disease in Asia in recorded history occurred in March and April 2016. During this time, 11 imported cases of the Angola genotype in unvaccinated Chinese nationals were reported in China.
In 1927, the yellow fever virus became the first human virus to be isolated, a monumental achievement that occurred in West Africa and paved the way for modern virology. The virus, an enveloped RNA virus 40 to 50 nanometers in width, belongs to the genus Orthoflavivirus and is the type species of the family Flaviviridae. Its genetic structure consists of a positive-sense, single-stranded RNA that is approximately 10,862 nucleotides long, encoding a polyprotein that is cut by host proteases into three structural and seven nonstructural proteins. The virus replicates in the rough endoplasmic reticulum and vesicle packets, where immature particles are processed by the host protein furin to release the mature, infectious virion. The pathogenesis of the virus involves infection of dendritic cells and hepatocytes, leading to the release of cytokines and the formation of apoptotic masses known as Councilman bodies. Despite the detailed understanding of its structure, no specific cure exists for yellow fever, and management remains symptomatic, focusing on rehydration and pain relief while avoiding drugs like aspirin that increase the risk of bleeding. The isolation of the virus in 1927 was followed by the development of two vaccines in the 1930s, with Max Theiler leading the completion of the 17D yellow fever vaccine in 1937, for which he was awarded the Nobel Prize in Physiology or Medicine. This vaccine, which is still in use today, provides protection that begins by the 10th day after administration and is now considered to confer lifelong immunity with a single dose.
The Panama Canal
The construction of the Panama Canal stands as one of the most significant public health victories in history, made possible only by the understanding of yellow fever transmission. Previous French efforts to build the canal had failed in part due to the high incidence of yellow fever and malaria, which killed many workers and created a death toll that made the project seem impossible. In 1904, the United States took over the project, and William Gorgas, applying the insights of the Reed Commission, launched a massive sanitation campaign to eradicate the Aedes aegypti mosquito. Gorgas's methods included spraying insecticides, eliminating breeding sites, and improving drainage, which transformed the swampy conditions of the isthmus into a habitable zone for workers. The campaign was so successful that yellow fever was eradicated from the area, allowing the canal to be completed. This victory was not just a triumph of engineering but of public health, as it demonstrated that vector control could eliminate a deadly disease. The success of the campaign in Panama also had far-reaching implications for global health, strengthening relationships between nations and setting a precedent for future disease eradication efforts. The campaign in Panama was part of a broader effort to control yellow fever, which included similar initiatives in Cuba and Brazil, where Oswaldo Cruz led a highly successful sanitation campaign that reshaped the physical landscape of Rio de Janeiro by pushing poor residents from city centers to the suburbs.
The Silent Jungle
While urban outbreaks of yellow fever were nearly eradicated from South America by the mid-20th century, the disease persists in a sylvatic cycle involving wild primates and forest-dwelling mosquitoes. In South America, the sylvatic cycle is currently the only way unvaccinated humans can become infected, as the urban cycle has not been re-established since an outbreak in Bolivia in 1999. The virus circulates among nonhuman primates, such as brown howler monkeys, which serve as sentinel species for yellow fever, and mosquitoes of the genus Haemagogus and Sabethes. People who become infected in the jungle can carry the virus to urban areas, where the Aedes aegypti mosquito acts as a vector, potentially sparking new outbreaks. This sylvatic cycle makes eradication of yellow fever impossible without completely eliminating the mosquitoes that serve as vectors, a task that is logistically and ecologically unfeasible. In Africa, a third infectious cycle known as the savannah cycle occurs between the jungle and urban cycles, involving different mosquitoes of the genus Aedes. This cycle has been the most common form of transmission of yellow fever in Africa in recent years. The persistence of the sylvatic cycle means that yellow fever remains a constant threat, with outbreaks occurring regularly in both Africa and South America. The disease has been increasing in number since the 1980s, due to factors such as fewer people being immune, more people living in cities, people moving frequently, and changing climate increasing the habitat for mosquitoes.
The Global Threat
In 2013, yellow fever was estimated to have caused 130,000 severe infections and 78,000 deaths in Africa, with approximately 90 percent of an estimated 200,000 cases of yellow fever per year occurring on the African continent. The disease is common in tropical areas of South America and Africa, but not in Asia, where the main vector Aedes aegypti already occurs. The absence of yellow fever in Asia is attributed to several factors, including the possibility that the strains of the mosquito in the east are less able to transmit the virus, or that immunity is present in the populations because of other diseases caused by related viruses. However, the trans-Atlantic slave trade probably introduced yellow fever into the Western Hemisphere from Africa, and the disease has never occurred in Asia on the same scale. In 2016, a large outbreak originated in Angola and spread to neighboring countries before being contained by a massive vaccination campaign. The first appearance of the disease in Asia in recorded history occurred in March and April 2016, when 11 imported cases of the Angola genotype in unvaccinated Chinese nationals were reported in China. The World Health Organization launched a vaccination campaign in Brazil in March 2017 with 3.5 million doses from an emergency stockpile, and by April 2019, Brazil planned to vaccinate all 77.5 million currently unvaccinated citizens. Despite these efforts, the demand for yellow fever vaccines has continued to increase due to the growing number of countries implementing yellow fever vaccination as part of their routine immunization programmes, while outbreaks in Angola, the Democratic Republic of Congo, Uganda, Nigeria, and Brazil have strained global vaccine supplies.