Yellow Fever

Yellow Fever

part of flavivirdae family, it is an RNA virus.

IT infects monocytes, macrophages, dendritic cells and schwann cells (connects to peripheral nervous system) and attach to cells via receptors.

It is an arthropod virus (arbovirus) through mosquito that has an incubation of 12 days before mosquito can pass it on to humans.

a large densely populated settlement is a requirement.

Yellow Fever and Aedes aegypti mosquito

most common urban vector.

among 3,500 known mosquito species, harbours numerous disease like dengue fever, chikungunya and zika virus.

It is also considered as a 'house haunting mosquito' because it thrives in close proximity to humans in cities or camps.

Its flight range is a few hundred meters. Females prefer humans as food source and egg laying perch is just above small pools (ex - rain barrell, gutter, empty tire)

Vectors and disease outbreak

microbes thrive in mosquitos are the host where they live and reproduce unless deposited in a human.

for mammals, mosquitos are vectors transmitting and receiving harmful pathogens in blood meals.

There are cycles of yellow fever transmission vary, ex - sylvatic (forest) cycle, urban cycle, or zone of emergence

sylvatic (forest) cycle

most transmission occurs between monkeys and various mosquito species in a tree canopy

urban cycle

a. aegypti cause transmissions between infected humans, can result in outbreaks

zone of emergence

humans are on outskirt of tree canopy, mosquitos feed on humans & monkeys leading to small scale outbreak

initial phase of yellow fever symptoms

virus multiplies in human host & enters blood stream (viremia).

Person is asymptomatic & non infectious for several day.

After, you will develop fever, intense headache, abdominal phase and vomiting.

Followed by a remission phase lasting 12-14 hours and most patients recover at this stage. but for about to 15-25% of cases, lead to intoxication phase

intoxication phase of yellow fever

kidney failure, sever liver damage leading to jaundice, vomit has ground coffee consistency.

final stage of yellow fever

results in delirium & sometimes seizures or muscle spasms because the virus is entering the schwann cells.

yellow fever virus

despite vaccines, there is no treatment for full blown yellow fever.

Mortality in severe cases 20-50%.

the virus evolves relatively slow and manifestation of disease has not changed dramatically over the centuries.

There are different strains in circulation today. Sources suggest that outbreaks varied in symptoms

ex - Mariners feared outbreak of the 'black vomit' disease - which was prob yellow fever

history of yellow fever

analysis of samples from 20 & 21st C suggests yellow fever strains originated around 1,500 years ago which began in central or eastern africa, although older variants may have circled among small populations of people and primates.

At some point, A. aegypti adapted to human settlements. North africa A. aegypti mosquitos evolved to survive near human made watering holes in Sahara Desert during dry spell in 4000-6000ya.

BUT genetic research suggests they relied on human settlements in West Africa 400-500ya. Domesticated A. aegypti arrived in west africa by 1500 & later accompanied ships bound for Caribbean and Brazil.

Since it originated in Africa, there was a belief that Africans are immune/resistent to the virus but there is no evidence of this

Yellow Fever Virus and children

children usually experience milder symptoms than adults.

Anti-bodies give life long immunity even after mild infection.

Individuals growing up in endemic regions had immunity after childhood.

Adult immigrants from elsewhere bore the full brunt of the disease

Emergence of tropical plantations

by 1650, A. aegpypti had a foothold in the caribbean and Central america. Portuguese nobles had refined sugar and techniques of human exploitation for 200 years.

in 1450s, nobles who controlled Portuguese island of Madeira shifted from logging & farming wheat to planting sugar crop which required a lot of financial capital and labour.

Similar agricultural technique eventually dominated the Caribbean Islands, coastal south America and SE NA (plantation complex).

On the island of Sāo Tomé had growing conditions of sugar cane that relied on slave labour. During this colonization process toward inland, saw yellow fever, malaria and other diseases were too much to contend with, leading to residing on coasts or islands.

By early 19th century, half of europeans who sailed to West Africa succumbed to the disease

Mosquitos and Plantations

Sāo Tomé 'labour model' spread to islands ruled by spain and Portuguese territories. Plantation model later adopted (17th C) by English in Virginia, the Carolinas & Barbados.

Mosquitos arrived via eggs laid in bilage tanks or moist cervices of slave vessels.

The sugar plantations are ideal for mosquitos - abundant source of fresh water (canals or shallow containers), supply of humans working on open air as blood meal for female mosqutios, sweet liquid for male and female and warm temp year round

Yellow fever in revolution era

Yellow fever and malaria worked in Tandem in Caribbean and Central America - which caused high mortality during severe outbreaks.

1788-1796 pronounced El Niño event which saw typical temps & rainfall severely disrupted.

In the Caribbean, there was extreme rain and drought increased A. aegypti breeding and yellow fever.

Post 1679, France acquired western 1/3 of Hispaniola. Colony became one of the largest producers of sugar and coffee.

Yellow fever & the haitian revolution

french revo raised questions concerning legitimacy of slavery & political equality of Saint-Dominque.

In 1793, France declared war on Britain, Britian deprived france of profits. Former slave, Toussaint L'Ouverture led the rebels and fought against the former plantation owners and rise of European armies.

Placed untrust in rainy season, would do more to destory foreign eneimes than any other weapon. Rebels conducted guerilla warfare against british & forced troops to stay near port cities (many british died in droves). in 1798 britsh withdrew troops and its estimated that 15,000 died due to disease.

By 1802, france duplicated britians failure wen 65,000 soldiers sent to the island and the french were powerless against the dieases (aka yellow fever).

L'Ouverture was captured in 1802, and french troops remained 17 months but tens of thousands of troops died from yellow fever. French abandoned plans for the americas due to setback of Haiti.

Yellow fever and revo in South america

A decade later, yellow fever was a challenge that loosened Spains grip of New Granada. Idea of independence began when napoleans forces distrupted spains rule in the Iberian Penninsula.

King Ferdinand VII sent 12,000 soldiers to 'reassert control' in the Americas and was led by some guy idk. Yellow fever & other dieseases killed large number of Spanish forces.

Pablo Murillo wrote about the impact of 'black vomit' & that a 'mere bite of a mosquito often deprives a man of life'.

Jan 1826, Spain sent another force, but most had been warned by Murillo's troops. The army was mutinied and never left the port and by 1826, only cuba and Puerto Rico were left under spains control until the americas

tropical medicine - Europe

late 19th century, researchers used new methods of microbiology to link specific bacteria to specific diseases.

Robert Koch - 1st scientist to accomplish in 1876 by highlighting the life cycle of anthrax pathogen, this method was applied to disease of 'tropics'.

tropical medicine emerged explore questions connected to European endeavours (naval medicine and ship hygiene).

The idea of tropical disease didnt relfect characteristic of diease or geographic range - tropical if interfered with colonial interests.

London school of medicine

In 1899, there was an opening of london school of hygiene & tropical medicine to identify - caused sleeping sickness (trypanosomes), life cycle of the worm causing guinea worm disease and staged demonstrations transmitted malaria to humans.

Tropical long been feared but thought to be no different than diseases from Europe.

Realize ecology of vectors, hosts and pathogens involved many organisms was complex

tropical medicine in Europe and Americas

closely aligned with colonial enterprises that would benefit from findings.

ex - physical health, buisness interests, and political objectives of European colonizers. In US, there were initiatives were linked to military (how to prevent soldiers from getting disease).

In 1895, Cubans revolted against spain, yet there was still a high mortality of small pox in Cubans but in spanish soliders there were mortality from yellow fever. Around 295,000 soldiers and cinvilians died and 95% of deaths were due to disease.

tropical medicine - Americas

Us had coltrol over Cuba where yellow fever was present. and Reed was proposing a yellow fever transmission and identiified mosqiutios a