Yellow Fever Attacks Philadelphia 1793
The summer of 1793 was unusually hot and dry. Insects infested every corner in the streets, and Philadelphia was the busiest port in the U.S. Workers paced back and forth, carrying goods in and shipping goods out. In the midst of July, a ship of Caribbean refugees came to port. With them, they carried the yellow fever virus. The virus traveled slowly at first; with just a few fatalities in the first week, numbers grew steadily over time.
No one suspected it was the aedes aegypti mosquito, retrieving the blood of an infected victim and transferring it to another healthy individual. The city’s leading physician Dr. Benjamin Rush had never seen anything like it before. Three to six days after being infected with the virus, the victim would begin to show symptoms such as headaches, muscle and joint aches, a fever, flushing, loss of appetite, vomiting and jaundice. Jaundice makes the eyes and skin look yellow, hence the name yellow fever.
 In the second stage, the symptoms would falsely leave after three days; at this time, most people would recover. Others could get worse within 24 hours.  The yellow fever virus is a dormant, single strand of RNA, packaged in a lipoprotein envelope.
The transmissions occur through bites of infected aedes aegypti or haemagogus mosquitoes. Human and nonhuman primates are the main reservoirs of the virus. Traveling through a lytic life cycle, the virus first enters the host and is phagocytosed by a macrophage. The virus then sheds its envelope to keep from being further digested. The macrophage continues with the virus to the lymph nodes where the virus begins its replication. The virus leaves the host macrophage and then goes out to infect others. As the lymph nodes carry the virus through the bloodstream, it enters the liver. Inside the liver, it infects the Kupffer cells that line the blood vessels. The cells are macrophages that are needed to clean cellular debris and dead damaged cells in the bloodstream. Due to the infection and deaths of Kupffer cells, damage occurs to the surrounding hepatocytes, and the formation of translucent hyaline. Now that the liver is damaged, it prevents the bile precursor bilirubin from being converted into biliverdin. Hence the symptom jaundice.
Extensive damage includes flu-like symptoms, joint pains, encephalitis, and hemorrhage. After being successfully infected, a mosquito can then come and collect the virus from the victim’s bloodstream, then find another human being to spread the disease to. In the third and final stage of the disease, complications begin to show in the patient’s organs. The heart and liver are affected by the virus; kidney failure, bleeding disorders, seizures, coma, and delirium are also symptoms of the disease. “Black vomit” is also an effect, whereas blood is found in vomit due to bleeding in the stomach.  Physician Benjamin Rush believed that having the patients release certain amounts of blood would help cure the disease. Rush asked members of the African American Society to help with health services, believing that they were immune to the disease. However in two months time, it was concluded that black skinned people were susceptible to the disease. They died at the same rate as white skinned folk. On August 9, 1793, 45 individuals were reported dead. From October 1st to 12th, the death toll climbed to 1,000. The mayor of the city ordered the streets and buildings to be quarantined due to Rush’s theory that the disease was caused by unsanitary conditions. In October, the first frost arrived.
The number of mosquitoes decreased. At last on October 31st, a white flag was placed on top of the city hospital, signaling that no yellow fever patients remained.  The yellow fever epidemic of 1793 had ended. From a population of 55,000, 5,000 people died from the disease and about 20,000 fled the city.  At the close of the 19th century, Westerners had become terrified of the disease. There were no known causes or effective treatments for the virus. In 1900, scientist Dr. James Carroll endangered his own life by allowing an infected mosquito to feed on him. With the help of his colleague, Walter Reed, they discovered that yellow fever was transmitted by mosquitoes. There has been many failed attempts at finding a cure for yellow fever. It was then discovered that there was no cure for the disease due to the jungle (sylvatic) cycle. In 1932, Professor Max Theiler was able to create a somewhat successful vaccine called 17D. Many people were given the vaccine, and the results showed no problem. Today’s vaccines have been derived from substrains like 17DD, and 17D-204. Theiler earned a Nobel Prize in 1950 after his work at the Rockefeller Institute. Yellow fever usually occurs in sub-Saharan Africa and tropical South America. Visitors traveling to that area must prepare for the risks of mosquito bites.
To take precaution, it is best to get a vaccination from your doctor before you leave. Avoid the outdoors as much as possible and use mosquito nets. If you do catch yellow fever, the only way to treat it is by getting rest, drinking fluids, and using analgesic and antipyretics to help with the fever and aches. Has yellow fever ever been used as a weapon in biological warfare? Should it be? It once occurred to the Americans to use yellow fever as a weapon in WWII timeframe. They planned to produce a large amount of aedes aegypti mosquitoes and infect them with the yellow fever virus. Infecting a large group of mosquitoes was the challenging part of the process. The plan was never put into action. Since the virus is passed through blood consumed by a mosquito, you must first find hosts to contain the virus. The Americans planned to infect non-human primates to infect the mosquitoes. Primates are not widely found in the US, and it is impossible to grow the disease in lab accumulated animals. Therefore, scientists found it hard to observe the disease in animal studies. It is very fortunate that yellow fever research has not extended to more detailed observation and understanding. If it were, countries like the U.S. could be using it as a biological warfare weapon just by releasing it into their enemies’ territory. No one should be using the scientific research collected on yellow fever, to create a deadly weapon. Such information should not be released to the public. If it were used as a weapon, the numbers of victims could accumulate so easily and the deadly virus could lead to another epidemic just like the one in Philadelphia of 1793.
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