What is yellow fever??

Yellow Fever looks a lot like dengue haemorrhagic fever and is transmitted by Aedes Aegypti mosquitoes. It also affects monkeys and other vertebrates and is caused by a virus called Flavivirus Fibricus.

A patient suffering from yellow fever remains infective during the first three to four days of illness and a mosquito becomes infective after eight to twelve days of biting a patient.

But, if you have had it once, you are done with it. One attack will give you life long immunity. Infants born to mothers, who are immune to the disease, inherit antibodies that last up to six months of life.

Yellow fever is more prevalent in Africa, the tropical forests of America, Bolivia, Brazil, Colombia and Peru. The virus breeds at a temperature of about 24 degrees Celsius.

Symptoms:
The disease lasts for about three to six days and could range from being clinically indeterminate to severe. Some cases develop jaundice and have haemorrhagic manifestations such as black vomiting, black stool, bleeding from the nose, restlessness and decrease in urine output, and may slip into a coma. What is scary about the disease is that the fatality rate is as high as 80 per cent.

Control:
Fortunately, India is yellow fever-free, though it has all the conditions that is congenial for the virus to thrive. The Aedes Aegypti mosquito is found in abundance and the climatic conditions are just right for the virus to survive.

Besides, most people in India are not vaccinated and are succeptible to yellow fever. If the virus is transported here with an infected person, it would not take long before people here begin falling prey to the virus.

The only way to stay away from it is by keeping our houses and surroundings mosquito-free and by ensuring that all international travellers are checked and vaccinated.

A single dose of a vaccine can be administered to children after they are a year old. This imparts an immunity, which begins to activate after seven days of vaccination, and lasts for more than 35 years, and sometimes for life.

However, the World Health Organisation recommends revaccination every 10 years, especially if you do a lot of international travelling.

Yellow fever (also called yellow jack, black vomit or vomito *****, or sometimes American Plague) is an acute viral disease.[1] It is an important cause of hemorrhagic illness in many African and South American countries despite existence of an effective vaccine. The yellow refers to the jaundice symptoms that affect some patients.[2]

Yellow fever has been a source of several devastating epidemics. During the 1802 Haitian Revolution, French soldiers were attacked by yellow fever: More than half of the army perished due to the disease.[3] Outbreaks followed by thousands of fatalities occurred periodically in other Western Hemisphere locations until research which included human volunteers (some of whom died) led to an understanding of the method of transmission to humans (primarily by mosquitos) and development of a vaccine and other preventative efforts in the early 20th century.

Despite the costly and sacrificial breakthrough research by Cuban physician Carlos Finlay, American physician Walter Reed and many others, over 100 years later, unvaccinated populations in many developing nations in Africa and Central and South America continue to be at risk.[4] As of 2001, the World Health Organization (WHO) estimates that yellow fever causes 200,000 illnesses and 30,000 deaths every year in unvaccinated populations.[5]

Contents [hide]
1 Pathogenesis
2 Symptoms
3 Prevention
4 Treatment
4.1 Research data
5 Prognosis
6 Epidemiology
7 History
7.1 Europe 541-549
7.2 Havana, Cuba: 1762-1763
7.3 Philadelphia: 1793
7.4 Haiti: 1802
7.5 Norfolk, Virginia: 1855
7.6 New York Harbor: 1856
8 Popular culture references
9 See also
10 References
10.1 Further reading
11 External links
11.1 Historical yellow fever information
11.2 Vaccine development



[edit] Pathogenesis

The female Aedes aegypti mosquito on a human host, about to obtain a blood mealYellow fever is caused by an arbovirus of the family Flaviviridae, and is a positive single-stranded RNA virus. Human infection begins after deposition of viral particles through the skin in infected arthropod saliva. The mosquitos involved are Aedes simpsaloni, A. africanus, and A. aegypti in Africa, the Haemagogus genus in South America,[5] and the Sasbethes genera in France.

Yellow fever is frequently severe, but more moderate cases may occur as the result of previous infection by another flavivirus. After infection, the virus first replicates locally, followed by transportation to the rest of the body via the lymphatic system.[6] Following systemic lymphatic infection, the virus proceeds to establish itself throughout organ systems, including the heart, kidneys, adrenal glands, and the parenchyma of the liver; high viral loads are also present in the blood.[1] Necrotic masses (Councilman bodies) appear in the cytoplasm of hepatocytes.[6],[7]

There is a difference between disease outbreaks in rural or forest areas and in towns. Disease outbreaks in towns and non-native people are usually more serious.[citation needed]


[edit] Symptoms
The virus remains silent in the body during an incubation period of three to six days. There are then two disease phases. While some infections have no symptoms whatsoever, the first, acute, phase is normally characterized by fever, muscle pain (with prominent backache), headache, shivers, loss of appetite, nausea and/or vomiting. Often, the high fever is paradoxically associated with a slow pulse (known as *****'s sign). After three to four days most patients improve and their symptoms disappear.

However, 15% enter a toxic phase within 24 hours. Fever reappears and several body systems are affected. The patient rapidly develops jaundice and complains of abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes and/or stomach. Once this happens, blood appears in the vomit and feces. Kidney function deteriorates; this can range from abnormal protein levels in the urine (proteinuria) to complete kidney failure with no urine production (anuria). Half of the patients in the "toxic phase" die within 10-14 days. The remainder recover without significant organ damage.

Yellow fever is difficult to recognize, especially during the early stages. It can easily be confused with malaria, typhoid, rickettsial diseases, haemorrhagic viral fevers (e.g. Lassa), arboviral infections (e.g. dengue), leptospirosis, viral hepatitis and poisoning (e.g. carbon tetrachloride). A laboratory analysis is required to confirm a suspect case. Blood tests (serology assays) can detect yellow fever antibodies that are produced in response to the infection. Several other techniques are used to identify the virus itself in blood specimens or liver tissue collected after death. These tests require highly trained laboratory staff using specialized equipment and materials.


[edit] Prevention
A vaccine for yellow fever was developed which gives a 10-year or more immunity from the disease and effectively protects people traveling to the affected areas whilst being a means to control the disease at the same time. Woodcutters working in tropical areas should be particularly targeted for vaccination. Insecticides, protective clothing and screening of houses are helpful but not always enough, but you should always use an insecticide spray while in certain areas. In affected areas mosquito control methods have proved effective in decreasing the number of cases.[8]

Recent studies have noted the increase in areas affected by mosquito-borne viral infections and have called for further research and funding for vaccines.[9],[10]


[edit] Treatment
There is no real specific cure for yellow fever; therefore vaccination is important. Treatment is symptomatic and supportive only. Fluid replacement, fighting hypotension and transfusion of blood derivates is mostly needed in severe cases. In severe cases resulting in acute renal failure, dialysis may be necessary. A fever victim needs to get lots of rest, fresh air, and drink plenty of fluids.


[edit] Research data
In the hamster model of yellow fever, early administration of the antiviral ribavirin is an effective early treatment of many pathological features of the disease.[11] Ribavirin treatment during the first five days after virus infection improved survival, reduced tissue damage in target organs (liver and spleen), prevented hepatocellular steatosis, and normalized alanine aminotransferase (a liver damage marker) levels. The results of this study suggest that ribavirin may be effective in the early treatment of yellow fever, and that its mechanism of action in reducing liver pathology in yellow fever virus infection may be similar to that observed with ribavirin in the treatment of hepatitis C, a virus related to yellow fever.[11] Because ribavirin had failed to improve survival in a virulent primate (rhesus) model of yellow fever infection, it had been previously discounted as a possible therapy.[12]


[edit] Prognosis
Historical reports have claimed a mortality rate of between 1 in 17 (5.8%) and 1 in 3 (33%).[13] The WHO factsheet on yellow fever, updated in 2001, states that 15% of patients enter a "toxic phase" and that half of that number die within 10-14 days, with the other half recovering.[14]


[edit] Epidemiology

Endemic range of yellow fever in Africa, 2005.
Endemic range of yellow fever in South America, 2005.Yellow fever occurs only in Africa, South and Central America, and the Caribbean.[15] Most outbreaks in South America are to people who work within the tropical rain forests and have direct contact with the organisms within the rainforest.

The disease can remain locally unknown in humans for long periods of time and then suddenly break out in an epidemic fashion. In Central America and Trinidad, such epidemics have been due to a form of the disease (jungle yellow fever) that is kept alive in Red Howler monkey populations and transmitted by Haemagogus mosquito species which live only in the canopy of rain forests. The virus is passed to humans when the tall rainforest trees are cut down. Infected woodcutters can then pass on the disease to others via species of Aedes mosquitoes that typically live at low altitudes, thus triggering an epidemic.[16]



[edit] History

Photograph taken during the 1965 Aedes aegypti eradication program in Miami, FloridaYellow fever has had an important role in the history of Africa, the Americas, Europe, and the Caribbean.


[edit] Europe 541-549
Fragile after the fall of Rome, Europe was further weakened by "Yellow Plague" (Yellow Fever). The Byzantine Empire suffered as well.[17]


[edit] Havana, Cuba: 1762-1763
English and American colonial troops died by the thousands in Havana between 1762-1763. Epidemics struck coastal and island communities throughout the area during the next 140 years.


[edit] Philadelphia: 1793
In 1793, the largest yellow fever epidemic in American history killed as many as 5,000 people or 10% of the population in Philadelphia, Pennsylvania.[18] At the time, the port city was the second largest, New York City being the first, in the United States and seat of the U.S. Government (prior to establishment of the District of Columbia). The city had recently seen the arrival of political refugees from the Caribbean. The summer that year was especially hot and dry, leaving many stagnant water areas as ideal breeding grounds for mosquitos.

The outbreak began in July and continued through November, when cold weather finally eliminated the breeding ground for mosquitos, although the connection had not yet then been established. Thousands of Philadelphians, including prominent government officials like George Washington and Alexander Hamilton fled the national capital. Benjamin Rush, the city's leading physician and a signer of the United States Declaration of Independence, advocated the bloodletting of patients to combat the disease, but the treatment was controversial. Stephen Girard also helped supervise a hospital established at Bush Hill, a mansion just outside Philadelphia. Though many high-ranking people of Philadelphia fled, a few officials stayed. Mayor Matthew Clarkson as well as the mayor's committee tried to hold the city together as the death toll increased.[19]

Matthew Carey published a fast-selling chronicle of the yellow fever crisis, A short account of the Malignant Fever, Lately Prevalent in Philadelphia that went through four editions. Although other ethnic groups were included, Carey's account failed to include the involvement of the city's African Americans in the community's response and relief efforts, despite the fact that African American leaders Richard Allen and Absalom Jones had rallied their church community to assist victims. Allen and Jones subsequently wrote a pamphlet, Narrative of the Proceedings of the Black People, During the Late Awful Calamity in Philadelphia, which detailed the contributions of the African Americans during the epidemic.[20]

The patients of the Yellow Fever went to a hospital called Bush Hill. Bush Hill mansion was used as a hospital for yellow fever patients in 1793. Patients at Bush Hill were treated using the French method which concerned giving the patients bed rest, fresh air, plenty of fluids, and keeping them clean and relaxed. Usually the poorest Philadelphians, who could not have enough money to pay for medical care, ended up at Bush Hill. The methods of French doctors turned out to be the most excellent way to take care of the disease, and many patients recovered.


[edit] Haiti: 1802
In 1802, an army of forty thousand sent by First Consul Napoleon Bonaparte of France to Haiti to suppress the Haitian Revolution was dwindeld out by an epidemic of Yellow Fever (including the expedition's commander and Bonaparte's brother-in-law, Charles Leclerc). Some historians believe Haiti was to be a staging point for an invasion of the United States through Louisiana (then still under French control).[citation needed]


[edit] Norfolk, Virginia: 1855
A ship carrying persons infected with the virus arrived in Hampton Roads in southeastern Virginia in June of 1855 .[13] The disease spread quickly through the community, eventually killing over 3,000 people, mostly residents of Norfolk and Portsmouth. The Howard Association, a benevolent organization, was formed to help coordinate assistance in the form of funds, supplies, and medical professionals and volunteers which poured in from many other areas, particularly the Atlantic and Gulf Coast areas of the United States. See also "The Mermaids and Yellow Jack. A NorFolktale." children's historical fiction written by Norfolk Author Lisa Suhay retelling of the event and founding of the Bon Secours DePaul Hospital system in the United States in response to the epedemic. (http://iparentingmediaawards.com/winners...


[edit] New York Harbor: 1856

An entomologist demonstrates the attraction of female yellow fever mosquitoes to his hand in an olfactometer.Dr.Walter Reed, M.D., (1851-1902) was an American Army surgeon who led the team which confirmed the theory first set forth in 1881 and proven by the Cuban doctor and scientist Dr. Carlos Finlay that yellow fever is transmitted by mosquitoes rather than direct contact.[21] The risky but fruitful research work was done with human volunteers, including some of the medical personnel such as Clara Maass and Walter Reed Medal winner surgeon Jesse William Lazear who allowed themselves to be deliberately infected and died of the virus.[22] By applying methods first suggested by Finlay, the elimination of Yellow Fever from Cuba was completed, as well as the completion of the Panama Canal. Lamentably, almost 20 years passed while the scientific community ignored Finlay's methods of mosquito control; the acceptance of Finlay's work was one of the most important and far-reaching effects of the Walter Reed Commission of 1900.[23]

Finlay and Reed's work was put to the test for the first time in the United States when a yellow fever epidemic struck New Orleans in 1905; according to the PBS American Experience documentary The Great Fever, houses were fumigated, cisterns for drinking water were inspected, and pools of standing water were treated with kerosene. The result was that the death toll from the epidemic was much lower than that from previous yellow fever epidemics, and that there has not been a major outbreak of the disease in the United States since, although no cure has yet been discovered.