yellow fever

Yellow Fever 

Definition

Yellow fever, which is also known as sylvatic fever and viral hemorrhagic fever or VHF, is a severe infectious disease caused by a type of virus called a flavivirus. This flavivirus can cause outbreaks of epidemic proportions throughout Africa and tropical America.

The first written evidence of such an epidemic occurred in the Yucatan in 1648. Since that time, much has been learned about the interesting transmission patterns of this devastating illness. It is thought that the disease originated in Africa and spread to the Americas in the 17th and 18th centuries through trading ships. The flavivirus that causes yellow fever was first identified in 1928 and the first vaccine against the disease was produced at the Rockefeller Institute in New York in 1937.

Description

In order to understand how yellow fever is passed, several terms need to be defined. The word "host" refers to an animal that can be infected with a particular disease. The term "vector" refers to an organism which can carry a particular disease-causing agent (such as a virus or bacteria) without actually developing the disease. The vector can then pass the virus or bacterium on to a new host.

Many of the common illnesses in the United States (including the common cold, many viral causes of diarrhea, and influenza or "flu") are spread via direct passage of the causative virus between human beings. Yellow fever, however, cannot be passed directly from one infected human being to another. Instead, the virus responsible for yellow fever requires an intermediate vector, a mosquito, which carries the virus from one host to another.

The hosts of yellow fever include both humans and monkeys. The cycle of yellow fever transmission occurs as follows: an infected monkey is bitten by a tree-hole breeding mosquito. This mosquito acquires the virus, and can pass the virus on to any number of other monkeys that it may bite. This form of yellow fever is known as sylvatic yellow fever, and usually affects humans only incidentally. When a human is bitten by an infected mosquito, however, the human may acquire the virus. In the case of South American yellow fever, the infected human may return to the city, where an urban mosquito (Aedes aegypti) serves as a viral vector, spreading the infection rapidly by biting humans. This form of the disease is known as urban yellow fever or epidemic yellow fever.

Yellow fever epidemics may also occur after flooding caused by earthquakes and other natural disasters. They result from a combination of new habitats available for the vectors of the disease and changes in human behavior (spending more time outdoors and neglecting sanitation precautions).

Cases of yellow fever are uncommon in the United States and Canada as of 2004. The last reported case in an American citizen concerned a man who contracted yellow fever in Brazil in 1996. The last epidemic in the United States occurred in New Orleans in 1905.

Symptoms

Once a mosquito has passed the yellow fever virus to a human, the chance of disease developing is about 5-20%. Infection may be fought off by the host's immune system, or may be so mild that it is never identified.

In human hosts who develop the disease yellow fever, there are five distinct stages through which the infection evolves. These have been termed the periods of incubation, invasion, remission, intoxication, and convalescence.

Yellow fever's incubation period (the amount of time between the introduction of the virus into the host and the development of symptoms) is three to six days. During this time, there are generally no symptoms identifiable to the host.

The period of invasion lasts two to five days, and begins with an abrupt onset of symptoms, including fever and chills, intense headache and lower backache, muscle aches, nausea, and extreme exhaustion. The patient's tongue shows a characteristic white, furry coating in the center, surrounded by a swollen, reddened margin. While most other infections that cause a high fever also cause an increased heart rate, yellow fever results in an unusual finding, called Faget's sign. This is the simultaneous occurrence of a high fever with a slowed heart rate. Throughout the period of invasion, there are still live viruses circulating in the patient's blood stream. Therefore, a mosquito can bite the ill patient, acquire the virus, and continue passing it on to others.

The next phase is called the period of remission. The fever falls, and symptoms decrease in severity for several hours to several days. In some patients, this signals the end of the disease; in other patients, this proves only to be the calm before the storm.

The period of intoxication represents the most severe and potentially fatal phase of the illness. During this time, lasting three to nine days, a type of degeneration of the internal organs (specifically the kidneys, liver, and heart) occurs. This fatty degeneration results in what is considered the classic triad of yellow fever symptoms: jaundice, black vomit, and the dumping of protein into the urine. Jaundice causes the whites of the patient's eyes and the patient's skin to take on a distinctive yellow color. This is due to liver damage, and the accumulation of a substance called bilirubin, which is normally processed by a healthy liver. The liver damage also results in a tendency toward bleeding; the patient's vomit appears black due to the presence of blood. Protein, which is normally kept out of the urine by healthy, intact kidneys, appears in the urine due to disruption of the kidney's healthy functioning.

Patients who survive the period of intoxication enter into a relatively short period of convalescence. They recover with no long term effects related to the yellow fever infection. Further, infection with the yellow fever virus results in lifelong immunity against repeated infection with the virus.

The course of yellow fever is complicated in some patients by secondary bacterial infections.

Diagnosis

Diagnosis of yellow fever depends on the examination of blood by various techniques in order to demonstrate either yellow fever viral antigens (the part of the virus that stimulates the patient's immune system to respond) or specific antibodies (specific cells produced by the patient's immune system which are directed against the yellow fever virus). The most rapid method of diagnosis as of 2004 is capture enzyme immunoassay. The diagnosis can be strongly suspected when Faget's sign is present. When the classic triad of symptoms is noted yellow fever is strongly suspected.

Treatment

There are no antiviral treatments available as of 2004 to combat the yellow fever virus, although researchers at the University of Texas are studying ribavirin (Virazole, Rebetol), a drug that is given by mouth to treat hepatitis C, as a potential treatment for liver damage caused by yellow fever. The only treatments for yellow fever are given to relieve its symptoms. Fevers and pain should be relieved with acetaminophen, not aspirin or ibuprofen, both of which could increase the already-present risk of bleeding. Dehydration (due to fluid loss both from fever and bleeding) needs to be carefully avoided. This can be accomplished by increasing fluids. The risk of bleeding into the stomach can be decreased through the administration of antacids and other medications. Hemorrhage may require blood transfusions. Kidney failure may require dialysis (a process that allows the work of the kidneys in clearing the blood of potentially toxic substances to be taken over by a machine, outside of the body).

Prognosis

Five to ten percent of all diagnosed cases of yellow fever are fatal. Jaundice occurring during a yellow fever infection is an extremely grave predictor. Twenty to fifty percent of these patients die of the infection. Death may occur due to massive bleeding (hemorrhage), often following a lapse into a comatose state.

Prevention

A very safe and very effective yellow fever vaccine exists. The Arilvax vaccine is made from a live attenuated form of the yellow fever virus, strain 17D. In the United States, the vaccine is given only at Yellow Fever Vaccination Centers authorized by the U.S. Public Health Service. About 95% of vaccine recipients acquire long-term immunity to the yellow fever virus. Careful measures to decrease mosquito populations in both urban areas and jungle areas in which humans are working, along with programs to vaccinate all people living in such areas, are necessary to avoid massive yellow fever outbreaks.

Persons planning to travel to countries where yellow fever in endemic may obtain up-to-date information on yellow fever vaccination from the Centers for Disease Control and Prevention by telephone (404-332-4559) or fax (404-332-4265).

Resources

Books

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Viral Diseases." Section 13, Chapter 162 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2002.

Periodicals

Barrett, A. D. "Current Status of the Arilvax Yellow Fever Vaccine." Expert Review of Vaccines 3 (August 2004): 413-420.

Lo Re, V., III, and S. J. Gluckman. "Travel Immunizations." American Family Physician 70 (July 1, 2004): 89-99.

Reeder, G. David, MD, and Theodore E. Woodward, MD. "Yellow Fever." eMedicine February 25, 2002. http://www.emedicine.com/med/topic2432.htm.

Sbrana, E., S. Y. Xiao, H. Guzman, et al. "Efficacy of Post-Exposure Treatment of Yellow Fever with Ribavirin in a Hamster Model of the Disease." American Journal of Tropical Medicine and Hygiene 71 (September 2004): 306-312.

Organizations

Centers for Disease Control and Prevention (CDC). 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.

Infectious Diseases Society of America (IDSA). 66 Canal Center Plaza, Suite 600, Alexandria, VA 22314. (703) 299-0200. Fax: (703) 299-0204. http://www.idsociety.org.

World Health Organization (WHO). http://www.who.int/en/.

Other

World Health Organization Fact Sheet. "Flooding and Communicable Diseases Fact Sheet: Risk Assessment and Preventive Measures." December 2004. http://www.who.int/hac/techguidance/ems/flood_cds/en/index.html.

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fever /fe·ver/ (fe´ver)

1. pyrexia; elevation of body temperature above the normal (37°C).

2. any disease characterized by elevation of body temperature.

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blackwater fever  a dangerous complication of falciparum malaria, with passage of dark red to black urine, severe toxicity, and high mortality.

boutonneuse fever  a tickborne disease endemic in the Mediterranean area, Crimea, Africa, and India, due to infection with Rickettsia conorii, with chills, fever, primary skin lesion (tache noire), and rash appearing on the second to fourth day.

cat-scratch fever  see under disease.

central fever  sustained fever resulting from damage to the thermoregulatory centers of the hypothalamus.

childbed fever  puerperal septicemia.

Colorado tick fever  a tickborne, nonexanthematous, febrile, viral disease caused by an arenavirus and seen in the Rocky Mountain area of the United States.

continued fever  one that varies only slightly in 24 hours.

Crimean-Congo hemorrhagic fever  a hemorrhagic fever caused by the Crimean-Congo hemorrhagic fever virus, transmitted by ticks and by contact with blood, secretions, or fluids from infected animals or humans; it occurs in the Crimea, Central Asia, and regions of Africa.

drug fever  febrile reaction to a therapeutic agent, such as a vaccine, antineoplastic, or antibiotic.

elephantoid fever  a recurrent acute febrile condition occurring with filariasis; it may be associated with elephantiasis or lymphangitis.

enteric fever  any of a group of febrile illnesses associated with enteric symptoms caused by salmonellae, especially typhoid fever and paratyphoid fever.

epidemic hemorrhagic fever  an acute infectious disease characterized by fever, purpura, peripheral vascular collapse, and acute renal failure, caused by viruses of the genus Hantavirus, thought to be transmitted to humans by contact with saliva and excreta of infected rodents.

familial Mediterranean fever  a hereditary disease usually seen in Armenians and Sephardic Jews, with short recurrent attacks of fever, pain in the abdomen, chest, or joints, and erythema like that of erysipelas; it may be complicated by amyloidosis.

Haverhill fever  the bacillary form of rat-bite fever, due to Streptobacillus moniliformis, and transmitted through contaminated raw milk and its products.

hay fever  a seasonal form of allergic rhinitis, with acute conjunctivitis, lacrimation, itching, swelling of the nasal mucosa, nasal catarrh, and attacks of sneezing, an anaphylactic or allergic reaction excited by a specific allergen (such as pollen).

hemorrhagic fevers  a group of diverse, severe viral infections seen around the world but mainly in the tropics, usually transmitted to humans by arthropod bites or contact with virus-infected rodents; they all have certain common features, including fever, hemorrhagic manifestations, thrombocytopenia, shock, and neurologic disturbances.

humidifier fever  malaise, fever, cough, and myalgia caused by inhalation of air that has been passed through humidifiers, dehumidifiers, or air conditioners contaminated by fungi, amebas, or thermophilic actinomycetes.

intermittent fever  an attack of malaria or other fever, with recurring fever episodes separated by times of normal temperature.

Katayama fever  fever associated with severe schistosomal infections, accompanied by hepatosplenomegaly and by eosinophilia.

Lassa fever  a highly fatal, acute, febrile disease seen in West Africa, caused by a virulent arenavirus and characterized by increasing prostration, sore throat, ulcerations of the mouth or throat, rash, and general aching.

metal fume fever  a disease of welders and others working with volatilized metals, marked by sudden thirst, metallic taste in the mouth, high fever with chills, sweating, and leukocytosis.

mud fever  a type of leptospirosis seen in workers in flooded fields and swamps in Germany and Russia.

nonseasonal hay fever , hay fever, perennial nonseasonal allergic rhinitis.

Oroya fever  see Carrión's disease.

paratyphoid fever  paratyphoid.

parenteric fever  a disease clinically resembling typhoid fever and paratyphoid, but not caused by Salmonella.

parrot fever  psittacosis.

pharyngoconjunctival fever  an epidemic disease due to an adenovirus, seen mainly in school children, with fever, pharyngitis, conjunctivitis, rhinitis, and enlarged cervical lymph nodes.

phlebotomus fever  a febrile viral disease of short duration, transmitted by the sandfly Phlebotomus papatasi, with dengue-like symptoms, seen in Mediterranean and Middle Eastern countries.

Pontiac fever  a self-limited disease marked by fever, cough, muscle aches, chills, headache, chest pain, confusion, and pleuritis, caused by a strain of Legionella pneumophila.

pretibial fever  an infection due to a serovar of Leptospira interrogans, marked by a rash on the pretibial region, with lumbar and postorbital pain, malaise, coryza, and fever.

puerperal fever  septicemia accompanied by fever, in which the focus of infection is a lesion of the mucous membrane of the parturient canal due to trauma during childbirth; usually due to a streptococcus.

Q fever  a febrile rickettsial infection, usually respiratory, first described in Australia, caused by Coxiella burnetii.

rat-bite fever  either of two clinically similar acute infectious diseases, usually transmitted through a rat bite, one form (bacillary) of which is caused by Streptobacillus moniliformis and the other form (spirillary) by Spirillum minor.

recurrent fever 

1. relapsing f.

2. recurrent paroxysmal fever occurring in various diseases, such as malaria.

relapsing fever  any of a group of infectious diseases due to various species of Borrelia, marked by alternating periods of fever and apyrexia, each lasting from five to seven days.

remittent fever  one that shows significant variations in 24 hours but without return to normal temperature.

rheumatic fever  a febrile disease occurring as a sequela to Group A hemolytic streptococcal infections, characterized by multiple focal inflammatory lesions of connective tissue structures, especially of the heart, blood vessels, and joints, and by Aschoff bodies in the myocardium and skin.

Rift Valley fever  a zoonotic febrile disease with dengue-like symptoms, due to an arbovirus, transmitted to humans by mosquitoes or by contact with diseased animals; first observed in the Rift Valley, Kenya.

Rocky Mountain spotted fever  infection with Rickettsia rickettsii, transmitted by ticks, marked by fever, muscle pain, and weakness followed by a macular petechial eruption that begins on the hands and feet and spreads to the trunk and face, with other symptoms in the central nervous system and elsewhere.

rose fever  a form of hay fever caused by grass pollens released while roses or other flowers are blooming.

scarlet fever  an acute disease caused by Group A β-hemolytic streptococci, marked by pharyngotonsillitis and a skin rash caused by an erythrogenic toxin produced by the organism; the rash is a diffuse, bright red erythema, and desquamation of the skin begins as fine scaling with eventual peeling of the palms and soles.

Sennetsu fever  a febrile disease seen in Japan and Malaysia and caused by Ehrlichia sennetsu, characterized by headache, nausea, lymphocytosis, and lymphadenopathy.

septic fever  fever due to septicemia.

South African tickbite fever  boutonneuse f.

trench fever  a louse-borne rickettsial disease due to Bartonella quintana, transmitted by the body louse, Pediculus humanus corporis, and characterized by intermittent fever, generalized aches and pains, particularly severe in the shins, chills, sweating, vertigo, malaise, typhus-like rash, and multiple relapses.

typhoid fever  infection by Salmonella typhi chiefly involving the lymphoid follicles of the ileum, with chills, fever, headache, cough, prostration, abdominal distention, splenomegaly, and a maculopapular rash; perforation of the bowel may occur in untreated cases.

fever of unknown origin  (FUO) a febrile illness of at least three weeks' duration (some authorities permit a shorter duration), with a temperature of at least 38.3°C on at least three occasions and failure to establish a diagnosis in spite of intensive inpatient or outpatient evaluation (three outpatient visits or three days' hospitalization).

West Nile fever  see under encephalitis.

yellow fever  an acute, infectious, mosquito-borne viral disease, endemic primarily in tropical South America and Africa, marked by fever, jaundice due to necrosis of the liver, and albuminuria.

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yellow fever

n.

An infectious tropical disease caused by an arbovirus transmitted by mosquitoes of the genera Aedes, especially A. aegypti and Haemagogus, and characterized by high fever, jaundice, and vomit that is dark in color as a result of gastrointestinal hemorrhaging.

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yellow fever,

an acute arbovirus infection transmitted by mosquitoes. It is characterized by headache, fever, jaundice, vomiting, and bleeding. There is no specific treatment, and mortality is about 5%. Recovery is followed by lifelong immunity. Immunization for travelers to endemic areas is advised. The vaccine against yellow fever is highly effective, producing a greater-than-10-year immunity to the disease. Nonhuman primates are a reservoir of infection.

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yellow fever

Tropical medicine An acute mosquito-borne infection–Aedes aegyptii, A africanus, Haemagogus spp of tropical Africa, Central and South America, by a flavivirus of the Togavirus family Clinical From benign nonspecific 'flu' Sx–mild subclinical infection is more common in children–to severe disease characterized by abrupt high fever with bradycardia–Faget sign, headache, anorexia, myalgia, lumbosacral pain, N&V–vomitus becomes blood-tinged up to 7–10 days post-onset, photophobia, flushing of face, red eyes, red 'strawberry' tongue, insomnia, constipation, hypotension, jaundice ± day 4, generalized petechial hemorrhages and hematemesis, hepatic and renal necrosis, dilated cardiomyopathy, stomach pain, delirium and seizures followed by coma; this is followed by a period of 'remission' of hrs to several days in duration, after which the Pt deteriorates and dies–up to 50% mortality Lab Leukopenia, ± pronounced, coagulation factor depletion, DIC, ↑ bilirubin, proteinuria, albuminuria with renal failure, ↑ neutralizing antibodies, ↑ transaminases