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Yellow Fever Virus

Yellow Fever Virus



NAME: Yellow fever virus

SYNONYM OR CROSS REFERENCE: YFV(1), YF(1,2,3), yellow fever(1,2,3,4,5,6,7,8,9,10), and black vomit(1).

CHARACTERISTICS: A member of the genus Flavivirus , and Flaviviridae family(2,6). YFV is a spherical, enveloped virus of 40 to 50 nm in diameter(1,5), and has a single-stranded, positive- sense RNA genome(1,4,5).


PATHOGENICITY/TOXICITY: It is estimated that 15 to 50 % of people infected with YF develop illness, beginning abruptly with fever, chills and headache(5). Of those that develop illness, approximately 57 to 85 % will abort their infection and recover without developing classic YF. Classic YF is characterised by three clinical illness stages: infection, remission, and intoxication.

Infection : This stage typically lasts 3 or 4 days and is characterised by intense viraemia with symptoms including fever, chills, malaise, headache, lower back pain, knee pain, generalised myalgia, nausea, and dizziness(2,4,5,6). On examination, the patient has a heart rate lower than would be expected for a fever (Faget sign), and congestion and erythaema of the conjunctivae, tongue and face. Most infections resolve at this stage. Temperatures up to 40.5°C are associated with severe illness and poor outcome(5).

Remission : This stage is typified by an abatement of fever and other constitutional symptoms for a period of about 48 hours. Viraemia may still be present but it is usually waning(4,5).

Intoxication : Approximately 15 to 25 % of people who develop any clinical symptoms (or 10 % of all infected people) progress to this stage, which generally occurs 3 to 6 days after the onset of illness and can last for 3 to 8 days. During this period, viraemia disappears, and antibodies, along with the classic signs of YF (jaundice, renal failure and haemorrhage), appear(4,5). Common symptoms of this stage include fever, relative bradycardia, vomiting, nausea, epigastric pain, jaundice, oliguria and haemorrhagic manifestations (melena, haematuria, non-menstrual uterine bleeding, petechiae, ecchymoses, epistaxis, and oozing of blood from the gums and needle puncture sites)(2,5). Many patients will progress to multi-organ failure dominated by hepatic, renal, haematological and cardiovascular involvement(5).

The case fatality rate of patients who develop hepatic and renal failure is 20 to nearly 50 %(5,6). Death is typically preceded by profound hypotension and shock that is difficult to manage with fluids and vasopressors(4,5).

EPIDEMIOLOGY: YF occurs only in tropical regions of Africa and South America(4,5,7). Approximately 200,000 cases of yellow fever occur annually(4), 90 % of them in Africa(1,7). Up to 5,000 cases of YF in Africa and 300 in South America are reported annually, but the true incidence is believed to be 10 to 50-folds higher than official reports(4).

Three distinct transmission cycles exist. A sylvatic (jungle) cycle occurs in the rainforests of Africa and South America whereby YFV is transmitted between non-human primates and mosquitoes(5). Human cases are rare and usually occur in people who are occupationally exposed in forested or transitional areas. An urban human-mosquito-human transmission cycle occurs in both Africa and South America; and a savannah cycle that occurs only in Africa involves transmission of YFV among monkeys, mosquitoes and humans.

HOST RANGE: Humans(1,2,5,6), non-human primates(1,2,5), hedgehogs, and golden hamsters(5).


MODE OF TRANSMISSION: YFV is transmitted to humans from infected non-human primates and other humans by the bite of Aedes and Haemagogus mosquitoes(2,4,5,6,8).

INCUBATION PERIOD: 3 to 6 days(2,4,5,6).

COMMUNICABILITY: No evidence for direct human-to-human transmission.


RESERVOIR: In urban areas: humans and mosquitoes (Aedes aegypti); in areas of rainforest: monkeys and mosquitoes; and in savannah areas: humans, monkeys and mosquitoes(1,2,5,8).

ZOONOSIS: Yes, indirectly from mosquitoes infected by non-human reservoir hosts (sylvatic and savannah YF transmission)(1,5,6).

VECTORS: The principal arthropod vectors of YF differ depending on their geographical location(5).
Urban YF : Aedes aegypti in both South America and Africa(5,6).
Sylvatic YF : Aedes africanus in Africa and members of the Haemagogus species in South America(5,6).
Savannah YF : Aedes furcifer , Aedes vittatus , Aedes luteocephalus , and Aedes africanus in West Africa, and Aedes africanus and Aedes simpsoni in East Africa(5).


DRUG SUSCEPTIBILITY: Ribavirin has activity against YF virus at high (potentially cytotoxic) concentrations in vitro(5).

SUSCEPTIBILITY TO DISINFECTANTS: Inactivated by 3 to 8 % formaldehyde, 2 % glutaraldehyde, 2 to 3 % hydrogen peroxide, 500 to 5,000 ppm available chlorine, alcohol, 1 % iodine, and phenol iodophors(11).

PHYSICAL INACTIVATION: Inactivated by heat (50 to 60°C for at least 30 minutes), ultraviolet light, and gamma irradiation(11).

SURVIVAL OUTSIDE HOST: Low temperatures preserve infectivity, with stability being greatest below -60°C(11).


SURVEILLANCE: Monitor for symptoms. Confirmation is via virus isolation from blood(1,2,6) or cerebrospinal fluid(2) during the viraemic phase. Other methods of detection include immunofluorescence(1,2,6), PCR(2,6), real-time PCR(2), compliment fixation, haemagglutinin inhibition, neutralization(1), and IgM capture ELISA(1,2,6).

Note: All diagnostic methods are not necessarily available in all countries.

FIRST AID/TREATMENT: Treatment is supportive and symptomatic, however it may vary as infection is highly case-dependent(2). Treatments and care may include maintenance of nutrition and prevention of hypoglycaemia, nasogastric suction to prevent gastric distension and aspiration, intravenous cimetidine to prevent gastric bleeding, treatment of hypotension by fluid replacement and vasoactive drugs, administration of oxygen, correction of metabolic acidosis, treatment of bleeding with fresh frozen plasma, dialysis if indicated by renal failure, and treatment of secondary infections by antibiotics(4).

IMMUNIZATION: There are 2 attenuated live YF virus vaccines available: the neurotropic French Dakar vaccine(2) and the 17D strain(2,5,6,7,8), the latter being the only preparation approved for use in Canada. Immunity develops 10 days after primary immunization and persists for more than 10 years(12). Only designated Yellow Fever Vaccination Centre clinics approved by PHAC can administer YF immunization(13), which should then be recorded on an appropriately validated International Certificate of Vaccination.

PROPHYLAXIS: Immunisation is required legally for travelers visiting areas of endemicity or traveling from areas of endemicity into counties that are free of YF(2). Also, passive antibody, interferon, and interferon inducers can be effective if given before YF infection or during incubation(3). Most often they are used when it is clear that the individual has been exposed to YFV (i.e. in a laboratory setting)(4,5). Travelers should also take precautions against mosquito bites when in areas with yellow fever transmission.


LABORATORY-ACQUIRED INFECTIONS: Thirty-eight cases were reported up until 1980 with 8 deaths(14).

SOURCES/SPECIMENS: Blood(1,4,5,6), liver tissue(6), and cerebrospinal fluid(2).

PRIMARY HAZARDS: Contact with infected blood and/or tissues(9,10).

SPECIAL HAZARDS: Direct or indirect exposure to aerosols of concentrated YF 17D vaccine(8). Evidence also exists of transmission of YFV from the infected blood of a patient to a caregiver(9), from infected monkey and mouse tissues, and from handling infected laboratory animals(10).



CONTAINMENT REQUIREMENTS: Containment Level 3 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.

PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street clothing and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes(16).

OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) or other appropriate primary containment device in combination with personal protective equipment. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animals or large scale activities(16).


SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (30 min).

DISPOSAL: Decontaminate all materials for disposal by steam sterilisation, chemical disinfection, and/or incineration(16).

STORAGE: In sealed, leak-proof containers that are appropriately labelled and locked in a Containment Level 3 laboratory(16).


REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.

UPDATED: October 2010.

PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.

Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.

Copyright © Public Health Agency of Canada, 2010 Canada

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