Yellow Fever Key Facts
- Nope, unfortunately we’re not talking about the Asian Persuasion here. That’s an entirely different case. The Yellow Fever we’re talking about is an acute viral haemorrhagic disease transmitted by infected mosquitoes. Yes, mosquitoes! Those little buggers! The “yellow” in the name refers to the jaundice that affects some patients.
- Symptoms that points to The Yellow Fever include fever, headache, jaundice, muscle pain, nausea, vomiting and fatigue.
- A small proportion of patients who are transmitted with the virus develop severe symptoms and approximately half of those symptomatic patients die within 7 to 10 days. Sounds like a bad rip off from the movie ‘The Ring‘, doesn’t it?
- The virus is endemic in tropical areas of Africa and Central and South America.
- Large epidemics of yellow fever occur when infected people introduce the virus into heavily populated areas with high mosquito density and where most people have little or no immunity, due to lack of vaccination. In these conditions, infected mosquitoes of the Aedes aegypti species transmit the virus from person to person. Yes, it’s quite similar to how Dengue is spread.
- Yellow Fever is prevented by an extremely effective vaccine, which is safe and affordable. A single dose of the Yellow Fever Vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease. A booster dose of the vaccine is not needed. However, International Certificates of Vaccination for the Yellow Fever is valid for only 10 years.
- The Yellow Fever vaccine provides effective immunity within 10 days for 80-100% of people vaccinated, and within 30 days for more than 99% of people vaccinated.
- There is currently no specific anti-viral drug for yellow fever. Good supportive treatment in hospitals improves survival rates.
Signs & Symptoms
Once the Yellow Fever virus is contracted, it incubates in the body for 3 to 6 days. Many people do not develop and experience symptoms. However, when symptoms do show up, the most common of them are fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting. In most cases, the symptoms of Yellow Fever are short-lived and disappear after 3 to 4 days.
A small percentage of patients, however, enter a second phase, which is much a more toxic phase within 24 hours of recovering from initial symptoms. High fever returns and several body systems are affected, usually the liver and the kidneys. In this second phase people are likely to develop jaundice which is the yellowing of the skin and eyes. This jaundice is the reason why the name is ‘yellow fever’. Some patients also complains dark urine and abdominal pain with or without vomiting. Like Dengue Fever, bleeding can occur spontaneously from the mouth, nose, eyes or stomach. Half of the patients who enter the toxic phase die within 7 to 10 days.
Yellow fever is very difficult to diagnose, especially during the early stages. A more severe case can be confused with severe malaria, leptospirosis, viral hepatitis (especially fulminant forms), other haemorrhagic fevers, infection with other flaviviruses (such as dengue haemorrhagic fever), and poisoning.
Polymerase chain reaction (PCR) testing in blood and urine can sometimes detect the virus in early stages of the disease. In later stages, testing to identify antibodies is needed (ELISA and PRNT).
Populations at Risk
A total of forty-seven countries in Africa (34) and Central and South America (13) are either endemic for, or have regions that are endemic for, yellow fever. A modelling study from African data sources estimates the burden of Yellow Fever during 2013 was 84,000–170,000 and around 200,000 severe cases worldwide with 29,000–60,000 deaths
Occasionally travellers who visit yellow fever endemic countries may bring the disease to countries free from yellow fever, to be later on spread by indigenous mosquitoes from person to person. In order to prevent the importation of such diseases, many countries require proof of vaccination against yellow fever (the International Certificate of Vaccination) before they will issue a visa, particularly if travellers come from, or have visited yellow fever endemic regions.
In past centuries (17th to 19th), yellow fever was transported to North America and Europe, causing a massive outbreaks that disrupted economies, development and in some cases decimated populations.
Treatment & Prevention
There are currently no specific anti-viral drug to treat for Yellow Fever. Good supportive treatment, that is focused on rehydration, fever control, and preventing liver and kidney damage is the mainstay of therapy, and may improve outcome.
The holy trinity of Prevention includes:
Vaccination is the most important method to prevent The Yellow Fever disease. The Yellow Fever vaccine is safe, affordable and a single dose provides life-long protection against yellow fever disease. A booster dose of yellow fever vaccine is not needed.
However, the International Certificate of Vaccination mandates that the Yellow Fever vaccination is valid for 10 years. Therefore, individuals often traveling to high risk regions must renew their Yellow Fever vaccination every 10 years before visa issuance.
People who are usually excluded from vaccination include:
- infants aged less than 9 months;
- pregnant women – except during a yellow fever outbreak when the risk of infection is high;
- people with severe allergies to egg protein; and
- people with severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or who have a thymus disorder.
In accordance with the International Health Regulations (IHR), countries have the right to require travellers to provide a certificate of yellow fever vaccination. If there are medical grounds for not getting vaccinated, this must be certified by the appropriate authorities. In Indonesia, this is usually done by Health Officials from the Port Health Office, and/or other Hospitals, Clinics, and/or Physicians that are certified by and registered at the Port Health Office. The IHR are a legally binding framework to stop the spread of infectious diseases and other health threats. Requiring the certificate of vaccination from travellers is at the discretion of each State Party, and it is not currently required by all countries.
The risk of yellow fever transmission in urban areas can be reduced by eliminating potential mosquito breeding sites. This includes applying larvicides to water storage containers and other places where standing water collects.
Both vector surveillance and control are components of the prevention and control of vector-borne diseases, especially for transmission control in epidemic situations. For yellow fever, vector surveillance targeting Aedes aegypti and other Aedes species will help inform where there is a risk of an urban outbreak.
Personal preventive measures such as wearing clothes that minimize skin exposure and applying mosquito repellents are recommended to reduce the risk for mosquito bites. The use of insecticide-treated bed nets is limited by the fact that Aedes mosquitos bite during the daytime.
Epidemic Preparedness and Response
Prompt detection of yellow fever and rapid response through emergency vaccination campaigns are essential for controlling outbreaks. However, underreporting is a concern – the true number of cases is estimated to be 10 to 250 times what is now being reported.