• Yellow fever occurs in sub-Saharan Africa and South America and is transmitted by mosquitoes.
• Disease may be severe in unvaccinated travelers and death may occur in over 50%.
• A highly effective vaccine is available.
• Due to potentially severe side effects the vaccine is used with caution in immunocompromised or elderly individuals, as well as in pregnant women.

As against all mosquito-borne diseases, prevention from mosquito bites is during day and night (see “Insect and tick bite protection” factsheet). The available vaccine is highly efficacious and provides a long-term protection. It is recommended for people aged 9 months or older who are travelling to yellow fever endemic areas. In addition, providing proof of vaccination may be mandatory for entry into certain countries.

The vaccine is a live-attenuated form of the virus. In immunocompetent persons, protection starts about 10 days after the first vaccination. Reactions to yellow fever vaccine are generally mild and include headache, muscle aches, and low-grade fevers.  Side effects can be treated with paracetamol but aspirin and other nonsteroidal anti-inflammatory drugs, for example ibuprofen or naproxen, should be avoided.  On extremely rare occasions, people may develop severe, sometimes life-threatening reactions to the yellow fever vaccine – which is why this vaccine is used with caution in immunocompromised individuals, pregnant women and the elderly for safety reasons. Talk to your travel health advisor if you belong to this group.

• Dengue fever is the world's most common insect-borne infectious disease.
• Great attention should be paid to mosquito protection during the day!
• The disease can cause high fever, muscle and joint pain, and skin rashes. In rare cases, bleeding may occur. There is no specific treatment.
• For personal safety, we strongly recommend that you inform yourself in detail about dengue.

Dengue fever is the most common insect-borne infectious disease worldwide. There are 4 known serotypes of dengue virus, so it is possible to be infected with dengue more than once. Approximately 1 in 4 infected individuals develop symptoms of dengue, resulting in high fever, muscle and joint pain, and skin rash. In rare cases, most often after a second infection, life-threatening bleeding and shock (severe drop of blood pressure) may occur.

In 3 out of 4 cases, an infection with the virus remains asymptomatic. After a short incubation period (5-8 days), 1 out of 4 infected people present an abrupt onset of fever, headache, joint, limb and muscle pain, as well as nausea and vomiting. Eye movement pain is also typical. A rash usually appears on the 3rd or 4th day of illness. After 4 to 7 days, the fever finally subsides but fatigue may persist for several days or weeks.

In rare cases, severe dengue can occur. Particularly susceptible are local children and seniors as well as people who have experienced a prior dengue infection. Tourists extremely rarely present with severe dengue. In the first days, the disease resembles the course of classic dengue fever, but on the 4th/5th day, and usually after the fever has subsided, the condition worsens. Blood pressure drops, and patients complain of shortness of breath, abdominal discomfort, nosebleeds, and mild skin or mucosal hemorrhages. In the most severe cases, life-threatening shock may occur.

There is no specific treatment for dengue virus infection. Treatment is limited to mitigation and monitoring of symptoms: fever reduction, relief of eye, back, muscle and joint pain, and monitoring of blood clotting and blood volume. Patients with severe symptoms must be hospitalised.

For treatment of fever or pain, paracetamol or acetaminophen are recommended (e.g. Acetalgin® Dafalgan®). Drugs containing the active ingredient acetylsalicylic acid (e.g. Aspirin®, Alcacyl®, Aspégic®) must be avoided.

Effective mosquito protection during the day and especially during twilight hours (i.e. sunset) is the best preventive measure:

1. Clothing: Wear well-covering, long-sleeved clothing and long pants and spray clothing with insecticide beforehand (see factsheet “prevention of arthropod bites”)
   
2. Mosquito repellent: Apply a mosquito repellent to uncovered skin several times a day (see factsheet “prevention of arthropod bites”)
   
3. Environmental hygiene: Do not leave containers with standing water (coasters for flower pots, etc.) in your environment to avoid mosquito breeding sites.

Note on dengue vaccines:

two vaccines against dengue are on the market: Qdenga®and Dengvaxia®. The Qdenga® vaccine was approved by the European Union in December 2022. 

However, due to the data available, many European countries, as well as the Swiss Expert Committee for Travel Medicine (ECTM), currently recommend vaccination with Qdenga® only for certain travelers and in special situations. Consultation with a specialist in tropical and travel medicine is therefore recommended.

Of note:

• Qdenga® is not yet licensed in Switzerland and the recommendations for travelers will be limited once Qdenga® is licensed  in Switzerland. 
  
• The vaccine Dengvaxia® is not a vaccine for travelers.
  

Consistent mosquito protection during the day (see above) is still considered the most important preventive measure against dengue!

• Chikungunya is a viral disease transmitted by Aedes mosquitoes.
• Chikungunya can be prevented by protection against mosquito bites.
• It typically presents with severe joint pain of the hands and feet. In a few patients, these may persist for weeks or months.

The infection may present with some or all of the following symptoms: sudden onset of high-grade fever, chills, headache, redness of eyes, muscle and joint pain, and rash. The rash usually occurs after the onset of fever and typically involves the trunk and extremities, but can also include the palms, soles of the feet, and the face.

Often fever occurs in two phases of up to one week duration, with an interval of one to two fever-free days in between. The second phase may present with much more intense muscle and joint pain, which can be severe and debilitating. These symptoms are typically bilateral and symmetric and mainly involve hands and feet, but may also involve the larger joints, such as the knees or shoulders.

About 5-10% of infected people continue to experience severe joint pain even after the fever has subsided, in some cases lasting up to several months or, albeit rare, even years.

• FOPH Switzerland: https://www.bag.admin.ch/bag/de/home/krankheiten/krankheiten-im-ueberblick/chikungunya.html
• WHO - Chikungunya fact sheet: https://www.who.int/news-room/fact-sheets/detail/chikungunya
• Center for Disease Control and Prevention (CDC): https://www.cdc.gov/chikungunya/index.html