Dengue, Zika and Chikungunya viruses on the rise

Dengue is the most common and fastest-spreading mosquito-borne viral disease in the world. A dengue vaccine has also recently been approved in Switzerland. No vaccine is currently licensed in Switzerland against the Zika and Chikungunya viruses, which are also mainly transmitted by the yellow fever mosquito or Asian tiger mosquito. In the case of the Zika virus, sexual transmission or viral infection through a blood transfusion is also possible. Antibody detection is important for all arboviruses, and suspected dengue cases should also be subjected to an antigen test.

Arboviruses (“arthropod-borne viruses”) is the umbrella term for a group of different viruses that are transmitted by arthropods. The invasive vectors that are currently the focus of European surveillance activities include, in particular, exotic mosquito species of the genus Aedes (e.g. Aedes albopictus, Aedes japonicus, Aedes aegypti) [1]. These can transmit infectious diseases that have so far mainly circulated in subtropical and tropical zones. As far as Switzerland is concerned, chikungunya, dengue, Zika and West Nile fever are of particular importance [1]. Prof. Dr. med. Maja Weisser Rohacek, Senior Physician, Head of Consultation Service, Research Group Leader, at the Clinic for Infectious Diseases & Hospital Hygiene at the University Hospital Basel, gave an up-to-date overview of important points in this context [2].

Dengue virus: WHO warning

The main vectors of the dengue virus (Fig. 1) are various mosquitoes, primarily the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus) (Fig. 2) [3,4]. For 2024, the highest dengue case numbers to date have been recorded in Brazil (over nine million cases), followed by Argentina, Paraguay, Peru and Colombia [5,6]. The cases reported on the European mainland this year (e.g. in Germany, Italy and France) are due to travelers returning from endemic areas. Human-to-human transmission is theoretically possible (e.g. with blood transfusions), but is rare.

Symptoms and course: An infection is asymptomatic in around 40-80% of cases, but can also cause a wide range of clinical symptoms. Classic dengue fever is characterized by high fever, headache, aching limbs and skin rashes [7]. The incubation period is 3-14 days, usually 7-10 days. Severe cases are rare overall (5%). Severe forms of the infection, up to 30% of which are fatal, are dengue hemorrhagic fever and dengue shock syndrome [8]. These complications often occur after secondary infections with different dengue virus strains.

Diagnosis: A dengue virus infection is suspected in people who have a fever plus at least two of the following criteria. two of the following criteria: Nausea/vomiting, rash, pain, positive tourniquet test, leukopenia. The warning signs for severe courses are shown in Overview 1 [2]. In order to clarify suspicious cases, a dengue virus NS (nonstructural protein) 1 antigen test should always be performed in addition to the IgM and IgG antibody test (box). In contrast to the antibodies, the NS1 antigen is usually detectable from the onset of symptoms, but only for about two weeks. The sensitivity of the NS1 antigen rapid test is 75-80%. When combined with antibody detection (IgG, IgM, combo rapid test), a sensitivity of >90% is achieved [2].

Treatment: To date, there is no effective medication, i.e. treatment is only symptomatic. Symptoms can be alleviated with antipyretic and analgesic preparations, although those based on salicylates are contraindicated due to their blood-thinning effects [7]. Patients should also be advised to drink plenty of fluids. In rare cases of severe courses, patients must be hospitalized and close monitoring is required [2].

Infection prophylaxis/vaccination: When staying in a dengue risk area, measures to protect against insects are recommended, especially during the day and at dusk. These include wearing long-sleeved, light-colored, insecticide-treated loose clothing; applying mosquito repellent (during the day and in the evening) and sleeping under a mosquito net with the windows closed and the air conditioning on [9].

There are currently two vaccines against dengue fever available on the European market, one of which has now also been approved in Switzerland** [7]. At the end of July 2024, Swissmedic approved the Qdenga® vaccine for people aged four years and older who travel to areas where dengue fever is ^widespread$ [14].

** Information as of 28.08.2024
$ This includes mainly subtropical and tropical areas in Central Africa, Latin America, India and Southeast Asia; the disease also occurs in the south of the USA (Texas).

Chikungunya virus is also spread worldwide

The name “Chikungunya” comes from the language of the Makonde – an African people in south-eastern Tanzania and northern Mozambique – and translates as “the one who walks bent”, which is due to a characteristic symptom of the disease [12]. The chikungunya virus is also mainly transmitted by the Asian tiger mosquito and the yellow fever mosquito. The chikungunya virus has been detected in over 60 countries worldwide (Africa, Asia, the Caribbean, South and Central America, isolated outbreaks in southern Europe). In the period from February to April 2024, the highest number of cases was recorded in South and Central American countries, with Brazil also leading the way here (243,024 cases), followed by Paraguay (3121), Argentina (382) and Bolivia (268). In regions outside South and Central America, there are reports from Thailand (208), India (195), Timor-Leste (195), Maldives (182), Pakistan (38) and Malaysia (13). According to the ECDC, Senegal (6) was the only African country to report cases of chikungunya this year [12,13].

Symptoms and course: The disease usually occurs 7 to 9 days (rarely 3 to 12 days) after being bitten by an infected mosquito and manifests itself as high fever, severe joint and muscle pain and headaches, sometimes accompanied by a skin rash (Fig. 3) [14]. As a rule, it is harmless; in a few cases, however, it can lead to prolonged fatigue and debilitating joint pain lasting weeks to months. In newborns, older people and people with chronic illnesses, a severe course can sometimes be observed.

Diagnostics: In addition to clinical assessment, serological procedures (enzyme immunoassay) and molecular biological procedures (RT-PCR^&) are used. It is generally recommended to perform an RT-PCR up to 5 days after the onset of symptoms, and an enzyme immunoassay after 5 days and beyond .

^& RT-PCR=Reverse Transcriptase Polymerase Chain Reaction

Treatment: There is currently no treatment for the virus itself. Symptoms can be alleviated with paracetamol .

Infection prophylaxis/vaccination: The most important measure to prevent infection is to protect yourself from mosquito bites. Aedes mosquitoes are active during the day and bite from dawn to dusk [16]. A vaccine against chikungunya fever for people over the age of 18 has been available on the European market since June 2024, but has not yet been approved in Switzerland (as of 28.08.2024) [14].

Zika virus: only a few cases in Switzerland so far

Until 2014, the disease had occurred sporadically in around 20 countries in Asia, Oceania and Africa. Since an epidemic in 2015/2016, 60 countries and regions in South and Central America, the Caribbean, the Pacific, Asia (Malaysia, Philippines, Singapore, Thailand, etc.) and Africa (Cape Verde, Guinea-Bissau) have been affected. After the epidemic in South and Central America subsided, the number of Swiss cases among travelers has also decreased again. The first locally vector-borne Zika cases in Europe were observed in France in 2019. The Zika virus is also mainly transmitted by the yellow fever mosquito or Asian tiger mosquito. However, transmission through sexual contact and pregnant, infected women can also transmit the virus to the foetus and transmission through blood transfusion is also possible .

Symptoms and course: In 60-80 percent of cases, the infection is asymptomatic [17]. In other cases, the symptoms are often milder than those of other mosquito-borne infectious diseases. The most frequently described symptoms are skin rash, headache, joint and muscle pain, inflammation of the conjunctiva and fever [18]. The symptoms usually subside on their own within 4 to 7 days [17]. In rare cases, neurological complications may occur. Infection with Zika viruses during pregnancy can also lead to serious neurological sequelae in the fetus.

Diagnostics: In Switzerland, samples from pregnant women must be sent to a National Reference Center in accordance with the amended Epidemics Ordinance of 5 May 2016 [17]. For the Zika virus, this is the Reference Center for Newly Emerging Viral Infections (NAVI) in Geneva.

Therapy: There is no specific medication for the treatment of the disease, i.e. therapy is symptomatic.

Infection prophylaxis/vaccination: Currently, the most important measure to protect against infection is to protect yourself from mosquito bites, both indoors and outdoors [17]. The FOPH recommends that pregnant women, people with a weakened immune system or with other chronic illnesses and travelers with small children consult a doctor to find out about any health risks associated with this and other tropical diseases.

Congress: medArt Basel

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