Pathogens and transmission
The Zika virus is transmitted to people primarily through the bite of an infected mosquito of the genus Aedes (primarily Aedes aegypti but also Aedes albopictus). Transmission through sexual contact is possible, and pregnant women who are infected can pass the virus to the fetus. Transmission by blood transfusion is possible.
In 60 % to 80 % of cases, the infection is asymptomatic. If symptomatic, a variety of clinical symptoms can occur, which generally resolve themselves within four to seven days. In rare cases, neurological complications like microcephaly and Guillain-Barré syndrome may occur. An infection with Zika-virus during pregnancy can lead to serious neurological sequelae in the foetus.
Distribution and frequency
Until 2014, the disease occurred sporadically in around 20 countries in Asia, Oceania and Africa. Since an epidemic in 2015-2016, which started in May 2015 in Brazil, more than 60 countries and territories in South and Central America, the Caribbean, the Pacific, Asia (Malaysia, the Philippines, Singapore, Thailand, etc.) and Africa (Cabo Verde and Guinea-Bissau) have been affected. After the epidemic in South- and Central America subsided, the Swiss case numbers for travel-associated Zika-infection have also declined.
In Europe, the first cases of locally vector transmitted Zika have been observed in France in 2019. Because introduced Asian tiger mosquitoes, Aedes albopictus, spread in Europe, also in Switzerland, there is a risk of transmission of Zika virus in Switzerland too. However, the risk is very low and occurs only under certain conditions. For example, the local mosquitoes would need to ingest the virus from a traveller infected with Zika.
There is no specific drug for treating Zika, so only the symptoms are treated. So far, the main measure for preventing infection has been protection from mosquito bites, both indoors and outdoors. It is recommended to wear loose-fitting, long clothes treated with insecticide, to use an effective repellent day and night, and to sleep under a mosquito net (especially in rooms without air conditioning).
Pregnant women, people with a weakened immune system or other chronic conditions, and those travelling with small children, should consult a doctor to find out about all the health risks associated with tropical diseases.
Under the terms of 5 May 2015 amendment to the ordinance on epidemics, samples from pregnant women must be sent to a national reference centre. For Zika virus this is the reference centre for newly emerging viral infections (NAVI/CRIVE) in Geneva.