Spread of the Zika virus in Europe, an ever-increasing risk

The Zika virus

Once again this virus is a hot topic. In fact, many athletes have refused to go the Rio Olympics because of the Zika epidemic currently affecting Brazil. Similarly, since August, all blood donations collected in the USA are now being tested for the virus before being used.

The Zika virus is a member of the virus family Flaviviridaeand the genus Flavivirus. It is spread by daytime-active Aedes mosquitoes (the virus is transmitted by the female mosquito when it bites to feed on blood). This virus is a member of the same viral family as dengue or yellow fever. It has already spread in Asia and Africa (discovered in Uganda in 1947), and has recently emerged in Central and South America (in 2015, in many South American countries, including Brazil, with 1.5 million people infected there alone). The illness it causes manifests itself three to twelve days after being bitten by the carrier insect, with various symptoms similar to those of dengue or chikungunya, which are also carried by the same mosquito: fever, headaches, skin rashes, fatigue, muscle and joint pains. This virus, for which there is as yet no treatment or vaccine, provokes only a few symptoms among most of the people infected. On the other hand, in the foetus of an infected mother, it causes serious lesions and malformations, resulting in particular in microcephaly, which is incurable and causes irreversible mental under-development in the child. Finally, in some cases the viral infection has been linked to the development of Guillain-Barré syndrome, consisting of gradually worsening paralysis, ultimately affecting the breathing muscles.

The spread of the disease is closely linked to its carrier, the mosquito

The insect carrying the disease is the female Aedesmosquito. It can easily be identified by the black and white stripes on its legs. The species currently capable of transmitting the Zika virus is Aedes aegypti, originating from Africa. Aedes albopictus (tiger mosquito, originally from Asia) could also prove to be a Zika virus carrier – it already carries dengue fever and chikungunya. The unusual feature of these two species of ‘tiger’ mosquito is, unlike many other species of mosquito, that they also bite during the day. These two species can, unusually, lay their eggs in very small quantities of water (just a few millilitres suffice, so possibly in flowerpot trays or gutters). The traditional protective measures (spraying swampland) are therefore only partly effective, because many small private pools and ponds remain untreated. The only effective prevention, in the absence of treatment and vaccines, is to protect yourself against bites. The female mosquito is infected by the virus when feeding on the blood of a person carrying Zika. The virus multiplies inside the mosquito without any effect on the insect. Next time it bites, the mosquito offloads the virus into the blood of a new person. The symptoms appear 3 to 12 days after the bite, but during this period that person can be the source of infection for other mosquitoes if he or she is bitten again. This is why people infected with Zika must avoid being bitten again in order to interrupt the cycle of viral transmission.

Risk of spreading in Europe

According to the European office of the World Health Organisation, the global risk of the Zika virus spreading in Europe is slight to moderate at the moment. The two main factors that are and will be decisive for the spread of the virus in Europe today are:

• The geographical areas of distribution (and their evolution) of the two species of mosquitoes in Europe (see fig. 1 and fig. 2)

• The opportunity for these two mosquitoes to bite people infected with the virus who have recently been travelling in countries where the epidemic is currently present (Brazil, for example).

 

Figure 1: distribution of the species Aedes albopictus in July 2016 | source: ECDC

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Figure 2: distribution of the species Aedes aegypti in July 2016 | source: ECDC

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At the moment, there is no epidemic of Zika virus in Europe, despite the presence and expansion observed of both mosquitoes in Europe, as the distribution maps show. However, the risk is considered to be high in the zones where Aedes aegypti – the main carrier of Zika – is spreading rapidly (shores of the Black Sea, Madeira). Aedes albopictus is spreading more rapidly in Europe, notably around the Mediterranean, although this species seems to be only a secondary carrier of Zika. Nevertheless, this species is expanding fast geographically, which makes it a serious risk factor for the spread of this virus. The essential factor in the epidemic outbreak of this virus is the opportunity for the mosquito to feed on the blood of a person who is carrying the virus and who was previously travelling abroad, because it is impossible for any epidemic to originate from an indigenous European reservoir of the virus.

Role of the Pest Control Operators in the prevention and management of the tiger mosquito

The various species of Zika-carrying mosquitoes are multiplying rapidly in Europe. The speed of travel today is making the prospect of an epidemic of this virus in Europe all too real. Unlike other species of mosquito, which generally need large surface areas of water to develop (external problem, natural space), the larvae of the two species of tiger mosquito are able to develop in just a few millilitres. Currently being handled by professional State organisations (EID), this problem of the tiger mosquito in the context of the fight against Zika necessarily involves and will involve the PCO’s, since this species essentially proliferates in areas like public parks and the gardens of people’s homes. So, the PCO’s can be involved at two levels in dealing with the tiger mosquito:

• In preventing the proliferation of this species by being involved in disseminating the diagnosis/surveillance of “Tiger” in towns and cities where we want to conduct joint prevention campaigns in public and private areas;

• In controlling these two established species, in particular by waging war against larval development on private and public land.

Involving the PCO’s in managing this public health problem is both logical and a guarantee of effectiveness and safety for the population of Europe.

Bibliography

Institut Pasteur
World Health Organisation
Confederation of European Pest Management Associations (CEPA)
ECDC

Dr Romain Lasseur
IZIPEST (www.izipest.com)
Expert on invasive species/carriers
romain.lasseur@izipest.com