Zika fever is caused by an arbovirus (a virus transmitted by insects) belonging to the flavivirus genus of the Flaviviridae family, like the dengue virus and yellow fever. The insect vector of the disease, the Aedes female mosquito, can be identified thanks to the black and white markings on its legs. The species currently able to spread the Zika virus is the Aedes aegypti, which originated in Africa. Aedes albopictus (or the tiger mosquito from Asia) could also prove to be a vector of the Zika virus, as it already transmits the dengue and chikungunya viruses. (Read the news 2016/03/04: Low competence of Aedes mosquitoes for Zika virus transmission)
A mosquito becomes infected with the virus during a blood meal when it bites a person with Zika fever. The virus multiplies in the mosquito without affecting the insect. Then, when the mosquito next bites, it releases the virus into the bloodstream of another person. Symptoms appear 3 to 12 days after the bite but, during this time, the person can infect other mosquitoes if they are bitten again. This is why people suffering from Zika must avoid getting bitten to break the viral transmission cycle.
Most people infected with the virus (an estimated 70 to 80% of cases) do not develop any symptoms. In the rest of the population, the symptoms caused by the Zika virus are flu-like and include tiredness, fever (not necessarily high), headaches, and muscular and joint pain in the limbs. Different types of skin rash also feature among the symptoms. Some patients also present with conjunctivitis, pain behind the eyes, digestive problems or even swelling of the hands or feet. In most cases, the symptoms are mild and do not require hospital treatment.
As these symptoms are non-specific and the Zika virus is found in the same regions as the dengue and chikungunya viruses, it is difficult to make an accurate diagnosis.
Complications are rare but, in the event of a major outbreak, they should not be overlooked. Some cases of Guillain-Barré syndrome-type neurological complications have been observed following infection in Brazil and French Polynesia. This syndrome is characterized by progressive ascending paralysis which can affect the respiratory muscles. (Read the press release: Zika: Confirmation of a causal link between the Zika virus and Guillain-Barré Syndrome - 2016/03/01)
Pregnant women can pass on the virus to their unborn children and this can lead to serious fetal brain development defects. (Red the press release: Zika and microcephaly: first trimester of pregnancy most critical - 2016/03/16)
The Zika virus was detected for the first time in a monkey in Uganda in 1947. A year later, it was isolated in an Aedes mosquito from the same region.
The first human cases appeared in the 1970s in Africa (Uganda, Tanzania, Egypt, Central African Republic, Sierra Leone, Gabon and Senegal) and then in some countries in Asia (India, Malaysia, the Philippines, Thailand, Vietnam and Indonesia).
In 2007, an actual epidemic broke out in Micronesia (Yap Islands in the Pacific Ocean), causing 5,000 infections.
In 2013 and 2014, 55,000 cases of Zika were reported in French Polynesia. The epidemic then spread to other islands in the Pacific, namely New Caledonia, the Cook Islands and Easter Island.
The Zika virus was detected for the first time in the northwest of Brazil in May 2015 and it quickly spread to other regions of the country. Brazil has declared the highest number of Zika cases ever recorded with between 440,000 and 1,300,000 suspected cases reported.
The virus has been present in Colombia, El Salvador, Guatemala, Mexico, Panama, Paraguay, Suriname, Venezuela and Honduras since October 2015.
On December 18, 2015, two cases were detected in French Guiana by the Institut Pasteur in French Guiana. Two cases were also identified in Martinique.
On April 7, 2016, there are 16 650 compatible reported cases in Martinique (biological confirmation in progress). There are 3 620 cases in French Guiana and 1 090 in Guadeloupe.
In metropolitan France, 176 cases have been laboratory confirmed in people returning from circulation area of Zika virus, whose 7 pregnant women and 1 case of neurological complications. A person has been infected by Zika virus by sexual transmission. (Source: Invs - the French Institute for Public Health Surveillance)
The Zika virus could spread to the regions where the Aedes mosquito is already present and where people already infected with Zika are staying. In mainland France, the Aedes albopictus mosquito (tiger mosquito) is present in 30 departments of the country. In general, the vector develops in May and is active (and therefore able to transmit the virus) between May and November.
Fighting the disease
There is currently no vaccine for preventing Zika virus infection and no specific medication for treating the disease.
Treatment involves taking pain killers to relieve the painful symptoms. However, aspirin should be avoided until infection by the dengue virus has been ruled out because, in this case, the anticoagulant effect of the drug could cause bleeding.
As soon as symptoms appear, blood and urine samples are taken to confirm the diagnosis using an RT-PCR (Reverse Transcriptase-Polymerase Chain Reaction) method to detect the presence of the virus's genes.
If doubt remains after a negative result using RT-PCR, serological screening will be able to confirm whether antibodies specific to the Zika virus are present or not.
These tests are only carried out by the National Reference Centers for Arboviruses (CNRs).
The only way of protecting against the Zika disease is to protect yourself from mosquito bites both day and night, especially in the early morning and early evening when mosquitoes are most active, using physical and chemical methods — wear clothes that cover up your skin (long sleeves, pants), use suitable repellents on your clothes and areas of exposed skin, and use insecticide-impregnated mosquito nets and electric insecticide diffusers indoors.
Pregnant women living in high-risk areas must protect themselves from mosquito bites using the above methods, particularly during the first six months of pregnancy when the risk of birth defects is at its highest. Regarding repellents, they must observe the precautions for use recommended for their condition.
Pregnant women wishing to travel to areas affected by the Zika epidemic must weigh up the risks beforehand with their family physician.
As well as these personal protection measures, disease prevention also involves combating the proliferation of mosquitoes. For this, all potential mosquito breeding sites, for example stagnant water in flower pots, gutters and old tires, must be removed. It is particularly advisable to empty any water containers located around your home after each spell of rain.
“The Geopolitics of the Mosquito” - Go further with our experts!
VIDEO - Virus Zika, pourquoi aujourd'hui ?
Arnaud Fontanet, responsable de l’unité d’épidémiologie des maladies émergentes, co-directeur de l’école Pasteur/CNAM de Santé publique
Arnaud Fontanet nous explique dans cette vidéo les résultats obtenus avec ses collègues de Polynésie française lors de l’épidémie de Zika de 2013-2014 : les scientifiques ont établi le lien de causalité entre le virus et certains cas graves avec syndromes de Guillain-Barré d'une part, et d’autre part des cas de microcéphalie chez des enfants nés de femmes ayant été infectées au cours de leur grossesse.
VIDEO - Zika Summit 2016
Zika virus poses many questions and concerns for humanity. Scientists and experts are racing to understand the relationship between Zika virus infection and associated neurological complications such a microcephaly and Guillain-Barré syndrome.
The Institut Pasteur, WHO and other partners convened reserachers and public health experts working on this ongooing public health emergency to share preliminary results and discuss next steps.