We know about chikungunya and dengue fevers, but now there’s another virus transmitted by mosquitos: Zika. This usually benign virus could cause severe birth defects. The World Health Organization predicts 3 to 4 million cases in the Americas. Europe meanwhile, is trying to anticipate and minimize the risk of fetus malformation by recommending that pregnant women defer any possible trips to a country that has already been hit by the epidemic. What is this virus really? What should we fear? E Professor Eric Caumes, specialist in infectious and tropical diseases at the Institute Pierre Louis of Epidemiology and Public Health (Inserm/UPMC), explains.
Aedes aegypti, the vector for dengue and chikungunya viruses. ©IRD/Nil Rahola
We hear a lot about Latin America, particularly Brazil, but Zika virus was identified long ago in other geographical areas. Where did it come from?
éric Caumes. The Zika virus is an arbovirus of the family Flaviviridae, which is similar to that of dengue and yellow fever. It was first isolated in 1947 from a Rhesus monkey in Uganda in the Zika forest, and it was then found in humans in 1952, still in Uganda and Tanzania. Since 2007, Zika virus epidemics have occurred in Micronesia, French Polynesia and New Caledonia.
What are the symptoms?
é. C. Zika may cause flu-like symptoms such as a mild fever, a rash that spreads across the chest, as well as headache and conjunctivitis. The incubation period ranges from 3 to 12 days. Joint pain can persist for up to 21 days after the first signs. Its severity is related to the existence of secondary neurological complications (Guillain Barre syndrome mainly)..
How is it transmitted? Is there a reliable diagnosis and effective treatment?
é. C. The transmission is mostly by vector, that is to say, via mosquitoes belonging to the family Culicidae and Aedes (sylvatic and urban transmission) called Ae. aegypti (main mosquito in question at present) and Ae. albopictus (urban transmission). The virus is transmitted to arthropods (invertebrates) when the mosquito takes blood from them. The virus multiplies in the host vector without affecting it, remains present in the insect throughout its life to be again transmitted to other animals during the next meal.
To date, only one case of sexual transmission has been reported in the United States by a sick patient returning from Senegal who has contaminated his wife while the Zika virus was not present in the United States. If transmission by blood transfusion has never been proven, the risk cannot be ruled out because there is a very transient viremia. During the epidemic in French Polynesia, two cases of perinatal transmission have been described. Newborns would be infected through the placenta or during delivery. Transmission through milk has not been demonstrated, but the question remains.
There is currently no commercially available diagnostic kit or serological kit (immunofluorescence, ELISA or rapid test) to detect the viral genome. In addition, the Zika virus physicochemical characteristics and sensitivity to disinfectants remain unknown, leaving little way for the development of antiviral therapy or a vaccine. In fact, the treatment should be symptomatic and pain relief without the use of anti-inflammatories.
Can we estimate the amplification and speed of the epidemic’s propagation?
é. C. To do this, we must conduct an epidemiological investigation in the field. Scientists and doctors refer to epidemic curves (number of cases over time) that take into account two key parameters: the ratio of reproduction and intergenerational gap. Epidemiological studies can plan the actions of community health and make the most of available resources, but can face logistical challenges, including inadequate human resources issues.
What is the risk of imported cases in mainland France?
é. C. The outbreak has been particularly virulent in Brazil since May 2015. But no virus recognizes borders. The High Council of Public Health (HCSP), including myself, took stock of the knowledge on the Zika virus, as well as its method of transmission, the epidemiological and clinical presentation of infection and means of laboratory diagnosis. Given the presence of mosquitoes and passenger flows, HCSP has evaluated the risk of introduction of the disease and possible Zika epidemic impact in the French departments of America, Reunion, Mayotte where Aedes aegypti operates and in metropolitan France where Aedes albopictus is present.
Rather than add to the emerging concern, we must insist on vector control that has to be done on a collective scale but especially by the individual, including a mosquito-net campaign and the elimination of stagnant water on the terraces and balconies. For now, mosquitoes are still in the process of hibernation, especially on the French Riviera and the entire south of France. But their inexorable geographical progression gradually leads to other regions, particularly into the île-de-France region since summer 2015. We must therefore prepare for the fight against mosquitoes as happens regularly in regions where there has been epidemics of dengue and chikungunya because the Aedes vectors share much in common, including the potential to trasmit Zika, in addition to dengue and chikungunya.
éric Caumes is a Professor of Infectious and Tropical Diseases at UPMC and Head of the Infectious Diseases Pitié Salpêtrière. This service has a real expertise in the management of highly contagious respiratory diseases such as those who require isolation.
The team members have specialized in the treatment of tropical diseases and pathologies found in patients after foreign travel and immunocompromised patients, including patients affected by HIV and organ transplant. Eric Caumes is also Chairman of the committee on travel-related and imported diseases; member of the High Council for Public Health; and editor of the Journal of Travel Medicine.
Institut Pierre Louis d’épidémiologie et de santé publique (Inserm/UPMC)
équipe « épidémiologie clinique de l’infection à VIH : stratégies thérapeutiques et comorbidités » (in French)
Haut conseil de santé publique (In French)
Read: Tintin’s travel traumas: Health issues affecting the intrepid globetrotter. éric Caumes, Loïc Epelboin, France Leturcq, Phyllis Kozarsky, Peter Clarke. Presse Med. (2015) Doi : 10.1016/j.lpm.2015.01.006