Emergencies

Dispelling rumours around Zika and complications

Updated
12 September 2016

Spotlight! There is no specific repellent that works better against the Aedes mosquito

There are many repellents that are effective against all mosquitoes including Aedes mosquitos. Effective repellents contain DEET (diethyltoluamide), or IR 3535 ((3- [N-butyl-N-acetyl], aminopropionic acid ethyl-ester) or KBR3023 (also called Icaridin or Picaridin). These are the most common biologically active ingredients in insect repellents. Active ingredients are listed on the product label. The following active ingredients repel or kill the mosquito when it rests or approaches the body: DEET (N, N-diethyl-3-methylbenzamide), IR3535 (3- [N-butyl-N-acetyl], aminopropionic acid ethyl-ester) or KBR3023 (also called Icaridin or Picaridin).

There is no minimum or maximum percentage of active ingredient required. Insect repellents may be applied to exposed skin to protect against the bites of mosquitoes or on the clothes. WHO recommends covering the skin with clothing as much as possible and using insect repellents as effective measures to protect against bites from mosquitoes that transmit viruses such as chikungunya, dengue, yellow fever and Zika.

Repellents must be used in strict accordance with the label instructions. There is no evidence of any restriction of the use of these repellents by pregnant women if they are used in accordance with the instructions on the product label.

Bacteria used to control the male mosquito population are not spreading Zika further

Wolbachia is a bacterium that can stop viruses such as, dengue and Zika from growing inside mosquitoes, therefore stopping mosquitoes from spreading these diseases to humans. When females mate with males carrying the bacteria, the eggs do not hatch, thus supressing mosquito populations. Wolbachia bacteria are found in 60% of common insects, including butterflies, fruit flies and some mosquitoes.

Aedes mosquitoes carrying Wolbachia bacteria have been released as part of trial tests in several places since 2011, including Australia, Brazil, Indonesia and Viet Nam, to help control dengue (which is transmitted by the same mosquito that transmits Zika). Scientists released thousands of Wolbachia-infected mosquitoes in a suburb of Rio de Janeiro in September 2014 and repeated this a year later. These pilot deployments need to be monitored and evaluated to see whether these new tools are successful in stopping the spread and control of disease. WHO’s Vector Control Advisory Group is preparing a manual on how best to design such studies. The manual will be released later this year.

No evidence that Zika virus and its complications are linked to releases of genetically modified mosquitoes in Brazil

There is no evidence that Zika virus disease or microcephaly in Brazil is caused by genetically modified mosquitoes. Only genetically modified male mosquitoes are released, so there is no risk of disease transmission to humans because only females bite humans. The genes of male mosquitoes are modified causing future offspring to die. This practice is designed to control mosquito populations.

WHO encourages affected countries and their partners to boost the use of current mosquito control interventions as the most immediate line of defence, and to judiciously test the new approaches that could be applied in future.

No evidence that sterilized male mosquitoes contribute to the spread of Zika

A technique being developed to stop Zika is the controlled mass release of male mosquitoes that have been sterilized by low doses of radiation. When a sterile male mates, the female’s eggs do not survive. When the sterile males outnumber the fertile males in a natural environment, the mosquito population dies out. The technique has been used in the past against insects and fruit flies, for example.

There is no evidence that the technique has been associated with increases in microcephaly cases or other human anomalies or defects. However, the evidence for the public health value of this technique needs to be established. WHO encourages affected countries and their partners to scale up the use of current mosquito control interventions as the most immediate line of defence, and to judiciously test new control tools that could potentially be applied in the future.

Most symptoms of Zika virus disease are different from those of seasonal flu

The symptoms common to both seasonal flu and Zika virus disease are fever (with varying intensity), muscle and joint pain.

Seasonal flu can cause severe illness or death. The disease is characterized by a sudden onset of high fever, cough (usually dry, can be severe), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and runny nose.

Zika virus disease usually causes mild illness, and most people will not develop any symptoms. The most common symptoms of Zika include low fever or rash, conjunctivitis, muscle and joint pain, appearing a few days after a person has been infected by an infected mosquito or after sexual intercourse with an infected person. However, there is scientific consensus that Zika virus is a cause of microcephaly and Guillain-Barré syndrome which can be a fatal condition.

No evidence that vaccines cause microcephaly in babies

There is no evidence linking any vaccine to the increases in microcephaly cases that were observed first in French Polynesia during the 2013-2014 outbreak and more recently in northeastern Brazil.

An extensive review of the literature published in 2014 found no evidence that any vaccine administered during pregnancy resulted in birth defects. The Global Advisory Committee on Vaccine Safety, which provides independent scientific advice to the World Health Organization (WHO) on vaccine safety issues, reached a similar conclusion in 2014.

In addition, national regulatory agencies are responsible for ensuring that products released for public distribution, such as vaccines, are evaluated properly and meet international standards of quality and safety. WHO assists countries in strengthening their national regulatory systems:

No evidence that pyriproxyfen insecticide causes microcephaly

A team of WHO scientists recently reviewed data on the toxicology of pyriproxyfen, one of 12 larvicides that WHO recommends to reduce mosquito populations. It found no evidence that the larvicide affects the course of pregnancy or the development of a fetus. The US Environmental Protection Agency and EU investigators reached a similar conclusion when they carried out a separate review of the product.

Larvicides are an important weapon in the public health practitioner’s arsenal. Especially in cities and towns with no piped water, people tend to store drinking water in outdoor containers. These sources of water, as well as standing water that may collect in garbage, flower pots and tyres, serve as ideal breeding grounds for mosquitoes.

Larvicides such as pyriproxyfen are often used in containers where people store water to kill the mosquito in its larval stage. When people drink water from containers that have been treated with pyriproxyfen, they are exposed to the larvicide – but in tiny amounts that do not harm their health. Moreover, 90% - 95% of any larvicide ingested is excreted into the urine within 48 hours. This product has been used since the late-1990s without being linked to microcephaly.

Fish can help stop Zika.

Some countries affected by Zika and dengue are using biological methods as part of an integrated approach to mosquito control. El Salvador, for example, with strong support from fishing communities, is introducing larvae-devouring fish into water storage containers.

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This page links all WHO information to its response on the Public Health Emergency of International Concern