Zika is transferred to humans by the Aedes mosquito.
Unlike malaria-carrying mosquitoes, Aedes is most active during the day. Barrier methods of prevention, such as mosquito nets, are less effective. The mosquitoes can survive in both indoor and outdoor environments.
Several species of Aedes can transmit Zika. The main ones are the Aedes albopictus, or Asian tiger mosquito, and the Aedes aegypti, known as the yellow fever mosquito.
The Zika virus was first identified in monkeys in Uganda in 1947, but it has affected people in Africa, Asia, the Pacific Islands, and South and Central America.
In 2016, a major outbreak in Brazil raised international awareness, and cases due to mosquito-borne transmission have been reported in the United States (U.S), in Texas and Florida.
The symptoms of infection are mild, but if a pregnant woman catches the virus, it can have a severe impact on the pregnancy and the unborn child.
- Zika virus cases typically occur in tropical climates.
- Infections in the U.S. are linked to travel to and from tropical regions.
- Symptoms of Zika virus infection can last for up to 1 week, but effects on a fetus can be severe.
- At present, there is no treatment for the virus.
- Avoiding mosquito bites is a key aspect of Zika virus prevention.
Zika virus may be symptomless, or the symptoms can be vague and mild. They last for up to a week.
Initial symptoms include:
- joint pain
- conjunctivitis, or red eyes
- muscle pain
- pain behind the eyes
Infection with the Zika virus is rarely severe enough to warrant hospitalization, and it is rarer still for an individual to die as a result.
However, complications of Zika can be devastating, especially if a woman contracts the virus while she is pregnant.
It can cause a brain defect known as microcephaly in the unborn child. The brain and head of the newborn will be smaller in size than is usual. Loss of pregnancy, stillbirth, and other congenital disabilities are also more likely.
During the recent outbreak in Brazil, there was a 10-fold increase in newborns with microcephaly after October 2015, compared with previous years.
There have also been reports of people developing Guillain-Barré syndrome following a Zika virus infection. Guillain-Barré syndrome is a rare but serious autoimmune disorder that affects the central nervous system.
Causes and risk factors
Travel to an area where Zika is present is the main risk factor for the virus.
It is mainly transmitted through mosquito bites, but it can also be passed on:
- From a pregnant woman to her fetus
- Through sexual contact
- Possibly, through a blood transfusion
To date, there have been no known transmissions of the virus from mother to infant during breast-feeding.
After a person has had the virus, they are protected from it in the future.
A woman who is pregnant should be particularly careful to avoid mosquito bites if she is living in or traveling to a country where Zika is present. It may be advisable to avoid travel to certain places during pregnancy.
The Centers for Disease Control and Prevention (CDC) issue travel warnings about Zika transmission.
These are mainly the tropical regions of:
- Central and South America
- North America
Travelers should refer to the CDC website for updates.
In the U.S., most cases have been linked to travel, but a few have resulted from mosquito-borne transmission. Zika-infected mosquitoes may be present in areas with wet lowlands and warmer temperatures.
Pregnant women who experience Zika symptoms should seek immediate medical attention.
Symptoms of Zika resemble those of flu, and they can be so mild that they go unnoticed. Most people will not visit a doctor or go to the hospital.
However, a pregnant woman who experiences symptoms should see a doctor for blood or urine testing.
Several rapid detection tests are available for qualified laboratories. These are distributed by the CDC.
These tests can confirm an infection.
Currently, there is no treatment for Zika.
A person with symptoms should:
- increase fluid intake to prevent dehydration
- take over-the-counter (OTC) pain killers to relieve pain and fever
The CDC also advise that pregnant women who are diagnosed with Zika should be considered for the monitoring of fetal growth and anatomy program every 3 to 4 weeks.
They also recommend seeing a doctor who specializes in pregnancy management and either infectious disease or maternal-fetal medicine.
There is currently no vaccination to protect against Zika. Avoiding mosquito bites is vital to avoid transmission.
To increase protection, people are advised to:
- use insect repellent
- wear long-sleeved garments and long pants
- place mosquito nets over beds (in some cases)
- use window and door screens
- avoid areas with standing water, by emptying tanks or choosing to camp away from lakes or ponds
Insect repellents should contain one of these:
- DEET (>10% concentration)
- oil of lemon eucalyptus (i.e., para-menthane-diol)
Insect repellent is most effective when applied:
- after applying sunscreen
- onto clothes as well as the body, for example, clothes treated with permethrin
- under clothing
Always check the instructions for the particular brand of repellent or sunscreen for guidance on use.
Avoid spreading the virus
A person who is infected with Zika should do everything possible to avoid being bitten by a mosquito for 3 weeks after symptoms appear, because the mosquito can pass the virus to the next person. This includes people who have returned from a trip with the disease.
The person must also be careful to avoid unprotected sex, as this, too, can pass on the virus. The CDC recommend using condoms during and after traveling to regions affected by the virus.
In some countries, including the U.S., health authorities recommend that men who visit an at-risk area but do not develop symptoms should use condoms for up to 6 months if they do not have symptoms and up to 6 months from the time of symptom onset. If their partner is pregnant, they should use condoms for the duration of the pregnancy.
A person who has had the Zika virus is normally protected, and unlikely to have it again.