Zika virus is a mosquito-borne illness that is spread by the Aedesspecies of mosquito, the mosquito also responsible for the transmission ofdengue and chikungunya viruses.1-3
Unlike malaria-carrying mosquitos, this species is mostly active during the day and so barrier methods such as mosquito nets are ineffective. These mosquitos can survive in both indoor and outdoor environments.1
The two known species responsible for Zika transmission are the Aedes albopictus, known as the Asian Tiger mosquito, and the Aedes aegyptispecies.2
The Zika virus was first identified in monkeys in Uganda in 1947. The first human case, however, was detected in Nigeria in 1954, and following that there have been further outbreaks in Africa, South East Asia and the Pacific Islands.
While the symptoms of Zika typically pass within the space of a week, there have been recent concerns about the virus are due to a potential link between Zika and birth defects such as microcephaly.
In light of a strongly suspected causal relationship, the World Health Organization (WHO) declared that the Zika virus outbreak constituted a Public Health Emergency of International Concern on 1 February 2016.
1 June 2016 update: The Centers for Disease Control and Prevention (CDC) has issued travel warnings for people traveling to areas and certain countries where Zika virus transmission is ongoing. These include:
Fast facts on Zika
- Central and South America: Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Cuba, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Nicaragua, Panama, Paraguay, Peru, Suriname, Venezuela
- Caribbean: Aruba, Barbados, Bonaire, Curaçao, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Puerto Rico, Saint Barthélemy, Saint Lucia, Saint Martin, Saint Vincent and the Grenadines, Sint Maarten, Trinidad and Tobago, US Virgin Islands
- Oceania: American Samoa, Fiji, Kosrae (Federated States of Micronesia), Marshall Islands, New Caledonia, Papua New Guinea, Samoa, Tonga
- North America: Mexico
- Africa: Cape Verde.
Here are some key points about Zika. More detail and supporting information is in the main article.
- Zika virus cases typically occur in tropical climates
- Infection in the US is linked to travel to and from tropical regions
- Symptoms of Zika virus infection can last for up to a week
- The majority of people infected with Zika virus do not display any symptoms
- Cases of Zika virus infection that result in hospitalization are uncommon
- A link between maternal Zika infection and infant microcephaly is currently being investigated
- As yet, there is not enough evidence to fully characterize the link between the two conditions
- Zika infection can spread from a mother to a fetus during pregnancy
- At present, there is no treatment for the virus
- Avoiding mosquito bites is a key aspect of Zika virus prevention.
Where does Zika virus occur?
While the majority of Zika virus cases occur in tropical regions such as Brazil, Colombia, Paraguay, Suriname, Venezuela and French Guiana, the possibility exists of mosquito infection in tropical-like climates in some cities, such as Houston and New Orleans in the US.1,2,4
Areas within the US which are of concern for potential Zika-infected mosquitos are those with wet lowlands, warmer temperatures and higher levels of poverty.2
Other countries with past or recent Zika virus infection include parts of Africa, Asia, the Americas, Oceania and the Pacific Islands.4Infection in the US is currently linked to exposure of travelers who return from other countries.1,2
Due to the fact that the species of mosquito that transmits Zika virus can be found throughout the world, the Centers for Disease Control and Prevention (CDC) believe it is likely that outbreaks of the disease will spread to new countries.1
WHO expects the virus to rapidly spread through the whole of the Americas and some virologists and epidemiologists also believe that Asia will be at risk.
Learn more about mosquitos and Zika
'Explosion' of Dengue fever reported in Brazil
A massive rise in cases of dengue
has also been reported in Brazil. This is particularly relevant because dengue is carried by the same Aedes
mosquito that carries Zika.
There has been a 50% increase in dengue cases in the last 3 weeks compared with the same period in 2015, with 74,000 cases having been described between 3rd and 23rd of January.
It seems likely that the escalation in dengue mirrors that for Zika and is evidence that attempts to control the mosquito are not working. Aedes aegypti
lays its eggs in standing water, and the Brazilian military has been drafted in to try and help exterminate the mosquito in these areas.
The mosquito also transmits chikungunya which, like dengue, causes marked fever
and joint pains, and if the incidence of this also rises, it gives further evidence that controlling and eradication techniques for the mosquito are failing.
Could Zika be transmitted by sexual intercourse?
Dr. Helen Webberley explained to Medical News Today
about another way that the virus could potentially be transmitted:
What is also of great concern is that the virus has been identified in patients who have not visited these areas and, along with the fact that Zika has been also identified in saliva, urine and semen (where it can exist for up to 2 weeks), raises the distinct possibility that Zika can be transmitted by sexual intercourse.
Although this does seem to be a rare event, it does raise the possibility that Zika can spread in any country, not just those that have the Aedes
Some countries are now recommending that men should use condoms for up to 28 days after visiting an "at risk" area if their partners are pregnant or likely to become pregnant, if they do not develop symptoms or for 6 months if they do.
The CDC state that men with a pregnant partner who have traveled to an "at risk" area should either "abstain from sexual activity (vaginal, anal, or oral) or consistently and correctly use condoms for the duration of the pregnancy."10
Evidence now shows that Zika infection can pass from a mother to a fetus during pregnancy.11
There is also a potential risk that the Zika virus could spread through infected blood. As a result, the US Food and Drug Administration (FDA) have advised people who have traveled to a region with active Zika virus transmission to defer from donating blood.12
Symptoms of Zika virus
Signs and symptoms of Zika virus are vague and can last for up to a week. Diagnosis of the virus is typically confirmed with a blood test.1
Symptoms of Zika virus include:1,2
According to the Pan American Health Organization (PAHO), only 1 in 4 people infected with Zika virus develop symptoms.5
In contrast, the CDC state the figure is 1 in 5.
In the past, there have also been reports of patients 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
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.6
Current research on Zika virus
A growing concern that is currently under investigation is a possible link between maternal Zika virus infection
and infant microcephaly
Brazil in particular has seen a surge in infants born with microcephaly since October 2015, at rates that have been reported to be 10 times higher than those in previous years.7
These infants have been tested for Zika virus with mixed results - some positive and some negative for the virus.7
Zika virus has been confirmed to be present in two amniotic fluid
samples of microcephalic babies.2,3
To date, there have been no known transmissions of the virus from mother to infant during breastfeeding.1
Other regions such as French Polynesia have seen an increase in fetal and newborn brain and spine defects over the past year.3
According to PAHO, "the French Polynesia health authorities hypothesize that Zika virus infection may be associated with these abnormalities if mothers are infected with the virus during the first or second trimester of pregnancy."3
What is microcephaly?
is a neurological condition where an infant's head circumference is significantly smaller than the average size for infants of the same age. Microcephaly can lead to developmental delays in movement and speech among other complications.8
Complications of microcephaly include:
- Dwarfism or short stature
- Facial distortion
- Mental retardation
Microcephaly is believed to be caused by both environmental and genetic factors. While there is currently no direct treatment for microcephaly, supportive therapy can assist infant development.
Treatments for Zika virus
Currently, there is no treatment or vaccination available for Zika and no rapid tests either, although several biotech companies claim to be on the brink of providing a rapid and sensitive test for detecting either the virus or antibodies to the virus.
However, the CDC recommend the following measures for people with the virus:
- Increasing fluid intake to prevent dehydration
- Pain and fever relief with medications like acetaminophen or paracetamol.
The CDC advise against using aspirin
or other non-steroidal anti-inflammatory medications until a diagnosis of dengue fever has been ruled out due to the risk of hemorrhage.1
Due to the concerns surrounding infant microcephaly, the CDC have advised that pregnant women who are diagnosed with Zika should be considered for the monitoring of fetal growth and anatomy
every 3-4 weeks. They also recommend a referral to a health care professional who specializes in pregnancy management and either infectious disease or maternal-fetal medicine.6
Preventing Zika virus
Since there is currently no vaccine to protect against the disease,avoiding mosquito bites is vital to preventing transmission of Zika virus
The CDC recommend using insect repellents, wearing long-sleeved garments and long pants, using window and door screens or running an air conditioner, and emptying areas with collected standing water, as this is a common environment in which mosquitos can lay their eggs.1
In some cases, mosquito bed netting may be recommended.1,4
It is recommended specifically that pregnant women traveling to countries which pose a risk for contracting Zika virus avoid mosquito bites.4,7
When choosing an insect repellent
, the CDC recommend using products which contain DEET
, and IR335
. Some products that contain oil of lemon eucalyptus
can also provide long-lasting protection.1,4
They also recommend applying insect repellant after the application of sunscreen, treating or wearing clothes treated with permethrin and not using insect repellent under clothing. Always check the instructions for the particular brand of repellant or sunscreen for guidance on use.1,4
If you are infected with the Zika virus, it is important to avoid being bitten by mosquitos during the first week of infection; the virus can be passed by humans to mosquitos via blood, increasing the risk of spread to others.1
People traveling home from an area affected by Zika should take steps to prevent mosquito bites for 3 weeks. By taking this precaution, people can help prevent the spread of Zika to uninfected mosquitos at home.
As Zika can be transmitted via sexual contact with a male partner with the virus, the CDC recommend the use of condoms, both during and after traveling to regions affected by Zika virus.
Travel recommendations for areas affected by Zika virus transmission
Due to current reports from Brazil concerning Zika virus, the CDC have issued a level 2 travel alert (practice enhanced precautions) for people traveling to several countries affected by Zika virus transmission. As of 1 June 2016, the alert is in place for the following countries:9
- American Samoa
- Cape Verde
- Costa Rica
- Dominican Republic
- El Salvador
- French Guiana
- Kosrae (Federated States of Micronesia)
- Marshall Islands
- New Caledonia
- Papua New Guinea
- Puerto Rico
- Saint Barthélemy
- Saint Lucia
- Saint Martin
- Saint Vincent and the Grenadines
- Sint Maarten
- Trinidad and Tobago
- US Virgin Islands
mosquito is not typically found at elevations above 6,500 feet (2,000 meters). As a result, the CDC state that travelers who intend to only be at this level of elevation are unlikely to become infected with the virus from a mosquito. People flying to an area of low elevation before traveling to an area of high elevation are still at risk of transmission from mosquitos, however.13
In addition, the CDC also advise that pregnant women consider postponing travel to any of the areas mentioned above. Any who decide to travel to these regions should discuss their journey with a health care provider, as well as measures to prevent mosquito bites.
In general, you are advised to speak with your health care provider if you are planning on traveling to a country in which Zika virus is a concern, as well as if you are experiencing symptoms of Zika virus.