This 2006 file photo provided by the Centers for Disease Control and Prevention shows a female Aedes aegypti mosquito in the process of acquiring a blood meal from a human host. Picture: James Gathany/Centers for Disease Control and Prevention via AP, File

Washington - The Centers for Disease Control and Prevention, which reported this week that a dozen cases of Zika virus have been confirmed in the United States, is expanding its advisory that pregnant women should avoid travel to countries currently seeing high rates of infection.

The agency's initial list contained 14 countries, but the CDC on Friday added eight more - in South America, the Caribbean and Polynesia - as places where the reach of the virus is growing.

The CDC now is working with authorities in Brazil to study a potential link between the mosquito-borne virus and a rare syndrome known as Guillain-Barré that can lead to paralysis. In Brazil, which is currently the epicentre of Zika, public health officials were already investigating a link between the virus and a rare birth condition called microcephaly. That country has seen nearly 3,900 suspected cases since October, with the babies involved suffering serious brain damage.

In recent days, several countries have taken drastic measures to try to combat the virus. Brazil, Colombia, El Salvador and Jamaica are all calling on women to consider delaying becoming pregnant.

Here's the latest on the virus:

QUESTION: What is Zika?

ANSWER: The virus was discovered in 1947 in a feverish rhesus monkey living in the Zika Forest of Uganda, but until 2007 scientists knew of only 14 human cases of the disease. That year it arrived on the travel-brochure-perfect Yap Island in the southwestern Pacific Ocean. Within a few months, nearly three-quarters of the island's 11,000 or so residents older than 3 had been infected.

In 2013 Zika popped up again, this time in Tahiti and other parts of French Polynesia. An estimated 28,000 people (about 11 percent of the population of those islands) felt sick enough with the virus to seek medical care. By 2014 it was showing up in several other South Pacific spots: New Caledonia, east of Australia; the Cook Islands; and, early this year, Easter Island, which marked the official arrival of the disease in the Americas, since that remote island is part of Chile.

Q: What's going on in Brazil?

A: The country is facing an unprecedented number of Zika virus cases - more than 1 million - as well as an unprecedented number of microcephaly cases that health officials believe are linked. In recent months, Brazil has spent more than $300 million to battle the mosquito, mobilising hundreds of soldiers in the effort and going door-to-door to try to wipe out places where mosquitoes breed.

According to Post correspondent Dom Phillips, the Brazilian Health Ministry says 80 percent of those who catch Zika show no symptoms. The rest may suffer fever, muscle pain and rashes for a few days. Most people who come down with it recover quickly.

On Wednesday, the government released new figures regarding Zika and microcephaly:

Total number of suspected Zika-related microcephaly cases since October 22 when the government introduced a mandatory reporting requirement - 3,893

Number of confirmed cases - 224 with six being caused by Zika,

Not microcephaly - 282 cases

The rest are still being investigated.

Q: What's the scientific basis for the suspected link between Zika and microcephaly?

A: The World Health Organisation and the CDC, which is assisting Brazilian authorities in their investigation, have yet to definitively establish a connection between Zika and microcephaly. But the CDC has confirmed the presence of Zika in the bodies of two newborns with microcephaly who died and in the placentas of two women who miscarried children with microcephaly.

Q: What other complications related to Zika should I be worried about?

A: The CDC is working with Brazilian health officials to investigate a possible link to a growing number of cases of Guillain-Barré syndrome, a rare disease that occurs when your own immune system damages nerve cells. Most people recover fully from it, but others experience long-term nerve damage or paralysis. In rare cases, people have died.

In Brazil, health officials have identified hundreds of cases of Guillain-Barré, a significant increase from last year.

Q: How is the virus transmitted?

A: When a mosquito bites an infected person and then bites someone else. It is cannot be transmitted from person to person.

Q: Where is Zika spreading??

A: Haiti said on Januuary 15 that it had confirmed its first cases of Zika virus in five people in the area of Port-au-Prince, the country's capital. There were cases last year in Panama and Puerto Rico.

Colombian officials said Wednesday that 13,500 people are infected already and that the number could grow rapidly.

"We expect an expansion similar to what we had with the chikungunya virus last year, to finish with between 600,000 to 700,000 cases," health minister Alejandro Gaviria told journalists, according to Reuters.

Q: What can I do to reduce my risk of becoming infected or sick?

A: According to CDC guidance issued this week, Zika virus can be spread from a pregnant woman to her unborn baby. There have been reports of a serious birth defect of the brain called microcephaly and other poor pregnancy outcomes in babies of mothers who were infected with Zika virus while pregnant. Knowledge of the link between Zika and these outcomes is evolving, but until more is known, CDC recommends special precautions for the following groups:

* Women who are pregnant (in any trimester): Consider postponing travel to any area where Zika virus transmission is ongoing. If you must travel to one of these areas, talk to your doctor first and strictly follow steps to prevent mosquito bites during your trip.

* Women who are trying to become pregnant: Before you travel, talk to your doctor about your plans to become pregnant and the risk of Zika virus infection. Strictly follow steps to prevent mosquito bites during your trip.

Specific areas where Zika virus transmission is ongoing are often difficult to determine and are likely to change over time.

As of Thursday, here are the counties and territories impacted, according to the Pan American Health Organisation:

Brazil, Colombia, El Salvador, French Guiana, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Saint Martin, Suriname and Venezuela, as well as Puerto Rico.

On Friday, the CDC added eight more countries to the list:

Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, and Samoa.

If you're travelling to one of these countries, here are some tips from the CDC for travellers to prevent getting bitten by mosquitoes:

* Wear long-sleeved shirts and long pants.

* Use insect repellent.

Washington Post