The Department of Foreign Affairs has issued travel advisories for pregnant women involving 19 central and southern American states - following an outbreak of a virus that can lead to birth defects.

Pregnant women intending to travel to countries including Brazil, Barbados, Colombia, Haiti, Mexico and El Salvador are advised to contact their healthcare professional before doing so and consider postponing travel plans.

The 'Zika' outbreak began in Brazil, which is hosting this year's summer Olympics. It can lead to babies being born with abnormally small heads and underdeveloped brains.

The US Centers for Disease Control and Prevention (CDC) has extended a travel warning to another eight countries or territories that pose a risk of infection with Zika.

The CDC issued a travel advisory last week warning pregnant women to avoid 14 countries and territories affected by the virus.

The mosquito-borne virus is spreading through the Caribbean and Latin America.

El Salvador has urged women there to avoid getting pregnant until 2018 to avoid their children developing birth defects from the virus.

The Zika virus is transmitted by the Aedes aegypti mosquito, which is also known to carry the dengue, yellow fever and Chikungunya viruses.

Health experts are unsure why the virus, which was first detected in Africa in 1947 but unknown in the Americas until last year, is spreading so rapidly in Brazil and neighboring countries.

Last week, US health authorities confirmed the birth of a baby with microcephaly in Hawaii to a mother who had been infected with the Zika virus while visiting Brazil last year.

US health authorities have now expanded the travel warning to avoid 22 countries in Latin America and the Caribbean.

Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde and Samoa are now included in the level two travel alert issued by the CDC.

Last week the agency urged pregnant women and women considering becoming pregnant to postpone visits to Puerto Rico, Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname and Venezuela.

Although research is still under way, significant evidence in Brazil shows a link between Zika infections and rising cases of microcephaly, a neurological disorder in which babies are born with smaller craniums and brains.

"We'd like to suggest to all the women of fertile age that they take steps to plan their pregnancies, and avoid getting pregnant between this year and next," said El Salvador's Deputy Health Minister Eduardo Espinoza.

He said the government decided to make the announcement because 5,397 cases of the Zika virus had been detected in El Salvador in 2015 and the first few days of this year.

Official figures show 96 pregnant women are suspected of having contracted the virus, but so far none have had babies born with microcephaly.

In Colombia, which has the second-highest Zika infection rate after Brazil, the government is also advising women to delay becoming pregnant, but only for six to eight months.

In Brazil the number of suspected cases of microcephaly increase to 3,893 by 16 January from 3,530 cases ten days earlier.

So far, health authorities have only confirmed six cases of microcephaly where the baby was infected with the Zika virus.

The surge of cases since the virus was first detected last year in Brazil led the ministry to link it to the fetal deformations and warn pregnant women to use insect repellent to avoid mosquito bites.

Some facts about Zika

The Zika virus is spread to people through the bite of an infected mosquito, the same mosquito that transmits dengue, chikungunya and yellow fever. There is no vaccine for Zika.

The Zika virus is usually relatively mild, with symptoms such as skin rash, fever, muscle and joint pain, lasting up to seven days. It is uncommon for people infected with Zika to need hospital treatment.

In the Americas, there is no evidence that the Zika virus can cause death, PAHO says, but sporadic cases have been reported of more serious complications in people with pre-existing diseases or conditions, causing death.

Researchers in Brazil and PAHO say there is growing evidence that links Zika to microcephaly, a neurological disorder in which babies are born with smaller than normal heads and brains.

In northeast Brazil, there has been a marked increase in cases of newborn babies with microcephaly. Brazil's health ministry has said the number of suspected cases of microcephaly in newborns increased by about 360 in the 10 days to 16 January to 3,893.

Research is under way into the effects of the Zika virus on pregnant women and newborn babies; information about the possible transmission of Zika from infected mothers to babies during pregnancy or childbirth is "very limited", PAHO says.

Brazil has the highest rate of infection, followed by Colombia. Zika outbreaks have also been reported in Ecuador, El Salvador, Guatemala, Haiti, Honduras, Mexico, Panama, Paraguay, Puerto Rico, Suriname and Venezuela, among other countries.

Colombia's health ministry says Zika has already infected 13,500 people across the country and there could be as many as 700,000 cases this year.

Jamaica has not reported any confirmed cases of Zika, but the health ministry has recommended women delay becoming pregnant for the next six to 12 months.

One in four people infected with Zika develop symptoms and many cases of Zika go undetected, making it difficult to estimate the true scale of the outbreak in the Americas. PAHO says there are no reliable estimates of the number of cases in the region.

Based on reports from affected countries, PAHO estimates there are at least 60,000 suspected cases of Zika, though the real figure is thought to be far higher