US adds 4 more countries to Zika travel alert list

World Health Organization Sounds Alarm on Zika Virus

(Reuters) -- The U.S. Centers for Disease Control and Prevention on Monday added four more countries and territories to a growing list of places where travelers risk being infected with Zika, a rapidly spreading mosquito-borne virus.

The CDC added American Samoa, Costa Rica, Curacao, and Nicaragua to a list of 28 other regions, on the day The World Health Organization declared the virus - linked to thousands of suspected cases of birth defects in Brazil - an international public health emergency.

SEE ALSO: WHO declares Zika virus a global health emergency

The CDC issued its first travel alert last month and has since been updating the list that cautions people, particularly pregnant women, from traveling to those areas. (http://1.usa.gov/1JuM6jt)

See photos related to the virus:

17 PHOTOS
Zika, Mosquito borne illness causing birth defects in Brazil
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US adds 4 more countries to Zika travel alert list
RECIFE, BRAZIL - JANUARY 29: Dr. Valeria Barros treats a 6-week old baby born with microcephaly at the Lessa de Andrade polyclinic during a physical therapy session on January 29, 2016 in Recife, Pernambuco state, Brazil. Health officials believe as many as 100,000 people have been exposed to the Zika virus in Recife, although most never develop symptoms. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 31: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is held by her mother Nadja Cristina Gomes Bezerra on January 31, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 29: David Henrique Ferreira, 5 months, who was born with microcephaly, is kissed by his mother Mylene Helena Ferreira on January 29, 2016 in Recife, Pernambuco state, Brazil. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 29: David Henrique Ferreira, 5 months, who was born with microcephaly, is held by his grandmother Maria Elisabeth as his mother stands at right on January 29, 2016 in Recife, Pernambuco state, Brazil. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
Pregnant woman Angelica Prato, infected by the Zika virus, is attended at the Erasmo Meoz University Hospital in Cucuta, Colombia, on January 25, 2016. Authorities in Brazil, Colombia, Ecuador, El Salvador and Jamaica have advised couples to avoid pregnancy for the time being due to the presence of the Zika virus because if a pregnant woman is infected by the virus, the baby could be born with microcephaly. The Zika virus, a mosquito-borne disease suspected of causing serious birth defects, is expected to spread to all countries in the Americas except Canada and Chile, the World Health Organization said. AFP PHOTO/Schneyder Mendoza / AFP / SCHNEYDER MENDOZA (Photo credit should read SCHNEYDER MENDOZA/AFP/Getty Images)
RECIFE, BRAZIL - JANUARY 27: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is placed in her crib by her father Joao Batista Bezerra on January 27, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)
Kleisse Marcelina ,24, bathes her son Pietro, 2 month, suffering from microcephalia caught through an Aedes Aegypti mosquito bite, in Salvador, Brazil on January 28 , 2016. AFP PHOTO / Christophe SIMON / AFP / CHRISTOPHE SIMON (Photo credit should read CHRISTOPHE SIMON/AFP/Getty Images)
RECIFE, BRAZIL - JANUARY 26: Grandmother Ivalda Caetano holds Ludmilla Hadassa Dias de Vasconcelos (2 months), who has microcephaly, at Oswald Cruz hospital on January 26, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. The Brazilian government announced it will deploy more than 200,000 troops to combat the mosquitos which are spreading the Zika virus. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 27: Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized and alerted authorities over the microcephaly crisis in Brazil, measures the head of a 2-month-old baby with microcephaly on January 27, 2016 in Recife, Brazil. The baby's mother was diagnosed with having the Zika virus during her pregnancy. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 31: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is held by her mother Nadja Cristina Gomes Bezerra on January 31, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
Physical therapist Isana Santana treats Ruan Hentique dos Santos, suffering from microcephalia caught through an Aedes Aegypti mosquito bite, at Obras Socias irma dulce hospital in Salvador, Brazil on January 28 , 2016. AFP PHOTO / Christophe SIMON / AFP / CHRISTOPHE SIMON (Photo credit should read CHRISTOPHE SIMON/AFP/Getty Images)
The parents of Icaro Luis , 2 month, suffering from microcephalia caught through an Aedes Aegypti mosquito bite, Physical therapist Isana Santan at the Obras socias irma dulce hospital in Salvador, Brazil on January 28, 2016. AFP PHOTO / Christophe SIMON / AFP / CHRISTOPHE SIMON (Photo credit should read CHRISTOPHE SIMON/AFP/Getty Images)
Physical therapist Isana Santana treats Ruan Hentique dos Santos, suffering from microcephalia caught through an Aedes Aegypti mosquito bite, at Obras Socias irma dulce hospital in Salvador, Brazil on January 28 , 2016. AFP PHOTO / Christophe SIMON / AFP / CHRISTOPHE SIMON (Photo credit should read CHRISTOPHE SIMON/AFP/Getty Images)
Ana Paula Santos, 34, holds her 45-day-old daughter Flavia Alessandra suffering from microcephalia supposedly caught through an Aedes aegypti mosquito bite, at the Obras Sociais Irma Dulce hospital in Salvador, Brazil on January 27, 2016. AFP PHOTO / Christophe SIMON / AFP / CHRISTOPHE SIMON (Photo credit should read CHRISTOPHE SIMON/AFP/Getty Images)
RECIFE, BRAZIL - JANUARY 25: Estafany Perreira holds her nephew David Henrique Ferreira, 5 months, who has microcephaly, on January 25, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. Microcephaly results in newborns with abnormally small heads and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to further spread in South, Central and North America. At least twelve cases of Zika in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)
RECIFE, BRAZIL - JANUARY 25: Mother Mylene Helena Ferreira cares for her son David Henrique Ferreira, 5 months, who has microcephaly, on January 25, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. Microcephaly results in newborns with abnormally small heads and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to further spread in South, Central and North America. At least twelve cases of Zika in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)
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The Zika virus is transmitted by the Aedes aegypti mosquito, which is also known to carry the dengue, yellow fever and Chikungunya viruses. There is no vaccine or treatment for the virus, which typically causes mild fevers and rashes. An estimated 80 percent of those infected suffer no symptoms whatsoever.

Brazil has reported nearly 4,000 suspected cases of microcephaly, in which infants are born with smaller-than-usual brains.

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