Daniele Ferreira dos Santos holds her son Juan Pedro as he undergoes visual exams at the Altino Ventura foundation in Recife, Brazil, on Jan. 28. Santos was never diagnosed with Zika, but she blames the virus for her son's microcephaly.
When a child has microcephaly, abnormal brain development results in an abnormal head size - much smaller than other children of the same age.
Daniele Ferreira dos Santos holds her son Juan Pedro outside her house in Recife on Jan. 26.
A municipal worker sprays insecticide to combat the Aedes aegypti mosquitoes that transmit the Zika virus in Recife on Jan. 26.
In the face of the health crisis, President Dilma Rousseff declared war on the Aedes mosquito, with the government set to deploy around 220,000 members of the Armed Forces to educate the population about how to prevent the mosquito's spread.
Physical therapist Isana Santana treats Ruan Hentique dos Santos, who suffers from microcephalia, at Obras Socias Irma Dulce hospital in Salvador, Brazil, on Jan. 28.
A sterile female Aedes aegypti mosquito is seen on the forearm of a health technician in a research area to prevent the spread of Zika in Guatemala City on Jan. 28.
Only Aedes aegypti mosquitoes are known for sure to spread Zika.
It's very hard to kill Aedes mosquitoes because they like to breed in unexpected places, such as bottle caps filled with water, trash cans and discarded tires.
Gleyse Kelly da Silva holds her daughter Maria Giovanna, who was born with microcephaly, as she undergoes visual exams at the Altino Ventura foundation in Recife on Jan. 28. Brazilian officials still say they believe there's a sharp increase in cases of microcephaly and suspect the Zika virus, which first appeared in the country last year, is to blame. The concern is strong enough that the U.S. Centers for Disease Control and Prevention warns pregnant women to reconsider visits to areas where Zika is present.
Gleyse Kelly holds her daugther Maria Geovana, in Recife, Brazil,on Jan. 25.
Nearly 4,000 suspected cases of microcephaly have been reported in Brazil since October, compared with fewer than 150 cases reported in the country in all of 2014.
A young man jumps off a tire swing into a polluted and slow-moving canal on January 26, 2016 in Recife, Pernambuco state, Brazil on, Jan. 26. Stagnant water provides potential breeding sites for mosquitoes which carry the Zika virus.
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 in Recife on Jan. 27. The baby's mother was diagnosed with having the Zika virus during her pregnancy. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development.
A municipal worker wears a protective suit during an operation to combat the Aedes aegypti mosquitoes that transmit the Zika virus in Recife on Jan. 26.
Researchers do not know whether a single bite can transmit the virus or how long the mosquito has to have been infected to spread it.
Geovane Silva holds his son Gustavo Henrique, who has microcephaly, at the Oswaldo Cruz Hospital in Recife, Brazil, on Jan. 26.
Microcephaly almost always causes significant brain damage and can be life threatening.
A health worker shows larvae of the Aedes aegypti mosquitoes found inside a warehouse during an operation to combat the mosquitoes in Recife on Jan. 26.
Matheus Lima and Kleisse Marcelina rela at home with their two-month-old son Pietro, who suffers from microcephaly, in Salvador, Brazil on Jan. 28.
Inspectors spray insecticide around the Sambadrome, where the city's Carnival parades will take place next month, in Rio De Janeiro on Jan. 26.
Brazil's health minister says the country will mobilize some 220,000 troops to battle the mosquito blamed for spreading a virus linked to birth defects.
A researcher looks at Aedes aegypti mosquitoes kept in a container at a lab of the Institute of Biomedical Sciences of the Sao Paulo University on Jan. 8.