Researchers in Brazil are scrambling to explain an outbreak of microcephaly, a rare and potentially fatal birth defect. Almost 3,000 cases of the condition, marked by an abnormally small head due to insufficient brain growth, were reported by Brazilian physicians in November and December alone, nearly 20 times the normal rate. During the same months last year, only 147 cases of microcephaly were identified in the entire country.
Thinking about birth defects in "epidemic" terms is strange. Most congenital abnormalities, no matter the organ system affected, are chalked up to a combination of genetic mutations and environmental factors, like toxins floating through the air or prescription drugs. But to say that a birth defect can "spread," from pregnant woman to pregnant woman? That's unheard of.
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Fortunately, it's probably not what's going on in Brazil, at least it's not microcephaly that's being transmitted like a communicable disease between patients. Instead, the most likely theory points the finger at mosquitos carrying a virus called Zika.
Transmitted by Aedes mosquitos, the same kind that carry dengue and yellow fever, the viral infection causes fevers, joint pain and pinkeye - but most people don't realize they have it. Speaking with WebMD, Dr. Amesh Adalja said only 1 out of 5 people will exhibit any symptoms after being infected.
Zika isn't airborne, and it usually requires a host body (like that of a monkey or mosquito) to be transmitted. Two cases of the virus being transmitted sexually, however, have been confirmed. Zika was also found in the amniotic fluid of two Brazilian women who gave birth to children with microcephaly, strong evidence that the virus may be to blame for the birth defect.
Zika first appeared in Uganda in 1947. At the time, the virus was confined to rhesus monkeys, not humans. The first human case was identified in 1954 in Nigeria, more than 2,500 miles west of Uganda.
Zika, though, had probably spread east to the islands of mainland Asia by the mid-20th century. Analyzing evolving strains of the virus, Senegalese researchers have placed Zika in Southeast Asia by at least 1945, although the first confirmed Asian case was found in Malaysia in the late 1960s. The trail goes somewhat cold after that, since Zika is easily confused for dengue fever, a virus epidemiologists have spent far more time and money investigating.
In 2007, an outbreak was reported on the Micronesian island of Yap. French Polynesia was next, with an outbreak in 2013 that left at least 28,000 people infected and 42 suffering from a rare autoimmune disorder called Guillain-Barre syndrome. Having already reached the fringes of Southeast Asia (Yap, for example, is separated from the eastern tip of Vietnam by more than 1,900 miles of the Pacific Ocean), it was only a matter of time before the virus made its way to the Americas.
Brazil has been hit worst; there's no question about that. The first cases were reported by the western state of Bahia in 2014.
While Bahia is much closer to Nigeria than Southeast Asia, but researchers believe the strain currently ravaging Brazil originated somewhere in the Pacific islands based on genetic research. A team from the UK's Lancaster University believes the FIFA World Cup, held in 12 cities across Brazil, may have brought visitors carrying the virus. More likely was an international canoe race held the same year, featuring exclusively teams from the Pacific.
Columbia, Guatemala and Venezuela have also reported recent cases. In November 2015, the first case was identified in Mexico. Puerto Rico reported its own Zika case in December. All signs suggest that Zika will eventually make landfall in the US, probably making landfall on the Gulf Coast.
In Harris County, Texas, health officials say they've identified the first case of Zika in a US patient. Centers for Disease Control staff have confirmed the diagnosis.
Dr. Peter Hotez, Chair of Tropical Pediatric Medicine at Texas Children's Hospital, said the new case of Zika "is a wake-up call," speaking to reporters at Medscape. For now, the virus hasn't been found in mosquitos; the patient diagnosed with Zika in Houston had recently returned from El Salvador.
Hotez warned, however, of a "perfect storm brewing for Zika virus in the US." He cited the presence of 2 mosquitos that could carry the virus in Houston, as well as the area's high poverty rate. "People living without window screens and near discarded tires and other water-catching containers where the mosquitoes can breed."
Hawaiian health officials have reported the first case of microcephaly linked to a Zika infection on US soil. A child on the island of Oahu was born with an abnormally small head, and researchers from the Centers for Disease Control & Prevention have linked the child's condition to its mother's infection with the Zika virus, CNN reported on Monday, January 18.
The mother had spent a month in Brazil last year, which is where CDC officials believe she was infected. The CDC says there is currently no risk of transmission. Neither the woman nor her child are infectious.
Experts say there's probably no reason for panic here. People in South America are exposed to mosquitos far more than residents of North America, and recent US outbreaks of similar viruses have proved limited in scope. This is, however, all part of a worrisome trend. Rare tropical infections are popping up in America now more than ever, and it's probably linked to global warming.
Mosquitos can only survive in sufficiently-warm environments. Moisture is important, too, so tropical regions that are both hot and wet sustain the largest populations. With the climate heating up everywhere, mosquitos who once found only tropical countries hospitable are now able to make a home further afield - including the United States.