If history repeats itself, the American media will make a dee doo hoot about the first confirmed case of Zika virus transmission that occurs in the United States of a mosquito to a person. Until now, such a transfer "indigenous" has not occurred, but scientists think it is very likely to occur in the coming weeks. . Given the attention that every imported case of Zika unleashed that day see here and here and here and here and here expect the American media to go full throttle
The policy will further increase the clamor: Just two days ago, the white House Secretary Josh Earnest in his daily briefing has a map that suggests the virus blanketing half of the continental United States in mid-summer. "The map behind me is a graphic illustration of the need for immediate action by the Congress," said Earnest, urging Congress to consider 3-month-old request from President Barack Obama to pump $ 1.9 billion in emergency aid to fight against Zika.
But researchers who have studied Zika and mosquitoes that transmit it to say that the country is currently in the calm before the calm. Damaging as Zika of fetuses, they predict that indigenous transmission will only affect a small strip of land that runs from Florida along the Gulf Coast of Texas. And the dynamics of the disease transmitted by mosquitoes in the United States are so different from those of Latin America, the number of confirmed cases will probably be in the hundreds, if not that, before the spread of autochthonous stammers.
there are many mysteries about Zika and how, in particular, it behaves in pregnant women, which triggers some miscarriage and others to give birth to babies with brain disorders such as microcephaly. There are also questions about how much the spread occurs without mosquito: Zika may persist in semen and be sexually transmitted, and there is a small chance that the viral RNA in saliva, which has never been linked to infection, may pose a risk. But when it comes to species of mosquitoes that harbor the virus and the transmission cycle with humans, much is known. Experience with two other diseases transmitted by the same mosquito, dengue and chikungunya, offer insight as well.
The United States simply does not have the ingredients to the type of explosive, indigenous transmission seen in Latin America, said Thomas Scott, an entomologist and epidemiologist at the University of California, Davis. "I do not want to blow this off and leave people with the impression that you do not have to worry about it, who knows where it goes," he said. "But I do not think we'll have a transmission in the United States, mainly because of our lifestyle. We do not have as enough mosquitoes."
The temperature sensitive Aedes aegypti , the principal mosquito vector lives only in high numbers in a small part of the United States, and especially develops during the summer months when the temperature is between 25 ° C and 32 ° C. There is a lot more a . aegypti Zika to spread in Brazil, which saw up to about 1.3 million infections in 2015 alone, the United States. There is also a celebration of the available human skin, as people in warmer climates often wear tank tops, flip-flops and shorts.
Poverty explains some of Zika success in Latin America. window and door screens are scarce in many places, and homes often have stagnant puddles bathroom or in dark places that provide breeding grounds for homebound A . aegypti , which calls Scott "the cockroach" mosquitoes. "They do not fly very far from where they emerge," he said. "It's mostly people who move the virus around." Add to this mix the Latin culture: "A lot of places Zika is common, people are incredibly social, and they go all over town to see family and friends," he said, while the States United, "people often come to the house and go inside and there is air conditioning and they are watching television."
dated May 11, the US Centers for Disease Control and Prevention ( CDC) had confirmed 503 "Travel -Associated" Zika case of the United States, 10 of which involved sexual transmission. No evidence exists that a mosquito has bitten again one of these people and spread the infection to another person the country.
Scott recently collaborated on a global Zika modeling project led by Simon Hay, chief of the division of geospatial science at the Institute for health Metrics and evaluation in Seattle, Washington. the team mapped the environmental relevance for Zika on the basis of annual precipitation, temperature, areas where a . aegypti persists and conditions where Zika has already occurred.
The researchers also included data for a . albopictus- better known as the Asian tiger mosquito that can harbor the virus. In the United States, A . albopictus has a broader scope than A . aegypti. But Scott doubt he can keep the transmission cycle go because, unlike A . aegypti it can bite a human being as an appetizer, then turn to several other species to complete its blood meal. "Small changes in the biting frequencies on an appropriate host can make a big difference" to the transmission, Scott said.
The model, published online April 19 by eLife , calculated that 2.17 billion people worldwide live in areas that are ecologically suitable for Zika. High-risk areas include more than half of Latin America where the virus is circulating now-and some parts of South and Southeast Asia, northern Australia, and broadband Africa around the equator.
Part of the Zika risk map published by Simon Hay and colleagues eLife .
eLife
But the potential Zika propagation in the United States is limited. The only regions "very suitable" are Florida and parts of neighboring states to the west, including the coastal regions of Alabama, Mississippi, Louisiana and Texas.
The map at the White House release came from another document, published online March 16 in PLOS current outbreaks . The White House appears as a "month by month look at the prevalence of mosquitoes that can carry the virus from mosquito," visible as a wave of yellow, orange, and red circles wash the country in 2016 progresses. (The site of the White House Zika has an even more alarming map prepared by CDC "from a variety of sources.")
map of the prevalence of mosquitoes produced by the white House.
the white House
in the document PLOS current outbreaks , however, the figures indicate the "potential plenty" of the size it could be based on a population model that mosquito, which uses climate data. This potential range far beyond the actual area where the mosquito is known to live. the card includes places as far north as Denver and Salt Lake City, where A . aegypti has never been seen.
"I have no explicit guidance on the use of the image of the white House," says Andrew Monaghan, a meteorologist at the National Centre for atmospheric research in Boulder, Colorado, who led the team that made the map. Monaghan notes that "we were clearly our map above shows the relevance of seasonal climate Aedes aegypti , and is not intended to be an accurate indicator of where the mosquito is found."
Monaghan and colleagues at NASA and North Carolina State University in Raleigh agree that A . aegypti is the most abundant in the area that will from Florida to the Gulf coast of Texas. the card includes another variable that will likely fuel the spread autochthonous :. the number of travelers (represented by circles) entering the United States from Latin America and Caribbean that have local extension Zika now
A card paper in PLOS current outbreaks combines abundance potential of Aedes aegypti data and travel.
PLOS current outbreaks
Monaghan said that where Zika will most likely begin to spread in the United States are where dengue chikungunya have done as well. These areas, dark brown on the map are Brownsville, Texas, which abuts Mexico and has a land border crossing busy, and South Florida.
If history repeats itself, they may be the only places Zika virus transmitted in the continental United States.
dengue was detected in the US in 1780 in Philadelphia, Pennsylvania but indigenous transmission stopped in 1945 and did not surface again until 1980 in Texas, when a 5 years -old girl in Brownsville has been infected. In 1986, Texas had nine documented indigenous cases, four were in Brownsville, and the city was still three indigenous cases in 05. Hawaii had 122 confirmed dengue cases in 01-02. Here, the vector was not A . aegypti , but A . albopictus. Florida had first indigenous transmission of dengue in 09-10, with the Ministry of Health collecting a total of 88 cases "associated with Key West," the southern part of the state. There have been other sporadic transmissions from local, all in the south and center of the state, with a serious epidemic in 2013 that involved 28 people.
Chikungunya has so far been just as easy on United States. the first confirmed indigenous transmission occurred in Miami-Dade County, Florida, June 27, 2014. Only 10 other cases followed, as CDC reported in December 2014. All of these products in the counties of south Florida, too.
a third map, published in on Lancet January 14, seals the deal as south Florida's first real estate Zika . These researchers analyzed passengers arriving in the United States who left Brazil airports located within 50 kilometers of areas that could potentially transmit Zika year. Moreover, they highlighted US regions that had the most hospitable climate for both Aedes species that transmit Zika. Miami and Orlando are proving to be the best airports of entry for the virus. (Brownsville did not get a mention because it does not have a major airport.)
Part of the map showing the potential for international spread of Zika in The Lancet .
The Lancet
DA Henderson, an epidemiologist who helped lead the program that eradicated smallpox and advised the government of the United States on several other infectious diseases, says the threat of Zika the United States does not guarantee the degree of fear and fear that it triggered. "I can not be very excited about the whole affair," said Henderson, who is now at the center of UPMC for Safety of Health in Baltimore, Maryland.
Although it is all for the efforts against the stepped-up mosquito, he stressed that the virus causes little, if any, symptoms in most people it infects and not spread well between people. "We do not see crush the great epidemics, "he said.
Henderson, who is 87 and has seen many epidemics come and go, said the US media coverage Zika is driven in part by the relatively recent rise in laboratories . that now work on viral diseases "their inclination, in good faith, is to say," This could be a real problem "to keep money flowing to their laboratories," says Henderson. "It is not bad and I do not want virologists lacks funds, but you need to keep in perspective that some of these things to say. It's got a little out of hand. "
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