BRASILIA/CHICAGO/GENEVA – International experts, including World Health Organization chief Margaret Chan, are visiting Brazil this week and next to check out a major increase in Zika virus infections, which have been blamed for birth defects.
Chan, whose organization has declared an international emergency over the mosquito-transmitted virus, is expected in Brazil on Feb. 23-24.
Experts from the U.S. Centers for Disease Control and Prevention are already in the country and officials from two other U.S. bodies, the Food and Drug Administration and the National Institutes of Health, are due to arrive, the Brazilian health ministry said.
Zika often has few symptoms, but Brazilian scientists say they have found a direct link between the virus and a serious birth defect called microcephaly in babies born to women who were infected while pregnant.
There is no vaccine for Zika and cases have shot up across Brazil and elsewhere, raising fears for local people and visitors, including during the August Olympics in Rio de Janeiro.
Brazilian authorities have launched a national campaign against the Aedes aegypti mosquito, which carries the virus. Military personnel have reinforced health authorities in a door to door campaign against mosquito breeding spots.
“We have a very effective fumigation campaign across Brazil,” Health Minister Marcelo Castro said Tuesday after meeting 24 EU ambassadors in the capital Brasilia.
“As happened in previous years, we hope that the mosquito population will be even lower,” he said, noting that by the Olympics the Southern Hemisphere winter will see a sharp drop in mosquito numbers.
The European Union delegation head to Brazil, Joao Gomes Cravinho, said: “The international community has many worries over Zika.”
The Zika virus may be particularly adept at entrenching itself in parts of the body that are shielded from the immune system, making it harder to fight off and possibly lengthening the timeframe in which it can be transmitted, top U.S. experts said on Friday.
Researchers reported that Zika virus can be detected in semen for 62 days after a person is infected, adding to evidence of the virus’s presence in fetal brain tissue, placenta and amniotic fluid. Their work is part of an international race to understand the risks associated with Zika, a rapidly spreading mosquito-borne virus thought to be linked to thousands of cases of birth defects in Brazil.
“Right now, we know it’s in the blood for a very limited period of time, measured in a week to at most 10 days. We know now, as we accumulate experience, it can be seen in the seminal fluid. We’re not exactly sure after the infection clears, where else it would be,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said.
“These are all things that need to be carefully examined in natural history and case-control studies,” he said.
Fauci said that Zika’s persistence in the body recalled findings during the 2014 Ebola outbreak, the worst on record. In individual patients, the highly deadly virus remained in semen and eye fluid for months.
Zika causes only mild symptoms, and in most cases may not result in illness at all. Its suspected link to the birth defect microcephaly and to neurological disorder Guillain-Barre syndrome has generated alarm among public health officials, though an association has not been proven. The World Health Organization on Feb. 1 declared Zika a global health emergency.
Several organs in the body, including the testes, the eyes, the placenta and the fetal brain, are “immune privileged” — protected from attacks launched by the immune system to neutralize foreign invaders.
These sites are safeguarded from antibodies to prevent the immune system from attacking vital tissues. But if a virus enters these protected sites, it is much harder to fight them off.
“The virus can continue to persist and or multiply,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Nashville, Tennessee. “The virus is in a bubble of sorts.”
Fauci said it is not entirely surprising that Zika persists in semen. There have already been at least two reports in which the virus was likely transmitted sexually. What has not been clear is for how long.
British researchers offered some clues on Friday. In a letter to the journal Emerging Infectious Diseases, scientists reported the case of a 68-year-old man who was infected with Zika in 2014. They detected Zika virus 62 days after the initial infection, but they were not able to confirm whether it could still infect another person.
Earlier this week, researchers in Slovenia published a paper in the New England Journal of Medicine describing a severely brain damaged fetus from a mother who was infected with Zika in Brazil and later terminated the pregnancy.
In an autopsy, the authors found high levels of Zika in the brain and some evidence that the virus had been replicating. They suggested that Zika may persist in the fetal brain because it is an immunologically privileged site.
That is true of many other viruses, such as rubella, cytomegalovirus or herpes, which can also cross the placenta and cause microcephaly, a birth defect marked by small head size and underdeveloped brains. Doctors commonly screen pregnant women for these infections, said Dr. Ian Lipkin of the Center for Infection and Immunity at Columbia University in New York.
Lipkin said the key concern about Zika harboring in immune protected sites is that it could be transmitted sexually through semen.
So far, there is little to suggest sexual transmission is common, said Dr. Eric Rubin, an infectious disease expert at the Harvard School of Public Health, “but it will bear looking at so that we can counsel individuals about the risk that they pose to others.”
U.S. health officials advise that men who come to the country from Zika outbreak areas should consider using condoms even with nonpregnant sex partners because the virus may persist in semen even after it clears the bloodstream.
“They don’t say for how long,” Schaffner said. “That’s because they don’t know. As it was with Ebola, we’re learning as we go.”
The WHO meanwhile said it may be necessary to use controversial methods like genetically modified mosquitoes to wipe out the insects that are spreading the Zika virus across the Americas.
The virus has been linked to a spike in babies born with abnormally small heads, or microcephaly, in Brazil and French Polynesia. The U.N. health agency has declared Zika a global emergency, even though there is no definitive proof it is causing the birth defects.
WHO said its advisory group has recommended further field trials of genetically modified mosquitoes, which have previously been tested in small trials in countries, including the Cayman Islands and Malaysia.
“Given the magnitude of the Zika crisis, WHO encourages affected countries … to boost the use of both old and new approaches to mosquito control as the most immediate line of defense,” WHO said in a statement. WHO says at least 34 countries have been hit by the virus in the current crisis, mostly in Latin America.
WHO said previous experiments that released sterile insects have been used by other U.N. agencies to control agricultural pests. The agency described the Aedes aegypti mosquitoes that spread Zika — as well as other diseases including dengue and yellow fever — as an “aggressive” mosquito that uses “sneak attacks” to bite people, noting that the mosquito has shown “a remarkable ability to adapt.”
Last month, British biotech firm Oxitec said tests in Brazil in 2015 showed that genetically altered sterile male mosquitoes succeeded in reducing a type of disease-spreading mosquito larvae by 82 percent in one neighborhood in the city of Piracicaba. The genetically modified males don’t spread disease because only female mosquitoes bite.
Environmentalists have previously criticized the genetically modified approach, saying wiping out an entire population of insects could have unforeseen knock-on effects on the ecosystem.
Some experts agreed it might be worth using genetically tweaked mosquitoes given the speed of Zika’s spread but were unsure of the eventual consequences.
“The way this is done wouldn’t leave lots of mutant mosquitoes in the countryside,” said Jimmy Whitworth, an infectious diseases expert at the London School of Hygiene and Tropical Medicine. He said the Zika mosquitoes are an imported species that were accidentally brought to the Americas hundreds of years ago, and was optimistic their eradication wouldn’t damage the environment.
However, he said such a move would be unprecedented and it would be impossible to know what the impact might be before releasing the insects into the wild.
“You would hope that the ecology would just return to how it was before this mosquito arrived,” he said. “But there’s no way of knowing that for sure.”
Last week, a group of doctors in Argentina, Physicians in the Crop-Sprayed Towns, suggested the jump in microcephaly cases may not be caused by Zika, but by Pyriproxyfen, a larvicide used in drinking water that aims to prevent mosquito larvae from developing into adulthood. The group said the larvicide has been used since 2014 in Brazil in several areas with a reported rise in babies with birth defects.
Spokeswoman Chaib said scientists at WHO and elsewhere had rejected any such link.
“They have reviewed all the scientific literature linked to this pesticide in particular and found the same conclusion: That there is no scientific evidence that can link this pesticide in particular to the cases of microcephaly,” she said.
Brazil’s government has repeatedly said pesticides were not connected to microcephaly, and has noted many cases of microcephaly in areas where Pyriproxyfen was not used. The government also noted that WHO had approved use of the chemical.