NOTE: This is from the online version of the newspaper, so no link to article.
UC San Diego, Brazilian scientists infect pregnant mice with virus and detect harm to their babies
Scientists from Brazil and UC San Diego said Wednesday that they have produced the world's first direct evidence of how the Zika virus causes brain defects. Previous research had inferred this mechanism, but never demonstrated it in the lab.
In their new study, the Brazilian and San Diego scientists worked with pregnant mice. They found that the Brazilian strain of Zika crossed the placenta and into the mice's pups, reducing growth in the brain and the rest of the body.
The brain defects were similar to the microcephaly reported in some human babies whose mothers were infected with Zika during pregnancy.
Additionally, the researchers discovered that the virus caused similar damage in brain “organoids,” which are peasized structures grown from human stem cells. In essence, the study confirmed earlier findings of Zika's effects on brain organoids, including a report published this month by UC San Diego scientists.
But one strain of mice resisted Zika, the latest study found. The pups of those mice didn't show any signs of infection and tested negative for the virus. This suggests that the virus never crossed the placenta in those cases.
This particular strain mounted a “robust” antiviral immune response, the report said. If the effect can be extended to humans, it would help explain why some Zika-infected mothers give birth to newborns who have no detectable brain damage.
Virus has already achieved pandemic status
The new study was published in the journal Nature. It can be found at Nature International Weekly. Zika's stealthy attack on fetal brains makes it especially worrisome. Unlike Ebola's direct and deadly assault, Zika is rarely fatal. Most infected people don't feel any symptoms. So if a pregnant woman is infected, the real damage may not be known until her baby is born. Another concern: Zika can harm fetal development at all stages of a woman's pregnancy. The Brazilian strain of Zika is more aggressive than the African strain, said UC San Diego's Alysson Muotri, one of the new study's authors and a Brazilian native. The two strains share about 90 percent of their genes, meaning that the 10 percent difference is responsible for making the Brazilian version more dangerous.
That fact represents a monumental challenge to Brazil, which is set to host the Summer Olympics in less than three months. People will travel to Brazil from around the world, possibly become exposed to Zika and carry the virus back to their home countries. Zika is usually carried by mosquitoes of the genus Aedes, but it also can be transmitted sexually. The virus has already achieved pandemic status, and it has been reported throughout the United States. San Diego County's first case this year was announced in February. The patient was a woman who had become infected while in Colombia. She was not pregnant at the time and has recovered fully, public health officials said.
From Jan. 1 through May 4, a total of 472 Zika cases were reported in the U.S., including 40 in California, according to the U.S. Centers for Disease Control and Prevention. Pregnant women were involved in 44 of those cases, and 10 of the infections were sexually transmitted.
There has been no “homegrown” Zika infection by mosquitoes in the United States, health officials said.
However, the potential for transmission is present in the form of the Aedes Aegypti mosquito. The species, a relatively recent arrival in San Diego County, is black with white stripes. Scientists not involved in the new study said it meshes with results from previous research and shows a way forward for potential counter- measures.
“This report has revealed a new approach to investigate the pathological outcomes of Zika infection in innovative experimental models and is the first of its kind,” said medical virologist Grant Hill-Cawthorne at the University of Sydney in Australia. His comments were provided by the Australian Science Media Center. “It has shown the experimental models used can reflect the clinical presentation of Zika infection and thus serve as an excellent basis to understand the disease process and evaluate strategies for prevention,” Hill-Cawthorne said. Dr. Nathalie MacDermott, a clinical research fellow at Imperial College London, said: “The study lends further support to the likelihood that the damage to the infant resulting in microcephaly, microencephaly and brain malformations occurs during the first and second trimesters of pregnancy, a time when the infant's brain is rapidly developing and nerve cells are migrating to the correct regions.” Her comments were provided by the United Kingdom-based Science Media Center.
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